Delamination study on SOIC L/F with high thermal conductivity die attach paste

In this paper, a high thermal die attach paste with 90% Ag filler content was evaluated on copper SOIC L/F, but a flag delamination around die was found after MSL3@260C; in contrary, control paste (non-high thermal) didn´t show any delamination around die. By comparing high thermal paste and control paste, it was found that there was obvious solvent bleed out after die attach with high thermal paste, but no such solvent bleed out for normal paste. TGA result showed there was a 10-13% weight loss for higher thermal paste, but only 2-3% weight loss for control. The large weight loss for high thermal paste was due to the non-reactive solvent evaporation in its formulation system. Besides, the solvent bleed out area was discolored during wire bonding process. Auger was also showed a much thicker Cu2O oxidation (>300A) on discolored area, but only about 30A with control. TOF-SIMS analysis on solvent bleed-out area after wire bonding showed a higher CxHy organic contamination than paste without solvent bleed-out. It was assumed that organic contamination and copper oxidation in solvent bleed area caused the flag delamination between leadframe flag and molding compound.