PCB007 Magazine

PCB-Apr2016

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16 The PCB Magazine • April 2016 by Michael Carano RBP CHEmICAl TECHnoloGy The printed wiring board fabrication process is an intricate maze of interrelated steps, both chemical and mechanical. A thorough under- standing of each of the process steps is critical in minimizing or eliminating non-conforming defects—the ones that cost the fabricator mon- ey and can lead to lost customers. It is also criti- cal to note that these profit-killing defects may have their origins elsewhere in the process. That is the difficult thing about trouble- shooting—the defect is often blamed on the process (such as electrodeposition of copper) because that is where the problem is first dis- covered. However, this is often false, as the ori- gin of the defect may have had its humble be- ginnings in a previous process step. To be successful at troubleshooting a prob- lem, common sense usually applies. Basically one must first: • Identify the problem or problems (be as specific as possible) • Determine possible causes (looks for links to those other less obvious processes) A Process Engineer's Guide to Effectively Troubleshooting PWB Defects • Identify methods and procedures to test to see which causes apply • Test the assumptions • Implement corrective action While this sounds like an oversimplifica- tion, this approach is required to properly iden- tify and attack the problem at hand. A struc- tured routine is really what is required. In upcoming columns we will attempt to provide some insight as to the cause or causes of non-conforming defects and the potential so- lutions. We will discuss process parameters and the importance of control of the processes. Let's discuss the step-by-step methodology for troubleshooting. Identify the Problem or Problems First and foremost, you must have a clear sense of what you are looking at. In trouble- shooting, I firmly believe in the team approach to solving the problem. However, the team must agree on what the defect is: is it hole wall pull-away (HWPA) or resin recession; is this an interconnect defect (ICD) or simply a line of de- marcation? These are just a few examples. But the wrong call will lead you down the incorrect feature

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