Low temperature gold wire bonding

We demonstrated that the bonding of gold wires for COB application was feasible at temperatures ~100°C or below by using a wedge bonder with a high frequency ultrasonic transducer (~138 kHz). An automatic rotary bondhead wedge bonder equipped with the transducer was employed to perform wire bonding. Bonding of gold wires was conducted on the aluminum pads of a test die and a gold-plated FR-4 PCB. The deformation of the bonded wire on die pad was as small as 1.2 times the diameter of the bonding wire. This provided greater room for bond placement on the pad, and hence a larger window for very fine pitch applications. The defect on the bond-heel was found to be less severe due to smaller bond deformation and the softness of gold. In some niche applications where gold wire and very low loop profile were required for the interconnections, wedge bonding of gold wire may be an option. In this article, the characteristics of the high frequency ultrasonic transducer, the specifications of the gold wire, wedge tool and gold-plated PCB as well as the bonding parameters for the wedge bonder are discussed in detail