ADHESION IMPROVEMENT OF EPOXY-RESIN COPPER LEAD FRAME JOINTS BY AZOLECOMPOUNDS

The adhesion strength of epoxy resin/copper joints is often very poor, due to the naturally formed copper oxide having a low mechanical stre ngth. To improve the adhesion strength of epoxy resin/copper lead fram e joints, copper lead frames were created with azole compounds as adhe sion promoters. The azole compounds used were benzotriazole (BTA), ben zotriazole-5-carboxylic acid (CBTA), 8-azaadenine, imidazole, 2-methyl imidazole, urocanic acid, adenine, benzimidazole, and polybenzimidazo le (PBI). The dependence of the adhesion strength of epoxy resin/azole -treated copper joints on the structure of the azole compound. the azo le treatment time, and the azole treatment temperature was investigate d. The surface coverage of azole-treated copper was examined by contac t angle measurements, a surface defect test, optical microscopy, and s canning electron microscopy (SEM), and the locus of failure was studie d by X-ray photoelectron spectroscopy (XPS). Triazole compounds such a s CBTA and 8-azaadenine showed excellent adhesion strength; imidazole- based azole compounds did not improve the adhesion strength. However, the adhesion strength of CBTA- and 8-azaadenine-treated joints decreas ed with increasing treatment time, since thick porous Cu-azole complex es had a weaker mechanical strength when formed. The polymeric azole c ompound PBI showed the highest adhesion strength, 785 N/m, because of complete coverage of the copper surface. The thermal stability of azol e compounds and epoxy resin/azole-treated copper joints was also inves tigated. CBTA and 8-azaadenine did not decompose up to 250 degrees C, while PBI was stable up to 500 degrees C in an air atmosphere.