Flex Circuit Shielding Design Options

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Figure 3: Silver paste screened over a coverlay showing the via stitches down to a ground line—another coverlay goes on top to protect the silver.

• EMI Thermoplastic Shielding film—latest technique. This technology is the newest and most flexible shielding technique. The ultra-thin, ultra-flexible materials were developed for the cell phone market. The manufacturing process has been dramatically improved, making it only slightly more expensive than the older technologies. North American flex shops who use this material are pushing their customers in this direction. It is the thinnest and most flexible. It is easy to apply and creates a 360 degree shield similar to a silver paste or stitched copper via.

 

Figure 4: Material stack of the thermoplastic shielding film.

 

Figure 5: Thermoplastic shielding film applied to circuits. Easy for your vendor to apply, but material is still expensive.

Shielding—Design for Manufacturing—a Review of what we learned

Most of the North American flex suppliers can provide all four solutions mentioned below, but they will steer you to the technique they are most comfortable with. The most important design decisions for shielding flex circuits are flexibility/bendability and cost.

Here are my impressions:

• Adding layers of copper to shield, while adding potentially excellent shielding characteristics, adds cost, weight and thickness, and can prove to be a disaster when trying to bend the circuit. This method requires via stitching to prevent “leakage.”
• Adding cross-hatch layers can provide excellent shielding characteristics again, but still adding layers, weight, and will affect flexibility. This also requires via stitching to prevent “leakage.”
• Conductive paste allows better flexibility and lighter weight, and better coverage of shielding. Requires via stitching.
• Thermoplastic shielding film is slick stuff. Easy to apply, thin, light, and bendable. It allows no side leakage. It was originally made for cellphones so the material has been proven, but is more expensive (by 25%) than shielding with normal/older techniques.

Mike Morando is VP of sales and marketing for PFC Flexible Circuits Limited.

07/07/2022 | Denis Jacques, Technic Inc.

About three decades ago, immersion silver, a nitrate-based process, gained a lot of market share in the world of PCB final finishes. More economical than ENIG, flat, solderable, and conductive, it had everything going for it—everything but corrosion resistance in a harsh environment, that is. Champagne voids were also an issue, along with line reduction. But the worst drawback, the characteristic that made the part short over time, was creep corrosion. A build-up of copper sulfide salt that grows in contact with a sulfur-rich environment, heat, and moisture resulted in failures in the field. This was enough to scar the process for good.

06/29/2022 | Pete Starkey, I-Connect007

Örebro, Sweden on June 15 brought a bright and early start to Day 2 of the EIPC Summer Conference for those who had enjoyed the previous evening’s networking dinner, but had resisted the temptation to over-indulge or to carry on their long-awaited catch-up conversations with old friends into the small hours. All but a few were in their seats for 9 a.m., awake and attentive for Session 4 of the conference, on the theme of new process technologies, moderated by Martyn Gaudion, CEO of Polar Instruments.

06/28/2022 | Pete Starkey, I-Connect007

At last, a live EIPC conference and this time in the Swedish city of Örebro, “where history and contemporary culture converge,” a pleasant and convenient location for an event that included a privileged visit to the Ericsson facility in Kumla. Around 100 delegates made the journey and the Örebro Scandic Grand Hotel was an excellent conference venue for the June 14-15 conference.