Via Fill Be Used in Flexible Or Rigid-Flex Circuit
Via fill is a PCB manufacturing process that uses a special screen-printing technique to cover the copper in the vias with conductive ink. Then, the excess ink is rinsed off during the etch process. This is a common manufacturing step in both rigid and flexible circuit boards, and it is used to improve signal transmission. It also makes it easier to route the traces around the components on your PCB.
In some cases, using pcb via fill can negatively impact your board’s performance. Vias carry signals from one layer to the next on your PCB, but they are susceptible to noise interference from physical or electrical properties of other layers in the board. This is especially true if you use traditional blind vias in your design.
A standard PCB via acts as a conductor that transfers heat from hot areas of the board to cooler parts. This is important in flex circuits where heat may be dissipated by the conductive metal of a component or by a rigid-flex layer that contains the component. In these cases, it is essential to have the shortest possible path for the heat flow.
However, the standard copper via’s metallic nature carries its own set of issues with it, particularly in flex circuits. The metal will expand much more rapidly than the surrounding dielectric material. This unequal expansion can cause stress fractures in the flex-to-rigid circuit.
To overcome this issue, a variety of methods have been developed for the via filling process. Conductive via fills can be capped to prevent them from conducting, reducing the potential for heat-induced fractures and enhancing the ability of your flex circuit to bend.
Can Via Fill Be Used in Flexible Or Rigid-Flex Circuit Designs?
The other option is to use non-conductive via fills. These fills are more practical for flex circuits as they do not conduct, and they can help to reduce the amount of solder that is needed at the connection point for your flex-to-rigid connections. However, the non-conductive fills tend to have an uneven surface that may create dents or small outward dimples in the area of the via.
If you are planning a flex or rigid-flex circuit, it is important to consider your via fill early in the design process. It can greatly impact the flexibility of your design and the cost of your final product.
In general, it is best to keep the number of layers in your flex-to-rigid sections as low as possible. More layers means stiffer materials, and they can be a challenge to bend correctly. Also, high layer counts can increase your manufacturing costs because the different dielectrics must be glued together and soldered to each other.
The best solution is to work closely with your fab house to discuss your requirements and ensure that they understand your design needs. They can also advise you on the best way to implement your design. This includes modifying your traces to avoid tight, narrow paths that will not be able to bend as expected. In addition, they can recommend alternatives to a conventional via fill if necessary, such as a conductive or non-conductive closure.