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Machine Vision Technique for Increasing the Integrity of Chip Alignment Data

IP.com Disclosure Number: IPCOM000107736D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 115K

Publishing Venue

IBM

Related People

Newman, A: AUTHOR [+3]

Abstract

This article describes a technique which includes several image processing algorithms to verify that C-4 pad images to be used for chip alignment data are good quality images.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Machine Vision Technique for Increasing the Integrity of Chip Alignment Data

       This article describes a technique which includes several
image processing algorithms to verify that C-4 pad images to be used
for chip alignment data are good quality images.

      The first step in the process of bonding silicon chips to
ceramic substrates involves a precise alignment of C-4 pads to their
respective points of electrical contact.  One method of aligning the
C-4 pads and substrates involves the use of machine vision to provide
chip and substrate position feedback to the chip placement device.

      For alignment algorithms which rely on establishing the
location and orientation of a chip by locating a series of
pre-specified C-4 pads, the alignment system must be able to detect
and compensate for poor image quality, identify the exact location of
two or more specific C-4 pad sites and verify the quality of the
information provided by the image of each C-4 pad.  The algorithms
described herein provide a method of increasing the level of
confidence in the final alignment data by detecting these conditions
and modifying the image data or, at least, minimizing the effect of
these conditions and notifying the chip placement system controller.
Chip Placement Algorithm
      The exact location and orientation of a chip may be determined
by comparing the location of (at least) two C-4 pads on a chip in the
image place of a camera and the position of the same pads on the chip
as presented on the chip mechanical drawing.  Also, operating as a
data driven system, the system setup and calibration is simplified.
C-4 Pad Sample Size
      Increasing the sample size from two to three C-4 pad locations
provides three redundant sources of chip alignment data and allows
the system to eliminate one C-4 pad sample for poor image quality or
some other irregularity.
Integrity of C-4 Pad Images
      Before the final alignment data is calculated, the system tests
the image of each pad to determine the quality of the C-4 pad.  This
is accomplished by the following:
      o    Finding the vertical and horizontal edges of each C-4 pad
and comparing the ratio of the pad dimensions.  After compensating
for the pixel aspect ratio, the ratio of width to height should be
one.  If not, the pad may be smeared or may be in the vicinity of
dense circuitry which has distorted the pad image.
      o    Test the final pad profile to determine the number of
maxima and minima points between the outer edges of the pad site.
For an ideal pad image, there should be one maxima and two minim...