Design of a More Robust QFN Package through Virtual Prototyping and Advanced Characterization

A new leadframe design is proposed as a solution to eliminate package cracking in a HVQFN (heatsink very thin quad flat no lead) package. The impact of the new design was first analyzed using finite element modeling (FEM) particularly the interfacial stresses brought about by coefficient of thermal expansion (CTE) mismatches between materials. Result was further verified experimentally using thermo mechanical analyzer (TMA) and actual engineering evaluation. TMA was used to determine and compare the delamination and cracking temperature between the standard HVQFN leadframe design and the new design. With the modification of the leadframe design, package cracking was eliminated. Package was able to pass MSL 1 (Pb-free condition) from a level 3 classification without changing the current assembly material set. It has even withstood the extended JEDEC standard number of thermal cycle test.