Directly deposited fluxless lead-indium-gold composite solder

Lead-indium-gold multilayer composite solder has been developed for bonding electronic devices without the use of flux. The composite is deposited directly on GaAs wafers in high vacuum to inhibit indium oxidation. The gold layer on the composite further protects the indium layer from oxidation in atmosphere. Using the composite solder without flux, GaAs dies have been successfully bonded to alumina substrates at a process temperature of 250 degrees C. Nearly perfect joints are achieved as verified by a scanning acoustic microscope (SAM). Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy results indicate that the joint consists of AuIn/sub 2/ grains embedded in an In-Pb solid solution phase, as predicted from the Au-In-Pb phase diagram. Thermal shock as well as shear tests confirm that high quality bonding is obtained with the lead-indium-gold composite.<
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