Looking to buy a reflow oven

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Twinscroll said:
I'm curious as to how one of these might perform for reflow operations.....
Click to expand...

I've hear of people making a go with it. However, I'd prefer heating the PCB from below, if possible, to limit the amount of IR being absorbed by the IC vs. the PCB / pads. That's the issue with chips... they're black and really good at picking up heat in the infrared range. So given an inexpensive choice, I'd go with a hot plate instead of that cooker.
 
I see reflow oven is not made by all brands that are involved in making ovens. SMTHouse is good for reflow oven. I see good popularity of SMTHouse T962 but I haven't used it as I have another oven from Oster!
 
No experience with the oven on Amazon, but the reviews make it seem reasonable. If I had to start from scratch I would consider it; people who have done the mods seem happy with performance.

As for controllers, this one came out shortly after I built mine (several years ago) and it's still for sale, albeit "out of stock". Not sure if that means "available later this summer" or "we're not making it any more" but you could try contacting them and hopefully they'll have good news:

http://www.rocketscream.com/blog/product/reflow-oven-controller-shield-arduino-compatible/

As for DIY, mine's pretty basic -- it's just a Mega328, thermocouple, piezo beeper, 2 line LCD, a couple pushbuttons, and a PowerSwitch Tail AC controller for the oven's AC power. The LCD and beeper aren't strictly necessary; you could keep it connected to a desktop / laptop and monitor it over the serial port.
 
All you need is a MANUAL POWER toaster oven (ticky knob, not electronic,) a 120V relay (or 240 for Europe) and a thermistor.
Then you can drive the relay with one pin, and read the thermistor with another pin, and Bob's your uncle.
I imagine a shield would be overkill for that. The sketch to apply a heat-soak-spike-cool temperature curve, and turning it into control for a solid state relay, should be quite simple!
For example: 25A, 280V, driven by 3V in: https://www.digikey.com/product-detail/en/crydom-co/PF240D25/CC1341-ND/278899

Btw: If you have a toaster oven that can turn off top power and just power the bottom, that will make for the most even heat AFAICT.
Some ovens can just be surgically altered to do that.

I have done toaster oven reflow, and made working boards (using a good stencil) but these days I let the friends at MacroFab make boards for me if they contain any kind of fine-pitch stuff.
They've always done right by me, and when they make a mistake, they fess up and make it right. (Like, turned a LED the wrong way once, and I could send it back to have it re-worked on their dime.)
While it takes 3-4 weeks to make a board, and is not SUPER CHEAP OMG!!! it's also surprisingly affordable given the labor involved, and they don't charge that much more for boards than OSH Park does. (Very roughly: Twice the price, twice the time of OSH park, and you get back a mounted/soldered board ready to go instead of just a bare board!)
 
thanks for that.

I spent some time looking at macrofab and was wondering about going that way.
I notice that their house parts are only very basic stuff like resistors, capacitors, switches, but not much else.
Do they procure the other stuff you want on the board? It does seem like a pretty cool system they have for supplying boards.

My toaster is 120VAC 1300W. Would this be ok?
Solid State Relay - 40A (3-32V DC Input)
 
@jwatte - thanks for the info on MacroFab, I had not seen them before.

@linuxgeek - yes that relay should be fine. Regarding your question on MacroFab part sourcing, from their FAQ (https://macrofab.com/faq/) it looks like they will use Digikey or Mouser to get parts they don't stock ("distributor parts") or you can send them yourself.
 
The benefit of the "house parts" is that you don't pay placement fees for them.
For any parts that are not "house," you will be presented with a search box when going through the BOM setup process, and you can plug in part numbers and find distributors. (They buy from at least Mouser and Digi-Key for you.)
You can also consign parts there -- i e, you mail them a box of labeled parts, and they keep them on a shelf for you until you say you need them.
For non-house parts you pay placement fees (labor) per part, somewhat depending on the difficulty of the part. Through-hole with lots of pins cost more; BGA with lots of contacts, too.
They also charge perhaps a 10% mark-up over the cost of Digi-Key direct, but they don't charge shipping for the parts; presumably they make one big order per week or something for all customers, where the shipping ends up not being a material cost.

To help with the "search for parts" GUI, I end up putting in Digi-Key part numbers (or, for house parts, the MacroFab part numbers) in the "Value" field for each part, rather than the "10K" or "22uF" or whatever it would normally have.
 
@linuxgeek Yeah, that relay looks like it will do great, as long as you are OK with wiring mains voltage safely :)

Just make sure you don't drive it with PWM from an Arduino, because it's a "zero crossing" relay which means it will only turn on 120 times per second (or even 60.) If you want to modulate the power input, doing so with a 1/10th second duty cycle would be sufficient. (This is totally OK for a toaster oven, because the thermal mass is much higher than that anyway.)
 
jwatte said:
@linuxgeek Yeah, that relay looks like it will do great, as long as you are OK with wiring mains voltage safely :)
Click to expand...

Not really, but maybe I'll ask for some help from more experienced people.

Just make sure you don't drive it with PWM from an Arduino, because it's a "zero crossing" relay which means it will only turn on 120 times per second (or even 60.) If you want to modulate the power input, doing so with a 1/10th second duty cycle would be sufficient. (This is totally OK for a toaster oven, because the thermal mass is much higher than that anyway.)
Click to expand...

Oh, I had to read that a few times, and I think I sorta understand.
Can I use the DAC to bypass the issue?
 
No, the relay wants an on- or off signal. The PWM of the Arduino system runs by default at a little over 400 Hz, which is faster than a zero-crossing SSR relay can turn on/off.

The best thing you can do is likely to just read the temperature every 100 milliseconds, and if it's below the target, turn the relay on, and if it's above the target, turn the relay off. This will be plenty good enough!

The other half is figuring out what the target "should be," which is the solder profile that various vendors have various ideas about.

The sketch would look simply like:

Code: 
void setup() {
  analogReadResolution(12);
  pinMode(A0, INPUT);
  pinMode(1, OUTPUT);
  digitalWrite(1, LOW);
}

float desired_temperature(uint32_t time) {
  int sec = time / 1000;
  if (sec < 120) {
    return sec + 30; // ramp 1C / sec to 150C
  }
  if (sec < 300) {
    return 150 + (sec - 120) * 50 / 180; // ramp to 200C over 3 minutes
  }
  if (sec < 325) {
    return 200 + (sec - 300) * 45 / 25; // ramp to 245C over 25 seconds
  }
  if (sec < 335) {
    return 245;
  }
  if (sec < 385) {
    return 245 - 4 * (sec - 335); // drop 4C / s to 45C
  }
  return 0; // off
}

void loop() {
  float temp = analogRead(A0) * TEMPERATURE_SCALE + TEMPERATURE_OFFSET; // you calibrate these values
  float desiredTemp = desired_temperature(millis()); // some curve over time
  if (temp < desiredTemp - 0.2f) {
    digitalWrite(1, HIGH);
  } else if (temp > desiredTemp + 0.2f) {
    digitalWrite(1, LOW);
  }
  delay(100);
}
 
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Ok, so desired_temperature(millis) would be a function that does a lookup in a table for a predefined temperature for the corresponding millisecond.

Wouldn't this run as fast as the loop will go, which would be faster than 100msec? Should I put in a delay of 100msec at the end of the loop?


nvm, it looks like you edited the post and answered my question before I actually asked it. :)

Thanks!
 
I edited the code to provide a sample temperature ramp, and add the delay(100) I accidentally deleted while typing. Good catch :)
 
I started ordering the SSR, but then I remembered that I need some kind of temperature sensor. Recommendation for a temperature sensor? If the sensor has to be calibrated how do people create known values at the extremes? ice, boiling water? If I need to get a fancy infrared thermometer I guess I might as well purchase something that has known outputs. I also understand the k-type thermocouples typically need amplification.

Do I need these?:
https://www.sparkfun.com/products/13266
https://www.sparkfun.com/products/13612

https://www.sparkfun.com/products/13715
or
https://www.sparkfun.com/products/251
 
This seems like an affordable part:
https://www.digikey.com/product-detail/en/us-sensor/103JL1A/615-1029-ND/1014557
They have a downloadable Excel sheet of resistance-vs-temperature, and it's rated at +/-0.5C, so I imagine with a precision resistor divider you'd get quite close.

Some temperature/resistance data points:
150C 186.10 Ohm
200C 65.66 Ohm
245C 30.36 Ohm

With a 220 Ohm pull-up to 3.3V, you'd get 1.512V, 0.759V, and 0.400V out, which should be reasonably easy to measure using the Teensy 12-bit ADC input. You'll notice a power consumption up to 13 milliamps through this divider, but that's probably not a problem for this application.

Note that you can't solder terminating wiring to the thermistor, because the solder will melt while re-flowing! You'll have to crimp, or use another mechanical force attachment (screws, for example.)
Also, use wires with high-temperature ratings. You could go all out and get fiberglass braid :) http://www.awcwire.com/productspec.aspx?id=mgt-1000

Write up a blog post when you're done, and post it on the PJRC forum user projects, for everlasting glory :)
 
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