Hi in this episode I'm going to show you how to do-it-yourself Reflow Stencil solder a PCB and I Got this one from the mailbag sometime back. If you haven't seen it, it's uh, based on Vincent Hy's uh book mastering surface mount technology. This is where the Uh part of the Um Elector LAB Works uh Series This is where the PCB comes from and it's a ring light uh for cameras and we're going to Reflow sold all of the parts on here using a solder paste stencil. This is a a quite a high quality uh, stainless steel stencil.

Now you don't necessarily, um, have to get a stainless steel one if you're doing it yourself. In fact, they're probably prohibitively, uh, expensive. but there's a lot of companies out there today that will laser cut you a uh, a Myar, or a Capon solder paste stencil direct from the file in your Uh 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 uh, basic, uh solder paste and a hot air uh Reflow gun and we're going to have a go at uh, reflowing 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 Aim solder here in Australia and it's a Um 63. It's Sn63 which stands for 63% uh 10 and 37% lead.

so it's quite close to your regular 6040 Leed solder. So this is not uh leadfree solder. it, it's only 15 G which doesn't sound like a lot, but you don't need much solder paste as we'll see to uh, do one of these um, stencils on, you know, a fairly a fairly typical board like this. So this one has been manufactured uh, fairly recently.

Now the solder paste has a couple of issues. The first one is that it does have a uh shelf life if you try and use it. Beyond that, well, its Uh, performance is not guaranteed I Mean this one might have say 6 months and if you use it in 12 months time H it's probably still going to work. but you know the performance is not guaranteed at all.

Now this one's in a syringe um format. Um, because it comes with a little uh 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 uh, you can do it manually with a syringe. or you can get an air pump which, uh, dispenses a past dispenser you can buy them on eBay fairly cheaply these days.

100 bucks or so I Think solder paste dispenser and 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 their solder paste stencil like this.

so all we're going to do is apply our solder paste on there. then we go over it with a squidy 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 uh, 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 uh, it must be kept in a fridge as well. It must be kept airtight so you got to put the uh 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, um, in room temperature for a couple of hours. You don't want to apply it.

uh, 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. Um, 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, uh, put it airtight and put it back in the fridge. So solder paste can be a bit annoying if you and quite an expensive way to do it.

If you just you know you want to do a oneoff board, you're doing one or two boards a year. H solder paste. You know it may not be worth your while, but anyway, um, we are going to give it to go. now.

the first thing you want to do is just inspect your uh, solder past stencil to make sure all of the holes are cut out. Now it just so happens that this one here, um, 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 padge shaped holes there for this solder paste. Now if you're really, um, you know, into high volume, uh, manufacturer, mobile phones or something really high density? Parts Very critical.

very dense, uh, spacing, then the type of stencil you use, the thickness of your stencil, the uh, exact type of solder paste, the exact angle that you apply the solder paste at, and uh, the size of your paste pad, uh, holes and everything like that can become quite critical to to um, your final yield in volume production. but just for do-it-yourself stuff, eh, 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 M, you know you just get one of those cheap laser cut Myer um or CA on sheets or something like that. And next up, you're going to require uh, a couple of Pcbs the exact same thickness as the board you're doing. Of course, this is like a standard 1.6 mm board.

So we've got two other 1.6 mm 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 itself, on the board you're doing.

especially if there isn't, uh, much room around the outside of the panel here, because then, um, when you apply your stencil on there, it may not sit very flat if there's some tape very close to the individual pads 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 uh, 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. uh, you know, a real, you know, like a mobile phone with little O201 components or something. something like that real ultra dense stuff. Then the alignment of, uh, 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. For a do-it-yourself application like this though, it's really not that, uh, critical.

You know, if you get get a little bit of warpage in there, it's not a problem. Now what we've got is a um spatula here. or sometimes called a squidy or you know it goes under various uh names in the industry. This one is not designed for this, uh, purpose.

This is just uh, one designed for cake mixing and uh, things like that. It's a um, silicone rubber, uh one and you know it's It's not ideal for the purpose, but for, uh, just to do-it-yourself oneoff like this, it's going to work just fine. I Think Ideally you'd want a proper stainless steel, uh, spatula to apply. Now, the angle that you use on this can, uh, be reasonably critical.

It may not matter just on a simple do- 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, uh, rip some of the solder paste back out of it all right 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 Squidy in here and move it. Drag it across our stencil like that and make sure you get the right angle. Make sure there's no retraction in there.

The salt, oh, 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 uh is not the best spatula at all folks. I'm not happy with this um at all.

I didn't have a metal one so I've had to make do here and there's a very good closeup of some uh solder retraction there. So I'm just going to put a little bit more paste in there and uh, this uh paste I I may not have, uh, may still be a bit cold, may not have let it uh, warm up enough. Now this isn't the world's best job I'm afraid cuz I use usually don't uh, do this so I'm I'm using uh new solder paste I haven't used before I'm using a new spatular I haven't used before so you know really and and I haven't um, 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 uh technique down uh Pat then you should be able to in theory, uh, do this in one pass of the spatula or the squeegee.

If you got a super wide one, it can go right across the board. but um 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 uh, 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 TDA 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, like the solder paste has got in 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 uh Reflow that solder with the hot air gun that they will not uh stay together and short the solder will just Reflow into to the well on the pad. uh and uh, it won't stick to the solder MK So it shouldn't be a problem if you actually miss one of the pads and it doesn't uh Reflow then really, that can ruin your day. So it's worth spending 5 minutes, just under a uh, 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 Um surface mount tweezers uh, nonmagnetic type make you make sure you get a good, uh, 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 pickup tools you can pick these up for you know, five or 10 bucks. Very cheap. They come with different width, um uh, heads on them for different parts so you just press the Uh button on this thing, put the suction cup on top Let It Go and Bingo! We picked up our part and we can move it over but as you can see you don't get it right. Ah, it falls off and ah you can ruin your day.

These are pain in the ass I Find tweezers much easier but uh, these particular just hand ones like this, these are. you know these are pretty crap and crusty. You can get uh much better. uh vacuum ones which actually have a proper Mains powered Vac Uum pump and then there's a foot pump on the floor so that uh 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, uh, vacuum in them than just these hand ones.

Now if you do get your parts in tape form uh, like this and you've got a lot of them to do, it can be worth actually, uh, labeling them on the bench. you know, put a little uh label next to them, get some uh, sticky tape actually. uh, you know, hold down the start 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 got a proper vacuum tool and it's right near it, you don't even have to raise your hand. Boop boop boop. Almost like a human pick and place machine.

Almost once you, you know if you get your uh technique down right. But of course we can't take too long doing this cuz as I said at the start, this solder paste has a not only a six-month uh, shelf life or a certain shelf life. but after you've uh, 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 uh, you know, so maybe like 2 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 your 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 your place your components back to front. Now take this Led I'm using here for example, How where are the markings on this to indicate which is the anode and which is the cathode. So make sure you uh, physically test these things before you put them on for these critical parts and or you're reading the correct data sheet trap.

For young players, nothing worse than go placing a 100 leads or something than finding you got them all back to front. And they've thoughtfully provided in the book identification for the LED here. But look at this. This is a much larger, uh, cut out.

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 showing that the uh cathode here is the one with the notch in it. Well, it's not on the ones I've got. The notch is the anode bastard.

Let's have a good look at placing that one manually. You can see that that, um, not all the solder paste applied to that uh 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 uh Reflow that Led and if we find it fails later, we can always add a bit more solder manually.

But not really a big deal. and I'm finding these LEDs incredibly annoying actually, because uh, trying to get them out of the tape and uh, 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 identifiers on them tediously.

Try and get my very fine point uh, tweezers inside the tape there and pick it out. and I didn't have much luck with the uh handheld, uh vacuum pump. That's just garbage. Um, so really, um, 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, um, you know, efficiency in this sort of thing matters.

Now it's not hugely critical that you actually get the Uh chip and parts you know, really bang Center on those pads because when this solder reflows, there will be 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 um, 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 Uh circuit and this is a practical circuit.

These are practical Parts these LEDs Paint in the ass. They've got no visual identifiers. this tiny little Um Six Pin so 23 Here you can just see the tiny little uh pin one marker on there I Can barely see that with my eye. it's much Clear it's much clearer on the screen here.

So I was going to 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 time. Little Six Pin: So 23 you notice that the uh solder paste is now you know it's it's all over the shop there really.

but the thing is that will uh Reflow quite nicely and uh, the solder mask it should Reflow Just fine and we shouldn't get any shorts at all and you'll notice I Got it the right way around. Pin one marker there. the Little Dot on the chip with the uh uh White notch on the top and when you're 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 the there we go one just popped out and if you drop these on your carpet you you will never find them again.

Um, they're just completely gone and these are uh 0603. You know if you're using 0 402s or something. oh man, forget it. Just be careful you don't bump the ones next next to them.

That's why you really need a fine pair of tweezers like I'm using here rather than ones with big fat Stumpy ends on them. uh 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 uh placing the components Dave robot pick and place machine is complete. All our parts are done.

Woohoo! Time to actually Reflow this thing now. ideally uh, we would use a Reflow oven to do this or one of those modified uh toaster ovens which are all the Vogue these days. but I don't have one and as it so happened I wanted to show um that you can do it just using a hot air gun like this because any well equipped lab Lab for surface mount work should have a basic hot air gun like this A10 858d plus I mean real cheap on eBay You know, like $60 $70 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. Uh, just here. Look at their data sheet for it and you'll get a Uh Reflow thermal profile for it and this is typically what you would program into your Uh Reflow oven or toaster oven. You would program in this profile.

here. where it ramps up. you know it ramps up to maximum temperature to 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 two curves up and low.

It should be somewhere smack in the middle of that and then reaches a Peak at around 180 seconds and taper off. But this will vary depending on the type of solder paste and it'll also vary depending a typ upon the Uh 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. And 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 uh, 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. Uh, thermal.

Uh, 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, preheater, or anything like that. I'm just showing you how you can do it quick and dirty using you know, a nonoptimal 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. Uh, for one of these, um, hot air guns, you probably want to get in a set at maybe 40 50 above that. So sort of like 250 is probably not a bad temperature.

to set it at sort of 250 260. You probably wouldn't want to go above that. to make it even more difficult. We have, um, quite, uh, temperature, uh, dependent, uh components on here.

These LEDs are, um, notorious for not surviving high temperatures, so you really got to sold them quick and uh, you know, really keep that temperature down to an absolute minimum otherwise your leads can be ruined. So there you go: I've got it set to around about uh 250 and uh, I'm going to try a wide I Actually don't have the nozzle, uh, the wide nozzle. so I'm just going to use the direct output. Usually, you'd use a wider nozzle for this purpose, otherwise you'd get a, uh, smaller nozzle like that if you want.

just wanted to get in there and do more. Um, 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 cuz there's not much um. adhesion on those components. All right now.

I'm just going to experiment with a couple of Uh components on the outside here and uh, we start out by bringing it down, swirl in motion around there until we can see the solder paste. Reflow And there we go. You can see that capacitor move into place there and we Reflow the LED Beautiful! Now here's an example on this capacitor here where it has uh, reflowed but you can see because it's a big 10 microfarad capacitor uh 0603 very thick one. so it's um, you know, the highter there it's the solder fillet is only on the bottom of the capacitor down in there, you can see it is actually quite, uh, quite clean.

I Rather like that you can see that uh LED there reflowed very nicely as well. All right, let's try the same thing on this: uh S 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 have to experiment with this.

It's all a matter of getting the uh correct amount of air flow 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 manufacturer's thermal profile for the paste and minimizes damage to parts and stuff like that. And here we go.

We're starting to go and can see the so there. There we go, can see the solder mask working perfectly. Brilliant. Look at that.

no more. No solder? Bridges No, Nothing fantastic. That's the magic of solder mask here is that? Look at. There's no shorts between any of those uh pins at all.

and each pin is perfectly solded. Brilliant. And here goes our six pin. So 23 Wham Look at that.

Oh yeah, there we go. Our solder Bridge went away. all that solder reflowed nicely. Oh beautiful.

Now, I've actually uh, turned up the temperature to about Uh 265 or thereabouts, and that seems to be reflowing these leads rather quickly. probably can't, uh, see that. But so yes, it's all a matter of getting the right temperature, the right air flow, and uh, you can Reflow these quite quickly I've got it set to about 265 I don't know how good that is on uh, this particular unit how well regulated. but uh.

anyway. I've got at like a U air speed of four I think 4 and 1 half something like that. so I had to uh increase it where I started off having it because this is pretty much a experimentation. It's going to vary greatly.

There goes the capacitor. It's going to vary greatly. uh, between individual units and uh, the type of board you have. as as I said, with uh, how many thermal relieves it has, how much copper it's got on there.

What all the thermal? Mass thermal mass of the parts, all sorts of stuff. it's all. uh, it's all a big gamble and it is. uh, trial and error.

and by the way, just be careful what surface you do this on I'm doing it on this uh, high temperature uh rubber ESD mat which is designed to uh, uh, not burn through with solder and uh, it is done I forgot to load the components on that board. By the way, if you, um, 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 I hand solder a couple of Uh components left. We'll just, uh, cut this out of the panel here.

use a your crap pair of side cut, 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 around 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 5volt power supply and Tada look at that all LEDs work I got them around the right way regardless of uh yeah, the Uh 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 yeah, you can hold it down. bang bang bang and woo Full brightness. It's pretty darn bright. You don't want to look.

look at the thing that's for sure. Very nice and you wouldn't believe it. Look at this doesn't fit over the uh Focus ring on my Canon Hfg10 which is my main camera I shoot the blog with ah well I've I've got to admit I normally wouldn't uh do Reflow solder in on a board like this I'd just get down my solder in iron and My5 mm solder and I just manually solder all of the leads and all the components cuz there's not that many because it is actually quite a hassle to do. uh Reflow soldering uh with stencil Reflow soldering.

and if Essen got to have a very good reason to do it one of the best, uh, 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 uh 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 sold.

Uh, the other thing is, um, you know there's no flux residue sorry left around from the Rosen cor 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 uh oven, a converted toaster oven or a proper Reflow oven.

Then you can program in the temperature profile and you can follow the manufacturers 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 Uh tools here today. We didn't even use the right type of uh spatula.

we used just a uh hot air uh Reflow gun and we were able to do it no problems whatsoever. We reflowed 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 a real uh, you know, critical board with a BGA and everything else that you can't afford to get wrong.

And of course, you got to design your boards properly for uh, thermal layout as well. That's a whole another video. So I guess you could argue. It's a bit of a tossup with on a board like this, whether or not it's quicker just to hand so the thing and be done with it, or whether or not you mck 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 very cheap uh, laser cut, Myar or other stencil and in fact some PCB uh suppliers are even provided a free stencil now. Yeah, give it a try, it's not as hard as you think. hope you found that interesting and if you want to discuss it, jump on over to the Eev blog. Forum Catch you next time.