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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