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56 FLEX007 MAGAZINE I JANUARY 2019 Article by Bob Burns PRINTED CIRCUITS LLC This article will dis- cuss how manufactur- ing rigid-flex boards is similar to manufactur- ing conventional rigid boards and flex circuits, and describe areas where it differs. My previous columns shared why rigid-flex circuit boards cost more than conventional boards, applica- tions where rigid-flex boards provide a supe- rior packaging solution, and what a designer needs to keep in mind when designing rigid- flex boards for manufacturing. Rigid-flex manufacturers use the same equip- ment and processes that you find in hardboard and flexible circuit manufacturing, but they are typically adjusted to meet the unique nature of these composite constructions. As a rule, the processes and techniques are much more con- servative to increase manufacturing yields. Combining thin, flexible laminates with soft rolled-annealed copper cladding, coverlayers and bondplies with adhesive bonding resin, glass-reinforced laminates, and no-flow pre- pregs require a longer and more conservative manufacturing cycle. The materials used have very dissimilar dimensional stability proper- ties and also move dissimilarly with changes in humidity, temperature, and processing. A lot of care and atten- tion is used to get these materials to move in unison and provide you with a stable end product. We will walk through a typical rigid-flex man- ufacturing cycle step by step to explore how the processes come together to build a high- reliability packaging medium. Front-end Engineering Once your design is complete, it is time to put it on the floor. A lot of engineering work goes into the front end to accommodate all of your requirements. Since rigid-flex boards are folded and used in three dimensions, there are usually far more dimensions and other requirements that must be met to make your design successful. A typical rigid-flex designer will spend a couple of days to a week in front- end engineering and quality assurance to work out the details of your design requirements. One of the most critical steps in creating a rigid-flex product that cannot be emphasized enough is involving the supplier from the begin- ning during your design phase. This activity helps to ensure the customer that the rigid-flex Manufacturing Rigid-flex Boards