Effect of material interactions during thermal shock testing on IC package reliability

This study attempts to elucidate the interaction of three main material components in a plastic package: mold compound, die attach, and die coating. The investigation was divided into three parts, addressing the combined effect of the previous three components, the influence of the thickness of the polyimide coating, and the effect of the mold compound alone, respectively. Five mold compounds (first generation low-stress, second generation low stress, third generation ultra low-stress, moisture resistant, and anti-crack compound for thin packages), two die attach resins (low-stress epoxy and ultra low-stress silicone-modified epoxy), and two die coats (standard polyimide and photo-sensitive polyimide) were tested. The authors discuss how combining different high- and low-stress materials affects the failure rate and the types of failures. Three main results were obtained: (1) die attach is the most important factor since its compliance during thermal shock affected the interfacial integrity of the die; (2) thicker coatings of polyimide (>8 μm) give better protection to the die surface; and (3) the anticrack molding formulation with the lowest CTE produces the fewest failures