CA1210053A - Apparatus and method for neutralizing static electric charges in sensitive manufacturing areas - Google Patents
Apparatus and method for neutralizing static electric charges in sensitive manufacturing areasInfo
- Publication number
- CA1210053A CA1210053A CA000431208A CA431208A CA1210053A CA 1210053 A CA1210053 A CA 1210053A CA 000431208 A CA000431208 A CA 000431208A CA 431208 A CA431208 A CA 431208A CA 1210053 A CA1210053 A CA 1210053A
- Authority
- CA
- Canada
- Prior art keywords
- electrodes
- pair
- airstream
- ions
- enclosure
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
- B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
- B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
- B03C3/02—Plant or installations having external electricity supply
- B03C3/04—Plant or installations having external electricity supply dry type
- B03C3/14—Plant or installations having external electricity supply dry type characterised by the additional use of mechanical effects, e.g. gravity
- B03C3/155—Filtration
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
- B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
- B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
- B03C3/34—Constructional details or accessories or operation thereof
- B03C3/38—Particle charging or ionising stations, e.g. using electric discharge, radioactive radiation or flames
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F3/00—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems
- F24F3/12—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling
- F24F3/16—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by purification, e.g. by filtering; by sterilisation; by ozonisation
- F24F3/167—Clean rooms, i.e. enclosed spaces in which a uniform flow of filtered air is distributed
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
- H01T23/00—Apparatus for generating ions to be introduced into non-enclosed gases, e.g. into the atmosphere
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05F—STATIC ELECTRICITY; NATURALLY-OCCURRING ELECTRICITY
- H05F3/00—Carrying-off electrostatic charges
- H05F3/04—Carrying-off electrostatic charges by means of spark gaps or other discharge devices
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S55/00—Gas separation
- Y10S55/29—Air curtains
Abstract
APPARATUS AND METHOD FOR NEUTRALIZING STATIC
ELECTRIC CHARGES IN SENSITIVE MANUFACTURING AREAS
Abstract of the Disclosure An apparatus and method for neutralizing static electric charges are disclosed, which include a cooperating pair of laterally spaced apart electrodes disposed in a moving airstream. A relatively high positive DC voltage is applied to one electrode, and a relatively high negative DC
voltage is applied to the other electrode. As a result, the electrodes generate free positive and negative ions, which are carried away by the airstream and delivered directly to the manufacturing area, where they are attracted to opposite static charges. Thus the ions act to neutralize static charges of either polarity, and the excess ions will eventually be attracted to each other or to ground, leaving no static in the area. In a preferred embodiment, the electrodes are mounted immediately downstream of a HEPA filter bank which removes essentially all particulate matter and dust before the ions are generated in the airstream.
ELECTRIC CHARGES IN SENSITIVE MANUFACTURING AREAS
Abstract of the Disclosure An apparatus and method for neutralizing static electric charges are disclosed, which include a cooperating pair of laterally spaced apart electrodes disposed in a moving airstream. A relatively high positive DC voltage is applied to one electrode, and a relatively high negative DC
voltage is applied to the other electrode. As a result, the electrodes generate free positive and negative ions, which are carried away by the airstream and delivered directly to the manufacturing area, where they are attracted to opposite static charges. Thus the ions act to neutralize static charges of either polarity, and the excess ions will eventually be attracted to each other or to ground, leaving no static in the area. In a preferred embodiment, the electrodes are mounted immediately downstream of a HEPA filter bank which removes essentially all particulate matter and dust before the ions are generated in the airstream.
Description
::~2~53 APPARATUS AND METHOD FOR NEUTRALIZING STATIC
ELECTRIC CHARGES IN SENSITIVE MANUFACTURING AREAS
The present invention relates to the neutraliza-tion or elimination of static electricity in critical or sensitive manufacturing areas, such as clean rooms used for the production of semiconductors.
The manufacture of inte~rated circuit boards typi-cally includes the steps of forming minute circuits on a silicon wafer, cutting the resulting wafers into chips of about 118 inch square, and then interconnecting a number of the chips on a circuit board to ~orm the desired circuit.
~hese manufacturing operations are usually conducted in a "clean" enclosure, such as a clean room or clean work sta- -tion, and which includes high eficiency particulate air filters for removing substantially all particulate matter and dust from the air circulating therethrough, to thereby minimi~e the possibility o con~amination o~ the work~
pieces.
While existing clean rooms and work stations are able to minimize contamination from particulate matter in eritical or sensitive manufacturing areas~ a continuing and persiste~t problem relates to the fact that statir electri-city tends to build up on the workpieces and other objects in the manu~acturing area by reason of the workpieces being subjected to friction, pressure~ or temperature change.
Also, static electricity is often brought into the area with entering persons or raw materials~ This static electricity is a principal factor in semiconductor con-tamination and degradation. More particularly, con-tamination can result from the static electricity ?~S3 attracting a dust particle to the workpiece, and degrada-tion can result from the rapid change in potential due to current flow when the workpiece comes into contact with a grounded or oppositely charged object.
In an attempt to alleviate static electricity in sensitive manufacturing areas such as the manufacture o~
integrated circuit boards as described above, it has been proposed to ground all persons and objects in the manufac-turing areaO However, this is a cumbersome procedure and it cannot be totally effective since many of the materials in the room are nonconductive and thus will not transfer a static charge to ground.
It has also been proposed to ionize the air at clean work stations or benches, by providing a grid imme-diately downstream of the filter which is subjected to arelatively low AC voltage, such as 4,000 to 5,0~0 volts, and which alternately produces positive and negative ions.
The resulting ions act to neutralize static charges on objects which are cvntacted by the ions. However, the AC
current is not able to throw off ions more than a very - -limited distance, since the aiternating nature of the current tends to pull back the ions upon each cycle rever-sal. l'hus while this ionization has achieved some success in very confined areas such as clean work stations or 2S benches where the workpieces are positioned a very short distance from the grid, it has not proven satisfactory for l~rge clean room or manufacturing area.
The prior U.S. patents to Best et al, Nos.
3,942,072 and 4,064,548 describe a system for reducing a positive or negative field in a manufacturing area, and which includes two serially spaced apart thin wire grids positioned in an air conditioning duct, and with one grid connected to a positive high voltage source and the other connected to a negative high voltage source, to pro~uce both positive and negative ions~ However, this system has not been found to be satisfactory in actual pr~ctice since th~ downstream duct apparently tends to ground the ions ~nd thus insufficient numbers of ions are able to be discharyed from the duct. Also, the -thin wire grid is susceptible to breakage.
It is accordingly an object of the present inven-tion to provide an apparatus and method which are able to effectively eliminate static electricity in critical or sensitive manu-facturing areas, including large clean rooms and the like.
It is a more particular object of the present inven-tion to provide an apparatus and method for generating large numbers of both positive and negative free ions within a relatively large manufacturing area, and such that the ions are able to rapidly eliminate static electricity on objects in the area, or objects brought into the area.
These and other objects and advantages of the present invention are achieved in the embodiments illustrated herein by the provision of a pair of electrodes which are operatively mounted so as to be spaced apart from each other in a direction extending transversely to the direction of air flow. Current generating means are also provided for supplying a relatively high positive DC voltage to one of the electrodes, and a rela-tively high negative DC voltage to the other of -the elec-trodes. Thus the two electrodes act to concurrently generate positive and negative ions which are carried by the airstream directly into the manufacturing area.
-3a-The elec-trodes include a plurality of needle like projections, which facili-tate the formation and emission of ions in-to the airstream, and in one preferred embodimen-t, -the electrodes are in the form of two elongate bars which are disposed parallel to each other, with the needle like projec-tions directed toward each other. In another embodiment, the electrodes are in the form of paraboloids, wi-th the needle like projections radiating therefrom.
In summary, according to a first broad aspect, the invention provides in a clean enclosure sized so as to be adapted to enclose a manufacturing area, means for moving an airstream along a path of travel through said enclosure, the improvement therein comprising apparatus for concurrently generating both positive and negative ions in the airstream such that the ions are able to rapidly neutralize static electricity on objects in or brought into the area, and comprising at least one pair of electrodes operatively mounted within the path of travel of said airstream in said enclosure, with each of said at least one pair of electrodes being in the form of elongate kars which are disposed parallel to each other, and with the electrodes of each pair being spaced apart from each other a distance of between about six to twelve inches in a direction extending transversely to the direction of the path of travel and having an in-tervening airspace therebetween which is free of any electrically con-ductive components, and each of said electrodes including a ~2~ ~53 -3b-plurality of needle~ e elec-trically conductive projec-tions which extend toward the other electrode of the pair, and means for supplying a positive direc-t current voltage to one of said electrodes of each pair, and a negative direct curren-t voltage to the other of said elec-trodes of each pair, with the magnitude of the supplied voltages being sufficient to cause the electrodes to interact and cooperate in drawing ions from each other, whereby both positive and negative ions may be concurrently generated and carried through the enclosure by the moving airstream.
According to a second broad aspect, the invention provides in a clean enclosure having provision for supplying virtually particle free air to sensitive manufacturing areas and the like, a filter bank comprising at least one high efficiency particulate air filter, and blower means for circu-lating air through said bank and into said enclosure, the improvement therein comprising means for concurrently generating both positive and nega-tive ions in the airstream and such that -the ions are able to rapidly neu-tralize static electricity on objects in or brought in-to the enclosure, said ion genera-ting means including at least one cooperating pair of electrodes mounted immediately adjacent said filter bank with each co-operating pair of elec-trodes being spaced apart from each other a distance of between about six to twelve inches in a direc-tion ex-tending generally parallel to the adjacent face of said filter bank and having an intervening airspace therebetween which is free of any electrically conductive components, and each of said electrodes including a plurality of needle-like electrically -3c conductive projections, and means for supplying a posi-tive direct current voltage -to one of the electrodes of each pair, and a negative/direc-t current vol-tage to the other elec-trode of each pair, with the magnitude of the supplied vol-tages being sufficient to cause the electrodes to in-teract and co-operate in drawing ions from each other, whereby both positive and negative ions may be concurrently generated in the air-stream moving into said enclosure.
According to a third broad aspect, the inven-tion provides in a clean room having provision for supplying virtu-ally particle free air to sensitive manufacturing areas and the like, and including a room like enclosure, a filter bank disposed within said enclosure and including a supporting frame-work defining a plurality of open areas, a plurality of high efficiency particulate air filters mounted on said framework with one of the filters covering each of the open areas, and blower means for circulating air through said bank and to a manufacturing area disposed in the remainder of said enclosure, the improvement therein comprising means for concurrently generating both positive and negative ions in the airstream delivered to the manufacturing area and such -that the ions are able -to rapidly neutralize static electricity on objects in or brought into the manufacturing area t said ion generating means including a plurality of cooperating pairs of elec-trodes mounted to said supporting framework and immediately downstream of said filter bank, with each cooperating pair of electrodes being laterally spaced apart from each other in a direction extending generally parallel to the adjacent face of said -3d-filter bank and thus transversely to the direction of the moving aixstream and having an intervening airspace -there-between which is free of any electrically conductive components, and each of said electrodes including a plurali-ty of needle-like electrically conductive projections which extend toward the co-operating e]ectrode, and means for supplying a positive direct current voltage to one of -the electrodes of each pair, and a nega-tive direct current voltage to the other electrode of each pair, and with the lateral spacing of said electrodes of each pair and the voltages supplied to said electrodes being co-ordinated so that the electrodes of each pair interact and co-operate in drawing ions from each other, and such that both positive and negative ions may be concurrently generated in the airstream moving into the manufacturing area of said enclosure.
Some of the objects having been stated, other sbje~t~ will appear as the description proceeds, when taken in c~nnection with the accompanying drawing in which -Figure l is a generally schematic sectional side elevation view of a clean roo~ which embodies the presenti~ention;
Figure 2 is a perspective view of an ion generating electrode as utilized in the clean room shown in ~i~ure l;
Figure 3 is a sectional end view of an alternative embodiment of an ion generating electrode adapted for use with the present invention;
~ igure 4 is a bottom plan view, looking upwardly fro~ the manufacturing area, of a filter bank and ion ge~erating electrodes, and which embody the present i~ve~tion;
Figure S is a fragmentary perspective view of the ilter bank shown in Figure 4, Figure 6 is a horizontal sectional view taken 2P ~ub~tantially along the line 6-6 of Figure 5;
Figure 7 is a bottom plan view of a similar filter bank, and illustrating a ~econd embodimen~ of the ion generating electrodes;
Figure 8 is a perspective view of one of the ~le~trodes shown in the embodiment of Figure 7, and Figure 9 is a sectional view of the electrode hown in Figure 80 Referring more particularly to the drawings, Figure l schematically illustrates a clean room lO
e~bQdying the features of the present invention. The room comp~ises an enclosure which includes a top wall 12, a bot-~Q~ wall 13, and bounding side walls 14, 15, 16 (the fourth side wall not being shown). A horizontally disposed filter bank 18 is positioned within the enclosure parallel to and sp~ced from the top wall eo define an open air supply ple-n~lm 20 therebetween~ A raised floor 21 is mounted above the bottom wall 13 to define a return air plenum 22, with the floor 21 including a number of perforated panels for permitting air to pass therethrough. The return air plenum 22 communicates with a vertical duct defined between the outer side wall 16 ancl an interior wall 24, and which contains the air handling unit or blower 19 for recirculating the air into the air supply plenum 20. Thus in use, the air delivered to -the air supply plenum 20 by the blower 19 passes downwardly through the filter bank 18 such that essentially all particulate contaminates are removed immediately before the air enters the working area of the room.
The air then passes vertically downwardly through the room under essentially laminar flow conditions, and then passes through the floor 21 to the return air plenum 22.
In the embodiment specifically illustrated in Figures 4-7, the filter bank comprises a hori~ontally disposed suppor-ting latticework frame composed o~ a plurality of interconnected U-shaped channels 28 having their open sides directed upwardly, with the channels being substantially filled with a suitab~e sealing fluid 29. A plurality of air filters 30 are positioned on the latticework with one of the filters covering each of the open areas defined by the latticework. Each filter 30 comprises a rec~angular frame 32 and a filter pack 33 sealably disposed within the frame. Typically~ the filter pack 33 comprises a sheet of high efficiency particulate air filtering media which is folded in accordion fashion in a manner well known in the art.
Also, each filter 30 includes a downwardly depending metal skirt ?I~S3 -5a-34 positioned about the outer periphery of the frame, with khe skirt being adapted to rest within the open channels 28 and so as to be sealably immersed in the fluid 29. If desired, a plurality of lighting fixtures 35 may be positioned intermediate certain of the filters and secured to the latticework. A
further description of the above described filter bank and fluid sealing arrangement may be obtained by reference to U.S. Patent No. 3,486,311 to Allan.
In accordance with the present invention, a plura-lity of pairs of electrodes 40 are mounted to the lattice-work and immediately downstream o~ the filter bank7 Each pair includes an electrode 40a of one polarity, and an electrode 40b of like construction and of the opposite polarity. The electrodes are spaced apart from each other in a direction extending generally parallel to the adjacent f2ce of the filter bank and thus transversely to the direc-tion of air flow through the bank.
In the embodiment of ~igures 4-6, each electrode 40 comprises an elongate bar of C~shaped cross section as best seen in Figure 2, and which is composed of epoxy or similar non-conductive material. A metal conductor 42 is embedded in the bar and extends along its length, and a line of spaced apart, metallic needle like projec~ions 43 communicate with the conductor and extend outwardly from the bight of the bar when viewed in cross section~
In most clean rooms, it is unnecessary that all of the air be moved between operative electrodes, and under normal conditions, it is only necessary that about 25 to - -50% of the air pass between cooperating pairs of elec-trodes. Thus in the illustrated embodiment, electrode bars 40a~ 40b are mounted beneath only one half of the filters 30, with the other filters being free of any underlying electrodes. Thus in the illustrated embodiment, only about 50% of the downwardly moving airstream moves between opera-tive electrodesO
As best seen in Figures 4 and 5, two cooperating pairs of electrode bars 40a, 40b are mounted beneath one half of the filters in the bank. More particularly, the bars are secured to a peripheral frame member 45 which is secured to the inwardly facing edges of the channels 28, and so as to be substantially co-planar with the channels 28. The bars are grouped so that a single bar 40b is mounted along each side edge of the filter, and a pair of contiguous b~rs 40a o~ the same polarity are mounted to extend lengthwise along the medial portion of the filter, and with the bars thus being parallel to each other. Since filters of,the illustrated type usually measure 24 by 48 inches, it will be appreciated that the electrodes of each cooperating pair 40a, 40b are spaced apart about 12 inches.
Also, the bars are oriented sP that the needle like projec-tions 43 of each cooperating pair of bars face horizontally toward each other. Preferably, the frame member 45 is removably attached to the adjacent channels 28, to permit its removal downwardly and thus permit access to the filter for periodic servicing or replacement.
Current generating means is also provided for supplying a relatively high DC voltage of one polarity to the electrode 40a of each pair, and a relatively high DC
voltage of the opposite polarity to the e:Lectrode 40b of each pair. This current generating means includes a control unit 48 of conventional design, and which may be located either inside or outside of the enclosure 10. The control unit 48 is adapted to deliver a select~d voltage, in the range between zero to about 35,000 volts to each electrode 40a, 40b. More particularly, the control unit includes a knob 49 for concurrently adjusting the total power to the two electrode~, and thereby permit adjustment of the overall rate OI ion production. A control lever 50 is also provided which~ upon upward movement, acts to increase the charge to bot~ electrodes positively, and upon downward movement, to increase the charge to both electro-des negatively~ When the lever arm is centered, the electrodes 40a, 40b are charged with equal vol~ages of opposite polarity. Thus the lever 50 permits a change in the relative percentage of positive and negative ions, so as to efficiently accommodate a manufacturing process which normally produces excessive positive or negative static charges.
An atmospheric static sensor 52 of known construc-tion i~ positioned in the enclosure, ,and is operativelyconnected to a meter 53 on the control unit 48. Thus the output of the sensor 52 may be used to determine whether an increased charge in either the positive or negati~e direc-tion is required.
The lateral spacing of the electrodes 40a, 40b of each pair is determined by a number of factors, including the static load in the clean room to be neutralized, the volume of air flow, and the applied voltage. However, it is preferable that the electrodes be positioned suf-ficiently clo~e to each other so that the electrodes o~
each pair 40a, 40b interact and cooperate in drawing the ions from each other by reason of their opposite charges, and so that the ions may be readily removed and carried away by the airstream. Typically~ the spacing should be about six to twelve inches to provide the desired coopera-tion. Also, the use of electrodes having the describedneedle like projection 43 is preferred, in that it appears that the projections tends to concentrate the electrical charge at their point free ends, which facilitates the emission of ions into the airstream. It is also preferred to position the electrodes of each pair with the needle like projections aligned and`facing each other, since this orientation is believed to further facilitate the emission o ions.
In operation, it will be understood that the air handling unit ~ of the clean room 10 will serve to recir-culate the air through the filter bank 18 and downwardly ; through the manufacturing or production area of the room, under essentially laminar flow conditions. The current -generating means is then operated so that a relatively high positive ~C voltage, such as between about 20>000 and 35,000 volts, is applied to one electrode of each pair~ A
negative DC voltage of corresponding magnitude is applied to the oeher electrode of each pair. Positive and negative ions are thereby generated at the respective electrodes, and the airstream passing becween the electrodes acts to carry the ions away from thé electrodes and dire~ly into ~l2~ . 53 the underlying manufacturing area withou~ contact with adjacent confining ductwork or the like. The absence o~
such ductwork is seen to minimi~e the loss of ions which would otherwise result from contact of the ions with such ductwork. Thus the manufacturing area is effectively "flooded" with substantially equal numbers of both positive and negative ions, which serve to rapidly eliminate static electricity on objects in the area, or objects brought into ~he area. More particularly, the ions are attracted to opposite static charges, and thus the ions act to neutr~-lize static charges of either polarity. The excess ions will eventually be attracted to each other or to ground, leaving essentially no static charges in the manufacturing area. Where a sensor 52 and control unit 48 are employed, the magnitude and polarity of the static electricity in the enclosure may be monitored, and the controls 49 and 50 may be operated so as to selectively vary the voltage to each electrode and thereby permit control of the number of ions emitted from each electrode. By this arrangement, the system may be efficiently operated to eliminate static electri~ity under changing conditions in the manufacturing area 9 or where the particular manufacturing process tends to generate either positive or negative static charges.
Figure 3 illustrates another embodiment of an 2S electrode bar 140 suitable for use with the presPnt inven-tion. The bar is generally similar to the bar 40, except that it includes three parallel conductors 142 and three rows of needle like projections 143 e~tending along its length. The additional projec~ions provided by this construction are believQd to increase the number of ions delivered into the airstream moving thereacro~s.
Figures 7-~ illustrate a further embodiment of the invention, and wherein the electrodes 240 are of a three dimensional solid configuration. More particularly, the electrodes 240 are in the form of a paraboloid, and they include an internal conductor 242 which supports a plural-5~
--1 o--ity of radiating needle like projections 243. Cooperatingpairs of these electrodes 240a, 240b are adapted to be mounted immediately downstream of a filter ~ank in the manner schematically illustrated in Figure 7, with the electrodes 240a being of one polarity, and the electrodes 240b being of the opposite polarity.
In the drawings and specification, there has been set forth a preferred embodiment of the invention, and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation. For example, while the specific embodiment of the invention described herein relates to a "cleanl' manu-facturing area, it will be appreciated that the invention may also be employed in any manufacturing, laboratory or production area where static electricity is a problem.
ELECTRIC CHARGES IN SENSITIVE MANUFACTURING AREAS
The present invention relates to the neutraliza-tion or elimination of static electricity in critical or sensitive manufacturing areas, such as clean rooms used for the production of semiconductors.
The manufacture of inte~rated circuit boards typi-cally includes the steps of forming minute circuits on a silicon wafer, cutting the resulting wafers into chips of about 118 inch square, and then interconnecting a number of the chips on a circuit board to ~orm the desired circuit.
~hese manufacturing operations are usually conducted in a "clean" enclosure, such as a clean room or clean work sta- -tion, and which includes high eficiency particulate air filters for removing substantially all particulate matter and dust from the air circulating therethrough, to thereby minimi~e the possibility o con~amination o~ the work~
pieces.
While existing clean rooms and work stations are able to minimize contamination from particulate matter in eritical or sensitive manufacturing areas~ a continuing and persiste~t problem relates to the fact that statir electri-city tends to build up on the workpieces and other objects in the manu~acturing area by reason of the workpieces being subjected to friction, pressure~ or temperature change.
Also, static electricity is often brought into the area with entering persons or raw materials~ This static electricity is a principal factor in semiconductor con-tamination and degradation. More particularly, con-tamination can result from the static electricity ?~S3 attracting a dust particle to the workpiece, and degrada-tion can result from the rapid change in potential due to current flow when the workpiece comes into contact with a grounded or oppositely charged object.
In an attempt to alleviate static electricity in sensitive manufacturing areas such as the manufacture o~
integrated circuit boards as described above, it has been proposed to ground all persons and objects in the manufac-turing areaO However, this is a cumbersome procedure and it cannot be totally effective since many of the materials in the room are nonconductive and thus will not transfer a static charge to ground.
It has also been proposed to ionize the air at clean work stations or benches, by providing a grid imme-diately downstream of the filter which is subjected to arelatively low AC voltage, such as 4,000 to 5,0~0 volts, and which alternately produces positive and negative ions.
The resulting ions act to neutralize static charges on objects which are cvntacted by the ions. However, the AC
current is not able to throw off ions more than a very - -limited distance, since the aiternating nature of the current tends to pull back the ions upon each cycle rever-sal. l'hus while this ionization has achieved some success in very confined areas such as clean work stations or 2S benches where the workpieces are positioned a very short distance from the grid, it has not proven satisfactory for l~rge clean room or manufacturing area.
The prior U.S. patents to Best et al, Nos.
3,942,072 and 4,064,548 describe a system for reducing a positive or negative field in a manufacturing area, and which includes two serially spaced apart thin wire grids positioned in an air conditioning duct, and with one grid connected to a positive high voltage source and the other connected to a negative high voltage source, to pro~uce both positive and negative ions~ However, this system has not been found to be satisfactory in actual pr~ctice since th~ downstream duct apparently tends to ground the ions ~nd thus insufficient numbers of ions are able to be discharyed from the duct. Also, the -thin wire grid is susceptible to breakage.
It is accordingly an object of the present inven-tion to provide an apparatus and method which are able to effectively eliminate static electricity in critical or sensitive manu-facturing areas, including large clean rooms and the like.
It is a more particular object of the present inven-tion to provide an apparatus and method for generating large numbers of both positive and negative free ions within a relatively large manufacturing area, and such that the ions are able to rapidly eliminate static electricity on objects in the area, or objects brought into the area.
These and other objects and advantages of the present invention are achieved in the embodiments illustrated herein by the provision of a pair of electrodes which are operatively mounted so as to be spaced apart from each other in a direction extending transversely to the direction of air flow. Current generating means are also provided for supplying a relatively high positive DC voltage to one of the electrodes, and a rela-tively high negative DC voltage to the other of -the elec-trodes. Thus the two electrodes act to concurrently generate positive and negative ions which are carried by the airstream directly into the manufacturing area.
-3a-The elec-trodes include a plurality of needle like projections, which facili-tate the formation and emission of ions in-to the airstream, and in one preferred embodimen-t, -the electrodes are in the form of two elongate bars which are disposed parallel to each other, with the needle like projec-tions directed toward each other. In another embodiment, the electrodes are in the form of paraboloids, wi-th the needle like projections radiating therefrom.
In summary, according to a first broad aspect, the invention provides in a clean enclosure sized so as to be adapted to enclose a manufacturing area, means for moving an airstream along a path of travel through said enclosure, the improvement therein comprising apparatus for concurrently generating both positive and negative ions in the airstream such that the ions are able to rapidly neutralize static electricity on objects in or brought into the area, and comprising at least one pair of electrodes operatively mounted within the path of travel of said airstream in said enclosure, with each of said at least one pair of electrodes being in the form of elongate kars which are disposed parallel to each other, and with the electrodes of each pair being spaced apart from each other a distance of between about six to twelve inches in a direction extending transversely to the direction of the path of travel and having an in-tervening airspace therebetween which is free of any electrically con-ductive components, and each of said electrodes including a ~2~ ~53 -3b-plurality of needle~ e elec-trically conductive projec-tions which extend toward the other electrode of the pair, and means for supplying a positive direc-t current voltage to one of said electrodes of each pair, and a negative direct curren-t voltage to the other of said elec-trodes of each pair, with the magnitude of the supplied voltages being sufficient to cause the electrodes to interact and cooperate in drawing ions from each other, whereby both positive and negative ions may be concurrently generated and carried through the enclosure by the moving airstream.
According to a second broad aspect, the invention provides in a clean enclosure having provision for supplying virtually particle free air to sensitive manufacturing areas and the like, a filter bank comprising at least one high efficiency particulate air filter, and blower means for circu-lating air through said bank and into said enclosure, the improvement therein comprising means for concurrently generating both positive and nega-tive ions in the airstream and such that -the ions are able to rapidly neu-tralize static electricity on objects in or brought in-to the enclosure, said ion genera-ting means including at least one cooperating pair of electrodes mounted immediately adjacent said filter bank with each co-operating pair of elec-trodes being spaced apart from each other a distance of between about six to twelve inches in a direc-tion ex-tending generally parallel to the adjacent face of said filter bank and having an intervening airspace therebetween which is free of any electrically conductive components, and each of said electrodes including a plurality of needle-like electrically -3c conductive projections, and means for supplying a posi-tive direct current voltage -to one of the electrodes of each pair, and a negative/direc-t current vol-tage to the other elec-trode of each pair, with the magnitude of the supplied vol-tages being sufficient to cause the electrodes to in-teract and co-operate in drawing ions from each other, whereby both positive and negative ions may be concurrently generated in the air-stream moving into said enclosure.
According to a third broad aspect, the inven-tion provides in a clean room having provision for supplying virtu-ally particle free air to sensitive manufacturing areas and the like, and including a room like enclosure, a filter bank disposed within said enclosure and including a supporting frame-work defining a plurality of open areas, a plurality of high efficiency particulate air filters mounted on said framework with one of the filters covering each of the open areas, and blower means for circulating air through said bank and to a manufacturing area disposed in the remainder of said enclosure, the improvement therein comprising means for concurrently generating both positive and negative ions in the airstream delivered to the manufacturing area and such -that the ions are able -to rapidly neutralize static electricity on objects in or brought into the manufacturing area t said ion generating means including a plurality of cooperating pairs of elec-trodes mounted to said supporting framework and immediately downstream of said filter bank, with each cooperating pair of electrodes being laterally spaced apart from each other in a direction extending generally parallel to the adjacent face of said -3d-filter bank and thus transversely to the direction of the moving aixstream and having an intervening airspace -there-between which is free of any electrically conductive components, and each of said electrodes including a plurali-ty of needle-like electrically conductive projections which extend toward the co-operating e]ectrode, and means for supplying a positive direct current voltage to one of -the electrodes of each pair, and a nega-tive direct current voltage to the other electrode of each pair, and with the lateral spacing of said electrodes of each pair and the voltages supplied to said electrodes being co-ordinated so that the electrodes of each pair interact and co-operate in drawing ions from each other, and such that both positive and negative ions may be concurrently generated in the airstream moving into the manufacturing area of said enclosure.
Some of the objects having been stated, other sbje~t~ will appear as the description proceeds, when taken in c~nnection with the accompanying drawing in which -Figure l is a generally schematic sectional side elevation view of a clean roo~ which embodies the presenti~ention;
Figure 2 is a perspective view of an ion generating electrode as utilized in the clean room shown in ~i~ure l;
Figure 3 is a sectional end view of an alternative embodiment of an ion generating electrode adapted for use with the present invention;
~ igure 4 is a bottom plan view, looking upwardly fro~ the manufacturing area, of a filter bank and ion ge~erating electrodes, and which embody the present i~ve~tion;
Figure S is a fragmentary perspective view of the ilter bank shown in Figure 4, Figure 6 is a horizontal sectional view taken 2P ~ub~tantially along the line 6-6 of Figure 5;
Figure 7 is a bottom plan view of a similar filter bank, and illustrating a ~econd embodimen~ of the ion generating electrodes;
Figure 8 is a perspective view of one of the ~le~trodes shown in the embodiment of Figure 7, and Figure 9 is a sectional view of the electrode hown in Figure 80 Referring more particularly to the drawings, Figure l schematically illustrates a clean room lO
e~bQdying the features of the present invention. The room comp~ises an enclosure which includes a top wall 12, a bot-~Q~ wall 13, and bounding side walls 14, 15, 16 (the fourth side wall not being shown). A horizontally disposed filter bank 18 is positioned within the enclosure parallel to and sp~ced from the top wall eo define an open air supply ple-n~lm 20 therebetween~ A raised floor 21 is mounted above the bottom wall 13 to define a return air plenum 22, with the floor 21 including a number of perforated panels for permitting air to pass therethrough. The return air plenum 22 communicates with a vertical duct defined between the outer side wall 16 ancl an interior wall 24, and which contains the air handling unit or blower 19 for recirculating the air into the air supply plenum 20. Thus in use, the air delivered to -the air supply plenum 20 by the blower 19 passes downwardly through the filter bank 18 such that essentially all particulate contaminates are removed immediately before the air enters the working area of the room.
The air then passes vertically downwardly through the room under essentially laminar flow conditions, and then passes through the floor 21 to the return air plenum 22.
In the embodiment specifically illustrated in Figures 4-7, the filter bank comprises a hori~ontally disposed suppor-ting latticework frame composed o~ a plurality of interconnected U-shaped channels 28 having their open sides directed upwardly, with the channels being substantially filled with a suitab~e sealing fluid 29. A plurality of air filters 30 are positioned on the latticework with one of the filters covering each of the open areas defined by the latticework. Each filter 30 comprises a rec~angular frame 32 and a filter pack 33 sealably disposed within the frame. Typically~ the filter pack 33 comprises a sheet of high efficiency particulate air filtering media which is folded in accordion fashion in a manner well known in the art.
Also, each filter 30 includes a downwardly depending metal skirt ?I~S3 -5a-34 positioned about the outer periphery of the frame, with khe skirt being adapted to rest within the open channels 28 and so as to be sealably immersed in the fluid 29. If desired, a plurality of lighting fixtures 35 may be positioned intermediate certain of the filters and secured to the latticework. A
further description of the above described filter bank and fluid sealing arrangement may be obtained by reference to U.S. Patent No. 3,486,311 to Allan.
In accordance with the present invention, a plura-lity of pairs of electrodes 40 are mounted to the lattice-work and immediately downstream o~ the filter bank7 Each pair includes an electrode 40a of one polarity, and an electrode 40b of like construction and of the opposite polarity. The electrodes are spaced apart from each other in a direction extending generally parallel to the adjacent f2ce of the filter bank and thus transversely to the direc-tion of air flow through the bank.
In the embodiment of ~igures 4-6, each electrode 40 comprises an elongate bar of C~shaped cross section as best seen in Figure 2, and which is composed of epoxy or similar non-conductive material. A metal conductor 42 is embedded in the bar and extends along its length, and a line of spaced apart, metallic needle like projec~ions 43 communicate with the conductor and extend outwardly from the bight of the bar when viewed in cross section~
In most clean rooms, it is unnecessary that all of the air be moved between operative electrodes, and under normal conditions, it is only necessary that about 25 to - -50% of the air pass between cooperating pairs of elec-trodes. Thus in the illustrated embodiment, electrode bars 40a~ 40b are mounted beneath only one half of the filters 30, with the other filters being free of any underlying electrodes. Thus in the illustrated embodiment, only about 50% of the downwardly moving airstream moves between opera-tive electrodesO
As best seen in Figures 4 and 5, two cooperating pairs of electrode bars 40a, 40b are mounted beneath one half of the filters in the bank. More particularly, the bars are secured to a peripheral frame member 45 which is secured to the inwardly facing edges of the channels 28, and so as to be substantially co-planar with the channels 28. The bars are grouped so that a single bar 40b is mounted along each side edge of the filter, and a pair of contiguous b~rs 40a o~ the same polarity are mounted to extend lengthwise along the medial portion of the filter, and with the bars thus being parallel to each other. Since filters of,the illustrated type usually measure 24 by 48 inches, it will be appreciated that the electrodes of each cooperating pair 40a, 40b are spaced apart about 12 inches.
Also, the bars are oriented sP that the needle like projec-tions 43 of each cooperating pair of bars face horizontally toward each other. Preferably, the frame member 45 is removably attached to the adjacent channels 28, to permit its removal downwardly and thus permit access to the filter for periodic servicing or replacement.
Current generating means is also provided for supplying a relatively high DC voltage of one polarity to the electrode 40a of each pair, and a relatively high DC
voltage of the opposite polarity to the e:Lectrode 40b of each pair. This current generating means includes a control unit 48 of conventional design, and which may be located either inside or outside of the enclosure 10. The control unit 48 is adapted to deliver a select~d voltage, in the range between zero to about 35,000 volts to each electrode 40a, 40b. More particularly, the control unit includes a knob 49 for concurrently adjusting the total power to the two electrode~, and thereby permit adjustment of the overall rate OI ion production. A control lever 50 is also provided which~ upon upward movement, acts to increase the charge to bot~ electrodes positively, and upon downward movement, to increase the charge to both electro-des negatively~ When the lever arm is centered, the electrodes 40a, 40b are charged with equal vol~ages of opposite polarity. Thus the lever 50 permits a change in the relative percentage of positive and negative ions, so as to efficiently accommodate a manufacturing process which normally produces excessive positive or negative static charges.
An atmospheric static sensor 52 of known construc-tion i~ positioned in the enclosure, ,and is operativelyconnected to a meter 53 on the control unit 48. Thus the output of the sensor 52 may be used to determine whether an increased charge in either the positive or negati~e direc-tion is required.
The lateral spacing of the electrodes 40a, 40b of each pair is determined by a number of factors, including the static load in the clean room to be neutralized, the volume of air flow, and the applied voltage. However, it is preferable that the electrodes be positioned suf-ficiently clo~e to each other so that the electrodes o~
each pair 40a, 40b interact and cooperate in drawing the ions from each other by reason of their opposite charges, and so that the ions may be readily removed and carried away by the airstream. Typically~ the spacing should be about six to twelve inches to provide the desired coopera-tion. Also, the use of electrodes having the describedneedle like projection 43 is preferred, in that it appears that the projections tends to concentrate the electrical charge at their point free ends, which facilitates the emission of ions into the airstream. It is also preferred to position the electrodes of each pair with the needle like projections aligned and`facing each other, since this orientation is believed to further facilitate the emission o ions.
In operation, it will be understood that the air handling unit ~ of the clean room 10 will serve to recir-culate the air through the filter bank 18 and downwardly ; through the manufacturing or production area of the room, under essentially laminar flow conditions. The current -generating means is then operated so that a relatively high positive ~C voltage, such as between about 20>000 and 35,000 volts, is applied to one electrode of each pair~ A
negative DC voltage of corresponding magnitude is applied to the oeher electrode of each pair. Positive and negative ions are thereby generated at the respective electrodes, and the airstream passing becween the electrodes acts to carry the ions away from thé electrodes and dire~ly into ~l2~ . 53 the underlying manufacturing area withou~ contact with adjacent confining ductwork or the like. The absence o~
such ductwork is seen to minimi~e the loss of ions which would otherwise result from contact of the ions with such ductwork. Thus the manufacturing area is effectively "flooded" with substantially equal numbers of both positive and negative ions, which serve to rapidly eliminate static electricity on objects in the area, or objects brought into ~he area. More particularly, the ions are attracted to opposite static charges, and thus the ions act to neutr~-lize static charges of either polarity. The excess ions will eventually be attracted to each other or to ground, leaving essentially no static charges in the manufacturing area. Where a sensor 52 and control unit 48 are employed, the magnitude and polarity of the static electricity in the enclosure may be monitored, and the controls 49 and 50 may be operated so as to selectively vary the voltage to each electrode and thereby permit control of the number of ions emitted from each electrode. By this arrangement, the system may be efficiently operated to eliminate static electri~ity under changing conditions in the manufacturing area 9 or where the particular manufacturing process tends to generate either positive or negative static charges.
Figure 3 illustrates another embodiment of an 2S electrode bar 140 suitable for use with the presPnt inven-tion. The bar is generally similar to the bar 40, except that it includes three parallel conductors 142 and three rows of needle like projections 143 e~tending along its length. The additional projec~ions provided by this construction are believQd to increase the number of ions delivered into the airstream moving thereacro~s.
Figures 7-~ illustrate a further embodiment of the invention, and wherein the electrodes 240 are of a three dimensional solid configuration. More particularly, the electrodes 240 are in the form of a paraboloid, and they include an internal conductor 242 which supports a plural-5~
--1 o--ity of radiating needle like projections 243. Cooperatingpairs of these electrodes 240a, 240b are adapted to be mounted immediately downstream of a filter ~ank in the manner schematically illustrated in Figure 7, with the electrodes 240a being of one polarity, and the electrodes 240b being of the opposite polarity.
In the drawings and specification, there has been set forth a preferred embodiment of the invention, and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation. For example, while the specific embodiment of the invention described herein relates to a "cleanl' manu-facturing area, it will be appreciated that the invention may also be employed in any manufacturing, laboratory or production area where static electricity is a problem.
Claims (16)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a clean enclosure sized so as to be adapted to en-close a manufacturing area, means for moving an airstream along a path of travel through said enclosure, the improvement therein comprising apparatus for concurrently generating both positive and negative ions in the airstream such that the ions are able to rapidly neutralize static electricity on objects in or brought into the area, and comprising at least one pair of electrodes operatively mounted within the path of travel of said airstream in said enclosure, with each of said at least one pair of electrodes being in the form of elongate bars which are disposed parallel to each other, and with the electrodes of each pair being spaced apart from each other a distance of between about six to twelve inches in a direction extending transversely to the direction of the path of travel and having an intervening airspace there-between which is free of any electrically conductive components, and each of said electrodes including a plurality of needle-like electrically conductive projections which extend toward the other electrode of the pair, and means for supplying a positive direct current voltage to one of said electrodes of each pair, and a negative direct current voltage to the other of said electrodes of each pair, with the magnitude of the supplied voltages being sufficient to cause the electrodes to interact and cooperate in drawing ions from each other, whereby both positive and negative ions may be concurrently generated and carried through the enclo-sure by the moving airstream.
2. The enclosure as defined in claim 1 wherein said voltage supplying means includes means for selectively varying the voltage to each electrode of each pair so as to permit adjustment of the rate of ion generation at each electrode.
3. The enclosure as defined in claim 1 further comprising high efficiency particulate air filter means mounted along said path of travel, with each pair of electrodes being mounted immed-iately downstream of said filter means.
4. The enclosure as defined in claim 1 wherein the portion of said enclosure immediately downstream of said electrodes is characterized by the absence of closely confining ductwork within said enclosure for enclosing the airstream, to thereby minimize the loss of ions which would otherwise result from contact with such ductwork.
5. In a clean enclosure having provision for supplying virtually particle free air to sensitive manufacturing areas and the like, a filter bank comprising at least one high efficiency particulate air filter, and blower means for circulating air through said bank and into said enclosure, the improvement therein comprising means for concurrently generating both positive and negative ions in the airstream and such that the ions are able to rapidly neutralize static electricity on objects in or brought into the enclosure, said ion generating means including at least one cooperating pair of electrodes mounted immediately adjacent said filter bank with each cooperating pair of electrodes being spaced apart from each other a distance of between about six to twelve inches in a direction extending generally parallel to the adjacent face of said filter bank and having an intervening air-space therebetween which is free of any electrically conductive components, and each of said electrodes including a plurality of needle-like electrically conductive projections, and means for supplying a positive direct current voltage to one of the elect-rodes of each pair, and a negative direct current voltage to the other electrode of each pair, with the magnitude of the supplied voltages being sufficient to cause the electrodes to interact and cooperate in drawing ions from each other, whereby both positive and negative ions may be concurrently generated in the airstream moving into said enclosure.
6. The clean enclosure as defined in claim 5 wherein each cooperating pair of electrodes is positioned immediately downstream of said filter bank, and said electrodes of each pair are in the form of elongate bars which are disposed parallel to each other, and wherein at least a substantial portion of the needle-like projections on each bar are directed toward the cooperating bar.
7. The clean enclosure as defined in claim 6 wherein said electrodes are sized and of a sufficient number such that at least about 25% of the air passing through said bank passes between a cooperating pair of electrodes.
8. The clean enclosure as defined in claim 7 further com-prising static sensing means positioned in said enclosure for pro-viding an indication of the magnitude and polarity of any static electric charges therein.
9. The clean enclosure as defined in claim 8 further inclu-ding first control means for concurrently increasing or decreasing the voltage to both electrodes, and second control means for selec-tively changing the voltage to both electrodes either positively or negatively.
10. In a clean room having provision for supplying virtually particle free air to sensitive manufacturing areas and the like, and including a room like enclosure, a filter bank disposed with-in said enclosure and including a supporting framework defining a plurality of open areas, a plurality of high efficiency particu-late air filters mounted on said framework with one of the fil-ters covering each of the open areas, and blower means for circula-ting air through said bank and to a manufacturing area disposed in the remainder of said enclosure, the improvement therein compri-sing means for concurrently generating both positive and negative ions in the airstream delivered to the manufacturing area and such that the ions are able to rapidly neutralize static electri-city on objects in or brought into the manufacturing area, said ion generating means including a plurality of cooperating pairs of electrodes mounted to said supporting framework and immediately downstream of said filter bank, with each cooperating pair of electrodes being laterally spaced apart from each other in a direction extending generally parallel to the adjacent face of said filter bank and thus transversely to the direction of the moving airstream and having an intervening airspace therebetween which is free of any electrically conductive components, and each of said electrodes including a plurality of needle-like electri-cally conductive projections which extend toward the cooperating electrode, and means for supplying a positive direct current vol-tage to one of the electrodes of each pair, and a negative direct current voltage to the other electrode of each pair, and with the lateral spacing of said electrodes of each pair and the voltages supplied to said electrodes being coordinated so that the elec-trodes of each pair interact and cooperate in drawing ions from each other, and such that both positive and negative ions may be concurrently generated in the airstream moving into the manufac-turing area of said enclosure.
11. A method for delivering air to a sensitive manufacturing area, and for rapidly neutralizing static electricity on objects in or brought into the area, and comprising the steps of moving an airstream between a cooperating pair of electrodes, with the electrodes being in the form of elongate bars which are disposed parallel to each other and spaced apart from each other a dis-tance of between about six to twelve inches in a direction exten-ding transversely to the direction of the airstream and having an intervening airspace therebetween which is free of any electrically conductive components, with each of said electrodes including a plurality of needle-like electrically conductive projections which extend toward the other electrode of the pair, while supply-ing a positive direct current voltage to one of said electrodes and a negative direct current voltage to the other of said elec-trodes, with the magnitude of the supplied voltages being sufficient to cause the electrodes to interact and cooperate in drawing ions from each other, and so as to concurrently generate both positive and negative ions in the airstream, and while directing the air-stream and entrained positive and negative ions directly to the manufacturing area and without the use of confining ductwork, to thereby minimize the loss of ions which would otherwise result from contact with such ductwork.
12. The method as defined in claim 11 wherein the supplied voltage to each electrode is at least about 20,000 volts.
13. A method for delivering virtually particle free air to a sensitive manufacturing area and for rapidly neutralizing static electricity on objects in or brought into the area, and comprising the steps of moving an airstream through high efficiency particu-late air filtering means to remove substantially all particulate matter therefrom, passing at least a substantial portion of the filtered airstream between a pair of electrodes, with the elec-trodes being positioned immediately downstream of the filtering means and spaced apart from each other in a direction extending transversely to the direction of the airstream and having an inter-vening airspace therebetween which is free of any electrically conductive components, and with each of said electrodes including a plurality of needle-like electrically conductive projections, and supplying a positive direct current voltage to one electrode and supplying a negative direct current voltage to the other elec-trode, with the magnitude of the supplied voltages being sufficient to cause the electrodes to interact and cooperate in drawing ions from each other, and so as to concurrently generate both positive and negative ions in the airstream, and directing the filtered air-stream and entrained positive and negative ions to the manufac-turing area.
14. The method as defined in claim 13 wherein the spacing between the electrodes is between about six to twelve inches, and the voltage supplied to each of the electrodes is in the range between about 20,000 to 35,000 volts.
15. The method as defined in claim 14 comprising the further step of sensing the magnitude and polarity of any static electri-city adjacent the manufacturing area and adjusting the voltage of the electrodes to effectively and rapidly neutralize such static electricity.
16. The method as defined in claim 15 wherein the step of directing the filtered airstream and ions to the manufacturing area includes moving the airstream under substantially laminar flow conditions and without the use of closely confining duct-work, to thereby minimize the loss of ions which would otherwise result from contact with such ductwork.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/392,531 US4477263A (en) | 1982-06-28 | 1982-06-28 | Apparatus and method for neutralizing static electric charges in sensitive manufacturing areas |
| US392,531 | 1982-06-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1210053A true CA1210053A (en) | 1986-08-19 |
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ID=23550945
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000431208A Expired CA1210053A (en) | 1982-06-28 | 1983-06-27 | Apparatus and method for neutralizing static electric charges in sensitive manufacturing areas |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US4477263A (en) |
| JP (1) | JPS5912600A (en) |
| CA (1) | CA1210053A (en) |
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-
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-
1983
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- 1983-06-27 CA CA000431208A patent/CA1210053A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4477263A (en) | 1984-10-16 |
| JPS5912600A (en) | 1984-01-23 |
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