The core process parameters of MIM copper plate mass production yield improvement cover the key nodes of the whole process of feed preparation, injection molding, degreasing, and sintering. Through precise control, the mass production yield can be increased from the industry average of 70% to more than 95%, while ensuring the high thermal conductivity and high precision performance required by the optical module scene.
Key process parameters of feed preparation
Control of copper powder particle size and oxygen content: High-purity spherical copper powder with an average particle size of 15 to 25 μm is selected, and the oxygen content is strictly controlled at ≤ 150 ppm to avoid impurity oxidation hindering sintering densification, and ensure that the thermal conductivity of the finished product is stable at more than 320W/m · K from the source.
Binder system ratio optimization: using a low-residue binder system of paraffin + high-density polyethylene + stearic acid, the powder loading capacity is controlled at 60% to 65%, which not only ensures the fluidity of the feed to meet the needs of thin-wall mold filling, but also avoids green cracking and bubbling defects during degreasing.
Mixing temperature and rotational speed control: The twin-screw mixing temperature is set at 130~ 150 ° C, and the rotational speed is controlled at 30~ 50 rpm to achieve uniform dispersion of copper powder and binder, and to eliminate the subsequent sintering deformation problem caused by local powder agglomeration.
Key process parameters of injection molding
The mold temperature is precisely controlled: the mold temperature is stably controlled at 70~ 90 ° C, and the injection curve optimized by the mold flow analysis is used to solve the problem of insufficient filling of thin walls caused by the rapid cooling rate of pure copper melt, and to avoid the ultra-thin shell of the optical module and the underinjection and cold sealing defects of the dense heat dissipation needle column.
Synergy of injection pressure and speed: The injection pressure is set at 80 to 120 MPa, a segmented high-speed injection curve is adopted, and the filling time is controlled at 1 to 3 seconds to ensure the complete filling of complex special-shaped cavities, while avoiding appearance defects such as flash and welding lines.
Optimization of pressure holding parameters: The pressure holding pressure is set to 60% to 70% of the injection pressure, and the pressure holding time is adjusted to 5 to 15 seconds according to the wall thickness of the component, effectively compensating for cooling shrinkage, completely eliminating the internal voids of the component, and controlling the internal porosity within 3%.
Key process parameters of degreasing process
Step-by-step degreasing curve: solvent degreasing + thermal degreasing step-by-step process is used, the solvent degreasing temperature is set at 40~ 60 ° C, and the connecting pores are formed after 4~ 6 hours of insulation; thermal degreasing is heated at a low speed of 0.5~ 1 ° C/min, and the remaining binder is slowly discharged to prevent the problem of green cracking and bubbling.
Furnace atmosphere uniformity control: the whole process of degreasing is protected by high-purity nitrogen gas, and the temperature field deviation in the furnace is controlled within ± 3 ° C to ensure that the binder diffuses evenly from the inside of the green body and avoids local residual carbon elements affecting the subsequent sintering densification.
The accurate determination of the end point of degreasing: through online weight loss monitoring, ensure that the removal rate of the binder reaches more than 98%, and then transfer to the sintering process to avoid the internal foaming of the parts caused by the decomposition of the residual binder at high temperature.
Key process parameters of sintering process
The sintering temperature is precisely locked: the sintering temperature is strictly controlled in a narrow window range of 1050 to 1085 degrees Celsius, close to the melting point of pure copper at 1085 degrees Celsius, and the holding time is set to 3 to 5 hours to achieve full diffusion and fusion of powder particles, resulting in a stable density of more than 97%.
High-purity hydrogen protective atmosphere control: high-purity hydrogen with dew point ≤ -60 ° C is introduced throughout the process, and the oxygen content in the furnace is strictly controlled at ≤ 50 ppm, completely inhibiting the oxidation of copper powder. At the same time, water vapor in the closed pores is eliminated through hydrogen reduction reaction to avoid hydrogen-induced expansion defects.
Segmented cooling and support tooling design: using "constant temperature sintering + segmented cooling" process, the cooling rate is controlled at 2~ 3 ° C/min, for complex parts with microchannels and special-shaped buckles, customized sintering support tooling is provided to completely offset the gravity deformation under high temperature softening state, and the dimensional tolerance is stably controlled within ± 0.1%.
Post-processing and testing of key process parameters
Surface polishing and passivation treatment: The plasma polishing process is used to reduce the surface roughness of the part to less than or equal to 0.5 μm, and a dense passivation film is formed on the surface to avoid oxidation and discoloration of the copper part during long-term use, and to ensure the stability of the contact thermal resistance with the optical module shell.
Full-batch non-destructive testing standard: 100% through X-ray flaw detection to detect internal micro-cracks and hidden pore defects, each batch of sampling to check the thermal conductivity, oxygen and carbon content, to ensure that the thermal conductivity deviation of the same batch of components is controlled at ≤ 5%, fully meeting the strict requirements of optical modules for heat dissipation consistency.
