Browse Prior Art Database

Alignment and Bond Patterns for Surface Emitting Lasers

IP.com Disclosure Number: IPCOM000117311D
Original Publication Date: 1996-Feb-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 387K

Publishing Venue

IBM

Related People

Jackson, KP: AUTHOR [+2]

Abstract

This invention solves two problems: the problem of having to keep track of the orientation of a very small symmetrical chip with asymmetrical features on it and the problem of needing alignment marks for accurately positioning an optical element. This invention solves these two problems by providing a rotational invariant wirebond pad and at the same time providing alignment marks.

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Alignment and Bond Patterns for Surface Emitting Lasers

      This invention solves two problems:  the problem of having to
keep track of the orientation of a very small symmetrical chip with
asymmetrical features on it and the problem of needing alignment
marks for accurately positioning an optical element.  This invention
solves these two problems by providing a rotational invariant
wirebond pad and at the same time providing alignment marks.

      Vertical Cavity Surface Emitting Lasers (VCSELs) are lasers
that emit their light perpendicular to the semiconductor substrate on
which they are fabricated.  They are also lasers which need less than
a 20 x 20 micron area for the active device.  This would imply
extremely small chips could be used except that current wire bonding
technology requires a minimum bond pad of at least 50 x 50 microns
and for reliability reasons it is preferred not to place the wire
bond too close to the laser.  As such, VCSEL chips are made to be
about 500 x 500 micron with the excess area being used for remote
placement of the wire bond pad and for easier handling capability.
With the VCSEL located in the center of the 500 x 500 chip and the
bond pad located in one corner or near one edge, it becomes very
important and difficult to keep track of the orientation of this
small chip so that when it is packaged, the bond pad ends up in the
correct position.  It is also vry important to know precisely where
the laser is in the center of the chip because of the fairly tight
alignment tolerance (<20 microns) for the position of the laser in
the package.  It is also very difficult to know precisely where the
laser is within the chip since typical manufacturing dicing position
accuracies (typically > 25 microns are larger than the required
alignment tolerances.  A solution to the problem of having to keep
track of the orientation of a very small square chip is to provide a
symmetrical wire bonding pattern that is rotationally invariant.  A
solution to the problem of not knowing with precision where the laser...