It seems so simple:
==Customer wants constant impedance lines -- he better specify layer
thickness or identifies the runs that are involved and let the manufacturer
determine (and verify) the thickness/impedance.
==Customer puts high voltage between runs on different sides of a layer --
he better specify thickness required. (Customer is supposed to have designed
for known voltage, frequency, amperage, operating environment, safety
factor.)
==Customer refers to spec document -- now you have a minimum thickness and
nothing else.
Have fun,
Ahne.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey (AZ75)
Sent: Thursday, 20 April, 2006 11:01
To: [log in to unmask]
Subject: Re: [TN] Dielectric Thickness Requirements
Thanks Valerie. I understand the frustration. I will be glad to help in this
area so we might start to clear up some of these inconsistencies.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Valerie St.Cyr
Sent: Thursday, April 20, 2006 10:52 AM
To: [log in to unmask]
Subject: Re: [TN] Dielectric Thickness Requirements
Brian,
I have also walked through these specs and their inconsistencies; it is
actually even worse.
Since it's minimum, you need to start with something thicker or you will
likely not comply.
Also, the terms minimum and nominal are crossed in the different specs, and
the method to ascertain compliance is troublesome. Add to that, it applies
to either cores or prepregs.
Dewey,
I did write up a recommendation for reconciliation of the various specs but
nothing came of it. I'm going to give it another shot.
Off line I will send you what I wrote.
Valerie
"Whittaker, Dewey (AZ75)" <[log in to unmask]> Sent by:
TechNet <[log in to unmask]>
04/20/2006 11:26 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to "Whittaker, Dewey
(AZ75)" <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] Dielectric Thickness Requirements
I'll refrain from sarcasm and humor and say welcome to the club. For the
last two years I have been trying to rewrite IPC-4101, IPC-6012, IPC-6011,
IPC-A-600, and IPC-2221 for the same reasons. There are too many undefined
sets of criteria. It is not until you read them for the ninth time and try
to follow a process and requirements definition protocol to completion that
you realize all the dichotomies that exist.
The same probably exists for IPC-6013 and IPC-2222. You have correctly
concluded, that unless otherwise specified the minimum dielectric spacing
shall be .09 mm(.0035).
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Guidi
Sent: Thursday, April 20, 2006 7:59 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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