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NOVEMBER 2020 I PCB007 MAGAZINE 111 Your Tank: A Process Engineer's Guide to Fi- nal Etching," the main focus for this column is not on chemical process issues. As written previously, there are several other causes of unetched copper that can find their genesis in the imaging/developing process steps of PWB fabrication. The re- maining copper is usually random and man- ifests itself as copper spots or even some- what larger (Figure 2). In this case, one must review several areas prior to final etching. This includes the fol- lowing: • Developer control in terms of pH and resist loading • Moisture or oxidation on the panel prior to resist lamination • Breakpoint in the developer needs to be adjusted • Overexposure, leading to partial polymerization of the resist where none was desired • Excessive hold times between resist lamination and exposure and between lamination and development Again, as the engineer responsible for this process, do not underestimate the influence of up and downstream processes. The defect or defects that are visible after a particular pro- cess step may have their origins several pro- cess steps earlier. PCB007 Michael Carano is VP of technology and business development for RBP Chemical Technology. To read past columns or contact Carano, click here. blocked nozzles or issues with filters plugging. Another interesting issue that is equipment- and process-related (not the etching chemis- try, however) is non-uniform etching. Basi- cally, some areas of the panels are complete- ly etched, while others show copper. Here, this is a good exercise in reviewing other processes involved in fabrication. An example of the un- etched copper is shown in Figure 1. Essential- ly, copper is visible in some areas of the pan- els after etching. There are several possibilities that explain why copper could remain on the panels af- ter etching. And while etching chemistry op- tions will be explored in Part 2 of "Trouble in Figure 1: Unetched copper caused by improper handling. Figure 2: Unetched copper. (Source: Michael Carano)