A fluxless oxidation-free bonding technology

A fluxless oxidation-free bonding technology is reported. The technology uses the direct deposition of multilayer composite in high vacuum to prevent oxidation. The outer layer of the composite is either gold or copper which protects the inner layers from oxidation when the composite is later exposed to atmosphere. As a result of oxidation prevention neither flux nor scrubbing action is required in the bonding process. Two processes based on Pb-Sn-Au and Sn-Cu have been developed for a processing temperature of 250°C to prove the working concept. GaAs dies have been well bonded on glass and alumina substrates as shown by scanning acoustic microscope. SEM and EDX studies verify the bonding principle, reveal the bonding mechanism and identify the intermetallic compounds in the joints. Apart from fluxless feature, other advantages include good control of joint thickness, good control of composition, and direct deposition of bonding media on wafers or substrates