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Rigid/flex CCA modeling

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Rigid/flex CCA modeling

I am looking to model a rigid/flex CCA. I was hoping to model the board and flexes as one entity all flat and then fold it up. The problem I am having is that the rigid areas and flex areas are different thicknesses so when I try to convert to sheetmetal it doesn't work. Any ideas on how to make this work?

Seems if I make the rigid areas and flex areas all different parts and assemble them, they loose connection when I bend them.

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Re: Rigid/flex CCA modeling

I have successfully created my rigid flex using family tables. It works fantastically and it is very easy to determine the flex lengths. Each rigid board was modeled and the parts were added via IDF export from Mentor Graphics. Each flex was modeled and converted to sheet metal. The boards and flexes were assembled. The family table allows me to have versions bent, flat, and with and without the parts. It is great. I bit of setup to define each table entry, but not bad. The only thing I found annoying was it would not allow me to select all the components on the board and add them to the family table. I had to do them one at a time. If you have a board with a lot of parts, that would be a pain. Would be nice if it would take them as a group. I did not see how to do that.

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Re: Rigid/flex CCA modeling

You cannot thin sheetmetal and have it remain a sheetmetal feature where it understands what you did.

There is Spinal Bend for flexures... and now we have Warp. Setting up flexures is not simple, but you can fool the system in many ways... including intelligent sections that allow for the deviation where the assembly can control the next level state with flexible component settings.

It all depends on what you want to do, but I suspect in your case, sheetmetal is not the right choice.

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Re: Rigid/flex CCA modeling

...and what is CCA?

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Re: Rigid/flex CCA modeling

Circuit Card Assy.

Flexible boards are a problem to model as you are capturing the behavior of a complex assembly of various materials. It's a composites stress analysis problem, though the properties of the component materials are uniform, the distribution of copper, reinforcements, attached components, and vias make it far from easy. Much cheaper to build and test.

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Re: Rigid/flex CCA modeling

That's a new one on me... PBA is the acronym I grew up with along with the fabrication, PCB.

The few flex circuits I've designed were done as assemblies to allow for the composite properties. When it came to "flat layout" and as-used configuration can be done one of many options. I'd still have to give serious thought to using sheetmetal to form the flexible sections over more conventional methods. To me, I would treat it more like wire assemblies. What about using the Ribbon feature?

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Re: Rigid/flex CCA modeling

I think you all are missing my point. I don't care about the board properties. We are interested in how long the flex areas need to be to fit in the housing the way we want and to make sure nothing is overlapping once folded up. I suppose I can just make the flex thick, same as the rigid area. It will throw the bends off a little, but probably not enough to matter. It just seems that if I have a string of boards and flexes I should be able to bend in the flex area, or board area... as long as I don't cross a thickness boundry.

Additionally, I would like this to be the master that I can then export the board outline from since it will be absolutley correct. Right now we hve to have each rigid board as a seperate assembly and then assembly them all up into the stack. Then I draw the flexes in so I can measure the lengths. This then gets feed back and the original gets corrected for the new lengths. Lots of room for error and a pain in the butt.

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Re: Rigid/flex CCA modeling

This is not something that PTC supports. You can sort of make something like it with a spinal bend, but a spinal bend doesn't (yet) conserve sizes. It can bend a 1 inch long straight part into a 3 inch diameter circle.

Also, I've done this job before. It's better to build a physical mockup because you can't simulate what you are after with the tools that are available.

Funny story. Some EEs figured flex-print will work, so lets just do it. Built up a 6 layer board and were surprised it didn't flex anymore. Just don't want you to be like those guys.

added "yet"

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Re: Rigid/flex CCA modeling

Actually, that's incorrect David. You just need to make sure that the total length of the curve you want the spinal bend to follow is the same length as the original part ("volume to bend"). For the sketch of the curve I want the spinal bend to follow, I use a perimeter dimension, and write a relation to force that length to be the same length as the object. You can use an existing dimension and then write a relation at the part level to control it, or, what I find better, is to create a reference dim at that sketch level, and write the relation there. Then you can see exactly the curve it will follow right there instead of having to do a regen. Try it!

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Re: Rigid/flex CCA modeling

I said the spinal bend doesn't conserve lengths, not that the user couldn't take measures to force the spinal bend to do so. This is unlike sheetmetal where lengths are conserved subject to the application of stretch formulas.

Length conservation isn't part of a spinal bend, though the presentation someone put up here today suggests it was a feature considered for Creo 3 back in 2012. Maybe the conservation option will be available in a future release.

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Re: Rigid/flex CCA modeling

That would be nice. I've been careful using it to make sure the lengths are correct. That was a problem when I, and some others here, first started trying to use them.

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Re: Rigid/flex CCA modeling

My point was that you can do some things in Creo to help make sure the part is reliable in both the flat state (design state) and installed state (drawing state). You can also do this in a single part and you can have relations to ensure the routed state is the the same size as the flat state. However, no matter how you want to tackle this issue, it will be a lot of planning and work. The good news is that you can build in a whole lot of associativity.

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Re: Rigid/flex CCA modeling

So I lost track here. Whole lot of stuff I don't understand. Being an EE and just dabbeling in mechanical stuff. Soundsl ike the bottom line is that there is no way to use sheetmetal mode with a part that varies in thickness. Is that a fact? Sounds like I might be able to do something with a spinal bend (I assume this is not a sheetmetal mode) I have not seen that option yet. My company is too cheap to buy the training and our initial technical support ran out so I'm grasping for straws here.

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Re: Rigid/flex CCA modeling

It's a basic feature. IN WF5 it;s under insert/advanced.

You create a curve that represents a path to take and then specify two planes which bound the material to bend. If the distance between the planes is not the same as the length of the curve, spinal bend will shrink or expand the material to fit.

Its interesting to use, and OK for pictures.

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Re: Rigid/flex CCA modeling

This sounds interesting. I will have to play with it.

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Re: Rigid/flex CCA modeling

You have to be VERY careful about the "volume to bend". Say you have a straight part, and only want to have a small jog in the middle, so, you do the spinal bend in the middle......only to have Pro/E cut off both ends. You must include the entire part as the volume to bend in between the planes, and as mentioned the 2D/planar (not 3D) curve must be exactly the same length as the overall length or you get stretching/compression. I also WISH you could use it on assemblies at an upper level assembly level above that. Think cables drawn flat (for the dwg), then routed at assembly using a 3D curve.

Maybe creo 4?

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Re: Rigid/flex CCA modeling

We have modelled a few rigid-flex pcbs and we are still developing the process but we do it as follows:

-The flexible "core" (around 0.3 mm) is modelled with a sheetmetal part. It can be created as sheet metal or as solid and converted. This part has 2 instances, one bended and one flatten. Control Y parameter or bend table (quite complex) to have the right bended-flatten lengths.

-Rigid areas (thickness around 2-3 mm) are modeled as independent solid parts

-The sheet metal and the rigid parts are mounted in an assembly with standard mate-align restrictions. This assy has again 2 instances, for bended and flatten.

-The ECAD areas to output are added to the sheetmetal "core" part after the "unbend" feature (this is, flatten). Note that "flat pattern" does not allow to to it that way, but the "unbend" feature does.

Several things can go wrong, mainly the rigid parts not following the constraints when the assy is flatten, but with the right restrictions it works!

Creo does not have the right tool to design these pcbs but I guess they will make it soon, and it will be somehow similar to the sheetmetal module. I think Catia 6 already has it.

Hope it helps

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Re: Rigid/flex CCA modeling

Thanks for the detailed reply, Carlos.

I suspected this was the case.

Good to see someone has refined the process to the level you have.

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Re: Rigid/flex CCA modeling

I suspect that PTC's intent is to have you buy the cabling extension. Technically, the flex circuits are like ribbon cables with "connectors" on it. I don't know anything about the cable extension so I have no idea about the limitations.

Also, the "no way" is not technically correct since you can make the actual circuit part out of sheetmetal and assemble the rigid pieces to it.

Before you get to carried away with trying the spinal bend, you might look into the "ribbon" feature. I find it to be very user-unfriendly, but it might do what you want. It is the one feature they left inn core Creo to simulate ribbon cables. One limitation is that I believe it is a fixed width.

Dabbling in 3D and Creo are not a good mix. You will find that most people that use Creo and actually "enjoy" it are seasoned mechanical CAD users. For casual work, Creo would drive me up a wall. You have to have a pretty good understanding of the tools in the box to know how to best address a design challenge.

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Re: Rigid/flex CCA modeling

They always want to sell you a "module" for every little thing, don't they? I had to do a bunch of ribbon cable routings before they had ribbon capability in cabling. It worked out pretty well, though it was a pain to do, because I had to put a 180deg twist in it, and a standard VSS was radically distorting the wires cross-section. Had to get creative.....

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Re: Rigid/flex CCA modeling

I have successfully created my rigid flex using family tables. It works fantastically and it is very easy to determine the flex lengths. Each rigid board was modeled and the parts were added via IDF export from Mentor Graphics. Each flex was modeled and converted to sheet metal. The boards and flexes were assembled. The family table allows me to have versions bent, flat, and with and without the parts. It is great. I bit of setup to define each table entry, but not bad. The only thing I found annoying was it would not allow me to select all the components on the board and add them to the family table. I had to do them one at a time. If you have a board with a lot of parts, that would be a pain. Would be nice if it would take them as a group. I did not see how to do that.

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