Plasma cleaning for plastic ball grid array (PBGA): a study on surface cleanliness, wire bondability and adhesion

An investigation of O/sub 2/, Ar and Ar/H/sub 2/ plasma cleaning was carried out on PBGA substrates to study its effects on surface cleanliness, wire bondability and moulding compound/solder mask adhesion. Optimisation of the plasma parameters was achieved using the contact angle method and verified by AES, XPS and wedge pull test. Generally, it was noted that the wedge bond quality and moisture sensitivity of a 225 I/O PBGA were improved after plasma cleaning. Furthermore, AFM characterization revealed that the solder mask has undergone plasma induced surface modification. Cross-contamination of Au and F traces on the solder mask which has occurred during plasma cleaning was analysed by XPS. Results from this study have demonstrated the benefits and consequences of plasma cleaning for PBGA.