Browse Prior Art Database

Solder Joint Reflow Under SILICON by IR Laser

IP.com Disclosure Number: IPCOM000112382D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Lees, S: AUTHOR [+4]

Abstract

Disclosed is a laser soldering method for silicon circuit chips which utilizes the property of IR transparency of silicon to locally reflow bumps under solder joints. It also offers the opportunity for quick controlled individual attention for the making of each chip joint and allows the chip to be attached/reflowed at the end of the process. An application is described for assembly of chips to circuit boards in which two process operations are reduced to one. Employment of the effect of silicon's transparency to IR for DCA chip assembly in blind locations is novel and could have applications in other technologies and circumstances.

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Solder Joint Reflow Under SILICON by IR Laser

      Disclosed is a laser soldering method for silicon circuit chips
which utilizes the property of IR transparency of silicon to locally
reflow bumps under solder joints.  It also offers the opportunity for
quick controlled individual attention for the making of each chip
joint and allows the chip to be attached/reflowed at the end of the
process.   An application is described for assembly of chips to
circuit boards in which two process operations are reduced to one.
Employment of the effect of silicon's transparency to IR for DCA chip
assembly in blind locations is novel and could have applications in
other technologies and circumstances.

      A particular Direct Chip Attach (DCA) circuit assembly process
first requires placement of a silicon flip chip on the circuit
conductors followed by solder reflow in a separate oven or focussed
heat lamps; two operations in different positions on a manufacturing
line.

      By taking advantage of the transparency of silicon to Infra-Red
(IR) radiation it became possible to construct a production machine
which precisely applies heat to the solder joints under the chip by
hitting the joint with IR radiation from a programmed laser.   The
laser would be positioned suitably above the chip and fire through
it.  The chip is very thin and essentially transparent to IR so the
focussed heat is almost unshielded.   Using a solid state laser it is
possible by switching and d...