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90 SMT007 MAGAZINE I MAY 2019 using epoxy to repair the laminate. Generally, this method is used to repair minor damage to the laminate. Second, you can use an area or corner transplant method. This is used when there is extensive damage to the PCB laminate or when the material is no longer existing, such as in the case when a corner is broken off. As the name of the method implies, a replacement laminate is used and glued using a tongue and groove joint to make the repair. The focus of this column will be on the epoxy method, which has been adopted for the repair of broken or damaged corners on rigid, assem- bled PCBs. The first step is discerning to what extent the PCB has been damaged. First, clean the area to make sure that the area can be thor- oughly inspected. Either through evaluation of the Gerber file set or X-ray analysis, determine if any inner layer circuit traces may have been damaged. If there are no circuits in the inner layers or missing parts due to the damage, then the repair method described will be the only one required. Use a ball mill to grind off rough edges or fibers of the laminate. If it is a large corner, perform an undercut into the laminate edge to increase the bonding area. If interior circuitry has been damaged, then you will need to have the approval and/or skill to make those repairs. Then, find a small plastic box that you would find for holding small tools or nuts and bolts. This will be a single use of the box, so make sure that if you "borrow" it from somewhere else that you can easily get a replacement. Next, mix the two-part resin and hardener over the manufacturer's instructions. Now, using the small container that has been mod- ified to leave only a single corner, place the remaining corner so that it aligns with the damaged corner. Pour the epoxy mixture into the box and smooth the surface. Cure the epoxy per the manufacturer's instructions as well. Using emery cloth and some water, wet sand to make fit the corner. You may have to add some epoxy and/or colorant to match the form, fit, and function of the corner (Figure 2). Clean and re-inspect the repaired area per the acceptance criteria based on the class of the electronics assembly. Using this epoxy method, you can success- fully straighten out the corner of the board and not have to discard it in the scrap heap. SMT007 Bob Wettermann is the principal of BEST Inc., a contract rework and repair facility in Chicago. To read past columns or contact Wettermann, click here. Figure 2: Repaired corner of a PCB (not color-matched for illustration purposes).