Electroplated Gold Microstuds for Thermocompression Bonding of UV LED Chips

A bonding technology using electroplated Au microstuds for ultraviolet (UV) light-emitting diodes (LEDs) has been investigated. Au studs with diameter, height, and pitch of about 15, 8, and 30 μm, respectively, were electroplated on standard UV LED chips on wafer level. The parameters for the thermocompression bonding (temperature, force, and time) were varied, and a critical temperature for bonding was identified. The electroplating process, in particular the plating base, strongly influences the adhesion of the Au microstuds and, therefore, the strength of the bond. Electro-optical measurements of bonded UVB LEDs as well as thermal resistance measurements and simulations of the devices show that Au-Au thermocompression bonding, using Au microstuds, can result in devices whose performance is similar to those fabricated using the conventional bonding technology of soldering with Au-Sn paste. Hence, the use of Au microstuds is an interesting alternative for bonding UV LED chips due to the ease of implementation, the stability of the bond, the comparable thermal resistance to Au-Sn, as well as the possibility to realize more complex and smaller chip geometries.