Effect of the Formation of the Intermetallic Compounds between a Tin Bump and an Electroplated Copper Thin Film on both the Mechanical and Electrical Properties of the Jointed Structures

The mechanical and electrical reliabilities of fine bumps with diameters and heights on the order of scores of microns were studied, considering the growth of the intermetallic compound (IMC) at the interface between a tin bump and a copper thin-film interconnection. It was found that an increase in the thickness of the IMC changed the stress and strain fields around the interface significantly, and thus, changed the fracture mode from a fatigue crack of the solder to a fatigue crack of the copper interconnection or to delamination between the IMC and the copper interconnection. This is because the mechanical properties of the grown IMC differ from those of copper and tin and that a large number of Kirkendall voids appeared around the interface. In addition, the resistance of the bumps increased dramatically with the increment of the IMC layer because of the growth of the Kirkendall voids. Therefore, it is very important to minimize the growth of the IMC in order to assure the reliability of the bump joint structures.