Claims
- 1. A method of capping a solder ball with at least one layer of low melting point metal, said method comprises the steps of(a) forming said solder ball on a substrate, (b) placing a mask over said solder ball such that said mask surrounds a portion of said solder ball and such that a portion of said solder ball is exposed, (c) depositing at least one layer of a low melting point metal over said solder ball through said mask, such that at least a portion of said solder ball has a capping layer of said low melting point metal, and wherein the melting point of said low melting point metal is lower than the melting point of said solder ball.
- 2. The method of claim 1, wherein said solder ball is selected from a group consisting of high melting point solder, low melting point solder or C4.
- 3. The method of claim 1, wherein said substrate is selected from a group consisting of organic substrate, multi-layer organic substrate, ceramic substrate, multi-layer ceramic substrate or an integrated circuit chip.
- 4. The method of claim 1, wherein said solder ball is on an electrically conductive feature of said substrate.
- 5. The method of claim 4, wherein material for said electrically conductive feature is selected from a group consisting of Au, Co, Cr, Cu, Fe, Ni, TiW, phased Cr and Cu, and alloys thereof.
- 6. The method of claim 4, wherein said electrically conductive feature is in electrical contact with at least one internal electrically conductive feature.
- 7. The method of claim 1, wherein holes for the low melting point metal deposition in said mask are formed by electro-etching from both surfaces of the mask and forming a knife edge along the inner sidewall within said hole in said mask.
- 8. The method of claim 1, wherein holes for the low melting point metal deposition in said mask are formed by electro-etching from one side of the mask only and forming a slope within said hole in said mask.
- 9. The method of claim 1, wherein said solder ball comprises lead-tin alloy and wherein said alloy contains between about 2 percent to about 10 percent tin.
- 10. The method of claim 1, wherein said solder ball comprises lead-tin alloy and wherein said alloy contains between about 98 percent to about 90 percent lead.
- 11. The method of claim 1, wherein said solder ball is placed on said substrate using a method selected from the group consisting of evaporation, electroplating or solder injection method.
- 12. The method of claim 1, wherein said at least one layer of low melting point metal is deposited on said solder ball by a method selected from a group consisting of Radio Frequency evaporation, E-beam evaporation, electroplating, electroless plating or injection method.
- 13. The method of claim 1, wherein said low melting point metal is selected from a group consisting of bismuth, indium, tin or alloys thereof.
- 14. The method of claim 1, wherein at least a portion of said capped solder ball is secured to an electrically conductive feature on a second substrate.
- 15. The method of claim 14, wherein material for said electrically conductive feature is selected from a group consisting of Au, Co, Cr, Cu, Fe, Ni, Ta, Ti, TiW, phased Cr and Cu, and alloys thereof.
- 16. The method of claim 14, wherein said second substrate is selected from a group consisting of organic circuit carrier or ceramic circuit carrier.
- 17. The method of claim 16, wherein said organic circuit carrier is selected from a group consisting of rigid organic circuit carrier or flexible organic circuit carrier.
- 18. The method of claim 17, wherein the material for said rigid organic circuit carrier is selected from a group consisting of epoxies.
- 19. The method of claim 17, wherein the material for said flexible organic circuit carrier is selected from a group consisting of polyimides.
- 20. The method of claim 1, wherein said low melting point metal, caps between about 10 percent to about 90 percent of the exposed surface of said solder ball, and preferably caps between about 20 percent to about 80 percent of the exposed surface of said solder ball, and more preferably caps between about 30 percent to about 50 percent of the exposed surface of said solder ball.
- 21. The method of claim 1, wherein said low melting point metal completely envelopes said solder ball.
- 22. The method of claim 1, wherein said solder ball having a layer of low melting point metal is secured to an electrically conductive assembly.
- 23. The method of claim 22, wherein said electrically conductive assembly is selected from a group consisting of an IC chip, capacitor, resistor, a circuit carrier card, a power supply or an amplifying device.
- 24. The method of claim 1, where the thickness of said low melting point metal cap is chosen to provide a eutectic volume of between about 5 percent to about 30 percent of the volume of said solder ball, and preferably between about 10 percent to about 20 percent of the volume of said solder ball.
- 25. The method of claim 1, wherein the average thickness of said low melting point metal cap is between about 15 to about 50 micro-meters.
- 26. The method of claim 1, wherein said solder ball is selected from a group consisting of Pb, Bi, In, Sn, Ag, Au, or alloys thereof.
CROSS-REFERENCE TO RELATED PATENT APPLICATION
This Patent Application is related to U.S. patent application Ser. No. 08/476474, entitled, “REFLOWED SOLDER BALL WITH LOW MELTING POINT METAL CAP”, filed on Jun. 7, 1995, now abandoned. Presently assigned to the assignee of the instant application and the disclosure of which is incorporated herein by reference.
US Referenced Citations (12)
Foreign Referenced Citations (2)
Number |
Date |
Country |
62-117346 |
May 1987 |
JP |
62117346 |
May 1987 |
JP |
Non-Patent Literature Citations (2)
Entry |
Dawson, et al., “Indium-Lead-Indium Chip Joining”, IBM Technical Disclosure Bulletin, vol. 11, No. 11, p. 1528, Apr. 1969. |
Microelectronics Packaging Handbook, edited by Rao R. Tummala & Eugene J. Rymaszewski, SR28-4413-00, pp. 366-391. No Date Given. |