You also need to consider the impact of non-functional pads on hole
quality on layer counts above 14, particularly if the board is destined
for a high-rel application as the increased Cu content impacts on drill
quality (in my experience at least). A high layer count board with a
full complement of non-functional pads will likely have a poorer hole
and therefore fatigue life of the barrel may be adversely affected. You
might therefore want to consider selective removal of pads on high-rel
boards so that you get adequate barrel support and acceptable hole
quality
Regards
Ian Fox
Goodrich ECS
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Ted
Tontis
Sent: 20 June 2007 22:51
To: [log in to unmask]
Subject: Re: [DC] Are multi layer boards with external planes patented
now?
I think the real question should be when is it cost effective to leave
non-functional lands in?
A six layer board with a low aspect ratio will have very little benefit
from having them left on the board. Where as a board with a high aspect
ratio will benefit from it tremendously. Also if a design is a
commercial product and high reliability is not necessary then why risk
the increased cost or production time?
So it depends,
What is the aspect ratio of the board? The way to calculate it is to
take the maximum thickness of the PCB and divided it by the smallest
drill hole. The maximum thickness is the is the stack-up plus the
thickness of the copper prior to plating. Do not use soldermask or
platting finish in your calculation. The ratio you come up with can be
used to compare with what your board supplier says they can handle.
What is the end use product? Is it a keypad for a microwave oven or
is it the controls to a fighter jet? If it is a product that is mass
produced and used in a commercial environment then you shouldn't need
them. If the end product is going to go into a life saving device or
something critical then it may be a good idea to leave them in.
Especially if your aspect ratio is close to what your board supplier
says is their comfort zone.
Ted T.
----- Original Message -----
From: "Jack Olson" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, June 20, 2007 3:40 PM
Subject: Re: [DC] Are multi layer boards with external planes patented
now?
> *I don't think IPC formally addresses this in their guidelines,*
> *but here's the scoop in a nutshell:*
> **
> *Your fabricator wants to remove them because it saves*
> *drill bit wear by not having to drill through so many*
> *non-functional pads.*
> **
> *IPC says (informally?) along with many reliability experts*
> *to leave them in, forming a more robust "rivet-like" structure,*
> *less barrel cracking, etc.*
> **
> *I leave them in.*
> **
> *hope that helps,*
> *Jack*
>
>
> On 6/20/07, Matthew Lamkin <[log in to unmask]> wrote:
> >
> > Apologies if this has already been posted, I just came across it
trying
to
> > find
> > some info on removing via pads on internal layers (can anyone point
to
any
> > articles for why/why not to do this?)
> >
> > The first hit on a Google search for "suppressing vias internal
layers
> > pcb" was this:
> >
> > http://www.patentstorm.us/patents/7016198.html
> >
> > eh?
> >
> > Matthew
> >
> >
> >
>
>
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