Process and Accelerated Aging Test of GANG Bonding for Gold‐PlatedTAB Outer Leads

Abstract

This paper presents the evaluation results of thermocompression GANG Bonding of gold‐plated TAB outer leads to three kinds of metallized ceramic substrates. Gold‐Selective Plating (GSP) substrates for multi‐chip package, Thick Film (TF) substrates for multi‐chip package and Single Chip Packages (SCP) which have a trimetal combination of refractory metal (tungsten), Nickel and Gold.The bonding parameters such as the bonding tool (thermode) temperature, pressure, bonding time and preheat temperature were examined on each substrate to get optimum values. As the result, a relation between pull strength and the lead deformation shows that the TAB leads should be bonded with 15–65 percent deformation, the recommended parameters are; the tool temperature of 380–430℃, the bonding pressure ranging from 35 to 45 kg/mm2, with the preheat temperature of 150℃ and the bonding time from 1.0 to 2.5 seconds.The evaluation of initial bondability shows that TAB GANG Bonding has the capability of excellent bonding strength; above 120 grams with standard deviation of less than 20 grams, and the necessity of OLB pads flatness; less than ±12 μm for one ounce copper lead. The normal storage of the substrate and the lead does not affect the bondability. And the results of accelerated aging test of 125℃, 150℃ and 175℃ for more than 8,000 hours show that a lifetime of greater than 70 years at 65℃ operating temperature is predicted. The effective activation energy for the pull strength degradation is 0.86–1.05 eV. This is in reasonable agreement with predictions for interdiffusion of Cu–Au. And no significant degradation of the electric resistance was observed on the GSP samples.The feasibility and the high reliability of the GANG Bonding for gold‐plated TAB outer leads were confirmed.