In satellite engineering photos, it is often seen that the surface of the spacecraft is covered with a shiny golden "blanket". Many people's first reaction is "gold" - in fact, this is a multi-layer insulation component (MLI), whose core layer material is PI aluminum plated film.

MLI is composed of dozens of alternating layers of aluminum plated films and spacer layers, with each layer of aluminum plated film serving as an efficient radiation reflection barrier. By stacking dozens of aluminum coated PI films with spacer layers under vacuum, MLI can reduce the equivalent thermal conductivity to the order of 10 ⁻⁵ W/(m ·° C). In the thickness spectrum of MLI, 25 μ m (approximately 1mil) is one of the most commonly used substrate thicknesses. In the product spectrum of PI aluminum plated film, commonly used thicknesses include 7.5 μ m, 12.5 μ m, 25 μ m, 50 μ m, 75 μ m, 125 μ m, etc., and 25 μ m is the specification that is at the core of the "combination of rigidity and flexibility". It does not require extremely high processing technology like 7 μ m or 12.5 μ m, nor does it compromise on weight and flexibility like 50 μ m or thicker specifications.

2、 Why 25 μ m: Industry Consensus from MLI to FPC

In the application system of polyimide film, 25 μ m is one of the most basic thickness units - the vast majority of PI film manufacturers use 25 μ m as the core specification in their standard product lines. The reason why 25 μ m has become the industry standard is due to its comprehensive advantages in multiple engineering dimensions:

3、 Vacuum evaporation: "growing" optical grade aluminum layer on a 25 μ m substrate

The aluminum layer preparation of 25 μ m PI aluminum coating film adopts vacuum evaporation process - in a highly vacuum environment, high-purity aluminum wire or aluminum block is evaporated into gas by heating, and then deposited on the surface of PI film to form a coating. This process requires precise control of parameters such as vacuum degree, evaporation temperature, and evaporation rate to ensure the quality and thickness of the coating.

The process window for vacuum evaporation on a 25 μ m substrate is quite mature. Compared to ultra-thin substrates, 25 μ m substrates have higher mechanical strength and thermal capacity, and have better tolerance for temperature and tension fluctuations during the evaporation process. Therefore, the uniformity and adhesion of the aluminum layer are easier to ensure. Advanced Institute Technology, relying on its independently built roll to roll vacuum evaporation production line, has achieved stable supply capacity for PI aluminum plating film from nanoscale thickness control to large-scale production. PI aluminum plated film can be divided into two types: single-sided aluminum plating and double-sided aluminum plating. Single sided aluminum plating maintains insulation on one side of the film while increasing conductivity and reflectivity on the other side; Double sided aluminum plating provides double-sided conductivity and reflection functions.

4、 Aluminum layer thickness: performance span from 0.5 μ m to 1 μ m

Based on a 25 μ m PI substrate, aluminum plated film products with different aluminum layer thicknesses can be prepared by precisely controlling the evaporation process parameters. The thickness of the aluminum layer varies from 0.5 μ m to 1 μ m, and different thicknesses correspond to different performance focuses:

Note: The thickness of the aluminum layer is the nominal reference value, and the specific performance is subject to the actual product specifications. The higher the OD value, the thicker the aluminum layer, and the higher the barrier and reflectivity.

5、 Key Performance: Technical confidence with 25 μ m specification

6、 Three major application layouts: from spacecraft to precision optics

7、 Selection considerations: from aluminum layer thickness to application scenarios

8、 Conclusion

The essence of 25 μ m PI aluminum plated film is an engineering product that finds the optimal balance point in high-end applications such as aerospace thermal control, electronic shielding, and precision optics. It is not the thinnest or thickest, but it is the "just right" choice in most high-end application scenarios: sufficient to meet the thermal control performance and reliability requirements of spacecraft MLI, support the electromagnetic shielding and flexibility requirements of FPC, maintain high yield and controllable cost in mass production.

For engineers, understanding the engineering logic behind the thickness of 25 μ m - why it is 25 instead of 12.5 or 50- is more valuable than simply remembering a specification. On this thickness platform, customizing products with different properties by adjusting the thickness of the aluminum layer (from 0.5 μ m to 1 μ m) is a key step in transforming the "standard answer" into specific engineering solutions.