Issue link: https://iconnect007.uberflip.com/i/1073397
58 FLEX007 MAGAZINE I JANUARY 2019 will perform as desired. Successful rigid-flex designs are always the result of collaboration between the designer, fabricator, and often the assembler as well. Once the front-end engineering work is com- plete, it is released to the floor. A simple rigid- flex design will have five or more travelers, and sometimes as many as 30. Each traveler is for a subcomponent that gets built to com- pletion before being combined into the final assembled circuit board. A straightforward rigid-flex usually will have five travelers: 1. Coverlayer and/or bondply materials 2. Flexible copper-clad laminate layers 3. Glass-reinforced hardboard layers 4. Glass-reinforced no-flow or low-flow prepreg material 5. The traveler for the finished assembly To see how they come together, and each of the process sequences, refer to Figure 1. Coverlayer and/or Bondply Coverlayer is used to protect the circuits in the flexible sections of the board. It performs like a solder mask, but is designed to withstand hundreds of thousands of flex cycles without failure or degradation. Coverlayer is comprised of a thin dielectric (usually 0.001" or 0.002") of polyimide, polyester or other film with a thin layer of adhesive. The adhesives are usually 0.001" or 0.002" but can be thicker depend- ing on the thickness of the copper circuits that will be encapsulated. Adhesives are typically acrylic, epoxy, polyimide, or a blended resin. Bondply is similar to coverlayer, but it has adhesive on two sides and is used to bond the flexible layers together in the flexible sections of the board. Figure 1: Rigid-flex simplified process flow.