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High Speed/High Frequency PTFE Rigid-Flex PWB

IP.com Disclosure Number: IPCOM000240187D
Publication Date: 2015-Jan-09
Document File: 3 page(s) / 107K

Publishing Venue

The IP.com Prior Art Database

Abstract

The technology to be developed is a PTFE rigid-flex printed wiring board (PWB) utilizing High Speed/High Frequency (HS/HF) flexible laminates (typically polytetrafluoroethylene (PTFE) based) in combination with rigid HS/HF laminate and prepreg intended for replacement of HS/HF PWB with coax cables. The use of these materials will enable the design to be constructed with thinner dielectrics improving flexibility and providing better performance than a comparable rigid-flex utilizing traditional polyimide film with polyimide or epoxy rigid laminate construction.

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Introduction:

High Speed/High Frequency (HS/HF) polytetrafluoroethylene (PTFE) flexible printed wiring boards (PWB) are procureable today. An all PTFE rigid-flex PWB may also be fabricated. Advantages include the potential to eliminate use of traditional coax cable and connectors with a one-piece PTFE rigid-flex construction.

Background

Design teams within Rockwell Collins have expressed the need for flexible Printed Wiring Boards (PWBs) providing High Speed/High Frequency (HS/HF) performance capability while simultaneously constrained by tight bend radii. Traditional flexible PWB materials and designs often cannot provide an adequate replacement for coax cables in areas with tight bend radii due to thickness restrictions in conjunction with impedance requirements. DuPont™ Pyralux® TK Film and Taconic fastRise™/fastFilm™ material sets were designed to provide improved flexibility and performance in HS/HF flexible PWB designs composed of six layers and less. Combining these materials with rigid HS/HF materials creates a rigid-flex PWB with the required electrical performance employing thinner dielectrics, resulting in a more flexible PWB as compared to traditional material sets.

Technical Discussion

Traditional material sets for rigid-flex PWB consist of polyimide film with rigid polyimide and/or epoxy resin systems. An example stack up for a traditional adhesive-based rigid-flex is shown in Figure 1. This rigid-flex stack-up has adhesive film throughout the entire structure. It is known in the industry that bonding adhesive present in a plated- through hole decreases long term PWB reliability due to the high thermal expansion of the adhesive. Therefore the best comparison between traditional rigid-flex materials sets and the HS/HF material set is shown in Figure 2.

COPPER CIRCUIT

RIGID LAMINATE (WOVEN GLASS RESIN IMPREGNATED)

 COVERLAYER (POLYIMIDE FILM, ADHESIVE)

RIGID PREPREG

METAL CLAD DIELECTRIC ADHESIVELY BONDED TO POLYIMIDE FILM

FLEXIBLE PWB REGION

ADHESIVE IN THROUGH‐HOLE STRUCTURE DECREASES PWB LONG TERM RELIABILITY (e.g. MTBF)

RIGID PWB REGION

PTH

OR VIA

RIGID PWB REGION

WITH CUTBACK COVERLAYERS

Figure 1 Traditional Adhesive Rigid-Flex PWB

© Copyright 2015 Rockwell Collins, All rights reserved.

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COPPER CIRCUIT

   RIGID LAMINATE

      RIGID PREPREG

          COVERLAYER (POLYIMIDE, ADHESIVE)

FLEXIBLE PWB REGION

PTH

OR VIA

ABSENCE OF ADHESIVE IN THROUGH‐HOLE STRUCTURE INCREASES PWB LO...