On Thu, 2009-03-26 at 15:06 -0500, solarwind wrote:
> * I thought heat damages components. I was consistently cautioned not
> to overheat components during hand soldering. If the idea is to heat
> up the solder just enough to melt (and maybe a bit more so as not to
> form a "cold soldered" joint), then wouldn't reflow soldering do the
> same damage to components?

Almost all components are DESIGNED for reflow, so no, they won't be
damaged by it, assuming you follow a recommended profile.

> * One of my DIP chips came with a notice saying that it should be
> "cooked" at 125 degrees Celsius prior to reflow soldering. I would
> never reflow solder a DIP chip, but this is interesting. Why do they
> have such requirements? Is it because of any possibility of trapped
> moisture in the chip that could rapidly expand in high heat and damage
> internals? What's the worst case for not obeying this notice?

Bingo. Think of a kernel of popcorn. Heat it up, it explodes. Same with
a chip. If you don't dry it out by "cooking" it, it will rupture during
reflow. The main issue is the damage may not even be apparent, very hard
to debug issues could result.

> * I've also heard of reflow soldering "profiles". What exactly are
> these profiles? Is it a requirement that I adhere to them for homebrew
> reflow soldering projects?

There are established profiles out there for reflow. Google should help
you there.

> * How do I apply solder paste on pads? Do I just squeeze it out of the
> tube and rub it consistently over the pads so that all of it is
> connected? Does a very precise amount need to be applied discretely on
> each individual pad? How is this done?

The pros have a mask and basically use a silk screen technique to get
the past on the board. While much more time consuming, simply squeezing
the paste on the pads will work pretty much just as well. Don't use
alot, experience will tell you how much. If you use to much chances are
either the joint will be rubbish, or you'll get a sometimes very had to
see bridge.

> * I've also heard that it is wise to calibrate or know where your
> skillet/stove reaches a certain temperature. What temperature is good
> for reflow soldering? 

The temp alone isn't enough, you have to follow a reflow profile, which
details what temps to stay at for how long, and how quickly to get to
each temp. Google is your friend.

> How do I measure this temperature?

A thermometer? I'd use an IR one in a pinch.

> * How long should the PCB be on the skillet/frying pan during the
> reflow soldering process?

See above.

TTYL

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