What Type of Flex Circuit Board Materials Should I Use?
Type of Flex Circuit Board Materials
Printed circuit boards (PCB) are essential to the operation of any electronic system. However, there are different types of PCBs depending on the specific application and environment that they will be used in. Rigid PCBs are essentially rigid laminate boards while flex circuits are more flexible and can be shaped into the necessary shapes to fit into an application. This makes flex circuits perfect for applications with space restrictions and limited mobility. But what is the best material to use for a flex circuit? There are a few important things to keep in mind when choosing a flex circuit material.
Conductors: The main conductors of a flex circuit are copper foils which are etched to create the circuit paths. The thickness of these foils will have a significant impact on the overall flexibility of the finished product. Thicker foils are more flexible than thinner ones, but there is also a risk that they will be susceptible to fatigue and work-hardening which can cause failures in the long run. The best way to avoid this is to choose a higher-grade rolled annealed (RA) copper foil. This will reduce the amount of strain on the flex board and extend its lifespan.
Insulators: These materials separate the electrical conductors on a flex circuit boards and can be made from a variety of materials including polyimide, polyester, and solder mask. They are typically held in place with a thermally-cured epoxy, acrylic or PSA adhesive. The thickness of the insulator is often chosen to match the copper foil thickness that will be used in the circuit, but it is also possible to build a flex circuit with no insulator.
What Type of Flex Circuit Board Materials Should I Use?
Stiffeners: Single-layer and multi-layer flex circuits can be made more rigid in certain areas by adding localized stiffeners which are attached with an acrylic or epoxy pressure sensitive adhesive. These stiffeners can help with stress reduction, weight balance and increase the abrasion resistance of the board by preventing it from snagging on components. Materials like FR4, Kapton, and aluminum are frequently used as stiffeners.
When selecting the materials for a flex circuit it is also vital to ensure that any bends in the board are designed correctly to minimize failures and cost. The area around the bend needs to be free of discontinuities such as vias, cut-outs, slits and holes, as these can lead to cracking and stress points which can result in failures and malfunctions.
It is also recommended to use wide ends on traces that will be exposed to bending so that they have greater strength against torsional stress. To do this, the traces should be rounded to an angle of around 90 degrees rather than being straight across as this will increase their tensile strength by about 50% compared to a sharp edge. If you are worried about the cost of your flex circuit then check out this detailed calculator by PCBway. It will let you know exactly how much your design will cost to manufacture.