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Flex Talk: Communication Goes Both Ways

The definition of new technology in the PCB industry varies from person to person. I have been chasing new technology for 20 years. Some of it has been new to me, while some of it is new to the industry. First, it was flexible circuit technology, which was not new to the industry but was my first experience in PCB manufacturing. This was followed by rigid-flex and then complex HDI structures, which, again, were not new to the industry but were new to me. 

I am also interested in and eager to learn about materials and processes new to the industry. Among those that have caught my eye is a new material from DuPont called Pyralux® GPL Sheet Adhesive. How exciting to think about the possibility of eliminating the bikini-cut adhesive for rigid-flex. And from a process perspective, learning about Averatek’s A-SAP™ process, a semi-additive PCB process enabling 15-micron trace and space—how could I not be excited for all of the possibilities that this opens up for PCB design and simplifying complex HDI designs? From a medical application perspective, what about gold traces instead of copper traces applied on polyimide for a simple, biocompatible solution? This just scratches the surface of new materials and processes being introduced to the PCB industry.

What is the best approach when searching out technology new to you but not necessarily new to the industry? Those who read my column regularly can probably guess that my first piece of advice is to work with your fabricator. After all, if your fabricator is working with this technology every day, they have a tremendous amount of knowledge built over time and are always happy to share and help guide customers through what can, at times, be a steep learning curve. 

Flex and rigid-flex are excellent examples. First, plan a deep dive before starting your first design using flex or rigid-flex construction. On the surface, it may seem that flex is not all that different than a rigid PCB, outside of the obvious benefits to space, weight, and packaging with materials able to bend, fold, and flex. Over the years, I have accumulated so many stories and examples that disprove that assumption. There are the obvious examples of the “flex that didn’t flex.” The thickness and rigidity of solid copper shielding in the tail area of a rigid-flex can build up much more quickly than anticipated. In working with your fabricator, they may recommend using “unbonded” layers in the flex area, which eliminates a layer of adhesive between 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 complications 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 coverlay was required to open the fine-pitch SMT pads. To ensure flexibility, the fabricator also had to use button plating to not introduce additional copper in the flex layers. These two things together forced the fabricator to use a smaller size fabrication panel to ensure proper 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 designer 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 communicate with your fabricator, but in a slightly different way. Many times, they will be learning right along with a designer. Often, it is the material suppliers or technology developers educating 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 easily 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 learning 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 collaborative approach benefits not only the end-user seeking the information but also the fabricator that will be providing the technology.

This column originally appeared in the September 2020 issue of PCB007 Magazine.