----- Original Message -----
Sent: Thursday, April 18, 2002 7:15
PM
Subject: Re: [TN] IPC SMT FOOTPRINT
DESIGN GUIDLINES VS SUPPLIERS
I would like to address a few of
the comments that have been made.
First, when the same component
parameters and design fillet goals are input into the current web based
calculator they should yield the same land pattern as listed in the RLP
section. We have on occasion found an error in the component data listed in
the hard copy or web calculator and have made appropriate corrects. Any
discrepancies found should be reported to John Perry at IPC.
Second is
that the calculator is based on the same principles as found in the hard copy
of the standard. It is true that land patterns for the newer components may
not have been tested as the earlier ones were. But in many cases the basic
principles remain untouched. However, the land pattern committee does approve
each new pattern based on an assessment culled from their own experiences with
that component as well as input from other industry sources.
The last
issue is that the 782 land pattern committee is currently working on a
complete revision to our land pattern document. I would point out that one
should not perceive the revised document as an indication that there is
something wrong with the current land patterns. This effort is addressing new
component families as well as a new concept going forward.
The new
standard will be identified as IPC-7351 and will be of a format that provides
slash sheets for the various component families. This will enable new
component additions to get released in a much more timely fashion. The
standard will contain four columns of data for each component. The first
column will be the existing 782 pattern data. The next three will represent
minimum, median and maximum applications. All component types not currently in
782 will be released to this new format. AS we move forward, we will NOT be
adding data under the 782 columns for components not currently listed in the
current 782.
As a general point of information, you will find that the
current 782 land patterns will fall someplace between the minimum and median
columns. What is important to recognize is that compromises were taken to
reach the smaller sizes and it will be quite apparent where they were made. It
would be wise for the designer to obtain approval from those affected by the
compromises before using the smaller sizes.
The first release will
contain the current 782 listed components with additional component slash
sheets released in rapid succession thereafter.
Regards,
Gary Ferrari
Executive
Director
IPC Designers Council
(860) 350-9300
Fax (413)
771-5386