ELECTRICAL-PROPERTIES OF SOLDER FILLED ANISOTROPICALLY CONDUCTIVE ADHESIVES

Electrical properties of four anisotropically conductive adhesives wer e characterised. The effect of bonding temperature as well as 60 degre es C/95% RH-test on contact resistance values of the adhesive joints w as studied. The resistivities of the adhesive joints were measured as a function of temperature. In addition, the joint microstructures were examined with optical and the scanning electron microscopy and weltin g properties of the solder alloys were measured with the wetting balan ce method. Regardless of the adhesive, the average contact resistance values were on the same level but the standard deviation was considera bly higher with Au/Ni-coated conductors than with bare copper conducto rs. In the hot and humid environment test the best results were achiev ed with tin-bismuth and tin-bismuth-zinc-filled adhesives on bare copp er conductors. On the contrary, joints produced with Au/Ni-coated cond uctors failed in this test. It is likely that the poor performance of the Au/Ni-coated circuits results from the strong oxidation of nickel in the presence of moisture. The small exposed area and anodic electro chemical potential of nickel compared with the large area of noble gol d accelerates this reaction.