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Clint you asked about the temperature of soldering the surface mounted  
devices.  Most of them are recommended to follow a heating curve that lasts  
about 2 or 3 minutes.  Here is a url to a file that shows the preferred way  
to heat and cool them.  It is for some capacitors,but other devices follow  
the same curve.  This is for heating them up in something that resembles a  
toster oven.  The professional devices have timmers and things like that to  
make the heat follow the curve.

Re: soldering

Ralph Mowery wrote:
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   We had a separate profile for every board we ran though the Heller
Reflow oven at Microdyne. The operator selected the profile by the board
type, and build number on a computer near the oven.

Re: soldering

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A few years back; Elektor magazine published a project to convert a pizza  
oven into an SMD oven.

There was pretty detailed tech info on heating curves and the reasons why it  
was done that way.  

Re: soldering
Ian Field wrote:

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I bought a big toaster oven in 2007 to reflow PC boards stuffed with my P&P  
machine.  I got a ramp and soak temperature controller on eBay and some  
micro-size thermocouple wire.  I first tried doing the boards with the  
thermocouple just hanging in the air, but that ended up toasting the boards  
to a crisp!  I then thought to poke the thermocouple junction into a through  
hole in one of the boards, and that has been working fine for years, now.

So, I can program in a ramp to 180 C, hold for one minute, then ramp to  
either 225 C (tin/lead) or 246 C (lead-free) and hold for one minute, then  
ramp rapidly to room temp.  Sometimes the boards at the corners of the oven  
don't completely reflow all the way to the edges, but when I get the profile  
right, they come out looking quite professional, and with minimal rework.

If the boards have been sitting around for a while, I usually bake them at  
50 C for a while, the up it to 75 C and hold for an hour or so.  Otherwise,  
absorbed moisture can cause the boards to split internally and break vias.


Re: soldering

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Probably ramping up too fast.

The epoxy encapsulation has a hygroscopic index - its very small, but  
expanding moisture can crack the encapsulations.

There's usually a slow ramp to drive out moisture, a short plateau then  
ramping up to the soldering temperature.  

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