0.635mm is not 0.65mm but both measurements are standard pin pitches along with
others.
 If a device 'appears' to have different pin pitches it means it comes in
different
package types, so I would be double checking the manufacturers website
(eg http://www.idt.com/packages/index.html) and the supplier to work out what
you
should be designing for.



_______________________________________________________________

Clive Broome
IDT Sydney Design Centre        Ph:         +61 2 9763 3513
8 Bayswater Dr, Homebush        Fax:        +61 2 9763 3409
Sydney,  NSW, 2127              Email:[EMAIL PROTECTED]
Australia

         Australia's Leading Semiconductor Designers
---------------------------------------------------------------






Duane Hague <[EMAIL PROTECTED]> on 03/04/2001 09:57:33 AM

Please respond to [EMAIL PROTECTED]

To:   Multiple recipients of list proteledausers
      <[EMAIL PROTECTED]>
cc:    (bcc: Clive Broome/sdc)

Subject:  [PROTEL EDA USERS]:  Confused Newbie on Footprints



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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