Re: [PROTEL EDA USERS]: Thruhole footprints

[Abd ul-Rahman Lomax <marjan@vom.com>]

<x-flowed>
At 10:50 AM 9/2/00 -0600, Westfeldt, Pat wrote:
>First posting here, but I have been a listener.  Running both Protel and
>Allegro, 2 years experience, but this is a design question.  I have much
>more trouble building thruhole than smt footprints, because I don't know
>where to look.  For SMT, IPC SM-782 is a good starting point in most cases.
>Is there a thru-hole counterpart from any source?

Through-hole footprints are a lot easier to build than surface footprints.

Generally it is sufficient to draw a top overlay outline that will include 
the physical component, and to place pads where the component data sheet 
indicates that the wire centers will be located. If you are bending leads, 
as with a resistor, there is a formula for minimum lead bend distance from 
the part, but unless the wires are thick, you could usually get away with 
as little as 50 mils from the body of the part (or any thickening in the 
lead), but 100 mils might be better.

The holes should be 8 to 20 mils larger in diameter than the leads. An 
exception may be made for square leads; I typically use a 40 mil hole for a 
25 mil square lead, which has a nominal diagonal dimension of 35 mils. If a 
hole ends up being a little small for a square lead, it will still go in...

Holes are typically specified as finished size. The actual drill will 
typically be 3 mils larger than the specified size, 1 oz plating being 
about 1.4 mils thick....

marjan@vom.com
Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433



</x-flowed>