Flexi PCB’s and making something wobbly like it’s not

Just like standard rigid PCB’s flexi’s and flex rigid PCB’s have to have components assembled onto them to make them useful in a circuit. However unlike rigid PCB’s flexi’s are well… flexible.

The flexible nature of a flexi is it’s strength in the field, but during manufacture causes nothing but problems! There are ways and means around this and that’s what’s going to be discussed here.

Part of the issue is that the fabricator needs to make the FPCB’s on a rigid panel that the assembler can accept and work with. In prototyping volumes this isn’t likely to be an issue, but if thousands or millions of FPB’s are to be made then there has to be a solid working interface between the fabricator and assembler to make it work optimally.

PCB’s are usually more efficient to assemble in larger volumes on a panel. Flex panels tend to have less circuits on them and a smaller as the panel, even with stiffeners are often weaker. If there are components on both side of an FPCB, then making the panel so that solder paste can be deposited onto the board also needs considering. Often stiffeners or panels sit above the FPCB, making paste deposition impossible. It’s for this reason that good communication is needed between designer and fabricator to get every detail right

Be warned – making a the same design in different companies can result in different approaches and things going wrong. Because there is so much more for the manufacturer to understand than rigid PCB’s like stiffeners, panels etc, there is more to get wrong.

Layer stackups are also something to watch out for, especially between different fabricators and sometimes different factories within the same company. The differences are often very minor and irrelevant but even small differences can have an effect on a design – especially in high speed circuits.

Good fabricators will highlight these changes and give their best alternative so keeping track of what’s being built can be done.

The nightmare every PCB designer needs to consider in FPCB’s is how any components will be assembled onto the board. If the flexi is on a panel this is a good first step, areas where components need to be assembled onto them will need to be secured or assembly will be impossible.

Fabricators will have tape or some other kind of way to secure
Component area’s on FPCB’s. Identify these area’s in the output data and label them to make it easier for the fabricator to identify these areas and process them accordingly. Doing this will make assembly far easier – the only problem after this might be peeling the flexi away from the panel without damaging the components or their solder joints.

It’s for this reason that assembling components onto FPCB’s should only be done when it absolutely has to be done.

If you’re not putt off yet, you should be – no one said it would be easy!

Circuit Mechanix © 2016

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