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|Lead Free Solder Plating Chemicals for Substrate Bumping|
|Keywords: Lead Free Plating Chemical, Solder Bumping, Substrate plating|
|Solder bumping is one of the key technologies for flip chip connection. Flip chip connection has been progressing towards further downsizing and higher integration with new technologies such as Cu pillar and micro bump in the wafer side. This technical trend is not only in the wafer side but also in the substrate (organic interposer) side. For substrate bumping, solder paste printing and μ-ball mounting technique have been used over the years. Since paste printing has a potential problem in the void and bump height uniformity, recently μ-ball mounting is getting more and more popular for substrate bumping. However, μ-ball mounting also has technical problems such as accuracy of flux, ball placement on pad by stencil mask, and missing ball failure. Moreover, the latest packaging design needs a wide variation of bumps such as different diameter, shape and pitch to enable 2.5D and 3D assembly, which is too challenging for the μ-ball mounting to meet. Due to these reasons, the electro plating method is expected to be the next promising technique for finer and wide variation of substrate bumping. For this upcoming future demand, we have developed a lead free solder plating chemicals for substrate bumping. One of the technical challenges in substrate plating is the filling ability, which is necessary for solder plating chemicals to flatten the dimple structure of the substrate caused by solder resist. Various influential factors on filling including process parameters and chemical formulation were studied. We would like to present our recent research and new substrate plating chemicals which has enough filling ability with good bump uniformity and minimal void.|
Mitsubishi Materials Corporation