One of my standard pieces of education when I train junior engineers is a
field trip to a PCB fab. They learn that multilayer boards are made from
stacked 2 layer boards with prepreg insulation inserted between boards. You
basically get two choices on vias, those that are made in a sub-board before
stacking and connect between just those two layers, and those that are
drilled after stacking and pass all the way through to connect any layers
you choose. Back drilling (expensive) can be used to remove excess copper
barrel length. Different board houses have different work flows, so visiting
the one you intend to use and asking lots of questions is highly
recommended. A good vendor will also have good phone support. So, you can
ask here but you really need to go talk to your vendor.
Orin
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of SI Guy
Sent: Friday, June 09, 2017 1:59 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Blind Vias & Plating Question
Hi Experts,
I did my first design with blind vias. It's already starting to kick my ass
AFTER I've already designed it. I realize the importance of contacting board
shop before design, too bad boss doesn't allow the engineer to control that.
My question is then, experts, if blind vias are used say 1-3 and 4-6 on a 6
layer foil lamination board, do those inner layers also have to have plating
in addition to the bare copper thickness? Always?
I used 1/2 oz cu on all layers and expected only outer layers to have some
extra thickness from plating. Now a shop is saying no no no, 3 and 4 will be
plated too. Now my inner layer transmission line equations are jacked up!
Not to mention the outer layers too.
Sad day. =(
Any experience would help. What in the world is the right way to approach
these situations. Books and seminars say one thing but then life kicks your
butt. So frustrating!!!
Thank you, experts.
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