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On 4/25/08, James, Ron CAR <[log in to unmask]> wrote:

My vague, limited understanding of the reasons for and against removing non-functional pads:

For leaving the pads in --- might improve reliability of plated barrels. But no conclusive data to support this?

For removing the pads --- increased yield at the fab house because of the reduction in copper features that could get misaligned. Lower drill wear because of less copper to be drilled through.

In the past, I believe we have allowed the fab house to remove the pads. We do fairly low-tech boards, with only a handful getting up to 6 layer. Nothing high density. I am not aware of any plated-thru hole reliability issues cropping up in our applications.

However, as part of my Google search I ran across an article suggesting that the higher soldering temperatures of a lead-free process requires that the inner pads be left in to improve durability of the barrels. ("Non-functional lands: keep them vs. remove them", by Werner Engelmaier, June/July issue of Global SMT & Packaging, at www.globalsmt.net)

For those of you who have allowed the fab house to remove non-functional lands in the past, did you reconsider this for lead-free designs?

Ron

From: Jack Olson [mailto:[log in to unmask]]
Sent: Friday, April 25, 2008 11:35 AM
To: (Designers Council Forum); James, Ron CAR
Subject: Re: [DC] Non-functional lands

You won't find a spec that says non-functional lands shall not be removed.

The IPC's postion is that if you think it is okay for the fabricator to remove

them, they are not going to argue with you about it, but it has always been

their position that they should be retained.

but...

If you decide that they can be removed with no detrimental effects, you still

need to have them in the coupon so measurements can be made.

If you want to retain them for hole reliability, you have to say it in a note

(I think... Does anyone disagree with this?)

There's plenty more discussion about why they should be removed or retained,

but you didn't ask that, so I assume you know the issues and were just asking

about the IPC specification

onward thru the fog,

Jack

.

On 4/25/08, James, Ron CAR <[log in to unmask]> wrote:

Senile designer needs help. ;-)

It has been a while since I have dealt with the question of removing or not removing non-functional pads from inner layers. I can't seem to find any record of what I told our board fabricators in the past. So I tried looking it up in the IPC specs.

IPC-2222, 9.1.4 says that non-functional lands "should" be included on internal layers for all plated-through holes. It says "should" where many other paragraphs say "shall" in bold type; I assume that was done deliberately? Is this just a recommendation, and not a requirement?

IPC-2221 only seems to mention non-functional lands in paragraph 12.4.1 describing test coupons, where it says that the coupon shall represent the design except that non-functional lands shall be included on all layers. The wording of this section suggests that non-functional lands would normally be missing, but they want them present on the test coupons.

I can't find anything else, but I don't have a searchable PDF copy of the IPC specs, so there may be information that I am missing while flipping through my paper copy.

A web search using the mighty Google shows multiple board suppliers who list removal of non-functional inner layer pads as a standard step in their CAM processing of customer Gerber files.

I guess my question is: what IPC spec can I refer to to tell the fab house that they shall not remove unused inner layer pads? Or is it really OK?

Ron

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