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What is the experience of using a humidity sensor with a ceramic substrate?

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  Ceramic substrate humidity sensors are generally divided according to the process, we can divide it into two categories, namely integrated sensors, thin film sensors, thick film sensors. Humidity sensors can be integrated with sensors that are manufactured using standard silicon-based semiconductor integrated circuit process technology. Some of the circuits used to initially process the signal under test are also integrated on the same chip. Thin film sensors and thick film sensors are different.


Ceramic Substrate


  Whether the thin film sensor or the thick film sensor prints the circuit directly on the substrate, the processing method is different. The thick film sensor is made by coating the substrate with the corresponding slurry. The substrate is generally oxidized. The aluminum ceramic substrate is then heat treated to form a thick film. The thin film sensor is formed by a film of corresponding sensitive material deposited on the substrate. A part of the circuit can be printed on the substrate by the same time of the mixing process.

  There are many advantages in using ceramic substrates, so we have to look at the advantages of ceramic substrates. Ceramic substrates have the following strengths:

  1. Higher thermal conductivity: The thermal conductivity of the traditional aluminum-based circuit board MCPCB is 1~2W/mk, and the thermal conductivity of copper itself is 383.8W/mK, but the thermal conductivity of the insulating layer is only about 1.0W/mK. A little better can reach 1.8W/mK. The thermal conductivity of alumina ceramics: 15 ~ 35 W / mk, the thermal conductivity of aluminum nitride ceramics: 170 ~ 230 W / mk, the thermal conductivity of copper substrates is 2W / (m * K), aluminum / copper base Circuit board: The aluminum itself has high thermal conductivity, but the aluminum/copper-based circuit board has an insulating layer, which causes the thermal conductivity of the whole board to decrease. We can replace the insulating layer with a ceramic base, with aluminum/copper as the substrate and ceramic as the insulating layer.

  2. More matching thermal expansion coefficient: The working temperature span of the humidity sensor is very large. In the high temperature and low temperature environment, if the thermal expansion coefficient between the data does not match, the line will fall off, and then the whole sensor will be scrapped, ceramic. The substrate has a coefficient of thermal expansion that more closely matches the humidity sensor and can have relatively good stability.

  3, good insulation: breakdown voltage up to 20KV / mm, can prevent any short-circuit damage, the maintenance of sensitive components can be the ultimate.

  4, the dielectric loss is small: the high-frequency circuit can be planned and assembled, the dielectric loss is very small, the signal output from the sensor can reach the lossless level.

  5, does not contain organic components: corrosion resistance, acid and alkali resistance, high temperature resistance, these are ensured that the humidity sensor can operate in harsh environments.

  The above is just a list of features that are helpful for humidity sensors. In fact, ceramic substrates have many advantages. The biggest difficulty with humidity sensors now is that they operate at high or low temperatures, and ceramic substrates are just right to handle these problems.
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