SNAU250 November   2020 HDC2010 , HDC2021 , HDC2022 , HDC2080

 

  1.   1
  2.   2
    1.     3
    2.     4
      1.      5
      2.      6
      3.      7
  3.   8
    1.     9
    2.     10
      1.      11
      2.      12
  4.   13
    1.     14
    2.     15
      1.      16
      2.      17
      3.      18
    3.     19
      1.      20
      2.      21
      3.      22
      4.      23
    4.     24
    5.     25
  5.   26
  6.   27
    1.     28
    2.     29
    3.     30
    4.     31
    5.     32
    6.     33
    7.     34
  7.   35

2.1 Exposure to Contaminants

Humidity sensors are not standard ICs and therefore must not be exposed to articles or volatile chemicals such as solvents or other inorganic compounds. The opening in the package exposes the sensing polymer to the environment and makes it susceptible to pollutants. Typical ambient conditions do not present a significant risk for chemical exposure but manufacturing and storage environments are a known source of volatile contamination. The HDC2021's factory-installed polyimide cover tape protects the device during manufacturing and assembly (see Figure 1-3). After tape removal the sensing element is again sensitive to contamination.

Exposure to a range of chemicals must be avoided or minimized. Exposure of the following chemicals is know to cause drift of the humidity output readings which may be irreversible:

  • Solvents such as:
    • Toluene: C7H8
    • Acetone: (CH3)2CO
    • Ethanol: C2H6O
    • Methanol: CH3OH
    • Isopropyl Alcohol: C3H8O
    • Di-isopropyl Ether: C6H14O
    • Ethylene Glycol: (CH2OH)2
    • Ethyl Acetate: C4H8O2
    • Butyl Acetate: C6H12O2
    • Methyl Ethyl Ketone: CH3C(O)CH2CH3
  • Acids such as:
    • Hydrochloric Acid: HCl
    • Sulfuric Acid: H2SO4
    • Nitric Acid: HNO3
  • Other Chemicals, including:
    • Ketenes
    • Ammonia: NH3
    • Hydrogen Peroxide: H2O2
    • Ozone: O3
    • Formaldehyde: CH2O

Such chemicals are an integral part of epoxies, glues, adhesives, or reaction by-products that outgas during baking and curing processes.

The sense layer must not have direct contact with cleaning agents such as PCB board wash after soldering. Applying cleaning agents to the sense layer may lead to drift of the RH output or even complete breakdown of the sensor. Avoid strong blasts from aerosol dusters and use only low pressure oil free air dusting.

If it is necessary to expose the HDC to contaminants, concentration and exposure time must be reduced as much as feasible. Good ventilation (fresh air supply) aids in lowering the concentration of volatile chemicals, particularly solvents.