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40 The PCB Magazine • September 2017 of plating chemistry, temperatures, etc.) and others can be changed only slightly, or with difficulty such as varying the geometry of an- ode/cathode placement. This adjustment is limited by the geometry of the plating line and individual tanks as installed. One of the very troublesome defects is cor- ner cracking in the electroplated copper with- in the PTH (Figure 3). The potential root causes and solutions are listed in Table 3. This real-life example underscores the need to have a deep understanding of how variations in one or more processes may cause the defect several steps removed. One can surmise that the processes or processes need improved controls as well as more sophisticated analytical meth- ods. In addition, regular tensile and elongation measurements will serve as a leading indicator for possible copper cracking. Finally, in Figure 4, the classic innerplane separation is observed. At first glance, it may be easy to determine that the root cause of the separation is that the electroless copper deposit separated from the innerlayer post. That is cer- tainly a logical conclusion. And one is viewing the section after solder excursion and without etching the specimen (which is correct proce- dure up to this point). However, further study is required. Is that separation due to some resin smear remaining on the post? Thus, preventing the adhesion of the electroless copper to the post? And whether the separation is due to resin smear or simply the copper separating, it is nonethe- less a separation and a non-conforming defect. Regardless, the unetched specimen shows a sep- aration. However, where does one go from here to troubleshoot the problem? Clearly there is no evidence of any etchback so it is possible there is drill smear remaining. It is somewhat diffi- cult at this point to detect smear without SEM/ EDAX. The skilled troubleshooter will now ac- cept the challenge of reviewing whether this de- fect is more widespread or an isolated case. Ta- ble 4 lists several possible causes for the defect seen in Figure 4. PROCESS ENGINEERING & DEFECT PREVENTION Figure 4: Separation of plated copper from the innerlayer post. (Source: IPC photo archive, Bannockburn, Illinois) Table 4: Possible causes and solutions for innerplane separation (excerpted from IPC-9121 Section 7.2 Hole Preparation and Protection)