dang...

That was a MUCH better answer than I gave!

I'm changing my answer to: "What he said."

Jack


On 6/20/07, Ted Tontis <[log in to unmask]> wrote:
>
> 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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