Browse Prior Art Database

Machine Vision Alignment Method for Ultrasonic Wire Bonding

IP.com Disclosure Number: IPCOM000112935D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 176K

Publishing Venue

IBM

Related People

Jordan, SR: AUTHOR [+3]

Abstract

Described is a hardware implementation methodology for aligning small wire conductors to appropriate connection pads. The concept utilizes a machine vision algorithm implemented on a commercial machine vision system designed for ultrasonic wire bonding.

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This is the abbreviated version, containing approximately 30% of the total text.

Machine Vision Alignment Method for Ultrasonic Wire Bonding

      Described is a hardware implementation methodology for aligning
small wire conductors to appropriate connection pads.  The concept
utilizes a machine vision algorithm implemented on a commercial
machine vision system designed for ultrasonic wire bonding.

The key features of the pad/wire alignment algorithm are as follows:

o   Utilization of multiple image processing projections with edge
    enhancement, such as:
     1.  Fast image processing;
     2.  Ability to enhance and locate certain object features, such
        as lines and edges; and
     3.  Suppression of image variations and noise.

o   Automatic circuit board alignment.

o   Automatic recovery routines:
     1.  Variable window position and size;
     2.  Variable contrast thresholds; and
     3.  Red/white light.

o   Statistical determination of image processing parameters.

      Typically, ultrasonic wire bonding is a method used in wire
attachment implemented in the assembly of products, such as used in
Direct Access Storage Devices (DASD) read/write heads.  Automated
assembly equipment must be able to quickly and reliably find, align
and bond wires to circuit pads.  However, variations in appearance
and positions of the wires and pads can present alignment problems.

      Often the read/write heads utilize small diameter wires, such
as 0.0015", to carry electric signals from the heads to a
pre-processing circuit board attached to a drive actuator assembly.
Many wires are used in the read/write head assembly where each wire
must be ultrasonically bonded to its corresponding circuit pad.

      In the automation process, each pad/wire must be identified and
positioned under the bonding tip.  One approach is to use a machine
vision system to "see" the pad/wire pair and  determine any
misalignment.  A positioning device, such as a translational stage,
can then be directed to move the wire pad under the bond tip.
However, machine vision systems have access only to photometric data
within the image in the form of a digitized value.  In addition, part
positioning and reflectivity variations present other complications.

      The Figure shows a typical pad/wire image as presented to an
automated bonding tool.  The following list will give an indication
of features in this image which present unique problems in the
development of a reliable alignment algorithm:

o   The pads and wires are arranged radially on the circuit board.

o   The gold circuit pads have a texture which results in a variable
    speckled image.

o   The circuit board is light blue resulting in a poor contrast
    image of the gold pad edges.

o   The circuit pads have large length and width variations.

o   The wires are predominately black due to the angle of
    illumination, but part variations include white glare on the
    wires as well as curves an...