The popcorn effect of lead and lead-free mixed assembly process in high density plastic packages

Abstract

The expansion of integrated circuit applications is driving chip costs down. To respond to the lower price the lower price expectations, manufacturers bring Plastic packages which is cost less expensive packaging solutions. Today although the electronic packaging industry there are still many enterprises were to have lead solder, but this does not preclude the “lead-free” has become the main topic of electronic materials and microelectronics. In this transitional period, lead and lead-free both assemble on the plastic package in the field of application is already unavoidable. Problem existed in lead or lead-free materials, technology, equipment, system compatibility and other issues. The reliability of the plastic package IC is becoming a key concern. The popcorn effect is caused when moisture inside a plastic package turns to steam and expands rapidly during infrared and vapor phase reflow solder process. Under certain conditions, the force from the expanding moisture can cause stresses inside the package. Solder ball inside with lead process and outside with lead-free may result in failure. It is prompted by the melting point of lead and lead-free material is different in the same BGA packaging chip. In most severe cases, the packaging defects and the stress may result in external package cracks. And in this paper, a sample is given that the BGA packaging chip exist void in the die/die attach interface. Capillary phenomenon is present in the package closest to the die attach, and lead to a short circuit between some pins. Pay more attention to the reliability of mixed assembly process is of great value.