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Re: where footprints come from (was Re: Re: Internal PCB Units?)


Dick Hollenbeck wrote:
> (units mil)
> (resolution 10)
> (const variable_def 30.4)

Do you really need the resolution if you already have floating-point
and a free choice of units ?

> We really don't need much in terms of expression support. Simple mx+b 
> support is about all for positioning a pad with given shape.

Yes, you usually don't need higher math. If you want to stay close to
the respective reference material (i.e., use the same parameters as a
basis), you may need to add or subtract distances and quite often
divide them by two. Multiplications come in the form of
dimension*integer or dimension*(integer+/-0.5).

Things get a little more interesting if you want to create more than
one footprint from a single definition, e.g., DIL/SIOC/SSOP/QFN/etc.
families. Also, large BGAs are basically begging for some nestable
loop construct.

What's your opinion on measurements ? E.g., like here:

But I think they were drawn manually, so there's no automatic
correlation of the numbers displayed and the real distance.

For comparison, all the measurements shown here are automatic (and
adding a measurement is a matter of seconds):

> KISS. 

Yup, as simple as possible but not simpler :)

- Werner


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