Thanks Olin, et al, for the tips. I'll also got to the suggested standard,
plus will include what sense I have made from the jedec drawing by now and
will share the results with any and all who care. I have noticed thatthe
trend seems to be to make pads much longer than the contact area, say about
2.0 long. I can see why you would want some meat hanging out for a solder
tip, but why bury bare pad out of sight?.......I also have noticed that the
PIC spec is a bit off when compared to the jedec. Mchip also deosn't seem to
participate w/ jedec. I'm not sure if it's much of a problem, except in long
runs where the mechanical error becomes recursive or cumulative and
considerable.

Chris

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Olin Lathrop
> Sent: Tuesday, January 21, 2003 5:54 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]:TGFP Footprint
>
>
> > I was hoping for a more qualified response that might reveal some
> insight
> > into such things as (hypothetically stated) 'leaning toward the Max
> > tolerance for pick & place, but the min for solderability'
> > Or perhaps 'be sure to make the pads longer than 1.5 X the
> lead contact
> > length, but exceeding 2mm will allow solder bridging that is hidden
> beneath
> > the part body and difficult to troubleshoot..' and the like...
>
> Many manufacturers have suggested pad layouts.  You could look at some
> other manufacturer's suggestions for 800nm SMD.  I like to
> make the pads
> about as wide as the pins.  These pins are 380nm nominal, with 800nm
> pitch.  I'd make the pads 400nm wide with 400nm spaces.  For machine
> placement, the length only needs to be a little longer than
> the worst case
> range between pin contact limits.  For hand soldering, it
> helps to have
> each pad extend out from the device a little further.  That
> gives you more
> room to put the soldering iron, and leaves space for a nicely visible
> bead.
>
>
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