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66 SMT007 MAGAZINE I MARCH 2020 An Overview of IPC-7093: A Standard to Be Released As you can see, there are many benefits of BTCs, but there are some major concerns as well. This IPC-7093A describes design and assembly guidance for implementing BTCs and focuses on critical design, materials, assembly, inspection, repair, quality, and reliability issues associated with this package. This document is not an academic exercise. The purpose of this standard is to provide use- ful and practical information to those who use or are considering using BTCs. The target audi- ences for this document are physical designers, process engineers, and reliability engineers and managers who are responsible for the design, assembly, inspection, and repair processes of printed board assemblies. The intent of the document is to help you suc- cessfully implement robust design and assem- bly processes for printed board assemblies so that you have a good understanding of how to troubleshoot design and assembly problems for improved reliability for both tin-lead and lead- free assemblies using BTCs. The team has been working on this revision for some time now but finally completed its revision a week before IPC APEX EXPO 2020. At the meeting, the committee voted unani- mously to release the document for ballot. There will be a phone meeting of the A-team to review the comments before the final release. If you have any comments on this docu- ment, please send it to me or IPC. If you have something entirely new to add, we welcome that too, but we will consider it for the next revision B. Summary BTCs have many benefits, such as smaller package size and excellent electrical (e.g., resistance, capacitance, inductance) perfor- mance, since there is no lead. They also have excellent thermal performance due to the direct thermal path to the PCB (Si die to die to Cu thermal pad to solder to PCB). And most important of all, BTCs are compatible with standard SMT processes (i.e., no special han- dling as in fine pitch QFP) and cheaper than any other package. When implementing BTCs into an electronic assembly, one must keep in mind that these parts are not the only components that must be mounted on the board. The board will have other packages such as BGAs, fine pitch, and even some through-hole components; those components may have their own unique design and assembly implementation requirements. There are two key issues with BTCs: provid- ing the appropriate amount of solder paste and ensuring solder joint reliability. Lower paste volume can reduce floating and voids but increases the risk of solder opens, so a balance is required to ensure overall solder joint reli- ability. When it comes to inspection, BTCs pose even more challenges than BGAs because endo- scopes provide at least some information about the condition of BGA balls. BTC joints are essen- tially like postage stamps, so aggressive flux should not be used. Side fillets are not always possible since ends are sawed or punched and may not wet. In the next two columns, I will discuss the details of design and assembly issues covered in this document that address these technical concerns to achieve higher yield, lower cost. In other words, I'll address how to meet the motto of IPC and "build electronics better." SMT007 Ray Prasad is the president of Ray Prasad Consultancy Group and author of the textbook Sur- face Mount Technology: Principles and Practice. Prasad is also an inductee to the IPC Hall of Fame— the highest honor in the elec- tronics industry—and has decades of experience in all areas of SMT, including his leadership roles implement- ing SMT at Boeing and Intel; helping OEM and EMS clients across the globe set up strong, internal, self-sustaining SMT infrastructure; and teaching on-site, in-depth SMT classes. He can be reached at smtsolver@rayprasasd. com and has upcoming SMT classes April 20–22 and July 20–22, 2020. More details at www.rayprasad.com. To read past columns or contact Prasad, click here.