Flex Circuit PCBs Affect Device Packaging
The base material of a flex circuit PCB is what sets its primary physical properties and characteristic behaviors. The flex circuit base material is typically laminated to other materials (typically copper foil) with epoxy or acrylic adhesives. Conductor traces are then etched onto the base material. In some cases, a dielectric coverlay may be laminated to the top of the copper layer for insulation and protection. This is most often a polyimide film. Depending on the application, a solder mask or other surface finishes are also added to provide a solderable surface and protection against copper oxidation.
Flex PCBs are much lighter than conventional rigid printed circuit boards. This is because they are designed using incredibly thin substrates made of polyester or polyimide materials–films that can be as thin as 12-120 microns. This allows designers to implement more complex functionalities in a smaller space. The lightweight nature of a flex circuit PCB also helps to minimize overall device weight. Customers commonly see weight reductions of up to 75% when converting designs from traditional rigid PCBs to a flex circuit design.
Choosing the right flex circuit pcb material is important because it determines the final performance and reliability of your product. Using high-quality rigid FR-4 or a more expensive polyimide material can increase cost, but it can also offer superior performance and reliability. There are also specialty flex materials available, such as Dupont XF-104 that is used to build circuit boards for medtech applications that come into contact with patients.
How Do Flex Circuit PCBs Affect Device Packaging?
The thickness of the flex circuit material is important because it impacts both the flexibility and cost. There are a range of thickness options, but the thicker the board is, the stiffer it will be. Additionally, higher thicknesses can impact signal integrity and noise.
Conductor layers can be constructed on both sides of the flex circuit to create double-sided flex PCBs. These are more durable than single-sided flex circuits and can be fabricated with or without plated through holes (PTH). PTHs allow components to be connected on both sides of the circuit. Alternatively, the conductor layers can be on one side of the circuit with a bare back to make it single-access flex.
Multiple-layer flex circuits are also available for more demanding applications. These circuits contain three or more conductor layers in a multilayer construction. They are bonded together with adhesive layers, and conductors can be accessed through plated through holes. Additional dielectric layers for insulation and stiffening are also included in the circuit to avoid wrinkling or buckling during thermal stresses.
It is important to know how to design a flex circuit to prevent damage during assembly and shipping. The most common problems with flex PCBs are caused by routing traces close to bend areas. Ideally, traces should be staggered in order to reduce the chance of damage due to stress. Using a 2:1 ratio of spacing to trace width is recommended. It is also important to ensure that your traces are designed with adequate copper thickness and width. This helps ensure that the circuit can handle a sufficient current rating and meet your design specifications.
