XO 1.5 Solder Reflow in Toaster Oven

[Anna]

On Sun, Aug 21, 2011 at 10:18 PM, Richard A. Smith <richard at laptop.org>wrote:

>
> Interesting.  If you did in fact reflow anything then it was probably due
> to the poor temp regulation of your toaster oven.  The solder in the XO is
> lead free and melts a higher melting point than 385.  I don't know the exact
> formulation that Quanta uses but most lead free formulations melt at > 215C
> which is 419F.
>

Thank you for being the first person to offer actual data on this.  Since I
baked it at 385, or thought I did, if in fact the melting point is 419, then
I didn't reflow the solder at all.  I need to get an independent oven
thermometer to stick in there if this turns into an habitual endeavor.


>
> If you actually didn't reflow anything then the forces from the large
> thermal gradient may have been sufficient to push the cracks back together
> enough to work again. (Sort of the same thing that happens when you test by
> pressing on the chip hard to see if it boots)
>
> A production line oven uses a soldering profile.  Pre-heat, then a brief
> spike over the melting point and then a cool down.
>
> If you do a search for lead free soldering profile you will see loads of
> information on various profiles.  Picking something that closely matches one
> of those profiles will give you the greatest chance of success.
>

Good to know.  Since this isn't like tempering steel, if something goes
wonky in the future, I can examine what production lines do and try to
emulate that as best I can.  The wikipedia entry on reflow ovens wasn't very
detailed, but I didn't know what else to search for so I just hauled off and
did the best I could.  I got most of my info from a message board where
folks put their HP laptop mobos in the oven.


> As James mentioned if you forget and bake the RTC battery then there is a
> very high probability it will explode.  At my previous job we once used old
> computer motherboards with thermocouples attached to tune our profile and we
> forgot to take out the RTC battery.  It exploded but thankfully it was while
> it was inside the oven and no one was injured.
>

Oh, yeah, I made sure to remove the battery.  And anything else that might
explode, catch fire, melt, or otherwise make a wicked mess.

A couple of hours ago, I baked the second XO 1.5 motherboard and yep, it
booted after that.  I took tons of pictures this time.  I'll post a writeup
with the pictures in the next few days.  At this point I feel like Julia
Child.  If Julia Child put circuit boards in her oven.

And no, this is definitely not for the "typical" user, but hey, on Friday I
had two dead XO 1.5's and now on Sunday evening I've got two working units.
No idea on the longevity of this fix, but OLPC is all about experimentation,
right?

Anna Schoolfield
Birmingham
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.laptop.org/pipermail/devel/attachments/20110821/0c409d6e/attachment.html>