Re: DIY SMT Solder Oven

Paul Hovnanian P.E. wrote:
Jacques St-Pierre wrote:
Hello Group,

This may not be the appropriate news group to discuss this, but the group
helps me before and I do not know a better place to find help again.

As many, I am trying to build a low cost SMT Reflow Oven using an of the
shelves small oven. I did have one first prototype working, but it was too
small and plague with many problems, mostly cause by uneven heat diffusion.

I am working on s second unit, build with a lot more powerful heaters,
cooling fan, and more evenly distribute heater surface. With this one, I
have more than enough power to raise temperature to target value with the
proper raise speed.

Not to say, that the unit is control by computer, PID is use to achieved
proper temperature control. The PCB temperature is raise to 150c at a rate
of 2c/second, the PCB soak at 150c for 60 seconds and it is raise to 215c at
the same rate. Next temperature is cool down by a fan. Time over melting
point (183c) is around 60 seconds has require by the paste we used.

The problem is that with those timing, we end up with a toasted PCB.
Reducing the time over melting point, did correct the problem, but barely;
the PCB still have trace of over heating. Trying the same process with RoHS
paste, using a higher melting point temperature (220c), resulted in PCB burn
up.

I tried to implement convection, but the blower is not powerful enough, it
has no effect on the result.

I use a thermocouple in contact with the PCB to pick up temperature. I am
not sure if I should monitor the air temperature at proximity of the PCB or
still use direct contact? Both methods results in quite different
temperature response.

Do you have any hints to the reason why the PCB toast? What is wrong with
the method? Do I heat too quickly or too high?

Here's my thinking: Most of these cheap toaster ovens heat unevenly. Its
possible that your sensor is reading in a cooler spot than where your PC
board sits.

Also, make sure that the PC board is not exposed directly to the heating
elements or direct radiation will heat it too fast.

One idea I've read about is to incorporate a small fan inside the oven
to keep the air mixed and at a more uniform temperature. A small
impeller on a long shaft with the motor sitting outside the oven will
do.


This is the classic toaster-oven soldering guide:
http://www.seattlerobotics.org/encoder/200006/oven_art.htm


The Sparkfun soldering ideas (here's a hotplate article, with
links to the toaster project too):
http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=59


Circuit Cellar article:
http://www.circuitcellar.com/library/print/0704/Lacoste_168/index.htm


Another, from Cornell, with controller:

http://instruct1.cit.cornell.edu/courses/ee476/FinalProjects/s2006/ki38/Webpage/index.html


The articles above discuss the various problems, solutions, and results.

HTH,
James Arthur
.

Relevant Pages

  • DIY SMT Solder Oven
    ... This may not be the appropriate news group to discuss this, ... have more than enough power to raise temperature to target value with the ... proper raise speed. ... The problem is that with those timing, we end up with a toasted PCB. ...
    (sci.electronics.design)
  • Re: DIY SMT Solder Oven
    ... This may not be the appropriate news group to discuss this, ... have more than enough power to raise temperature to target value with the ... proper raise speed. ... The problem is that with those timing, we end up with a toasted PCB. ...
    (sci.electronics.design)
  • Re: DIY SMT Solder Oven
    ... This may not be the appropriate news group to discuss this, but the group helps me before and I do not know a better place to find help again. ... I have more than enough power to raise temperature to target value with the proper raise speed. ... The problem is that with those timing, we end up with a toasted PCB. ...
    (sci.electronics.design)
  • Re: DIY SMT Solder Oven
    ... have more than enough power to raise temperature to target value with the ... The problem is that with those timing, we end up with a toasted PCB. ... Do I heat too quickly or too high? ... Most of these cheap toaster ovens heat unevenly. ...
    (sci.electronics.design)
  • Re: DIY SMT Solder Oven
    ... have more than enough power to raise temperature to target value with the ... proper raise speed. ... The problem is that with those timing, we end up with a toasted PCB. ... I did solder many PCB with the first prototype, ...
    (sci.electronics.design)
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