Investigation on the effect of molding compounds on package delamination

Although adhesion strength between molding compound and other substrates (leadframe, die pad, die, and passivation coat etc.) is an important parameter to evaluate the susceptibility of an IC package to delamination, there have been few systematic studies on this subject. This paper presents such a study, particularly the effect of the components (base resin, accelerator, and other additives) in the molding compound on adhesion strength and delamination at the interlayers in an IC package during IR reflow soldering. C-Mode Scanning Acoustic Microscopy (C-SAM), Al peel test and TBA (Torsion Braid Analysis) were used to characterize the adhesion sensitivity of the molding compound. Not surprisingly, epoxy with low molecular weight and hardener with flexible structure have a better adhesion strength than standard epoxy/hardener resin. We have also investigated the relationship between adhesion characteristics and viscoelastic properties of the molding compound. It was seen that elastic shear modulus (G') has a good correlation with the Al adhesion strength. It was also found that the other components such as catalyst, coupling agent, and flexibilizer have a great effect on the adhesion strength of the molding compound to leadframe/die pad and passivation PI coat. The extent of their effects depends on the amount and kind of components used.