[hpsdr] SMT Soldering and Circuit Board Heat Question

[S. Cash Olsen]

Steve and the group,

Bob gave you some really good tips on how to reflow your boards, but I'd
like to add some advise of my own.

Skillets and hot plates are very hard to control and for small board 2" x 2"
I have used a beverage warmer for about a year or so. The beverage warmer
takes a little while to warm up but just simply won't exceed the 100°C
temperature. This simplifies things because your won't have to worry about
temperature regulation. I bought mine at Wal-Mart and I think the candle
warmers at crafts stores will work well, also.

If you haven't seen my movie of the soldering process I'd like to point you
to a long and short version:
<http://www.zianet.com/erg/SMT_Soldering_Movie.mov>
<http://www.zianet.com/erg/SMT_Soldering_Short.mov>

The short version requires less bandwitdth but all you see is the solder
melt portion of the longer version which gives you some idea of applying the
hot air.

I have a complete turorial on applying paste and placing parts:
<http://www.zianet.com/erg/SMT_Soldering.html>

For bigger boards I use a ceramic top, two burner hotplate by GE that I
purchased at Wal-Mart. This is a nice surface that you can built you boards
on, it conductive so it will help to dissipate any static electricity and is
flat so you can find you parts if one gets away from you. The problem with
this hotplate is the it has to be run on about the lowest setting in order
to get the right temperature. I have checked the profile of this burner with
my IR heat gun and it is quite consistent. Electric Skillets have hot spots
generally where the heater is and vary widely in temperature across the
surface.

One final comment to add to Bob's after removing the hot air from the heat
gun leave the boards on the warmer ( hot plate ) for several minutes to
allow the temperture to come down to about 100°C before moving them to room
temperature. Absolutely no harm will be done if the parts and boards were
left at this temperature regardless of how long.

Cash

Cash Olsen, KD5SSJ

Kits to build Scotty's Spectrum Analyzer http://www.zianet.com/erg
Scotty's Spectrum Analyzer website http://users4.ev1.net/%7Ewsprowls/
Yahoo Builders Group http://groups.yahoo.com/group/spectrumanalyzer/

-----Original Message-----
From: hpsdr-bounces at hpsdr.org [mailto:hpsdr-bounces at hpsdr.org] On Behalf Of
Steve Nance
Sent: Friday, July 28, 2006 12:19 PM
To: 'Bruce K3CMZ'; hpsdr at hpsdr.org
Subject: Re: [hpsdr] SMT Soldering and Circuit Board Heat Question


***** 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

-----Original Message-----

 I have been trying to learn how to solder these smt parts.

What I have is some solder paste with a melting temp of
361 degrees F, and a cheap six inch hot plate. The hot plate is made out of
cast iron and I an able to measure the temp with fair accuracy.

 Now my concern is this; how much heat can the circuit board stand before it
turns to junk? My plan is to heat the circuit board with the smt parts and
solder paste and finish this off with the embossing tool that Cash Olsen
uses. But, I am worried about the heat on the board being too much, prehaps
some of you have gone throuh this and know if the boards can stand the heat.

 Bruce K3CMZ

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