WO1992021451A1

WO1992021451A1 - Printed circuit board cleaner

Info

Publication number: WO1992021451A1
Application number: PCT/US1992/004704
Authority: WO
Inventors: Joseph Baia; James Nathan Elliott
Original assignee: Manufacturing Concepts & Technologies, Inc.
Priority date: 1991-06-05
Filing date: 1992-06-04
Publication date: 1992-12-10

Abstract

A printed circuit board cleaner (20) has upper (24) and lower (26) conveyor runs spaced-apart uniformly along a common upright plane of travel. The upper (24) and lower (26) conveyor runs comprise axially spaced-apart rollers (30), at least along the bottom conveyor run. Boards (22) captured between the upper (24) and lower (26) conveyor runs travel in an upright position at desired intervals in series along the conveyor. The conveyor runs produce an edgewise squeezing pressure on opposite edges of each upright board inserted into the space between the conveyor runs. The conveyor moves the squeezed boards (22) axially while resisting significant vertical or sideways movement of the board during its travel. The entire opposite side surfaces of each board are exposed in the space between the conveyors. Impinging spray jets (132) simultaneously direct cleaning fluid toward both sides of each board (22) for removing residue. The impinging spray jets (132) are under high pressure, spaced at close range, and are directed at desired angles to the plane of the board to enhance the cleaning action. The boards are subjected to different fluid processing zones in sequence, which can include: pre-wash (42), wash (44), pre-rinse (46), rinse (48) and drying (50) zones.

Description

PRINTED CIRCUIT BOARD CLEANER

Field of the Invention

This invention relates to the cleaning of printed circuit boards, and more particularly, to an improved system for thoroughly cleaning flux residue and other process and surface residuals from circuit boards after the board fabrication and/or assembly process.

Background of the Invention The fabrication and assembly of printed circuit boards require certain process steps which ultimately leave process and surface residuals on the boards. These residue materials must be removed from the board before the board is used. The residue left on circuit boards after fabrication and assembly can include flux residue, ash, solder balls, dust, foreign particles, handling contaminants, and the like. Some residues may have an immediate harmful effect on the operation or performance of the circuit; other residues may gradually degrade and erode the performance over time, and yet other harmful residues may be latent and become activated or accelerated by operating environment of the user, such as humidity. Another class of residues may be described as non-harmful but may be regarded as cosmetically unacceptable based on the end user's application and product quality standards. Although cosmetic residues may themselves be non-harmful to product performance, it is possible for them to attract and hold other contaminants that are harmful, and therefore cleaning may still be required. This invention is directed to the problem of removing the flux residue left after circuit components are soldered or attached to circuitry on the board; however, the invention is also concerned with the removal of other residue materials from circuit boards. For example, even though some "no-clean" fluxes are said to leave low residues and non-ionic residues, other dirt and solder balls can be embedded in this residual material. Therefore, even if the solder residue is non-ionic, it can hold other unwanted contaminants, and the present invention is capable of removing these additional process and surface residuals. The invention is, therefore, directed generally to the removal of any type of flux residue or other process or surface residuals or contaminants which are referred to generally herein as "residue," although the invention is described principally herein in the context of removing flux residue from circuit boards.

Further, such residue can be left on either bare boards after the board fabrication process, or on assembled circuit boards after circuit components are soldered or attached to circuitry on one or both sides or the board. The invention is applicable both to the cleaning of bare boards and assembled circuit boards. Bare boards, typically in the last step after a solder mask layer is applied, are dipped into a flux bath and then dipped into molten solder. The board is then put through a hot oil or hot air leveling step, followed by a board cleaning operation. The process is intended to coat all the exposed vias (thru-holes) and component attachment points with solder and then level the solder coating. The board surfaces can have surface and process residuals and contaminants that must be removed.

Fabricated printed circuit boards are further assembled into electronic products. These printed circuit boards, known in the art as "populated" circuit boards, typically have a number of circuit elements mounted to the circuit patterns imprinted on one or both sides of the board. Thru-holes formed in the board receive the leads of certain circuit components mounted to the board, while other components may be attached to surface circuit patterns. After . the components are positioned on the board, the leads are connected to the printed circuitry by well known fluxing and soldering steps. When soldering is completed, the surfaces of the board have flux residue and other surface and process residuals which can later cause problems if not removed from the board. Therefore, the residue is thoroughly cleaned from both sides, including all surfaces, holes and cavities of the circuit board, before the board is used.

In the past, finished printed circuit boards have been cleaned by a number of techniques. One type of circuit board cleaner is a wave cleaner in which the boards are submerged in low-velocity water or solvent waves. This approach has several drawbacks, among which is the inability to obtain the cleaning force necessary to thoroughly remove all flux particles as required of high-quality circuit boards.

Another type of circuit board cleaner uses low- velocity water or solvent waves in combination with rotating brushes. The brushing action does not greatly improve cleaning, particularly flux particles trapped in tiny spaces between the circuit elements and the board. This method is more commonly used on fabricated circuit boards (bare boards) since the brushed may damage populated circuit board components. A further type of circuit board cleaner is a spray cleaner in which boards are transported through a bath on screen belts and sprayed from the top and bottom with water or solvent. Although a high-impact spray would be desirable to thoroughly clean the board, especially in the stand-off spaces beneath the circuit components, the spray force and spray angles are limited because the boards are loosely placed on the screen and are thus moved about in reaction to a high- impact spray.

As circuit components become smaller and smaller and the lead pitch densities increase, the job of thoroughly cleaning all residue particles from the board becomes more difficult. In addition, solvents are generally more effective in cleaning circuit boards than aqueous cleaning solutions, but the use of solvents such as CFC's has been restricted or banned or is being phased out under governmental regulations because of environmental concerns. Use of other types of solvents such as terpene also is undesirable because of their flammable characteristics.

Thus, there is a need for a circuit board cleaner that can thoroughly clean residue from a circuit board, whether the board is a bare board or an assembled board. As to assembled boards, the board cleaner should effectively clean all the residue, including particles trapped in the stand-off spaces between the circuit elements and the board. The board should be cleaned thoroughly on both sides, all edges and from all holes and cavities. High-quality board cleaning efficiency should be achieved with aqueous cleaners rather than solvents. In a spray-type cleaner, the system should provide high-impact spray forces and desired spray angles to obtain maximum cleaning efficiency. The present invention provides a spray-type circuit board cleaner that thoroughly cleans both sides of a circuit board with high-pressure spray jets operating from close range at desired angles to maximize cleaning efficiency. Bare boards and assembled boards are both effectively cleaned on all sides, including holes and cavities and edges. Moreover, high-quality cleaning is produced using aqueous cleaning solutions. In addition, the circuit board cleaner can be efficiently operated continuously, through a number of different cleaning cycles, and with minimal operator handling requirements. The circuit board cleaner also has the advantages of a high-volume throughput with minimal space requirements and low operating costs. Other advantages also are provided.

^gιιmm-ιτγ n the Invention

Briefly, the present invention provides techniques for cleaning residue from printed circuit boards, either bare boards, or assembled boards having a planar board and circuit components mounted on one or both sides of the board. According to the invention, a pair of spaced-apart board conveyor runs capture and transport the boards in series along a path of travel through the cleaning machine. The spaced-apart conveyor runs are positioned so they extend generally parallel to one another along a common plane of travel through the machine. A board is inserted in the space between the conveyor runs so the conveyor runs capture the board by edgewise pressure applied to opposite edges of the board. The captured board is transported by the conveyor runs along the plane of travel, leaving essentially the entire opposite side surfaces of the board exposed in the space between the conveyor runs. The exposed portions of the moving board are impinged by spray jets to clean residue particles from either side or both sides of the board. The captured board is retained in a fixed position by the edgewise pressure applied by the conveyors as the board moves through the cleaning system. The fixed board is thus able to resist the forces of high pressure spray jets impinging on the board from close range. This provides maximum cleaning efficiency because of the high forces of the cleaning fluids impinging on the board and because of the variety of spray angles that can be used. The boards also travel in series through the cleaning system and are thus able to pass through a series of cleaning cycles, any of which can be operated at high pressures. Pre-wash, wash, pre-rinse, and rinse cycles are examples of cleaning cycles.

Preferably, the board is held in an upright position along the plane of travel, and high-pressure spray jets impinge on opposite exposed faces of the fixed, upright board from close range. Residues are removed from the board surfaces under pressure and fall away to drain under gravity. With the upright positioning of the board, once residue is removed from the surface of the board it travels under gravity away from the work zone instead of flowing across a work surface where it may become entrapped as residue again. In a preferred form of the invention, the conveyor run along the bottom side of the board comprises spaced-apart rollers which allow drainage under gravity between the rollers. Preferably, the rollers have aligned recesses along the plane of travel in which the boards are captured, together with separate compliant board support members in the recess of each roller for applying resilient edgewise pressure to the opposite edges of the board.

In one form of the invention, the bottom run of the conveyor has a fixed orientation while the top run of the conveyor is movable and applies a controlled, resilient edgewise pressure to the board uniformly along the plane of travel. This mechanism also provides means for adjusting to different board heights.

Another form of the invention includes impinging the board with a continuous spray of aqueous cleaning fluid in combination with a pulsing air jet to enhance the cleaning action on the board.

During use, the circuit board cleaner thoroughly cleans residue from the board, including particles in the stand-off spaces between the circuit elements and the board. The board is cleaned thoroughly on all surfaces, holes and cavities, and cleaning efficiency is achieved with aqueous cleaners rather than solvents. The boards are captured and held in a fixed position sufficiently to resist impingement forces from the sides by the high-pressure spray jets. Essentially the entire board is exposed at both sides to the close range high-pressure spray jets. Holding the boards solely by edgewise pressure exposes the entire board surface to the cleaning jets. This prevents any contact between the cleaning mechanism and the circuits and/or circuit components, while the vertical positioning of the boards also aids in the washing process by removing dislodged particles under gravity.

These and other aspects of the invention will be more fully understood by referring to the following detailed description and the accompanying drawings.

Brief Description of the Drawings

FIG. 1 is a fragmentary perspective view showing one embodiment of a printed circuit board cleaner according to principles of this invention; FIG. 2 is a diagrammatic side-elevation view of the circuit board cleaner;

FIG. 3 is a top view of the circuit board cleaner shown in FIG. 2;

FIG. 4 is a top view showing an arrangement of spray jet nozzles impinging upon both sides of a circuit board travelling through the circuit board cleaner;

FIG. 5 is a cross-sectional view showing upper and lower conveyor runs comprised of spaced-apart rollers and a drive system for the bottom run of rollers;

FIG. 6 is a cross-sectional view of the system shown in FIG. 5;

FIG. 7 is a cross-sectional view illustrating an alternative form of the invention in which continuous drive belts transport a circuit board through the circuit board cleaner;

FIG. 8 is a side view showing the input end of a circuit board cleaner having the drive belt configuration of FIG. 7; FIG. 9 is a semi-schematic end elevation view illustrating a means for uniformly controlling the edgewise pressure of the transport means applied to the opposite edges of a circuit board travelling through the circuit board cleaner; FIG. 10 is a semi-schematic end elevation view similar to FIG. 9, but showing the controller in an operative position engaged with opposite edges of a circuit board;

FIG. 11 is a side elevational view illustrating spray jet and air jet systems for successive steps in the cleaning process, which include: pre-wash, wash, pre-rinse, final rinse and drying cycles; FIG. 12 is an end elevational view showing spray jets from the washing section and a cross-sectional view showing upper and lower conveyor runs holding an exposed board between the opposed spray jet nozzles; and

FIG. 13 is a fragmentary cross-sectional view showing an air jet nozzle and a fluid spray jet.

Detailed Description

FIG. 1 illustrates the general principles of operation of a printed circuit board cleaner 20 for cleaning fabricated printed circuit boards (bare boards) or assembled circuit boards having electrical circuit components fluxed and soldered or attached to printed circuits on either or both sides of the board. In the illustrated embodiment, printed circuit boards 22 of either type are illustrated as planar, rectangular boards passing through the circuit board cleaner 20. Circuit components and the printed circuits that may normally be on the board are not shown for simplicity. Circuit boards of shapes other- than with parallel opposite edges also may be processed. In these instances the boards can be placed in separate modules (with parallel edges) freely inserted into the machine.

The embodiment of FIG. 1 principally shows a linear conveyor which is one component of the circuit board cleaning system. The conveyor includes an upper conveyor run shown generally at 24 and a lower conveyor run shown generally at 26. The two conveyor runs are spaced apart with uniform spacing along the axis of board travel. The two conveyor runs also are aligned in a common plane, preferably a common vertical plane defining an upright axis of board travel. This invention can produce good cleaning if the boards are mounted in a horizontal or other plane, but the vertical plane is preferred. During use, the boards are inserted into the space between the upper and lower conveyor runs, and the conveyor runs are arranged to capture the board between them by applying an edgewise retaining force to the upper and lower peripheral edges of the board. The upper and lower conveyors then move the captured board along the upright plane of travel through the machine. The upper and lower conveyors capture the board and control and guide it along the plane of travel while resisting vertical movement or sideways movement of the upright board. Thus, the moving board is rigidly held in a fixed upright position during its travel through the cleaning system. The board is retained with sufficient retaining force that allows use of high- pressure spray jets impinging on both sides of the board from close range, at any selected angle, to produce a thorough cleaning action. The upright board, during its travel through the machine, is subjected to a series of separate cleaning cycles. Because of the vertical travel of the board, residue particles dislodged from the board during the cleaning cycles are removed under gravity to drainage below the impinging spray jets and the conveyor. Residue removed from one board therefore does not transfer to other boards in process.

In the embodiment of FIG. 1, the upper and lower conveyor runs comprise a series of longitudinally spaced-apart upper rollers 28 and a corresponding series of longitudinally spaced apart lower rollers 30. The upper rollers are uniformly spaced apart longitudinally with their axes of rotation perpendicular to their alignment along a common longitudinal axis of board travel. The upper rollers are mounted along the common longitudinal axis within a downwardly opening, U-shaped upper supporting frame 32. Similarly, the lower rollers are uniformly spaced apart longitudinally with their axes of rotation perpendicular to their alignment along a common axis of board travel. The lower rollers are mounted along the common axis of travel within an upwardly opening, U- shaped bottom supporting frame 34. The axis on which the upper and lower rollers are aligned defines a common axis of board travel through the circuit board cleaner. FIG. 1 also illustrates travel of the circuit boards 22 through the cleaning system. The top and bottom edges of the boards are captured between the upper and lower rollers. Preferably, the bottom rollers are driven to rotate in unison, at a common speed, and in a common direction to move the boards at a controlled (fixed but adjustable) speed past the series of cleaning stations. Although other means of control are possible, it is preferable to move the boards at a selected speed continuously through the machine, from one end to the other. The upper frame 32, which holds the upper rollers 28, is pivotally mounted on a counterbalancing system. The upper frame moves up or down to move the upper rollers toward- or. away from the top edges of the boards. This provides a means for controlling the amount of edge pressure applied to the top edges of the boards. It also provides a means for adjusting the spacing of the conveyors to the height of the boards. FIG. 1 also schematically illustrates an upright cleaning bar 36 having a series of vertically spaced- apart spray nozzles 38 for impinging a cleaning fluid on a face of the upright board travelling through the cleaning system. This schematically represents one cleaning station. FIG. 1 also illustrates a drying bar 40 from which hot air is forced toward the board during a drying cycle at the end of the conveyor.

The description to follow provides a more complete description of: the upper and lower conveyor rollers, an alternative means of transporting the boards, a technique for applying a controlled amount of uniform edgewise pressure to the edges of the board, and a system of washing and rinsing cycles.

Referring to FIG. 2, both sides of the circuit boards travelling through the circuit board cleaner are simultaneously subjected to a series of separate and independent cleaning cycles which include, in sequence. a pre-wash zone 42, a wash zone 44, a pre-rinse zone 46, a final rinse zone 48 and a drying zone 50. Upright cleaning bars 52 are shown in the pre-wash zone; a series of longitudinally spaced-apart, upright cleaning bars 54 are shown in the wash zone; upright cleaning bars 56 are mounted on opposite sides of the pre-rinse zone 46; and upright cleaning bars 58 are mounted on opposite sides of the final rinse zone 48. The drying zone 50 has drying bars 60 for impinging hot air on opposite sides of the boards.

FIG. 2 also shows a conveyor counterbalance bar 62 for counterbalancing the frame to which the upper conveyor rollers are mounted. This frame is pivotally suspended from left and right lift mechanisms 64 and 66 connected to the counterbalancing bar. Water for each cycle is circulated through a pre-wash tank 68, a wash tank 70 and a pre-rinse tank 72, all located sequentially beneath the conveyor. A dryer 74, located at the bottom end of the conveyor system, supplies air to the drying bars 60.

FIG. 3 is a top view of FIG. 2 and illustrates the travel of the circuit boards along the common vertical plane of travel defined by an axis 76 extending lengthwise through the series of cleaning zones. A fluid pump 76 supplies fluid to the pre-wash bars 52; a fluid pump 78 supplies cleaning fluid to the wash bars 54; and a fluid pump 80 supplies cleaning fluid to the pre-rinse and rinsing bars 56 and 58. An electrical power and control panel is shown at 82. FIGS. 5 and 6 illustrate one embodiment of the board conveyor system in which the upper and lower runs of the conveyor are formed by the series of upper rollers 28 and lower rollers 30. The upper rollers are uniformly spaced apart along the axis of the upper conveyor, and the lower rollers have the same uniform spacing along the lower conveyor. All rollers are identical. The upper rollers 28 are preferably idler rollers each comprising a pulley, with a generally V- shaped annular recess or groove 83. A separate compressible O-ring 84 is seated in the bottom of each groove in the upper rollers. The upper rollers are disposed between opposite side walls of the U-shaped frame 32, and the rollers rotate about corresponding shafts 86 spaced apart uniformly along the upper frame. The bottoms of the upper rollers project downwardly into the open space between the upper and lower conveyors so that the bottom portions of the resilient 0-rings 84 combine to provide a resilient means of support aligned at the same level along the upper conveyor.

The lower conveyor run is formed by a similar series of identical pulleys, each having a generally V- shaped recess or groove 88 and a separate, compressible O-ring 90 seated in the bottom of each groove in the lower rollers. The lower rollers are disposed between opposite side walls of the lower frame 34 and rotate about corresponding transverse shafts 92 spaced apart uniformly and aligned along a common axis on the bottom frame. The axes of rotation of the upper rollers are aligned with the axes of rotation of corresponding lower rollers. The tops of the lower rollers project upwardly into the open space between the upper and lower conveyors so that the upper portions of the resilient 0-rings 90, in the recesses of the lower rollers, combine to provide a resilient means of support at the same level along the lower frame. The bottom rollers are driven by an endless belt drive system mounted to the frame 34 below the row of bottom rollers. The drive system includes longitudinally spaced-apart driven rollers 94 engaged by an endless drive belt 96 located below the row of bottom rollers. The drive belt is positioned so that the top run of the drive belt engages the V-shaped groove 88 of the bottom rollers 30 along the length of the conveyor drive. Preferably, at least one of the driven rollers 94 is coupled to a drive motor for driving the drive belt 96 to cause the upper run of the drive belt to travel at a desired speed to rotate the bottom rollers 30 at the speed necessary to control the rate at which the boards travel through the cleaning system. The driven rollers 94 are mounted opposite side walls of the frame 34 on corresponding rotating shafts 98 aligned along a common axis below the bottom rollers 30. The driven rollers are mounted at uniformly spaced-apart positions and at the same level so that a uniform drive force can be transferred from the drive belt to the series of bottom rollers.

The cross-sectional view of FIG. 6 also illustrates mounting of the circuit board 22 between the series of upper and lower rollers for controlling travel of the board through the cleaning system. In a preferred embodiment, the series of bottom rollers and the drive system are held in a fixed, stationary position at the bottom of the conveyor while the upper frame 32, to which the upper rollers are mounted, is movable vertically toward or away from the bottom rollers. Positioning of the upper frame 32 and the upper rollers provides a means to control the height of the space between the upper and lower sets of rollers to match the height of the boards being processed. Travel of the upper series of rollers also provides a means for controlling the pressure acting edgewise on the upper and lower edges of the board as each board is held between the upper and lower rollers. During use, a resilient edgewise pressure is applied to the top and bottom edges of the boards by the resilient O-rings 84 and 88 on the upper and lower rollers. The amount of edgewise pressure on each board can be controlled; further downward movement of the upper series of rollers increases the edgewise pressure acting on the upper and lower edges of the boards, for example. The system for controlling the amount of edgewise pressure on the boards is described with respect to the counterbalancing system shown in FIGS. 9 and 10 and described in more detail below. FIGS. 7 and 8 illustrate an alternative embodiment of a conveyor system for capturing and moving vertically positioned circuit boards through the cleaning system. In this embodiment, the upper and lower conveyor runs are each formed by endless drive belts engaged with pulleys at opposite ends of the conveyor. As shown best in FIG. 7, the upper conveyor comprises an endless upper conveyor belt 100, and the lower conveyor comprises an endless lower conveyor belt 102. The bottom run of the upper conveyor belt is disposed in a rectangular recess 104 in a rigid, elongated support base 106. Guide plates 108 are secured to the bottom side of the base 106 on opposite sides of the lower run of the upper conveyor belt. The guide plates 108 retain the belt in the groove 104 and provide a small space between them for guided travel of the upper portion of the board as it contacts the upper conveyor belt. Similarly, the lower endless conveyor belt is mounted in an upwardly facing groove 110 in a rigid base 112, and guide plates 114 on opposite sides of the base 112 retain the upper run of the lower conveyor belt and provide a small space for guiding the lower portion of the circuit board 22 as it contacts the lower conveyor belt.

Preferably, the upper and lower conveyor belts 100 and 102 are made from a compliant material such as a resilient meshlike material made of fiberglass, or rubber.

FIG. 8 illustrates a side view of the upper and lower conveyor belts at the entrance opening to the conveyor where the circuit board 22 is inserted into the space between the upper and lower conveyor belts.

This view also illustrates upper and lower pulleys 116 and 118 at the entrance ends of the upper and lower conveyors.

Thus, in the arrangement shown in FIGS. 7 and 8, each endless conveyor belt is positioned in a longitudinal groove within an elongated solid block running the length of the conveyor. The belt slides in the groove of each block, and the blocks form a rigid means of support behind the compressible belts that maintains the belts at a fixed, uniform spacing along the entire length of the conveyor. The circuit boards are manually or mechanically fed into the space between the conveyor belts, and the boards are captured between the compressible surfaces of the upper and lower runs of the belts. The boards can be fed into the conveyor system with random spacing between the boards, and the belts hold the boards rigidly between the belts by resilient pressure contact only with the peripheral edges of the boards. Thus, essentially the entire board is exposed at both sides to the close range, high-pressure spray jets in the sequential cleaning cycles. Holding the boards solely by edgewise pressure exposes the maximum surface area on both sides of the board to the spray jets. It also prevents any contact between circuits or circuit elements on the board and any part of the cleaning system. This prevents any potential damage to circuits and/or circuit components on the boards. The vertical positioning of the boards also aids in the washing process by removing dislodged residue by gravity from both sides of the board simultaneously.

FIGS. 9 and 10 illustrate the means for moving the upper conveyor for adjusting the height of the vertical space between the conveyors and for controlling the edgewise pressure applied to the top and bottom edges of the board. In this embodiment, the upper and lower conveyors are shown in the form of the upper and lower endless conveyor belts 100 and 102, although the system shown in FIGS. 9 and 10 is equally applicable to the embodiment in which the upper and lower conveyors are formed by the series of rollers. In the embodiment illustrated in FIG. 9, the bottom conveyor remains stationary, while the top conveyor is moved vertically by the lift bars 64 and 66 (see FIG. 2) connected to opposite ends of the upper frame 32 which holds the upper conveyor. Each lift bar pivots to the upper frame through a pivot pin 118. The upper end of each lift bar has a pivot 119 which pivots the lift bar to the end of a long lever arm 120. Identical lever arms 120 extend along opposite ends of the cleaning machine. A central portion of each long lever arm has a pivot pin 122 for pivoting the lever arm to the bottom of a fixed support 124 extending downwardly from a stationary base or frame 126. The end of the lever arm spaced from the upper conveyor is balanced by the counterbalancing member 62 which extends the length of the conveyor between the lever arms 120 at opposite ends of the conveyor. The counterbalancing bar 62 balances the weight of the upper conveyor, and by rotating in an upward direction, from the position of FIG. 9 to the position of FIG. 10, lowers the upper conveyor to reduce the space between the upper and lower conveyors. This also provides a means for adjusting the edgewise pressure at the opposite ends of the board 22 shown in FIG. 10. A drive system connected to the counterbalancing bar 62 can be used to controllably adjust rotation of the counterbalancing bar to adjust the spacing between conveyors and apply a critical amount of pressure to the ends of the boards passing through the cleaning system.

FIG. 11 is a side view illustrating the systems for supplying aqueous cleaning fluids and drying air to the successive cycles of the board cleaning system.

FIG. 4 illustrates a top view of the cleaning fluid and drying air supply systems. Referring principally to FIG. 11, the pre-wash zone 42 has the four upright cleaning bars 52, two on each side of the circuit board. There is preferably one conventional cleaning bar on each side of the board and one power-pulse cleaning bar on each side of the board. (The power-pulse cleaning bars are described in more detail below.) There are preferably six vertically spaced apart spray nozzles 132 directed from each cleaning bar toward the moving circuit board. Spray nozzle spacings and spray jet angles provide full coverage of each side of each board in process. The washing fluid is contained in a 40-gallon heated, filtered and recirculated fluid system. The pre-wash system is preferably heated by a 9 kw heater and is powered by a. 3.0 hp pump.

The wash zone 44 comprises a system of eight cleaning bars 54, four on each side of the board. There is preferably one power-pulse cleaning bar on each side of the board and there are three conventional cleaning bars per side. A series of six spray nozzles on each bar is shown at 132. The system is heated by two 9 kw heaters and is powered by a 5.0 hp pump. The washing fluid is contained in an 80 gallon heated, filtered and recirculated fluid system. The pre-rinse zone 46 is preferably a 40 gallon heated, filtered and recirculated system. There are four cleaning bars 56, two on each side of the board. There is preferably one conventional cleaning bar per side and one power-pulse cleaning bar per side. The spray jets are shown at 132. The system is preferably heated by one 9 kw heater and is powered by a 3.0 hp pump. The system is supplied by an overflow cascade from the final rinse with an overflow to a drain.

The final rinse zone 48 has four cleaning bars 58, one conventional cleaning bar per side and one power- pulse cleaning bar per side. The system is supplied by a direct inlet of clean water. The spray jets are at 132.

The spray jets 132 on the cleaning bars of the wash zone 44, pre-rinse zone 46 and final rinse zone 48 can be directed at various angles and have nozzle spacings to ensure full coverage of both sides of each board.

The pressure applied by the spray jets at each zone also can be controlled separately and independently from the other processing zones.

The drying bars 60 are shown three per side, comprised of stainless steel tuned drying bars, preferably powered by a 7.5 hp blower partially • recirculated air system. Air outlets are shown at 133, The conventional spray nozzles and power-pulse nozzles are best understood by referring to FIGS. 12 and 13. As shown best in FIG. 11, each of the cleaning bars in the zones 42, 44, 46 and 48 comprises a series of six vertically spaced apart nozzles 132 directed toward the space between the conveyors so that cleaning fluid forced through the nozzles can impinge on the opposite sides of the boards travelling through the cleaning zones. Referring to FIGS. 12 and 13, a pair of the cleaning bars is illustrated generally at 130, extending vertically along opposite sides of the board 22 travelling along the conveyor, which in this embodiment is in the form of the upper and lower endless belt conveyors 100 and 102. Six vertically spaced apart nozzles 132 are preferably mounted to each upright cleaning bar 130. Cleaning fluid such as water is forced under pressure through each tubular cleaning bar 130 and passes through an inlet 134 in which each spray nozzle 132 is mounted. The spray nozzles can be mounted in various orientations to control the angles at which the spray jets impinge upon the board. Separate, high-velocity air jets 136 are vertically spaced apart along each cleaning bar. The air jets are coupled to a supply of air under pressure which is fed through an inlet 138.

Nozzles 140 from the air supply jets are directed through the inlet 134 along the axis of each spray jet 132. Thus, each spray jet is capable of producing a continuous spray of cleaning fluid along with controlled high-pressure air jets. In one form of the invention, the cleaning fluid is impinged continuously through the spray nozzles 132 while a pulsating air jet at higher pressure than the spray jet is directed toward the board from the air jets. Both jets, are directed along a common axis. The power-pulse cleaning bars further accelerate and enhance cleaning and rinsing provided by the continuous spray jets. In the power-pulse jets, controlled jets of air alternately drive pulses of fluid to clean or rinse the boards under high pressure. Each high-pressure cleaning pulse is followed by a fluid flushing cycle. Pulsing patterns and pressures are entirely programmable so that air and fluid pressures and cycling patterns can be adjusted.

The system is programmable to allow a selection of adjustable conveyor speeds, board width adjustment and pressure adjustment, spray pressure, fluid or gaseous solutions, temperatures, airpulse/fluid pulse pressures and ratios, drying conditions, and others to accommodate a broad range of variables to achieve a high state of product cleanliness.

Example

In one embodiment of the invention, the angles at which each spray jet is set on each cleaning bar in each processing zone of the machine is controlled to a desired angle. In a presently preferred form of the invention, the spray angles vary by zone, and the machine has five zones as described previously, i.e., four cleaning zones in which a fluid jet spray of a liquid cleaning fluid is impinged on both sides of the board, followed by a drying zone in which hot air is applied to both sides of the board. There are a total of twenty wet cleaning bars (spray bars) installed with ten wet cleaning bars installed on one side of the conveyor system and a mirror image of ten more on the opposite side of the conveyor. The wash zone has four cleaning bars on each side, whereas the other wet processing zones have two cleaning bars on each side. There is one power-pulse cleaning bar per wet processing zone, and it is always on the last cleaning bar of each zone. All individual nozzles are set at a compound angle directed toward the board at an angle in the vertical plane and an angle on the horizontal plane, both vertical and horizontal planes being perpendicular to the board's plane of travel. All nozzles are adjusted to aim downwardly at approximately a 45° angle (in the vertical plane) . The first cleaning bar for all wet zones, in addition to facing downward, is set at a 45° angle (in the horizontal plane) toward the exit end of the machine. All last cleaning bars in each zone (the power-pulse units) are adjusted at a compound 45° angle facing the entry end of the machine in addition to facing downward. The wash zone is different from the other three wet processing zones, in that it includes the two middle cleaning bars on which the jet nozzles are both set at a 45° downward angle and approximately a 30° angle facing toward the entry end of the machine. All nozzles are placed approximately 1-1/2 inches from each side of the board.

All dryer tubes are adjusted between 30° to 40° toward the entry end of the conveyor.

Although all nozzles can be adjusted to almost an infinite variety of angles, a significant feature of the invention is that board cleaning is highly effective because each board can be attacked by multiple spray jets from an angle and at a high pressure.

A further advantage is that these angles can be changed to accommodate the board design, the components used, and the directional placement of the component. A current problem with other board cleaning machines is that their limited ability to spray at angles frequently causes residual material to remain on the board, especially in densely packed areas, or under low stand-off parts. This phenomena is generally referred to as "shadowing" and is eliminated or greatly reduced with the present invention.

In a preferred embodiment, all liquid spray jet nozzles operate at 70 psi and the input air to each power pulse unit is at 90 psi. In one embodiment, all spray jets of each zone have essentially the same operating pressure and are driven by a pump dedicated to that zone. In addition, all power-pulse jets in all zones have the same operating pressure. These parameters can be changed in other system arrangements. The dryer is operated at maximum output delivery of the blower, and the blower is basically designed to deliver approximately 450 cfm at about 2 psi. The drying is due mainly to the velocity of air, which is approximately 15,000 fpm. The system is configured so as to recirculate a high percentage of the air, and the product air is heated by friction while recirculation heats it further. Although other machines may require infrared heater zones which are more costly to operate, the present invention does not require heaters because of the more efficient use of air pressure on the captured board and the advantage of the board's vertical orientation.

The fact that the circuit board cleaner of this invention captures the board and holds it in place during each cleaning cycle allows use of spray jets and air blowers that can apply greater forces of fluid or air to the board at closer range. The result is more efficient cleaning and drying with less applied power in the form of smaller motors, less energy per cleaning power, and less floor space occupied to achieve a given level of cleaning. Moreover, cleaning time can be reduced because one pass through the machine produces the required level of cleaning without re-running boards through the machine as is common with prior art circuit board cleaners. Tests on the circuit board cleaner of this invention have shown that boards passed through the machine commonly measure zero micrograms per square inch on the standard omegameter, which is well below the eight or fourteen micrograms per square inch specification level typically required by board manufacturers.

Claims

WHAT IS CLAIMED IS:

1. A method of cleaning residue from printed circuit boards, the method comprising the steps of: providing a pair of spaced-apart board conveyor runs for capturing and transporting the captured boards in series along a path of travel; positioning the spaced-apart conveyor runs along the path of travel so they extend generally parallel to one another along a common plane of travel; inserting a board into the space between the conveyor runs so the conveyor runs capture the board by applying edgewise pressure to opposite edges of the board while transporting the captured board along the plane of travel, leaving essentially the entire opposite faces of the board exposed in the space between the conveyor runs; and impinging fluid spray jets on one or more of the exposed faces of the board to clean residue from the board, the captured board being supported by the edgewise pressure of the conveyor runs during its travel sufficiently to resist the force of high- pressure spray jets impinging on the board.

2. The method according to claim 1, including positioning the conveyor runs one above the other so the board is captured and transported in a substantially upright position and so that residue can be removed from the board under gravity.

3. The method according to claim 2, in which at least the bottom conveyor run comprises spaced-apart rollers contacting the board, with the space between rollers providing drainage for residue removed by the spray jets.

4. The method according to claim 1, including a resilient means of support in a recess of each roller for use in applying a resilient means of edgewise pressure to the board.

5. The method according to claim 1, including applying a resilient edgewise pressure to the opposite edges of the board during its travel past the impinging spray jets.

6. The method according to claim 5, including moving one of the conveyor runs toward the other conveyor run to controllably adjust the edgewise pressure applied to the board.

7. The method according to claim 1, in which the board travels in series past fluid spray jets defining different processing zones, including, at the least, a washing zone, a rinsing zone and a drying zone.

8. The method according to claim 1, in which the impinging spray jets include a spray of a liquid cleaning fluid and a pulsating air jet along a common axis.

9. The method according to claim 1, in which the impinging spray jets include a spray of a liquid cleaning fluid at one pressure and an air jet at a higher pressure.

10. Apparatus for cleaning residue from printed circuit boards, the apparatus comprising: a pair of spaced-apart board conveyor runs for capturing and transporting the captured boards in series along a path of travel, the spaced-apart conveyor runs being positioned so they extend generally parallel to one another along a common plane of travel; the conveyor runs capturing the board in the space between them by edgewise pressure applied to opposite edges of the board, the conveyor runs being movable to transport the captured board along the plane of travel while leaving essentially the entire opposite faces of the board exposed in the space between the ■ conveyor runs; and spray jet means for impinging a cleaning fluid on one or more of the exposed faces of the board to clean residue from the board, the captured board being supported by the edgewise pressure of the conveyor runs during its travel past the impinging spray jets sufficiently to resist the force of high- pressure spray jets impinging on the board.

11. Apparatus according to claim 10, including means for positioning the conveyor runs one above the other so the board is captured and transported in a substantially upright position and so that residue can be removed under gravity.

12. Apparatus according to claim 10, in which at least the bottom conveyor run comprises spaced-apart rollers contacting the board, with the space between rollers providing drainage for residue removed by the spray jets.

13. Apparatus according to claim 12, including a resilient means of support in a recess of each roller for use in applying a resilient means of edgewise pressure to the board.

14. Apparatus according to claim 9, including means for applying a resilient edgewise pressure to the opposite edges of the board during its travel past the impinging spray jets.

15. Apparatus according to claim 10, including means for moving one of the conveyor runs toward or away from the other conveyor run to controllably adjust the edgewise pressure applied to the board.

16. Apparatus according to claim 10, in which the board travels in series past different fluid spray jets defining separate processing zones including, at the least, a washing zone, a rinsing zone and a drying zone.

17. Apparatus according to claim 10, in which the impinging spray jets includes a spray of a liquid cleaning fluid and a pulsating air jet directed along a common axis.

18. A printed circuit board cleaner for cleaning residue from printed circuit boards, the circuit board cleaner comprising: an upper board conveyor run; a lower board conveyor run spaced below the upper conveyor run, the two conveyor runs being spaced apart uniformly and along a common substantially upright plane of travel; the upper and lower conveyor runs cooperating to produce edgewise pressure on opposite peripheral edges of a board inserted into the space between the conveyor runs, the conveyor runs further cooperating to cause the upright board to move axially along said plane of travel in a substantially upright position while resisting significant vertical or sideways movement of the board during said axial travel, said edgewise pressure being applied to opposite edges of the board while leaving essentially the entire opposite side faces of the board exposed in the space between the upper and lower conveyor runs during said axial travel; and spray means impinging on both exposed faces of the board simultaneously during said axial travel to clean residue from the board, the upright board being supported by the edgewise pressure of the conveyor runs during its travel sufficient to resist the force of the high-pressure spray jets impinging on the board.

19. Apparatus according to claim 18, in which at least the bottom conveyor run comprises spaced-apart rollers contacting the board, with the space between rollers providing drainage for residue removed by the spray jets.

20. Apparatus according to claim 18, including means for directing the spray jet toward the board at an angle in the vertical plane and at an angle in the horizontal plane.

21. Apparatus according to claim 18, including means for applying a resilient edgewise pressure to the opposite edges of the board during its travel past the impinging spray jets.

22. Apparatus according to claim 18, including means for moving^' one of the conveyor runs toward the other conveyor run for controllably adjusting the edgewise pressure applied to the board.

23. Apparatus according to claim 18, in which the board travels in series past different fluid spray jets defining separate processing zones including, at the least, a washing zone, a rinsing zone and a drying zone.

24. Apparatus according to claim 18, in which the impinging spray jets include a continuous spray of a liquid cleaning fluid and a pulsating air jet.

25. A method of cleaning residue from printed circuit boards, comprising: moving a plurality of circuit boards in series along a plane of travel, the boards being moved in a substantially upright position through applied edgewise pressure substantially restraining the boards from movement in directions other than along the upright plane of travel, thereby exposing at least one face of the planar boards during said travel; and impinging a spray jet of cleaning fluid on one or both exposed faces of the moving restrained boards to clean residue from the boards and remove the residue under gravity from the boards.

26. A method according to claim 25, comprising impinging the spray jets of cleaning fluid on both exposed faces of each board simultaneously.

27. A method of according to claim 26, including impinging the spray jet of cleaning fluid on the moving restrained boards in a series of cleaning zones in which the pressure of the spray jet of cleaning fluid in one zone is controllably adjustable to differ from the pressure applied in the succeeding zone.

28. The method according to claim 25, comprising moving the boards through a cleaning zone in series, in which the cleaning zone comprises means for impinging the spray jets of cleaning fluid on both exposed faces of each board simultaneously.

29. The method according to claim 25, including directing one or more fluid spray jets toward the boards at an angle in the vertical plane and an angle in the horizontal plane.