The specific properties of molybdenum-copper alloys are greatly affected by their composition ratios, and different molybdenum-copper ratios will directly affect their thermal, mechanical and electrical properties, thereby affecting the performance of electronic packaging.
Effect on thermal properties
In electronic packaging, heat dissipation performance is crucial, especially in high-power electronic devices, where the thermal conductivity of the packaging material directly determines the stability and lifetime of the device. The thermal conductivity of molybdenum-copper alloys increases with the increase of copper content, but at the same time, it also leads to an increase in the coefficient of thermal expansion. For example:
The thermal conductivity of Mo70Cu30 (70% Mo, 30% Cu) alloy is about 120 W/m·K, and the thermal expansion coefficient is about 7.8 x 10??/K.
The thermal conductivity of Mo50Cu50 (50% Mo, 50% Cu) alloy is about 180 W/m·K, and the thermal expansion coefficient is about 9.5 x 10??/K.
The thermal conductivity of Mo30Cu70 (30% Mo, 70% Cu) alloy can reach more than 250 W/m·K, but its thermal expansion coefficient also increases to about 12 x 10??/K.
For packaging materials that require high thermal conductivity, such as high-power semiconductor devices, Mo50Cu50 or Mo40Cu60 are usually used to avoid interfacial stress problems caused by thermal expansion mismatch while maintaining high thermal conductivity.
Effect on mechanical properties
Molybdenum has a higher hardness and copper has better ductility, and different Mo-Cu ratios will affect the mechanical properties of the material. For example:
High Mo content (>70%): The material has high hardness and high mechanical strength, but the brittleness increases, and the processing difficulty is large, which is suitable for packaging with high strength requirements, such as electronic packaging for aerospace.
Mo-Cu equilibrium (50:50): It has both high mechanical strength and certain toughness, and has good processability, which is the most common proportion of packaging materials.
High Cu content (>70%): The material is soft and easy to process, but the high temperature resistance is reduced, making it suitable for low-power electronic packaging.
Effect on electrical performance
The resistivity of molybdenum is high, while the conductivity of copper is better, so the resistivity of Mo-Cu alloy increases with the increase of Mo content. For example:
The high electrical conductivity of the Mo30Cu70 makes it suitable for electronic packages with high requirements for current transmission.
The high resistivity of the Mo70Cu30 makes it suitable for applications that require shielding or reduced current leakage.
In radio frequency (RF) and microwave packages, Mo50Cu50 or Mo40Cu60 are more common because they offer a good balance between conductivity and mechanical strength.
The choice of alloys with different molybdenum-copper ratios in electronic packaging depends on the specific application requirements:
High-power devices (IGBT, LED substrate): Mo50Cu50 or Mo40Cu60 is recommended to ensure high thermal conductivity and moderate thermal expansion coefficient.
High-reliability packaging (aerospace, military electronics): Mo70Cu30 is recommended to provide lower thermal expansion coefficient and higher mechanical strength.
RF and microwave packaging: Mo40Cu60 or Mo30Cu70 is recommended to optimize electrical and thermal conductivity.
