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38 The PCB Magazine • September 2017 both devastating financially as well as compro- mising confidence of the customer. Let's look at some real-world examples where several differ- ent root cause issues lead to the "observed de- fect" or non-conformance. Etching Most process problems that appear dur- ing the etching stage of printed circuit produc- tion can be traced to one of two general areas. The most obvious causes (though not nec- essarily the most common) of etching prob- lems occur in the etching equipment itself, ei- ther through equipment failure or mis-adjust- ment or chemistry outside normal operating parameters. As is often the case in printed cir- cuit processing, anomalies detected during or a fter the etching step may trace back to techni- cal issues induced during prior processing steps but not detected until the boards are processed through the etcher. An example would be resist scum left on the board during the stripping of a plating resist, which can cause uneven etch - ing to occur, although blocked nozzles, "track- ing" from rollers, uneven distribution (top to bottom, or across the machine) of spray pres- sure can all mimic the effects of incomplete re- sist removal under some circumstances. Figure 1 shows what appears as unetched copper. The excess remaining copper will lead to either a short or at the very least violate the spacing requirements. The possible causes for this defect as well as likely solutions are listed in the Table 1. Figure 2 depicts a circuit trace that has been etched out and is very close to having an open created. It would be easiest to point the finger at the etching operation. However, the skilled troubleshooter will not fall into that trap. The engineer should note that the defect is not widespread. The issue is isolated to a few spots. While it would be easiest to blame the etching operation, experienced process engi- neers would look elsewhere first. A few of the most likely causes and solutions are shown in Table 2. While there are many more possible de- fects related or at least attributable to etching, this column is not meant to address them all. In addition, one needs to review defects that manifest themselves in the plated through- hole (i.e., electroplating). Electroplating Electroplating in the manufacture of print- ed wiring is used to deposit a metallic pattern, PROCESS ENGINEERING & DEFECT PREVENTION Figure 1: Excess or unetched copper. (Source: IPC photo archive, Bannockburn, Illinois) Table 1: Possible causes and solutions for unetched or excess copper. (Excerpted from IPC-9121 "Troubleshooting for Board Fabrication Processes," Section 10.1 Etching)