Re: gEDA-user: TO-92 Best Practices

[Paul Probert <paulprobert@xxxxxxxxxxxxx>]

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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