PCB007 Magazine

PCB007-July2020

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70 PCB007 MAGAZINE I JUNE 2020 Introduction: Etching-Related Defects, or so It Seems In my last column, I presented issues that were found at final assembly. However, the defects that manifested themselves after the boards were assembled had their genesis in electrolytic copper plating. In this month's edition, I will discuss two interesting techni- cal problems. The first defect I will present is the case of circuit open or etch-out, which will also include circuit width reduction related to undercut. The second defect relates to extra- neous copper remaining on the board. Both issues illustrate the complex nature of PWB troubleshooting and defect analysis. Most process problems that appear during the etching stage of printed circuit produc- tion can be traced to one of two general areas. The most common and obvious cause of etch- ing problems is the etch- ing equipment itself, ei- ther through component failure (spray nozzles, pressures) or mis-adjust- ment, including convey- or speeds. The second most com- mon cause during the etching step is with prob- lems that occur during prior processing steps but are not detected until the boards are processed through the etcher. One example is resist scum left on the board dur- A Process Engineer's Guide to Advanced Troubleshooting, Part 2 ing the stripping of a plating resist, which can cause uneven etching to occur. Another factor relates to the control or lack of control related to the chemical operating pa- rameters. These are just a few of the possibili- ties that will be presented in future editions of "Trouble in Your Tank." For the purposes of this month's column, the main defects to be discussed are the etched-out circuit trace and extraneous copper remaining after etching. Etched-Out Circuit Trace One of the most disconcerting issues related to bare board fabrication is to find an opening in one or more of the circuit traces after etch- ing (Figure 1). Of course, this defect did not manifest it- self until after the inner layer etching step was Trouble in Your Tank by Michael Carano, RBP CHEMICAL TECHNOLOGY Figure 1: Circuit traces etched away. (Source: RBP Chemical Technology slide library)

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