this is being driven (and may possibly be worth the trouble) because 
the customer really really (did i say really?) wants a single side board
they saw someone else who did it single sided (not skipping pads but 
accomplished a single side board in a comparable application - although
it was a different circuit and they had a lot less leads)

they will settle for a double sided if it is silver through hole
phenolic or CEM

someday they may bond out the chip for us with less leads

BTW, i think i am pretty good at IMHO AFAIK etc. etc.
but what the fk is TANSTAAFL ? 
i must have missed that one in BBS school

Dennis Saputelli

Abd ulRahman Lomax wrote:
> 
> At 06:13 PM 6/7/2002 -0700, Dennis Saputelli wrote:
> >i've got a 144 pin PQFP 0.5mm pitch
> >there are only a small number of connected pins, maybe a dozen or so
> >excluding power
> >
> >i am thinking about deleting a lot of unused pads to possibly open up
> >top side routes and reduce inspection and bridging concerns
> >
> >am i crazy?
> 
> Dennis, yes, you are crazy :-), but that doesn't answer the question....
> Even crazy people sometimes have good ideas....
> 
> >do you think the leads will short thru the solder mask to traces below?
> 
> Mr. Selfridge gave a good answer, I think. But maybe the idea does not have
> to be completely tossed.
> 
> >is this good practice even if i don't run traces there, i.e. will it
> >solder and align properly with missing pads?
> 
> As an experiment, you might try this:
> 
> Determine a set of pads that you want to solder, make it symnetrical so
> that the part will be firmly held. Maybe most pads would be soldered, or at
> least more than half. Do leave solder mask openings so that the extra leads
> are not stressed, but the openings might be reduced a bit. This *might*
> allow you to run a thin trace between the pads, but I wouldn't be on it. If
> it will not be enough to allow 1-thrus, I'd leave the mask openings the
> same as for the pads to be soldered.
> 
> The only advantage of this, in the latter case, would be less possibility
> of bridging, but I don't know how much of a factor that is, anyway, my
> knowledge of current assembly criteria is somewhat in need of renewal....
> 
> In short, however, the whole affair is probably not worth the trouble, but
> ultimately that is an engineering question which I am sure you are
> qualified to answer.... with a little help from your friends.
> 

-- 
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