Claims
- 1. A method for mounting an electronic component to a substrate, said substrate comprising a first faying surface formed of copper metal, said component comprising a second faying surface formed of a solder-wettable metal, said method comprising
- applying a first layer onto the first faying surface, said first layer being formed of a tin-base metal,
- applying a solder paste onto the first layer to form a deposit comprising solder particles composed of tin alloy containing zinc,
- assembling the component with the substrate to form an assembly wherein the second faying surface is in contact with the deposit, and
- heating the assembly at a temperature and for a time sufficient to melt the tin alloy to form a solder liquid that fuses to the first layer and bonds to the second faying surface.
- 2. A method in accordance with claim 1 wherein the first layer is formed of a metal comprising at least 90 weight percent tin.
- 3. A method in accordance with claim 1 wherein the solder particles are composed of an alloy comprising between about 4 and 12 weight percent zinc and the balance tin.
- 4. A method for mounting an electronic component onto a printed circuit board, said printed circuit board having a metallic copper bond pad, said component comprising a contact formed of solder-wettable metal, said method comprising
- coating the metallic copper bond pad with a first layer composed of a metal comprising at least 90 weight percent and having a first melting temperature,
- applying a solder paste to the first layer to form a deposit, said paste comprising solder particles dispersed in a vaporizable vehicle, said solder particles being composed of solder alloy containing between about 4 and 12 weight percent zinc and the balance substantially tin and having a second melting temperature less than the first melting temperature
- assembling the component with the substrate to form an assembly wherein the contact touches the deposit,
- heating the assembly to a temperature above the second melting temperature and below the first melting temperature to melt the solder particles to form a solder liquid, and
- cooling to solidify the solder liquid to form a second layer that is bonded to the first layer and the contact to connect the component to the printed circuit board.
- 5. A method in accordance with claim 4 wherein the step of coating the metallic copper bond pad comprises applying onto the metallic copper bond pad a deposit of a paste comprising particles of said metal dispersed in a vaporizable vehicle, heating the deposit to a temperature sufficient to melt the metal to form a liquid that wets the copper pad, and cooling to solidify the liquid to form the first layer.
- 6. A method in accordance with claim 4 where in the first melting temperature is at least 220.degree. C. and the second melting temperature is less than 220.degree. C.
- 7. A method in accordance with claim 4 wherein the assembly is heated to a temperature less than 220.degree. C.
- 8. A method in accordance with claim 4 wherein the solder particles are composed of a solder alloy containing between about 9 and 11 weight percent zinc.
- 9. A method in accordance with claim 4 wherein the layer has a thickness between about of at least about 25 microns.
- 10. A method in accordance with claim 4 wherein the second layer has a thickness between about 50 and 100 microns.
- 11. A method in accordance with claim 4 wherein upon heating and cooling of the assembly, the second layer is fused to the first layer.
Parent Case Info
This is a division of application Ser. No. 08/057,233, filed on May 3, 1993, now U.S. Pat. No. 5,390,080.
US Referenced Citations (5)
Foreign Referenced Citations (1)
Number |
Date |
Country |
3220558 |
Sep 1988 |
JPX |
Non-Patent Literature Citations (1)
Entry |
Journal of the Electrochemical Society, "Semiconductor Joining by the Solid-Liquid-Interdiffusion (SLID) Process", Leonard Bernstein, vol. 113, No. 12, pp. 1282-1288, Dec., 1966. |
Divisions (1)
|
Number |
Date |
Country |
Parent |
57233 |
May 1993 |
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