Common Mistakes Made By Pcb Designers While Designing A Flexible Circuit

Flex circuits are typically considered as the advanced form of PCB circuits. They are the ones who are gradually replacing the PCB model and since they have an interconnected market it is not difficult to find a PCB designer actually working on a FPC application. However given the inherent difference between the two designs, there is a big scope of differences which can be made by a flexi- circuit designer.

Let’s look at some of the basic mistakes which are common in this arena

Tolerances

Designers often make a big mistake when it comes to tolerance definition. PCB has a more stable and glass weave design which is missing in FPC. Most FPC’s are made from polyamide which is very robust but not at all stable like the FR4. In FPC’s tight tolerance levels are not required and designers are comfortable accepting the stretch and shrink experience in FPC.

If there is any area which requires tighter tolerance, the requirement can be added to the FPC design. Another big difference with PCB lies in the fact that it is not easy to be trimmed like PCB’s. FPC’s requires some type of punch for pallet renewal

Covers (SMOBC) — The big mistake occurs in the area of design where the designer used a similar design for FCP fabrication as well as in the area of Solder Mask Over Bare Copper which is commonly known as SMOBC. Ideally a polyimide cover should be used which can be levered or punched and still requires some kind of width between pads for stability.

Artwork Features

FPC’s have an ability to bend and create various kinds of issues for copper conductors, which is typically missing in case of hardboards. A forgotten fillet pad does not create much of an issue for a PCB. However when it comes to an FCP design a pad fillet is an absolute must. The designers can also use cross-hatched shields for greater flexibility.

Assembly

A material from which a PCB is made is not at all moisture absorbent. On the other hand polyamide used in FCP’s reacts favorably with moisture. Apart from this featuring is also important for a flexible circuit, as it goes through high temperature areas. PCB’s are usually stiffer and the rails are often considered as part of pallet design. FCP’s on the other hand is constantly requires a conveyance to support the body

There is nothing to feel intimidated with this long list of mistakes. Instead realize the fact that FCP’s have many characteristics which can offer you much more cost and time saving options.

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