PCBs used in harsh and extreme environments mean that they need to operate under extreme temperatures, humidity, constant vibration, strong shocks, and other conditions that can affect reliability and their normal performance. Due to the differences in environmental requirements across industries and applications, in the medical industry, this could mean conditions such as high temperatures, high pressures, high humidity, and high radiation, while in aerospace it could mean extreme conditions such as extreme cold, low air pressure, strong vibration and so on.
The operating temperature of a satellite in space may vary depending on its position and orientation relative to the sun. If satellites are in a position in direct sunlight, they may suffer extreme temperatures due to the intense heat of the sun. Temperatures on the sunny side may reach 200°C (392°F) or higher, while temperatures on the shaded side may be as low as -200°C (-328°F) or lower. Therefore, PCBs used in satellites must be able to withstand high temperatures and can be applied in extreme conditions, which requires that PCBs be manufactured with a substrate that can withstand high temperatures, i.e., a high TG of the board. ocba.com has experience in manufacturing satellite PCBs for customers who usually require:
- TG of the board >200, for the board, usually choose Rogers board.
- Plug holes must comply with IPC4761 Type VII.
- Surface treatment using immersion gold or nickel-palladium gold process.
- Manufacturing and acceptance standards are strict.
- Impedance requirements must be in strict accordance with customer requirements, and the need to allow customers to confirm the pre-production of the working draft and engineering issues, not without the consent of the customer to start production.
Sheets used in extreme conditions are shared below.
- Polyimide resin has high-temperature resistance due to its high glass transition temperature and high decomposition temperature, making it highly resistant to high temperatures, and PCBs made from it also have high reliability and high-temperature resistance. Excellent resistance to space radiation, used in space, will not be affected by space radiation to produce any physical and chemical changes, thus ensuring the stability of electrical properties.
- High Tg, thus providing very good PTH and pad reliability.
- High Td, which enables it to be used in any high-temperature environment.
- Stable dielectric constant, suitable for impedance-controlled applications
Main application areas for polyimide materials
Military and applications with high-reliability requirements. In Europe and the United States, flight control such products can not tolerate any PCB failure risk of applications that must use polyimide materials as PCB substrate. This type of material application is unlikely to have problems can not be reworked, and is directly involved in extreme conditions of the pilot’s life, which is the experience of decades to prove the fact. Other, if the PCB involves human life, such as high-precision medical equipment, etc., should also use polyimide materials. As BOEING, Raython, and Honewe11 used 35N, 85N as the control circuit.
- High-temperature applications. Such as oil drilling probe control systems, semiconductor performance testing under high-temperature conditions (commonly known as aging test), and high-power power supply modules. Polyimide material’s high-temperature resistance becomes the main reason for such applications. Such as Schlumberger oil drilling control, INTEL chip aging test, etc. are used 85N.
- Space applications. Space satellite rocket control systems, etc., due to PCB working conditions in space, there is a lot of space radiation, to ensure the stability of the electrical characteristics of the PCB, at the same time, the very high-reliability requirements also use polyimide materials. Such as NASA/JPL MARS Lander.
- Very high number of PCBs, because of the high number of layers, especially when it comes to buried holes blind hole design, may use multiple sequential laminations, the material needs to withstand high temperatures for many times, and the reliability of the PTH can be guaranteed. aerospace pcb assembly
The following points should be noted when using polyimide materials for PCBs:
- The curing temperature should be higher than FR-4, around 200°C. Therefore, when selecting the inner layer oxidation treatment, use an oxidation system that can withstand high temperatures, such as brown oxidation.
- Curing time is slightly longer.
- Polyimide materials are prone to moisture absorption, so pay attention to the storage conditions of the semi-cured sheet and vacuum pack it. During the transition from low to room temperature, the same is guaranteed in a vacuum bag. After oxidizing the inner layer, dry it before lamination.
- The resin system of polyimide is slightly different from that of FR-4, so it is important to avoid drill breakage on drilling.
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