Mr. Davy,

I will take issue with your last posting.  Much of the text implies that the
IPC developed standards are nothing more than technical opinions, developed
without hard data.  Some similar postings in the past have also raised my
hackles, so I thought I might take a few minutes (and pontificate) and
describe what goes on in the development of these standards.

Let us take IPC-SM-840 for example.  As I have been part of this group for 10
years and now am vice-chair, I have a fair insight on how things went, having
been through two revisions.

First, in my previous reply, there are two  CLASSES of solder mask, not two
reliability ratings.  CLASS T and CLASS H, not Reliability T and Reliability
H.  There are far to many factors related to reliability to make it a two
class system.  In reality, almost all solder mask is class 3.  The only
difference being the requirements to which the solder masks are tested.
 Class T has different levels than Class H.

Here is how the C revision of SM-840 came about.  It is not much different
from other specifications.  Starting with the B revision, you have a
committee comprised of most of the technical specialist from 6-8 solder mask
vendors.  Notice I say technical specialist, not the marketing turkeys
(apologies to all such turkeys listening).  These are the people who get
called by the customer when there is a problem with their mask.  Just as I,
in my job, get to see every conceivable way to mess up electronics
manufacturing, they see all kinds of uses and misuses of solder mask.
 Several of those individuals contribute to Technet.  Larry Fisher comes to
mind.

We debated the issue of Class 1,2,3 vs Class T and H for a LONG time.  You
would not believe the amount of flame that came our way for breaking with
hallowed IPC tradition.  We did it because for this material, class 1,2,3,
did not make sense.  In reality, you have three levels of mask, but Class 1
mask is so cheap that no solder mask manufacturer (usually Pacific Rim in
most cases) will spend money to qualify to SM-840.  All of the reputable
solder mask vendors make high quality mask.  They do not add "reliability
additive XYZ" for Class H, nor do they remove "critical element ABC" to make
it Class T.  In most cases, it is the same mask.  The class T and Class H
made it more specific for military and Telecom buyers.

When we discuss the various levels to input into a specification, yes, in
some cases it is technical opinion, but backed by experience, and in many
cases data.  Reliability should be a prime consideration, but not the only
consideration.  With 6-8 different companies present, and a sprinkling of
users, no one will allow the slanting of a spec towards a competitive
advantage to another.  Having worked with these individuals for 10 years, I
also find them individuals of honor, with a desire to see a good levels put
into the spec.

As to your suggestion that we footnote all technical opinions as such, I
don't recommend it.  In many cases, the opinions of the focused task group
can be backed with data.  It just is not published and has not been drawn
together in a specific technical presentation.  I have lots of SIR data that
I have not published (and may not), but that knowledge underlies my technical
opinions.  Dave Hillman is a good example.  He has a very broad knowledge of
metallurgical information and the relation to manufacturing processes.  When
he talks, I listen closely.  I don't need to see his data because his
experience is based on data.  This is true for many of the technical experts
on IPC task groups.

Just as with other IPC specs, once the specification revision has been
drafted, it goes through several rounds of circulation to a broader and
broader base.  If there is something you see that you don't agree with, by
all means, suggest an alternative.  If you have data to support your claim,
excellent.  We'd love to see it.  As an old IPC addage goes "In God we trust,
all others bring data".  All task group chairman welcome new blood and more
helpers.

Should we include all of the underlying data as an Appendix?  Have you any
idea how many forests we would kill printing that data?  There are many
issues in any specification.  Consider J-STD-001B.  Would you want us
publishing data on:  materials selection, materials compatibility, solder
joint embrittlement, solder joint formation, solderability, cleaning, residue
measurement, process qualification.  The list is endless.  The J-STD-001
Handbook committee is working on a handbook for J-001B, and it is over 200
pages, just talking about the issues.  It would be over 1000 pages if we
included all of the failure rate data you suggest.  Perhaps when we publish
everything on CD-ROMs.

As to your suggestion about relating reliability to the end use environment,
I say no.  I like the present definition of class 1, if it goes out it's a
minor annoyance.  Class 2, it's a hassle, but no one dies.  Class 3, if it
goes out, people die.  The consideration of end-use environment should be in
the design and ruggedization of the assemblies - do I conformally coat, do I
build a hermetic box, do I use redundant circuits, etc.  I might call a
portable computer an office item, except when taking it from a -40C car in
northern Wisconsin into a heated office.  Can you say condensation?  For your
proposed class structure, I could find numerous exceptions.  The present
system deals with the consequences of failure, and that should be the primary
consideration.

Secondly, you talk about risk of failure.  The issue is so complex, and so
difficult to do, that I would challenge anyone to put it into a
specification.  Keep in mind that you cannot write to a college PhD level,
you have to write for the average reader, a high school education level at
best.  I've tried, and I'm a good technical writer, and I can't do it.  If
you can, more power to you.

I'm sorry if this response sounds a little acidic, but the idea that the IPC
specifications and standards, put together with 1000s of hours of volunteer
effort, is nothing more than a collection of unsubstantiated technical
opinions, with no concern for reliability considerations, really honks me
off.  Plus its raining here, ice later, and I'm in Indiana.  Sue me.

I invite you, or others who feel as Mr. Davy does, to participate in the
specification task group activities.  If you have ideas on how to improve the
process and make for a sounder specification, the IPC will roll out the red
carpet and I'll personally strew it with rose petals.

Doug Pauls
CSL.

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