Ni Electroless Plating Process for Solder Bump Chip on Glass Technology

In the solder bump chip on glass process, for the connection of the driver chip to Al pad on the glass substrate, the process of the electroless plating was developed to coat Ni on Al/photoresist system. It is necessary to pretreat Al surface to remove the oxide layer before the plating. In order to find the pretreatment process which does not damage photoresist or the substrate glass, the alkaline and fluoridic zincate processes have been investigated. Because the photoresist and Al thin film could be easily dissolved in the alkaline solution, it was considered that the fluoridic zincate process was a suitable one. After immersion in the zincate solution containing 1.5 g/ l NH₄HF₂ and 100 g/ l ZnSO₄, electroless Ni plating was performed well. The additives in the zincate solution and thiourea in the plating solution enhanced the flatness of deposited surface. Acid dip improved the uniformity of the surface.