2001-05-05
First of all, the spacing of pins on chips is a JEDEC standard. The 2.54 mm
spacing is one of the firsts. Since then the spacing has shrunk to 1.27 mm
and smaller. In the early '90s, JEDEC changed the rules for what the chip
spacing must be.
Now, all spacing must be in millimetres, to a maximum of two decimal places,
in which the second decimal place can be only a zero or a five. In other
words, spacing must be in increments of 50 �m.
When 1.27 mm was halved to 0.0635 mm, this did not follow the JEDEC rules,
so the size became 0.65 mm. This was in the early 90's. Now, chips are
being made with 0.5 mm spacing.
This rule only reflects new designs. Legacy designs still being produced
may follow their old spacing.
Even though 2.54 and 1.27 mm are soft conversions of 0.1 and 0.05 inches, I
see no reason why some chips can not be made to 2.5 and 1.25 mm. The error
is so trivial. On a 20-pin chip, where there are 10 pins per side, the
maximum error from the first pin to the last is 0.36 mm. That is 0.04 x 9.
I have never handled a chip that had perfectly straight pins. All are bent
or off alignment to some degree. More then the 0.04 mm per pin pitch that
they would be off if they were made to 2.5 mm instead of 2.54. I always
try to "straighten" pins before inserting them into sockets.
Also, keep in mind that these old chips styles will eventually become so
obsolete, they will cease to be produced. I have no idea at this time how
many of the old designs are made and how much that decreases on a yearly
basis.
Let's see if someone who knows has a response.
John
Keiner ist hoffnungsloser versklavt als derjenige, der irrt�mlich glaubt
frei zu sein.
There are none more hopelessly enslaved then those who falsely believe they
are free!
Johann Wolfgang von Goethe (1749-1832)
----- Original Message -----
From: "Han Maenen" <[EMAIL PROTECTED]>
To: "kilopascal" <[EMAIL PROTECTED]>; "U.S. Metric Association"
<[EMAIL PROTECTED]>
Sent: Saturday, 2001-05-05 04:12
Subject: Re: [USMA:12608] Bill Roland again
> I do not know about the situation at Intel, but I know that not that long
> ago, wafers were habitually called 8, 12 etc. inch wafers. Yes, why would
> any computer magazine convert inch sizes to metric? I think that the
industy
> has gone metric in these fields.
> BTW, is the computer industry changing from 0.1 inch to 2.5 mm spacing for
> chips? And what about clean rooms, where they measure(d) dust particles
per
> cubic foot?
>
> Han
>
>
> Han
>
>
> ----- Original Message -----
> From: "kilopascal" <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>; "U.S. Metric Association"
<[EMAIL PROTECTED]>
> Cc: <[EMAIL PROTECTED]>
> Sent: Saturday, May 05, 2001 12:39 AM
> Subject: Re: [USMA:12608] Bill Roland again
>
>
> > 2001-05-04
> >
> >
> > 1.) A couple of Imperial only people: Boeing Corporation, the Unites
> States
> > Military (even though some gun sizes are measured in metric, they have
> > imperial equivalents commonly used),
> >
> > How metric is the military compared to FFU? Does anyone know?
> >
> >
> > 2.) NASA (they claim to be metric, but everything is designed and built
> in
> > imperial, and flight plans are also being converted back to imperial).
> >
> > What does he mean by flight plans are being converted back? Is any part
> of
> > NASA reverting?
> >
> >
> > 3.) Also of interest, Intel Corporation, who I'm sure you've all heard
of,
> > is more imperial than is commonly known. The press loves to mention 0.18
> > micron and 300 mm wafers, but Intel itself uses "mils," or 1,000 of an
> inch,
> > far more commonly than any metric measurements.
> >
> > If Intel and others used FFU, why would the trade journals convert to
SI?
> A
> > few years back on this list server, someone mentioned processing a 200
mm
> > wafer. And stated it was 200 mm and not 8 inch. Who was that and can
> > anyone verify what system these companies use internally?
> >
> >
> >
> > John
> >
> > Keiner ist hoffnungsloser versklavt als derjenige, der irrt�mlich glaubt
> > frei zu sein.
> >
> > There are none more hopelessly enslaved then those who falsely believe
> they
> > are free!
> >
> > Johann Wolfgang von Goethe (1749-1832)
> >
> >
> >
> >
> >
> >
>
