NICK-The aspect ratio that is being discussed is for the plating of said
holes, therefore, your vendor should be talking about an aspect ratio of
drilled hole to board thickness over base laminate, not the nominal
finished plated hole. But, my vendors are taking this aspect ratio from the
nominal finished plated hole (which does help us designers). We don't
really have a issue with this, being that a 6:1 aspect ratio on a .062"
board would allow a .010" finished hole (my smallest hole is a .012 via).
You had also stated that "the drilled hole size is up to the
fabricator", this is not completely true, your internal pad stacks are to
be figured, for your annular ring, to the drilled hole not to the plated
hole. So you, or your librarian should know what tool your fabricator is
using to achieve not only the required finished hole but equally important,
your required annular ring. This may be bad news if you are now
figuring your internal annular ring to the finished hole! Remember that the
external annular ring is only figured from the plated hole.
Question... My fabrication drawings state: "FABRICATE AND TEST PER
IPC-RB-276 AND..." this spec is obsolete and replaced by IPC-6011 and
IPC-6012 AS OF 7/96. Has anyone switched over?
Dan Lorinser
BFGoodrich Aerospace
Burnsville, MN.
[log in to unmask]
>>> Wander, Nicholas G RV <[log in to unmask]> Jan 2,
1997 4:49 pm >>>
This may sound like splitting hairs, but I think there is some confusion
(maybe only on my part) about whether the finished or the drilled hole
size should be used. In the example below, if the .020 diameter is the
nominal finished hole size and the hole is drilled .025 diameter, the
aspect ratio based on the drilled hole would be 2.4 to 1. IPC-T-50E
defines aspect ratio as "The ratio of the length or depth of a hole to its
preplated diameter". I assume this means that the drilled hole size, not
the finished hole size, should be used.
>From the designers' viewpoint, using the finished hole size would be
more convenient, since this is what is usually specified. The drilled hole
size is up to the fabricator.
Nick Wander
Printed Circuit Engineering
Unisys Corporation
Roseville, MN [log in to unmask]
----------
From: David Bergman[SMTP:[log in to unmask]]
Sent: Tuesday, December 31, 1996 10:05 PM
To: Isaac Stringer
Cc: [log in to unmask]
Subject: Re: Aspect Ratios
Sure,
Aspect ratio is the thickness dimension of the PWB divided by the
diameter dimension of the plated thru hole. So an 0.060 inch thick pwb
with a 0.020 inch diameter pth would have an hole aspect ratio of 3 to 1.
Regards
__________________________________________________
David W. Bergman, V.P. of Technical Programs
IPC
2215 Sanders Road
Northbrook, IL 60062-6135
847-509-9700 x340 Phone
847-509-9798 Fax email [log in to unmask] www
http://www.ipc.org faxback support 800-646-0089
---------------------------------------------------
On Tue, 31 Dec 1996, Isaac Stringer wrote:
> Greetings:
>
> Would someone be so kind as to explain 'aspect ratios' in a way
> that will make sense to someone who understands hole sizes and
> trace width/space?
>
> Thank you!
>
> Isaac Stringer
> KML Engineering Corp.
> [log in to unmask]
>
>
>
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