First Spin PCB Success Rate - Page 1
Forum section: electronics / general

author: Fratink
author_rank: Contributor
timestamp: August 30, 2019, 08:26:39 pm
content: We just got a board back from assembly and after testing have found a few issues. We had been betting on being able to get the board right-enough to work first time (customer driven, not our choice).This led me to wonder, how often do others get reasonably complex boards (>2 layers) right the first time?

author: spongle
author_rank: Regular Contributor
timestamp: August 30, 2019, 08:42:52 pm
content: extremely rarely.and I don't even feel bad about it anymore, with how cheap PCB fab is these days it's much more economical to do a second spin than spend hours double and triple checking my design.pcb is the new breadboard

author: Kilrah
author_rank: Unknown
timestamp: August 30, 2019, 08:52:24 pm
content: Quote from: Fratink on August 30, 2019, 08:26:39 pmThat's a customer you don't want to have as it's pretty much a guaranteed losing bet.

author: CM800
author_rank: Frequent Contributor
timestamp: August 30, 2019, 09:37:23 pm
content: Quote from: Kilrah on August 30, 2019, 08:52:24 pmI do have one great story on this.We had a servo drive designed for us, very compact unit, eight layer, lots of components the company hadn't tried before...The first spin worked, near flawlessly, the only change that had to be done was some termination resistors for some RS422 lines...Impressed as frig with them.

author: Fratink
author_rank: Contributor
timestamp: August 30, 2019, 09:50:05 pm
content: Wow, that is really impressive. Those servo controllers are not simple. I love how they managed to get all the really hard stuff right but forgot some termination resistors though haha.Quote from: CM800 on August 30, 2019, 09:37:23 pm

author: Fratink
author_rank: Contributor
timestamp: August 30, 2019, 09:52:33 pm
content: Yeah.... New management team that doesn't seem to understand the engineering process as well as the old team did. Oh well, we told them the risks and they paid upfront.Quote from: Kilrah on August 30, 2019, 08:52:24 pm

author: Kilrah
author_rank: Unknown
timestamp: August 30, 2019, 10:02:58 pm
content: Quote from: CM800 on August 30, 2019, 09:37:23 pmNice!At work I'm currently working with external companies on 2 different designs for us, gonna be interesting how this pans out.One's a pretty standard low requirement microcontroller but with focus on high immunity aganst ESD/EMI and a need for very high ruggedness and reliability so isolated transceivers and protection diodes everywhere, and the other is just a micro taking some serial input and driving a display but there are tough size constraints and that display has bastard voltage and timing requirements that require a lot of high freq signals moving around so 6-layer, impedance and length-matched board...The first involves RS485 and CAN, will check the termination resistors twice

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 31, 2019, 06:10:09 am
content: Varies with the skill of the engineers responsible.I've completed many zero to one rev projects. Most often the rev is the one stupid thing no one caught in review, like swapped pins or signals (RXD/TXD), or a wrong size part, or something we couldn't have possibly foreseen because the customer decided they really need it done such-and-such way (which again tends not to be too big, it seems we're pretty good with our customer selection also).I've also worked on many boards bearing a "REV F" or something ridiculous like that. Some of that is due to product evolution, not so much the customer's fault, as something unforeseeable that they had to add support for, and mutating the current product is far better than creating a new one to replace it. But some of those are also due to inexperience of the customer, and we've been called in to clean up the design, or to add features that they know they aren't prepared to do by themselves.From a business standpoint, the amount of evolution a design can go through, depends on how complex it is, and how quickly it can be brought to market ("minimum viable" sort of things). If the prototypes are relatively cheap and quick to turn, and the engineering team is making good use of them, sure, multiple revisions are fine. If it's something hugely expensive like some kind of massive FPGA telecoms something or other board, you want to spend extra time and money, hiring experts, maybe even contracting outside reviews, to do it right the first time, or at the very least to do as much as possible the first round, learn as much as possible, everything needed to change in the rev, and then to be done.Or even further still: low quantity, mission critical hardware -- aerospace for example. You'll probably make, say, three prototypes: test one to hell, apply whatever changes are needed to the others, fly the one, and keep the other for on-ground testing. With such high demands on reliability, the engineering and review process may extend recursively to finer and finer degrees of the system itself -- not just PCB layout and gross mechanical design, but engineering of the soldering process itself, of connectors and wiring harnesses themselves, of basic materials like wire and insulation and plating. (A lot of which is already done, and public info by NASA, there for the reading, pretty amazing stuff.)Tim

author: mrpackethead
author_rank: Super Contributor
timestamp: August 31, 2019, 06:37:04 am
content: I've had one or two first hit sucesses' but more often than not, it will be three versions to get to a first releasabe version. More often that not, the improvements from 2-3 are about manufacturability, things you may not see untill you've made a few.

author: Rerouter
author_rank: Super Contributor
timestamp: August 31, 2019, 07:13:53 am
content: Increasing with time,A number of my recent boards have had small issues that did not stop them from being shipped or harmed the functionality in any way, then patched on later orders, things like 1 of the 12 alignment pegs being off by 0.5mm, so we cut that one off on the first run, or that someone made a change after parts had been ordered, so had to solder a much smaller smd crystal to a larger footprint, or that an ICSP header is a fraction too close the enclosure so the programming cable plug needed to be filed thinner.When its already taken a week to design, layout, create a BOM, and write test software for, another day to sit down and double check everything is not that hard to work in to your initial scheduling, also gives you some margin for error.Complex to me is a bit of test gear I made a few years back, 4 layers, and while only being loaded on one side, had 396 IO with various protocols, interfaces and other fun stuff, and every mm of that board was packed to fit an existing 100mm x 120mm card form factor, that thing took a month to design and layout, and a full 3 days to review. that sadly took up to revision 3 to have everything working, as at the end of the day your only human, and there are limits to how much you can unpack about a circuit at once.

author: Brutte
author_rank: Frequent Contributor
timestamp: August 31, 2019, 07:23:41 am
content: Quote from: Fratink on August 30, 2019, 09:52:33 pmThat is a good decision.Leave managing to managers and engineering to engineers.You never know - it might be worth taking huge risk if it were justified by increased profit of faster time to market. But to answer that question you need to be a manager, not an engineer.As for the revisions:A first version of the project that is a-priori managed to ship after 3 revisions is much different than first and only version the project that is managed to ship after no revision. That is especially true for size constrained stuff.In first case you can order big, modular PCB full of test points, shunts and alternative footprints and focus on meeting generic constraints (of functionality, limit of power, volume, BOM cost etc). This is super fast because decomposed in nature so everything is made in parallel: N teams develop N modules.In second case everything has to be managed by mostly one team only so this is an approach for very simple low risk projects.

author: forrestc
author_rank: Unknown
timestamp: August 31, 2019, 07:50:46 am
content: Quote from: Fratink on August 30, 2019, 08:26:39 pmFor me, it really depends on how much new to me tech is on the board.A lot of what I end up doing is pretty cookie-cutter i.e. combine two well-proven circuits. Those are almost always right the first time, with the caveat that I don't consider minor nits we fix when we order the first set of production boards as being wrong - for instance, sometimes we'll realize that if we changed spacing between a couple of parts it would be easier to assemble/rework/etc., so we just fix those between the prototype and production step.For boards with a lot of "new to me" tech, it's pretty typical that there are 4-5 board spins. But with as fast and as cheap as board spins are anymore (the joys of assembling in-house), I tend to be willing to trade 'spend a lot of time getting it right the first time' for 'let's get a board in here which we know won't be perfect, but will allow me to learn what I would need to get it right the first time in a lot quicker fashion'. There is something to be said for getting R&D hardware on the bench quickly, even if it's not perfect.

author: Ice-Tea
author_rank: Super Contributor
timestamp: August 31, 2019, 08:01:38 am
content: Funny thing, my first ever professional board was flawless. After that: once or twice. And a few boards that were close enough to ship with a few patches.

author: Fratink
author_rank: Contributor
timestamp: September 03, 2019, 01:50:35 pm
content: What you're saying makes sense, I should ask the guys doing schematic design about how it changes for the different products we make. This project in particular is mission critical so we usually get to rev F by the time we're meeting all the required specifications, which from what I understand are pretty intense. I imagine the telecom stuff we do on a regular basis don't require as many revisions.Quote from: T3sl4co1l on August 31, 2019, 06:10:09 am

author: Fratink
author_rank: Contributor
timestamp: September 03, 2019, 01:57:41 pm
content: You did much better than me, my first board designed at a workplace (not sure it's professional since I was still a student) caught fire the moment I turned it on. I was trying to be really clever and had put in a special power saving circuit but got in wrong and the result was as soon as the relay closed it caused a short and the little guy caught fire. I stood there for a good few seconds just staring at the fire with my mouth open haha.The most important lesson I learned: ALWAYS use a current limited power supply for prototyping. Batteries cause fires.Quote from: Ice-Tea on August 31, 2019, 08:01:38 am

author: tszaboo
author_rank: Super Contributor
timestamp: September 03, 2019, 02:03:03 pm
content: I always plan 2 prototype cycles. It is very rare to get it right the first time, especially if you have requirements, like EMC performance, RF performance or anything precision stuff. I've read that designers have some 30% change of getting EMC right the first time. And once you get the first board typically it takes 5 minutes to want some changes, because text is over something or you dont like how it looks like IRL.Something working and something proper is two different things.

author: Neilm
author_rank: Super Contributor
timestamp: September 03, 2019, 07:51:50 pm
content: A couple of years ago I did a board with 4 components on it. It went into production on rev 3. Rev 1 didn't quite fit into the hole it had to go into - the models were wrong and the caps touched the metal. Rev 2 had the copper flood in slightly the wrong place and shorted out (or leaked) to the metal work of the hole it was in. It was a very sensitive ammeter and the leakage from the one to the other was significant.

author: ehughes
author_rank: Frequent Contributor
timestamp: September 06, 2019, 05:02:06 pm
content: Always prepare clients for a minimum of three1st : Get something working2nd : Fix problems from the 1st3rd : Update for needs of high volume manufacturing.Rarely have I seen a design go through fewer than 3 unless it is a trivial project. i.e. some sort of connector interface board, etc.Specs always change along the way.... So always budget for a minimum of three.Prototypes are cheap compared to engineering labor.

author: Gribo
author_rank: Frequent Contributor
timestamp: September 06, 2019, 05:35:40 pm
content: My best was the entire product (Electronics, Certification, plastics, 30K units with 99% yield) on the 1st try. My worst is ver G00, and going..

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 06, 2019, 05:57:27 pm
content: Depends on the job - if I know there will probably be changes later anyway I don't spend too much time checking and worrying about errors.Where it's a job on an insane timescale, usually a 1-off build of a few panels, I spend a bit more time, and get maybe 95%, and the 5% are mostly easy fixes ( e.g. software tweak, minor track-hack to avoid PCB respin)However most of my designs are fairly simple, often based on already-proven blocks (circuitry, not layout), and I've done this a LOT - many hundreds of designs.The errors are usually on stupidly simple boards - you don't check these as carefully as more complex ones.Many years ago I did once do a batch of single-layer PCBs mirror-imaged.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 10, 2019, 07:25:07 am
content: Maybe 10% of the time completely spot-on.Maybe 5% of the time, respin is needed.85% of the time, some bodges needed, varying from very minor (change a resistor value) to some headache-causing (need to air-wire a bunch of components in a tight space) but still doable.The answer depends very much on how "success" is defined. For small batches, having to add bodges usually isn't a problem. Say, for 20 units, and 10 minutes per unit, it's less than half a day of work. In 10 minutes, you add a bodge wire or two, replace a few components, etc.For >50 units, I very much want to make a test batch (say 10 pcs) which is actually stress-tested in actual use for some time (weeks, months) to find any ugly surprises. Yet they still remain.

author: AndyC_772
author_rank: Super Contributor
timestamp: September 10, 2019, 10:50:23 am
content: I normally expect rev B to be good - though it's often the case that later revisions will be needed to accommodate any last minute "can you just...?" requests, like changes to mounting points or connectors. Further revisions, in my experience, are often needed as components go EOL or customers request new features.Rev A is the board on which you discover all the interesting quirks of the parts you've chosen which aren't properly documented. For example, I completed a design earlier this year which worked OK from a functional perspective, but it turned out to need revising because an analogue component that really shouldn't have produced much electrical noise, did.That's not something which was predictable. The rev B design swapped the offending part for a functionally similar device which completely solved the problem, but it's not a change that should really have been needed. Prototyping with evaluation boards was never an option because the design is layout critical; building a rev A PCB was absolutely the right way to test it out, both technically and commercially.

author: tom66
author_rank: Super Contributor
timestamp: September 10, 2019, 12:07:20 pm
content: Success rate? 100% right first time?Basically never bar, the simplest product.But usable and mostly working is almost always the case, with the odd tweak required here or there.

author: EEEnthusiast
author_rank: Frequent Contributor
timestamp: September 10, 2019, 12:20:08 pm
content: I have been a Hardware designer at Texas Instruments for more than 17 years now and even with that, there is still chances of errors. It all depends upon the complexity of the board. For low frequency analog boards, it is easy to get first pass success. With high speed and RF boards, it takes couple of revisions. The craziest part is where the board fails FCC emission tests and we dont know which part of the board is radiating. These are tough to fix and take up multiple revs. As others have pointed out, the PCB cost is very low these days and the time spent to make them is also low. (Typically 4 to 5 days for 4 layer PCB). So don't break your head to get it right the first time.

author: Psi
author_rank: Super Contributor
timestamp: September 10, 2019, 12:55:51 pm
content: Yep, on any complex project, even with senior design engineers you have to expect the first PCBs probably wont work without some minor hacks or tweaks. If they work fine great, but you never expect or rely on it.Usually it's not a problem if the first boards need some hacks because they are just for development, writing firmware etc.There's some time needing for writing firmware, or at least updating it for the new PCB and that gives enough time to get a new PCB made without affecting the project plan at all.It's pretty rare to have the first board totally unusable but even that does happen from time to time.Of course it depends on the board complexity, and if you're just getting PCBs or getting PCB assembly done as well.When i have been employed to work on firmware/PCB design in a team we always assembled the development PCBs ourselves which saved a lot of time. All the time spent getting the BOMs and pick n place files ready and signed off plus the delay actually getting someone to populate them was like 3 weeks verses like 2 days for us to just populate the raw PCBs ourselves.If we needed less than 30 boards it was faster to populate ourselves.<rant>The damn worst thing ever, and i'm sure others will have had this too, is when you spend time making and assembling 3 PCBs to use for development. You're all ready to get into some firmware dev and word comes down from above that"We MUST send out some non-functional but part-complete sample units to a customer today." and bam, there goes all your nice working dev PCBs used for something that is non-functional !

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 10, 2019, 02:49:38 pm
content: Quote from: EEEnthusiast on September 10, 2019, 12:20:08 pmNow I /know/ you're lying! I've yet to see a single TI dev board that could even begin to pass EMC!Tim

author: EEEnthusiast
author_rank: Frequent Contributor
timestamp: September 12, 2019, 01:05:42 pm
content: Quote from: T3sl4co1l on September 10, 2019, 02:49:38 pmWell not.. The series of WiFi MCU boards from TI are tested to conform to FCC limits. You could search for the CC3220 Launchpad. I had designed them and they do pass the FCC Part15 . The test reports are also available online for those. The reason these are tested is to ensure that the customers are easily able to pass the FCC tests if they copy the design. (at least the critical parts)Link to the SDoc is below.http://www.ti.com/lit/ml/swrq055b/swrq055b.pdfIf you could locate the design files for the board, I have my name on the schematics.

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 12, 2019, 01:38:10 pm
content: To add to what others have explained.....If you are designing a circuit which you have never designed before, or using components or manufacturing processes which are new, you better hedge your bets and plan for a board re-spin.My personal case: In the early 1990's we were told that our next product would be largely made with SMT components.Boy, were we excited about the possibilities! Smaller components made for a much tighter packaging. The reduced hole amount meant that there were fewer constraints routing signals. You could place components on both sides, and this was OK!What we were not told, or at least it did not register in our minds, were the SMT caveats. Nowadays they are well understood, but back then we walked into a cliff with a smile in our face.For us the rude awakening were the MLCC flex cracks.

author: asmi
author_rank: Super Contributor
timestamp: September 12, 2019, 02:07:53 pm
content: When I first started designing complex FPGA boards, the one nasty surprise I found was that the factor determining if you board will work or not is layout, and not just schematics. This is especially true for Dc-DC converters - their performance (especially noise) very heavily depends on how you lay out components, and the difference is drastic! So now whenever I use some part that I didn't use before, I always prototype this sub circuit on a separate PCB, test the crap out of it, and then take advantage of my eCAD's tool to save parts of a board as pre-paid-out-and-routed module that I can just place on any board, and it maintains original layout so I can be reasonably sure it will work. With that approach I've managed to design some boards which worked on a first try because they contained such pre-tested and pre-verified sub components.So if you eCAD supports such functionality, take the time to learn how to use it as it will save you a ton of time and hassle!

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 12, 2019, 04:33:29 pm
content: Depends heavily on the situation. Often the design specs are not well known or easy to determine and my first iteration is really a tool to measure what the specs are. It is often faster and easier that way than other methods. Unless my guesses have all been lucky there will be another iteration.

author: jonroger
author_rank: Regular Contributor
timestamp: November 18, 2019, 04:55:31 pm
content: I had a case where a proven schematic (done by someone fast but not so careful) was used for a new layout and it passed testing. But way late in the process, we found that it sometimes failed. The error was very hard to find and very expensive to fix.While there are valid questions about just how much care/checking is cost effective, I don't believe at all in "do it fast, another prototype spin doesn't cost much". So I err towards excessive time spent checking. Some customers think I'm slow, but I avoid the occasional really upset customer.That being said, I had a recent customer who specifically asked for low hours and agreed that I wasn't responsible for the increased risk of errors. But I'm suspicious that he still won't be a return customer if there is an error.