In the mass production of optical modules, the core technical challenges of MIM copper plates are concentrated in the three dimensions of sintering densification, high thermal conductivity stability, and precision structural yield control, which are currently limiting their large-scale and comprehensive replacement of traditional machined copper plates.
Core technical challenges of sintering densification
The sintering window of pure copper is extremely narrow: the difference between the degreasing temperature of pure copper and the sintering temperature is very small, and the sintering temperature needs to be controlled in the range of 1050 to 1085 degrees Celsius, which is close to the melting point of copper at 1085 degrees Celsius. If the temperature deviation exceeds 20 degrees Celsius, there will be local overmelt deformation or insufficient density. The process control difficulty is much higher than that of the mature stainless steel MIM process.
Hydrogen-induced expansion defect risk: During the sintering process, the copper oxide in the closed pores reacts with hydrogen to generate trapped water vapor, which can lead to pore expansion, internal foaming of the parts, and directly inhibit the densification process. It is difficult to stabilize the density to more than 97% under conventional processes.
The prevention and control of oxidation pollution is difficult: ultrafine copper powder is highly susceptible to oxidation, and the CuO/Cu 2O O layer formed on the surface directly hinders the bonding of particles during sintering. A high-purity hydrogen or hydrogen-nitrogen mixed protective atmosphere with a dew point of < -60 ° C must be used throughout the process. The oxygen content in the furnace needs to be strictly controlled below 50 ppm, which requires extremely high cleanliness of the sintering equipment.
High thermal conductivity consistency challenge
The strong negative impact of impurities on thermal conductivity: 0.3% of the copper powder contains iron, cobalt, nickel, and other transitional impurities, which directly reduce the thermal conductivity of the finished product by 10% to 15%; for every 0.05% increase in oxygen content, the thermal conductivity will be lost by 10~ 15W/m · K, and the thermal conductivity of ordinary suppliers' mass-produced parts is generally only 280~ 320W/m · K, which is far lower than the theoretical 380W/m · K level.
Residual pores interrupt the thermal conductivity path: Even if the overall density is up to standard, the uneven distribution of micron-level residual pores will directly interrupt the continuous thermal conductivity path, resulting in a thermal conductivity deviation of more than 15% between the same batch of components, which cannot meet the stringent requirements of the optical module for heat dissipation consistency.
The performance balance problem of alloying: the addition of tin, nickel and other activated sintering elements to improve the hardness of components will further sacrifice thermal conductivity, making it difficult to simultaneously balance high thermal conductivity and high wear resistance. The current balance scheme in the industry is still in the optimization iteration stage.
Precision Structural Forming Yield Challenge
Thin-walled filling molding is difficult: pure copper has a very high thermal conductivity, and the melt cooling rate during injection molding is much faster than that of stainless steel feeding. The ultra-thin shell with a wall thickness of less than 0.5mm in the optical module and the dense heat dissipation pin structure are prone to insufficient filling and cold sealing defects. It requires a precise mold temperature control system and a multi-stage high-speed injection process to stabilize the molding.
Defects in the degreasing process are high: too fast removal of the binder can directly lead to cracking, bubbling, and internal residual carbon elements in the parts. A multi-stage step-by-step degreasing process must be adopted, first forming connected pores through solvent degreasing, and then slowly discharging the remaining binder through thermal degreasing. The entire degreasing cycle is 2 to 3 times that of ordinary stainless steel MIM parts.
Special-shaped structure sintering deformation out of control: the optical module with chute, snap, internal microchannel complex special-shaped parts, different wall thickness area sintering shrinkage difference of up to 3% or more, prone to warping, size problems, shrinkage prediction and mold pre-compensation design experience threshold is very high, the early mold iteration cost is more than 2 times the ordinary MIM parts.
Mass production and validation landing challenges
The cost of whole-process traceability and non-destructive testing is high: the optical module-level MIM copper plate requires 100% X-ray inspection to detect internal micro-cracks and hidden pore defects, and each batch must complete the full performance sampling of thermal conductivity and oxygen and carbon content. The inspection cost accounts for more than 15% of the total cost of components.
The structural limitations of microchannel integrated molding: the completely closed internal complex microchannel cannot be formed at one time through the conventional demoulding process, and most solutions still need to use the split sintering splicing process, which poses a risk of weld leakage. The production yield of true all-in-one molding without welds is still less than 70%.
The long-term verification threshold for the optical module industry: High-speed optical modules have extremely high reliability requirements for components, and MIM copper plates need to complete rigorous verification such as 1000 hours of high-temperature and high-humidity cycles, 500 hot-swap life, etc. The complete qualification certification cycle lasts for 12 to 18 months. It is difficult for new suppliers to quickly enter the core supply chain of leading optical module manufacturers.
