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68 PCB007 MAGAZINE I SEPTEMBER 2020 build up much more quickly than anticipated. In working with your fabricator, they may rec- ommend using "unbonded" layers in the flex area, which eliminates a layer of adhesive be- tween layers and can significantly improve flexibility. Alternatively, they may recommend using crosshatch patterning in the flex area to improve flexibility. Involving your fabricator early in the design process can also help prevent an approach that, while functional, may add unnecessary com- plications and expenses. Let me share a real- world example. A fabricator was asked to do a design review of a rigid-flex design being built at a competitor. This design was in production and functioning well, but the fabrication yield was consistently low, increasing costs beyond what the final product could bear. In this case, a designer new to rigid-flex had designed the circuit with a flex layer on the outer layer. This particular attribute created a chain reaction in fabrication. Because the flex was on the outer layer, laser cutting the cov- erlay was required to open the fine-pitch SMT pads. To ensure flexibility, the fabricator also had to use button plating to not introduce ad- ditional copper in the flex layers. These two things together forced the fabricator to use a smaller size fabrication panel to ensure prop- er registration. Each added cost, but together they had an exponential impact on cost. This was redesigned using a rigid layer for the outer layers and a flex tail between the rigid areas. Although material costs were higher with the added rigid layer, the laser cut coverlay was eliminated, the button plating was eliminated, and the fabricator could use a larger panel size. Yields increased, and the cost to the end-user decreased by over 20%. Again, fabricators can be a valuable source of information when you are learning about new technologies and can help prevent costly mistakes and guide a de- signer along the learning curve. Other times, other things are new to the industry as a whole, such as new materials, chemistries, and processes, to name a few. In these situations, it is also important to commu- nicate with your fabricator, but in a slightly dif- ferent way. Many times, they will be learning right along with a designer. Often, it is the ma- terial suppliers or technology developers edu- cating the OEMs, the design community, and the fabricators. When there is a strong benefit for your application, it is important to discuss that with your fabricator so they can more eas- ily understand the market need and timing for the demand from their customers. One example of this is Averatek's A-SAP™ process. This semi-additive process fits in with subtractive etch processes to enable 25-micron line and space. This technology has been available for a couple of years and is now currently being licensed by four PCB fabrication facilities. Other fabricators are discussing the demand for this technology with their customers and making decisions on when or if it will be implemented. Just as they are happy to help someone new to flex or another technology along the learn- ing curve, they are equally happy to receive feedback from their customers that help them make informed decisions. Technology, whether new to you or new to the industry, requires communication between both the end-user and the fabricators. A collab- orative approach benefits not only the end-user seeking the information but also the fabricator that will be providing the technology. PCB007 Tara Dunn is the president of Omni PCB, a manufacturer's rep firm specializing in the PCB industry. To read past columns or contact Dunn, click here. Involving your fabricator early in the design process can also help prevent an approach that, while functional, may add unnecessary complications and expenses.

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