Organic contamination in IC package assembly and it's impact on interfacial integrity

To build reliable plastic packages, it's essential to achieve excellent adhesion at all internal interfaces. One common inhibitor to good interfacial adhesion in plastic packages is surface contamination, most commonly organic in nature, accumulated prior to molding and causing poor adhesion with the mold compound. The most vulnerable and important surface is the chip's topside passivation where organic contaminants are often responsible for delamination observed after molding or after stressing. Organic contamination also causes degradation of wire bond quality and in some instances pad corrosion failures. To successfully study adhesion or interfacial problems, it's important to ensure the adherend's (i.e., substrate) surface cleanliness prior to depositing the adhesive (mold compound). This paper discusses a low-cost, fast, and quantitative method for characterizing surface cleanliness by combining UV/ozone cleaning with contact angle measurements. The level of organic contamination on silicon from various assembly processes was quantified using this methodology. To demonstrate the impact of organic contamination, delamination performance of the silicon-mold compound interface is determined as a function of cleanliness (contact angle) on the silicon surface. The critical contact angle to achieve Level 1 crackfree performance in 148 PQFP with the window flag leadframe is determined.