[hpsdr] SMT Soldering and Circuit Board Heat Question

[David Toepfer]

Ignorance shines like a beacon.  I guess I should accuant myself better with
this method before offering improvements.  Sorry.

dt
.

--- David Toepfer <davetoepfer at yahoo.com> wrote:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> QUESTION:
> 
> Since you say the point is to head the board up to 100C (212 deg F), can't
> one
> simply stick the board in a sealed bag (suck out most air you can) and drop
> it
> in a pot of boioling water?  Boiling water never get's hotter than 100C. 
> Some
> simple trial/error should be able to determine how long of a boil boards of
> specific material and size.  Seems cheaper.  No hot plates, ovens, or
> thermometers to buy either.
> 
> dt
> .
> 
> --- Bob Fish K6GGO <rwfish at comcast.net> wrote:
> 
> > ***** High Performance Software Defined Radio Discussion List *****
> > 
> > Hi Bruce,
> > The hot plate is only to bring the board and the parts on it up to an 
> > idle temperature of about 100deg C. (212 Deg F). No hotter than that. 
> > The board and parts can stay at that temp all day without damage. The 
> > temperature profile that the manufacteurs use in the big reflow ovens 
> > goes like this; the temperature ramps up to 100 degrees C (your hot 
> > plate temperature) and stays there for 3 or 4 minutes. This is to 
> > achieve thermal stability and to let the solder paste outgas a little 
> > bit, then it continues to ramp up to around 200 degrees C (this is where 
> > the solder melts) but does not stay there, it imediately cools down to 
> > room temperature.
> > To simulate this profile with the tools you have, all you have to do is 
> > put the solder paste on the pads where the parts go and this is the big 
> > secret to success: use way less paste than you think you will need. On 
> > the fine pitch parts all you really want is a sweat joint, other wise 
> > they will bulge over and short to the adjacent pin. After you place the 
> > parts in the paste, place the board on the hot plate and bring it up to 
> > 100C (220F) let it soak there for 3 or 4 minutes, then with the board 
> > still on the hot plate at 100C use the heat gun on the board with a 
> > waving motion until the solder paste turns from dull gray to a shiny 
> > silver in color. It may not happen to the whole board at once, 
> > especially if it is a large board, but once it does your done. Turn off 
> > the hot plate and heat gun and let the whole works cool down to room 
> > temperature. The higher teperature is where damage could occur if left 
> > there for too long. So, once the paste turns shiny silver take the heat 
> > gun away. By the way, you can do two sided boards if you put small metal 
> > stand offs on the board and let the previously soldered parts hang 
> > upside down while you do the other side. They just reflow again.
> > I was a little worried when I first tried it also, But it works great 
> > with a little practice you will be a Pro. Just make sure you keep the 
> > hot plate at 100C and no hotter. The parts can stay at that temp all 
> > day. Just use the heat gun to briefly heat the paste to melting temp.    
> > Good Luck! Let me know how it went!
> > 
> > 
> > Bob   K6GGO
> > 
> > 
> > Bruce K3CMZ wrote:
> > 
> > >***** High Performance Software Defined Radio Discussion List *****
> > >
> > >
> > > 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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