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28 DESIGN007 MAGAZINE I FEBRUARY 2019 There are three methods commonly used for bonding multiple layers of RF and microwave PCB laminates such as PTFE (Teflon) materials like Rogers duroid. These three methods are thermoplastic films, thermoset prepregs, and direct bonding (often called fusion bonding). Each has their own pros and cons that PCB designers need to understand to balance cost and performance. Thermoplastic Film Bonding Bonding films are designed to flow into the laminate stackup under heat and pressure to encapsulate the traces left on the surface of the inner layers after the etching process. This means that the bond is primarily mechanical in nature. Several thermoplastic bond films are available for use in PCB applications including polyethyl - ene (PE), chlorotrifluoroethylene (CTFE), fluo- rinated ethylene propylene (FEP), and polytet- rafluoroethylene (PTFE). Major suppliers of this material over the past 40 years include Rogers, Taconic, and Arlon. Thermoplastic bonding films are not well suited for use in hybrid mul - tilayers due to the temperature required to melt these materials. The lower thermal degrada- tion point of thermosetting materials may cause these materials to oxidize and decompose. Microwave PCB Bonding Methods: What Designers Need to Know Standard of Excellence Feature Column by Anaya Vardya and John Bushie, AMERICAN STANDARD CIRCUITS

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