Dual Row QFN Roughen Lead Frame Mold Flash Challenges & Resolution

Dual row quad flat no lead (DRQFN) is known to be a preferred low cost package which provide higher I/O and smaller package size. Therefore, it can be widely used in semiconductor packaging for various applications, including both automotive and non-automotive. However, in punched DRQFN assembly process, mold flash is a key challenge in film assisted molding (FAM). This paper provide a detail study in robust molding process with FAM on DRQFN and lead frame surface roughness control to overcome mold flash package challenges. High mold flash was found at inner row bottom lead finger surface due to floated half etched design and higher surface roughness S-ratio value at bottom lead finger surface. S-ratio refers to ratio of S to SO, where SO is surface area of a planar surface and S is surface area of uneven surface part formed on planar surface. Key factors contributing to mold flash are mold released film design and lead frame roughness consistency control. First, with regards to mold released film design, there are 2 layers in the mold released film. Top layer is base film which is in contact to mold chase. Bottom layer is release layer which is in contact to lead frame. The study found that FAM film surface finish of top and bottom layer as well as thicker released layer are able to minimize mold flash. Secondly, it is found that lead frame bottom side roughness consistency with low surface roughness S-ratio is able to reduce mold flash. A detailed reliability validation plan is carried out to validate both factors. The study includes post temperature cycle (TC) and unbiased high accelerated stress test (uHAST) with electrical testing and physical delamination inspection. This solution achieves a high assembly yield of above 99%.