Hi Vijay!
I think we have a difference of opinion! I did not mean to imply that
we should "disregard" specifications - only that specifications are
not and should not be viewed as cast in stone, never to change, always
perfectly correct documents. Specifications provide a level playing
field, a format allowing comparisons between different manufacturing
practices which produce a similar product. Specifications provide a
starting point for a producer and a customer to reach a common ground.
You stated "Shouldn't specifications provide the necessary information
for companies to meet the level of quality and reliability demanded
of their products?" - how do you legislate a product's quality without
knowing what its use environment will be? It is not possible to be that
specific without condemning a perfectly viable manufacturing practice that
a customer may be perfectly happy with.
We do agree on one point "role of standards is to set precise criteria
based on a thorough analysis of the associated parameters and to reduce the
misinterpretation that arises out of differences of opinion" - but very few
standards ever reach a point where they never change. Technology changes,
processes change, materials change - specifications must change. In fact the IPC
itself views the IPC specifications as "living documents". The ANSI/ASME
Y14.5.1M you mentioned is a great example - it is a specification on dimensions
which allows better communication between different designers - it doesn't
dictate what the design should look like or how the process should be set up but
instead designates a common format for agreement to be reached. Blind
implementation of a specification has been tried - do you recall MIL-STD-2000?
The use of this specification allowed for the manufacture of very good
electronics equipment. However the blind implementation of this document caused
avoidable cost and cycle time which the electronics industry and DOD recognized
as an action that could be improved.
If suggesting that documentation showing a specific process can provide a
reliable product for a specific use environment despite being contrary to a
specification is to belittle the specification, well I guess I'm going to
belittle the specification. I think that the JSTD family of specifications
allows the customer and producer to find such common ground where it makes
sense. As for wanting and promoting the improvement of specifications - heck,
just come see the IPC Solderability task groups work on JSTD 002/003 (or any of
the specification groups for that matter) and you will see a whole bunch of
people giving of their time and talent to improve specifications.
Dave Hillman
IPC Solderability Task Group chair
[log in to unmask]
______________________________ Reply Separator _________________________________
Subject: Re: melf's, J-STD-001, IPC-610
Author: [log in to unmask] at ccmgw1
Date: 1/19/97 8:51 PM
Hi Dave:
Let me ask YOU these questions: When you say that specifications should
not be set in concrete, is that because the specifications are
themselves
circumspect? Shouldn't specifications provide the necessary information
for companies to meet the level of quality and reliability demanded
of their products? If not, why call them specifications, and why involve
reputable organizations such as IPC and ANSI to mandate them?
I think that the role of standards is to set precise criteria based on
a thorough analysis of the associated parameters and to reduce the
misinterpretation that arises out of differences of opinion. No company
should find it necessary to conduct experiments to prove that its
assembly will perform reliably in its designed environment.
This should be provided by an industry specification such as
J-STD-001 or IPC-610. (of course, not every company is capable of
such research and a new service industry could be spawned off as a
result!!!)
Inspection and rework are costly and should be based on a commonly
accepted norm that is flexible to the extent that it tells you the
related variables that influence or are impacted by the one being
verified. It may take many years to understand the true impact of
the variables and settle upon a range of limits that make better sense.
But once established, they should serve as a self-contained reference
for BLIND implementation so that the INDUSTRY as a whole will
benefit from it. The ANSI/ASME Y14.5.1M for dimensions and tolerances
is a classic example of such a well supported standard.
So instead of belittling the current standard by asking
people to disregard the wording (in which I think you played an
important
role), I strongly urge you to stimulate a discussion of how to make the
specifications more meaningful. This TechNet forum is possibly the best
place to communicate our thoughts freely. Moreover, there seem to be
more people on Technet who are knowledgable about the
process-shape-property
relationship than at any meeting. We can provide the continuous
improvement that is a natural characteristic of the technologies in
electronics manufacturing.
Regards,
Vijay Sankaran
Research Associate
Center for Integrated Electronics and Electronics Manufacturing
Rensselaer Polytechnic Institute
Troy, NY 12180
Ph: (518) 276-2721
Fax:(518) 276-2990
ddhillma wrote:
>
> Hi Phil -
>
> Let me ask this question: When you do put adhesive on a MELF for wave
> soldering purposes, do you have an failures? I would put forth that if
> you have sufficient documentation showing that your procedure results
> in no reduction of reliability for the use environment the assembly is
> going in then ignore the "specification". Specifications are not
> (well, should not be anyway) set in concrete - JSTD 001 is an example
> of a specification that allows for processes to be fit to their use
> environments. I wouldn't get wrapped up in the specifications words if
> you can show proof that a process/assembly method is reliable.
> Hopefully your customer will look at the situation the same way. Good
> luck.
>
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
> ______________________________ Reply Separator
_________________________________
> Subject: melf's
> Author: [log in to unmask] at ccmgw1
> Date: 1/16/97 9:23 AM
>
> Technetters
>
> I have a customer who asks?
>
> How can you apply adhesive to MELF's that will be wave soldered,
> when section 2.4.2 of IPC-610 states that "Adhesive contacts an
> unsleeved glass body component." is a nonconforming defect.
>
> I say that there is a difference.
> Adhesives used to bond a component in section 2 is for mechanical
> holddown and the component could crack if it were applied to the
> glass body.
>
> Adhesive used for staking in section 10 has very little strength and
> used only to hold the part until it is soldered.
>
> anyway thats my story and I'm sticking to it.
>
>
> Phil Belliveau
> Sippican, inc.
> 7 Barnabas Rd
> Marion, MA 02738
> TEL: 508-748-1160 x379
> FAX: 508-748-3086
> EMAIL: [log in to unmask]
> HOME PAGE : HTTP//WWW.SIPPICAN.COM
>
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