A study about solder bumping process by using the electro-plating method

Solder bump whose pitch is 150-300 /spl mu/m was fabricated on Si substrate by electroplating with the medium thickness (/spl sim/30 /spl mu/m) photoresist. TiW/Cu/Cu mini bump was used as a UBM (under bump metallurgy) layer. TiW (0.3 /spl mu/m)/Cu (0.7 /spl mu/m) was deposited by sputtering and Cu mini bump (5-15 /spl mu/m) was formed by electroplating. After UBM formation, subsequently, solder bump of mushroom shape was formed by electroplating. In electroplated solder bumping process, the control of the composition is one of the most important key technologies. However, during the formation of a solder mushroom, the composition of solder bump changes due to the variation of plating area. In order to obtain the uniform solder composition with the variance of plating area, applied current was controlled under the consideration of plating area. By controlling the applied current, the composition of solder bump can be controlled within 4%. Solder ball size after reflow could be controlled by calculating the amount of plated solder and measuring the mushroom diameter.