Donald Tillman wrote:
Hey folks,
What's considered Best Practices for TO-92 packages?
I'm working on a project that involves a lot of discrete transistors in
TO-92 packages -- the regular style, 3 in-line, no fancy triangular
pinouts or lead forming or anything.
The TO92 package in pcblib-newlib seems to be larger than necessary, in
pin spacing, pad size, and hole size.
Pin spacing: The actual package has the pins 50 mils apart. Is this used
in practice? Or is it too problematic, and maybe it's more practical to
just spread the leads a little by hand? Are there machine insertion
issues? (Not that I care right now, but I'd like to be as uptown about
it as possible.)
The TO-92 leads are 20 mils diameter. Would a 24 mil hole be fine
then? And maybe a 35 mil pad?
Anybody have success (or failure) stories or advice?
-- Don
Well, I had a disaster once where I used a footprint with the triangular
hole pattern, but my transistors all had straight leads, like yours. We
just spread the leads a little by hand and then pushed the transistors
in. As they went in, the holes acted like lathe tools and machined curly
chips off the leads that then shorted about 10 percent of the
transistors. So the next time I ordered transistors that had the leads
already bent out into the triangular pattern. Maybe there's a tool that
will bend them properly so that you can use your existing stock.
Paul Probert
University of Wisconsin
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