A more technical explanation about laser based AOI can be found at:
http://www.orbotech.com/tech_lib_pcb_aoi.asp
For reflective light systems:
http://www.circuitree.com/CDA/ArticleInformation/features/BNP__Features_
_Item/0,2133,125413,00.html

Tuan
-----Original Message-----
From: Pete menuez [mailto:[log in to unmask]] 
Sent: Thursday, March 31, 2005 6:57 AM
To: [log in to unmask]
Subject: Re: [TN] What does AOI (Automated Optical Inspection) equipment
do?

There are (I think) three different technologies to AOI -
Reflective Pixel to pixel
Laser design rule
Reflective Pixel to pixel/design rule combination.

I've only had experiance with reflective pixel to pixel so my comments
are
directed to this technology...

To begin with you create a program that represents the image you are
inspecting.  The program will tell the AOI where to inspect and what
tolerance to apply to each aperature.  With pixel to pixel the image
being
inspected will be digitized and compared to this programed image.

On the actual AOI unit  a light is directed at the image to be
inspected.
The light is reflected back into a camera where the image is captured
and
digitized.  Each pixel of this digitized data will be compared to the
programmed data.

There are algorithms in the AOI that analyze the raw input to
differentiate
between real defects and false defects.  For example, a water spot on
copper
will not reflect back to the camera as well as clean copper.  The
algorithm
will evaluate the raw data and make a determination - is this a real
defect
or a false defect. If it determines that its real it is reported; if its
false it is ignored.

In a nutshell this is how one type of AOI works.  Hope it helps.

pete




>From: Suganthi <[log in to unmask]>
>Reply-To: Suganthi <[log in to unmask]>
>To: [log in to unmask]
>Subject: [TN] What does AOI (Automated Optical Inspection) equipment
do?
>Date: Thu, 31 Mar 2005 16:29:08 +0530
>
>Hi all,
>
>         How does AOI (Automated Optical Inspection) equipment will
work?
>.I
>would like to know more info on this ..
>
>Thanks and Regards
>
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>Sug

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