Cu and Cu-Al2O3 Powders for Thermal Management Devices
Date Issued
2010
Date
2010
Author(s)
Lin, Yueh-Ju
Abstract
Heat pipes have been widely applied in thermal management devices for notebook computers and light emitting diodes. But, there is still room for improvement. The first subject studied in this work is to improve the performance of heat dissipation by adjusting the characteristic of Cu powders. The other subject is to resolve the defects encountered during mechanical deformation during heat pipe assembly. These defects are mainly caused by the coarse grains, low hardness, and low strength of the sintered copper tubing. To improve the performance of heat dissipation, a copper with a low oxygen content, larger mean particle size, narrow particle size distribution, and spherical powder shape is preferred for preparing the porous Cu wicks. It is also noticed during evaluation of the heat dissipation performance that the permeability and the capillary pressure, which have been widely used in the past, can be replaced by the capillary speed, which is simpler and more accurate.
For increasing the strength and the hardness, the oxide dispersion strengthened Cu (ODS Cu) has been used in rods, plates, or bars, which have simple cross-sections. In this study, the development of the ODS Cu is aimed for press-and-sintered and powder injection molded parts, which are net-shaped. To attain good distribution of fine alumina particles in the Cu matrix, three methods are used. The first one is to use the cementation process to form alumina in the powder. The second approach is to add metal-containing lubricant, which forms alumina during sintering. The third method is to form alumina using the high energy milling process and Cu-Al pre-alloyed powders.
The results of the cementation method show that the relative density up to 99 % and the hardness of 45.4 HB can be attained with the addition of 0.108 wt% aluminum (0.456 vol% Al2O3). These properties are better than the 91.8 % and 32.4 HB of the alumina-free copper. For 0.263 wt% aluminum (1.111 vol%Al2O3), the density is 95.4 % and the hardness is 60.2 HB. The electrical conductivity of Cu-Al2O3 sintered compacts decreased with increasing amount of alumina. The electrical conductivities of these two Cu-Al2O3 sintered compacts are about 84 %IACS, slightly higher than the 82.5 %IACS of the alumina-free copper. The results of adding metal-containing lubricant reveal that adding 1.0 wt% lithium stearate is effective and increases the relative density of sintered compacts from 94.6% to 97.5%. In high energy milling process, the results exhibit that compact containing 0.117 wt% aluminum (0.498 vol%Al2O3) has the highest relative density of 96.5% and electrical conductivity of 83.1 %IACS. The highest hardness of compact is 33.7 HRB when the aluminum content in the compact is 0.587 wt% (2.453 vol%Al2O3). Considering the mechanical and electrical properties, the suggested optimum aluminum content is 0.352 wt% (1.483 vol%Al2O3), which gives a sintered density of 96.4 %, a hardness of 27.3 HRB, and an electrical conductivity of 82.3 %IACS.
Subjects
Copper powders
heat pipe
dispersion strengthening
Cu-Al2O3 powders
high energy milling
thermal management
capillarity
permeability
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