| Aluminum nitride direct bond copper(AlN-DBC)substrates were widely used in high-power,high-density packaging of power electronic devices for combining advantages of excellent electrical properties of copper and high thermal conductivity of ceramic.But the wettability between the ceramic and metal was poor,which severely limited its performance and preparation,so it is critical how to prepare AlN-DBC substrates with high binding strength.Based on the Al2O3-DBC method,this paper adopted the pre-oxidized method to oxide copper sheet and AlN substrate respectively,after that the corresponding Cu2O and Al2O3 oxide layer can be formed.Owing to the oxidation of copper sheet,the Cu-O eutectic liquid could be formed at the bonding temperature,which can wet the surface of oxidized AlN ceramic substrates and form a good seal interface by chemical reaction.Finally the AlN-DBC substrates were obtained with the decrease of temperature.A pure Cu2O oxide layer was produced on copper surface through high pre-oxidized method,when the oxide temperature was between 900~1050℃ and the volume fraction of oxygen was under 2%~10%.The thickness of Cu2O layer increased as increasing the oxidation temperature and oxygen content,however the Cu2O layer will fall off from the copper once the Cu2O layer reached a certain thickness.When the oxidation temperature and O2 volume fraction were 1000℃ and 4% respectively,the dense oxide layer can be obtained and the relation between thickness and time meet the parabolic law: x2=194t-955,which showed that the thickness of the oxide layer can be controlled by adjusting the time.The surface morphology of oxide layer depended on the oxidation rate,a dense Cu2O oxide layer was formed at a low rate of oxidation and the Cu2O nano-spherical particles were formed at a high oxidation rate.At last the preparation condition of the uniform Cu2O nano-spherical particles was 1000℃,4%O2 and 10 min.The AlN substrates were pre-oxidation systematically,the results showed that when the oxidation temperature and the oxidation time were 1200 ℃ and 30 min respectively,AlN substrate surface was not completely oxidized to Al2O3.The white Al2O3 oxide layer was produced under other conditions.The thickness of oxide layer increased slowly at 1200℃,and the oxide layer surface was smooth and dense.Some holes were appeared on the surface of the oxide layer at 1250℃,and the number of holes decreased as the time increased from 30 min to 120 min.The oxide layer surface had cracks at 1300 ℃,since the oxidation rate was too fast.The ultimately determined bonding temperature and time were 1080℃ and 25 min respectively,through the exploration of bonding process.By characterizing substrate section and cross-section showed that the joint between the ceramic substrate and its oxide layer was the most vulnerable part of the AlN substrate,where the main objects of this section were Al2O3 and AlN.The oxide layer on the copper surface was consumed with oxygen dissolved in Cu-O eutectic liquid.Due to the pressure exerted by the experiment,Cu-O eutectic liquid will overflow from the interface,resulting in interfacial reaction product was difficult to characterize.The bonding strength of AlN-DBC substrates was inversely proportional to the thickness of the copper oxide layer,the bonding strength of the substrate decreased with the increasing of the copper oxide layer thickness. |
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