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April 2006

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Subject:
From:
Brian Guidi <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Thu, 20 Apr 2006 10:58:39 -0400
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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]



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