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#27- An Evaluation of Aluminum Wire Bondable Surfaces for Automotive Lead Frame Applications

Abstract: Aluminum inlaid into copper base metal has been the material of choice for automotive lead frames connecting hybrid and multi-chip modules to control circuits. The aluminum bond surface provides for a wide process window with very high capability and extremely low internal scrap. This is a significant point because quite often the value of the electronics is at least two orders of magnitude higher than the cost of the lead frame.

The advent of global manufacturing has increased pressure to investigate a more conventional and transportable manufacturing technology for the bond surface. Electroplating processes address this need.

Silver Electroplate

Silver electroplate is a suitable surface for gold wire bonding. There are documented problems with Al wire bonds. Aluminum wire will bond to clean silver surfaces. However, intermetallic compounds formed at the interface are selectively corroded in humid environments and may lead to bond interface failure. Electroless nickel phosphorous (NiP) has been used as a bondable surface.

Al-Ag bond vs. NiP bond

Drawbacks with this process include the affixing of parts, control of P content and shelf life. The purpose of this Materion Technical Materials study is to revisit the Al-Ag bond integrity issues and perform a preliminary assessment of the NiP bond surface produced using the reel-to-reel electrolytic NiP process.