Epec's Blog | Electronics Manufacturing Solutions

At the conclusion of our webinar, Electrical vs Mechanical Requirements in Flex & Rigid-Flex PCB Designs, we had several questions submitted to our presenter, Paul Tome, Product Manager Flex and Rigid-Flex, at Epec. We have compiled these questions into a readable format on our blog.

Identifying the differences between rigid PCB FR4 materials and flex circuit polyimide materials can be useful to customers who are implementing flex circuit designs for the first time. Beyond the obvious difference in flexibility, the two types of materials have different available thicknesses, copper types, and properties that impact high-speed controlled impedance signals.

The hot air solder leveling surface finish (HASL) is the second oldest surface finish available for printed circuit boards and up until a point in time was virtually the standard surface finish used in the electronics industry (originally with leaded solder and more recently the RoHS version with lead-free solder).

Flex circuits have many unique capabilities to solve design challenges. One of these is a lap joint capability that allows a flexible circuit board to be directly attached to another circuit or component eliminating the need for any type of connector.

Flexible circuits can withstand significant bending when designed and handled within their intended limits, but they are not immune to mechanical failure. When a flex circuit is bent or handled beyond the capabilities of its materials, trace fractures and cracked circuits can occur.

Heat dissipation is the ability of a part, whether a circuit or any other component, to take the heat that's being generated by a component or an element of the design and to distribute it, dissipate it, and make the heat go away, for lack of a better phrase. This prevents the temperature of the part from continuing to elevate as the device is operated.

Flexibility is a critical element in most flexible circuit board designs. Whether it’s to meet a tight “one-time bend-to-fit” application or a “dynamic” infinite bend cycle application. To meet these requirements, a flex circuit design must be kept as thin as practically possible, use the correct copper type, and utilize the correct copper plating process.

Mechanical bend reliability is a critical element in a successful flex or rigid-flex PCB design. One area that can have a significant impact is the transition line(s) that occurs from a rigid area, in a rigid-flex circuit design, or from a stiffened area, in a flex circuit with stiffeners design, to the flex layer(s) only areas.

Dome switches are a very popular solution for use as a momentary switch. They are a good solution that provides tactile feedback that the switch has been depressed and an event registered. Many applications require a dome switch mounted to a flexible circuit board.

We get many inquiries from our customer base regarding updating or converting an existing design from its current configuration of rigid printed circuit boards interconnected with a wiring harness to a rigid-flex printed circuit board. With our experience, we can quickly determine if a conversion option is worth investigating further. We can also see how some are relatively obvious that they would need a complete redesign to convert.