Poly(imide-siloxane) passivation layer was investigated for tapeless lead-on-chip (LOC) packaging. Various molecular weights of siloxane diamine (SDA), alpha,omega-(aminophenoxypropyl)-poly(dimethylsiloxane) were synthesized and incorporated to synthesize poly(imide-siloxane). Effects of molecular weight and content of SDA on the adhesion strength of poly(imide-siloxane) with Alloy 42 lead frame and silicon dioxide were studied. Poly(imide-siloxane) having high molecular weight of SDA showed good adhesion strength with Alloy 42 lead frame. On the other hand, poly(imide-siloxane) having low molecular weight of SDA showed good adhesion strength with silicon dioxide. Therefore, blends of poly(imide-siloxane) having high and low molecular weight of SDA showed good adhesion strength with both Alloy 42 lead frame and silicon dioxide. The origin of different adhesion behavior of poly(imide-siloxane) depending upon the molecular weight of SDA with Alloy 42 lead frame and silicon dioxide was examined by contact angle measurement and X-ray photoelectron spectroscopy (XPS). (C) 2000 Published by Elsevier Science Ltd.