Die bonding of silicon and other materials with active solder

The surfaces of optoelectronic materials such as silicon, GaAs, nitrides and oxides are known to be very difficult to bond with low melting point solders (<;300°C). Small portion of active elements (3.1~4.1wt% Ti and 0.2% Ce) added into conventional SnAg solder could improve its solderability with inorganic material surfaces. In this work, some bonding experiments using active solder containing active elements were carried out. Bonding and mechanical behaviors of active solder were compared with SnAg solder preform and PbSn solder paste. The bonded joints were studied using SEM and the distribution of elements using energy-dispersive x-ray (EDX) analysis. Tensile test results revealed that, silicon could be directly bonded with copper, Kovar and silicon without metallization and the bonding strength of silicon bonding was 3.67 MPa. The successful bonding was attributed to the migration of active element to the solder-silicon interface for chemical reaction and the creation of an interfacial layer that contained active element oxide. Such oxide-bondable solders could be useful for 3D packaging and optoelectronic integration.