Phil,
Yes, we have kept the customer in the loop regarding the product in
question. The outcome should be favorable to both. I spoke with Frank
Kimmey and we agree that in the absence of a specified value, it may be in
the best interest of the fabricator to ask the question. A loose
interpretation could also be made if a specific impedance requirement is
invoked at the drawing level. If it is necessary to use one ply to achieve
the desired value, you are arguably compliant.
We've historically defaulted to a design rule of 2 ply's minimum (one 1080
& one 106), and will continue to use this standard. Although there may be
cases where there are exceptions to this due to overall thickness and/or
impedance requirements.
Thank you for your input.
Brian Guidi.
Phil Nutting
<PNutting@KAISERS
YSTEMS.COM> To
Sent by: TechNet [log in to unmask]
<[log in to unmask]> cc
Subject
04/20/2006 11:13 Re: [TN] Dielectric Thickness
AM Requirements
Please respond to
TechNet E-Mail
Forum
<[log in to unmask]>
; Please respond
to
Phil Nutting
<PNutting@KAISERS
YSTEMS.COM>
Brian,
Clearly you have done your due diligence... And then some.
Have you called the customer for the requirement? If they state a
standard and don't do their homework, like the procuring document, then
shame on them.
Just my opinion.
Phil
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Guidi
Sent: Thursday, April 20, 2006 10:59 AM
To: [log in to unmask]
Subject: [TN] Dielectric Thickness Requirements
I'm looking for some guidance with regards to dielectric thickness
requirements. We are currently fabricating boards for a customer in
which
IPC-6013 is invoked on the drawing. Within IPC-6013A you will find the
following:
"3.7.15 Dielectric Thickness: The minimum dielectric spacing shall be
specified on the procurement documentation."
Well, that's pretty clear. However, it is not on the procurement
documentation, and it very rarely is. Since IPC-600 is invoked within
IPC-6013 as a sub-tier acceptability document, I figured I'd head down
that
road. IPC-600G specifies the following:
"3.1.8 Acceptable - Class 1, 2, 3: The minimum dielectric thickness
meets
the minimum requirements of the procurement documentation. If not
specified, must be 0.09 mm [0.0035 in] or greater."
Okay, so as a result of this statement one may interpret this as the
controlling requirement (0.0035" in this particular case). Unless of
course
you head back to IPC-6013 which states the following in section 2:
"2 Applicable Documents: The following specifications form a part of
this
specification to the extent specified herein. If a conflict of
requirements
exists between IPC-6013 and the listed applicable documents, IPC-6013
shall
take precedence.
So at this point, I'm right back to where I started. There is no defined
dielectric thickness specified on the procurement documentation.
Additionally, the cross sectional view on the drawing does not define
the
number of ply's between layers. This is obviously desirable for the
manufacturer to ensure they/we have the freedom to develop the
construction
based on a balance between the customers needs and the manufacturing
"sweet
spot". However from a compliance stand point, I'm in a quandary. If I
had a
multilayer construction with a single ply of 1080 prepreg between two
1/2
ounce layers (one signal, one ground), would the resulting board comply
to
the spec? In looking for further clarification, I deferred to IPC-6012B,
IPC-2222 and IPC-2221A and found the following:
IPC-6012B = .0035" minimum
IPC-2222 = .0035" minimum
IPC-2221A = Shall be specified on procurement documentation
I hope the use of direct quotes is acceptable here. It's the only way
for
me to really characterize my problem. Has anyone out there come across
this
issue? I've searched the archives, and similar issues have not been
discussed (as far as I can see) since 96'/97'.
Brian Guidi
R&D/Quality Systems Specialist
Teledyne Printed Circuit Technology
Tel: (603) 889-6191 X:310
Fax: (603) 886-2977
E-mail: [log in to unmask]
Visit us @ http://www.tetpct.com
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