Design of 0.35-mm pitch QFP lead and its assembly technology

The solder joint reliability of a 0.35-mm lead pitch, 42" wide x 42-mm long x 23-mm high, 396 pin, ceramic quad flat package (QFP) was studied in terms of: 1) finite element analysis simulation; 2) temperature cycling tests between -65' C and +125'C. Using the study results, physical design of the QFP leads, in terms of thickness, standoff, and Au surface finish were optimized. If the von Mises stress of a QFP solder joint can be optimized to be no more 16.7 kilogram square millimeters, we can guarantee QFP solder joint reliability over requested design life. Also, we developed a thermocompression (TK) soldering process for the QFP.