Via on flat-flex - Page 1
Forum section: electronics / general

author: CM800
author_rank: Frequent Contributor
timestamp: November 05, 2017, 06:16:10 pm
content: I'm looking into a project where I need to put some inductors on a flat-flex cable (pcb inductors)is it possible to do a 2 layer flat-flex with a single via on it? the whole thing needs to be flexible as this is a wearable clothes style concept.how do they do the RFID coils that are flexible?The width of the active / inductor area would be around 10x10mm

author: wraper
author_rank: Unknown
timestamp: November 05, 2017, 06:24:35 pm
content: Vias are not a problem to make.

author: CM800
author_rank: Frequent Contributor
timestamp: November 05, 2017, 06:29:04 pm
content: Quote from: wraper on November 05, 2017, 06:24:35 pmon the flexable part of a flat flex? (there won't be any rigid on it, beyond the part at the connector)

author: wraper
author_rank: Unknown
timestamp: November 05, 2017, 06:37:39 pm
content: The only concern is cost. However at small quantities there should not be much difference.

author: CM800
author_rank: Frequent Contributor
timestamp: November 05, 2017, 06:42:37 pm
content: Quote from: wraper on November 05, 2017, 06:37:39 pmWho would you recommend?and got any idea of how much I'd be spending for:8x8mm square flat-flex double layer (with a via)and a 3-4mm trailing lead about 300mm longtotal: 8mm x 250mm long. I'd imagine ordering 10 for sample.an alternative design would require a single flex pcb of 150 x 250mm

author: wraper
author_rank: Unknown
timestamp: November 05, 2017, 08:04:52 pm
content: pcbway has online calculator to estimate the cost.https://www.pcbway.com/flexible.aspx

author: Mr. Scram
author_rank: Super Contributor
timestamp: November 06, 2017, 07:18:14 am
content: Quote from: wraper on November 05, 2017, 08:04:52 pmThat seems to be quite a bit cheaper than last time I looked. That's cheap enough to have some prototyping fun with.

author: CM800
author_rank: Frequent Contributor
timestamp: November 06, 2017, 07:34:50 am
content: Quote from: Mr. Scram on November 06, 2017, 07:18:14 amIndeed, looks good to me too!Cheers wraper!

author: KL27x
author_rank: Super Contributor
timestamp: November 07, 2017, 10:58:26 am
content: QuoteMy experience is the opposite. On my most recent orders of similar total area, for instance, FPC is 74 cents per square inch (w/ tab routing), and rigid 63 cents per (just scoring). More components on the FPC, to boot, but maybe a similar number of pads and vias.But if you want a prototype, you can get rigid boards made for like 20 bucks. I don't know where you can get that kind of price for an FPC in <10 quantity.Another thing about flex is you usually are making odd shapes which "waste" a lot of space, so it feels like you are paying a lot more per area, but the same would hold true if you did that on FR-4. The manufacturer I have been using essentially charges by the smallest rectangle that your board will fit into. If this is the case, you wouldn't want to go designing your board on a diagonal axis.

author: smoothVTer
author_rank: Regular Contributor
timestamp: November 08, 2017, 08:23:08 pm
content: If possible, put some via hold-down anchors so that the metal via barrel is held in place under the coverlay. This will help somewhat if that area of the via undergoes flexion. Something like this:Note that those "X"'s intersecting with the vias are both on top copper & bottom copper, so the via is help in place from top as well as bottom.

author: CM800
author_rank: Frequent Contributor
timestamp: November 08, 2017, 08:35:56 pm
content: Quote from: smoothVTer on November 08, 2017, 08:23:08 pmOh cool! that's precisely what I was concerned about. Good tip

author: KL27x
author_rank: Super Contributor
timestamp: November 08, 2017, 11:30:04 pm
content: I don't think you would normally make an opening in the coverlay for a via to begin with? And even thru holes with opening in the coverlay don't rip off very easy, IMO, unless you solder/desolder them several times. It's a cool idea, but I think it is probably not going to be necessary.IMO, there is no special concern with putting vias on FPC in an area of flex.

author: rx8pilot
author_rank: Super Contributor
timestamp: November 09, 2017, 02:31:12 am
content: Glad to see this conversation, I am starting my first flex design next week. After calling a USA vendor, price was a major concern.Short and misplld from my mobile......

author: Mr. Scram
author_rank: Super Contributor
timestamp: November 09, 2017, 02:52:14 am
content: Quote from: smoothVTer on November 08, 2017, 08:23:08 pmI'm obviously misunderstanding what you're trying to prevent here, by doing what. Could you elaborate?

author: noras
author_rank: Contributor
timestamp: November 09, 2017, 03:56:20 am
content: It is important to confirm that the supplier can do it,good luck

author: KL27x
author_rank: Super Contributor
timestamp: November 09, 2017, 04:26:58 am
content: QuoteYou have made your first mistake.There are USA manufacturers, and I think they stay in business from aerospace and medical (I.E. nepotism and corruption.) Even these guys, I wonder if their value is more in the design side and for the assembly/inspection/testing and overall quality control part of the actual manufacturing process, things like expertise in setting up lines for odd ducks like assembling flex-rigid composite boards and x-ray inspection and stuff like that.There are USA based companies who make your board, who have "affiliations with" overseas manufacturers. I.e., they take your Gerber and do the insanely difficult job of ordering the board (joke). And they can provide some real value, maybe, by assembling your boards for you.In my search, I have found no legit manufacturer of flex in the USA that I would consider using unless I was spending someone else's money and a company rep was taking me out to strip clubs.Unless the assembly and inspection and testing is something you can't quite figure out how to relay without meeting and going over in person, you probably don't have anything to gain from trying to find a US based company.The biggest difference between flex and rigid is that small prototyping quantities are much more expensive. So you will spend a few bucks figuring out the physical properties and what you can and cannot do.Also, I have heard first-hand from people who have designed boards in a way to nest together in order to save space/money. This might be a viable loop-hole for a given quantity/company. But they do not cram the panel with boards, like they do with rigid. If you submit a panel the same way you do rigid, it will be rejected. In short, don't spend much time trying to optimize space usage until you get a feel for what is acceptable. At first, I would focus more on getting the board into the smallest rectangle as possible. Perhaps, more detailed way to say it, if you can get maybe 2 boards to nestle together into a smaller rectangle, that might work. Then they will put a huge space between these. But if you design a board that has to nestle together across the whole panel, you wasted a lot of time.

author: rx8pilot
author_rank: Super Contributor
timestamp: November 09, 2017, 05:33:42 am
content: Quote from: KL27x on November 09, 2017, 04:26:58 amPretty crazy, indeed.Wondering if a house like PCBway can help with high-speed stuff like USB3 and other interfaces - getting impedance controlled designs right.

author: KL27x
author_rank: Super Contributor
timestamp: November 09, 2017, 05:38:58 am
content: Heh, no idea.*Also, I should clarify. When I said prices were not much different from rigid in higher quantities, my experience is with small board, and I accept x-outs in a panel.If you were doing larger boards and/or not accepting x-outs, your prices would probably shoot up. I believe the error rate is higher in flex. I can see a pretty high number of x-outs, considering my pitches. A lot of etching shorts which are probably more common because of the flex in the material in the tank. Also, I am quite forgiving of my manufacturer on overlay/mask alignment on the boards I have made so far. This error is pretty gigantic compared to what I am used to on a rigid board. But if I can get the parts on there, it's good enough for me.*I have used ITEAD for prototypes. I can't remember exactly, but it is on the order of 100.00 for a 10 small FPC. I think once you start doing dialog back and forth with an overseas manufacturer, I they are already going to shoot your price up, expecting a headache. I have seen my prices for flex drop over the years. I do check with other companies once in awhile, and I ask for a requote on occasion, if I use the same board for a long time. But if you pay money and don't give any trouble, you are an ideal customer, lol. American customers are the most expensive in the world, IME, statistically speaking. My GF is the prime example. She finds people to give her special treatment in everything. I think a Chinese manufacturer will either drop her as a customer or just smile and nod while charging her triple.

author: rx8pilot
author_rank: Super Contributor
timestamp: November 09, 2017, 05:42:35 am
content: Was your design 2 layer? It seems that multilayer explodes the price of flex.

author: KL27x
author_rank: Super Contributor
timestamp: November 09, 2017, 05:47:42 am
content: ^Yes. I have never designed a board over 2 layers.

author: KL27x
author_rank: Super Contributor
timestamp: November 09, 2017, 06:49:06 am
content: Oh, almost forget. And I still forget this on my own boards:Wherever you have pads at a place that flexes? The place where the pad meets the trace (this is a confluence of coverlay and no coverlay, and between big pad and little trace), this is where the traces will break under flex. This leaves a microtiny fracture and can cause intermittent continuity. Where possible, thicken up the traces next to the pads to protect from this. Esp if you have to put a lot of holes in the coverlay which make a straight line across a part that bends, which concentrates the bend in that spot. Actually, the holes in coverlay might be more important than the thickness of the traces. So, for instance, if you have a couple of connectors on one end of the board, you might consider staggering them. At least take a look at your mask layers to avoid any obvious hot spots. (The resolution of the coverlay is also a lot lower; on an IC, for instance, you are probably going to get one big rectangular cutout for a row of pins). If you have other side bare, you can specify a "stiffener" where needed. Just put it in a Gerber.