Suitable Cu Leadframe Material and Design to Achieve High Reliability Requirement and Good Manufacturability

In terms of automotive application, AEC-Q100 Grade0 (AECG0) is an important reliability requirement for wire bonding package. Delamination at stitch bond region is one of key roadblocks to achieve this high reliability requirement. Hence leadframe and EMC (epoxy mold compound) selection is very important and one objective is to enhance the adhesion between EMC and Cu leadframe materials to form a stronger bond that is capable of withstanding the vapour pressures induced during reflow and following temperature cycling
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. Roughened leadframe surface of Ag plated Cu leadframe can improve interlocking with EMC which can help eliminate delamination after stress test. However, this kind of adhesion may also increase and cause bigger warpage / deformation after de-gating process, the warpage may lead to machine stoppages. How to improve packaging manufacturability is very important when using roughened lead frame.This paper investigated the impact of different leadframe material and design combination on LQFP (Low-profile Quad Flat Packages) delamination and manufacturability. Roughened Ag plated Cu leadframe was used to study delamination situation after moisture sensitivity level 3(MSL3) and AATC (air to air temperature cycling) CSAM (C-mode Scanning Acoustic Microscopy), SEM (Scanning Electron Microscope) and wire peel test was used to assess delamination and stitch bond integrity. The result showed roughened leadframe can enable the LQFP package to achieve AECG0 requirement and no delamination after 1x/1.5x/2x AATC reading (-55 to 150C, 2000cycles, 3000cycles and 4000cycles respectively), moreover stitch bond integrity is very good as well thru SEM checking after decapping. As mentioned, in terms of leadframe warpage / deformation two approaches were considered and tested for improvement: 1) Cu Leadframe Materials A and B with different hardness were evaluated; 2) modified leadframe strip design with different slot type at runner area. The experiment results show harder Cu leadframe Material B has a good ability to resist warpage, warpage can improve 44%, while leadframe with bigger slot design at mold runner position can improve warpage 25%. Based on the evaluation result suitable roughened leadframe Material B with modified slot at runner region can achieve both high reliability and good manufacturability for LQFP product.