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Converting Au Stud Bumps to a Non-Embrittling Surface for Sn Based Solders
Keywords: Gold, Stud, Bump
Flip chip has the advantages of smaller footprint on the PCB, improved electrical performance, reduced manufacturing steps at assembly and excellent long term reliability. A major problem is every die is not available in a flip chip package. CVInc has processes that convert gold and copper stud bumps to flip chip bumps. Copper has been selected in the past due to embrittlement issues of Sn and Au. CVInc has developed a technique to add a barrier layer of NiAu to thick gold (including gold stud bumps) eliminating the need for copper stud bumps and providing alternatives for thick gold on traditional wire bond pads. Updates have included adding NiAu to Au pads (nitride passivation opening) and Au plated headers. Cross sections show solder is indeed adhered to the Ni layer instead directly in contact with the gold. Gold to aluminum bonds have historical reliability data assuring the converted solder bump will have the minimum shear strength of a gold stud to aluminum. When the aluminum pad is converted to NiPdAu or NiAu prior to gold stud bump the resulting reliability is furthermore increase..........though once NiPdAu or NiAu is added CVI can directly bump die with solder eliminating the need for a gold stud bump.
Terence Collier, President
CV Inc.
Richardson, TX

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