Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "electronut" <electronut@...> wrote:
>
>  Stephanie, the parts I'm looking at are about BGAs with 400-500 
> balls.
>  You seem to know a lot more than me about the process. Any tips you 
> can share are much appreciated.
> 
>  timbomcnuckle: what king of PCBs have you done with your reflow 
> oven ? What kind of parts have you done ? Have you done BGAs, or 
> 0.5mm TQFP ? Did you do two layers PCBs ?
I just did a batch of boards with 0.5 mm MQFP's and some other SSOP
with 0.5mm pitch.  These were heat-sinked 14x20 mm rectangular ASICs
we had made by MOSIS.  I made my own solder stencils and used
too-thick shim stock, and so I got too much solder.  The stencils were
.005" thick.  I had some under-etching of the resist pattern which
made the apertures larger, too.  So, some of the chips floated on a
lake of solder and the leads had to be repositioned manually.  But,
that was due to my inexperience knowing how much solder volume to use.
 The toaster oven could take 6 of these boards (roughly 3 x 4") at a
time.  I poked the controller's thermocouple into a PTH on one of the
middle boards to control actual board temperature.  These were 6-layer
boards, with roughly 135 parts per side.  The back was mostly
decoupling caps, and that worked beautifully.  Due to the big, heavy
chips next to small passives on the top, the soldering was a little
less uniform, but really worked quite well.

Once I get this solder stencil aperture x thickness worked out better,
the whole process is going to be wonderful.

Jon