JEDEC - JEP95 JEDEC STD NO. 95-1
JEDEC Standard No. 95-1 Section 4 Design Guidelines
|Publication Date:||1 March 1997|
JEDEC REGISTERED AND STANDARD OUTLINES FOR SEMICONDUCTOR DEVICES, JEDEC PUBLICATION 95, is the official JEDEC Publication that contains the registered or standard mechanical outlines of solid state products and related items. The introduction of this document states:
"The primary purpose of solid state products outline registration is to assure complete mechanical interchangeability of all products conforming to a particular outline regardless of when or from whom it was obtained."
The reality of the situation is that the Publication 95 outlines have become "umbrellas" or "catch-alls" in order to accommodate the various nominal dimensions of different manufacturers. The effect has been to increase tolerances to the point that they reflect large size variations rather than small variations around a common nominal or mean dimension. Another factor has been the attempt on the part of the manufacturers to use the largest possibie tolerances in order to allow production to proceed at high speed and high volume.
From a component production point of view, the use of wide tolerances is an economically desirable goal. From a system point of view, such use results in the transfer of costs to the user who has to accommodate the large tolerances. The user is also limited in the selection of vendors because of a lack of complete interchangeability of the products of different manufacturers.