Issue link: https://iconnect007.uberflip.com/i/857644
68 The PCB Magazine • August 2017 for cost and reduced lead-time is to work closely with your fabricator to develop a stack-up. In general terms, laminates with ½- or 1-ounce copper and 1- or 2-mil polyimide will be less expensive than other combinations. However, cost and lead-time will boil down to the materials that your selected fabricator works with most regularly. Please don't spec an adhe- sive-based laminate just because it should be less expensive. If your fabricator manufactures with more adhesiveless materials (highly recom- mended for rigid-flex), they may be purchasing laminate in enough volume that pricing is re- duced and that savings will be passed along to you. The same thing is true for lead-time; design- ing with materials that are in stock will elimi- nate the delays from material lead-time when the prototype is placed and lead-time is critical. My recommendation is to work with your fabricator for a stack-up and be clear about your requirements. Let them know if materials are not critical and ask that they use com- monly stocked materials. That eliminates all assumptions and will result in the low- est cost, best lead-time scenario. Communicate clearly in the fab notes Typically, 75% of flex and rigid-flex de- signs go on hold while being tooled at the fabricator. A significant portion of those questions that need to be asked stem from unclear fab notes. An unclear stack-up is a very common issue with rigid-flex. Make sure that you are clearly calling out which layers are flex and which are rigid. If you have asked for the stack-up prior to releas- ing the design, this is simple to include. Flex and rigid-flex designs can make peo- ple unsure and the basics are sometimes overlooked. Another requirement that can be eas- ily overlooked on the fab notes is the UL requirement. There are many examples where after failing a burn test and inves- tigating the cause, it is found that the UL requirements are clear in the assembly drawings, but not in the fab notes. Your fabricator will not necessarily default to UL materials in the absence of the spec and the contract manufacturer will rou- tinely separate the fab notes from the assembly drawings when asking for a flex quotation. Al- ways clearly state any quality requirements in both the assembly drawings and the fab notes. What do these have in common? I believe the best way to reduce cost and lead-time is to work with your fabricator throughout the de- sign process and communicate requirements clearly. They say experience is the best teacher and they work with new designs every day. Take advantage of that knowledge! PCB Tara Dunn is the president of Omni PCB, a manufacturer's rep firm specializing in the printed circuit board industry. To read past columns or to contact her, click here. KNOWLEDGE IS POWER