TANSTAAFL - There Ain't No Such Thing As A Free Lunch

http://www.apc.net/ia/scrmaim.htm
http://www.magicpub.com/netprimer/acronyms.html#T

Cheers!
Drew


----- Original Message -----
From: "Dennis Saputelli" <[EMAIL PROTECTED]>
To: "Protel EDA Forum" <[EMAIL PROTECTED]>
Sent: Saturday, June 08, 2002 2:51 PM
Subject: Re: [PEDA] unused QFP pins


> 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.
> >
>
> --
>
___________________________________________________________________________
> www.integratedcontrolsinc.com            Integrated Controls, Inc.
>    tel: 415-647-0480                        2851 21st Street
>       fax: 415-647-3003                        San Francisco, CA 94110
>

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