TAB inner-lead bond process characterization for single-point laser bonding

Results are presented for a set of screening experiments used to characterize a process for performing inner-lead bonding (ILB) using a continuous-wave (CW) laser. Three key parameters were selected for initial analysis: the force exerted by the bonding stylus; the laser power; and the on-time of the laser. Using a Box-Behnken statistical design for the experiment, an efficient set of tests was derived. Four sets of experimental samples were fabricated, to be used for the as-fabricated testing, high-temperature aging, and thermal cycling. Only the as-fabricated results are reported here. Using a design-of-experiments software package for the PC, a quadratic equation was derived from the data explicitly defining the relationships among the three parameters and relating them to bond strength. Using the techniques of surface response methodology, a response surface was created, showing the optimum operating region for the ILB process based on the parameter range chosen. The initial screening experiments show that good bond strength occurs in a range of constant energy (power times on-time) for the CW laser bonder; in the range of the three parameters tested, bond strength was optimized at forces of 20 grams, a power of 4.3 W, and laser on-time of 150 ms