Diffusion and oxidation of copper in polymer of Fan Out-Panel Level Package (FO-PLP) under High Temperature Storage (HTS) Conditions

Securing package reliability for the fan out-panel level packages (FO-PLPs) is a major challenge as they have organic substrate and multiple redistribution layers (RDL) of organic dielectric and copper (Cu) conducting paths. In particular, the interface between the organic dielectric layer and the Cu patterns has a large reliability concerns because the adhesion of the polymer and Cu is weak and both the polymer and Cu are vulnerable to oxidation at high temperatures in an atmospheric atmosphere. In the present study, we investigated the growth of copper oxide at the polymer/Cu interface of FOPLP under high temperature storage (HTS) conditions using two types of organic dielectrics. The microstructure and chemistry of copper oxidation were studied using a focused ion beam (FIB) and a transmission electron microscope (TEM). We found that copper oxidation and reduction occur at the interface and copper atoms diffuse into the polymer leaving voids at the interface. Our results also show that the growth of copper oxide depends on the chemistry of the polymer. We propose a cyclic redox reaction mechanism between the polymer and copper, in which the polymer is oxidized and decomposed by catalytic copper oxides ($Cu_{2}\mathrm{O}$, CuO) to generate acidic functional groups such as carboxylic acids, then the acidic groups in the polymer may dissolve copper from $Cu_{2}\mathrm{O}$.