Development of Copper wire bonding on C65 Ni-P/Pd/Au bond pad Low-k wafer with BOA structure

Abstract

This paper presents the development of evaluating the Palladium-coated Copper (Pd-Cu) and Bare Cu wire bonding material, along with two different type of `Low-k' and conventional capillaries on two different Aluminium (Al) thickness underneath a C65 Nickel-Phosphorus/ Palladium/ Gold (Ni-P/Pd/Au) bond pad low-k dielectric material wafer with Bond Over Active (BOA) pad structure. A 7.9mm×8.5mm test chip on LQFP-176 Rough micro Pre-Plated Frame (RμPPF) lead-frame design was evaluated with the wire bond temperature of 240°C. The latest Shinkawa model UTC3000 wire bonder retrofitted with newest Cu kit design and multiple-step software feature was used to ensure good bondability and Free Air Ball (FAB) oxidation free. With the benefit of the latest Multi-step (M-step) software in gradually bond force steps, both of the wire materials, Pd-Cu and Bare Cu and the capillaries, `Low-k' and conventional demonstrated a promising evaluation outcome. All of the legs achieved good Gold-Copper (Au-Cu) solid solution coverage and met all the wire bonding process requirement for instance wire pull and shear strength. However, the Thin Al thickness surpassed Thick Al thickness in term of better pad bend ratio and lesser pad deformation. The verification on the final set of Bill of Material (BOM) was subjected for pad oxide crack analysis and managed to achieve zero oxide crack underneath bond pad with a sample size of 50k pads by de-layering process. In addition, sample was subjected for several essential reliability stress tests and the outcome was encouraging denoted a good bond integrity was achievable. The other traditional wire bonding process control were examined and managed to meet the requirements.