Circuit Board Prototyping Part 2: Solder Mask, Solder Paste, Reflow Oven and Hand Soldering

in the previous video we got to this point we have a circuit board that has been etched and tin plated and in this video I'm going to cover the rests I'm going to apply a solder mask going to expose it and develop it then I will apply solder pastes and place the surface mount components I'll then bake the board in a toaster oven as a cheap reflow oven and finally I will hand solder a few components the first step for the solder mask is to cut it to shape so if you go to eBay and type in dry film solder mask you can buy a small roll for about 20 or 30 dollars we need to cut it so that it covers all of the copper but does not overhang the board if you have the solder mask film overhanging the board when you run through the laminator it will stick to the rollers and that's of course a bad thing so see I'm gonna go ahead and cut this to shape alright so there we got it on it's covering all the copper but not over hanging in the board we need to peel off one of the protective films on the solder mask one side is glossy the other side is matte we need to peel off this matte film an easy way to do that is with a couple pieces of tape and actually before I do that I'm gonna turn on my laminator and let it warm up okay so a couple pieces of tape if you pick a corner of the solder mask stick it on to one side stick the other one on the other side you have to pull these apart quick if you pull slowly the table just to peel off so you have to kind of jerk it apart like that try not to touch the solder mask what you want to do is place it on one edge I guess the leading edge of your board and gently press it down on that leading edge peel off the tube and just gently press down a leading edge leave the rest of it just kind of sitting on the board it it won't fall off but it isn't stuck down either I'm going to wait for this laminator to heat up and then I'll run it through a few times alright my laminator is now up to temperature and I'll go ahead and run it through so I pressed down on this edge which will be my leading edge all right so it's been through one pass it's stuck down reasonably well there's no big air pockets or voids or anything like that if we look on the back we can see well it may not be obvious to you but there's a few spots where you can see the yellow of the board and that would indicate that it hasn't been pushed all the way down to the bottom I'm using 10 mil spacing which is really kind of pushing the limits of well pushing beyond the limits of a dry film solder mask that you can do at home so I'm not going to able to get all of those perfectly fixed but I'll run it through the laminator a few times and I'll have a little bit better coverage I would recommend if you are doing a circuit that doesn't need such tight spacing to do maybe 15 or 20 mil spacing but that's what I'm doing so there's now quite a bit less of the yellow showing right through again all right so that's about as good as it's going to get to turn the laminator off so the board is now quite warm its if it was any hotter it'd be really uncomfortable to hold so that's kind of really how hot it is you can see there is very little yellow between the traces so the majority of the mask has been pushed down into the grooves and on to the fiberglass board something like this cool back down to room temperature and then we can expose it it's been just over a minute and the board has cooled back down to room temperature now I need to take my solder mask layer and printed it out to a transparency I'm going to go into I'm going to place it on the board carefully align it you want to be careful that you check alignment everywhere especially on the corners because if you have it a little bit off it may look great here and then be off here so just be very careful take your time and yeah so you place the transparency down get it aligned and then carefully place your UV transparent sheet of plastic on top all right so I've got it aligned properly and I've got the plastic sheet on top you want to now double-check that at every corner of the plastic sheet that it is actually sitting in flat it's not for example like I'm using that cardboard or surface make sure your cardboard isn't wavy and keeping the plastic sheet from sitting flat and that looks fine so we now know that the transparency is properly aligned we have the plastic sheet to keep pressure on it and we know that the plastic sheet is sitting flat on the board we can now expose it with my particular lamp I find that I need to expose for at least 10 minutes and 11 to 12 seems to work a little bit better so I'm going to expose for 12 minutes all right it's the 12 minutes have gone by and we're done exposing the board the datasheet for the dry film of solder mask recommends that you let it sit for half an hour as part of the curing process so I'm going to put this board in a drawer for a half an hour and we get back we'll go ahead and peel off the protective film and develop it it's almost been half an hour and I might as well to accept the developer for the solder mask I use a ratio of half a gram of sodium carbonate to twelve ounces of water and now that I say that it's kind of weird that I mix metric and imperial but anyway that's the ratio that I use and so you can use pH increase or at like a pool supply store I think I even got this it okay so it's it's been half an hour I got this I think it Walmart or Target or something like that but it's a dirt cheap maybe five or ten dollars and you have a lifetime supply all right I'm going to measure out half gram all right so it's a not very much at all you can see there is barely any in there and I'll go ahead and add twelve ounces of water developer is mixed up and we can now take the board and peel off the glossy protective film I find that using a razor blade or a box cutter exacto knife works pretty well you just kind of work it into one of the edges pry it up carefully and then just peel off all right double-check that all of the powdered sodium carbonate has dissolved and it has and go ahead and stick the board in the developer my experience that will take about five minutes maybe a little bit longer to develop so you just gently brush the surface and eventually you'll see the pennants visible without the solder mask on top all right so I just washed it off and realized this really weird defect so you can see that the solder mask stuck to the copper while tin plated copper but did not stick to the fiberglass board that's really weird I haven't had that happen before I'm not entirely sure because it could be one of our thinking it could be one of two things my solder mask film is about a year old and I don't know how old it was before I got it so it may be an issue related to shelf-life it's also possible that maybe my UV lamp is getting a little bit weaker over time and it wasn't exposed long enough because I've done exposure it's at ten minutes which was shorter than this exposure and had no problems before and I'm not entirely sure what the cause was but the board is still usable so I'm going to go ahead and continue on with the project as you can see there is a pretty good solder mask coverage on pretty much every trace just nothing on the fiberglass itself and there's a few spots where there's a little bit missing like right there but overall I think it'll still work just fine and it is a very simple board or relatively simple board so the next step in this procedure is to expose the board again to UV light for about half an hour so let's go ahead and do that half hour has gone by and we're finished with the final UV exposure of the board and the final step in the solder mask process is to bake it the datasheet recommends 145 degrees Celsius for half an hour so that's what I'll do that's pretty much the end of a solder mask process I'm going to let this cool back down to ambient temperature and then I will cut the board to shape and sand it to shape and then we can go on with the rest of populating and soldering got the board cooled down to room temperature and I'm going to take my tin snips and trim the board recently close to the perimeter and then I will do the final shaping with a little belt sander I forgot to show on camera but I also drilled out the two holes for my heatsink and I'm now ready to apply solder paste and all the components so I have my solder paste tweezers of course I'm using a heatsink that I scavenged off of a motherboard and then all the components pretty mostly a surface mount I have a few through-hole transistors that I'm going to make surface mount but other than that it's all pretty much all surface now alright so I'm going to start by mounting the the trickiest component which is going to be the microcontroller it isn't too bad but it's the one that will be the most difficult after that all then mount the three gate drivers and then the other items should be trivial all right so I've gotten solder paste applied for all of the surface mount components and as you could probably see it's rather difficult to apply pressure to the syringe of solder paste and keep your hand studies so if you're going to do this for very many boards you're probably going to want to buy a solder paste dispenser which I think I will probably do pretty soon anyway let's place the rest of the components I have a cheat sheet that I'm looking at that kind of tells me where everything goes alright I've got all the surface mount components placed and I'm just going to take a I loop and double check that all the components are correct and then I will go ahead and put it in my reflow oven well toaster oven SR reflow oven alright so I double-checked that all the components on the board are in fact the correct components and placed in the right spots and we are now ready to reflow all right for preheat I'm going to set it to about 150 degrees Celsius which is about 300 degrees Fahrenheit I'm going to let it warm up for half a minute to a minute and then I'll run the temperature up higher and keep on until the solder melts all right I'm now going to adjust the thermostat and let run hotter until the solder melts alright it looks like all the solder has melted so I'm going to let it cool down it's far from perfect but it worked out pretty well and let's go use some flux and a soldering iron to clean up looks like there's a one or two Oh 805 s that need to be cleaned up and then can you have some solder bridges alright so I'm not sure if it was really obvious on camera but I have a capacitor here that has tombstoned and then I have some solder bridges on the microcontroller other than that we can else looks alright it's certainly not you know a professional level but it's a should be certainly good enough for a a hobbyists prototype so I'm going to resolder that capacitor fix my solder bridge and then I'll go ahead and mount all the other through-hole components of them going to mount them on the surface just because I don't feel like drilling all right so I've got all the surface-mount stuff cleaned up that ended up being taking way more time than it should have but oh well I figure is when I have it on camera I always end up doing stuff like that but oh well so now I'm going to go ahead and finish up with the through-hole items that I'm going to make surface mount you you all right so it's almost done all I'm going to do now is I'm going to take some isopropyl alcohol and a brush and I'm going to clean off all the flux residue so I'll be right back alright so I forgot to set up my camera for it but I cleaned off the circuit board with the isopropyl alcohol and a little brush and so now there's not a whole bunch of flux residue all over the place all that's left is to mount the heatsink so as I mentioned earlier this was off of a computer motherboard and it is intended to be kind of pushed through holes on a motherboard but these aren't going to reach long enough for this application so I'm going to cut these off and then use regular screws and nuts to retain it all right so this was a fun project it turned out pretty well I'm going to now have to go through the process of writing the firmware which will be the fun part but yeah it turned out all right so if you saw the first part of this two-part video the first part went much better than this one the etching and tin plating of course went kind of without a hitch the second video was a kind of a string of problems which is unfortunate I was tempted to not post this video yeah I was tempted to not post this video but I'm going to go ahead and post it anyway just because especially if you're a hobbyist it's important to realize that not everything goes as great as a typical YouTube video might indicate a lot of people don't post things unless they turn out perfectly or close to it so as you saw the solder mask didn't work out as well as I'd hoped I have a feeling it was either due to the the age of the solder mask film or perhaps I didn't expose it long enough or both the solder paste didn't work out nearly as well as it usually did for me because I had quite a few solder bridges and I also entirely my fault I forgot to use thermal reliefs on a lot of the pads so that caused issues in reflow as well other than that it turned out all right um if you're wondering why I went to the trouble of modifying the to-220 transistors to be surface mount it's because I have a few of them laying around and I want to use them up before I buy some proper modern surface mount transistors same with this potentiometer I just had this one laying around and it'll work out so I just made it work the other or not it should work out pretty well and hopefully this will be at least a little bit of help to the the hobbyists out there that I'll only see videos that are of success but anyway so if you have any questions or comments leave them down below hope this video was helpful or at least entertaining I'll see you next time

Channel: upgrdman

Views: 145,522

Rating: 4.858182 out of 5

Keywords: Dry film solder mask, solder paste, reflow oven, prototyping, pcb, flux, laminator, uv light, exposing, developing, sodium carbonate, isopropyl alcohol, soldering iron, toaster oven

Id: AHNv0eOq7Rk

Length: 27min 16sec (1636 seconds)

Published: Mon Apr 13 2015