Soldering from Hell. (was: Re: DSP Stuff)

[Irish]

Sorry if this doesn't make the synth part of synth DIY... 

Martin Keefe wrote:
> Hmm, I'd have a go at normal SMT stuff but these things have two 
>connections per mm! That's 0.25mm pads with 0.25mm gaps between. And 
>they're about 13mm on a side. Pretty demanding precision without 
>specialist tools. Fabricating a PCB to those precisions and with 
>multilayers would also be a challenge. 

I ran a SMT machine that would place .25 parts at the rate of 60,000
parts per hour (standard sized chip resistors at upwards of 120,000 pph). Had
to rework by hand when the machine missed... 
PCB suppliers will usually go to that pad size (but not smaller) for about the
same price as thru-hole. Actually less for unmixed technology - no drilling! 

Quint wrote:
>None of this is really meant to be soldered really, I dont see that you 
>could, if so its by wave.  The parts are too small and low in voltage to 
>traditionally solder.

SMT parts are not usually soldered by wave, but by oven - a
solder paste is screened onto the board, and hold the parts in place when the 
machine places them. Then it gets baked :) But again, we did hand rework when
things went wrong. Had nice irons (and a heat gun), but really wasn't any
different than TH; you just had to be good! 

Then Steve wrote in another thread:
>I learned to repair traces 3 layers down  on a damn flex-print, fix broken
>(as in 2 pieces) circuit boards,  non-destructive conformal coating removal
>and a host of other fun tasks that  are required to be done to specs that meet
> / exceed those of NASA. 

Man, now *there's* stuff I wouldn't try to MilSpec! The multi-layer flex I
wouldn't even try, period. Although I have repaired unit that were in pieces
('run-overs') sucessfully, I doubt they would have passed any standard other
than 'smoke test' :) 

OK, I'll shut up now....

Irish