On Sat, May 21, 2011 at 11:42 PM, PICdude <picdude3@narwani.org> wrote:
> How are you reflowing the top and bottom? =A0I assume in two individual
> passes? =A0What happens if you swap the order you reflow them?
>
> I usually get shorted pins with SSOP PIC's also, but wick them off.
> Using a 6-mil thick stencil, and on my next stencil, I'm going to try
> 5-mils, and perhaps smaller apertures to get less solder.

I do use two passes. I've actually been doing the bottom side first as
it has fewer semiconductors (figuring it'd stress them less to only be
heated once). The ring shows up on the bottom only, and after the
first reflow. The second time through doesn't seem to do much to the
rings. I haven't tried swapping the order, though that was something
that occurred to me earlier today too! I wonder if there's something
on the board that burns off during the first pass, thereby leaving the
second pass less ring-y. That said, if one side had to have rings, I'd
rather keep it as is, the bottom is much less populated and easier to
clean.

I've been wicking with the SSOP parts as well, seems to work. I'm
using a 4 mil mylar stencil, laser cut. I think I need to reduce the
aperture size, particularly on some components where I've deliberately
made a large landing pad to facilitate hand soldering (if needed).
Resizing the aperture should allow a better relation of solder paste
to actual component size, rather than just covering most of the pad
with paste.

Josh
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