Bidens-Inspired Anchor-Locking Microstructure for Improving the Reliability of Advanced Quad Flat No-Lead Packages

Delamination frequently occurs at the interface of epoxy molding compound (EMC) and leadframe (LF) in advanced quad flat no-lead (aQFN) packages. It is caused by inadequate adhesion and can lead to a possible failure of the electronic device and, hence, decreased device or system reliability. We developed an anchor-locking microstructure approach, which is a simple, compatible, and low-cost procedure for the current package industry to enhance the bonding strength of the LF and EMC for raising reliability of the aQFN packages. The anchor-locking feature was inspired by Bidens pilosa, where the bur hooks itself to fabrics and animal furs thereby spreading the seeds; there is some difficulty in releasing the burs once it hooks on the fabric or fur. To fabricate the anchor-locking microstructures, several microfabrication processes, such as photolithography, etching, and electroplating, were employed to produce the lead and anchor-hook microstructure in the LF. Furthermore, fabricated microstructures were individually mounted using solder balls and EMC pillars to form the pull-test samples. The pulling tests were used to characterize all samples, and the failure loads of the lead and anchor-locking microstructure samples were 14.3 and 26.2 N, respectively. The anchor-locking microstructure samples showed almost two times of the adhesion strength. The finite-element method was utilized to study the theoretical failure loads of the lead and anchor-locking microstructure samples, which were 14.1 and 26.1 N, respectively. Therefore, the developed nature-inspired locking lead approach has a high potential for applications in the microelectronics industry.