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| Reply To: | TechNet E-Mail Forum. |
| Date: | Tue, 13 Jul 2004 13:17:45 -0400 |
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I see a .014 spacing (yield is actually ~.013" since resin is used to
fill some of the plane geometry) with a microstrip line thickness of
.0012" (0.5 oz + plate) will yield ~ a 50 OHM value with a .022" line.
7628 is glass rich and has a slightly higher Dk, but in a build like
this the Dk variation only effect the impedance by a few %. Using 7328
is preferred in this build since the predicted yield is stable verses
using multiple plies of a resin rich build that produces a much higher
standard deviation in thickness. Designs requiring higher frequencies
with smaller lines - example in this case a .005" dielectric with a
.007" line yields the same impedance value, but will tend to have a
higher variation then the first build, although the resulting
characteristic impedance is more stable at higher frequencies due to the
resin content of the dielectric.
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
-----Original Message-----
From: Brooks,Bill [mailto:[log in to unmask]]
Sent: Tuesday, July 13, 2004 12:46 PM
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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