Claims
- 1. A method for forming solder bumps directly on a substrate having a plurality of wettable pads using solder paste and a non-wettable, photoimageable material, comprising:
- forming a thin non-wettable photoimageable mask on the substrate with the material:
- forming a plurality of apertures in the mask 10 align with the pads;
- applying solder paste to the mask such that the solder paste loads the mask apertures;
- heating the solder paste, such that the solder paste coalesces to form solder bumps on the pads: and
- removing the mask after formation of the solder bumps.
- 2. A method as in claim 1 wherein the photoimageable mask is made of photoimageable polyimide, dry film photomask, liquid photoimageable photomask, silicon or ceramic.
- 3. A method as in claim 1 further comprising inspecting the substrate/paste/mask assembly prior to reflow.
- 4. A method as in claim 3 further comprising adding additional paste to unfilled mask apertures after inspection.
- 5. A method as in claim 1 further comprising inspecting the substrate/solder bump assembly after mask removal.
- 6. A method as in claim 5 further comprising replacing missing bumps on the substrate/solder bump assembly after inspection.
- 7. A method as in claim 5 further comprising repairing damaged bumps on the substrate/solder bump assembly after inspection.
- 8. A method as in claim 1 wherein the solder paste contains metal powder in a flux vehicle.
- 9. A method as in claim 1 wherein the solder paste contains an alloy of at least one metal that can be made into a powder and a flux vehicle for said powder.
- 10. A method as in claim 1 wherein the solder paste contains an 63 Sn 37 Pb alloy.
- 11. A method as in claim 1, wherein the coefficient of thermal expansion of the mask is substantially similar to the coefficient of thermal expansion of the substrate.
- 12. A method as in claim 1 wherein the bumps have pitches in the range of 150 to 350 microns.
- 13. A method as in claim 1 wherein the apertures are approximately cylindrical.
Parent Case Info
This is a continuation, of application Ser. No. 08/287,453, filed Aug. 8, 1994, now U.S. Pat. No. 5,539,153.
US Referenced Citations (37)
Non-Patent Literature Citations (1)
Entry |
"Metal Mask Solder Transfer Technique", International Interconnection Flip Chip Technology Impact Report, Jun. 1992, Chapter 5, pp. 37-38. |
Continuations (1)
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Number |
Date |
Country |
Parent |
287453 |
Aug 1994 |
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