In general, what happens if a PCB house totally screws up your big $ PCBA job? - Page 1
Forum section: electronics / general

author: Psi
author_rank: Super Contributor
timestamp: November 08, 2021, 07:25:33 am
content: Don't worry, this has not happened to me yet.But I do have a rather costly (at least for me) PCB order coming up and I was just curious what actually happen in the case of a total screw up by the PCB/PCBA fab.Lets say an inner layer VCC to GND short in 50 places (their fault). Something that is not fixable in any way.You get delivered 250 boards with $40k of parts on them that are totally useless.For the purpose of this discussion we will assume the PCB/PCBA fab is in china and you are not.What happens?

author: nctnico
author_rank: Super Contributor
timestamp: November 08, 2021, 08:03:19 am
content: You wish you paid extra for electrical testing of the PCBs... don't skimp on that. If it is not specified then ask for it.What you can do yourself is to add an extra 3% of margin to your PCB design; don't make the traces as thin as the production process allows but make them a little bit wider. Same goes for minimal distances, annular rings, drill sizes, etc, etc. Where you don't need minimum widths / holes sizes / distances, make then bigger.When I order expensive boards for the first time, I let the assembler make 2 prototypes which I test thouroughly before giving the go-ahead for the rest of the boards. However I work with local assemblers only. For 250 boards there is no use to go to China and take chances.

author: AndyC_772
author_rank: Super Contributor
timestamp: November 08, 2021, 08:23:04 am
content: This is why you order complete, assembled PCBAs from your supplier, and let them procure the bare boards themselves. If they arrive with fabrication faults, which mean your components are wasted, it's 100% on them.If you buy the bare boards yourself and free-issue, your assembler is not responsible for them. If they turn out to have faults, you may be able to recover the cost of the bare boards from the fabricator, but that's all. You'll end up eating the entire cost of parts and assembly yourself.Changing track and gap sizes really won't make any difference; a scratch on a photo plot will easily break multiple traces whatever their geometry.Bare board electrical testing is absolutely mandatory, but still not a guarantee the boards are good. My company once found a ~25% failure rate in a batch of assembled boards, which was eventually traced to a scratch on one copy of the artwork for a PCB which was made 4 up on a panel. The moron doing the testing had decided to exclude the affected trace from the electrical test 'because it was always failing'.

author: tszaboo
author_rank: Super Contributor
timestamp: November 08, 2021, 09:28:52 am
content: There are a few things you can do to avoid this:1) Dont order from China, order it from a local fab where you have contractual agreements.2) Let your assembly house order the PCBs3) 100% electrical test, and prototypes. Order the prototypes from the same factory and process as the production.I had PCBs in the past, that were faulty. It a question of when that happens, not if, when you done over 100 projects. It was caught before assembly, sent pictures to the local PCB fab, they sent new PCBs in 2 days, free of charge.I also had messed up gerber files, which got corrupted during export. So get prototypes. It's going to cost more for each projects, until you find a mistake, and then it suddenly doesn't cost more.And get used to the pressure. Usually I handle projects that cost several times my salary, only way to get good jobs. Get somewhat detached, "This is someone else's money". It is not worth to loose sleep over it. On the long term this is more healthy. Just let your managers have the final say on where you order from, and how to protect against failures, and if something goes wrong, you can always raise your shoulders and say that they decided.

author: jmelson
author_rank: Super Contributor
timestamp: November 08, 2021, 04:33:17 pm
content: Quote from: Psi on November 08, 2021, 07:25:33 amMake sure the PCB fabricator does a full electrical test. That should catch any such defect in the board.

author: Jester
author_rank: Frequent Contributor
timestamp: November 08, 2021, 05:12:12 pm
content: Never order a multilayer board without 100% electrical test.I have yet to get a really bad board from China, quality seems to be as good or better as the affordable PCB houses we use in The Toronto area.Some shops are fine for simple boards but simply can’t produce reliable complex boards. So you need to figure out where you can save a few bucks and where it will cost you if the boards are not 100%. Same thing applies to population, some shops have iffy yields with dense BGA type boards.We did get plenty of sketchy boards from low cost PCB houses near us. If you get burned once by a low cost supplier don’t give them a second chance in my experience things don’t get better.

author: nctnico
author_rank: Super Contributor
timestamp: November 08, 2021, 10:51:54 pm
content: Quote from: AndyC_772 on November 08, 2021, 08:23:04 amIndeed. But it can still lead to issues; the assembler will do anything to put the blame on you. In the end the cost of the lawyers may not be worth it.QuoteI have to disagree. Manufacturing a PCB is still a lithographic and chemical process. Uneven distribution of copper can lead to problems causing uneven etching. PCB manufacturers prefer that boards have an even distribution of copper and that as much of the design as possible is not at their process' limits. This will get them a better yield and you as a customer a board that is being reproduced more evenly.

author: VK3DRB
author_rank: Super Contributor
timestamp: November 13, 2021, 07:31:25 am
content: Bare board electrical testing is the way to go. Not that much more expensive. These days, I opt for bare board testing, especially on 4 layers or more. For simple two layer boards, I might forego bare board testing if it is cost sensitive and there is functional testing down the track (excuse the pun).This brings to mind two stories that may be of interest:In the early 1990's, I had a PCB with a bug. I tracked it down to roughly 200 ohms resistance between two parallel tracks 2oz copper spaced about 0.3mm. The resistance was proven to have nothing to do with connected components. Optically under a microscope, the PCB looked fine - nothing seen. But running an Exacto knife between the two tracks cleared the resistance. I have never seen this weird phenomena on any other PCB in my life. I cannot explain how with copper you can get 200 ohms resistance from a lack of etching over such a short path.I did a design for a tiny RF board recently (1.7GHz). The board was around 25x20mm, double sided only, packed with tiny components down to 0201's. It was very challenging because the insertion losses had to be incredibly low and the hand soldering was bloody near impossible. Ten samples of therawPCB from Speedy in Taiwan cost $800. A big cost factor was impedance control and of course bare board testing was included. Could have got the boards from China for 1/5 of the price, but there was no room for any variances or mistakes, so Speedy in Taiwan was the place to go. Ironically, Speedy is not speedy, but a little slow. However, they are VERY thorough, they use Valor reports and produce top quality.In general, you get what you pay for.

author: Psi
author_rank: Super Contributor
timestamp: November 13, 2021, 08:59:27 am
content: Quote from: VK3DRB on November 13, 2021, 07:31:25 amBare board e-test wouldn't pick up if the board house accidently changes your gerbers, which is more the sort of total screwup i was thinking of.

author: AndyC_772
author_rank: Super Contributor
timestamp: November 13, 2021, 09:06:11 am
content: I've had them changed deliberately on more than one occasion. Normally I take it as a not-so-subtle sign that a particular vendor never wants to work for me again - but even so, it's not as rare as you might hope.

author: Psi
author_rank: Super Contributor
timestamp: November 13, 2021, 10:13:29 am
content: Sometimes it's an honest mistake because they need to convert your gerbers into the final set of files that their fab machinery uses.

author: AndyC_772
author_rank: Super Contributor
timestamp: November 13, 2021, 08:48:11 pm
content: That may be true, but I'm specifically thinking of a few "WTF?" examples that were deliberate, and definitely not just bugs in format conversion.