MOTM

> > It must not be all SMT if it has 4 layers...   :-)
> 
> I'll disagree. Just because there are multiple layers doesn't mean there
> are
> through-hole parts.

[drifting off topic here]

I suppose I should have clarified, although I thought a smiley would
indicate that I wasn't 100% serious.

I'm currently starting to consider using SMT for my own DIY projects, and
hence am curious about such things as a 4-layer board that uses SMT
components finding its way into a MOTM module. I understand that the
connectors must be through-hole, and that the remaining components can all
be SMT (as Paul described). What I'm puzzled by is why four layers are
necessary, and how they are utilized. I assume that vias are used to make
transitions from one layer to another, but it still surprises me that four
layers are necessary for a CPU, the DACs, and associated support devices. I
imagine that it is because of the density of the board, given its small
size.

The other thing I'd like to find, and have googled for without success, is
something which tells me what SOP, SSOP, SOIC, TQFP, etc. mean in terms of
actual size, lead spacing, etc. I'm beginning to think I'll have to order
one of each from Digi-Key just to have a frame of reference.

--Adam