www.sensirion.com / D1

Version 4

– November 2022

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5.5 Thermal Information

Symbol

Description

Heater off, die

pad soldered

(K/W)

Heater on, die

pad soldered

(K/W)

Heater off,

die pad

not soldered

(K/W)

Heater on,

die pad

not soldered

(K/W)

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Junction-to-ambient

thermal resistance

246

308

297

357

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Junction-to-case

thermal resistance

189

255

191

257

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Junction-to-board

thermal resistance

159

225

193

258

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Junction-to-board

characterization

param.

159

223

191

254

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Junction-to-top

characterization

param.

38

105

44

112

Table 9. Typical

values for thermal metrics. In the “heater on” columns a heater power of 200 mW was

assumed. Soldering of the die pad is not recommended, therefore the two right hand side columns are bold.

Values are based on simulation.

6 Protection Options

6.1 Membrane Option

The filter membrane option for SHT4x family members inherently provides an additional barrier for

all pollutants to enter the sensor opening, thus lowering negative influences on the sensing

element. Mostly designed to keep particles and dust from accumulating and reducing the response

time, the membrane also enables more efficient and easy cleaning, as it helps to reduce liquid

intrusion into the sensor opening. Even though not selectively filtering, in general, physical barriers

allow to reduce the amount of unwanted chemical contamination and help to remove potentially

harmful components by facilitating wiping (flat sensor surface).

The integrated SHT4x PTFE membrane provides additional protection, from particles, and enables

sensor operation in harsh conditions. The membrane has a thickness of 100 µm offering a filtration

efficiency of >99.99% for particles of 200 nm size and larger. Owing to the high permeability and

the small volume between sensing element and membrane, the specified response time of the RH

sensor is unaltered.

Figure 19. SHT4x with integrated PTFE membrane, highlighting the beneficial flat geometry of the SHT4xI.

To ensure full functionality of the sensor and avoid damaging its integrated filter membrane, when

mounting the sensor, follow the reflow soldering process as described in the Handling

Instructions [2]. Furthermore the therein described care regarding board wash and cleaning still

apply.