Manufacturing Flexible Circuits
When your electrical engineering design requires flexible circuits, you might wonder “What are the typical lead times for manufacturing these custom PCBs?” The answer to this question depends on a variety of factors including the complexity of your design and the thickness of the layers. The thicker the layers, the longer it will take to build your flex board. Let’s look at the different types of flex PCBs and their lead time requirements.
Single sided flex circuits are the simplest and most common type of flexible circuits PCB. They are typically built with a single thin conductive layer hot-pressed and glued together with a flexible dielectric film to provide electrical insulation and protection from the elements. A single sided flex PCB has to be bent a certain number of times in order to perform its intended functions, but the amount of bends is limited by the bending radius and by stress testing.
In addition to the bending radius, there is also a temperature range that a flex circuit must be able to withstand. Depending on the environment where it will be used, a flex circuit can be designed to withstand temperatures as low as -200 degrees Celsius and as high as 400 degrees Celsius. This flexibility makes them an ideal choice for use in environments where heat would otherwise damage rigid circuit boards, such as the borehole measurement equipment used in oil and gas exploration.
What Are the Typical Lead Times for Manufacturing Flexible Circuits?
A flex circuit may have stiffeners inserted in specific regions of the board to increase its strength or to provide protection for attached components and connectors. The stiffeners are placed on the opposite side of the conductive layer and they can be made from a variety of materials, such as polyimide, FR4, aluminum or stainless steel. If you are using a stiffener in your flex circuit, be sure to include it in your fabrication drawing and make note that the board will need to be bent on that side.
The copper features of a flex circuit are usually protected by a cover layer. This layer is similar to a solder mask layer and should be created in the layout file with the same etching parameters. The flex manufacturer should be aware of the thickness of this cover layer, as well as the total stack-up thickness and the number of flex layers.
Flex circuits have less mass than rigid circuit boards, making them lighter and easier to handle. This reduced weight and size leads to cost savings when the finished product is shipped or packaged. They are also more reliable than rigid circuits because they can be manufactured with a thinner material that dissipates heat faster than most rigid materials. The lower mass and ductility of a flex circuit also reduces vibrations that can cause stress on the solder joints.
The flex circuit manufacturers you work with will have their preferred file formats, which typically include Gerber and DXF. Many flex circuit producers will also accept newer standards such as IPC-2581 and ODB++, which incorporate more design information. If you have questions about which file format your flex circuit manufacturer prefers, it is best to discuss this with them before beginning the design process.