Realizing low cost and high reliability in CSP packages with surface treatment and material technology - plasma treatment technology

CSP packages are key devices that are expanding recently in the semiconductor industry. In many cases, CSP packages production has been done because of its low cost and proven results. In this case, the wire bonding electrode and solder ball attach electrode are made by the same plating process. As wire bonding electrodes become thinner, there is degradation bonding quality because the Ni compounds migrate toward Au plating surface when subjected to the heat processes. Therefore, to insure good wire bonding quality, we usually have to use thick Au plating. The larger Au weight % resulted in poor shear strength of solder ball attach. Moreover if you use electroless Au plating to get high density wiring, you have to use nickel-phosphorus rich layer at the barrier layer underneath the Au plating. In this case, phosphorus rich layer at the interface of solder bond could be detrimental to solder ball attach reliability. This has been a big problem that should be solved according by reducing the solder ball diameter. Thus there is a discrepancy in optimized Au plating thickness between the wire bonding and the solder ball attach electrode. In order to overcome this contradiction, we have developed a plasma cleaning process that can realize excellent wire bonding quality even with thin Au plating.