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SMT007-Sep2022

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74 SMT007 MAGAZINE I SEPTEMBER 2022 Because of PCB layout problems or required circuit modifications, at times a trace on the surface of a PCB needs to be severed. In this procedure a small section of the trace is removed, thereby forming a "break" in the cir- cuit. In general practice, the length of this trace cut is as least as wide as the minimum conduc- tor spacing. In most cases, a very sharp-edged knife or high-speed mill will make the cut. Aer cutting the area is tested and sealed with epoxy. To make this cut, the following should be on hand to the intermediate-level PCB rework and repair technician, including but not lim- ited to: • Isopropyl alcohol for cleaning • Continuity meter and test probes for measuring electrical continuity • PCB epoxy • Oven for curing the epoxy Opening a Trace on the Surface of a PCB • Sharp knife for precision cutting of trace • Stereo microscope with proper lighting for inspection • Low lint wipes for cleanup • Colorant matching the PCB mask color e first step (Figure 1) is to make sure the proper location of the cut can be determined given the physical limitations of the neighbor- ing components to the cut location. Use the mechanical assembly drawings in addition to the Gerber files. Determine where the min- imum trace-width cut will take place. Clean the area using the isopropyl and the lint-free cloth. e cut should be perpendicular to the trace edges. Make the cuts (Figure 2) by using a straight edge and the knife, making the two cuts per- pendicular to the trace direction cuts. Apply even pressure using a straight edge as a guide, slowly cutting through the trace so as to not Knocking Down the Bone Pile by Bob Wettermann, BEST INC. Figure 1: Determine the trace cut location. Figure 2: Use a sharp-edged knife to make the trace cuts.

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