Issue link: https://iconnect007.uberflip.com/i/1111672
20 SMT007 MAGAZINE I MAY 2019 unless they are a turn-key assembler respon- sible for purchasing PCBs and components as well. In this column, I will focus on how the assembler can help the customer in making DFM decisions. Some of the examples of DFM issues that can cause defects, including land- pattern design, inter-package spacing, compo- nent orientation, types of laminates, surface finishes, solder mask design, via size, and line width and spacing. Who Knows Better Than the Assembler? Most boards are designed by OEMs and not by the assembler, but very few designers have any understanding of manufacturing pro- cesses. We are not talking about circuit design here; we are talking about the design of the board for manufacturing. Who knows better than the assembler about poor designs causing defects in manufacturing? This is where the assembler can help the customers—especially customers who do not have in-house manu- facturing capabilities and have very little idea about the complexity and interdependence of design and manufacturing. Why Should the Customer Listen to the Assembler? With the help of assembler, if the customer can eliminate or at least minimize some of the root causes of defects under their control, defects will go down substantially as well as the cost. An added bonus is that reliability will improve because of reductions in defects and rework; hence, there is less potential for rework-related damage. This also improves on- time delivery since the products are not held up for rework. There are many good reasons for the customer to work with the assembler for the mutual benefit of cost, reliability, and on-time delivery. How Should the Assembler Proceed in Helping the Customer? Start with helping the customer understand the basics of SMT processes, such as paste printing, placement, and all of the soldering process, repair, cleaning, test, and inspec - tion with a focus on how the design impacts defects. For example, if you are having lots of tombstoning, the land-pattern design is most likely not good (too much space between the lands). I am not talking about making the designer a process engineer but helping them to fully understand how the design impacts process yield. The next step for the assembler is to have the customer follow the assembler's DFM or develop their own in-house, company-spe- cific DFM. In my global audit, I find that less than 10% of companies have their own in- house, company-specific DFM even though every company needs one. A DFM document requires the cooperation of both the assembler and OEM. I have taught classes at major OEMs where they invited all of their major EMS sup- pliers to make sure both parties were on the same page as far as DFM was concerned. Using an industry standard, such as IPC- 7531 (formerly IPC-782 when I chaired it) is a good place to start. However, you should keep in mind that industry standards are try- ing to solve world hunger and not company- specific issues. There are many common issues that can apply to every company, but there are many company-specific issues since every company builds different products for various applications, such as Class 1, 2, or 3. Here are some specific areas where the assembler can help the customer. Each area is also a major section of DFM (and some of them are potential topics for columns): • Establish design rules and guidelines while emphasizing the importance of differences between them Who knows better than the assembler about poor designs causing defects in manufacturing?