Abstract
Tape automated bonding (TAB) is an interconnection technique for integrated circuits (ICs) with a small lead pitch and a thin assembly thickness. During inner lead bonding the flying (Au plated Cu) leads of the TAB foil are connected to the Au bumps on the bondpads of an IC. The Au bumps are deposited in the openings of a thick Novolac based resist layer by electroplating. The resist is coated on a sputtered TiW‐Au metallisation; TiW is the barrier layer between Au bump and Al bondpad. Bonding of the leads to the Au bumps requires substantial plastic deformation of the bump and lead. As a result of this deformation, the TiW barrier layer underneath the bump may crack easily. A theoretical model has been used to describe the occurrence of these cracks. This theoretical model is compared with experimental results of deformation and cracking behaviour by visual inspection of the TiW barrier and the etched cross‐sections. Separate (single point) and simultaneous (gang) bonding techniques, different gold plating baths and TAB tapes are used to study the cracking behaviour.
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