WO1996037089A1 - A connective medium and a process for connecting electrical devices to circuit boards - Google Patents

A connective medium and a process for connecting electrical devices to circuit boards Download PDF

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Publication number
WO1996037089A1
WO1996037089A1 PCT/CA1996/000323 CA9600323W WO9637089A1 WO 1996037089 A1 WO1996037089 A1 WO 1996037089A1 CA 9600323 W CA9600323 W CA 9600323W WO 9637089 A1 WO9637089 A1 WO 9637089A1
Authority
WO
WIPO (PCT)
Prior art keywords
melting point
point solder
spheres
high melting
alloy
Prior art date
Application number
PCT/CA1996/000323
Other languages
French (fr)
Inventor
Karel Hajmrle
Kenneth G. Reid
Anthony P. Chilkowich
James B. Ramsden
Original Assignee
Westaim Technologies Inc.
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Westaim Technologies Inc. filed Critical Westaim Technologies Inc.
Priority to AU56829/96A priority Critical patent/AU5682996A/en
Publication of WO1996037089A1 publication Critical patent/WO1996037089A1/en

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/24—Selection of soldering or welding materials proper
    • B23K35/26—Selection of soldering or welding materials proper with the principal constituent melting at less than 400 degrees C
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
    • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
    • B23K35/0244—Powders, particles or spheres; Preforms made therefrom
    • 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
    • H05K3/341—Surface mounted components
    • H05K3/3431—Leadless components
    • H05K3/3436—Leadless components having an array of bottom contacts, e.g. pad grid array or ball grid array components
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/24—Selection of soldering or welding materials proper
    • B23K35/26—Selection of soldering or welding materials proper with the principal constituent melting at less than 400 degrees C
    • B23K35/268—Pb as the principal constituent
    • 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
    • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/10—Details of components or other objects attached to or integrated in a printed circuit board
    • H05K2201/10613—Details of electrical connections of non-printed components, e.g. special leads
    • H05K2201/10954—Other details of electrical connections
    • H05K2201/10992—Using different connection materials, e.g. different solders, for the same connection
    • 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
    • H05K2203/041—Solder preforms in the shape of solder balls
    • 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
    • H05K2203/0435—Metal coated solder, e.g. for passivation of solder balls
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a connective medium and a process for connecting electronic devices to circuit boards.
  • solder alloy composition of choice contains by weight 63% tin and 37% lead. It will be understood that all percentages used herein are by weight.
  • discrete spheres of solder alloy are used as the connective medium in systems called ball grid arrays.
  • the discrete spheres in a ball grid array connect the electromc device to the circuit board while maintaining the electronic device separate from the circuit board.
  • the discrete spheres are formed from an alloy composition having a relatively high melting point, such as 90% lead and 10% tin. Adhesion between the discrete spheres and the electronic device and the circuit board is secured by coating the respective mounting pads on the electronic device and on the circuit board with a lower melting point solder alloy composition, such as 63% tin and 37% lead, which melts during the subsequent joining (reflow) heat treatment.
  • the process involves printing the solder paste onto the device, reflowing the paste and attaching the ball to the device, printing the solder paste onto the board and again reflowing the solder paste on the board and the solder on the device.
  • High speed printing of the solder paste is a difficult operation since the amounts of dispensed solder paste can vary from one soldering location to another. This can decrease the reliability of the whole assembly.
  • this lower melting point solder alloy composition is melted it provides the necessary bond strength, ductility and electrical conductivity between the electronic device and the circuit board.
  • the electronic device becomes faulty in subsequent operation and has to be replaced, the device must be removed by remelting the low melting point solder on the mounting pads, and then substituting a new electronic device.
  • the solder on the mounting pads has too high a lead content, as a consequence of the aforementioned leaching, the device removal from the board is difficult and the discrete spheres and coating will no longer create a satisfactory bond having the required strength, ductility and electrical conductivity for the new device.
  • An object of the invention is to provide an improved connective medium for connecting electronic devices to circuit boards.
  • circuit board which is easy to repair so that when an electronic device has to be replaced, the remnants of solder left on the mounting pads are of the correct alloy composition for re-soldering a new electronic device. It is desirable to provide a circuit board which is easy to repair, so that when the electronic device is replaced, a cleaning step is not necessary to remove remnants of old solder on the mounting pads.
  • An aspect of the process of the present invention comprises the step of electroplating a high melting point solder alloy sphere, such as 90% lead and 10% tin, with a well controlled amount of a low melting point solder alloy composition, such as 63% tin and 37% lead, to form an uniformly thick coating of the low melting point solder on the high melting point solder alloy sphere concentric therewith.
  • a product may then be used in ball grid arrays to mount electronic devices on circuit boards while eliminating the need for precoating the mounting pads on the electronic device and/or the circuit board with low melting point solder.
  • the low melting point solder alloy forms the mechanical bond between the solder balls and mounting pads on the circuit board and the mounting pads on the electrical device.
  • the connective medium of the invention for use in ball grid array assemblies for connecting electronic devices to circuit boards comprises discrete high melting point solder alloy spheres and an outer concentric layer of low melting point solder alloy of uniform thickness electroplated on each said discrete high melting point solder alloy spheres.
  • the process for connecting an electronic device to a circuit board comprises electroplating a coating of a low melting point solder alloy onto high melting point solder spheres to form an outer concentric layer of low melting point solder alloy of uniform thickness on said high melting point solder spheres, placing an array of said electroplated solder spheres against a solderable portion of the electromc devices, heating said array of spheres to a predetermined temperature to melt said low melting point solder alloy, whereby said melted low melting point solder alloy forms a bond between the unmelted high melting point spheres and said electronic devices; and juxtaposing the solderable portion of the electronic device having the array of spheres in abutment with the solderable portion of the circuit board and reheating the abutting array of electroplated high melting point solder spheres coated with a layer of low melting point solder to connect the electronic device to the circuit board.
  • a further aspect of the process of the present invention comprises the step of coating the high melting point solder alloy spheres with a leach or diffusion barrier.
  • the leach barrier will help prevent lead from the high melting point solder alloy spheres from leaching into, and contaminating, the outer coating of low melting point solder alloy.
  • the leach barrier will prevent leaching at temperatures up to 230°C.
  • Such a leach barrier coating might be nickel, silver, copper, tungsten, chromium, ruthenium, molybdenum or other appropriate meial or metal alloy.
  • the latter embodiment of the invention further comprises a leach barrier coated on said high melting point solder alloy spheres intermediate the spheres and the concentric layer, whereby when said outer layer of low melting point alloy is melted said leach barrier prevents lead from leaching from said high melting point solder alloy into said outer layer of low melting point solder alloy.
  • Figure la is an illustration of a schematic view of a solder sphere alloy and solder cream of the prior art, before the solder cream is melted to connect the solder sphere alloy to the electronic device;
  • Figure lb is a schematic view of the prior art solder sphere alloy and solder cream shown in Figure la after the solder cream is melted to connect the solder sphere alloy to the electronic device;
  • Figure 2a is a schematic view of an embodiment of the present invention of a high melting solder alloy sphere with a concentric, uniformly thick electroplated coating of a low melting solder alloy coating positioned on an electronic device;
  • Figure 2b is a schematic view of the embodiment of
  • Figure 3a is a schematic view of an embodiment of the invention showing a high melting point solder sphere coated with a leach barrier and electroplated with a low melting solder alloy coating;
  • Figure 3b is a schematic view of the embodiment of
  • Figure 3 a after the low melting point solder is melted to connect the high melting point solder sphere to the electronic device.
  • Figure 4 is a photograph of a cross section of 90PblOSn solder spheres of the invention coated with 63Sn37Pb solder (Mag.50X); and
  • Figure 5 is a photograph of a cross section of a
  • High melting point, high lead solder alloy sphere 20 having a composition such as 90Pbl0Sn has a concentric coating 22 of uniform thickness plated thereon, such as by electroplating, of a low lead, low melting point solder alloy such as 63Sn37Pb.
  • Figure 2a shows coated sphere 20 seated on copper contact pad 24 of device 26.
  • Figure 2b shows low melting solder alloy 22 melted onto contact pad 24 to effectively interconnect sphere 20 thereto.
  • Figures 3 a and 3b illustrate another embodiment of the invention wherein a leach or diffusion barrier 30 is coated, such as by electroplating, onto the surface of high melting point solder alloy spheres 32.
  • the leach barrier material 30 may be nickel, silver, copper, tungsten, chromium, ruthenium, molybdenum, copper or the like metal or a metal alloy thereof.
  • a low melting point solder alloy 34 is electroplated onto diffusion barrier 30.
  • the composite micro spheres are seated on connector pad 36 of electronic device 38 and, when heated to the melting point of low melting point solder alloy 34, flow onto pad 36 to connect spheres 32 thereto.
  • Embodiments of the invention for producing an improved ⁇ connecting medium of high melting point solder spheres with an electroplated low melting point solder coating and with an intermediary leach barrier will now be described in the following non-limitative examples.
  • Example 1 Commercially available 90PblOSn solder spheres were electroplated with 63Sn37Pb to form a continuous, concentric coating of uniform thickness as shown in the cross section of the spheres illustrated in the microphotograph of Figure 4.
  • Example 2 Example 2
  • Figure 5 is a microphotograph of a cross section of the product of Example 2.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Electric Connection Of Electric Components To Printed Circuits (AREA)

Abstract

A connective medium for use in ball grid arrays for connecting electronic devices to circuit boards comprising high melting point solder alloy spheres (32) coated, by electroplating, with an outer concentric layer of a lower melting point solder alloy (34) of uniform thickness. In a further aspect, a leach barrier (30) is coated on the high melting point solder alloy (32) prior to electroplating the low melting point solder alloy (34) thereto. The leach barrier (30) forms a barrier to prevent the lead from leaching from the high melting point lead solder spheres (32) into the low melting point solder alloy (34) during the reflow heat treatment in the mounting process.

Description

A CONNECTIVE MEDIUM AND A PROCESS FOR CONNECTING ELECTRICAL DEVICES TO CIRCUIT BOARDS Field of Invention
The present invention relates to a connective medium and a process for connecting electronic devices to circuit boards. Background of Invention
It is commonly known to use spheres of solder alloy in the manufacture of conductive inks and pastes to form conductive traces and mounting pads, respectively, for connecting electronic devices to circuit boards. The solder alloy composition of choice contains by weight 63% tin and 37% lead. It will be understood that all percentages used herein are by weight.
More recently, discrete spheres of solder alloy are used as the connective medium in systems called ball grid arrays. The discrete spheres in a ball grid array connect the electromc device to the circuit board while maintaining the electronic device separate from the circuit board. The discrete spheres are formed from an alloy composition having a relatively high melting point, such as 90% lead and 10% tin. Adhesion between the discrete spheres and the electronic device and the circuit board is secured by coating the respective mounting pads on the electronic device and on the circuit board with a lower melting point solder alloy composition, such as 63% tin and 37% lead, which melts during the subsequent joining (reflow) heat treatment. The process involves printing the solder paste onto the device, reflowing the paste and attaching the ball to the device, printing the solder paste onto the board and again reflowing the solder paste on the board and the solder on the device. High speed printing of the solder paste is a difficult operation since the amounts of dispensed solder paste can vary from one soldering location to another. This can decrease the reliability of the whole assembly. When this lower melting point solder alloy composition is melted it provides the necessary bond strength, ductility and electrical conductivity between the electronic device and the circuit board.
During this heat treatment, some lead from the high melting point solder alloy of the discrete spheres leaches into the liquid low lead alloy coating on the mounting pad. This leaching is highly undesirable.
If the electronic device becomes faulty in subsequent operation and has to be replaced, the device must be removed by remelting the low melting point solder on the mounting pads, and then substituting a new electronic device. However, if the solder on the mounting pads has too high a lead content, as a consequence of the aforementioned leaching, the device removal from the board is difficult and the discrete spheres and coating will no longer create a satisfactory bond having the required strength, ductility and electrical conductivity for the new device.
It will be appreciated, therefore, that there also exists a need to improve the manufacturing process of a circuit board assembly to avoid the leaching problem. Summary of the Invention
An object of the invention is to provide an improved connective medium for connecting electronic devices to circuit boards.
It is desirable to provide a process for producing a circuit board assembly with ball grid arrays by eliminating the step of precoating the mounting pads on the device or preferably on both the device and the circuit board with a low melting point solder alloy or solder cream.
It is desirable to provide precisely controlled amounts of low melting point solder to the soldering locations so that variations of the solder in each soldering location do not degrade the reliability of the soldered joint.
It is desirable to provide a circuit board which is easy to repair so that when an electronic device has to be replaced, the remnants of solder left on the mounting pads are of the correct alloy composition for re-soldering a new electronic device. It is desirable to provide a circuit board which is easy to repair, so that when the electronic device is replaced, a cleaning step is not necessary to remove remnants of old solder on the mounting pads.
An aspect of the process of the present invention comprises the step of electroplating a high melting point solder alloy sphere, such as 90% lead and 10% tin, with a well controlled amount of a low melting point solder alloy composition, such as 63% tin and 37% lead, to form an uniformly thick coating of the low melting point solder on the high melting point solder alloy sphere concentric therewith. Such a product may then be used in ball grid arrays to mount electronic devices on circuit boards while eliminating the need for precoating the mounting pads on the electronic device and/or the circuit board with low melting point solder. The low melting point solder alloy forms the mechanical bond between the solder balls and mounting pads on the circuit board and the mounting pads on the electrical device.
In its broad aspect, the connective medium of the invention for use in ball grid array assemblies for connecting electronic devices to circuit boards comprises discrete high melting point solder alloy spheres and an outer concentric layer of low melting point solder alloy of uniform thickness electroplated on each said discrete high melting point solder alloy spheres. The process for connecting an electronic device to a circuit board comprises electroplating a coating of a low melting point solder alloy onto high melting point solder spheres to form an outer concentric layer of low melting point solder alloy of uniform thickness on said high melting point solder spheres, placing an array of said electroplated solder spheres against a solderable portion of the electromc devices, heating said array of spheres to a predetermined temperature to melt said low melting point solder alloy, whereby said melted low melting point solder alloy forms a bond between the unmelted high melting point spheres and said electronic devices; and juxtaposing the solderable portion of the electronic device having the array of spheres in abutment with the solderable portion of the circuit board and reheating the abutting array of electroplated high melting point solder spheres coated with a layer of low melting point solder to connect the electronic device to the circuit board.
A further aspect of the process of the present invention comprises the step of coating the high melting point solder alloy spheres with a leach or diffusion barrier. The leach barrier will help prevent lead from the high melting point solder alloy spheres from leaching into, and contaminating, the outer coating of low melting point solder alloy. Preferably, the leach barrier will prevent leaching at temperatures up to 230°C. Such a leach barrier coating might be nickel, silver, copper, tungsten, chromium, ruthenium, molybdenum or other appropriate meial or metal alloy.
In its broad aspect, the latter embodiment of the invention further comprises a leach barrier coated on said high melting point solder alloy spheres intermediate the spheres and the concentric layer, whereby when said outer layer of low melting point alloy is melted said leach barrier prevents lead from leaching from said high melting point solder alloy into said outer layer of low melting point solder alloy.
Description of the Drawings
The present invention will be better understood with reference to the detailed description below and the following figures:
Figure la: is an illustration of a schematic view of a solder sphere alloy and solder cream of the prior art, before the solder cream is melted to connect the solder sphere alloy to the electronic device;
Figure lb: is a schematic view of the prior art solder sphere alloy and solder cream shown in Figure la after the solder cream is melted to connect the solder sphere alloy to the electronic device;
Figure 2a: is a schematic view of an embodiment of the present invention of a high melting solder alloy sphere with a concentric, uniformly thick electroplated coating of a low melting solder alloy coating positioned on an electronic device; Figure 2b: is a schematic view of the embodiment of
Figure 2a after the electroplated low melting solder alloy is melted to connect the high melting solder sphere alloy to the electronic device;
Figure 3a: is a schematic view of an embodiment of the invention showing a high melting point solder sphere coated with a leach barrier and electroplated with a low melting solder alloy coating;
Figure 3b: is a schematic view of the embodiment of
Figure 3 a after the low melting point solder is melted to connect the high melting point solder sphere to the electronic device. Figure 4: is a photograph of a cross section of 90PblOSn solder spheres of the invention coated with 63Sn37Pb solder (Mag.50X); and Figure 5: is a photograph of a cross section of a
90PblOSn solder sphere coated first with nickel and then with a 63Sn37Pb layer (Mag 100X). Detailed Description of the Invention
Referring first to Figures la and lb, prior art technology for attaching an array of solder alloy spheres 10 to a device 12 is depicted. High lead solder alloy sphere 10 having a composition such as 90Pbl0Sn and low lead solder cream 14 having a composition such as 63Sn37Pb upon which sphere 10 is seated as shown in Figure la are heated, allowing the low lead, low melting solder cream 14 to interconnect sphere 10 to copper contact pad 16 of device 12, as shown in Figure lb. This process necessitates the printing of solder cream 14 on contact pad 16.
With reference now to Figures 2a and 2b, the connective medium of the present invention is illustrated. High melting point, high lead solder alloy sphere 20 having a composition such as 90Pbl0Sn has a concentric coating 22 of uniform thickness plated thereon, such as by electroplating, of a low lead, low melting point solder alloy such as 63Sn37Pb. Figure 2a shows coated sphere 20 seated on copper contact pad 24 of device 26. Figure 2b shows low melting solder alloy 22 melted onto contact pad 24 to effectively interconnect sphere 20 thereto. Figures 3 a and 3b illustrate another embodiment of the invention wherein a leach or diffusion barrier 30 is coated, such as by electroplating, onto the surface of high melting point solder alloy spheres 32. The leach barrier material 30 may be nickel, silver, copper, tungsten, chromium, ruthenium, molybdenum, copper or the like metal or a metal alloy thereof. A low melting point solder alloy 34 is electroplated onto diffusion barrier 30.
The composite micro spheres are seated on connector pad 36 of electronic device 38 and, when heated to the melting point of low melting point solder alloy 34, flow onto pad 36 to connect spheres 32 thereto.
Embodiments of the invention for producing an improved δ connecting medium of high melting point solder spheres with an electroplated low melting point solder coating and with an intermediary leach barrier will now be described in the following non-limitative examples.
Example 1 Commercially available 90PblOSn solder spheres were electroplated with 63Sn37Pb to form a continuous, concentric coating of uniform thickness as shown in the cross section of the spheres illustrated in the microphotograph of Figure 4. The use of the spheres of the present invention, as shown schematically in Figures 2a and 2b, effectively connected the spheres to the contact pad of an electronic device by a first stage heating and allowed interconnection of an electronic device to a circuit board without use of a conventional solder cream by a second stage reflow of the solder. Example 2
Commercially available 90PblOSn solder spheres were first plated with a leach barrier of nickel and then with a layer of 63Sn37Pb solder, as shown schematically in Figure 3a.
Figure 5 is a microphotograph of a cross section of the product of Example 2.
It will be understood that changes and modifications may be made to the above described embodiments of the invention without departing from the scope of the invention as defined in the claims.

Claims

We Claim:
1. A connective medium for use in ball grid array assemblies for connecting electronic devices to circuit boards comprising discrete high melting point solder alloy spheres and an outer concentric layer of low melting point solder alloy of uniform thickness electroplated on said discrete high melting point solder alloy spheres.
2. The connective medium as claimed in claim 1, further comprising a leach barrier coated on said high melting point solder alloy spheres intermediate the spheres and the outer concentric layer, whereby when said outer concentric layer of low melting point alloy is melted said leach barrier prevents lead from leaching from said high melting point solder alloy into said outer layer of low melting point solder alloy.
3. The connective medium as claimed in claim 2 wherein said leaching is prevented at temperatures up to 230°C.
4. The connective medium as claimed in claim 1, 2 or 3, wherein the said discrete high melting point solder alloy spheres have an alloy composition of 90% lead and 10% tin.
5. The connective medium as claimed in claim 1, 2 or 3, wherein the said outer layer has a composition of 63% tin and 37% lead.
6. The connective medium as claimed in claim 2 or 3, wherein the leach barrier is nickel, silver, copper, tungsten, chromium, ruthenium, molybdenum or an alloy thereof.
7. A process for connecting an electronic device to a circuit board comprising electroplating a coating of a low melting point solder alloy onto high melting point solder spheres to form an outer concentric layer of low melting point solder alloy of uniform thickness on said high melting point solder spheres; placing an array of said electroplated solder spheres against a solderable portion of the electronic device; heating said array of spheres to a predetermined temperature to melt said low melting point solder alloy, whereby said melted low melting point solder alloy forms a bond between the unmelted high melting point spheres and said electronic device; and juxtaposing the solderable portion of the electronic device having the array of spheres in abutment with the solderable portion of the circuit board and reheating the abutting array of electroplated high melting point solder spheres coated with a layer of low melting point solder to connect the electronic device to the circuit board.
8. The process as claimed in claim 7 wherein the high melting point solder spheres comprise 90% lead and 10% tin.
9. The process as claimed in claim 8 wherein the low melting point solder comprise 37% lead and 63% tin.
10. The process as claimed in claim 7, 8 or 9 further comprising, the step of coating the high melting point solder sphere with a leach barrier selected from the group consisting of nickel, silver, copper, tungsten, chromium, ruthenium, molybdenum or an alloy thereof, prior to electroplating the high melting point solder sphere with the low melting point solder thereon, to prevent leaching of lead from the high melting point solder into the layer of the low melting point solder up to a predetermined temperature.
11. The process as claimed in claim 10 wherein the predetermined temperature is not less than 230°C.
PCT/CA1996/000323 1995-05-18 1996-05-17 A connective medium and a process for connecting electrical devices to circuit boards WO1996037089A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU56829/96A AU5682996A (en) 1995-05-18 1996-05-17 A connective medium and a process for connecting electrical devices to circuit boards

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Application Number Priority Date Filing Date Title
GBGB9510085.5A GB9510085D0 (en) 1995-05-18 1995-05-18 A connective medium and a process for connecting electronic devices to circuit boards
GB9510085.5 1995-05-18

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GB (1) GB9510085D0 (en)
TW (1) TW314686B (en)
WO (1) WO1996037089A1 (en)
ZA (1) ZA963988B (en)

Cited By (3)

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Publication number Priority date Publication date Assignee Title
US6043990A (en) * 1997-06-09 2000-03-28 Prototype Solutions Corporation Multiple board package employing solder balis and fabrication method and apparatus
US6678144B2 (en) 2001-03-01 2004-01-13 Shinko Electric Industries Co., Ltd Capacitor, circuit board with built-in capacitor and method for producing the same
CN103731983A (en) * 2012-10-15 2014-04-16 三星电机株式会社 Printed circuit board and method for manufacturing the same

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US5324569A (en) * 1993-02-26 1994-06-28 Hewlett-Packard Company Composite transversely plastic interconnect for microchip carrier
JPH0799385A (en) * 1993-09-29 1995-04-11 Ibiden Co Ltd Solder ball, manufacture thereof and connection structure
JPH07106750A (en) * 1993-09-30 1995-04-21 Ibiden Co Ltd Solder ball, its manufacture and connection structure
EP0650795A2 (en) * 1993-10-28 1995-05-03 International Business Machines Corporation Solder ball connections and assembly process

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EP0084464A2 (en) * 1982-01-20 1983-07-27 North American Specialities Corporation Connector for electronic subassemblies
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TW314686B (en) 1997-09-01
AU5682996A (en) 1996-11-29
GB9510085D0 (en) 1995-07-12
ZA963988B (en) 1997-01-27

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