Understanding Non-Stick on Lead Wirebond Failure Due to Leadfinger Surface Roughness

Non-stick on lead (NSOL) failure in the wedge bonding process of wirebonded semiconductor and electronic devices is a key issue for wedge bondability. The defect has been correlated with different factors but little has been established on the quantitative correlation with surface roughness (SR). Herein, the direct empirical correlation between SR of substrate leadfinger and the occurrence of NSOL in two (2) ball grid array (BGA) packages namely, P1 and P2 is reported and discussed. SR response was quantified by R_a (arithmetical mean SR) and R_z (10-point mean roughness) integrated over the whole surface (JIS B0601:1994 standard) using an atomic force microscope (AFM). Direct correlation has been established where high occurrence of NSOL was observed on substrates with high SR. This general correlation was found to be true for the two (2) packages evaluated in this study. R_a values of 0.192 ± 0.028 μm and R_z of 1.49 ± 0.18 μm were found to produce lower NSOL rate compared with R_a value of 0.239 ± 0.023 μm and R_z of 2.75 ± 0.52 μm for P1. Likewise, R_a of 0.272 ± 0.037 μm and R_z of 3.00 ± 0.57 μm were found to have higher occurrence of NSOL compared with R_a of 0.239 ± 0.037 μm and R_z of 2.34 ± 0.32 μm for P2.