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Study on Adhesion on Substrate and Solderability of Laser Micro-Cladding Electronic Coating

Author: ZhangJie
Tutor: ZengXiaoYan；CaiZhiXiang
School: Huazhong University of Science and Technology
Course: Physical Electronics
Keywords: laser micro-cladding electronic coating substrate adhesion solderability
CLC: TN05
Type: Master's thesis
Year: 2011
Downloads: 33
Quote: 0
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Abstract

With the rapid development of the electronic industry, conductive layers for industrial use, not only requires economic performance, high stability, large electrical conductivity, but also strong adhesion and good solderability. In this paper, an idea of fabricating thick-film gold paste on the substrates which were used in the thin-film technology was proposed. The effect of laser processing parameters, properties of substrates to adhesion on substrate and solderability of laser micro-cladding electronic coating was studied. It aimed at proposing theoretical reference for application of laser micro-cladding technology.The results showed that it was easier to get gold layers on the substrates for short wavelength (λ=532nm) than long wavelength (λ=1064nm). Gold paste on different substrates had different critical power density of sintered—FⅠ,and critical power density of burned—FⅡ. Increase of laser power density between FⅠand FⅡwas useful to increase the adhesion on substrate of gold layer. The highest level of adhesion testing standard was 5B, the adhesion of 6~8μm thickness of pre-set gold film on silicon could reach 4B~5B under the laser scanning. The parameters of laser were, 1064nm wavelength, 1mm/s scan velocity and 1.29×106W/cm2~2.00×106W/cm2 power density range. For the compactness of coating after laser scanning was less than the high-temperature sintering, the effective of ultrasonic aluminum wire bonding on gold coatings was not good. The laser processing parameters needed to be further explored, but the density of laser micro-cladding electronic coating was improved by subsequent heat treatment (500~600℃), which effectively improved the coating adhesion strength on substrate and solderability.Through some analysis technology such as SEM, thermal analysis, this paper analyzed the electronic coating on silicon substrate fabricated by laser micro-cladding technology, got the adhesion mechanism of gold coating and silicon and the solderability mechanism of the gold coating: the eutectic reaction occurred between the gold and silicon substrate under laser irradiation. The product from the eutectic reaction ensured the adhesion on silicon substrate of laser micro-cladding gold coating. At the same time, the eutectic reaction also took place between Au and Bi in the coating. The Au-Bi eutectic not only increased the adhesion of coating, but also prevented diffusion of the aluminum wire from the ultrasonic aluminum wire bonding to the gold coating, and improved the solderability of gold coating.

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