Thermal Coupling Of The Sensor Element - Bosch BME280 Mounting Instructions

Bosch Sensortec | HSMI BME280
Figure 4: A fast response time can only be ensured by directing the air flow (breath) straight along z-axis onto the sensor lid
of the BME280 and a gasket/rubber (in black) is added (top middle). This implies that vent hole and air flow must have same
direction. The other two shown scenarios (top left and top right) may cause a lower response time.

5.2. Thermal coupling of the sensor element

The BME280 has a specific thermal mass. Therefore the temperature of the BME280 reacts very slowly
on changes of the environmental temperature. There are some methods to realize fast temperature
response times like
 Strong thermal coupling of the sensor to the environment.
Careful placement of the sensor is very important to achieve the best temperature measurement.
Excellent thermal coupling between the sensor and the environment the sensor is guaranteed with
placement of the sensor as close as possible to the environment (ambient air). Position at the corner or
pretty close to the edge of the device is favorable. Air flow of ambient air will additionally enhance the
thermal coupling.
 Weak thermal coupling of the sensor to the thermal mass of the housing and board (PCB)
Minimized coupling of the sensor and the housing and board (PCB) is assured if the heat conduction is
decreased as described in section 5.1.
Figure 5: Thermal decoupling of the sensor from the PCB by means of milled trenches (a) or small PCB connections
(b).
Document number BST-BME280-HS006-00 | May 2018
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Note: Specifications within this document are subject to change without notice.
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