Organic-based substrates, like those used in BGA packages and metal leadframes are susceptible to delamination. Delamination is caused by poor adhesion of the encapsulant compound to the multiple interfaces on the substrate package including solder mask, the die top passivation, and the substrate metallization. Peel tests and C-mode scanning acoustic microscopy (C-SAM) have proven that delamination issues are significantly reduced when packages are plasma treated prior to molding. Plasma processing greatly improves adhesion of mold compounds by increasing the substrate surface energy and results in increased package reliability.
The figure below displays the effect of plasma on adhesion of mold compound to differing solder mask formulations. In general, with increasing plasma exposure the adhesion level increases.
The figures below display the adhesion enhancement with plasma. Note that the failure mode for the plasma treated sample results in cohesive failure of the substrate as opposed to adhesive failure in the non-treated substrate.
Without plasma treatment:
With plasma treatment:
Plasma treatment is also used for other microelectronic applications including wafer cleaning prior to wafer dice, surface activation prior to package marking, improvement in solder wetting, and to enhance the conformal coating process. In conformal coating applications the encapsulating resin may not completely wet the substrate surface resulting in coating voids and delamination. Plasma ensures that the fluid completely wets the numerous materials on the PCB and enhances the coating adhesion.
Die Attach |
Wire Bonding | Underfill | Encapsulation & Mold