Wafer bumping technology for LDI application by electroless nickel plating

Electroless nickel layer has been used to provide an under bump metallization on the aluminum bond pads, as part of low cost wafer bumping process, prior to solder deposition. Recently, it has also found increasing use in wafer bumping for LDI(LCD for Drive IC) type device. However, the application of electroless nickel to the LDI wafer bumping is limited by the fact that bath stability of nickel is closely related with passivation opening size. In the present work, the effects of nickel bath parameters of stabilizer concentration, temperature and pH on the formation of electroless nickel bump have been investigated and optimum process conditions for LDI bumping were suggested. The measurements of bump surface and height distribution have been performed for the bump quality estimation by optical microscope and thickness profiler.