To meet the requirements of high speed driving LSI packages with powerful output, a combination leadframe has been developed which is made up of a two-metal-layer FPC (flexible printed circuit) and an outer leadframe. The use of thin copper foil minimizes the inner-lead pitch to 120 mu m. The combination structure of the FPC and leadframe greatly shortens the surface mounting. The developed method of joining the FPC to the leadframe using Au-Sn eutectic soldering is reliable at high temperatures and temperature cycles. This leadframe has some excellent characteristics. The electrical impedance of the leads can be easily controlled by rearrangement of lead widths, gaps, and dielectric insulation. The heat spreading effect by plain metal, which halved the apparent thermal resistance, is excellent. The adhesiveless copper clad laminate has a positive effect in preventing electromigration.
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