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Best Re-flow Oven for Hobby electronics
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Simon:
My Zhenbang oven is a marked improvement. It has an air circulating fan. All of these IR ovens have a tiny glass window that has always worked for me. I just did some really heavy boards where I had to watch for it to reflow as it was taking longer than the standard profiles allows.
Doctorandus_P:
Simon says exactly why you want to be able to monitor the soldering process, either via a "frying-pan" option or a glass window in the oven.
Different boards need different soldering profiles, and with a closed oven this is much more difficult to get right.
jmelson:

--- Quote from: wilfred on April 07, 2019, 11:06:29 am ---I went and bought one. But I certainly don't recommend it for food. When starting from cold it goes to 295 Celcius and switches off after 4min22sec. Then it cools to 136 Celcius and switches on. It takes a minute and a half  to get back to 295 Celcius. And the cycle repeats.

--- End quote ---
Yes, the built-in thermostat is pretty awful, it is more of a power regulator than an actual temperature measuring device, at least on mine.  I never expected it to work, and immediately bypassed it with a thermocouple temperature controller and solid state relay.

Well, the problem is you want a controlled temperature of the BOARD, not the air in the oven.  I didn't know until I started doing this, there is almost NO RELATION between the two.  The air heats slowly (I guess due to the thermal mass of the oven's walls) but a board in the middle will heat quickly, due to IR transfer.  So, I got a big roll of an odd (Type E) thermocouple extension wire and a ramp-and-soak controller on eBay.  The micro-size thermocouple wire can be poked into a hole in the PCB to measure actual PCB temperature.  The ramp-and-soak controller allows you to program temperature points and time between them, so you set it like :
10 C : 3 minutes : 180 C : 1 minute : 247 C : 1 minute : 10 C : 2 minutes

Jon
wilfred:
I added the graph of time/temperature to my earlier post.  It looks like the oven can heat up hot enough and fast enough to work.

The comment about measuring the temperature is one that has always intrigued me. How do you measure the temperature properly to do solder reflow. I'm certainly not claiming any expertise here. I've seen both probe in free air and inserted or in close contact with a PCB. Either way the temperature reading must be the actual probe tip temp. Both seem to work for melting the solder as does just sticking the PCB in a frypan and switching it on.

I suspect the profile is more relevant to the survival of the components. But then there are different profiles for different solder.



jmelson:

--- Quote from: wilfred on April 07, 2019, 11:51:04 pm ---I added the graph of time/temperature to my earlier post.  It looks like the oven can heat up hot enough and fast enough to work.

The comment about measuring the temperature is one that has always intrigued me. How do you measure the temperature properly to do solder reflow. I'm certainly not claiming any expertise here. I've seen both probe in free air and inserted or in close contact with a PCB. Either way the temperature reading must be the actual probe tip temp. Both seem to work for melting the solder as does just sticking the PCB in a frypan and switching it on.

--- End quote ---
My first test was with the thermocouple in air.  The boards burned while the temp indicated 230 C or so.  So, obviously, the boards absorbed more IR than the thermocouple.  Next test, I poked the thermocouple into a plated through-hole in the board, and got beautiful reflow soldering.  So, unless you attach the thermocouple to some kind of PC board simulator that has well-matched IR characteristics, you won't get the right temperatures.

Jon
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