Here is hoping that some knowledgeable "old hand" could point me in the 
right direction.  Or have I just stumbled into the rabbit hole?  I am now 
starting to understand the problems with footprint libraries and why "you 
do your own" but am very confused about one area of detail.  Any help would 
be greatly appreciated.  It appears to me that no one is very consistent 
about the use of metric/"english" measurements in their package definitions 
(specifically with reference to pin pitch).  For example, on QFPs the same 
manufacturer will refer to a part as having a 25 "mill" (0.025 inch) pin 
pitch and then provide a package drawing in metric showing a pitch of 0.65 
millimeters "Typical" (and the other dimensions on the drawing indicate 
that the original was in "inches" and then converted to metric).  Since "25 
mill" is actually 0.635 millimeters; after about ten linear pin pads, the 
pin is no longer on the pad.  Which reference measurement does one use?  Do 
different manufacturers use different meanings when talking about pin 
pitch?  Are there some hidden "rules" about this to confuse newbies?  Is 
this a problem only for older parts?  Or does this whole question 
demonstrate how ignorant I am????  Any wisdom would be welcome.  Cheap 
shots will be evaluated on their humor level.

Thanks in advance,
Duane Hague


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