Elimination mold flash by mold design enhancement and leadframe process control on flat power package

Abstract

This paper will explained detail of challenge to eliminate mold flash in mold assist film technology on flat power package. Film assist molding uses a film is coated with an adhesive layer on one side which works as a soft cushion to cover of the heat sink / paddle. This thin film also holds the lead frame paddle for prevention the paddle to tilt. Tilting of the paddle causes the mold to flow towards the paddle area during molding process and causes a reject known as “Pad Bleed”. The flash layer on the heatsink is unable to be removed by typical deflash setting, thus it prevents tin plating coverage during plating process. As a result, the solder-able pad is unable to be mounted at end customers' application circuit. The hypothesis of mold flash occurrence is due to paddle deformation caused by over-clamping during mold process. This paper will emphasis on effectiveness of combining mold design enhancement and lead frame incoming quality control to eliminate mold flash on exposed heatsink flatpower product using film assisted molding system. Distribution clamp force evenly in mold tool is major area to investigate for mold tool design enhancement. Furthermore, process control on supplier to minimize paddle tilting is another main contributor factor need to evaluate in order to maintain incoming quality. By identifying and establishing a control on a critical lead frame dimension and redesigning the mold tool, mold flash or resin bleed was able to be eliminated. The verification run showed paddle tilting is the most critical factor that needs to be controlled in order to minimize resin bleed issue, these thin resin bleed or flashes are able to be removed by the subsequent “Deflashing” process.