SMT techniques (was Re: group buy for homebrew CPUs?)

[Don]

Dave McGuire wrote:
> Ethan Dicks wrote:
>> I _have_ thought about that for replacement -8/L and -8/i boards -
>> design a simple board with, say, 4 to 6 16-pin SO pads and decoupling
>> caps and a dual row of jumper pads to cross-connect the edge fingers
>> to the various chip pads to be able to replicate, say, an M111 vs an
>> M117.  The "problem" is that I doubt you could get real TTL (not
>> LS-TTL) parts in SO.  I haven't experimented with replacing TTL with
>> LS parts in any of my -8s, so I don't know if there would be any
>> issues or not.  So far, I've always had enough of the right things on
>> hand when I go to replace a chip on an M-series module.  I would think
>> that the dimensions could be on the order of 2 x the size of just the
>> area of the fingers.
>>
>> The advantage, of course, is that it would be easy to make a large
>> number of these on one PCB panel, reducing per-unit costs.  Using one
>> (or maybe two at most) base designs would also help quantity issues.
>> You could sit down one day and make a stack of a dozen M111s, then
>> make two dozen M113s the next day with the same PCB; just add the
>> right SO-parts and configure the jumpers in the right order, and there
>> you are.
> 
>   A variation on this theme might be to build a very small number of 
> different types of boards, but with a CPLD on each one...a small, cheap 
> one like a Xilinx XC9536 (something like $3/ea qty. 1)...then have a 
> JTAG connector on each board, and squirt the "personality" into the 
> board that way.  I've not had a chance to work closely with 
> FlipChip-based machines (unfortunately) so I don't know how much 
> consistency there is on things like power pins and such, so I don't know 
> if this'd be practical, but I think it's an interesting idea.

I think that skirts the appeal of a *real* "miniture PDP".
E.g., why not just do the whole design in an FPGA?  It would
be a pretty boring accomplishment...  :-(

OTOH, having the exact same design done in "miniature
technology" would be cool!

I've a friend who had a miniature pinball machine (intended
as a "bar top" device).  Roughly 10"x24" with everything
scaled down (and made in stainless!).  *That* was cool!