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Texas Instruments Humidity Sensor: Storage and Handling lines Application notes
Application Report
SNIA025 – October 2017
Humidity Sensor: Storage and Handling Guidelines
Ben Kasemsadeh
ABSTRACT
Texas Instruments’ family of humidity sensors, or Humidity-to-Digital Converters (HDCs), provide excellent
measurement accuracy at industry’s lowest power consumption levels. The low power consumption
facilitates use in battery powered IoT applications such as smart thermostats, and wireless data loggers
while the excellent accuracy supports applications such as white goods, smart home assistants and gas
sensing. The HDC ICs come factory calibrated for ease of use and are available in small packages
(WSON or DSBGA) to simplify board design.
In contrast to ordinary ICs in WSON or DSBGA packages, the exposed humidity sense layer of the HDC
requires additional precautions during storage, assembly and packaging to meet datasheet performance
specifications. Special handling is also required during PCB assembly. Reducing stress on the package
helps to ensure the best performance. This application note describes storage and handling guidelines of
humidity sensors, including the HDC1010, HDC1080, and HDC2010.
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Contents
Exposure to Contaminants .................................................................................................
Packaging and Storage .....................................................................................................
Assembly......................................................................................................................
Application In Extreme Environments .....................................................................................
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Exposure to Contaminants
Humidity sensors are not standard ICs and therefore must not be exposed to particles or volatile
chemicals such as solvents or other organic compounds. The opening in the package exposes the sense
layer 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 innovative DSBGA package of the HDC1010 and HDC2010 with the
sensing element placed on the bottom part of the device (see Figure 1) makes the sensor more robust
against dirt, dust, and other particulate contamination compared to the WSON solution (HDC1080).
Figure 1. DSBGA Package with Sensing Element on Bottom of the Device (HDC2010)
Exposure to a range of chemicals must be avoided or minimized. Exposure of the following chemicals is
known to cause drift of the humidity output readings which may be irreversible:
• Solvents such as
– Toluene: C7H8
– Acetone: (CH3)2CO
– Ethanol: C2H6O
SNIA025 – October 2017
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Humidity Sensor: Storage and Handling Guidelines
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Packaging and Storage
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www.ti.com
– 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
– Sulphuric 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 contaminates, concentration, 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.
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Packaging and Storage
TI’s Humidity sensors are shipped in sealed anti-static tape and reel cavities. The sensors may be stored
in a humidity and temperature controlled environment after being removed from the tape and reel cavity
prior to assembly. Storage temperature and humidity limitations are defined by the MSL level of the
sensor. Refer to application note MSL Ratings and Reflow Profiles for details.
Do not store the humidity sensors with anti-static polyethylene bags or packing materials (pink foam) as
these materials emit gases that can affect the sensor. Metallized, anti-static, sealable bags are
recommended for storage. Do not use adhesives or tape inside the storage container.
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Assembly
The HDC must be added in the last assembly step. In case the PCB passes through multiple solder cycles
(as is the case for PCBs that are assembled on the top and bottom side), it is recommended to assemble
the HDC in the last solder cycle. This reduces the risks of sense layer exposure. Contaminants such as
those listed in Section 1 must be avoided or minimized. Maximum assembly temperatures and exposure
times must not be not exceeded.
NOTE: It is important that “no-clean” solder paste is used and no board wash is applied once the
sensor is assembled onto the PCB.
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Humidity Sensor: Storage and Handling Guidelines
Copyright © 2017, Texas Instruments Incorporated
SNIA025 – October 2017
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Application In Extreme Environments
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Application In Extreme Environments
Some applications require usage of the HDC in harsh environments. Ensure that the exposure of the
sensor to the maximum limit of temperature and humidity operating conditions meets the datasheet
guidelines. Limiting exposure to volatile organic compounds at high concentration and long exposure time
is critical. Usage in harsh environments must be carefully tested and qualified.
Exposure to any aqueous solutions is highly discouraged. In the event that some aqueous exposure
cannot be avoided, use the following guidelines:
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Exposure to acids or bases may affect humidity output accuracy readings.
Bases are less damaging than acid solutions. All acid solutions must be considered damaging to the
sensor. Etching substances such as H2O2 or NH3 at high concentrations is damaging to the sensor.
Corrosive solutions at very low concentrations are not damaging to the sensor itself. However, care
must be taken to ensure that the solder contacts are not attacked.
SNIA025 – October 2017
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Humidity Sensor: Storage and Handling Guidelines
Copyright © 2017, Texas Instruments Incorporated
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