Ask the expert.

Featured Arlon Expert Vince Weis, Applications Engineer

Q: We are trying to design reduced-cost polyimide flex-rigid products for applications requiring bend to fit but that don't necessarily need to undergo dynamic flexure. Do you have any suggestions?

A: Several years ago Arlon began a joint development effort with a rigid-flex PWB manufacturer aimed at that specific application, and not only developed a concept for bend-to-fit, but found that with a polyimide film coverlay, the designs, based on Arlon's 2 mil (0.002") thick 85NT nonwoven aramid product, could withstand over 100,000 dynamic flex cycles.

85NT is a polyimide resin system with a nonwoven aramid reinforcement that was originally developed to provide high Tg (240[degrees]C) and low X-Y CTE (6-9 ppm/[degrees]C) for reliable direct SMT applications involving leadless ceramic chip packages. The 85NT system also provides excellent registration stability, flatness and light weight (25% lighter than glass polyimide for the rigid segments of your design). The homogeneous nature of the nonwoven reinforcement eliminates the stress risers in PTH's caused by fiberglass, bundles and in some designs has resulted in 2-3X the mean time to failure when compared to glass polyimide systems. The nonwoven aramid also reduces the tendency to develop CAF growth by limiting the direct pathway between adjacent holes when compared to woven glass reinforced products.

Specific advantages related to your potential use as a bend-to-fit board include the use of one lamination and cure cycle for both the rigid and the flexible elements of the system; elimination of sticky and hard to drill acrylic adhesive; significantly improved flexibility over woven glass laminates and a smooth surface that permits ultra fine line definition with thin copper foil. Additional information is available on Arlon's website at www.arlon-med.com.

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