I agree with Istvan. There are fab houses that can laser drill through the
outer two dielectric layers without requiring build-up layers. I would shop
for a fab house that can do this. As Istvan noted, it will depend on your
dielectric thickness, I assume you're using standard thicknesses (3-4 mil) for
the significant layers. Else, you'll be forced to use build-up technology.
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Curt McNamara
Sent: Saturday, June 10, 2017 5:38 PM
To: leeritchey <leeritchey@xxxxxxxxxxxxx>; silistguy@xxxxxxxxx;
si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Blind Vias & Plating Question
Lee and i are agreeing :-) that the board will most likely be drilled (and vias
plated) as a 3 layer structure. The plating process (required to fill the L1-3
vias) will increase copper thickness on L3.
Curt
________________________________
From: leeritchey <leeritchey@xxxxxxxxxxxxx>
Sent: Saturday, June 10, 2017 4:39:01 PM
To: Curt McNamara; silistguy@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: Blind Vias & Plating Question
Actually, a 6 lever boated will be built with L2 and L3 on a piece of laminate,
L4 and L5 on a,piece of laminate and the two outer layers as pieces of foil.
Sent via the Samsung Galaxy S(r) 6, an AT&T 4G LTE smartphone
-------- Original message --------
From: Curt McNamara <CurtM@xxxxxxxxxxx>
Date: 06/10/2017 9:04 AM (GMT-08:00)
To: silistguy@xxxxxxxxx, si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Blind Vias & Plating Question
Lots of great answers!
Here is my simple version:
PCB material (sometimes called clad) comes with copper on one or two sides.
Board houses often build from the center out.
So 3-4 (your inner layer pair) would (normally) be built by itself (as would
1-2 and 5-6).
Building a layer pair consists of:
-- imaging the circuits onto the bare copper
-- etching the unwanted copper away
-- drilling holes where vias go through the layer pair
-- plating the layer pair if there are via holes that don't pass through the
whole PCB. Plating is required to get copper in the via barrel.
In your case, they might have wanted to build 1-2, 3-4, and 5-6 separately.
Then laminate together, and plate through vias. However, then they would be
trying to build up via wall material with one side plugged (for your 1-3 and
4-6 vias). This probably can't be done with normal via aspect ratio.
Since you have vias from 1-3 and 4-6, this board will be made a different way.
How? As others have suggested, you have to ask them. It might be that they
built 1-2-3 and 4-5-6 so they could plate your 1-3 and 4-6. Then they would
laminate 1-2-3 to 4-5-6 and do final plating for through-board vias.
How do they build 1-2-3? With 1-2 or 2-3 as double sided clad, and then a
second operation to add the other layer as single sided clad. Followed by
drilling for the 1-3 vias, and finally plating to fill those via walls/barrels.
That may not be the explanation, however it could fit your description.
Curt
http://www.4pcb.com/media/presentation-how-to-build-pcb.pdf
Curt McNamara, P.E.
Engineering Consultant
612.305.0440 x248
www.npe-inc.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of SI Guy
Sent: Friday, June 9, 2017 3:59 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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