First PCB assembled: how to start debugging? - Page 1
Forum section: electronics / beginners

author: lukego
author_rank: Frequent Contributor
timestamp: October 20, 2020, 11:57:14 am
content: I have just assembled my first complete PCB, ever. It's an open source design that I downloaded from GitHub and order from Mouser and JLCPCB. I learned to solder along the wayI don't dare to turn it in yet though! I'm sure I'll have made diverse mistakes in the soldering and placement and likely heat damage. Is there some systematic "bring up" approach I can take to diagnose these without causing destruction along the way?Specifically I'm wondering how much visual inspection to do, what to check with a multimeter, when to apply power from a bench supply, etc. Tips welcome!

author: SerieZ
author_rank: Regular Contributor
timestamp: October 20, 2020, 12:25:14 pm
content: Personally I only check Polarity of the ICs Visually with the Assembly Drawing in hand and after that Plug it in and hope no magic smoke appears and all works fine.If it does, I check affected circuits (shortcuts, bridges, polarity, wrong values etc.) and replace the probable culprits and try again.No reason to be too scaredjust go for it

author: Mark
author_rank: Frequent Contributor
timestamp: October 20, 2020, 12:57:55 pm
content: Buy a set of precision multimeter probes and a microscope, visually check around the QFN parts especially and probe any suspect connections with the multimeter probes. You will undoubtedly have shorts and opens, that is normalhttps://www.keysight.com/en/pd-1000000534%3Aepsg%3Apro-pn-34133A/precision-electronic-test-leads?nid=-31908.536880343&cc=GB&lc=engNote that these probes have very lightweight leads so they are not suitable for current measurements at all and not suitable for low resistance measurements unless you use the "delta" function on your multimeter.Nice looking board!best of luck getting it working!

author: wraper
author_rank: Unknown
timestamp: October 20, 2020, 01:08:54 pm
content: Quote from: Mark on October 20, 2020, 12:57:55 pmStrange suggestion. Normally you should do visual inspection, maybe make a few measurements on high power related things to ensure nothing explodes. If everything looks OK, just power it. Dumbly measuring QFN all around will only disturb small solder joints. Also to make any use of such measurements, you need to know what is expected measurement to begin with. Otherwise it's nothing but waste of time.QuoteIn no way it's normal. If you judge by yourself, my condolences.

author: austfox
author_rank: Regular Contributor
timestamp: October 20, 2020, 01:10:19 pm
content: The photo is not real sharp, but is U8 orientated correctly?

author: lukego
author_rank: Frequent Contributor
timestamp: October 20, 2020, 02:32:54 pm
content: Quote from: austfox on October 20, 2020, 01:10:19 pmSorry about that! Here's a somewhat better image in case people want to point at things that I seem to have bodged :-)I've been so focused on learning to solder that honestly when I'm in doubt about how to read silkscreen I've often just made a guess rather than take the "context switch" of stopping to google it...

author: lukego
author_rank: Frequent Contributor
timestamp: October 20, 2020, 02:39:51 pm
content: Here is how it's supposed to look too!

author: hans
author_rank: Super Contributor
timestamp: October 20, 2020, 02:43:26 pm
content: U12 seems misplaced

author: lukego
author_rank: Frequent Contributor
timestamp: October 20, 2020, 02:50:03 pm
content: Quote from: hans on October 20, 2020, 02:43:26 pmThanks!I realize that I need to practice my PCB photography. Having a really high quality image with all of the markings and solder joint textures visible would be a really convenient way to do a quick pass at inspection. I'll break out my photographic lighting book and put my thinking cap on..

author: wraper
author_rank: Unknown
timestamp: October 20, 2020, 03:30:20 pm
content: U8, U12 are reversed, U32 and half of 6 leg ICs in 4 rows of 4 IC on the right side of it seem to be reversed as well. You need to recheck orientation of all ICs. Inconsistent sign of component orientation on silkscreen does not help either.EDIT: BTW what are U32 and ICs on the right side of it? There is some chance you don't need to fix those depending on what they are.

author: pwlps
author_rank: Frequent Contributor
timestamp: October 21, 2020, 06:38:25 am
content: Quote from: SerieZ on October 20, 2020, 12:25:14 pmUsually I first power the circuit in a current-limited mode and increase the max current until either it stops growing or becomes suspiciously bigger than my estimation of the total current that should be drawn, this sometimes may prevent blowing a component having a short because of wrong polarity or similar error. I learned this very quickly when I started teaching an electronics lab and saved many transistors since

author: Electro Fan
author_rank: Super Contributor
timestamp: October 21, 2020, 08:42:34 am
content: There are some good suggestions here. I especially like what pwlps said.After seeing how far you have gone already I’m confident you will get everything sorted and running successfully.The good news is that worst case you know how and where to get another board with partsGood luck

author: lukego
author_rank: Frequent Contributor
timestamp: October 21, 2020, 01:01:33 pm
content: Quote from: wraper on October 20, 2020, 03:30:20 pmYikes! Yeah it really looks like I oriented those six-legged chips (transceivers, not reversible) at random. I was probably distracted concentrating on soldering issues like trying not to overheat etc. Going to try and fix them up now...Meanwhile here's a "walk of shame" video across the PCB, some godawful joints at the end that will be very satisfying to fix I hope...

author: wraper
author_rank: Unknown
timestamp: October 21, 2020, 01:18:06 pm
content: Quote from: lukego on October 21, 2020, 01:01:33 pmFrankly many people solder much worse despite decades of experience. Never learn how to do it properly. It's as good as you can possibly get without experience.

author: wraper
author_rank: Unknown
timestamp: October 21, 2020, 01:47:55 pm
content: Watch this video for how to get 2 lead SMD components properly positioned. As of removing 6 leg ICs, I suggest using 2 soldering irons simultaneously if you have them. Make solder blobs on each side, then heat from both sides at the same time and lift or move sideways. Basically soldering tweezers without tweezers. Hot air is hard to use in this case since it's very easy to melt TH connectors located nearby.

author: lukego
author_rank: Frequent Contributor
timestamp: October 21, 2020, 01:50:36 pm
content: Quote from: wraper on October 21, 2020, 01:47:55 pmProphetic! I did reoriented them with hot air, and I did carelessly melt one of the throughhole connectors (and will have to replace that too now.)Sure was worth it though to take my new Quick TR-1100 micro air station for a spin together with my homebrew lazy susan! I love it when a plan comes together

author: m k
author_rank: Super Contributor
timestamp: October 21, 2020, 03:34:25 pm
content: Quote from: lukego on October 20, 2020, 02:50:03 pmWhen you're visually checking it you're most likely rotating it around in your hands and reflecting light all the way.You can't replicate that with even some pictures.I tried it first, even seeing things properly, with many kinds of magnifiers but finally cheap USB microscope was a decent solution.

author: lukego
author_rank: Frequent Contributor
timestamp: October 21, 2020, 04:12:03 pm
content: I've corrected the known problems and tried powering the board now. It doesn't draw any current and doesn't show voltage in very many places (pointed out by the developers on IRC.) Tomorrow I'll make a fresh inspection of the board and especially look obliquely at the solder joints and check for missed connections. Any other soldering inspection thoughts that occur?

author: nicknails
author_rank: Regular Contributor
timestamp: October 21, 2020, 06:57:29 pm
content: Make sure all your diodes are in the right way. The cathode lines are damn hard to see on a lot of them.

author: Ctrlocti
author_rank: Regular Contributor
timestamp: October 22, 2020, 07:46:17 am
content: Quote from: wraper on October 21, 2020, 01:47:55 pmthat board is so clean!how do I get my joints to look like that? I always get some gunk/residue around the pads.Cleaning it with IPA doesn't really get it off.

author: lukego
author_rank: Frequent Contributor
timestamp: October 22, 2020, 10:54:10 am
content: I have some LEDs on now! Whacko!The #glasgow IRC channel have been patiently tutoring my in debugging the board. In addition to the soldering mistakes I'd also accidentally swapped some parts.Have 5V and 3V3 rails stable now but 1V2 for the FPGA is unstable and might be time to have another crack at soldering that BGA part. I think that I have a spare, and otherwise I have some solder spheres...

author: mikerj
author_rank: Super Contributor
timestamp: October 22, 2020, 11:15:04 am
content: Quote from: lukego on October 21, 2020, 01:01:33 pmHonestly you've done a very nice job for hand soldering SMD parts, nothing to be ashamed of there. You should see some of the lash-ups on our engineering protoypes at work, some people shouldn't be allowed near a soldering iron.

author: Mr. Scram
author_rank: Super Contributor
timestamp: October 22, 2020, 11:28:46 am
content: Quote from: m k on October 21, 2020, 03:34:25 pmThat's what rainbow lighting and photography is for.

author: Mark
author_rank: Frequent Contributor
timestamp: October 22, 2020, 12:53:13 pm
content: Quote from: wraper on October 20, 2020, 01:08:54 pmStrange interpretation and understanding.You suggest visual inspection, yes, that is what I said.Dumbly measuring QFN all the way around? huh? Who said that, not me. If you see anything suspect, check that for shorts and opens, it's possible without "disturbing small solder joints". If you are that clumsy, my condolences.This OP says he was practicing his soldering on his FIRST PCB, I assume he might make some mistakes along the way, not judging him by my own standards.Hopefully others can understand my post better than you.

author: SerieZ
author_rank: Regular Contributor
timestamp: October 23, 2020, 08:53:11 am
content: Quote from: lukego on October 22, 2020, 10:54:10 amCool!The burnt plastic on the socket gave me PTSD tho, hate when that happens...

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 23, 2020, 09:54:08 pm
content: Quote from: Ctrlocti on October 22, 2020, 07:46:17 amI do not plating footprints. I take a drop of solder on the tip, press the component down, and touch it with the soldering iron. 1210 can be safely held with tweezers and moved, with 0402 this focus will not work, it will have to be pressed on top of the PCB.

author: wraper
author_rank: Unknown
timestamp: October 23, 2020, 09:59:45 pm
content: Quote from: S. Petrukhin on October 23, 2020, 09:54:08 pmAnd that's why you have poor component orientation and too much solder on the joints.QuoteCan be done just fine with 0402 if you hold component with small tweezers properly. If it does not lie flat after soldering first joint, push on top of it with tweezers and touch up the joint with soldering iron again.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 23, 2020, 10:04:53 pm
content: Quote from: Ctrlocti on October 22, 2020, 07:46:17 amYou may be using too high a temperature or low-quality flux, including flux that is contained in low-quality solder - it burns and leaves dirt.If you have 1210 components that are located two light-years apart and you can afford to wash each footprint separately for each soldering, and you can solder the PCB until the New year, then your PCB will be as clean as a baby's tear.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 23, 2020, 10:08:47 pm
content: Quote from: wraper on October 23, 2020, 09:59:45 pm

author: wraper
author_rank: Unknown
timestamp: October 23, 2020, 10:46:48 pm
content: ^ solder joints have excessive amount of solder, though I would not say anything of big concern. U12 has bad joint, U4 probably as well but it might be simply a light reflection. The issue with using solder on the iron is that it oxidizes by the time you solder the joint. More problematic when you solder lead-free due to higher temperature needed. Also you probably used large amounts of gel flux to make it work reasonably well.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 24, 2020, 12:51:13 am
content: Quote from: wraper on October 23, 2020, 10:46:48 pmThere is no difference in the dosage of solder when applied to the footprint or to the soldering iron tip. There is also no difference where the solder is heated and oxidized (in small amounts). I like soldering with a slide so that the entire output of the element is covered with solder. In order to have less solder as in the case of stencil application, you just need to take less solder on the tip.But there is a difference in how long the soldering iron heats the board, while the hot component is installed and leveled. When you need to solder a couple of components during repair, you can indulge, but when there are several hundred of them, dropping and drowning them in a pile of solder on a tinned footprint is unpleasant. An extra operation that increases the time by 1/3.Soldering with the supply of solder appeared relatively recently. When soldering output components that were previously all used in the production of a sting in the form of a hollow tube. And even earlier, when the installation was not on the PCB, but mounted, the solder would not have been enough for the 3rd hand. And it was taken on the sting of a soldering iron. It was also a thick bar of tin.

author: wraper
author_rank: Unknown
timestamp: October 24, 2020, 01:03:57 am
content: Quote from: S. Petrukhin on October 24, 2020, 12:51:13 amI'm talking about 2 terminal SMD. No nice fillets there but blobs of solder. Just FYI such amount of solder may cause cracks in MLCC. As of U12 there is a spike protruding from solder joint.QuoteIf you are talking about Soviet hobbyists not having rosin core solder, and only having like 8mm thick stuff, it was not a thing for the rest of the world. Thin rosin core solder was used for many decades, nobody bothered with that nonsense of dipping iron tip into rosin as a way of transferring flux to the board. How old do you think the video below is? 40 years but actual soldering part seems to be even 10 years older and them simply reusing videos later.QuoteNope, it's your approach is which is significantly slower and with much worse results. It's not a professional way of soldering. If you think that soldering on the video was slow, then it's because it's an education video. Nobody prohibits soldering a few components components in a minute that way.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 24, 2020, 01:54:29 am
content: Quote from: wraper on October 24, 2020, 01:03:57 amYou have given examples for automatic installation and reflow in the oven.Holding components with tweezers is a risk of breaking them also.Quote from: wraper on October 24, 2020, 01:03:57 amThe video credits indicate the year 1980.Probably, your desire to show the backwardness of the USSR overshadowed the view.But, to your regret, the same 8mm thick stuff and rosin were used all over the world.Are you young and don't know how to solder lamp devices?I think people here will confirm.Quote from: wraper on October 24, 2020, 01:03:57 amPerhaps you are a professional soldering of SMD components manually, without a stencil, and you know better. And I expressed my experience.I manually solder makets and prototypes only. Even prototypes are soldering using paste and stencil in the oven. Most likely, I understand why you are so alarmed and you forgot to support your unambiguous conclusions with any explanations.For example, why 3 movements: tinning, installation and sealing are faster than 2: installation and sealing...

author: wraper
author_rank: Unknown
timestamp: October 24, 2020, 02:06:38 am
content: Quote from: S. Petrukhin on October 24, 2020, 01:54:29 amI'm here to tell you that I had no choice but to use it as well in my childhood. And it's does not mean that you need to continue doing that nonsense 30 years after USSR collapse when proper solder is readily available.QuoteI solder SMD manually when reworking or making prototypes. And yep, I solder professionally. I soldered way more solder joints than you may think. I can easily solder that you won't distinguish it from reflow and wave soldering after cleaning flux residues, and that's lead-free as leaded stuff is much easier to do. And there are not much of residues left to begin with since I don't have any need for tons of flux.QuoteI repaired plenty of lamp TVs and some radiolas.

author: wraper
author_rank: Unknown
timestamp: October 24, 2020, 02:13:01 am
content: Quote from: S. Petrukhin on October 24, 2020, 01:54:29 amThere is example of solder joint on top. It's universal for any type of soldering as it causes stress. And crack may happen well afterwards due to mechanical stress. Hand soldering is way more dangerous for MLCC than reflow BTW.

author: LootMaster
author_rank: Regular Contributor
timestamp: October 24, 2020, 02:23:17 am
content: Good job bro... Honestly, you have skill.BGA is not easy.Test for short and pray when debugging.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 24, 2020, 02:33:33 am
content: Quote from: wraper on October 24, 2020, 02:06:38 amI told you about tin soldering as a story. It's strange that you didn't have any solder. There were several large production facilities in Riga. I still listen S-90 speakers. And there was no solder, a good Soviet POS-61. Apparently, all were soldered by a wave, where the solder was oxidized for days.Quote from: wraper on October 24, 2020, 02:06:38 amFor some reason, I thought that professionals do not solder manually after 30 years... That they can afford to use a stencil and an oven, or an installation machine even. I always order a stencil along with the boards, even if it is a single prototype. I'm wasting money, everything can be solved by tinning footprints.I also didn't know that it is very important for a professional to solder a prototype that will not live long and will be thrown in the trash, very evenly, so as not to distinguish it from machine soldering. I've noticed that professionals spend more time for design and programming, and don't waste it for beauty.

author: LootMaster
author_rank: Regular Contributor
timestamp: October 24, 2020, 02:42:32 am
content: @S. PetrukhinI have a reflow oven. Stencils.Let me tell you the problem with this, when you dont have framed stencil jig its difficult to have perfect quantity/position/immoveable for a perfect reflow.And if you make a short and cant find it because you dont have that cold spray to identify the spot...If you go 1 by 1, it can be finished faster as you measure all the time and find the problem immediately.The story of the turtle and the fox? Remember...I had no microscope/no jig, and I regretted going with reflow for full board because I basically could not find the short, put in oven again and removed all that stuff.I just reflowed a lead-free BGA and rest done manually.

author: wraper
author_rank: Unknown
timestamp: October 24, 2020, 03:07:48 am
content: Quote from: S. Petrukhin on October 24, 2020, 02:33:33 amDoing good soldering takes about as much time as doing shit soldering if you have the skill.QuoteAnd I guess you never do any experiments, never repair something. Or do something right away without designing and waiting for board to arrive.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 24, 2020, 03:08:43 am
content: Quote from: LootMaster on October 24, 2020, 02:42:32 amI do not know what "cold spray" is and how they detect closures. Tell me, please.When I didn't have a microscope, I used an clock magnifying glass that I put on my eye and looked at carefully. When there was no support for the stencil, I did not solder, for example, processor in the oven - it has very little distance between the pins and soldered manually. I don't use BGA, because I don't have x-ray machine to check the quality of soldering.Now I boldly solder all the components, but just in case I add flux where there is a very dense soldering - this helps well. But there are still soldering problems, I still check under the microscope.By the way, I don't know the story of the turtle and the fox. In Russian culture, it does not exist or other characters.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 24, 2020, 03:13:35 am
content: Quote from: wraper on October 24, 2020, 03:07:48 amYou can think what you want, it doesn't matter to me, and in this topic, your "unambiguous", "well-founded" and "thoughtful" conclusions about my identity and skil are probably not very interesting either.

author: LootMaster
author_rank: Regular Contributor
timestamp: October 24, 2020, 03:15:39 am
content: Input 300 mV and the coldspray changes at that spot...When you press button, you look/pay attention...Something like that... I have not tried, I dont have a adjustable PSU and I dont got cold spray.The story of the fox is self explanatory...Or maybe it was a rabbit?Anyways, you go fast, but there is many mistakes along the way....You go slow...You get annoyed less. Slow and steady.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 24, 2020, 03:35:40 am
content: Quote from: LootMaster on October 24, 2020, 03:15:39 amFunny technology. This is a flying needle on the contrary-it supplies current to different tracks to determine the short circuit.After all, this can be done with an ordinary ohmmeter.I always check the boards after soldering with ohmmeter for short circuits on the power supply and power lines.Quote from: LootMaster on October 24, 2020, 03:15:39 amIn Russia, it sounds literally "quietly go - farther be" - slowly safe.

author: Ctrlocti
author_rank: Regular Contributor
timestamp: October 24, 2020, 08:32:32 am
content: Quote from: S. Petrukhin on October 23, 2020, 10:04:53 pmmight be too hot, I like to use 360-370c with leaded solder and I'm in and out in 1s max. multicore solder is high quality, my extra liquid flux is so-so quality. it's also no-clean flux so it's obviously harder/impossible to get off with just IPA.haha I love the figure of speech about soldering until New Year and clean as a baby's tear.I can solder 0402 but it's such a pain to actually physically hold and manipulate the 0402. It's not the act of soldering that's tough, it's getting the damn component where I want it and to stay where I want it. It's just too annoying.

author: Microdoser
author_rank: Frequent Contributor
timestamp: October 24, 2020, 12:06:05 pm
content: What I do after constructing and populating a board is to give it a full visual check under magnification checking for component orientation, dry joints, bridges, and of course that the right component is in the right place! After this, I give it a basic multimeter check testing selected components for shorts to ground and, if known, that path resistance if correct.Then I give it power and see if it works. When powered, I check that proper voltage and signals are in the places where they should be. On boards I design myself I make sure there are test points for checking this.I quite like the suggestion posted here to slowly current limit initially and see if power draw is out of spec. I think I will adopt that procedure.

author: perieanuo
author_rank: Frequent Contributor
timestamp: October 24, 2020, 12:35:29 pm
content: hi,in some r&d company who developed electronic modules/machines on-demand, procedure for testing a new design (populated pcb) was:- visually inspect pcb/compare with schematic- apply rising voltage from linear supply set on some small current (in eventuality of misplaced unobserved component you protect the dc-dc's or the uC or fpgs chip bla bla bla) up to target Vcc- verify if voltage regulators were starting the regulation normally (on almost every pcb you have local voltage reg or dc/dc or mini-smps)- increasing the current if all is on the right pathIf all was correctly mastered here, it's a 100% good method to keep the components alive even if you screwed some component placement. if you set the current with good logic, everything is safe.I guess all the companies with r&d apply the same techniqueregards, pierre

author: tooki
author_rank: Super Contributor
timestamp: October 24, 2020, 12:55:45 pm
content: Quote from: Ctrlocti on October 22, 2020, 07:46:17 amBasically, everything is new and super clean before — clean the bare board with solvent, the solder wire too (!), the tip is impeccably clean —, they're in and out quickly, and the temperature will be set as low as possible that still achieves a quick, complete melt. And the cleaning at every step means that any flux residue from a prior joint isn't getting overcooked on the next one. They may also have cut the solder wire open before each joint, as some high-reliability procedures dictate. (That ensures the flux isn't sealed in by a solder blob at the end of the wire.)Regarding your other comment about no-clean fluxes being hard to remove: indeed! It's well worth it to spend some money on proper flux remover for those fluxes. For that, I quite like theElectrolube Lead Free Flux Remover. It's not the cheapest, but I found it to be more effective on no-clean fluxes than other cleaners, meaning I don't need to use as much of it.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 24, 2020, 01:04:14 pm
content: Quote from: Microdoser on October 24, 2020, 12:06:05 pmLimiting the current will protect you from white smoke, but some short circuits will not lead to increased consumption, such as closing two inputs.I always try to make a test firmware that checks the circuit in a simple way. For example, input 1 directly controls output 1 and sends the message "input xxx state changed to x" to the console. For one of the commercially available PCBs, I made a test stand for this.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 24, 2020, 01:11:31 pm
content: Quote from: perieanuo on October 24, 2020, 12:35:29 pmI don't think that's enough. If there is a short circuit of two rail-to-rail outputs or one such output short to GND, then at the first start, then they are both normally turned off, everything will be fine. When one of them turns on later, there will be trouble. Even limiting the current can not save because the normal current can be quite large, and only a small current is needed for the MCU output transistor to burn out.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 24, 2020, 01:38:09 pm
content: Quote from: Ctrlocti on October 24, 2020, 08:32:32 amI do not commercial repairs, sometimes I repair for my own or for friends, and these are most often damaged tracks, buttons, and connectors. I've never had to change 0402 during repairs. But I decided to master manual soldering 0402 for myself and, in order not to just solder, I made a toy watch round on LED 0402. It seemed like a good workout - placing components in a row or column is easy enough, it is much more difficult to arrange them in a circle so that they look even.Applying the paste without a stencil manually for this little thing requires a very precise dosage. If there is a lot of paste, these parasites pop up or become tombstones. I've never seen this before. And it is very easy to apply a lot paste. I tried to use a small puck with a soldered handle as a stencil for each footprint, but it didn't work either - the extra paste was smeared everywhere and the puck crawled on the footprint. I had to solder with a soldering iron... My patience did not speak with me for several days out of resentment.

author: lukego
author_rank: Frequent Contributor
timestamp: October 24, 2020, 04:01:50 pm
content: I've also tried to master 0402. One thing that helped a lot was to do a couple of sessions with 01005s. I think this taught me to correct my posture and keep my forearms supported. I don't consider 0402 small not challenging since that experience although my technique is still far from perfect.