Michael,
I have found that getting a straight, definitive answer to questions like
yours is almost impossible. I went through the same exercise trying to get
the definition of a micro via. After doing extensive research and talking
to a lot of PCB fabricators, I came up with the following:
1. Any via with a hole < .008"
2. Any via with a hole < .006"
3. Any via with a hole too small to be mechanically drilled, usually blind.
Since it appears to be a moving target, I settled on number 3.
The closest answer to your question that I've seen was found on the Resource
Center section of the Merix Web site, http://www.merix.com. Specifically,
at http://www.merix.com/resourcecntr/papers/highasp.pdf, a high aspect ratio
is defined as:
* Typical HAR criteria 7:1
o Example: 125 mil thick board w/ 18 mil drill
* Aspect Ratio does not tell the whole story!
o Example: 56 mil board w/ 8 mil drill
o HAR definition expanded to include:
* All small holes 13.5 mil or less
* All boards over 93 mil
Best regards,
Ray Humphrey
Senior PCB Designer
Maxim Integrated Products
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Michael Simms
Sent: Tuesday, April 03, 2001 6:34 AM
To: [log in to unmask]
Subject: [TN] Low Aspect Via definition
Hello T'Netters,
I've not received a single reply from the last posting
of this question, so I'd like to repeat:
What document defines a low aspect via?
Is there a numerical cut-off between a low aspect via
and other vias? Certainly, in the 6012A document, acceptable
minimum average copper thickness and absolute minimum
copper thickness are defined for typical vias and
low aspect vias. Is 3:1 a low aspect via? How about 4:1?
Or 5:1?
Any help out there?
Mike Simms
Trace Laboratories - Central
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