PCB007 Magazine

PCB007-Apr2021

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74 PCB007 MAGAZINE I APRIL 2021 Introduction One of the most difficult things about trou- bleshooting PCB defects is getting to and un- derstanding the root cause of defects. Many of these defects can have multiple origins. And many may not manifest themselves in the pro- cess where the defect actually occurred. us are the perils of jumping to conclusion about the defect. Not understanding the true genesis of the defect will lead to incorrect remedies to these issues. I will now present some of these defects and the possible remedies. Blisters (Hole Wall Pull-away) e common complaint one hears is that "the copper plating is peeling." Okay, but where? From the surface or from within the via? What about the interconnect? And is the peel- ing layer the electroless copper deposit or the electrolytic copper? ese are the questions one must answer to properly troubleshoot the defect. Figure 1 shows a real-life example of a blistered or peeling deposit. In Figure 1, the copper deposit has actually flaked off or blis- tered from the hole. In some cases, the depos- it did not completely flake off the surface, but indeed did pull away from the hole wall. is condition is referred to as hole wall pull-away (HWPA). Now the question is, where is the origin of the blister? e good news in this case is that we are only looking at the electroless copper. ere has yet to be an electrolytic copper de- posit applied to the circuit board. But that is all one can tell at this point. Figure 2 shows an actual cross-section of a circuit board that was part of the production lot related to the photo in Figure 1. Trouble in Your Tank by Michael Carano, RBP CHEMICAL TECHNOLOGY Plating Anomalies and Defects, Part 2 Figure 1: Arrow points to blisters in the via. Figure 2: Electrolytic copper applied to board. Arrow points to a blister (HWPA) that originated in the electroless copper.

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