This PLCC (Plastic Leaded Chip Carrier) was imaged through the top side at 15 MHz in the reflection mode. Gating includes the lead frame, paddle and die surface.
The unusually symmetrical pattern of the delaminations (red) of the molding compound from the leads is probably caused by incompatible tinning of the leads. Tinning is sometimes done with a noble metal such as gold to improve the adhesion of bond wires. The problem is that some molding compounds do not adhere well to the noble metals. Since each lead is tinned for the same portion of its length, the result of non-adhesion is the interesting pattern of delaminations seen here. |
