New Method of Wire Sweep Detection in Plastic Moulded Semiconductor Component Using Time Domain Reflectometry (TDR)
Wire sweep is a critical defect found in backend process of semiconductor components. The most common methods of detecting wire sweep defect is by using electrical testing. However, electrical testing is known to have challenges in detecting wire sweep that are in near short conditions. In this paper, we are presenting the first ever investigation on using the Time Domain Reflectometry (TDR) to detect wire sweep defect in plastic molded semiconductor component. We focused our investigation on wire sweep defect that was directly in contact as well as wire sweep in proximity (near short) with adjacent lead post. During the measurement with TDR, all the samples were placed on a custom-made jig and measured using Single Pin Grounded method. The TDR results were then being compared with results from electrical testing to understand which methods was better in detecting wire sweep defect. In order to validate the physical wire sweep defect, the samples were laser decapsulated and checked under Scanning Electron Microscope (SEM). The actual gap between the wire sweep was measured. We discovered there was a strong correlation between the gap of wire sweep to the dip in TDR response. The smaller the gap between wire sweep was causing more dip in the TDR response that indicating lower impedance was detected. From our investigation, we demonstrated that TDR is capable of detecting wire sweep defects that are in contact as well as in near short conditions. In fact, the TDR method is better in detecting wire sweep that is near short conditions (with gap up to 12 µm) and thus overcome the limitation of conventional electrical testing.
Keywords- wire sweep; TDR; near short; semiconductor component