7628 aginst 2 oz copper is not recommended. Possible lamination issues are
likely, i.e. lam voids.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Brooks,Bill
Sent: Tuesday, July 13, 2004 9:46 AM
To: [log in to unmask]
Subject: Re: [TN] 7628 prepreg?


So in a stackup that requires a .031 core with 2 oz. Cu both sides and a
symmetrical build up of 2 layers of 7628 on both sides (4 total) and then
1.5 oz Cu finished outside... Would the objective then be to control the
spacing from the outer conductors to the inner ground plane at .014 in.?

Is the DK of 7628 different than other glass epoxy materials? I would like
to calculate the impedance of the traces on this board.

Is there a materials sheet available on-line that describes the electrical
and physical characteristics of the prepreg material? And does it change
when laminated?

This is an older board and I'm just trying to decipher the designer's
intent.

Thanks in advance...

Bill Brooks
PCB Design Engineer , C.I.D., C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
http://pcbwizards.com

-----Original Message-----
From: Jeffrey Bush [mailto:[log in to unmask]]
Sent: Tuesday, July 13, 2004 4:10 AM
To: [log in to unmask]
Subject: Re: [TN] 7628 prepreg?

7628 glass has different yield thickness based on resin content and the
rheology.  You can purchase 7628 in epoxy from a yield per ply thickness
of .0065" to where you are with yours.  7629 glass can give you up to
.009" in yield as this is some what heavier glass.  I think the standard
has been a .007" per ply yield - this is fairly standard from laminate
suppliers.



Jeffrey Bush
Director, Quality Assurance and Technical Support

                          76 Technology Drive - POB 1890
                             Brattleboro, Vermont 05302-1890
                                Tel. 802.257.4571.21 Fax. 802.257.0011
                                    [log in to unmask]
                              http://www.vtcircuits.com

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