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Browse Prior Art Database

Variable Intensity Focused Illumination

IP.com Disclosure Number: IPCOM000112054D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 85K

Publishing Venue

IBM

Related People

Kolber, JC: AUTHOR [+5]

Abstract

Proper illumination intensity level is critical to the successful optical inspection of controlled collapse chip contact (C4) solder balls on Devices Under Test (DUTs). Since different DUTs reflect different amounts of light due to process variations, control of illumination intensity level is required to achieve the level required by a specific product.

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

Variable Intensity Focused Illumination

      Proper illumination intensity level is critical to the
successful optical inspection of controlled collapse chip contact
(C4) solder balls on Devices Under Test (DUTs).  Since different DUTs
reflect different amounts of light due to process variations, control
of illumination intensity level is required to achieve the level
required by a specific product.

      Initially, inspection workstations were limited to the testing
of one or two product lines and used a fixed 200-watt mercury vapor
lamp diffused to illuminate the masked area uniformly.  As testing of
additional product lines were attempted, it was found that too much
reflected light was saturating the camera.

      An initial solution was to use neutral density filters to
reduce the intensity of the light.  Although this worked for specific
products, it became impractical as the range of tested devices
increased.

      To ensure successful inspection, a quick, easy means of
adjusting intensity levels was required.  The Variable Intensity
Focused Illumination (VIFI) system disclosed herein satisfies this
requirement, eliminating errors by allowing the operator to control
illumination intensity levels to accommodate the full range of tested
devices.

      While the VIFI system is described in terms of its current
applications (on the Pad Analysis System (PAS) and Individual Chip
Inspection System (ICIS)), the technology can be used in any
application requiring precise light level control.

      VIFI is a lens-and-iris illumination control system based on
the Koehler illumination system for microscopes.  As shown in Fig. 1,
the source is imaged in the aperture of a substage condenser by an
auxiliary condenser; the substage condenser in turn forms an image of
the auxiliary condenser on the object.  Iris diaph...