Optimisation of CO2 laser soldering process

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Supervisor:
Dr. Gordon Péter Róbert
Department of Electronics Technology

One of the most developable subfield of the selective soldering technologies is the laser soldering. Due to its favorable properties, precise and exact soldering can be created by laser equipments. During my investigation I whether it is possible to create solder joints with a workstation developed for non soldering tasks.

In my thesis work I soldered melf diodes onto a suitable integrated circuit board with a CO2-laser (type: SYNRAD 48-2W) in the Department of Electronics Technology of BME. I worked out a qualifier method based on the optical microscopic analysis of the cross sectioned samples and the push off tests of the soldered joints. According to my expectations the soldered joints should be melted entirely, and the ambience of the diode shouldn't be damaged by the coupled heat.

The solder joint were prepared by defocused laser beam, whose diameter of the focal spot was nearly as large as the diameter of the soldering surface. During my experiments the exact amount of energy needed to create soldered joint was determined, so as the preheating and the soldering time. The technologic window of the soldering process is quite tight. The required energy for melting the whole solder in the given composition was 180 J. Soldering under 165 J energy, the solder was unable to melt entirely, however soldering with 195 J resulted in the degradation of the ambience of the diodes. According to my investigation, using 10 s preheating and 15 s soldering time at 7,2 W proved to be the optimum soldering parameters.

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