One other advantage to single ply construction other than lowering cost is 
flatness enhancement.  We have actually seen lower warp and twist with 
single-ply construction.  As long as your board fabricator is using quality 
material and vacuum assist lamination, single ply construction should not be a 
problem.
Tom Coyle
Field Services Engineer
HADCO Corporation
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.=20
     
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.=20
     
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.=20
=20
I hope this helps.
     
Ed Cosper
Graphic Electronics Inc.
Tulsa OK=20
     
----------
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=20
layers. In our standards it is specified a minimum of two prepregs to = 
secure good=20
reliability. However, in order to reduce cost we would like to use only = 
one. What kind=20
of drawbacks can I expect? Is there a minimum prepreg thickness or epoxi = 
content that=20
can be used?
     
Every comment is highly appriciated
     
Thanks in advance,=20
     
                  //Markus=20
     
     
     
Markus Gauffin  M.Sc.
Printed Board Assembly Technology
Ericsson Telecom AB
e-post: [log in to unmask]
     
*************************************************************************= 
**
* TechNet mail list is provided as a service by IPC using SmartList = 
v3.05 *
*************************************************************************= 
**
* To subscribe/unsubscribe send a message <to: [log in to unmask]>  =
 *
* with <subject: subscribe/unsubscribe> and no text in the body.         =
 *
*************************************************************************= 
**
* If you are having a problem with the IPC TechNet forum please contact  =
 *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]     =
 *
*************************************************************************= 
**
     
     
*************************************************************************** 
* TechNet mail list is provided as a service by IPC using SmartList v3.05 * 
*************************************************************************** 
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   * 
* with <subject: subscribe/unsubscribe> and no text in the body.          * 
*************************************************************************** 
* If you are having a problem with the IPC TechNet forum please contact   * 
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      * 
***************************************************************************
     

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************