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62 SMT Magazine • December 2016 The IPC-7711/21 Rework of Electronic Assem- blies/Repair and Modification of Printed Boards and Electronic Assemblies is being "upreved" from version "B" to version "C" and will soon be re- leased to the industry. There are a couple of no- table changes that strengthened, modernized and brought together changes from the previ- ous "B" version, which was approved in 2007. Several of the changes from the previous version deal with the manner in which lead- less devices are being reworked. Leadless devic- es have become the most widely placed in terms of units worldwide. In addition to the methods previously described when the initial version of the IPC7711/21 "B" came out, the new "C" ver- sion includes three new methods, summarized below: • Method Prebumping the lead- less device using a polyimide stencil • Method Prebumping the device using polyimide stencils with the "bumped" component then fitting in to stay-in-place capturing stencil on the rework location on the PCB • Method Hand bumping center ground and hand soldering the IO connection method Another area in which some newer rework techniques are memorialized in the new "C" version are the various pad repair techniques including: • Method 4.7.4: Land repair land with integral via repair film method which leans on the previous repair film method for pad repair • Method 4.7.5: SMT/BGA land repair with integral via repair circuit extension film adhesive method Other areas of change for this "C" version include: Method focused IR for BGA rework and Method 5.7.12 focused IR placement of BGAs. These changes mirror the inroads that IR rework have made since the B standard as the focused heating is important for ever high- er board part densities and the continuing pro- liferation of underfilled devices, very small de- vices and highly temperature sensitive devices finding their way onto PCBs. In addition to the above procedure up- grades there are a variety of other changes due to operations running in a mixed alloy envi- ronment of both lead-free and tin-lead solders. One of the changes with the IPC 7711/21 has to do with the segregation of the hand solder- ing equipment limiting cross-contamination. These changes are due to there being signifi- cant rework differences between the processing by Bob Wettermann BEST INC. Rework and Repair Standard Getting Updated KNOCKING DOWN THE BONE PILE Figure 1: Prebumping of QFN for rework.

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