Coverlayers are polymer materials used to cover and protect the copper traces of the flex circuit product. Flexible soldermask is one method for protecting the circuits, and in terms of cost, is generally the least expensive. Flexible soldermask is a different formulation than standard soldermask, modified to allow the polymer to flex and bend without cracking or loss of adhesion. While the most cost-efficient solution, factors such as cost, performance, and flexural endurance optimization must be considered when making this decision. Some one- or two-layer flex circuits that will not be subject to multiple flex cycles or extreme radius bends can easily be coated with a flexible soldermask. However, this is not recommended when the design requires any dynamic or extreme flexing. Understanding the application of the flex PCB is the most critical consideration. Flexible soldermask will typically be the right choice if the circuit will be bent just one-time during installation or intermittently; but is not the correct choice if the circuit is flexed dynamically millions or even billions of times over its useful life.
