EEVblog #415 - SMD Stencil Reflow Soldering Tutorial

hi in this episode I'm going to show you how to do it yourself reflow stencil solder 8 PCB and I got this one from the mailbag some time back if you haven't seen it it's a based on Vincent EMPs book mastering surface mount technology this is where the part of the Elector lab works series this is where the PCB comes from and it's a ring light for cameras and we get a reflow solder all of the parts on here using a solder paste stencil this is a quite a high quality stainless steel stencil now you don't necessarily I'm have to get a stainless steel one if you're doing it yourself in fact they're probably prohibitively expensive but there's a lot of companies out there today that will laser cut you a a mylar or a Kapton solder paste stencil direct from the file in your CAD package it can generate the paste stencil and that's a whole video in its own right but I'm going to show you how to do that using some basic solder paste and a hot-air reflow gun and we're going to have a go at reflow in the parts onto here after we apply the solder paste with a stencil so let's give it a go and the solder paste I'm going to use today comes from chem tools or Ames solder here in Australia and it's a m63 possess n63 which stands for 63% 10 and 37% lead so it's quite close to your regular 6040 leaded solder so this is not lead-free solder it's it's only 15 grams which doesn't sound like a lot but you don't need much solder paste as we'll see to do one of these um stencils on you know a fairly a fairly typical board like this so this one is that being manufactured fairly recently now the solder paste has a couple of issues the first one is that it does have a shelf life if you try and use it beyond that well it's performance is not guaranteed I mean this one might have saved us six months and if you use it in 12 months time it's probably still going to work but you know the performance is not guaranteed at all now this one's in a syringe format because it comes with a little tip like this which you can plug it on you can use it as a syringe and you can individually put paste on each pad like that and you can either do it manually with a syringe or you can get an air pump which dispenses a paste dispenser you can buy them on eBay fairly cheaply these days 100 bucks or so I think solder paste dispenser you can go around and manually dispense solder paste on each pad but hey that's time-consuming you end up missing the pads it's much quicker and simpler to use there solder paste stencil like this so what we're going to do is apply our solder paste on there then we go over it with a squeegee like this and we're going to apply all of our solder paste in there and we lift it off and we should be left with an even amount of solder paste on each one of our pads here that's the plan and then we place the parts and then we will reflow the solder the other problem with solder paste of course is that it must be kept in a fridge as well it must be kept out airtight so you're going to put the nozzle back on it in a fridge and then even then it still has a shelf life now when you go to use it like this make sure you sit it in room temperature for a couple of hours you don't want to apply it out cold it's not an issue that is going to reflow incorrectly it's just that it won't apply through the solder paste stencil very nicely arm so you really have to let it warm up to room temperature for a couple of hours first before you can use it and when you're done with it make sure you put it airtight and put it back in the fridge so solder paste can be a bit annoying if you end a quite an expensive way to do it if you're just you know you want to do a one-off board you're doing one or two boards a year ah solder paste you know it may not be worth your while but anyway we are going to give it a go now the first thing you want to do is just inspect your solder paste stencil to make sure all of the holes are cut out now it just so happens that this one here hasn't you can see that there's still one there that didn't punch out correctly so we're now left with all of our precisely cut pad shaped holes therefore the solder paste now if you're really you know into high-volume manufacturing mobile phones or something really high density parts very critical very dense space in then the type of stencil you use the thickness of your stencil the exact type of solder paste the exact angle that you apply the solder paste at and the size of your paste pad holes and everything like that can become quite critical to your final yield in volume production but just for do-it-yourself stuff it doesn't matter this is a stainless steel stencil more than good enough it's about 150 microns thick doesn't matter it's going to work whether you use like a might you know you just get one of those cheap laser cut mylar or right kept on sheets or something like that and next up you're going to require a couple of PCBs the exact same thickness as the board you're doing of course this is like a standard 1.6 millimeter board so we've got two other 1.6 millimeter boards this will hold this board in place and ensure that it just doesn't move around on the bench like that so we're going to put it down there we're going to get some sticky tape and you don't want any tape on the board it's so on the board you're doing especially if there isn't a much room around the outside of the panel here because then when you apply your stencil on there it may not sit very flat if there's some tape very close to the individual heads that you're doing and next up we're going to have to align our stencil over these pads as you can see it's a it's fairly critical there's not much movement in my fingers there you can see how critical this would be if you were doing you know a real you know like a mobile phone with little oto 1 components or something like that real ultra dense stuff then the alignment of these stencils becomes a big deal so I'm going to I think that's right so I'm going to apply some sticky tape on the outside of that either side and it's it's sitting fairly flat the thing you don't want to do is have this warp during your paste application before a do-it-yourself application like this though it's really not that critical you know if you get a little bit of warpage in there it's not a problem now what we've got is a spatula here or as sometimes called a squeegee or you know it goes under various names in the industry this one is not designed for this purpose this is just one design for our cake mixing and things like that it's a silicone rubber one and you know it's it's not ideal for the purpose but for right just to do-it-yourself our one-off like this it's going to work just fine I think ideally you'd want a proper stainless steel spatula to apply now the angle that you use on this can be reasonably critical it may not matter just on a simple do-it-yourself one like this but you know if you use too shallow an angle like that it can or too sharp an angle like that then it can actually rip some of the solder paste back out of it alright now let's give it a go now we shouldn't need a huge amount of solder paste at all let's just maybe put that much on there perhaps there we go a little bit more now let's get our squeegee in here and move it drag it across now stencil like that and make sure you get the right angle make sure there's no retraction in there the salt up you can see that one I think you can see that one just there you can see some of the paste has retracted out of that one normally you only have to like you know do this in one pass usually don't be afraid to go back over existing pads you can certainly do that and I really you know this is not the best spatula at all folks I'm not happy with this at all I didn't have a metal one so I've had to make do here and there's a very good close-up of some solder retraction there so I am just going to put a little bit more paste in there and this paste over I may not have may still be a bit cold may not have let it warm up enough now this isn't the world's best job I'm afraid because I usually don't do this I'm using a new solder paste I haven't used before I'm using a new spatula I haven't used before so and I really enter and I haven't done any practice at all so this one this particular job is a little bit hit-and-miss I'm afraid but you get the idea so ordinarily you know if you've got your technique down pat then you should be able to in theory do this in one pass of the spatula or the squeegee if you've got a super wide one it can go right across the board but anyway we just want to inspect make sure you inspect like the big ones are really obvious for the LEDs but just inspect those little ones in there just to make sure that they're make sure that they're covered very carefully peel it off and don't touch it and you should be left with a board with tada solder paste on it and there you have it you can see the solder paste on the individual pads there and of course if you have a look in here you can see some what looks like you know I like the solar pace has gotten between the pads but don't worry about that your solder mask that green stuff on your board there is going to take care of that when that reflows so when you were reflow that solder with the hot-air gun that they will not stay together and short the solder will just start reflow into the well on the pad and it won't stick to the solder mask so it shouldn't be a problem if you actually miss one of the pads and it doesn't reflow then we're really that can ruin your day so it's worth spending five minutes just under a under a magnifying lamp going around inspecting everything now as for placing parts there is a couple of ways to do it of course the fully automated way to do it is to use a pick and place machine but we don't have one of those and you don't either I'm sure because that's why you're watching this video so the traditional way to do it is just a pair of surface mount tweezers are non-magnetic type make you make sure you get a good high-quality pair and you can individually place them one by one down like that and the other way to do it is with one of these vacuum pick up tools you can pick these up for you know five or ten bucks very cheap they come with different widths heads on them for different parts so you just press the button on this thing put the suction cup on top let it go and bingo we've picked up our part and we can move it over but as you can see you don't get it right it falls off and you can ruin your day these are pain the ass I find tweezers much easier but these particular just two-hand ones like this these oh you know these are pretty crap in crusty you can get much better vacuum ones which actually have a proper mains-powered vacuum pump and then there's a foot pump on the floor so that you know you operate with your foot and it picks up your part and moves it over and they have much better and more consistent vacuum in them than just these hand ones now if you do get your parts in tape form like this and you've got a lot of them to do it can be worth actually labeling them on the bench and I put a little label next to them get some sticky tape actually that's you know a hold down the staff and the end of it and then you can if you have a vacuum tool then you can just go along and pick them out like that and you can actually be you know quite efficient if you've got a proper vacuum tool and it's right near it you don't even have to raise your hand buh buh buh almost like a human pick and place machine almost once you you know if you get your technique down right but of course we can't take too long doing this because as I said at the start this solder paste has a not only a six month a shelf life or a certain shelf life but after you've taken out of the fridge let it warm down you've applied it here you've only got a couple of hours before the solder paste isn't going to work that well and you know so maybe like two hours is usually the recommended figure but yeah you've probably got you know four or five for a simple do-it-yourself one like this but you certainly don't want to apply the paste and then come back the next day it's just not going to work so make sure you got all these stuff sorted ready to go after you've applied your paste now if there's one thing that will really ruin your day and Murphy will ensure it probably happens is you place your components back to front now take this led I'm using here for example how do where are the markings on this to indicate which is the anode and which is the cathode so make sure you physically test these things before you put them on for these critical parts and all your reading the correct data sheet trap for young players nothing worse than going placing a hundred LEDs or something then finding you've got them all back to front and they're thoughtfully provided in the book identification for the led here but look at this this is a much larger cutout they've actually supplied a different type of LED and guess what the supplied one is actually the opposite polarity to what's showing here it's shown that the cathode here is the one with the notch in it well it's not on the ones I've got the knotch is the anode bastard let's have a good look at placing that one manually you can see that not all the solder paste applied to that bottom pad there so let's place our LED on there and push it down into place but even though all our solder paste didn't go on there that will be enough to reflow that led if we find it fails later we can always add a bit more solder manually but not really a big deal I'm finding these LEDs incredibly annoying actually because trying to get them out of the tape and keep the orientation they keep flipping around and ah it's just it really is pretty awful when you use these components which have virtually no visual identify us on them tediously try and get my very fine point tweezers inside the tape there and pick it out and I didn't have much luck with the handheld vacuum pump this is garbage so really anyway it's done I mean you know in the end it only took me a few minutes but if you really had a lot of these to do you know efficiency in this sort of thing matters now it's not hugely critical that you'll actually get the chip and parts you're not really bangs Center on those pads because when this solder reflows there will be a surface tension on there and it will actually pull the chip directly into the center now I was going to say that this is this project is probably not a good example of you know just being able to easily place parts on a board like this but well I guess the whole idea is to show a practical circuit and this is a practical circuit these are practical parts these LEDs pain in the arse they've got no visual identifiers is tiny little arm six pin SOT 23 here you can just see the tiny little pin one marker on there I can barely see that with my eye it's much clearer it's much clearer on the screen here so I was going to hit complain that it's really a pain in the butt I was hoping to have a real quick video just showing this sort of stuff but this is this is more real-world there is our tiny little 6 pin SOT 23 notice that the solder paste is now you know it's all over the shop there really but the thing is that will that reflow quite nicely and the solder mask it should refloat just fine and we shouldn't get any shorts at all and you'll notice I got it the right way around pin 1 marker there the little dot on the chip with the white notch on the top and when you peeling the tape back on these things just be careful these if you fling these these little capacitors will go everywhere and if you drop one of there we go one just popped out and if you drop these on your carpet you'll never find them again they're just completely gone and these are oh six oh threes you know if you use you know 402s or something oh man forget it just be careful you don't bump the ones next to them that's where you really need a fine pair of tweezers like I'm using here rather than ones with big fat stumpy ends on them should try and self center themselves when they reflow there we go that will be the end of the most tedious part of all this which is placing the components Dave robot pick and place machine is complete all our parts are done whoo-hoo time to actually reflow this thing now ideally we would use a reflow oven to do this or one of those modified toaster ovens which are all the vogue these days but I don't have one and as it so happened I wanted to show that you can do it just using a hot-air gun like this because any well equipped Lev lab for surface mount work should have a basic hot-air gun like this 18 9 8 5 8 D plus I mean real cheap on eBay you know like 60 70 dollars I've done a review on this and good enough for this purpose now there's one thing you should do if you want to take this reflow soldering business seriously look up the manufacturer of your particular solder paste and I've done that just here look at their data sheet for it and you'll get a reflow thermal profile for it and this is typically what you would program into your reflow oven or toaster oven you would program in this profile here where it ramps up you know it ramps up to maximum temperature at about 180 seconds there so you put your entire board in and boom it ramps up it's going to be you know it needs to be within these margins that's why it's got to curves up and low it should be somewhere smack in the middle of that and then reaches a peak and around 180 seconds and taper off but this will vary depending on the type of solder paste and it'll also vary depending a titin upon the layout of your board as well because if you've got a board with you know lots of ground planes on there not enough thermal relief this is where the design of your PCB comes into it because your components can tombstone they can one end of a component can reflow quicker than the other end and your component can tombstone and lift up like that and that's bad news and well I don't know it may happen today but a lot of that is a lot of art in PCB design and designing thermal thermal relieves on your pads and things like that so but that's a whole video in its own right because we don't have a reflow oven here we can't set a temperature profile we don't have a board pre heater or anything like that I'm just showing you how you can do it quick and dirty using you know a non-optimal tool like a hot-air gun but it can work so really what we want is our maximum temperature there is you know 220 or something like that for one of these hot-air guns you're probably want to going to set it maybe 40 50 degrees above that so sort of like 250 is probably not a bad temperature to set of that sort of to 50 to 60 you probably wouldn't want to go above that to make it even more difficult we have quite a temperature dependent our components on here these LEDs are notorious for not surviving high temperatures so you really got to solder them quick and you know really keep that temperature down to an absolute minimum otherwise your LEDs can be ruined so there you go I've got it set to around about 250 and I'm going to try a wide I'd actually don't have the nozzle the wide nozzle so I'm just going to use the director output usually you'd use a wider nozzle for this purpose otherwise you'd get a smaller nozzle like that if you what just wanted to get in there and do more you know more direct work and you want it set to a reasonably low level on your airflow as well because you don't want to blow your components off the board because there's not much adhesion on those components all right now I'm just going to experiment with a couple of components on the outside here and we start out by bringing it down swirling motion around there until we can see solder paste reflow and there we go you can see that capacitor move into place there and be reflow the LED beautiful now here's an example on this capacitor here where it has that refloat but you can see because it's a big 10 micro farad capacitor Oh 603 very thick one so it's some you know the height of there it's the solder Philip is only on the bottom of the capacitor down in there but you can see it is actually quite quite clean I rather like that you can see that led there refloat very nicely as well alright let's try the same thing on this side so8 and these resistors down here circular motion on your hot-air gun there and it will take a little bit because there is a thermal mass in the board that you have to heat up you do have to experiment with this it's all a matter of getting the correct amount of airflow and temperature this is why a proper thermal oven is much better it just does it all in one hit and it correctly matches the manufacturers thermal profile for the paste and minimizes damage to parts and stuff like that and here we go it's starting to go and can see the solder that there we go and see the solder mask working perfectly brilliant look at that no more no solder bridges no nothing fantastic that's the magic of our solder mask here is that look at there's no shorts between any of those are pins at all and each pin is perfectly soldered brilliant and here goes our six pin SOT 23 wham look at that ah yeah there we go our solder bridge went away all that solder refloat nicely ah beautiful now I've actually turned up the temperature to about two six t5 or there abouts and that seems to be reflow in these leads rather quickly I probably can't see that but so yes it's all a matter of getting the right temperature the right air flow and you can reflow these quite quickly I've got it set to about 265 I don't know how good that is on this particular unit how well regulated but anyway I've got it like a air speed of four I think four and a half something like that so I had to increase it where I started off having it because this is pretty much experimentation it's going to vary greatly because the capacitor it's going to vary greatly between individual units and the type of board you have as I said with how many thermal relieves it has how much copper it's got on there what all the thermal mass then will master the parts all sorts of stuff it's all it's all a big gamble and it is trial and error and by the way just be careful what surface should do this on I'm doing it on this high temperature rubber ESD mat which is designed to not burn through with solder and it is done I forgot to load the components on that board by the way if you that's actually a double-sided load board so what I'm actually going to do actually what I'll do is I'll just reflow now before a hand solder a couple of components left we'll just cut this out of the panel here use a your crap pair of side cutters have a good pair for good work and a crap pair for something like this and get in there the flat side if it's a round board like that you want the flat side of your side cutters in there and bang all right we have our nicely assembled board moment of truth plug in my five volt power supply and tada look at that all LEDs work I got them around the right way regardless of yeah the instructions being slightly wrong pays not to follow the instructions sometimes but look at that we have a ring light if we go up we can see it hopefully increasing brightness it looks like oh you can hold it down bang bang bang and whoa full brightness see it's pretty damn bright you don't want to look at the thing that's for sure very nice and you wouldn't believe it look at this doesn't fit over the focus ring on my canon hf g 10 which is my main camera i shoot the blog with oh well I've got to admit I normally wouldn't do reflow soldering on a board like this I just get down my soldering iron on my point five millimeter solder and I just manually solder all of the LEDs and all the components because there's not that many because it is actually quite a hassle to do reflow soldering art with stencil reflow soldering and you've essentially got to have a very good reason to do it one of the best reasons of course essential reason is if you've got like a BGA component for example that you can't do with the manual method you've got to use a stencil and paste and then reflow underneath the BGA you can just see the consistency on all of those solder joints there it is very very nice you can tell it's been reflow solder the other thing is you know there's no flux residue sorry left around from the rosin core solder or so it looks very clean and very professional like it was machine assembled and well it you know it almost is the only difference is you place the parts instead of a machine so really to do reflow stencil soldering properly you should have a proper thermal oven I converted that toaster oven or a proper reflow oven then you can program in the temperature profile and you can follow the manufacturer's instructions precisely you minimize risk to all your components and it's just going to work a lot quicker as well but as you saw we just used basic tools here today we didn't even use the right type of spatula we use just a hot-air reflow gun and we were able to do it no problems whatsoever we refloat all our parts lots of delicate leds didn't damage one of them but you have to be very careful if you're using one of these hot-air guns just to experiment and make sure you've got it right on non critical components first before you trust it on you know a real you know critical board with a BGA and everything else that you can't afford to get wrong and of course you've got to design your boards properly for a thermal layout as well that's a whole nother video so I guess you could argue it's a bit of a toss up with on a board like this whether or not it's quicker just to hand solder the thing and be done with it or whether or not you're muck around with a stencil and a reflow oven or a hot-air gun but certainly the results are first-class and you can easily do it yourself using a very cheap laser-cut mylar or other stencil and in fact some PCB supplies are even providing a free stencil now yeah give it a try it's not as hard as you think hope you found the interesting and if you want to discuss it jump on over to the eevblog forum catch you next time you you

Channel: EEVblog

Views: 516,720

Keywords: surface mount, smd, soldering, soldering tutorial, how to, diy, surface mount soldering, stencil, smd stencil, stainless steel stencil, solder paste, paste, lead free, squeegee, led, elektor, reflow, reflow soldering, hot air, hot air gun, toaster oven, reflow oven, oven, application, tutorial, hints, tips, pick and place, component, placement, temperature, air flow, paste dispenser, foot pump

Id: qyDRHI4YeMI

Length: 31min 0sec (1860 seconds)

Published: Thu Jan 24 2013