Plasma technology optimization for a robust flip chip package

As we move forward to newer silicon technologies requiring finer FC interconnect pitch and packaging solutions with tighter process margins, it is becoming imperative to maximize the benefits of plasma by implementing it prior to UF process. Firstly, key plasma machine parameters were identified, namely plasma processing time, radio frequency (RF) power, gas flow rate and base pressure. Contact angle measurements, UF flow variations and substrate discolorations were used as the output parameters to identify the plasma process window. As part of this study, design of experiments was conducted to identify the critical plasma process parameters for different die sizes. Furthermore, the effect of plasma machine configuration (one with direct vertical plasma mode and the other with horizontal plasma movement for enhanced cavity penetration) was also investigated. The results show that plasma machine configuration play a critical role in uniform spatial contact angle in UF cavity. This paper documents all the evaluations, simulation studies and verification runs done to optimize the plasma process to establish a stable plasma and underfill process, delivering robust FC packages.