CA2135508C - Method for forming solder balls on a semiconductor substrate - Google Patents
Method for forming solder balls on a semiconductor substrateInfo
- Publication number
- CA2135508C CA2135508C CA002135508A CA2135508A CA2135508C CA 2135508 C CA2135508 C CA 2135508C CA 002135508 A CA002135508 A CA 002135508A CA 2135508 A CA2135508 A CA 2135508A CA 2135508 C CA2135508 C CA 2135508C
- Authority
- CA
- Canada
- Prior art keywords
- solder
- substrate
- fixture
- apertures
- contact sites
- 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 - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
- H01L21/48—Manufacture or treatment of parts, e.g. containers, prior to assembly of the devices, using processes not provided for in a single one of the subgroups H01L21/06 - H01L21/326
- H01L21/4814—Conductive parts
- H01L21/4846—Leads on or in insulating or insulated substrates, e.g. metallisation
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
- H05K3/32—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
- H05K3/34—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
- H05K3/3457—Solder materials or compositions; Methods of application thereof
- H05K3/3485—Applying solder paste, slurry or powder
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L2224/10—Bump connectors; Manufacturing methods related thereto
- H01L2224/11—Manufacturing methods
- H01L2224/11001—Involving a temporary auxiliary member not forming part of the manufacturing apparatus, e.g. removable or sacrificial coating, film or substrate
- H01L2224/11003—Involving a temporary auxiliary member not forming part of the manufacturing apparatus, e.g. removable or sacrificial coating, film or substrate for holding or transferring the bump preform
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/01—Chemical elements
- H01L2924/01087—Francium [Fr]
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/013—Alloys
- H01L2924/0132—Binary Alloys
- H01L2924/01322—Eutectic Alloys, i.e. obtained by a liquid transforming into two solid phases
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
- H05K2203/04—Soldering or other types of metallurgic bonding
- H05K2203/043—Reflowing of solder coated conductors, not during connection of components, e.g. reflowing solder paste
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
- H05K2203/05—Patterning and lithography; Masks; Details of resist
- H05K2203/0548—Masks
- H05K2203/0557—Non-printed masks
Abstract
A method for forming solder ball contacts on a ball grid array is described. The solder balls are formed by sqeegeeing a solder paste through apertures in a fixture into contact with pads on a substrate, heating the fixture, paste and substrate to reflow the solder paste into solder balls that attach to the pads and are detached from the fixture.
After cooling, the fixture is readily separated from the substrate and leaves the solder balls in conductive contact with contact pads on the substrate.
After cooling, the fixture is readily separated from the substrate and leaves the solder balls in conductive contact with contact pads on the substrate.
Description
METHOD FOR FORMING SOLDER BALLS ON A SEMICONDUCTOR SUBSTRATE
The Purpose of the Invention The present invention provides a simple and reliable method for forming solder ball contacts on a densely packed contact grid array.
Introduction The need for high density connections to integrated circuit devices has lead to the development of ball grid array packages which require large numbers of solder ball connections in a small area. This has been achieved in the prior art by the robotic pick-and-place of small standard sized eutectic solder spheres onto precise locations on the package. This method is very costly and requires very specialized equipment and materials.
The present invention overcomes the difficulties of the prior art by providing a solder screening method that avoids the need to precisely pick up a high precision solder ball and locate it on the package. The method enables solder balls to be formed from the paste directly on the package.
The present invention provides a method of forming solder connections to a substrate by placing a fixture over the substrate and screening solder paste onto the substrate through the fixture. The fixture is made of a material that is non-wettable by the solder and forms solder balls at the contact sites on the substrate when the solder is reflowed. Some suitable materials which are not wettable by the solder are titanium, molybdenum and graphite.
Prior Art USP 4,914,814 describes a process for forming pins on a ceramic 213~508 substrate carrier. A non-wettable pin mold having an array of pin holes is placed over the carrier and the pin holes are filled with high temperature melting point solder balls or solder wires. The pin mold is formed of a material having a thermal coefficient of expansion matching that of the substrate and is non-wettable by the solder. The preferred material in the patent is graphite. The pin mold and substrate carrier are then passed through a high temperature furnace to form the solder pin connections to the substrate. The mold is then removed and the substrate carrier assembly can be mounted on an organic circuit board with connections made through low melting temperature solder paste to pads on the board. This patent requires the use of pre-formed solder balls or wires. The present invention screens a solder paste through a fixture or mask. This provides more flexibility in the design as the solder ball size can be readily modified and paste is much easier to apply and use.
USP 5,211,328 describes a process where a transfer member is formed from graphite, ceramic or titanium with a plurality of holes located in it. The holes are located to precisely align with contact locations on a substrate. Solder is sqeegeed into the holes and the transfer member placed in precise position OIl the substrate and the solder reflowed to form contacts at the contact sites. The transfer member is non-wettable by the solder. The patent differs from the present invention in that the solder is squeegeed onto the transfer member and then brought into position on the substrate whereas with the present invention the fixture is placed on the substrate and then the solder is squeegeed into the holes in the fixture. This provides a much more flexible and reliable process than the one described in the patent.
USP 5,024,372 describes a method of forming high density solder bumps on a substrate. According to the patent, solder bumps have been formed by squeegeeing solder paste through a stencil or placing solder 2135~
balls in precise locations on the substrate. The stencil process has limited density due to slumping of the paste when the stencil is removed. The placing of the solder balls creates a reliability problem as it is difficult to ensure that solder balls are everywhere they should be and not where they shouldn't. The patent overcomes these problems by the use of a thick layer of photo definable solder resist which is selectively removed to provide wells at solder pads on the substrate. Solder paste is sqeegeed into the wells and the solder reflowed. The solder paste wets and wicks to the metalized pads on the substrate. The resist is then removed to leave solder bumps on the metalized pads. By reflowing the solder while the non-wettable fixture remains in place, the present invention overcomes the problems of slumping while providing a fixture that is readily detached rom the substrate without the need of photoresistive techniques such as those used in the patent. Also, the present invention does not require the melting point of the solder to be lower than that of the contact pad on the substrate as taught in the patent.
USP 4,412,642 describes a process for casting solder leads to a leadless chip carrier. A molding plate having a plurality of mold cavities at predetermined locations each receive a solder preform. The preform is preferably spherical and the cavities are tapered. The plate and solder preforms are subjected to heat and pressure is applied to the preforms to force the solder preforms into the cavities. The molding plate with the leads is then mounted adjacent a leadless chip carrier with the solder leads aligned with contact areas on the carrier. The carrier and the mold plate are heated to reflow the solder and transfer the solder to the contact areas of the carrier. The molding plate may be made of titanium according to the patent as it can withstand a casting process. Titanium is a material that would not make wetting contact with the solder and therefore would facilitate the release of the solder onto the carrier. However, the process described in the patent requires the 2135SO~
use of expensive solder preforms whereas our invention uses much less expensive solder paste. Also, with our invention, the size of the solder balls ultimately produced is controlled by the size of the apertures in the fixture. In the patent, the solder preform determines the size of the connector.
USP 5,284,287 describes a vacuum tool that picks up solder balls and places them in position for soldering. The solder balls are aligned by the vacuum tool.
USP 4,712,721 describes systems for delivering preformed solder to contact sites. The preformed solder shapes are held in a positioning means which is adapted to hold the solder. The positioning means is placed in a fixture and the solder reflowed to form connections to a chip carrier package or the like. The patent does not use a stencil or template to locate the solder.
USP 3,647,533 describes a process for forming bonding bumps on a substrate array by thin film vacuum deposition through a mechanical mask. The bumps formed by the deposition are then dipped in a solder bath.
USP 5,261,593 describes a method for connecting flip chips to flexible printed circuit substrates. Solder paste is placed on the contact areas on the printed circuit board and solder bumps formed on the chips are brought into registration with the contacts and the whole assembly heated to reflow the solder and form contacts between the chips and the printed circuit board.
USP 5,197,655 describes a process for applying solder to fine pitch leads. In one embodiment, paste solder is screened through an apertured mask onto land locations on a printed circuit substrate. A heated platen 2135~i08 having an active element corresponding to the size and shape of the lands is then brought into contact with the solder paste to reflow the solder and form contacts on the lands. Tlle heated platen is made of non-wettable material such as stainless steel or titanium.
USP 5,118,027 describes a process for attaching high melting point solder balls to contacts on a substrate through the use of low melting point solder paste. The solder balls are placed in cavities in an alignment boat that holds the solder balls in place through apertures connected to a vacuum source. The solder paste is then deposited on the solder balls through a metallic contact mask. A self-aligning plate is then placed over the boat and the substrate aligned on the plate so that the contact areas on the substrate are in contact with the solder paste.
Pressure is applied to the substrate to ensure firm contact with the paste. The self-aligning plate is then removed and the substrate, solder and alignment boat are fed through a low temperature furnace to solder the solder balls to the substrate through the solder paste. The substrate is then available for solder joining operations where the high temperature solder ball is soldered to a board or like structure. The solder paste screen is of stainless steel, brass or copper. Stainless steel is preferred because of its wear characteristics. The alignment boat is preferably made of graphite because of its thermal conductivity and coefficient of expansion compatibility with a ceramic substrate.
USP 3,458,925 describes a process for forming mounds of solder on lands on an integrated circuit chip. A mask covers the surface of the chip except for the land and the immediately surroundinq area and a layer of solder is evaporated onto the lands and surrounding area. The solder is then heated to a temperature above its melting point and the solder dewets the area around the lands and forms solder mounds on the lands.
213~S08 The article by Dave Hattas in Advanced Packaging Summer 1993 describes a Bump Grid Array (BGA) package which has an array of solder bumps formed on an FR-4 printed circuit board. The bumps are formed from solder paste which is deposited on the substrate through a stencil. A
solder paste that overcame slumping problems was used and the use of a nitrogen reflow oven overcame problems with the unwanted formation of solder balls. The article does not disclose what material is used for the stencil although one would presume that it is a non-wettable material that would withstand soldering temperatures. With our method the relative width of the opening in the fixture relative to the width of the solder pad connector can be selected so that the solder wets to the pad and does not adhere to the fixture and thereby forms a solder ball of predetermined size. The size of the aperture is selected so that the fixture does not contact the solder ball after solder reflow. According to Hattas design, direct screening without a physical barrier is limited to a certain pitch and screen printing variations in volume. With the fixture of our invention, an exact volume of paste is provided. Hattas also requires a customized paste whereas we can use a wide variety of solder pastes. Our invention also makes it possible to alter the volume of the solder balls simply by altering the thickness of the fixture or the size of the apertures in the fixture. Hattas does not provide any method for doing this. Also, stencils such as those described by Hattas are incapable of releasing high volumes of solder at a fine pitch or in a tight area.
Statement of Invention The present invention provides a method of forming solder balls on a solderable surface on a substrate. The method includes positioning a fixture in aligned orientation with the substrate so that holes in the 2135~08 fixture are in substantial alignment with solderable surface positions on the substrate, filling the holes with solder paste, heating the fixture, solder paste and substrate so the solder paste forms solder balls that adhere to the solderable surfaces and detach from the fixture, cooling the fixture and substrate leaving the solder balls in physical and electrical contact with the solderable surfaces on the substrate and separating the substrate from the fixture.
The present invention also enables circuit chips to be simultaneously mounted on the side of the substrate opposite the solderable pads. The substrate is flipped and chips are placed in solderable contact with pads on the substrate. The fixture, substrate and chips are all heated at the same time to form both the solder balls and reflow solder on the pads.
Objects of the Invention A primary object of the present invention is to form solder balls on a contact grid inexpensively and reliably.
It is a further object to enable circuit chips to be electrically connected to a substrate simultaneously with the formation of the solder ball contacts.
Description of the Drawings Figure 1 is a diagram of the process flow of the invention.
Figures 2A and 2B illustrate a typical substrate that is processed in accordance with the present invention.
Figure 3A is a schematic illustration of the substrate when mounted and aligned in a holding fixture.
Figure 3B is a magnified view of a portion of the substrate and 213~0~
fixture shown in Figure 3A.
Figure 4 illustrates the solder paste being squeegeed into apertures in the holding fixture.
Figure 5 shows a component mounted on the top side of the substrate when held in the holding fixture.
Figure 6 schematically illustrates the formation of the solder balls and solder joints on the substrate while continuing to be held by the holding fixture.
Figure 7 schematically illustrates the substrate with solder balls and an attached component when removed from the fixture.
Figure 8 shows a preferred holding fixture.
Figure 9 is a schematic representation of a portion of a fixture in accordance with the invention.
Figures 10A to lOD illustrate the solder connections formed on a substrate according to the present invention when using different fixtures.
Description of the Invention With the continuing evolution of more and more complex and denser chip modules it is necessary to provide denser substrate connections.
One approach to providing these denser connections is the Ball Grid Array (BGA) where solder balls are placed on a grid on the base of a substrate which holds a plurality of modules or chips. Up to the present it has been difficult to form or place the solder balls on the substrate efficiently or effectively. In one approach, individual solder balls were picked and placed on the substrate and then solder reflowed to it.
This process requires expensive pick and place equipment and is relatively slow. Additionally, the solder balls are much more expensive than the equivalent solder paste. Attempts have been made to form the solder connections to the substrate using solder paste and a mask.
However, these processes have been less than satisfactory either because 21~5508 the mask was difficult to remove and resulted in some broken connections or a new mask had to be formed on each substrate, which is expensive and time consuming.
The present invention overcomes these prior art problems by providing an easily removable holding fixture for holding the substrates while solder paste is squeegeed into apertures in the holding fixture.
The solder paste is reflowed while the substrate is held by the holding fixture. The fixture is formed of a material that is not wetted by the solder and repels the solder so that it forms solder balls or bumps on the substrate. Molten solder has a natural tendency to coagulate into a ball in a gaseous medium.
Figure 1 illustrates the process flow for forming ball grid arrays in accordance with the present invention. As indicated at 1, a substrate which includes solder pads for attaching components or modules to the substrate on one side and a matrix array of solderable surfaces on the other side is provided for processing.
The substrate is then clamped in a holding fixture that is fitted with alignment guides to properly orient the substrate in the holder as indicated at step 2 in the figure.
When the substrate is held in the fixture a solder paste is sqeegeed over the surface of the fixture and into apertures corresponding to the matrix array of solderable surfaces on the substrate as indicated at step 3.
After the solder paste is sqeegeed onto the fixture, the fixture is inverted as indicated at step 4. Components are then placed on the upwardly facing surface of the substrate with the component connectors in contact with the solderable pads on the substrate as indicated at 21:~508 step 5.
After step 5, the solder paste and solderable pads are ready for solder reflow as indicated at step 6. In step 6, the flux in the solder paste is driven off and the remaining solder is repelled by the fixture and coagulates into solder balls on the circuit paths on the substrate.
At the same time the components on the upper surface of the substrate are solder connected to the pads on the substrate.
After cooling, the substrate can now be removed from the fixture as indicated at step 7. Because the solder is repelled by the fixture the integrity of the solder balls is easily retained as the balls do not touch the walls of the fixture.
The above brief description highlights the steps of the process.
The invention will now be described in more detail.
Figures 2A and 2B illustrate a typical BGA substrate that may be processed in accordance with the present invention. For ease of reference, the substrate surface receiving the components or modules will be described as the upper surface of the substrate and the surface holding the solder balls will be described as the lower surface of the substrate. This is not intended to be limiting of the invention.
The substrate 11 may be made of any suitable printed circuit board material. Some examples are glass epoxy commonly known as FR-4 and ceramics. The solder pads 12 may be formed of any solderable material such as copper, nickel, gold or tin-lead alloys.
The lower surface of the substrate has a matrix of solderable surfaces 13 which also may be formed of any suitable solderable material. The holes 14 at each corner of the substrate enable the 21~5~08 substrate to be held in a properly aligned position in the holding fixture 15.
As shown in Figures 3A and 3B, the substrate 11 is held in the fixture 15 by clamps 16. The alignment holes 14 and the depression 18 in the fixture 15 assure that the pads 13 are substantially centrally aligned with the apertures 19 in the fixture 15. The alignment must be sufficient to enable the solder to reflow into a complete solder ball which is in contact with the pad on the substrate. The fixture 15 is made of titanium or other durable material that will not make a wetting contact with the solder being used. Of course, the material used for the fixture must be capable of withstanding the mechanical and thermal stresses inherent to the soldering process.
With the substrate 11 held in the fixture 15, the assembly is inverted and solder 21 is squeegeed into apertures 19 by a squeegee blade 20 or the like. When the apertures 19 are all filled with solder paste the assembly is returned upright and components 31 are placed on the solderable pads 12 on the substrate 11 as shown in Figure 5. The substrate 11 is now ready for heating to reflow the solder paste 21 in the apertures 19 and the solder on the pads 12.
When heat source 42 heats the solder paste 21, the flux in the paste is driven off and the remaining solder adheres to the substrate 11 in the form of solder balls 41. The solder balls 41 are not in contact with the walls 17 of the titanium fixture 15 as the fixture positively repels the solder in its molten form. Because there is no contact between the walls 17 of the fixture 15 and the balls 41, it is relatively easy to separate the substrate 11 from the fixture 15 without damaging any of the solder ball connections.
2135~08 Figure 7 shows the completed substrate 11 with the solder ball connectors 41 on the lower side of the substrate 11 and the components 31 electrically attached to the upper side of the substrate 11.
Figure 8 shows the top and bottom plan views of the titanium holding fixture 15. The tooling holes 45 enable the fixture 15 to be properly aligned in a mounting device (not shown). The recessed pocket 18 in the upper surface of the fixture 15 aligns the holes 19 in the fixture 15 with the solder pads 13 on the substrate 11.
The Joint Electron Device Engineering Council (JEDEC) has set certain standards for the size of solder balls acceptable for use with electronic chip devices. The present invention enables the volume and size of the solder balls to be predetermined while at the same time enabling the balls to be formed in situ. Figure 9 shows schematically the dimensions of the fixture that can be designed so as to form a solder ball of a desired size using a solder paste of a particular composition. As shown in Figure 9, the diameter ~A and height hB f the aperture in the fixture will determine the volume of solder paste that can be associated with the solderable pad and, therefore, determine the dimensions of the solder ball.
Figures lOA through lOD illustrate schematically four different fixture apertures. In Figure lOA, the aperture is too narrow and too high with the consequent result that a solder ball is not formed.
Instead, a tall, thin solder pin is constructed which, if used, would readily break. Figure lOB illustrates a situation where the solder ball is formed but the width of the aperture is too narrow. The surface of the solder ball is too close to the wall of the aperture so the solder ball may be easily displaced or broken when the fixture is removed.
Figure lOC illustrates the optimum situation. Here the solder ball is 2135~08 formed in good contact with the solderable pad and has sufficient clearance from the walls of the aperture to enable the fixture to be easily removed without disturbing the solder balls. Figure lOD
illustrates the situation where the aperture is too wide. In this situation, the solder balls may not make good contact with the solderable pads or may actually slump. Obviously, it is necessary to control the thickness of the fixture and the diameter of the apertures to ensure that solder balls of the desired size and shape are formed. An additional factor that must also be considered is the ratio of solder to flux in the solder paste. The amount of flux used must be kept below a certain maximum to ensure that sufficient solder is available to form the desired solder ball. This ratio determines the amount of solder available to form the solder ball and, therefore, in conjunction with the aperture height and diameter, determines the solder ball size.
A preferred solder paste is a eutectic tin/lead composition. The most suitable composition has been found to be 63% lead and 37% tin.
The preferred range of soldering temperature is between 25 and 350 degrees Celsius. The length of time of the soldering cycle is directly proportional to the temperature used.
Although the methods of the present invention have been primarily described with respect to forming contacts in a ball grid array, it is not intended that the invention be limited to this type of array. The invention can obviously be applied to any contact arrangement that requires the use of solder balls or the like. The present invention is intended to include all embodiments amenable to forming contacts in the manner described and as defined by the following claims.
The Purpose of the Invention The present invention provides a simple and reliable method for forming solder ball contacts on a densely packed contact grid array.
Introduction The need for high density connections to integrated circuit devices has lead to the development of ball grid array packages which require large numbers of solder ball connections in a small area. This has been achieved in the prior art by the robotic pick-and-place of small standard sized eutectic solder spheres onto precise locations on the package. This method is very costly and requires very specialized equipment and materials.
The present invention overcomes the difficulties of the prior art by providing a solder screening method that avoids the need to precisely pick up a high precision solder ball and locate it on the package. The method enables solder balls to be formed from the paste directly on the package.
The present invention provides a method of forming solder connections to a substrate by placing a fixture over the substrate and screening solder paste onto the substrate through the fixture. The fixture is made of a material that is non-wettable by the solder and forms solder balls at the contact sites on the substrate when the solder is reflowed. Some suitable materials which are not wettable by the solder are titanium, molybdenum and graphite.
Prior Art USP 4,914,814 describes a process for forming pins on a ceramic 213~508 substrate carrier. A non-wettable pin mold having an array of pin holes is placed over the carrier and the pin holes are filled with high temperature melting point solder balls or solder wires. The pin mold is formed of a material having a thermal coefficient of expansion matching that of the substrate and is non-wettable by the solder. The preferred material in the patent is graphite. The pin mold and substrate carrier are then passed through a high temperature furnace to form the solder pin connections to the substrate. The mold is then removed and the substrate carrier assembly can be mounted on an organic circuit board with connections made through low melting temperature solder paste to pads on the board. This patent requires the use of pre-formed solder balls or wires. The present invention screens a solder paste through a fixture or mask. This provides more flexibility in the design as the solder ball size can be readily modified and paste is much easier to apply and use.
USP 5,211,328 describes a process where a transfer member is formed from graphite, ceramic or titanium with a plurality of holes located in it. The holes are located to precisely align with contact locations on a substrate. Solder is sqeegeed into the holes and the transfer member placed in precise position OIl the substrate and the solder reflowed to form contacts at the contact sites. The transfer member is non-wettable by the solder. The patent differs from the present invention in that the solder is squeegeed onto the transfer member and then brought into position on the substrate whereas with the present invention the fixture is placed on the substrate and then the solder is squeegeed into the holes in the fixture. This provides a much more flexible and reliable process than the one described in the patent.
USP 5,024,372 describes a method of forming high density solder bumps on a substrate. According to the patent, solder bumps have been formed by squeegeeing solder paste through a stencil or placing solder 2135~
balls in precise locations on the substrate. The stencil process has limited density due to slumping of the paste when the stencil is removed. The placing of the solder balls creates a reliability problem as it is difficult to ensure that solder balls are everywhere they should be and not where they shouldn't. The patent overcomes these problems by the use of a thick layer of photo definable solder resist which is selectively removed to provide wells at solder pads on the substrate. Solder paste is sqeegeed into the wells and the solder reflowed. The solder paste wets and wicks to the metalized pads on the substrate. The resist is then removed to leave solder bumps on the metalized pads. By reflowing the solder while the non-wettable fixture remains in place, the present invention overcomes the problems of slumping while providing a fixture that is readily detached rom the substrate without the need of photoresistive techniques such as those used in the patent. Also, the present invention does not require the melting point of the solder to be lower than that of the contact pad on the substrate as taught in the patent.
USP 4,412,642 describes a process for casting solder leads to a leadless chip carrier. A molding plate having a plurality of mold cavities at predetermined locations each receive a solder preform. The preform is preferably spherical and the cavities are tapered. The plate and solder preforms are subjected to heat and pressure is applied to the preforms to force the solder preforms into the cavities. The molding plate with the leads is then mounted adjacent a leadless chip carrier with the solder leads aligned with contact areas on the carrier. The carrier and the mold plate are heated to reflow the solder and transfer the solder to the contact areas of the carrier. The molding plate may be made of titanium according to the patent as it can withstand a casting process. Titanium is a material that would not make wetting contact with the solder and therefore would facilitate the release of the solder onto the carrier. However, the process described in the patent requires the 2135SO~
use of expensive solder preforms whereas our invention uses much less expensive solder paste. Also, with our invention, the size of the solder balls ultimately produced is controlled by the size of the apertures in the fixture. In the patent, the solder preform determines the size of the connector.
USP 5,284,287 describes a vacuum tool that picks up solder balls and places them in position for soldering. The solder balls are aligned by the vacuum tool.
USP 4,712,721 describes systems for delivering preformed solder to contact sites. The preformed solder shapes are held in a positioning means which is adapted to hold the solder. The positioning means is placed in a fixture and the solder reflowed to form connections to a chip carrier package or the like. The patent does not use a stencil or template to locate the solder.
USP 3,647,533 describes a process for forming bonding bumps on a substrate array by thin film vacuum deposition through a mechanical mask. The bumps formed by the deposition are then dipped in a solder bath.
USP 5,261,593 describes a method for connecting flip chips to flexible printed circuit substrates. Solder paste is placed on the contact areas on the printed circuit board and solder bumps formed on the chips are brought into registration with the contacts and the whole assembly heated to reflow the solder and form contacts between the chips and the printed circuit board.
USP 5,197,655 describes a process for applying solder to fine pitch leads. In one embodiment, paste solder is screened through an apertured mask onto land locations on a printed circuit substrate. A heated platen 2135~i08 having an active element corresponding to the size and shape of the lands is then brought into contact with the solder paste to reflow the solder and form contacts on the lands. Tlle heated platen is made of non-wettable material such as stainless steel or titanium.
USP 5,118,027 describes a process for attaching high melting point solder balls to contacts on a substrate through the use of low melting point solder paste. The solder balls are placed in cavities in an alignment boat that holds the solder balls in place through apertures connected to a vacuum source. The solder paste is then deposited on the solder balls through a metallic contact mask. A self-aligning plate is then placed over the boat and the substrate aligned on the plate so that the contact areas on the substrate are in contact with the solder paste.
Pressure is applied to the substrate to ensure firm contact with the paste. The self-aligning plate is then removed and the substrate, solder and alignment boat are fed through a low temperature furnace to solder the solder balls to the substrate through the solder paste. The substrate is then available for solder joining operations where the high temperature solder ball is soldered to a board or like structure. The solder paste screen is of stainless steel, brass or copper. Stainless steel is preferred because of its wear characteristics. The alignment boat is preferably made of graphite because of its thermal conductivity and coefficient of expansion compatibility with a ceramic substrate.
USP 3,458,925 describes a process for forming mounds of solder on lands on an integrated circuit chip. A mask covers the surface of the chip except for the land and the immediately surroundinq area and a layer of solder is evaporated onto the lands and surrounding area. The solder is then heated to a temperature above its melting point and the solder dewets the area around the lands and forms solder mounds on the lands.
213~S08 The article by Dave Hattas in Advanced Packaging Summer 1993 describes a Bump Grid Array (BGA) package which has an array of solder bumps formed on an FR-4 printed circuit board. The bumps are formed from solder paste which is deposited on the substrate through a stencil. A
solder paste that overcame slumping problems was used and the use of a nitrogen reflow oven overcame problems with the unwanted formation of solder balls. The article does not disclose what material is used for the stencil although one would presume that it is a non-wettable material that would withstand soldering temperatures. With our method the relative width of the opening in the fixture relative to the width of the solder pad connector can be selected so that the solder wets to the pad and does not adhere to the fixture and thereby forms a solder ball of predetermined size. The size of the aperture is selected so that the fixture does not contact the solder ball after solder reflow. According to Hattas design, direct screening without a physical barrier is limited to a certain pitch and screen printing variations in volume. With the fixture of our invention, an exact volume of paste is provided. Hattas also requires a customized paste whereas we can use a wide variety of solder pastes. Our invention also makes it possible to alter the volume of the solder balls simply by altering the thickness of the fixture or the size of the apertures in the fixture. Hattas does not provide any method for doing this. Also, stencils such as those described by Hattas are incapable of releasing high volumes of solder at a fine pitch or in a tight area.
Statement of Invention The present invention provides a method of forming solder balls on a solderable surface on a substrate. The method includes positioning a fixture in aligned orientation with the substrate so that holes in the 2135~08 fixture are in substantial alignment with solderable surface positions on the substrate, filling the holes with solder paste, heating the fixture, solder paste and substrate so the solder paste forms solder balls that adhere to the solderable surfaces and detach from the fixture, cooling the fixture and substrate leaving the solder balls in physical and electrical contact with the solderable surfaces on the substrate and separating the substrate from the fixture.
The present invention also enables circuit chips to be simultaneously mounted on the side of the substrate opposite the solderable pads. The substrate is flipped and chips are placed in solderable contact with pads on the substrate. The fixture, substrate and chips are all heated at the same time to form both the solder balls and reflow solder on the pads.
Objects of the Invention A primary object of the present invention is to form solder balls on a contact grid inexpensively and reliably.
It is a further object to enable circuit chips to be electrically connected to a substrate simultaneously with the formation of the solder ball contacts.
Description of the Drawings Figure 1 is a diagram of the process flow of the invention.
Figures 2A and 2B illustrate a typical substrate that is processed in accordance with the present invention.
Figure 3A is a schematic illustration of the substrate when mounted and aligned in a holding fixture.
Figure 3B is a magnified view of a portion of the substrate and 213~0~
fixture shown in Figure 3A.
Figure 4 illustrates the solder paste being squeegeed into apertures in the holding fixture.
Figure 5 shows a component mounted on the top side of the substrate when held in the holding fixture.
Figure 6 schematically illustrates the formation of the solder balls and solder joints on the substrate while continuing to be held by the holding fixture.
Figure 7 schematically illustrates the substrate with solder balls and an attached component when removed from the fixture.
Figure 8 shows a preferred holding fixture.
Figure 9 is a schematic representation of a portion of a fixture in accordance with the invention.
Figures 10A to lOD illustrate the solder connections formed on a substrate according to the present invention when using different fixtures.
Description of the Invention With the continuing evolution of more and more complex and denser chip modules it is necessary to provide denser substrate connections.
One approach to providing these denser connections is the Ball Grid Array (BGA) where solder balls are placed on a grid on the base of a substrate which holds a plurality of modules or chips. Up to the present it has been difficult to form or place the solder balls on the substrate efficiently or effectively. In one approach, individual solder balls were picked and placed on the substrate and then solder reflowed to it.
This process requires expensive pick and place equipment and is relatively slow. Additionally, the solder balls are much more expensive than the equivalent solder paste. Attempts have been made to form the solder connections to the substrate using solder paste and a mask.
However, these processes have been less than satisfactory either because 21~5508 the mask was difficult to remove and resulted in some broken connections or a new mask had to be formed on each substrate, which is expensive and time consuming.
The present invention overcomes these prior art problems by providing an easily removable holding fixture for holding the substrates while solder paste is squeegeed into apertures in the holding fixture.
The solder paste is reflowed while the substrate is held by the holding fixture. The fixture is formed of a material that is not wetted by the solder and repels the solder so that it forms solder balls or bumps on the substrate. Molten solder has a natural tendency to coagulate into a ball in a gaseous medium.
Figure 1 illustrates the process flow for forming ball grid arrays in accordance with the present invention. As indicated at 1, a substrate which includes solder pads for attaching components or modules to the substrate on one side and a matrix array of solderable surfaces on the other side is provided for processing.
The substrate is then clamped in a holding fixture that is fitted with alignment guides to properly orient the substrate in the holder as indicated at step 2 in the figure.
When the substrate is held in the fixture a solder paste is sqeegeed over the surface of the fixture and into apertures corresponding to the matrix array of solderable surfaces on the substrate as indicated at step 3.
After the solder paste is sqeegeed onto the fixture, the fixture is inverted as indicated at step 4. Components are then placed on the upwardly facing surface of the substrate with the component connectors in contact with the solderable pads on the substrate as indicated at 21:~508 step 5.
After step 5, the solder paste and solderable pads are ready for solder reflow as indicated at step 6. In step 6, the flux in the solder paste is driven off and the remaining solder is repelled by the fixture and coagulates into solder balls on the circuit paths on the substrate.
At the same time the components on the upper surface of the substrate are solder connected to the pads on the substrate.
After cooling, the substrate can now be removed from the fixture as indicated at step 7. Because the solder is repelled by the fixture the integrity of the solder balls is easily retained as the balls do not touch the walls of the fixture.
The above brief description highlights the steps of the process.
The invention will now be described in more detail.
Figures 2A and 2B illustrate a typical BGA substrate that may be processed in accordance with the present invention. For ease of reference, the substrate surface receiving the components or modules will be described as the upper surface of the substrate and the surface holding the solder balls will be described as the lower surface of the substrate. This is not intended to be limiting of the invention.
The substrate 11 may be made of any suitable printed circuit board material. Some examples are glass epoxy commonly known as FR-4 and ceramics. The solder pads 12 may be formed of any solderable material such as copper, nickel, gold or tin-lead alloys.
The lower surface of the substrate has a matrix of solderable surfaces 13 which also may be formed of any suitable solderable material. The holes 14 at each corner of the substrate enable the 21~5~08 substrate to be held in a properly aligned position in the holding fixture 15.
As shown in Figures 3A and 3B, the substrate 11 is held in the fixture 15 by clamps 16. The alignment holes 14 and the depression 18 in the fixture 15 assure that the pads 13 are substantially centrally aligned with the apertures 19 in the fixture 15. The alignment must be sufficient to enable the solder to reflow into a complete solder ball which is in contact with the pad on the substrate. The fixture 15 is made of titanium or other durable material that will not make a wetting contact with the solder being used. Of course, the material used for the fixture must be capable of withstanding the mechanical and thermal stresses inherent to the soldering process.
With the substrate 11 held in the fixture 15, the assembly is inverted and solder 21 is squeegeed into apertures 19 by a squeegee blade 20 or the like. When the apertures 19 are all filled with solder paste the assembly is returned upright and components 31 are placed on the solderable pads 12 on the substrate 11 as shown in Figure 5. The substrate 11 is now ready for heating to reflow the solder paste 21 in the apertures 19 and the solder on the pads 12.
When heat source 42 heats the solder paste 21, the flux in the paste is driven off and the remaining solder adheres to the substrate 11 in the form of solder balls 41. The solder balls 41 are not in contact with the walls 17 of the titanium fixture 15 as the fixture positively repels the solder in its molten form. Because there is no contact between the walls 17 of the fixture 15 and the balls 41, it is relatively easy to separate the substrate 11 from the fixture 15 without damaging any of the solder ball connections.
2135~08 Figure 7 shows the completed substrate 11 with the solder ball connectors 41 on the lower side of the substrate 11 and the components 31 electrically attached to the upper side of the substrate 11.
Figure 8 shows the top and bottom plan views of the titanium holding fixture 15. The tooling holes 45 enable the fixture 15 to be properly aligned in a mounting device (not shown). The recessed pocket 18 in the upper surface of the fixture 15 aligns the holes 19 in the fixture 15 with the solder pads 13 on the substrate 11.
The Joint Electron Device Engineering Council (JEDEC) has set certain standards for the size of solder balls acceptable for use with electronic chip devices. The present invention enables the volume and size of the solder balls to be predetermined while at the same time enabling the balls to be formed in situ. Figure 9 shows schematically the dimensions of the fixture that can be designed so as to form a solder ball of a desired size using a solder paste of a particular composition. As shown in Figure 9, the diameter ~A and height hB f the aperture in the fixture will determine the volume of solder paste that can be associated with the solderable pad and, therefore, determine the dimensions of the solder ball.
Figures lOA through lOD illustrate schematically four different fixture apertures. In Figure lOA, the aperture is too narrow and too high with the consequent result that a solder ball is not formed.
Instead, a tall, thin solder pin is constructed which, if used, would readily break. Figure lOB illustrates a situation where the solder ball is formed but the width of the aperture is too narrow. The surface of the solder ball is too close to the wall of the aperture so the solder ball may be easily displaced or broken when the fixture is removed.
Figure lOC illustrates the optimum situation. Here the solder ball is 2135~08 formed in good contact with the solderable pad and has sufficient clearance from the walls of the aperture to enable the fixture to be easily removed without disturbing the solder balls. Figure lOD
illustrates the situation where the aperture is too wide. In this situation, the solder balls may not make good contact with the solderable pads or may actually slump. Obviously, it is necessary to control the thickness of the fixture and the diameter of the apertures to ensure that solder balls of the desired size and shape are formed. An additional factor that must also be considered is the ratio of solder to flux in the solder paste. The amount of flux used must be kept below a certain maximum to ensure that sufficient solder is available to form the desired solder ball. This ratio determines the amount of solder available to form the solder ball and, therefore, in conjunction with the aperture height and diameter, determines the solder ball size.
A preferred solder paste is a eutectic tin/lead composition. The most suitable composition has been found to be 63% lead and 37% tin.
The preferred range of soldering temperature is between 25 and 350 degrees Celsius. The length of time of the soldering cycle is directly proportional to the temperature used.
Although the methods of the present invention have been primarily described with respect to forming contacts in a ball grid array, it is not intended that the invention be limited to this type of array. The invention can obviously be applied to any contact arrangement that requires the use of solder balls or the like. The present invention is intended to include all embodiments amenable to forming contacts in the manner described and as defined by the following claims.
Claims (7)
1. A method of applying solder to solderable contact sites on a substrate, said method comprising the steps of:
providing a reusable fixture of material not wettable by solder having a plurality of apertures therein;
positioning said fixture with said apertures in aligned orientation relative to a substrate having a plurality of solderable contact sites thereon such that each of said apertures is substantially aligned with a respective one of said solderable contact sites;
substantially filling said plurality of apertures of said fixture with solder paste such that said solder paste is deposited on said solderable contact sites of said substrate;
positioning said fixture and said substrate such that said solderable contact sites of said substrate face in a substantially downward direction;
heating said substrate and fixture to a predetermined temperature while said solderable contact sites of said substrate face in said substantially downward direction to cause said solder paste within said apertures of said fixture and on said contact sites of said substrate to become molten;
cooling said molten solder such that as said solder solidifies it adheres to said solderable contact sites and is repelled from said fixture; and separating said substrate from said fixture.
providing a reusable fixture of material not wettable by solder having a plurality of apertures therein;
positioning said fixture with said apertures in aligned orientation relative to a substrate having a plurality of solderable contact sites thereon such that each of said apertures is substantially aligned with a respective one of said solderable contact sites;
substantially filling said plurality of apertures of said fixture with solder paste such that said solder paste is deposited on said solderable contact sites of said substrate;
positioning said fixture and said substrate such that said solderable contact sites of said substrate face in a substantially downward direction;
heating said substrate and fixture to a predetermined temperature while said solderable contact sites of said substrate face in said substantially downward direction to cause said solder paste within said apertures of said fixture and on said contact sites of said substrate to become molten;
cooling said molten solder such that as said solder solidifies it adheres to said solderable contact sites and is repelled from said fixture; and separating said substrate from said fixture.
2. A method for forming solder connections on a substrate having a plurality of solderable contact sites on a first surface thereof, said method comprising the steps of:
placing a substrate in a reusable substrate holding fixture of material not wettable by solder having a plurality of apertures therein wherein each of said solderable contact sites of said substrate is in substantial alignment with a respective one of said apertures;
substantially filling said plurality of apertures of said fixture with a solder paste;
inverting said fixture and said substrate such that said solderable contact sites of said substrate face in a substantially downward direction;
placing at least one electrical component having a plurality of solder connections thereon on a second surface of said substrate, said second surface having a plurality of solderable contact pads thereon, said solderable contact pads contacting said solder connections on said at least one electronic component;
heating said substrate, said fixture and said at least one electronic component to cause said solder paste to become molten and said solder connections on said at least one electronic component in contact with said solder contact pads to reflow, said solder paste forming solder balls attached to said solderable contact sites on said substrate and detached from said fixture, said solderable contact sites of said substrate facing in said substantially downward direction during said heating;
cooling said substrate, said fixture and said at least one electronic component to thereby solidify said solder balls on said sites and solderably connect said pads to said at least one electronic component; and separating said substrate from said fixture.
placing a substrate in a reusable substrate holding fixture of material not wettable by solder having a plurality of apertures therein wherein each of said solderable contact sites of said substrate is in substantial alignment with a respective one of said apertures;
substantially filling said plurality of apertures of said fixture with a solder paste;
inverting said fixture and said substrate such that said solderable contact sites of said substrate face in a substantially downward direction;
placing at least one electrical component having a plurality of solder connections thereon on a second surface of said substrate, said second surface having a plurality of solderable contact pads thereon, said solderable contact pads contacting said solder connections on said at least one electronic component;
heating said substrate, said fixture and said at least one electronic component to cause said solder paste to become molten and said solder connections on said at least one electronic component in contact with said solder contact pads to reflow, said solder paste forming solder balls attached to said solderable contact sites on said substrate and detached from said fixture, said solderable contact sites of said substrate facing in said substantially downward direction during said heating;
cooling said substrate, said fixture and said at least one electronic component to thereby solidify said solder balls on said sites and solderably connect said pads to said at least one electronic component; and separating said substrate from said fixture.
3. The method of claim 1 or claim 2 wherein said fixture is of a material comprised of titanium, molybdenum or graphite.
4. The method of claim 1 or claim 2 wherein said solder paste is a eutectic tin/lead composition.
5. The method of claim 1 or claim 2 wherein said solder paste is a eutectic composition of about 63% lead and 37% tin.
6. The method of claim 1 or 2 wherein said substrate and fixture are heated to a temperature between 25 and 350 degrees Celsius.
7. The method of claim 2 wherein said reflow of said solder connections and said solder paste occurs simultaneously.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002135508A CA2135508C (en) | 1994-11-09 | 1994-11-09 | Method for forming solder balls on a semiconductor substrate |
| US08/558,577 US5658827A (en) | 1994-11-09 | 1995-10-31 | Method for forming solder balls on a substrate |
| JP28302495A JP3202903B2 (en) | 1994-11-09 | 1995-10-31 | Method of forming solder balls on a substrate |
| US08/859,546 US6030889A (en) | 1994-09-11 | 1997-05-20 | Substrate-holding fixture of non-wettable material |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002135508A CA2135508C (en) | 1994-11-09 | 1994-11-09 | Method for forming solder balls on a semiconductor substrate |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2135508A1 CA2135508A1 (en) | 1996-05-10 |
| CA2135508C true CA2135508C (en) | 1998-11-03 |
Family
ID=4154645
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002135508A Expired - Fee Related CA2135508C (en) | 1994-09-11 | 1994-11-09 | Method for forming solder balls on a semiconductor substrate |
Country Status (3)
| Country | Link |
|---|---|
| US (2) | US5658827A (en) |
| JP (1) | JP3202903B2 (en) |
| CA (1) | CA2135508C (en) |
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| US7928585B2 (en) * | 2007-10-09 | 2011-04-19 | International Business Machines Corporation | Sprocket opening alignment process and apparatus for multilayer solder decal |
| US8424748B2 (en) * | 2009-12-21 | 2013-04-23 | Intel Corporation | Solder in cavity interconnection technology |
| US8936967B2 (en) | 2011-03-23 | 2015-01-20 | Intel Corporation | Solder in cavity interconnection structures |
| US8993378B2 (en) | 2011-09-06 | 2015-03-31 | Taiwan Semiconductor Manufacturing Co., Ltd. | Flip-chip BGA assembly process |
| US20140055961A1 (en) * | 2012-08-23 | 2014-02-27 | Shayan Malek | Printed Circuit Boards with Recesses |
| US8955735B2 (en) * | 2013-05-17 | 2015-02-17 | Zen Voce Corporation | Method for enhancing the yield rate of ball implanting of a substrate of an integrated circuit |
| US9120170B2 (en) * | 2013-11-01 | 2015-09-01 | Zen Voce Corporation | Apparatus and method for placing and mounting solder balls on an integrated circuit substrate |
| US9953908B2 (en) * | 2015-10-30 | 2018-04-24 | International Business Machines Corporation | Method for forming solder bumps using sacrificial layer |
| AU2019396232A1 (en) * | 2018-12-12 | 2021-07-01 | Connlaoth MULHOLLAND | Soldering block for led tape light |
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| US3569607A (en) * | 1969-08-01 | 1971-03-09 | Ibm | Resolderable connector |
| US4412642A (en) * | 1982-03-15 | 1983-11-01 | Western Electric Co., Inc. | Cast solder leads for leadless semiconductor circuits |
| US4655164A (en) * | 1985-12-04 | 1987-04-07 | Rca Corporation | Fixture for solder processing integrated circuit package leads |
| US5039628A (en) * | 1988-02-19 | 1991-08-13 | Microelectronics & Computer Technology Corporation | Flip substrate for chip mount |
| US5024372A (en) * | 1989-01-03 | 1991-06-18 | Motorola, Inc. | Method of making high density solder bumps and a substrate socket for high density solder bumps |
| US4914814A (en) * | 1989-05-04 | 1990-04-10 | International Business Machines Corporation | Process of fabricating a circuit package |
| US5372295A (en) * | 1991-10-04 | 1994-12-13 | Ryoden Semiconductor System Engineering Corporation | Solder material, junctioning method, junction material, and semiconductor device |
| JP3086066B2 (en) * | 1991-10-29 | 2000-09-11 | 富士通株式会社 | Cream solder printing method and electronic component soldering method |
| US5403671A (en) * | 1992-05-12 | 1995-04-04 | Mask Technology, Inc. | Product for surface mount solder joints |
| US5211328A (en) * | 1992-05-22 | 1993-05-18 | International Business Machines | Method of applying solder |
| US5268068A (en) * | 1992-12-08 | 1993-12-07 | International Business Machines Corporation | High aspect ratio molybdenum composite mask method |
| US5480835A (en) * | 1993-05-06 | 1996-01-02 | Motorola, Inc. | Electrical interconnect and method for forming the same |
| US5478700A (en) * | 1993-12-21 | 1995-12-26 | International Business Machines Corporation | Method for applying bonding agents to pad and/or interconnection sites in the manufacture of electrical circuits using a bonding agent injection head |
| US5539153A (en) * | 1994-08-08 | 1996-07-23 | Hewlett-Packard Company | Method of bumping substrates by contained paste deposition |
| US5536677A (en) * | 1994-12-01 | 1996-07-16 | Motorola, Inc. | Method of forming conductive bumps on a semiconductor device using a double mask structure |
| US5782399A (en) * | 1995-12-22 | 1998-07-21 | Tti Testron, Inc. | Method and apparatus for attaching spherical and/or non-spherical contacts to a substrate |
-
1994
- 1994-11-09 CA CA002135508A patent/CA2135508C/en not_active Expired - Fee Related
-
1995
- 1995-10-31 US US08/558,577 patent/US5658827A/en not_active Expired - Lifetime
- 1995-10-31 JP JP28302495A patent/JP3202903B2/en not_active Expired - Fee Related
-
1997
- 1997-05-20 US US08/859,546 patent/US6030889A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US6030889A (en) | 2000-02-29 |
| CA2135508A1 (en) | 1996-05-10 |
| JPH08213505A (en) | 1996-08-20 |
| US5658827A (en) | 1997-08-19 |
| JP3202903B2 (en) | 2001-08-27 |
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