Issue link: https://iconnect007.uberflip.com/i/253291
February 2014 • SMT Magazine 77 tion specified during test procedures and veri- fication at the foundry? Or is it one of those devices from the middle of the batch run? This latter one has the potential of being the culprit because it might be slightly marginal when it comes to the required performance at high speeds. Today's expensive com- ponents and their possible shortcomings aren't to be taken lightly. Assembly pro- cess engineers and PCB lay- out engineers must be con- sulted so they can figure out ways to satisfactorily handle the constraints and other anomalies that chip and component makers factor into their products. Also to be considered is the OEM's speed grade specification for an FPGA design, for exam- ple, and when the FPGA was designed. Were constraints properly implemented? What are the consequences if that device is marginal or when it's not out of spec quite yet, but extremely close to the limit? An example of where a high- speed problem may lie in an FPGA deals with its two sets of pins. One set is composed of hard- wired control pins; the other set is user-defined pins. The OEM customer can use those user-de- fined pins without having specific knowledge of how the FPGA works. However, let's say the FPGA design engineer may have inadvertently, inefficiently, or wrongly programmed and de- signed some aspect of those pins. A misstep like this can create issues to prevent a PCB from at- taining the higher-level speeds. Also, as a device gets more mature, more data is available. Device binning gets more re- fined. The duration for which these ICs are built plays a significant role in this scenario. In the initial processes, binning is not mature or re- fined. When it becomes more mature, you have multiple grades. Some are tops within 5–10%, which are the best of the best. There is also a wide range of middle-of-the- road components. These are defined at the bin- ning stages and sold at different price points. Finally, there is a third grade, which includes devices that are barely passing, but not expen- sive FPGAs. The low-grade devices are normally used at highly discounted prices, mostly for consumer products. back to the FPGa It's fair to say that one or more highly advanced FPGAs are at the heart of most high- speed boards. It's like the el- ephant in the room. We may conclude the device could have something to do with a high-speed board passing at lower speed, but failing at some higher-level speeds. The FPGA certainly has to be included among the other usual suspects and can have some association with the is- sues those boards are experi- encing. At this point in the inves- tigation, you have to take cer- tain considerations and actions into account, which are outside the EMS realm and in particular, the respon- sibility of the EMS company because they're not involved in the manufacture of that FPGA. However, because you are a reputable contract manufacturer (CM) or EMS provider, you must get intimately involved because the PCB is fail- ing on your assembly floor. At the top of the list is contacting the com- pany that designed and manufactured that par- ticular FPGA that you think is causing issues on the board you're working on. It makes good business sense for the FPGA maker to become a close partner in this investigation not only because it is to their benefit to determine and fix the problem, but also to properly serve the OEM with a reliable product. But why would an EMS provider with this kind of problem bring it to the chipmaker's at- tention? You don't have to be a rocket scientist ZUlKI'S PCb NUggETS uNCOVerING aSSeMbLy PrObLeMS OF HIGH-SPeeD PCbS continues At the top of the list is contacting the company that designed and manufactured that particular FPGA that you think is causing issues on the board you're working on. It makes good business sense for the FPGA maker to become a close partner in this investigation not only because it is to their benefit to determine and fix the problem, but also to properly serve the OEM with a reliable product. " "