I think the quote you are looking for is Paragraph 9.2.6 of  IPC-2221. 
 
 "9.2.6 Aspect Ratio The aspect ratio of  plated-through holes plays an important part in the ability of the manufacturer to provide sufficient plating within the plated through hole."
 
What the aspect ratio is however is not included in the statement. The calculation I prefer to use is maximum board thickness to minimum drilled hole size, i.e. an 62mil overall PCB has a maximum thickness of 69mil,  so that a 20mil nominal finished hole could be drilled at 20mil and have a ratio of ~2:7. 
 
-----Original Message-----
From: Victor Hernandez [mailto:[log in to unmask]]
Sent: Wednesday, April 23, 2003 5:19 PM
To: [log in to unmask]
Subject: Re: [TN] Aspect Ratio&Area Ratio Defines

Thomas,
 
    During the design of a PCB the total thickness will guide you as to what is the smallest size drill you can use to ensure that adequate plating is placed on the barrel of a PTH.   This is the DOCUMENT that I have been searching for.ie ASPECT RATIO.   If this guideline is violated there is a potential for LOW plating in the barrel.   I recall the document.   However I need to make a QUOTE to it.   Therefore, I need to review the page and verse once again.
 
victor,
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