Issue link: https://iconnect007.uberflip.com/i/1475010
30 SMT007 MAGAZINE I AUGUST 2022 the site location is clean and dry prior to plac- ing the adhesive-backed stencil. Peel the sten- cil from the release liner and align it with the lands on the PCB. Roll solder paste through the apertures of the stencil by using a small hand- held squeegee (Figure 5). e squeegee can be moved back and forth several times before removing the stencil. Now carefully place the component onto the bricks of the solder paste printed at the rework location. Reflow the solder paste using a hot air or infrared heat source. Clean and inspect per the guidelines of the work. Summary In the point-to-point soldering technique, a technician will be soldering each connection individually, which allows for adjustment of the applied heat, dwell time, and solder vol- ume to suit each particular connection. is technique gives the technician a lot of discre- tion regarding the rework process, but also reduces the uniformity and consistency of the solder connections. e downside of the point- to-point soldering method is that it is time-consuming and tends to burn out tips more quickly. In drag soldering, a highly skilled technician can move through components much more quickly. However, it is imperative to have a high- quality solder station and iron with active tip temper- ature monitoring and con- trol, as well as plenty of liq- uid flux (may not be suitable for all applications). When done properly, the drag sol- dering technique results in more uniform solder fillets. F i n a l l y , t h e s t e n c i l approach requires the use of a custom-made stencil while reducing the soldering skill level of the technician. Each of these methods can be used to effectively solder a QFP in place. e method chosen is a function of the solder- ing skill level of the technician and the pitch and lead count of the component. SMT007 Resources 1. IPC 7711.21 Rework and Repair of Printed Circuit Assemblies, Revision C 2020. 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, click here. Figure 5: Solder paste squeegeed through apertures of the stencil.