Sulfur Ingression on Encapsulated Leadframe of Discrete Semiconductor Package

Methanesulfonic acid (MSA) has been widely used in the electroplating step at a backend semiconductor assembly process. This process comes after component encapsulation, which serves primarily to protect internal components of a device as well as to prevent ingression of chemical byproducts. The objective of this article is to study sulfur (S) ingression activities with respect to both electroplating and encapsulation processes and their effect on leadframe surface conditions. This can be achieved through observation of leadframe surface condition on samples prepared through laser ablation or mechanical decapsulation. Results from 17 engineering lots show that 25% of samples analyzed were observed with leadframe surface irregularities. The energy-dispersive X-ray spectroscopy (EDX) analysis confirmed the trace of S element on the area with surface irregularities, which can be linked to S ingression based on the trace of its path from outside, probably due to the existence of a microgap on the package. These findings provide a clearer understanding of the ingression path of S for encapsulated copper (Cu) leadframe. Even though ingression of S does not directly cause a failure, it is thought that this could act as a precursor to further failure mechanisms such as corrosion-like phenomena.