Re: gEDA-user: TO-92 Best Practices

[John Luciani <jluciani@xxxxxxxxx>]

   On Tue, Mar 2, 2010 at 1:25 AM, Donald Tillman <[1]don@xxxxxxxx> wrote:

   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.

   I use 1.39mm for the non-formed leads (apx 55mils).
   (* jcl *)

   --
   You can't create open hardware with closed EDA tools.
   twitter: [2]http://twitter.com/jluciani
   blog:    [3]http://www.luciani.org

References

   1. mailto:don@xxxxxxxx
   2. http://twitter.com/jluciani
   3. http://www.luciani.org/


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