A recent visit to me by a large PCB fab house based in Hong Kong explained
that for a hi layer count such as yours with 1.6 final thickness needs
careful selection of pre-prig. Pre-Prig with a hi resin count will cause
inner layers to want to move sideways as the PCB is pressed & cured, similar
to a many layer sandwich with cheese instead of pre-prig. The resin is the
"liquid" portion of the pre prig. The solid part is the glass fibers.
The inner layers will go their own way from each other resulting in higher
inter-layer mis-registration. So with this in mind, the PCB designer must
know from the start how the end will be as he (she) can then give more
allowance on inner routing & copper features to allow for higher
mis-registration.
This made sense.....
Talk to a reputable fab house with lots of experience with your tech of PCB.
I am sure there are ways to minimize risk. They are the experts...
Regards
TDK
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Billy
Bharath
Sent: Wednesday, April 06, 2005 6:33 AM
To: [log in to unmask]
Subject: Re: [DC] PCB TECHNOLOGY (2 oz copper)
Hi,
Many years ago(+/- 6 years) we designed 14 layers into a 1.6 thick pcb using
1 ounce copper on the internal layers, sadly the manufacturing houses
experienced "copper spreading" on the internal layers. The explanation
provided was that squeezing 14 layers into 1.6mm pcb was causing the
internal layer copper to spread sideways. We were than advised to consider
0.5 ounce(17u) copper. We changed to 0.5 ounce and NEVER had a problem
since. Using that as an argument I would than assume using 2 ounce copper
could have made that pcb almost impossible to manufacture, than again it
also depends on the number of layers.
regards
Billy Bharath
-----Original Message-----
From: Sanchez-Benavides Erika
[mailto:[log in to unmask]]
Sent: Wednesday, April 06, 2005 2:12 PM
To: [log in to unmask]
Subject: [DC] PCB TECHNOLOGY (2 oz copper)
Hello all,
One of our PCB suppliers came out with a PCB design that have 2 ounces
of copper on all layers. Until now we have worked with PCB that have 2
ounces of copper only on the exterior layers, and only one ounce of
copper on the interior layers.
We do not have experience working with PCBs with 2 ounces of copper on
all the layers.
Would you mind helping us to gain more knowledge regarding these PCBs?
Are there any risks associated with this design: thermal events,
concerns, things that we should be aware of?
Thanks in advance,
..........................................................
Kind regards
Erika E. Sanchez
PCB Designer
Siemens VDO
Internet: http://www.siemensvdo.com
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