[hpsdr] SMT Soldering and Circuit Board Heat Question

[Darrell Harmon]

On Fri, Jul 28, 2006 at 02:18:47PM -0500, Steve Nance wrote:
> ***** High Performance Software Defined Radio Discussion List *****
> 
> Bruce,
> 
> I went the hot plate route and gave up the idea. To get enough heat to melt
> the paste on top of the board the bottom side gets so hot the white
> silkscreen turns brown/yellow. The major problem is the airspace between the
> hot plate and the board. The actual hot plate surface gets so hot my digital
> thermometer pegs out. To me this is just asking for trouble. I even have a
> temperature controller with a thermocouple on it and it is useless as it
> can't control the hot plate since it's temp is completely out of range.
> 
> I actually bought a high end cast iron hot plate ($100) thinking that it
> would have better heat distribution across it's surface, which it does, but
> it takes forever to cool off, also bad.
> 
> I've scrapped the hot plate idea and gave it to my wife who told me nobody
> uses the things anymore, I'll make somebody a really good deal on it
> though...
> 
> Other people use them as warmers in conjunction with hot air on the top side
> which works ok if you keep the hot plate temp down. I have a hot air rework
> station that works well for me. The only problem is it is slow as you can
> only do one part at a time. 
> 
> I think a good quality convection Toaster Oven with a reflow controller is
> the way to go. Everything gets heated up at the right time based on the oven
> air temperature which is much easier to control. Somebody mentioned here a
> while back having bought a nice convection oven with quartz elements from JC
> Penny I think for around $100, but I can't find that post.
> 
> Just my 2 cents worth.
> 
> 73
> Steve
> 

I use the toaster oven method for BGA parts, and I solder everything else by
hand. I just don't like dealing with the paste. I just finished soldering a 
board with an AD Blackfin DSP in an 0.8mm pitch lead free BGA. I was afraid
I would have problems due to the fine pitch and lead free balls, but it worked
just fine. The 1mm pitch FPGAs are no problem at all to solder.
The silkscreen yellowed a bit but was not bad considering I let the
board peak at 235 C. The toaster oven I use is a $20 sunbeam with quartz 
elements. I got it from Walmart. I use a MAX6675 thermocouple to SPI converter
connected to the parallel port of my laptop and a relay to control the oven.
The code and schematic is in here:
http://dlharmon.com/solder/toaster.tar.gz
Some information is at 
http://dlharmon.com/solder/smd.html

-- 
Darrell Harmon
http://dlharmon.com

 1154196411.0