Female Speaker: So I've got my robotic reflow skillet ready to go. I do all the testing and I am putting that anexo on a graph and it looks like this is going to be okay. So the next thing is I have to go back and put solder onto the circuit board, so I can solder this little chip here. Only a couple of these little pins have to be soldered. Some people use like syringe and they really carefully just inject a little bit of solder onto each pan, but because there is a laser cutter, I can cut the stencil and so this is my circuit board holder. I cut the outline of the circuit board. Then this is Kapton, this is a heat-resistant, pretty strong thin film. If you look carefully, you can see the little holes match up on the little pans that need to be soldered.
So what you do is, it's just like a silk-screen, you put down solder in, you squeegee it over. Then when you lift the capped-off or the film, little bits of solder are left where it need to be. Here are some other examples of previously cut stencils. This one is made out of a 3 mil Mylar. This works okay. You can get Mylar pretty cheap, it's like $10 for a huge amount, but probably this is going to thick and also the Mylar melts a little bit. So you can get really fine cuts. This is another sheet of Kapton. I write the settings. This is a 100 speed, 15 power, 500 hertz frequency. You try a couple of different settings. Kapton coming -- now you can see hydromolar tests on the sheet until I get what I think is pretty good setting and usually -- machine in my life. So let's go with the circuit screening.
Circuit boards in the nice holders, it's nicely lined. Then I take the top off just because it's really easier to dispense. I put a blob of solder, that's enough for a couple of boards, then we're going to do a demo right now. Make a whole bunch -- Then you just take a piece of acrylic, this is square, you can use I guess like a paint scraper or a squeegee, but this works okay. You just squeegee it over. So you see there is solder in the little holes that were cut out of the stencil. Now when you lift this up, if you look carefully, you can see a little deposit of solder. Now normally you would have holes for every single pin but this chip only has ten pin solder, that's why I didn't cut them all out -- then here is your chip, replace your chip and by hand, but most people use tweezers. So now it's placed, and now we're ready to reflow it.
Okay, so this is the reflow skillet I built. This system is not really ideal but it's just kind of what I had in the house. So we have the thermocouple, this is a thermocouple. I got the one that has the insulated glass -- so that I can withstand high temperature, because this gets up to like almost 250, it could possible get up to 300 degree Celsius. I tapped it down with Kapton tape. This is actually the same material that I made silk-screen out of. It's like a couple of dollars -- for a roll but it's really handy because it doesn't melt under high temperatures. It's designed for this sort of stuff for attaching thermostats and stuff.
Okay, time to reflow. So this is the chip, it's got the silk-screen solder on it, like a chip on top. Now I place it in my reflow skillet. So this skillet has a servo connected to a little wheel and the wheel turns the temperature now. That's pretty much how I turns it on and off. It's running open loop but I calibrated it and it pretty much just run the same every time. So plug in the Arduino, and this got an LCD on it, and this is a servo controller.
So when it starts up, it tells me what the temperature it's reading from the sensor. This is approximately what temperature it should be, a sort of guesses based on the profile published on the -- data sheet. At this important time, we should be around 55 degrees and it's around 55, so it's being okay. Like I said, I calibrated it.
So first you do the warm-up. That's the first part of the curve. You can see this is slowly turning. The warm-up basically takes the board up to about a 120 degree Celsius. That's just kind of gets the board ready for the reflow, there are some chemical processes occur at that temperature. Okay, at around 90 seconds of warm-up, we go to the sock phase and so this is where basically the skillet is between 120, 150, maybe up to 180 degrees. Basically, it seems like the solder paste socks into the joints. It doesn't quite melts, but this is sort of a preparatory step for the actual reflow. This happens for about 30, 60 seconds.
Okay, so now we are actually at the reflow phase. So at this phase, it gets up to around 250 degrees. You'll see -- especially around here, you'll see something gets very shiny instead of -- that's the solder reflowing into the joints. So you see this is getting up kind of 200 degrees; it'll probably peek at around 220 degrees. So you can see how this is now a little shiny, that's the solder ring reflowed.
Finally after we hit around 220 degrees, we do cool down. So basically, slowly cool down everything. Again, this sets the solder hopefully -- anything. Usually, it's supposed to cool down a little faster than this, but I don't think it's a really big deal if it cools down a little slower than it ought to. You can turn a fan on and it helps. Finally, it's cooled down and I take it off the skillet once it's down to about 80 degree Celsius, so it's not too hot to touch. You can see here that these pins are nicely soldered but there are no bridges. It's just a nice clean minimal solder joint on these pins here. So now this board is ready to go into the -- it's a Through-Hole Bread-Boarding Arduino Clone, then I made about a year-ago. You can get it.
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