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PCB-Oct2016

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68 The PCB Magazine • October 2016 Introduction Sometimes the problems can really get pretty ugly. One would assume these uglies would be easy to correct. But most often, solv- ing such a problem requires a much deeper dig into the process. In this column this principle will be illustrated with a real-life case study. In this real-life troubleshooting exercise, plating anomalies were detected on the PWBs plated in two different plating cells. This study points out that the root of the defects is rooted in two different causes. One is related to addition agent control, the other to solution filtration and anode maintenance. The study digs into plating roughness and multiple causes and cor - rective actions. Severe Plating Roughness/Nodules In previous columns, this author has pre- sented many possibilities for copper plating nodules. However, what occurred with one PWB fabricator was on the extreme (Figure 1). In Figure 2, a somewhat different type of nodule appeared on circuits at the same fabrica- tor. Only this defect occurred on circuit boards plated in a different cell. Basically this fabricator was seeing two dif- ferent types of nodules/roughness. The nod- ules depicted in Figure 1 clearly show "normal" copper grain structure (fine-grained equiaxed). However, in Figure 2, the grain is quite large. In addition, the nodule/roughness shown in Figure 1 can be traced to what looks like debris that has been essentially plated up and around. So what does the troubleshooting exercise look like? Again, two different issues are evident. Yes, both are nodules/roughness related. However, the origins of the roughness/nodules appear to be different. Thus the troubleshooting ap- proach needs to take on a much wider view. Several steps are needed immediately. First ob- tain an analysis of all of the chemical processes by Michael Carano RBP CHEMICAL TECHNOLOGY Case Study: Plating Nodules— Where Did These Come From? TROUBLE IN YOUR TANK Figure 1: Severe plating nodules. (Source IPC-9121 Process Effects Handbook) Figure 2: Severe nodules—but copper is crystalline in nature. (Source IPC photo archive, Bannockburn, Illinois)

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