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Reflow Fred Style! :-) 
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Lot's more pics coming, and a 300C open door cool down test. However I need to attach the tcouple to a pcb for that to be valid, and I'm unsure what with.

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Sat May 05, 2012 1:35 am
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olv elapsed time, IAT, CHT

iat for temp
cht for marks
time for time in seconds

http://stuff.fredcooke.com/speedy950.real.test.bin.bz2

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Sat May 05, 2012 3:08 am
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I have a nice clean log now.

When the element goes off at 297C there is an exactly flat bit for 5 seconds, and an almost flat bit for 15 (inc the 5) before the descent to normal.

~1C/second up and ~0.5C/second down with the door closed.

Next test is opening the door, BUT, I need to attach the sensor to something or it's a meaningless test of the air rushing in as shown by the other curve posted.

From what I have I can design a profile, mount the sensor better and fit up the solid state relay to control it. I don't think I'll bother with increasing the power as it gets to melting point from cold in 4.5 minutes anyway. With a soak period, it'll only be up in the critical zone for a little while and should work nicely. It'll be a matter of opening the door at the right time by the right amount to get a good downward curve.

Will post up pics and screenies tomorrow, too tired now.

Fred.

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Sat May 05, 2012 10:43 pm
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My first project's primary component has the following specs:

  • Storage Temperature Range .............................-65°C to +150°C
  • Soldering Temperature (reflow) .......................................+260°C

Solder appears to be melting at about 210 to 215 or so.

What I'll probably do is this:

  1. Full power up to just shy of soak period
  2. 1-2 minutes soaking in the 110C-150C range
  3. Full power up to 230C
  4. Power off with door closed for 10-20 seconds of soak/flow/slow descent
  5. Open door by some controlled amount for a faster ramp down (not fully open which would cause thermal shock)
  6. Close door again at some point for a slow final cool down to reduce stress?

I'll get a pretty picture of this up soon if no one has any objections to my game plan.

Fred.

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Sat May 05, 2012 11:27 pm
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Shopping list:

Heatsink for relay (possibly not needed?)
Momentary push button for marking logs
Plastic enclosure to house relay/insulate it
Socket and plug to intercept the power lead

Monday morning I'll go with the wife into town and acquire these things. Then it's all down to software, which should be a piece of cake, software is by bag, baby.

Image

Image

:-)

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Sat May 05, 2012 11:49 pm
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My reflow profile design consists of full power to 120C, flat for 80 seconds, full power to 230C, natural cooling for a few seconds, door open cooling for a few more, natural cooling again down to cold. Something like this should be achievable IMO.

Image

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Sun May 06, 2012 1:34 am
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Parameters that I'm going to want to watch:

Oven temperature (IAT)
Target temperature (CHT)
PWM output percent / heat power applied (or both)
Time since power applied/start of run
Various internal PID values to assist in tuning it

The logic will need to be something like:

Set target temp at 120C
Start timer when target achieved
When timer expires change target to 230
Switch off power when target achieved

I'll need accurate steady state PWM output "feed forward" for the two target temperatures to allow the PID to work properly. These can be obtained through experimentation with a pot input and proportional PWM output.

Fred.

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Sun May 06, 2012 1:49 am
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This was the clean run, without the door ajar, 25 starting, 297 peak, 33 final, temps in C. just a hair over 1 hour runtime. 5 minutes from cold to 230 goal. Plenty of room for 1 to 2 minute pause at ~120C :-)

Image

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Sun May 06, 2012 1:56 am
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I'm not getting why you need a controller if you're just turning it on full for a bit then turning it off? That's not a controller, that's a timer.

How slow does it heat up with door open?

My suggestions are crack door and have a fan in there that can circulate the air all the time. Will cool down nice and you can still heat it nicely.

Anyway, that aside, I would hold a flat temp at the solder melting temp, instead of the natural cool down. A solenoid to open door would be awesome (if unneeded), or a stepper motor, etc. Nothing a fan in there wouldn't fix faster. Again, most of the systems I've seen have used a constant cooling and heating to overpower it - the advantage of all the flow being more even heating - so a fan blowing in over the heating elements should heat the oven faster, and let you cool it faster and hold a more precise temperature than not doing any of that.

All looks awesome anyway. I like the idea of a pre-heat. Many places will do a 24 hour bake at 105 or 85 C (depending on sensitivity of parts) as it bakes moisture out of the leads, which can lead to issues durring soldering. With your fancy controller I think you could make that happen.
-Abe.
P.S. When I grow up, I'm going to learn how to spell During


Mon May 07, 2012 12:10 am
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Oh, Kapton Tape, and a bit of thermal grease to take up any gap. Totally the way to go. It's either that or a clamp (hard to keep things level) or a screw (works awesome,but then you're taking the temp of the screw not the board.

If you're sitting on $50,000 you can get a nice IR camera and take the temp of everything at once. Totally the way to go. Anyway, Kapton (I have good luck with aluminum tape too, or as I said, clamps and bands and such, the secret is the thermal paste.

Lastly, in my fantasy world where you listen to me, the fans blowing over the heaters would draw from over your transistor, cooling it.


Mon May 07, 2012 12:13 am
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