Adhesion evaluation of adhesiveless metal/polyimide substrate for MCM and high density packaging
Directly metallized polyimide films are being widely used as advanced high-density packaging substrates. Adhesion of metal to polyimide is a key performance requirement of the film. Excellent initial adhesion and good retention after severe process steps and reliability stresses are required. In this paper, the adhesion performances of films with different types of polyimide and tie layer from multiple vendors have been evaluated. The interface failure mechanisms are also examined via SEM micrographs and XPS survey scans. Peel strength and its retention behaviour are characterized in term of tie layer materials, environmental stresses and surface analysis results. The object of this work is to select the proper base material for high-density flexible multilayer substrates, a technology which is under development by FCPT.
Changes in the adhesion strength between copper thin films and polyimide substrates after heat treatment
The adhesion strength between a copper (Cu) thin film and a polyimide [pyromellitic dianhydride-oxydianiline (PMDA-ODA)] substrate is reduced by heat treatment at 150°C in air. In this work, we determined the changes in adhesion strength between Cu films and polyimide substrates using Auger electron spectroscopy (AES), attenuated total reflection Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The analysis showed that the weak boundary layer (WBL) shifted towards the Cu interface as the heat treatment time was increased. To confirm this shift, we looked at two other polyimide substrates: biphenyl dianhydride-p-phenylene diamine (BPDA-PDA) and biphenyl dianhydride-oxydianiline (BPDA-ODA). Comparing the adhesion strength for the Cu thin film, the adhesion strength was high for the Cu/PMDA-ODA and Cu/BPDA-ODA laminates, but very low for the Cu/BPDA-PDA laminate. One of the possible reasons for this behavior could be that the ether moiety between the two benzene rin...
An XPS study of the in-situ formation of the polyimide/copper interface
Abstract X-ray photoelectron spectroscopy has been used to follow the chemistry occuring at the surface of PMDA-ODA polyimide during thermal deposition and ion-sputtering of Cu. At low coverages, Cu has been found to selectively react with the carbonyl groups of the PMDA unit to form Cu+-O--C linkages. The Cu+ valence state manifests itself in the CuLMM spectra as a distinct feature shifted by ∼2 eV from the main peak to lower kinetic energy. Compared to thermal deposition, ion-sputtering of Cu results in more severe chemical changes at the polyimide surface, indicating a partial destruction of the polymer surface layers.