Seeed Studio Flexible Circuit Board service - Page 1
Forum section: electronics / general

author: dingari
author_rank: Contributor
timestamp: December 02, 2016, 07:46:23 pm
content: Hi, I posted on the electronics subreddit this morning but got no attention, so I want to try my luck here.TL;DR: Not satisfied with Seeed Studio FPC, suggestions on alternatives?I've been using Seeed Studio's Fusion PCB service for quite some time now, and have always been satisfied with the quality of boards vs. price. I tried their flexible printed circuit (FPC) service and can't say the same.The first assembled board had a short to ground from the 3.3V rail. I inspected every solder joint for bridges but couldn't for the love of all holy find the culprit. I figured I'd just assemble another one and see if I'd experience the same issue. Top layer? all good. Now for the bottom layer... wait what? There's soldermask covering half of my micro-usb footprint!Then I started inspecting the other boards and found soldermask issues on other ones as well:That's when I started thinking the shorting issues were a cause of poor manufacturing. I measured the 3.3V output on all the other boards and found that a part of the ground plane next to the pad was exposed, and lead to solder bridging over. This could be found on other pads as well.I managed to find one defect-free board to assemble, and it works fine. But one board out of ten is a really poor yield.I checked to make sure I followed all specifications stated on their website. Then I emailed them and got the response that " the problem was due to  manufacturer process limit.", and they offered me a refund.I applaud them for taking the time to look into it and admit the fault. But I was really just hoping that this was a one-off faulty batch and they'd send me a new one. Especially since the soldermask issue looks like something just went wrong with the machine for a few seconds.Now I need to find a new place to get FPC's made. Have you got any suggestions? I'm tempted to try Itead Studio but I suspect they're using the same manufacturer as Seeed Studio.

author: timb
author_rank: Super Contributor
timestamp: December 03, 2016, 12:12:40 am
content: That's a soldermask issue, not silkscreen.That's also a lot of copper for such a small FFC... What's the intended use of these boards? It's so densely packed, I can't see it taking much flex anyway...

author: dingari
author_rank: Contributor
timestamp: December 03, 2016, 12:35:39 am
content: Quote from: timb on December 03, 2016, 12:12:40 amOh yeah, my mistake, I meant soldermask.It's really only intended to be bent in two places, so it's more segmented than fully flexible. We kept it purely flex for reduced overall thickness.This is for a small device that goes on your index finger.

author: mrtn
author_rank: Contributor
timestamp: December 14, 2016, 07:38:20 pm
content: Flex PCB are usually really expensive to get good quality.I've only used full-feature companies like Sanmina for flex because it's usually pretty important that they come out correct.http://www.sanmina.com/contract-manufacturing-design/printed-circuit-boards/I can find some more options if you're interested in hearing about them (none are inexpensive)

author: thm_w
author_rank: Super Contributor
timestamp: December 15, 2016, 01:34:17 am
content: The soldermask on the USB connector is crazy, surprised something like that can happen.In the second photo it looks like they are forced to do a round cutout in the soldermask where the pad is (mistake or on purpose?). So its a compromise to not cut into your plane and also have the pad clear. I would widen up the plane clearance to pad, what were your rules? (their spec is 4mil, and clearly you were within that). Maybe consider rounded rectangle pads as well.Some old reviews:https://ssj3gohan.tweakblogs.net/blog/9815/iteadstudios-flex-pcb-quality.htmlhttps://www.eevblog.com/forum/reviews/iteadstudio-fpc-mistake/

author: KL27x
author_rank: Super Contributor
timestamp: December 15, 2016, 07:20:12 pm
content: QuoteYeah, that's poo. OTOH, I think some of the others have only minor issue. Useable as-is, or perhaps with help of exacto knife?For prototype, I don't usually use more than 3 of these boards, anyway. Bonus, maybe all this error shows you potential areas of improvement with your layout if you need higher quantity. Keep in mind that soldermask on flex pcb is laminated onto the board, not sprayed, like with regular pcb. I would not be so fast to write them off. I think you will have a hard time to find better price than Seed/Itead. They must be panelizing your board with other boards to get this price, and must make your board in one-go, on the soldermask, along with the rest of the panel. If taken to mass production, manufacturer will find better way... or at least they will mark off the bad boards and you will get final quantity you ordered. Use your salvageable board(s) to verify your own work and for firmware dev and component tweaking. And even the electrically bad boards are still useful to verify housing/assembly and other production concerns. Since 1/10th cost of most other places, I think is still perfect for verifying prototype. You aren't going to use Seed/Itead for production, anyway.I prefer they make 10 boards, cheap, with bad quality control, than to increase cost to give 10 good boards. Most people don't need 10 good boards for single prototype revision. That over-quantity serves as the quality control.

author: jt
author_rank: Regular Contributor
timestamp: December 18, 2016, 02:10:38 am
content: I ordered a 2-layer flex from Itead with 2-mil spacing (this was within their published design rules). The yield was awful and they preemptively gave me a refund. This didn't come as a surprise, but for the price point I figured it was worth a try. This was ~3 years ago so maybe the situation has changed.You might find you'll need to open your budget up quite a bit to get good quality on low volume runs. Within the U.S., I found a company called AltaFlex that seemed to offer significantly lower prices than others (still much more expensive then the Chinese options however). I've given them around a dozen jobs and have been very happy with the results. I notice they were recently acquired by OSI, so hopefully that doesn't change anything for the worst.http://www.altaflex.com/

author: Kelbit
author_rank: Regular Contributor
timestamp: December 25, 2016, 03:06:33 am
content: Flex boards are tricky. I recommend taking a look at the IPC standard for flex PCBs (IPC-2223), it really covers a lot of the caveats.A couple of rules I work by:Involve your PCB manufacturer as early as possible in the design process. The flex manufacturing process varies a lot more between manufacturers than typical rigid boards, so each board house will know what they're capable of. Often the board house can recommend a stackup for your application. Plan for a couple of gerber revisions before the first articles based on board house feedback.Figure out the the IPC recommendation for minimum flex for your stackup (formula for this is in IPC-2223), and follow that minimum religiously. Keep in mind the continuous flex vs. flex-to-install have different minimum bend radii. Don't let your mechanical engineers or industrial designers browbeat you into breaking this rule - give them a minimum and tell them that you can't exceed that.Use redundant traces wherever possible, especially over sharp bends. This way if one trace tears, there's still another for electrical connection.Use curved traces wherever possible, as this reduces local stress concentrationsStrongly consider doing your initial production "locally" (ie: on your continent). If you're outside of Asia it'll be much more expensive, but you'll have local design support and you won't be dealing with a huge faceless fab in mainland China that couldn't care less about your tiny volumes.Unless it really is cost prohibitive, do 100% e-test. Flex boards have low yields, especially high density ones. Most flex products are high-value, so the extra cost of e-test is worth it.