Laser Pre-cut and Its Effect on the Leadframe Warpage

Abstract

ATSLP, a package in QFN type family, was introduced by Infineon using Molded Interconnect Substrate (MIS) leadframe. The MIS leadframe contain materials such as, copper, pre-mold, solder mask, and etc. With combination of MIS leadframe and high temperature flip chip die bond cause high CTE mismatch, thus, effect in higher warpage. The higher warpage affects the processability along the assembly processes which has direct relation with productivity performance and quality concerns. Stress relieve concept is introduced to improve productivity and quality, whereby warpage was reduced by separating the pre-mold and copper materials. By doing this, shrinkage of the materials was separated from each other along the change of assembly process temperature. Laser is selected as the source to perform cutting of pre-mold array. Polyimide tape is attached to the leadframe to hold the separated pre-mold array. Laser with non-contact cutting method, low thermal influence as well as having clean cut edges without burr or dust formation is ideal solution for this separation method. Through the laser precut on array method, productivity, material consumption, and output quality were improved as the warpage is significantly reduced. This paper further describe the selection of laser type, reaction of laser to polyimide tape, cutting process methods, and as well as the challenges faced along the assembly process.