First off, a disclaimer:
WARNING!
This project involves wiring that will be carrying dangerously high AC mains voltages, as well as devices that are designed to generate hazardous temperatures (in case the hazardous voltages weren't scary enough). Improper construction can cause significant risk of injury and/or damage. No liability or responsibility of any sort is assumed or implied if you attempt this project without proper tooling, equipment, and/or expertise. In short, don't try this unless you know damn well what you're doing!
One other thing... Don't use the griddle or whatever for food preparation once you solder with/on it. Some things aren't at all good for you to eat, and lead is pretty high on that list. Anything you use this with should be dedicated only to soldering.
Images are included as thumbnails - click one for the full-sized version - then, use your "back" button to return here.
Our journey begins with the simple idea that a cheap griddle can be made into a decent reflow-soldering plate if you are reasonably understanding of reflow curves and have access to a temp sensor and timing device.
Reflow soldering on an electric griddle or inside a toaster oven is hardly a new idea. Of course, some implementations worked better than others, but the principle is sound: bring the populated board to a "soak" temp and keep it there for a moment or so, raise to solder-melting temp and hold there just long enough to do the job, and cool it all back down, under at least semi-controlled conditions. The "soak" temp serves the important purpose of giving the parts time to reach a common temperature, and the actual cooking time performs the task of soldering the entire thing in one operation. A controlled cooldown then ensures the solder sets up properly and doesn't suffer crystallization from thermal issues as it cools.
Our project will be to build a controller that can convert a heat source - a cheapie toaster oven, electric griddle, or hotplate - into a more precisely controlled reflow soldering system than these would be by themselves with the generic and hideously imprecise temp controls that come as part of such devices.
The basic plan is to employ an industrial programmable process controller as the brains, a thermocouple temp probe as its means of detection, and a solid-state relay as the switch that powers or cuts power to the actual heating element(s). Enclosing all of the guts into a metal box with an outlet for plugging in the heating device makes it into something that can be moved around and used with just about anything that could properly "cook" a PC board, and the only thing needed in such a case is some means to get a temp probe into and onto the board(s) to be "cooked." For a griddle or hotplate this means NO modifications to the device, although a toaster oven might mandate the addition of a port through which to get that temp probe inside the oven.
Our brain for this project is the SYL2352-P programmable temp controller with ramp/soak, from Georgia-based Auber Instruments. It's a real process controller of the sort used to manage production-line systems, and as such comes in a standardized package called 1/16 DIN, which is a smidgeon shy of 2" square by about 4" deep.
This unit was chosen because (1) it could do programmable temp ramps, (2) it could drive a solid-state relay directly, and (3) at less than a C-note its price is reasonable. (Process controllers can easily cost a few hundred dollars!) It also has the added benefits of flexibility in design (e.g., it can use several thermocouple and probe types) and is a workable size. It can be bought direct from the mfr. via their E-commerce website, along with the solid-state relay (I used their 25-amp unit) and thermocouple if you see something that might suit your application..
The enclosure selected was an EX-4522 extruded aluminum enclosure from Bud Industries, a company that makes all manner of enclosures and rackmount gear.
Being aluminum, the solid-state relay could be affixed to it to act as a heatsink.
The first step in construction was simply figuring out how the hell it would all fit. The controller itself was best placed in the center, and flanked by the outlet and outlet-live indicator on the left and barrier strip for connecting a thermocouple on the right. The thermocouple wiring needs to be kept away from power wiring so that it doesn't pick up interference, thus the mount location for the barrier strip.
(Editor's Note: I did NOT use the proper type of wire for connecting barrier strip to controller. I used plain wire, and as a result there is a certain amount of accuracy loss as a result. The amount of loss isn't enough to be a concern though.)
I measured and cut, and miracle of miracles, it all fit! The rear panel would also get the same treatment to hold a power socket of the type commonly seen on computers (the standard IEC-320 style), a power filter (to make sure rough AC wouldn't make the controller freak out), a master power switch, and a 15-amp circuit breaker (for safety).
Note that the middle area was left blank - the solid-state relay would be bolted to the enclosure's bottom behind the process controller, so nothing was placed on the rear panel that might cause interference issues.
Wiring all that crap was LOADS of fun, lemme tell ya... Ugh...
First, I wired up the back panel. The filter slash power socket fed the master power switch, and from there the hot lead visited that 15-amp circuit breaker and then branched off into two pigtails - one went to the solid-state relay and the other powered the controller through a separate fuseholder. (I used a DPST power switch so that I could cut both sides of the AC feed instead of just one.)
Next, the front panel got the treatment. The barrier strip's terminals were connected to the controller's thermocouple inputs, the indicator lamp was connected to the power outlet, and pigtails to connect the outlet to the solid-state relay (and neutral line from the outlet and controller to the power switch) were added.
WARNING!
There's a lot of exposed wiring here. When powered up, there's a lot of exposed 120VAC here. NEVER operate this with the plates off!
The button-up time approacheth as I mounted the faceplate, made the interconnects, and prepared to bolt the solid-state relay into place.
The back panel interconnects were next, and then everything carefully manipulated into the close-the-box position.
Almost there...
Ah, finished! Time to test it...
I connected the thermocouple, plugged it into an AC outlet, and no magic smoke appeared. Flipped the power switch, still no smoke, which is a good sign.
Looked at the front and ooo, preeetty!
The next step was programming the controller. I set it up with a basic program to mimic the temperature profile for soldering with lead-free solder pastes, which involved the following steps:
C01: -1 T01: -1 (first step is halt the controller - this prevents it autostarting when turned on.)
C02: 300 T02: 5 (ramp to 300 degrees Farenheit in five minutes, controlled preheat)
C03: 300 T03: 2 (maintain 300 degrees for two minutes - soak the board(s) to equalize temps)
C04: 450 T04: 2 (ramp to 450 degrees in two minutes)
C05: 450 T05: 1 (maintain 450 degrees for one minute - this is when the actual soldering happens)
C06: 100 T06: 5 (controlled cooldown to 100 degrees in five minutes, assuming the heatsource cools that fast)
C07: -1 T07: -1 (halt the controller)
This program set results in running the temp up to 300 degrees Farenheit, holding that for two minutes, ramping to 450 for the actual soldering and holding that for only one minute, and then cooling down. Note that leaded solder needs lower temps, and it's a good idea to keep temps to the lowest possible for the shortest time possible to prevent damage to the parts you're trying to solder.
My only complaint about the Auber process controller is the fact that it only understands time in minutes. If I could set it to seconds for timing instead of minutes, I'd have gone 90 seconds for the soak and either 45 or 60 seconds for the actual soldering, depending on what's being cooked. But alas, it's minutes only. Perhaps Auber Instruments might add that in the future? (Hint, hint!)
Placed the probe onto an aluminum weight-slash-support I cranked out on my lathe, placed that in the center of my $20 electric griddle, plugged said griddle into the outlet on the controller box, and pressed the "go" button... (Note: the temp control for the griddle was set to its highest setting. Otherwise it might never reach its temp setpoint!)
It fired up, warmed the griddle as per my cycle (while autotuning itself - these controllers have self-adjusting capabilities), and then shut down at the end.
During the cooldown I watched the griddle temp (in red) come down while its autotune function drove the set temp (green) to room temp to end the shake-and-bake. (Yes, it's sitting on a stack of oil filters. No, you really don't want to know. :-D )
And there you have it, one completely self-contained temp controller that makes reflow soldering tremendously easy and relatively inexpensive. The whole project cost about $200 - using all new parts - and that's a darn sight better than $400+ for a refurbed reflow hotplate and a grand or more for a reflow oven. As an added plus, if I want to build a hotplate I can do so easily and simply bolt it to the side of the controller to make it a total package deal.
Editor's Note: I'll be doing some tests to make sure it solders properly - pic of that will be coming...
