Re: gEDA-user: TO-92 Best Practices

[Donald Tillman <don@xxxxxxxx>]

On Feb 27, 2010, at 3:57 PM, John Luciani wrote:

>   I use two different footprints. Both footprints have the pins  
> inline.
>   One footprint spaces the leads 1.39mm the other 2.60mm.
>   The 2.60mm is the common formed lead pattern. I believe
>   I used the spec from On-Semi.
>   I use a finished hole size of 29mils. The fab tolerance is +-4mils.


Hey John,

Thanks for that.

Researching this a little more...  Fairchild's TO-92 spec says that  
the leads are rectangular, 0.46mm by 0.38mm, and the diagonal there  
works out to 23.5 mils.  With a little extra room for tolerance, yeah,  
a 29 mil hole sounds good.

But with 29 mil holes spaced 50 mils apart, that doesn't leave enough  
room for the pads and the space between.  Maybe 7 mils each.  So  
breaking away from the 50 mil grid by just a little bit and moving the  
outer legs 5 mils beyond allows the DRC to work.

  -- Don

--
Don Tillman
Palo Alto, California
don@xxxxxxxx
http://www.till.com






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