 The Great Search, brought to you by Digikey and Adafruit, thanks Digikey. Every single weekly data user power of engineering to help you, yes you. Find the things that you need on digikey.com. Lady, what is the great search of this week? This week's great search is solder paste. I was showing on Desk of Lady Ada how to rework this board under the overhead. I'll show it real fast. I was reworking this board which had a module with underpads. The pads are on the bottom of the module and so you have to, you can't solder this by hand. You have to solder it with a hot air station or a hot plate, in this case I was using a hot plate and I was using a syringe with solder paste. This is a go-to technique, I mean this board is going to be tossed so I'll just show what it's like but you know if you need to put some paste down, I find a syringe to be great. Let's see, I'll use the zoom in feature again. With the rework, how are you sure the pins don't bridge with solder? Very carefully. You don't put too much, you get used to it. There you go, maybe move it so it's a little bit better. Yeah, I know. You might want to zoom out a little bit. Yeah, I know. I'm just, I'm getting used to, whoa, too much. Hold on, let me see if I can, I'm just messing around. That's not too bad. Okay, so yeah, I mean you would put some paste down and you could hot air it to get it to bubble and cover the pads or use the tip of a soldering iron, either way, or if I'm just even reworking chips that have pins on the outside, a little bit of paste, especially because the flux is already in it, it's sitting in flux, it's a great and easy way to do SMT re-work and this is kind of one of the tricks and secrets. If you have paste, solder paste in a syringe, you don't need to have very fine wire, sometimes it's very hard to heat up the wire solder, especially if you have a very fine tip and very fine pitch parts. Luckily, you can get solder paste from DigiGain, you can get overnighted if you want to keep it cold, but personally at work we keep the solder paste in the fridge to keep it nice and cold at temperature, at home, you know, from just messing around, I keep it in a cool dark area and it lasts quite a while as long as it doesn't dry out. So let's go to DigiGee. Okay, so let's search for solder paste, so you can get all sorts of different solder paste, it's going to be under solder, so solder paste comes in basically two or three different containers, so it comes in tubs, it's what you use on a paste printer because you scoop it out and you put it down on the stencil and then the squeegee squeegees it down. We have tons of videos that we show on our Wednesday show if you want to see what this looks like on the automation process and then of course you can get it, like I said, as a tube. There's two sizes of tubes, there's like mega tubes, this is 600 grams, so this is as much, sorry, this is more solders in this tub and these are actually, the big ones are for automated stencil deposition machines usually, like normally a human doesn't hold a half a kilogram, more than half a kilogram of, take a sausage worth of solder paste. Usually I want to go with the smaller, you know, 35 gram, this one that I've got here I think is 35 grams too, yeah, yeah, 35 grams, so 35 grams is in less is what I suggest. A 35 gram solder paste syringe can last you a very long time, by the way, like easily a year or two, like this, you know, is from 2020, so they last quite a long time, so you get the smallest one you can get. So let's go to stacking, let's start with it's only active and let's only get a syringe to this only we're looking for. And then there's a couple different options. So there's leaded and there's lead free, so this is the first kind of differentiator we want to make. Chances are if you're manufacturing in the industry, you're all lead free anyway, so of course you're going to select lead free. If you're soldering at home, you can use leaded solder or some industries where leaded solder is acceptable, you know, when I'm doing rework again, if I'm doing prototypes at home, especially if I have something that is, you know, I need to be able to rework it very easily, leaded solder is going to be easier to rework, you know, doesn't go to a customer, I'll do that at home, otherwise I use a lead free. Lead free needs a higher temperature of rework, so you need hot plates and hot air guns that can go up to that temperature, like 240 degrees, you know, 250 or higher, leaded needs a lower temperature. That said, I think I'm going to just select lead free because I'm going to assume that you guys need lead free, so I'm going to not select 63, 37 or 63, 37, that's the lead, PB is lead. Okay, next up, flux type, no clean or water soluble. This is sneaky, a lot of people are like, oh, I want it with water soluble, I want it to be like, you know, cleanable. If you get flux that's water soluble, you must clean it because it's actually more activated. So, unless you have a water washing system that you're going to put your boards through, you should select no clean. There's nothing wrong with no clean, I mean, it leaves a little bit of residue, but that residue is non-conductive and it's not harmful for your electronics and it's protective, it's like the flux that covers it. I personally always use no clean, I've used no clean, all I've had if I use is no clean, there's no reason for us to wash. If you have boards that you want to wash or you have a washer, go with water soluble otherwise. No. Okay, next up, mesh type 345. So I was actually like, what is the difference? I know at Adafruit for our stencil machine, we actually use mesh 4 because we have 0.4 millimeter pitch parts that we use. If you're using 0.4 millimeter pitch, yes, you'll want maybe mesh 4 if you're using 0.2.0.1, 0.0.1.0.5, sorry, 0.1.0.0.5, you can use 4 or 5. I just googled really quickly and there's some nice web pages that talk about the sizes of the solder balls. In general though, pretty much everyone uses 3. This paste that I have here is 25 to 40, this is actually, oh funny, this is, no, sorry, yeah, mine is type 3, so this is a type 3, I use type 3 for pretty much everything again other than 0.4 millimeter or smaller BGA components, really fine apertures. You'll want 4 or 5 otherwise, 3 is perfectly fine and it's the most common, okay? So I only have 4 options left. So now there's, these are both from, these are all 4, these are from ChipQuik, which will surprise me, ChipQuik makes a lot of rework, stuff especially home rework or small scale rework. They have two types of products here, one is, you'll see here the differences in the temperatures. One has like 220 degree C melting point, that's going to be your standard lead free solder and then they have this low temp, 138 C, so the 138 C stuff, again, that's really low temperature. That's low enough that a very hot component will desolder itself, right, which we probably don't want, so keep in mind what you're using it for, 138 C is not very warm. If you're doing, I think, rework where you're removing parts, I think people tend to like that because it's easier to keep everything, you know, the board stays pretty hot, on your hot plate you can remove and rework stuff very easily. That said, I don't actually use the low temp stuff that much. ChipQuik is famous for it, try it out, but for general purpose, I tend to use your standard lead free 1096 silver III copper, 96.5, 3.5 and then finally they have what's left and there's two versions, one is a 35 gram and one is a 15 gram, same equipment, you know, same material and everything, just one is a little smaller, it's 5 cc's not 10 cc's, honestly, I would just get like, unless you really need a lot, just get this, you know, it's about half the price, 35 grams is a lot, unless you're really making a lot of boards, you know, if you're just doing prototypes at home, you do a couple of prototypes a week, I think this 15 gram syringe of lead free no clean solder paste will do great and another nice thing is, as you can see, it comes with the plunger and the tip also, so the dispenser tip and you can get other dispenser tips from Digikey, we will cover that next week. I tend to use the yellow tip, whatever that size is, but depending, you know, it doesn't really matter, just depends on whether you'd like to be able to squeeze more in one squeezing, but this is my pick and that's a great search.