9.2.1 Design Requirements

In order to correctly sense the ambient temperature and humidity, the HDC1010 should be positioned away from heat sources on the PCB. Generally, it should not be close to the LCD and battery. Moreover, to minimize any self-heating of the HDC1010 it is recommended to acquire at a maximum sample rate of 1sps (RH + Temp). In home systems, humidity and the temperature monitoring rates of less than 1sps (even 0.5sps or 0.2sps) can be still effective.

9.2.2 Detailed Design Procedure

When a circuit board layout is created from the schematic shown in Figure 15 a small circuit board is possible. The accuracy of a RH and temperature measurement depends on the sensor accuracy and the setup of the sensing system. The HDC1010 samples relative humidity and temperature in its immediate environment, it is therefore important that the local conditions at the sensor match the monitored environment. Use one or more openings in the physical cover of the thermostat to obtain a good airflow even in static conditions. Refer to the layout below ( Figure 20) for a PCB layout which minimizes the thermal mass of the PCB in the region of the HDC1010, which can improve measurement response time and accuracy.

9.2.3 Application Curve

The data showed below have been acquired with the HDC1010EVM. A humidity chamber was used to control the environment.

Figure 16. RH vs. Time

9.3.1 Soldering

For soldering HDC1010 use the standard soldering profile IPC/JEDEC J-STD-020 with peak temperatures at 260 °C. Refer to the document SNVA009 for more details on the DSBGA package. In the document refer to DSBGA package with bump size 0.5mm pitch and 0.32mm diameter.

When soldering the HDC1010 it is mandatory to use no-clean solder paste and no board wash shall be applied. The HDC1010 should be limited to a single IR reflow and no rework is recommended.

9.3.2 Chemical Exposure and Sensor Protection

The humidity sensor is not a standard IC and therefore should not be exposed to particulates or volatile chemicals such as solvents or other organic compounds. If any type of protective coating must be applied to the circuit board, the sensor must be protected during the coating process.

9.3.3 High Temperature and Humidity Exposure

Long exposure outside the recommended operating conditions may temporarily offset the RH output. Table 11 shows the RH offset values that can be expected for exposure to 85°C and 85% RH for duration between 12 and 500 hours (continuos).

Table 11. Induced RH Offset Due to Extended Exposure to High Humidity and High Temperature (85°C/85% RH)