Issue link: https://iconnect007.uberflip.com/i/1456062
84 SMT007 MAGAZINE I MARCH 2022 Solder mask can be repaired using one of several different techniques, each with its own advantages and disadvantages. One method, as outlined in IPC 7721 2.4.1, is via the use of liq- uid solder mask. is can be spread onto the areas that need repair. is replacement mask is then either heat- or UV-cured. Aer read- ing the manufacturer's directions, UV- cured solder mask is selectively applied and placed underneath the UV lamp of the right wavelength. Based on the out- put of the UV lamp (which can be mea- sured using a radiometer) a cure time for the given solder mask along with lamp-mask distance, a controlled pro- cess can be documented by the repair technician. Another method (Figure 3) is a sim- ple technique for "spot" solder mask repair by using a repair "pen" (IPC 7721 2.4.1) which is typically cured by air drying or a bakeout cycle. e liquid oozes out of the so-tipped pen and then can be air- or heat-cured. e pen tips themselves are large with respect to the size of modern BGA pads, making it a challenge to precisely dispense the mask mate- rial. Due to the porous nature of the dispensing tip, it tends to pick up debris from the board (including flux residue, remnant mask, and cleaning agents). is soaked-up debris then can re-contaminate other areas of the board. Figure 2: Example of solder mask adhesion problems. Figure 3: Spot solder mask repair with repair pen. (Source: Chemtronics)