[Noisebridge-discuss] Reflow soldering (was A simpler circuit for ... [driving multiple LEDs)

[Jonathan Foote]

On Wed, Jan 19, 2011 at 9:29 PM, T <t at of.net> wrote:
> ...
>> Unfortunately, I couldn't convince Dr. Foote to make a video of his
>> SMD reflow soldering hack @noisebridge - I don't know how he did it,
>> just that he did it.
>> It would come in handy now (not just @noisebridge ...)
>
> What, doesn't want his teaching moments spread too far?

This was not a teaching moment but a learning moment. Specifically,
learning the temp curve of a $20 toaster oven with the thermocouple on
my Fluke. I didn't actually solder anything but I put in some
scavenged boards from which to harvest the smd caps.

I learned that electrolytics pop like popcorn when you overtemp them
accidentally.

Takeaway:  toast cycle at the middle setting produces a reasonable
temp curve, but make sure to start cool and watch the temp sensor like
a hawk.  The oven could really use a temp controller. And I really
should have made a video because exploding caps are awesome.

Having dabbled in reflow using hot air, toaster ovens, and hot plates
I prefer hot plates because it's easier to see that the solder has
flowed on all parts of the board. Hot air is great for rework or
one-offs but I wouldn't do a lot of boards with them.

Reflow is surprisingly forgiving, despite the crazy-precise temp
curves in a lot of specifications. My one major screwup happened when
I trusted someone who assured me that his expired solder paste would
be fine. It might have been had we been using stencils; as it was the
paste didn't flow well and left a conductive sheen under components.
Subsequently I'm careful to use new paste (buy the smallest container
available) and have not had a problem since.

If anyone sees a covered electric skillet that's not too grody at a
thrift shop (or has a spare) get it and we'll make a hot plate with a
temp controller  like Jeff "Mightyohm" Keyser's.