Reflow soldering in kitchen with ceramic hub - Page 1
Forum section: electronics / general

author: tatus1969
author_rank: Super Contributor
timestamp: May 08, 2017, 09:52:12 pm
content: I do have a reflow oven (the old PCB-Pool mini oven "convertible"), but I realized that it has one big disadvantage when soldering prototype boards: I cannot access them while reflowing. As I find this possibility very handy to fix a tombstoned part or to check correct floating of a QFN chip, I came up with another solution.Here is the complete process in a series of pictures, plus a video. The board shown is the battery management system as part of my current projecthttps://www.eevblog.com/forum/projects/introducing-my-project-'kicksurfer'/msg1170253/#msg1170253.Preparing a fixture for solder paste applicationAligning the stencil, fixing it with tapeInspection of correct alignment, pushing down the stencilUsing leaded solder paste for my prototypes, that just makes the process easier; store in refrigerator, let it warm up and thoroughly stir before useApplying a blob of paste - note the board added to the right, which is to support the stencil and keep it from flexing in the next stepSpreading the paste, the right angle is important, move slowly, distribute pressure evenly, go all the way in one pass without stoppingFinished spreadingStencil removed - be careful here as well, move slowly but steadilyClose inspection of critical structures - this is a 0.4mm pitch QFNPreparing component placementPlacement - my hands are not too steady (you'll see that in the video), so I use my other hand for stabilization, creating sort of a bipodFully populated board, not all components are spot on but that can be fixed during solderingVideo showing the reflow process in our kitchen. I did some tests with an infrared thermometer before, in order to find the right power setting. It's a pity that it is limited to single-sided boardshttps://youtu.be/hptbgbDvaskFinished board!

author: KL27x
author_rank: Super Contributor
timestamp: May 08, 2017, 10:51:16 pm
content: Mmmm. Nothing like the smell of burnt FR4 and solder flux in the kitchen. You're not married, are you?

author: tatus1969
author_rank: Super Contributor
timestamp: May 09, 2017, 08:48:41 am
content: Quote from: KL27x on May 08, 2017, 10:51:16 pmNot if you do it rightAnd clean up with flux remover afterwards...Quote from: KL27x on May 08, 2017, 10:51:16 pmYes, I am! Since almost 17 years now. I have done worse things in our house, like having a 250W power resistor explode in our living room (that one in my profile picture). While she was watching TV. We couln'd use that room for the rest of the evening.

author: ar__systems
author_rank: Frequent Contributor
timestamp: May 09, 2017, 11:23:23 am
content: Your wife deserves a medal for patienceNot only it is in-hygienic, it stinks the kitchen, contaminates surface, but more importantly you can't control heating rate. Look, your board was done at 2:20. Compare that time to the recommended re-flow profile.

author: Nusa
author_rank: Super Contributor
timestamp: May 09, 2017, 11:37:58 am
content: So the iron in the pins and contacts is being used to solder the board. That sounds like an extremely high thermal cycle for the chips themselves. Obviously getting away with it, at least so far.

author: ar__systems
author_rank: Frequent Contributor
timestamp: May 09, 2017, 12:38:32 pm
content: Quote from: Nusa on May 09, 2017, 11:37:58 amNo. Solder paste.

author: tatus1969
author_rank: Super Contributor
timestamp: May 09, 2017, 12:47:55 pm
content: Quote from: ar__systems on May 09, 2017, 11:23:23 amYes she does. But she sees and acknowledges that electronics is my passion.Quote from: ar__systems on May 09, 2017, 11:23:23 amBasically yes, although we do not cook our food directly on the hubI am using no-clean solder paste though. The flux component does not smell, and can easily be cleaned.Quote from: ar__systems on May 09, 2017, 11:23:23 amI also saw that the reflow time was too long, when I watched the video. But that is not caused by the soldering "process", but by me tinkering around with the components. I should have done the boards sequentially.The peak temperature duration can easily be controlled by removing the boards from the hot area. It is in fact shorter than with the PCB pool oven. And the thermal stress could be lower than using infrared (nicely heating all the black packages first and much later the reflective metals), because board and components are more evenly heated.Surely, is is far from any JEDEC profile, but I have been using it for a while without problems so far.

author: tatus1969
author_rank: Super Contributor
timestamp: May 09, 2017, 12:52:18 pm
content: Quote from: Nusa on May 09, 2017, 11:37:58 amAs mentioned, it is using solder paste. Peak temperature was set to roughly 200 ~ 210°C.

author: Nusa
author_rank: Super Contributor
timestamp: May 09, 2017, 01:15:50 pm
content: Quote from: tatus1969 on May 09, 2017, 12:52:18 pmI thought inductive heating only worked on ferrous metals? Are you saying the tin or lead in solder is being heated directly as well?

author: tatus1969
author_rank: Super Contributor
timestamp: May 09, 2017, 01:40:28 pm
content: Quote from: Nusa on May 09, 2017, 01:15:50 pmit is a conventional hub, not inductive. the hub heats the pcb, the pcb heats the solder paste.

author: ar__systems
author_rank: Frequent Contributor
timestamp: May 09, 2017, 02:02:51 pm
content: Quote from: tatus1969 on May 09, 2017, 12:47:55 pmActually I meant that it the boards were done too fastEvery type of flux stinksThose fumes that you can see in the video, are you saying they are odorless? Well even so you don't want to inhale those.

author: rs20
author_rank: Super Contributor
timestamp: May 09, 2017, 02:16:11 pm
content: I'm surprised tombstoning is such a big issue for you that it warranted such a radical change in process for you. Having reflowed hundreds of SMD 0805's and 0603's, I've only ever had one tombstone, and even then it was trivial to fix with a hot air gun (two soldering irons would have sufficed too). And I do all my soldering with a hot air gun, which ought to be unusually susceptible to tombstoning since the spatial temperature gradients across my board will be much higher than in a half-decent reflow oven. Is it possible that you're using bad paste?Interesting fromhere:QuoteAs for QFNs, I just use extra-long pads and drag solder any bridges away along the lengthened pads.

author: Nusa
author_rank: Super Contributor
timestamp: May 09, 2017, 02:33:04 pm
content: Quote from: tatus1969 on May 09, 2017, 01:40:28 pmAha, that explains my confusion. My brain heard inductiive when you called it a hob on the video title. Partly because common cooktop terms are a bit different in American English.So it's the frying pan method without the frying pan. That I understand. I cook with gas, so I'd still need a frying pan to do that.

author: tatus1969
author_rank: Super Contributor
timestamp: May 09, 2017, 02:48:22 pm
content: Quote from: Nusa on May 09, 2017, 02:33:04 pmThat makes sense. I googled that word because I didn't know it. But shouldn't Google be American biased?

author: tatus1969
author_rank: Super Contributor
timestamp: May 09, 2017, 02:55:54 pm
content: Quote from: ar__systems on May 09, 2017, 02:02:51 pmSolder starts melting at 1:09, and I remove the boards at 2:31, is that too short?Quote from: ar__systems on May 09, 2017, 02:02:51 pmNot odorless, but nothing that fills the room noticeably. You have to stick your nose into it to smell it. I also use hot air gun soldering and that produces the same amount of fume. Really not a big deal to me.

author: tatus1969
author_rank: Super Contributor
timestamp: May 09, 2017, 03:05:10 pm
content: Quote from: rs20 on May 09, 2017, 02:16:11 pmI do not have excessive tomb stoning, there is none in the video if you look closely. I just adjusted some parts that I had not placed straight enough before. Please don't treat this thread too seriously, I had this idea out of curiosity and just wanted to share it with you. I thought it could be interesting for someone not owning a reflow oven or a hot air gun. Soldering SMD with an iron is a PITA. Stencils have become so cheap nowadays and I encourage everybody to try this or another type of DIY reflow technique, instead of thinking that SMD stuff at home is out of reach and stick to vintage all through hole component boards. This was also the reason for the picture series, I hope it encourages the one or other to try this out. All you need is solder paste and the stencil, maybe some spare FR4 material, The rest should be available in a typical household, including the kitchen

author: tatus1969
author_rank: Super Contributor
timestamp: May 09, 2017, 03:08:44 pm
content: Quote from: rs20 on May 09, 2017, 02:16:11 pmThanks, I also noticed that, I had quite a few solder bridges and will change the design in this direction. I again did the mistake to follow the datasheet recommendations. It was a 100u stencil, maybe a bit too thick for that pitch either. It works perfect for .5 QFN though, so I was optimistic.

author: janoc
author_rank: Super Contributor
timestamp: May 09, 2017, 03:20:56 pm
content: Nice hack, but I think the last thing I would want in the kitchen is leaded solder paste. Leaded solder alone is not very toxic unless you literally eat it but the tiny particles of lead in the paste are a different matter. They are both more reactive than normal solder wire due to their much larger surface area and the small size allows them to get in the body much easier. It is very easy to smudge it somewhere by accident and never clean it completely, especially if the surface is not perfectly smooth. Then you (or your kid/wife/etc) puts food there ... Or it dries out after a while and you inhale the dust when it gets disturbed. It won't kill you outright but a slow lead poisoning is not fun.Do yourself a favor and get a dedicated hotplate for this kind of work - and keep it out of anywhere where food is routinely handled.

author: tatus1969
author_rank: Super Contributor
timestamp: May 09, 2017, 07:06:17 pm
content: Quote from: janoc on May 09, 2017, 03:20:56 pmDon't worry, I am aware of the toxicity of leaded solder paste, and I will not allow that anyone gets in touch with it and work cleanly. And I don't smoke, so I am also not afraid that the fumes will harm me. If I would be doing this day by day, it would be a completely different story. I don't feel too good when cleaning the boards with flux remover and no gloves, but that is nothing compared to what women do with their nail polish remover.

author: janoc
author_rank: Super Contributor
timestamp: May 09, 2017, 11:09:31 pm
content: Quote from: tatus1969 on May 09, 2017, 07:06:17 pmI know you are not an idiot but you obviously don't understand - accidents and mistakes happen even to the best of us. Imagine that you trip over your cat (=dog/kid/wife/own shoe ...) on the way to the hob and drop a pasted up board on your kitchen counter. You clean the mess up but it is never perfect and traces of that lead will stick there. And then you or your wife will be handling food there. I somehow doubt that you are covering everything in the kitchen up before working there.Quote from: tatus1969 on May 09, 2017, 07:06:17 pmI didn't mean fumes, those are not likely to be too toxic (or at least any different from normal leaded solder). I meant dried leftovers of the paste, e.g. after an accidental spill, aka dust particles. Those you will inhale or eat if you disturb them.Toxic chemicals and food just don't mix - a small electric hotplate for your bench will cost you perhaps 20 euro and save you all this aggravation.Quote from: tatus1969 on May 09, 2017, 07:06:17 pmThat's just acetone - not good for your skin but that's about all.

author: KL27x
author_rank: Super Contributor
timestamp: May 10, 2017, 07:12:37 am
content: If it's done in 2:00 that is pretty fast. I hardly ever use my reflow oven. I forget how long it takes, but it's more like 5 to 10 minutes before the "flash" and then another 5 minutes cooldown? And boy does it stink to high heaven. Smells like burnt capacitors.I would be worried about the solder paste splattering when it reaches sizzling temp, though.I suppose a "hob" reflow would be mostly IR + direct contact heating? I'm sure it works fine. But I wouldn't be able to de-tombstone the parts while the pcb is on the hob. Without somewhere to anchor my hand and at least a mag lamp, I wouldn't stand a chance.Honestly, I would probably hand solder those boards faster than stencil and pasting.... tinning and hot air for the QFN's. This why my oven doesn't see much daylight.QuoteHeh, Congrats! My SO is the kitchen gestapo. I rule the garage. I win.

author: tatus1969
author_rank: Super Contributor
timestamp: May 10, 2017, 01:54:05 pm
content: Quote from: KL27x on May 10, 2017, 07:12:37 amSame problem with the PCB pool oven. And when you want to accelerate cooldown by opening the door, the vibration ruins the soldering.Quote from: KL27x on May 10, 2017, 07:12:37 amI have never observed anything like this.Quote from: KL27x on May 10, 2017, 07:12:37 amPossibly. But I consider the reflow process being more reproducable, reliable and less heat stressing both components and board. Total time for three boards was roughly 30 mins for paste application, 1 hour to place all components, 10 minutes for soldering. And it scales better when doing more identical boards.Quote from: KL27x on May 10, 2017, 07:12:37 amIf I had a garage with electricity, I would immediately emigrate to it. Needs to have a postal address then for the pizza deliveryQuote from: janoc on May 09, 2017, 11:09:31 pmI totally agree to that, and that is also a good idea. But again, I am not too concerned about poisoning from leaded solder paste, there is probably more heavy metal in food like fish or pork liver and I still like to eat them. Lets summarize for others, reading this thread, that working with solder paste in the kitchen is not advisable.

author: janoc
author_rank: Super Contributor
timestamp: May 10, 2017, 07:40:44 pm
content: Quote from: tatus1969 on May 10, 2017, 01:54:05 pmConsidering that leaded solder paste is 60% lead, umm, I think your math is wee bit off. If a fish contained 60% of heavy metals, I don't know ...

author: tatus1969
author_rank: Super Contributor
timestamp: May 10, 2017, 08:03:10 pm
content: Quote from: janoc on May 10, 2017, 07:40:44 pmdoes your math take into account that I don't eat solder paste like fish?

author: james_s
author_rank: Super Contributor
timestamp: May 10, 2017, 08:20:20 pm
content: Quote from: tatus1969 on May 10, 2017, 08:03:10 pmYou're missing out, I like to spread it on crackers

author: tatus1969
author_rank: Super Contributor
timestamp: May 11, 2017, 07:28:11 am
content: Quote from: james_s on May 10, 2017, 08:20:20 pmIf you don't spread it too thick, then it should be not much worse than a fish mealI just googled that out of curiosity, and read that the EU plans to raise the limit for mercury in predator fish from 1mg to 2mg per kg. What? 2mg?

author: JuKu
author_rank: Frequent Contributor
timestamp: May 11, 2017, 11:54:02 am
content: Quote from: tatus1969 on May 09, 2017, 02:55:54 pmThe paste manufacturer has the recommended profile for their paste, but yes, that is short.A typical profile is slow heating (<2C/s) to 150C, so this alone should take well over a minute. At that temperature, the chemicals in the paste activate. Then, you let those chemicals do their work for 1 to 3 minutes. This is called dwell or soaking time. For this, you really want to look at the paste data sheet, as there is a largish variation on best time. You want the chemicals to have done their job in getting the solder to stick to parts, but you want the flux still be there. Then the temperature is raised so that solder melts. It is not enough that the solder melts, the flux and other chemicals need some time for best results; typical reflow time recommendation is 60 to 90 seconds but again, see your paste data sheet. And finally, the boards should cool with a controlled rate as well, 6C/s max.Of course, this is for industrial grade reliability, where one failed joint in a million is poor quality. Prototype builders and hobbyists can't always do things by the book and it is ok; for us it is fine to push parts in place manually, fix the odd tombstone or cold joint. A real factory will do it as above.

author: tatus1969
author_rank: Super Contributor
timestamp: May 12, 2017, 07:49:26 am
content: Quote from: JuKu on May 11, 2017, 11:54:02 amThe video doesn't show the preheat and soak phases that went before this. I wanted to keep it short and cut that part, maybe not such a good idea in the end.

author: JuKu
author_rank: Frequent Contributor
timestamp: May 12, 2017, 12:10:43 pm
content: Ok, gave a wrong idea what happened.

author: KL27x
author_rank: Super Contributor
timestamp: May 13, 2017, 01:25:31 am
content: The preheat and soak phases are not complete BS, but... it has more to do with the board and components than the paste. On a small board with small components, you can get a proper "reflow" much faster than the "recommended profile," without overheating the board. Proper cooling is probably important, but not so much on smaller boards like these.To illustrate:QuoteI promise no one in their right mind is going to keep a joint flowing for 60 seconds when using an iron or a hot air station, no matter what paste/solder they may use. The reason this is the recommended time is to make sure all the parts reach flow temp before the ramp down begins.

author: SeanB
author_rank: Super Contributor
timestamp: May 13, 2017, 03:21:30 pm
content: Quote from: tatus1969 on May 11, 2017, 07:28:11 am2mg is about the mercury dose of a CFL lamp, which might have a life of around 2 years before going out in the waste stream, and most likely being broken in the process as well.

author: tatus1969
author_rank: Super Contributor
timestamp: May 14, 2017, 08:55:34 am
content: Quote from: SeanB on May 13, 2017, 03:21:30 pmThat comparison shows how ridiculous this limit value is. They allow fish for sale that has the same amount of mercury per kilo as a CFL lamp, which they highly recommend to be replaced by LEDs because of their health risk.

author: SeanB
author_rank: Super Contributor
timestamp: May 14, 2017, 09:47:52 am
content: The LED chips also contain large amounts of Arsenic as well in the dies, and that is not shown on the package.

author: james_s
author_rank: Super Contributor
timestamp: May 15, 2017, 02:58:30 am
content: True, although the arsenic in LEDs is a lot less likely to get out than mercury in a CCFL.

author: DigitalDeath
author_rank: Regular Contributor
timestamp: May 18, 2017, 06:39:14 am
content: That was a cool hack. Thanks for posting it and for the post nannies please let a guy enjoy his passion without that much criticizing. It was a just cool thing he felt sharing.

author: tggzzz
author_rank: Super Contributor
timestamp: May 18, 2017, 07:56:59 am
content: My technique is:small saucepan with a glass lid; reduces chance of splattering and might allow a little heating from the topthin layer of sand in saucepan; spreads heat avoiding hotspots and enables more control of temperature profilegas ring, not electric hobThe only thing that doesn't allow is a "rapid" cooloff as shown in the temperature profile. That can be ameliorated by lifting the PCB out when solder has reflowed

author: tatus1969
author_rank: Super Contributor
timestamp: May 18, 2017, 11:34:10 am
content: Quote from: tggzzz on May 18, 2017, 07:56:59 amSounds interesting... I wonder how homogenous the heating would be with a gas ring.

author: tggzzz
author_rank: Super Contributor
timestamp: May 18, 2017, 12:12:33 pm
content: Quote from: tatus1969 on May 18, 2017, 11:34:10 amThat question is equally valid for an electric hob; the constructiondetailswill matter. My (very cheap) saucepan has a relatively thick base, which will spread the heat. The sand, or rather the air in between the sand grains, will also spread the heat. I presume that would also be the case if you spread sand directly on your electric hob. Why not try it with a sacrificial/scrap board (no components) and see? (And let us know the results!)As far as I can see, it is even: 0603 sized components anywhere on a 5cm*5cm board start to reflow more or less simultaneously. Larger components may take a little longer, but that is due to their thermal mass, not uneven heating.I have not seen any scorching on boards' undersides. A few grains of sand lightly stick to the underside, and are simply brushed off when cool.If I wanted to try double-sided boards, I would experiment with mounting spacers on the board and putting it in the saucepan, optionally with less sand.

author: tatus1969
author_rank: Super Contributor
timestamp: May 19, 2017, 10:15:28 am
content: Quote from: tggzzz on May 18, 2017, 12:12:33 pmThat does certainly help, maybe comparable to the thick glass top of my hub.Quote from: tggzzz on May 18, 2017, 12:12:33 pmI don't need any thermal conductor, because the glass top is naturally perfectly flat.Quote from: tggzzz on May 18, 2017, 12:12:33 pmI will make a measurement with my IR thermometer and see how even the heat is spread, and how close I can come to something that deserves calling it reflow profile. I am already thinking of a dedicated hub with temperature sensor and triac controller

author: tggzzz
author_rank: Super Contributor
timestamp: May 19, 2017, 10:39:12 am
content: Quote from: tatus1969 on May 19, 2017, 10:15:28 amBut is the PCB perfectly flat?The sand also helps to slow down heat transfer and thus make temperature more controllable. I would expect that to be more beneficial on an electric hob which, in my limited experience, are less easy to control than gas hobs. Obviously there is a tradeoff between speed, control, and profile - experiments requiredQuoteI find thatIam a satisfactory heat controller

author: KL27x
author_rank: Super Contributor
timestamp: May 20, 2017, 03:45:59 am
content: QuoteA gas burner, you just turn to the size flame you want. The glass (halogen bulb?) hob in my kitchen appears to have thermostatic control. It turns on/off as needed, all by itself. If you turn it on without a load, for instance, it will spend a lot of the time totally off. Large enough load, and it will be 100% duty cycle. And it can be anywhere in between. And no, it's not very fine.... the hysteresis/oscillations are quite lengthy.

author: cdev
author_rank: Super Contributor
timestamp: May 20, 2017, 04:11:56 am
content: Couldn't the current/voltage being induced in the nearby boards conductors potentially damage something?

author: tatus1969
author_rank: Super Contributor
timestamp: May 20, 2017, 07:14:41 am
content: that is just a heating spiral, not an inductivehubhob.

author: KL27x
author_rank: Super Contributor
timestamp: May 20, 2017, 08:40:36 am
content: edit: deleted(I just had to google "ceramic hob." I thought that was a different word for a halogen cooktop, which looks similar. When it's off, at least.)

author: tatus1969
author_rank: Super Contributor
timestamp: May 20, 2017, 10:06:39 am
content: Quote from: KL27x on May 20, 2017, 08:40:36 amIt's the second time this happened in this thread. As I am not native english, I may have chosen a misleading term. After some more googling, I think that this is the correct one: "ceramic glass halogen hob". It is basically a regular heating spiral covered in a thick layer of glass. They are very common in Germany.Like this:

author: SeanB
author_rank: Super Contributor
timestamp: May 20, 2017, 11:42:33 am
content: Also called a glass top stove, very common as a built in item here as well. Benefits are easy to clean, and looks flatter than a regular stovetop with either heating plates or coils, but of course there are disadvantages in that it takes longer to heat up and it is a little less efficient power wise.

author: Nusa
author_rank: Super Contributor
timestamp: May 20, 2017, 03:57:10 pm
content: https://www.merriam-webster.com/dictionary/hobQuoteWhile dictionary correct, the cooker definition of "hob" seems to be specific to British English (maybe regional as well). In Americian English, most people would have no idea that a "hob" is a cooker. The word "cooker" is also uncommon, but it'll be understood since the word "cook" is in it. American terms are more likely to be stove, stovetop, range, cooktop or burners.Iduction cooking is the exception to that rule. What little there is in US has been imported, and the importers call them "inductive hobs". Those of us who have heard of it at all, have probably heard of it in connection with induction. Hence the confusion.In short, while your translation is correct, it isn't the best word choice for a global audience. There are a lot of regional/cultural language gotchas, and I'm sure you'll run into more of them. That's the difference between booklearning and actually talking to people.

author: tatus1969
author_rank: Super Contributor
timestamp: May 21, 2017, 09:01:30 am
content: Quote from: Nusa on May 20, 2017, 03:57:10 pmNot even booklearning, but hit-and-hope like googling random missing wordsTo my apologize I can say that I went to the USA for four months during my study, and that was when I learned 80% of my English. Sold popcorn in Chicago in a movie theater that sadly does not exist anymore ->http://cinematreasures.org/theaters/409

author: james_s
author_rank: Super Contributor
timestamp: May 21, 2017, 04:31:53 pm
content: In the US you'd almost always hear it called a "stove", occasionally "range". "Cooktop" is typically a separate unit used in conjunction with a wall oven.I'd never heard the term "hob" until I started chatting with a guy from England.