Issue link: https://iconnect007.uberflip.com/i/1456062
86 SMT007 MAGAZINE I MARCH 2022 e skill level for someone making solder mask repairs using this technique will need to be at the advanced level and, even so, the repair aes- thetics tend to be low compared to the tech- nique outlined in IPC 7721 2.4.1. In addition to this repair pen method there is another technique which repairs the mask underneath the BGA using a polyimide, adhe- sive-backed, stay-in-place stencil. is serves as a reliable way to place the BGA while simul- taneously repairing the mask. is stencil, while having the benefit of being a simple way to place a BGA, also provides isolation between pads and prevents shorting between the IO. is will fix the standoff height between the base of the BGA and the PCB to control col- lapse height, while serving as a mask "band- aid." Once in place, the stencil acts like a solder mask repair stencil. is allows even the begin- ning repair technicians to repair damaged sol- der mask underneath the BGA. Lastly, there is the mask repair stenciling technique (Figure 4). is method saves repair time when a large area requires mask repair. An ultra-thin stencil defines the area where the mask is repaired. Replacement mask mate- rial is squeegeed into the stencil apertures and then cured. Post curing, the stencil is peeled away, leaving hardened replacement mask in its path. is method, while time saving for multiple boards requiring the exact same area of repair or for a very complex large area of repair, requires a repair technician with an advanced skill level. Like all PCB repairs, the customer must need to be informed if mask repair is called for in repairing the PCB. ere are many techniques depending on the purpose of the assembly, the cost, and the complexity of the mask repair required. SMT007 References 1. "Rework, Modification and Repair of Electronic Assemblies," IPC-7711C/7721C, IPC January 2017. Bob Wettermann is the principal of BEST Inc., a contract rework and repair facility in Chicago. For more information, contact info@ solder.net. To read past columns or contact Wettermann, click here. Figure 4: Stenciling technique for multiple location solder mask repair.