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Selective Self Limiting Laser Processing

IP.com Disclosure Number: IPCOM000110073D
Original Publication Date: 1992-Oct-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 1 page(s) / 49K

Publishing Venue

IBM

Related People

Brewer, WD: AUTHOR [+4]

Abstract

Disclosed is a self-limiting laser processing technique for selective surface modification. We have discovered a set of processing rules based on basic physics and materials properties which allow simple, selective surface modification with a wider process window than previously available, allowing higher yield, greater process latitude, and more flexible manufacturing. In addition, due to the self-limiting nature of the process, it allows the fabrication of miniature, surface alloyed metal structures which would not be manufacturable by other processes.

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Selective Self Limiting Laser Processing

       Disclosed is a self-limiting laser processing technique
for selective surface modification.  We have discovered a set of
processing rules based on basic physics and materials properties
which allow simple, selective surface modification with a wider
process window than previously available, allowing higher yield,
greater process latitude, and more flexible manufacturing.  In
addition, due to the self-limiting nature of the process, it allows
the fabrication of miniature, surface alloyed metal structures which
would not be manufacturable by other processes.

      This technique employs material systems and/or surface
preparations coupled with the correct laser wavelength to yield a
decrease in absorbed laser power upon melting of the material
surface.  As an example, consider photolithographically defined
copper leads for a typical TAB leadframe.  Such a lead will melt to
form a ball when exposed to CE YAG fundamental radiation (1.064
microns).  When an identical lead is electroplated with gold, only
the gold surgace melts on xposure to the CW YAG fundamental
radiation, leaving a smooth, porefree surface with no copper melting,
hence no ball formation.  Crosssectioning revealed that the copper
and gold did not interdiffuse significantly.  Models showed that the
melted gold acted as a mirror, and the energy input to the 4-mil-wide
by 1.5-mil-thick beam was reduced upon the melting of the gold,
thereby halting fu...