Si guys
designing any HDI pcb without knowing fab rules will surely put you in huge
amount of rework. you must know their rules very clearly.
important things to know... laser drill diameter, applicable aspect ratio
of laser drill, via-pad size
lets say, if in your case laser drill dia is 4mil and aspect ration of
0.75, then you can't use dielectric thinness more than 3mil for blind via
layer. This is just an example. laser-via aspect ratio is normally 0.5 -
1.0. L1-L3 direct transition is stacked-via approach, which will be super
expensive. This must be avoided.
But, 1st of all you need to justify using HDI via in your PCB. is you BGA
pitch less than 0.65mm? mechanical through-hole via can be used upto
0.65mm pitch. some people even use it till 0.6mm pitch. anything less that
this will surely need HDI via.
you must get your stackup from FAB house before proceeding to HDI PCB
design.
Thanks
Sanjeev
On Mon, Jun 12, 2017 at 12:27 PM, Leif Jiao <
leif.jiao@xxxxxxxxxxxxxxxxxxxxxx> wrote:
I just encountered the same things weeks ago.
It depends on laminate thickness between L1-L3 and L4-L6.
Here is what I communicated with my vendor ant team by PPT files, hope it
will help you.
http://www.pdfescape.com/shared/?39A6C216A3D283E65E6842AB8B3F4A
EDA96E30B521164193
Regards,
----------------------------------
Leif Jiao
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of SI Guy
Sent: Saturday, June 10, 2017 4:59 AM
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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