Marcus,

Most people use a minimum 2 ply construction. Some us this a minimum due to some misconceptions regarding UL requirements. Check your UL file and determine what the specified minimum dielectric thickness is for the pre-preg you intend to use. Unless a single ply would not meet the minimum thickness or a 2 ply minimum is stated in the file notes, I don't see a problem using a singe ply. 

The only restriction I can find regarding UL is in UL 796 specification section 12.8 under electrical insulation. It states that "the total buildup shall be equivalent to a base material layer with respect to its electrical relative thermal index."  If  a single ply meets that requirement, then it should be acceptable. 

I would not recommend a single ply for dielectrics below .004". This may create some electrical problems in the board. For this concern, I would check with designer of the part. 
 
I hope this helps.

Ed Cosper
Graphic Electronics Inc.
Tulsa OK 

----------
From:  [log in to unmask][SMTP:[log in to unmask]]
Sent:  Monday, April 28, 1997 6:52 PM
To:  [log in to unmask]
Subject:  one prepreg?

Hi everyone!

I have a question to you about the minimum numbers of prepregs between two conductive 
layers. In our standards it is specified a minimum of two prepregs to secure good 
reliability. However, in order to reduce cost we would like to use only one. What kind 
of drawbacks can I expect? Is there a minimum prepreg thickness or epoxi content that 
can be used?

Every comment is highly appriciated

Thanks in advance, 

                  //Markus 



Markus Gauffin  M.Sc.
Printed Board Assembly Technology
Ericsson Telecom AB
e-post: [log in to unmask]

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