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DIY Vapour Phase Frying Pan Project

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wraper:
As of ideal profile, generally you should preheat PCB by some other means and then move PCB into chamber with vapor phase. What I've done and what this thread is about is making workaround by slowly rising vapor phase to preheat PCB by air and small amount of vapor above vapor phase. The issue is that when liquid reaches boiling point, vapor phase rises extremely fast and has a lot of heat capacity. But before it reaches boiling point PCB simply stays cool.

wraper:

--- Quote from: trevwhite on December 16, 2019, 10:40:23 pm ---So once vapour reaches the right height then its just about dropping power delivery to maintain the height or temperature.

--- End quote ---
It's will be somewhat controllable that way only if you place multiple temperature sensors at different heights. Also control is extremely laggy. It's not like you stop heating and vapor will stop to rise.

--- Quote ---phase 2 would implement a second pid control specifically to maintain the temperature which would reduce the power delivery dramatically.
--- End quote ---
The problem with PID is that by time when it adjusts itself, solder is already melted. Basically you need to shut down heating even before vapor rises. Unless you want to heat with extremely small power extending reflow profile to unreasonably long time.

Here is what I've done with my oven


--- Quote from: wraper on January 01, 2017, 11:28:12 pm ---RTD position was lowered by about 5mm but it still reads lower than temp on the PCB, and there is significant inertia. Right now it works like this (PID would be useless in this case):
1. Start heating
2. Once reached 80oC, stop heating, wait 25s (after this PCB will be about 150-160oC hot)
3. Heat 14s, likely a little bit more would be better, like 18s.
4. Stop heating, wait 25s (after this PCB will be about 180-190oC hot)
5. Start heating
6. Once 195oC is reached, stop heating and turn on cooling.

--- End quote ---

Here is profile. In volts, not temperature units but you get the idea. Not perfect but order of magnitude better than it was originally. As you see, I start cooling fans way before 230o C reflow temperature is reached. Because I know that once I add a bit more heating, PCB temperature will shoot to max.

trevwhite:
Thanks for the information. How long does the board sit at 230 or 240C? I think the paste profiles like it to be for at least 45 seconds.


wraper:

--- Quote from: trevwhite on December 16, 2019, 11:08:33 pm ---Thanks for the information. How long does the board sit at 230 or 240C? I think the paste profiles like it to be for at least 45 seconds.

--- End quote ---
There is no issue not staying long enough above melting point. The problem is cooling fast enough. Also with vapor phase you don't need to keep it under max temperature for long. All of the solder melts basically instantly everywhere. There is no such thing as heavier parts or large copper planes taking significantly more time.

trevwhite:
I emailed Peter a bit who designed and makes the Controleo3. He has indicated that the profile language he created means that timers, wait for temp to be reached and ramp control can all be sequenced with his product. It seems the Controleo3 is not the typical reflow oven controller.

So based on Wraper's profile, is there much variation depending on the board size? I am thinking there must be some but maybe the vapour cloud has so much energy in it that there is capacity and one profile would do all boards.

Also cooling has been raised as important. Are fans blowing air at the pan proving good enough?




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