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Flex Talk: New Materials or New to You?

I think the phrase, "There is something new for everyone," absolutely applies to the PCB industry. Our industry offers a wide range of materials just on the fabrication side, and I feel like we are consistently exposed to materials that are new to us. Reflecting back on just the last couple of weeks, I have learned about copper coins, which is something new to me, and also had a request for ENIP, which is a surface finish I am not yet familiar with. I have also introduced a couple of different groups to a palladium-based ALD-type ink that is enabling an additive process capable of very high-density interconnect as well as MINA, a surface treatment for aluminum. Other questions I have answered revolve around rigid-flex materials for someone starting one of their first rigid-flex designs and different coverlay options for a flexible circuit application.

This leads me to the thought that our industry is growing quickly with new processes and materials being introduced on a regular basis. Even if you have been in the industry for your full career, I would place a wager that there is something new for you or something new to you.

When you have questions, who do you go to for answers? Have you built a strong network to reach out to? If not, what could you do to help expand that network? Personally, as a manufacturer’s representative serving the PCB industry, I try my best to help my customers learn about new materials, processes, and technologies, and at the same time, I am intentional about attending industry events and being sure that I am learning about all three as well. I am very interested in how others approach the issue of keeping up to date with new things in our industry and welcome suggestions for events to attend.

Regularly, I am asked to help answer questions regarding flexible circuit materials, so I wanted to put together a brief explanation of materials available and things to be aware of when creating a stackup. First, for flexible circuits, specifically polyimide-copper laminates, there are a wide variety of options available. Polyimide is available in both adhesive-based and adhesiveless options from 0.5–5 mils, and copper is available from 0.25–2 oz. Other thicknesses are available, but these are the most widely used. From there, it is important to research what you preferred fabricator regularly stocks. Each fabricator stocks a group of materials based on existing customer demand and preferred materials. If you can create a stackup around those materials, it will save time and project costs.

Flexible coverlay options are also something that is asked about frequently. There are two primary options. First, and most common, is polyimide film-based coverlay. This option is highly recommended for dynamically flexing applications and rigid-flex. It is important to specify the adhesive thickness in accordance with the copper height on the base laminate to ensure full encapsulation. Another option for flexible cover coat is flexible photoimagable coverlay. This option provides a better resolution for dense SMT component areas and produces crisp, square SMT pad openings. But while this material is flexible, it is not intended for dynamically flexing applications. If you need dense SMT pad openings on flex, laser-skived, polyimide-based coverlay is an excellent solution. It is a bit more expense than drilled or routed coverlay, but it is a viable option when those things are critical.

I am also frequently asked about ALD ink supporting the semi-additive process (SAP) domestically. This process has been proven with prototypes and is on the cusp of transitioning to production in North America. This is an exciting new chemistry that enables line width and space at 0.001” and below. Numerous applicationareas are investigating how to incorporate this technology, and fabricators are exploring how to bring this process on-line to meet those needs best. Over time, this will be quite the game changer for the PCB industry by reducing layer count and lamination cycle requirements as well as supporting the technology needed for increasing complex pinouts.

The previous technologies are areas that I am familiar with. But, as I mentioned in the introduction, I am also consistently asked about processes and materials that are new to me. Copper coin technology is not something that I have been familiar with. After seeing an application that was built with this technology, I did a little research and learned that it is used to dissipate heat when thermal vias or metal core materials are not sufficient. The concept is based on getting a copper coin press-fit into a premade cut-out in the board directly under the area that is a hot spot. Interesting!

What an exciting time to be in this industry. There are so many new processes and materials in the PCB segment that it can be a challenge to keep up with all the new developments. It is fun to start chasing the next new thing, but I also think it is important to keep in mind that even materials and processes that have been around for a while are still new to someone. Not everyone has used flex materials or copper coin technology, and only a select few have used additive processes for PCB fabrication. Thank goodness our industry is supported by strong technical publications and industry events to help us all learn about technology that is new to us and help us build a strong network of people to reach out to with questions.

Tara Dunn is the president of Omni PCB, a manufacturer’s rep firm specializing in the PCB industry.

This article was originally published in the May 2019 issue of PCB007 Magazine.