Rigid-Flex vs Flex with stiffeners - What is the practical difference?
Looking at Flex-Rigid PCB technology vs Flex PCB with added stiffeners under sections with components I struggle to see the advantage of Flex-Rigid for low layer counts, as it seems more complex to manufacture and is more expensive as a result.
There is a lot of information online explaining what Flex and Flex-Rigid is, but I could not find many discussions about the advantages for one over the other, just some claims like 'Flex-Rigid is more reliable' without explaining how or why.
The only thought I had was that rigid allows for high layer count. Is there more to it, could someone please explain with some real world examples when one is more appropriate than other and why?
Edit: Let me expand on the definitions of Flex-Rigid and just Flex with stiffener.
Flex-Rigid:
Flex with stiffener:
So in the Flex-Rigid case flex part is integrated in rigid part, whereas Flex with stiffener is just a polyimide with FR4 or similar material to reinforce certain sections, but the stiffener itself does not provide electrical connections.
2 answers
Flex with stiffeners
The main purpose of flex with stiffeners is to be able to place SMT components onto the flex board. Without a stiffener a flex has a somewhat undetermined shape, and pick&place would miss the pads. The components can be placed only on one side of the stiffener. The amount of components on such assemblies tends to be small. Typically they're cables-like with few component: connectors, LEDs, sensors.
Historically flex with stiffeners appeared well before flex-rigid.
By the way, it’s also possible to have metal stiffeners which can conduct heat.
Flex-rigid
Consider the flex-rigid as rigid PCBs which can bend in some places. It's a rigid PCB first. All of the technology available for rigid PCBs is also available for flex-rigid (microvias etc). Components can be mounted on both sides. Flex-rigid is used when space is very constrained. Often the rigid sections are larger than the flex section.
0 comment threads
This is really something you should be asking your board house. I am not convinced the various terms for combinations of flexible and rigid circuit boards are all that standard. There may well be variations between processes.
Just from the images you posted, it looks like what you call "flex-rigid" has the polyimide layer extending thru the whole board. Those then become the inner layers of the rigid part, which adds its own outer layers.
Your "flex with stiffener" process looks more like rigid fiberglass glued onto a flex board for mechanical strength in selected areas. That could be useful for mounting, for example.
"Flex-rigid" seems like it's better if the flex board has to have components mounted on it. A flexing board with rigid components is is going to fail. Basically, the flex parts are flexible interconnects between rigid boards with parts on them.
I would evaluate each case separately, and not be afraid to talk to the board house about tradeoffs and options.
The one time I did a mixed flexible and rigid board was for something that basically needed to be flexible, but with a connector solidly mounted at one end. I don't remember what marketing terms the board house used to describe the process. The solution was arrived at after a back and forth discussion with one of their application engineers.
0 comment threads
1 comment thread