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 Ra (arithmetical mean SR) and Rz (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. Ra values of 0.192 ± 0.028 μm and Rz of 1.49 ± 0.18 μm were found to produce lower NSOL rate compared with Ra value of 0.239 ± 0.023 μm and Rz of 2.75 ± 0.52 μm for P1. Likewise, Ra of 0.272 ± 0.037 μm and Rz of 3.00 ± 0.57 μm were found to have higher occurrence of NSOL compared with Ra of 0.239 ± 0.037 μm and Rz of 2.34 ± 0.32 μm for P2