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72 PCB007 MAGAZINE I JUNE 2020 completed. There are several possibilities re- lated to the root cause of this defect. Figure 2 shows a partial etch-out of the circuit trace. It is not likely the issue was caused by the etching process since the areas of partial etch- outs were sporadically seen on the panel. The most likely causes for the defect relates to sur- face preparation of the copper surface and the potential for resist lifting, allowing the etchant to gain access to the underlying copper. Es- sentially during the re- sist lamination process, resist did not complete- ly conform to the cop- per surface. Remaining moisture on the panel may have vaporized, allowing the resist to blister at that point. In addition, when you investigate the glass weave texture related to the copper foil you see that a heavy glass weave may have nega- tively impacted the ad- hesion of the photore- sist at that point. Extraneous Copper Now for something completely different. The view of the layer in Fig- ure 3 shows excess cop- per that remained after etching (this is an inner layer). In broad terms, this is clearly a develop-etch- strip (DES) issue. Howev- er, do not discount con- cerns with imaging. First, as part of the trouble- shooting protocol, con- sider the actual etching operation as a starting point. At first glance, the panel is under etched, but why? Check the fol- lowing variables in the etching system: • Conveyor speed too fast • Temperature of etching solution too low • Spray pressures have dropped for any number of reasons, including plugged spray nozzles • Inadequate replenishment of required chemical additives Figure 2: Schematic shows partial etch-out of the copper trace (Source: IPC) Figure 3: Unetched copper remaining. (Source: RBP Chemical Technology slide library)

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