Bumping Technology For MEMS Flip Chip Packaging

Characteristics and development situation of Flip Chip technology and MEMS(MicroElectro Mechanical System) were briefly introduced and a bumping method, sputteringUBM(Under Bump Metallurgy) and electroplating solder bump, was chosen to implementbump system. The optimal process parameters by which UBM and Solder was formedwere concluded in experience. After bumps were formed the bumping system'sperformance was analyzed. Preparation process of UBM system achieved by magnetron sputtering was presented.After the function and structure of UBM was explained and a typical and simply UBMstructure was chosen for bumping system. The principle of magnetron sputtering andequipment characteristics were briefly introduced. The sputtering power, air pressure anddeposition rate were determinated in this thesis. As a result, the deposition rate of metalfilms, Ti and Cu, were found increasing firstly and then decreasing with the air pressureincreasing. There was an optimal value of air pressure under which the maximumdeposition rate was obtained. The process of preparing solder bump by electroplating was introduced. The factorsthat influenced the electroplating quality were discussed, such as surface brightness,throwing ability, covering ability and deposition rate. It was found that Dk was in relationwith minimum stirring speed. Then, throwing ability and deposition rate was suitable forelectroplating at different Dk and deposition time. Furthermore, when the concentration ofmethylsulfonic acid and Dk were not varied, increasing the stirring speed would improvethe bump quality. Oxide was the main obstacle of solder forming bright surface and regular shape inreflow process. Under the flux protected, oxygen could not approach the solder surfaceand the metal oxide would be removed, so the solders can form perfect outline. The sheartest of bump showed that the shear strength of bump degraded significantly with theformation of micro-voids in bump.