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Using Selective Additive in Material to Absorb Energy from a Tuned Laser

IP.com Disclosure Number: IPCOM000115468D
Original Publication Date: 1995-May-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Lees, SP: AUTHOR [+4]

Abstract

Disclosed is a technique for reflowing solder paste during the assembly of SMT circuit boards. Traditionally, the paste is reflowed using an infrared oven or a vapor phase machine. In both cases the entire card assembly is subjected to general heating when what is required is a method of only heating the paste. This general heating causes premature aging, forces the card and component designers to use expensive materials which are heat resistant and causes additional manufacturing workload and costs in trying to maintain a heat profile during assembly, especially when cards are becoming more thermally massive.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 65% of the total text.

Using Selective Additive in Material to Absorb Energy from a Tuned
Laser

      Disclosed is a technique for reflowing solder paste during the
assembly of SMT circuit boards.  Traditionally, the paste is reflowed
using an infrared oven or a vapor phase machine.  In both cases the
entire card assembly is subjected to general heating when what is
required is a method of only heating the paste.  This general heating
causes premature aging, forces the card and component designers to
use expensive materials which are heat resistant and causes
additional manufacturing workload and costs in trying to maintain a
heat profile during assembly, especially when cards are becoming more
thermally massive.

      Research into using lasers to reflow paste has concentrated on
using a beam which has enough power to melt the solder and which is
either switched or scanned around the joints to avoid heating the
board material.

      While still using a switched or scanned laser beam, the
absorption of the lasers energy may be much enhanced if a chemical
additive in the solder paste medium (the wet chemical component of
the paste) is carefully chosen to match the frequency of the laser
beam, which itself is chosen to match the additive.  Using the
principle that chemicals absorb 'heat' energy in certain specific and
measurable frequencies it is possible to design a laser/additive
combination optimized for rapid heating.  It may be possible to take
an existing paste and select a...