DIY hot plate for reflow soldering - Page 1
Forum section: electronics / projects

author: newbie666
author_rank: Regular Contributor
timestamp: January 02, 2019, 10:55:06 pm
content: Hello,I've recently learned about those silicone heater matts that can get up to 300 degC and that gave me an idea of sticking one to a copper plate and using it as a (precision) hot plate for reflow soldering.I'd probably have to build two of those and keep them at constant temperature - one for presoak and the other for reflow temp, but in theory that should give me a pretty consistent reflow process.Did anybody try to do anything similar or this idea is plain stupid?https://uk.rs-online.com/web/p/silicone-heater-mats/0245641/

author: Peabody
author_rank: Super Contributor
timestamp: January 03, 2019, 05:13:29 am
content: I'm not familiar with the silicone heater mats, but I posted before about using two cheap hotplates, one at soak temperature and one at reflow temperature:https://www.eevblog.com/forum/manufacture/reflow-using-two-hot-plates/msg1975487/#msg1975487I found that the temperature control of the hotplate I tested (the Walmart $10 open-element model) has far too much hysteresis to maintain a consistent temperature. But I've built a "controller" that cycles the mains power through an SSR every two seconds per an adjustable duty cycle, and it can maintain the temperature of a circular saw blade on top of the heating element at a constant temperature.So I think it's still an interesting possibility. In a 120VAC system like here in the US, there could be a problem running two 1000W hotplates at the same time without tripping a 20A circuit breaker. But one controller could make sure the two are not ON at the same time. But I think the controller and single hotplate can follow the required temperature profile well enough.The silicone mats apparently work up to 300C, but are only rated at 200W. I'm not sure how that works.

author: texaspyro
author_rank: Super Contributor
timestamp: January 03, 2019, 06:26:35 am
content: For the price of a heater mat you could buy a toaster oven and build a reflow controller.

author: LapTop006
author_rank: Unknown
timestamp: January 03, 2019, 12:40:17 pm
content: Or, for not much more than that, buy the pre-existing cheap Chinese hot plates that already have a temperature controller.

author: soldar
author_rank: Super Contributor
timestamp: January 03, 2019, 02:07:00 pm
content: That sillycone heater is only 200 W and I am not sure that is enough. I would not go that way.I find hotplates in the trash (see my other thread) and you can easily add temperature control (on/off or even proportional) for very little.

author: Mr. Scram
author_rank: Super Contributor
timestamp: January 03, 2019, 02:59:45 pm
content: What power should a moderately useful preheater be? Or are we talking actual soldering?

author: kosine
author_rank: Regular Contributor
timestamp: January 03, 2019, 04:08:05 pm
content: A DIY hotplate can work quite well. Mine uses two 750W cartidge heaters from ebay with a PID/SSR controller/heatsink kit. Total cost was about £20. (Original design was 300W, but that was nowhere near enough.)I just drop the board onto the plate once it's up to temp, and remove after 20-30 seconds once the solder paste has melted. Takes about 5 minutes to get up to 250C, but about 5 hours to cool down afterwards! Still a very useful tool to have.

author: rstofer
author_rank: Super Contributor
timestamp: January 03, 2019, 04:57:10 pm
content: I use a 1000W hotplate something like this:https://www.target.com/p/elite-cuisine-electric-burner-hot-plate/-/A-51107299?preselect=49124277#lnk=sametabControl is simple: I turn the hotplate fully on and wait for the solder to flow and then I carefully lift the board off the hotplate and place it on the counter to cool.There is not one bit of science or math involved in my hotplate method. And, yes, it works fine!I also have a converted toaster oven for larger boards.

author: Peabody
author_rank: Super Contributor
timestamp: January 03, 2019, 11:00:29 pm
content: When I first looked into all the reflow stuff, I was surprised at how many people use hotplates. I mean, it just seems all wrong. :-) But apparently it works well, and is very forgiving. I was hoping to develop a hotplate system that at least attempted to follow the standard temp profile, and I'm getting there, but I'm not at all sure it's really needed.The commercial preheat hotplates from Ebay look pretty slick, but I think they are still over $100, and I was looking for something a lot less than that.

author: DaJMasta
author_rank: Super Contributor
timestamp: January 04, 2019, 12:49:37 am
content: Hotplates work well for smaller boards, though they rarely advertise temperature uniformity, so you have to do some testing for hotspots and such. You want a good temperature range (one that extends up high is nice too), enough power to make the heat up fairly fast, and as even as possible a heat distribution. An IR thermometer or a few thermocouples can show you hotspots, and you can try to place your boards accordingly. Also worth marking it so you don't try to use it for foodYou can do a lot of small scale reflow stuff without a preheater, but as your boards get bigger, your layer count goes up, your parts get finer pitch and more sensitive, that's when it starts coming into play more clearly. For your average small to medium two layer board, you can probably get very high yield rates using a single hotplate with a good temperature setting.

author: cdev
author_rank: Super Contributor
timestamp: January 04, 2019, 03:39:41 am
content: I got a nice purpose built digital hotplate for under $50 new shipped ($46) on ebay. It has an aluminum block and distributes heat evenly. Its made for preheating and reflow. Ive also been using two small bimetal thermometers which I bet you could duplicate for cheap, I thought they were ancient unobtainium parts but it turned out they are still made by a company in LA and cost around $50 each, way too expensive for a tiny thermometer. But they are very useful and also accurate. You could make your own, the key part is the bimetal spiral. If you can find a bimetal thermometer thats all metal you'll be good. It responds faster than the digital readout. Also if your area is well lighted you can see the solder melt clearly because no glass door.