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Not long ago, IC chips had their pin spacing set at 0.1
inch or 2.54 mm. About 1990, the organisation in charge of the standard
defining the pin pitch called JEDEC, changed the specification for all future
designed chips to use a rounded metric pin pitch.
The rule basically states that the pitch series can only
be to two decimal places in millimetres and the second digit can only be a 0 or
a 5. For example, a pin pitch of 0.025 inches can not exist, as 0.025 in
millimetres is 0.635. If this number is rounded to two places to satisfy
the first part of the rule, then we have 0.64 mm. To satisfy the second
part of the rule, the 4 must be changed to either a 0 or a 5, or the legal
pitch would have to be either 0.60 or 0.65 mm.
0.65 mm was the first metric pitch chosen. The
electronics industry has moved beyond this to create pitches of 0.5 mm and 0.4
mm.
My question is:
Does anyone know of or has heard of this standard, and if
so, what document number is it contained in?
Euric
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