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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 10. 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 on-package filter membrane option for SHT4x family, protected by several patents16, 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 (according to IP67). 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 SHT4x.

16

US 10,281,442 ; EP 2871152 ; CN 104627945