A 36" long board will cost plenty. But, there are workarounds.
I have need for a long flex cable (~36"). I sent for quotes, and they all came back as “no-bid.” Are long flex circuits really that much more difficult to build?
Long FPCs are more difficult to build. There are a lot of reasons for this. This month I will cover each, with possible workarounds.
Raw material size limitations. If your bids are from US-based manufacturers, they are probably getting their raw copper-clad materials in 24" x 36" sheets (unless special ordered). So even if the manufacturer makes its processing panel size 36" long, a 36"-long FPC would not fit unless it was run diagonally, which is not practical from a cost perspective. You may want to see if the fabricator is willing to purchase materials from Asia, which typically are delivered on long rolls. This would solve the raw material issue, but not any of the processing issues (covered later).
Also, most FPC suppliers use two or three standard panel sizes for virtually every circuit they make. These standard processing panel sizes are driven by raw material sheet size and the fabricator’s equipment and processing limitations. All a fabricator’s tooling and fixturing is set up to support these two to three standard processing panel sizes. This does not mean no fabricator is willing to run a non-standard processing panel, but rest assured, you will pay a hefty premium for it. A few US flex suppliers have developed the equipment and processing techniques for extremely long flex circuits and may be best suited for an application like yours. The downsides are your vendor base will be very small, and since super-long circuits are a very specialized product, they will be expensive.
Equipment limitations. Most PCB processing equipment has size limitations in both width and length. Some pieces of equipment such as etchers or resist strippers can run unlimited lengths of panels or materials and are restricted only in material width. Unfortunately, these are the exception, not the rule. There are processing techniques and tricks to get around these limitations on many pieces of equipment, but all come with associated processing yield impacts. Examples are:
While all these methods will work to process extra-long material or panels, a limited number of FPC vendors are willing to incorporate them, unless this is a very high volume or very high revenue project.
If your application does not have enough volume or revenue to interest manufacturers you contacted, try these design options to (hopefully) meet your requirements without pushing the processing limits of potential suppliers:
All these options have some drawbacks, such as changes in the circuit profile in connection areas or the added bulk of discrete wires. These may or may not be a problem in a given application. If a single, continuous flex over 30" long is still needed, the best bet is probably one of the flex shops that specializes in this type of product. If you have a “go-to” flex vendor, have a conversation on your specific needs. That vendor should be able to tell you quickly if it is something it can support. If not, it should be able to steer you to a fabricator more suited to build very long flex circuits.