Bruce,
First of all, as Franklin has accurately stated - you need to have an internal land with sufficient annular ring in every case where you have an internal trace connecting the via.
The question is what to do when there is no trace and the pad is non-functional (therefore these lands are called Non-Functional-Lands).
Please let me confuse you a little bit, since in this case opinions differ between manufacturers that prefer to remove these Non functional lands and those who prefer to leave them in.

One on the main reasons to take the lands out is their effect of the drilling quality and from this - the hole wall plating quality. The PCB is made up of several materials that differ very much in their mechanical (and thermal) properties  - resin (each resin system with its own typical properties), glass (or some other reinforcement system) and copper. One of the actions that shortens the life of the drill is the frequent change when it goes through - resin - copper - glass - resin .....
If you take the copper out where you can, the drill will go through some more homogenious material and it will live longer (and leave a better hole wall topography).
On the other hand - copper does serve in some plating systems as an "anchor" for the electroplate and these are cases when manufacturers prefer to leave them in.

In addition, if my memory serves me right, there is a difference in the effect of these innerlayer lands between smaller and larger holes. I suppose that everyone draws the line in  a different place between small and large but I think that it goes through about 20-30 mills, above which I would call the drills "larger". I understand that you hole is for component placement which means that I would call it "large", is it?
This difference deals with the mechanical stresses existing in the hole during thermall excursions (that infamous Z-expansion). In the larger holes people tend to leave the non-functional lands in for the purpose of better stress distribution on the internal post-interconnect (= land to PTH). 
In the smaller holes they tend to take them out in order to leave a uniform hole wall as possible and create a uniform hole barrel. Since in the smaller holes, the dominant failure mechanism is usually a hole barrel fatigue type - every non-uniformity in the barrel might serve as the weakest spot where the failure will start.

Well, that's about my two cents and I hope it does make some sense.

Have a great week,
Yehuda


Yehuda Weisz
Tel: (972)-3-6342045
Cel: (972)-53-556897
----- Original Message ----- 
From: "Bruce D Stilmack" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, February 09, 2004 2:22 PM
Subject: [TN] Annular rings for plated through holes


> My question is for the PCB manufacturers out there.  It was my
> understanding that on a plated through-hole (part location not via) all
> layers of a PCB should have an annular ring.  Am I mistaken?  Are only
> certain layers required and what guides the manufacturer in this area?
> 
> Bruce Stilmack
> GDLS-TO Manufacturing Engineer
> (850) 574-4773
> [log in to unmask]
> 
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