Datasheet SHT25
Humidity and Temperature Sensor IC
Fully calibrated with 1.8%RH accuracy
Digital output, I
2
C interface
Low power consumption
Excellent long term stability
DFN type package – reflow solderable
Product Summary
SHT25, the new humidity and temperature sensor of
Sensirion is about to set new standards in terms of size
and intelligence: Embedded in a reflow solderable Dual
Flat No leads (DFN) package of 3 x 3mm foot print and
1.1mm height it provides calibrated, linearized signals in
digital, I
2
C format.
With a completely new designed CMOSens® chip, a
reworked capacitive type humidity sensor and an
improved band gap temperature sensor the performance
has been lifted even beyond the outstanding level of the
previous sensor generation (SHT1x and SHT7x). For
example, measures have been taken to stabilize the
behavior at high humidity levels.
Dimensions
3.0
0.3 typ
Every sensor is individually calibrated and tested. Lot
identification is printed on the sensor and an electronic
identification code is stored on the chip – which can be
read out by command. Furthermore, the resolution of
SHT25 can be changed by command (8/12bit up to
12/14bit for RH/T), low battery can be detected and a
checksum helps to improve communication reliability.
With made improvements and the miniaturization of the
sensor the performance-to-price ratio has been improved
– and eventually, any device should benefit from the
cutting edge energy saving operation mode. For testing
SHT25 a new evaluation Kit EK-H4 is available.
Sensor Chip
SHT25 features a generation 4C CMOSens® chip.
Besides the capacitive relative humidity sensor and the
band gap temperature sensor, the chip contains an
amplifier, A/D converter, OTP memory and a digital
processing unit.
1.1
0.2
SHT25
D0AC4
0.8 typ
2.0 typ
1.4
typ
3.0
2.2
Material Contents
While the sensor itself is made of Silicon the sensors‟
housing consists of a plated Cu lead-frame and green
epoxy-based mold compound. The device is fully RoHS
and WEEE compliant, e.g. free of Pb, Cd and Hg.
Additional Information and Evaluation Kits
Additional information such as Application Notes is
available from the web page
www.sensirion.com/sht25.
For more information please contact Sensirion via
info@sensirion.com.
For SHT25 two Evaluation Kits are available: EK-H4, a
four-channel device with Viewer Software, that also serves
for data-logging, and a simple EK-H5 directly connecting
one sensor via USB port to a computer.
Bottom View
NC
VDD
SCL
0.4
0.75
0.3
0.4
1.5
2.4
1.0
1.0
NC
VSS
SDA
Figure 1:
Drawing of SHT25 sensor package, dimensions are
given in mm (1mm = 0.039inch), tolerances are ±0.1mm. The
die pad (center pad) is internally connected to VSS. The NC
pads must be left floating. VSS = GND, SDA = DATA.
Numbering of E/O pads starts at lower right corner (indicated by
notch in die pad) and goes clockwise (compare Table 2).
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Version 2 – December 2011
1/14
Sensor Performance
Relative Humidity
1234
Parameter
Resolution
1
Accuracy
tolerance
2
Repeatability
Hysteresis
Nonlinearity
Response time
3
63%
Operating Range extended
4
Long Term Drift
5
normal
RH (%RH)
± 10
maximal tolerance
±8
±6
±4
±2
±0
0
10
20
30
40
50
60 70 80 90 100
Relative Humidity (%RH)
typical tolerance
Temperature
567
min
typ
0.04
0.7
max
Units
%RH
%RH
%RH
%RH
%RH
%RH
%RH
s
100
< 0.5
%RH
%RH/yr
T (°C)
± 3.0
± 2.5
± 2.0
± 1.5
± 1.0
± 0.5
± 0.0
-40
-20
0
20
40
60
80
100 120
Temperature (°C)
maximal tolerance
typical tolerance
Condition
12 bit
8 bit
typ
max
Parameter
Resolution
1
Accuracy
tolerance
2
Repeatability
Condition
14 bit
12 bit
typ
max
min
typ
0.01
0.04
max
Units
°C
°C
°C
°C
°C
1.8
see Figure 2
0.1
1
<0.1
8
0
0.2
see Figure 3
0.1
-40
5
< 0.04
125
30
Operating Range extended
4
Response Time
7
Long Term Drift
63%
°C
s
°C/yr
Figure 3
Maximal tolerance for temperature sensor in °C.
Figure 2
Typical and maximal tolerance at 25°C for relative
humidity. For extensive information see Users Guide, Sect. 1.2.
Packaging Information
Sensor Type
Packaging
Tape & Reel
Tape & Reel
Quantity
400
1500
Order Number
1-100769-01
1-100768-01
Electrical Specification
Parameter
Conditions min
Supply Voltage, VDD
2.1
sleep mode
-
Supply Current, IDD
6
measuring
200
sleep mode
-
Power Dissipation
6
measuring
0.6
average 8bit
-
Heater
Communication
VDD = 3.0 V
typ
3.0
0.15
300
0.5
0.9
3.2
max Units
3.6
V
0.4
µA
330 µA
1.2 µW
1.0 mW
-
µW
SHT25
5.5mW, T = + 0.5-1.5°C
digital 2-wire interface, I
2
C protocol
This datasheet is subject to change and may be amended
without prior notice.
Table 1
Electrical specification. For absolute maximum
values see Section 4.1 of Users Guide.
1
Default measurement resolution is 14bit (temperature) / 12bit (humidity). It can
be reduced to 12/8bit, 11/11bit or 13/10bit by command to user register.
2
Accuracies are tested at Outgoing Quality Control at 25°C and 3.0V. Values
exclude hysteresis and long term drift and are applicable to non-condensing
environments only.
3
Time for achieving 63% of a step function, valid at 25°C and 1m/s airflow.
4
Normal operating range: 0-80%RH, beyond this limit sensor may read a
reversible offset with slow kinetics (+3%RH after 60h at humidity >80%RH). For
more details please see Section 1.1 of the Users Guide.
5
Value may be higher in environments with vaporized solvents, out-gassing
tapes, adhesives, packaging materials, etc. For more details please refer to
Handling Instructions.
6
Min and max values of Supply Current and Power Dissipation are based on
fixed VDD = 3.0V and T<60°C. The average value is based on one 8bit
measurement per second.
7
Response time depends on heat conductivity of sensor substrate.
www.sensirion.com
Version 2 – December 2011
2/14
Users Guide SHT25
1 Extended Specification
For details on how Sensirion is specifying and testing
accuracy performance please consult Application Note
“Statement on Sensor Specification”.
1.1 Operating Range
The sensor works stable within recommended Normal
Range – see Figure 4. Long term exposure to conditions
outside Normal Range, especially at humidity >80%RH,
may temporarily offset the RH signal (+3%RH after 60h).
After return into the Normal Range it will slowly return
towards calibration state by itself. See Section 2.3
“Reconditioning Procedure” for eliminating the offset.
Prolonged exposure to extreme conditions may accelerate
ageing.
Relative Humidity (%)
100
80
60
40
20
0
-40
-20
0
20
40
60
80
100 120
Temperature (°C)
Please note that above values are maximal tolerances (not
including hysteresis) against a high precision reference
such as a dew point mirror.
1.3 Electrical Specification
Current consumption as given in Table 1 is dependent on
temperature and supply voltage VDD. For estimations on
energy consumption of the sensor Figures 6 and 7 may be
consulted. Please note that values given in these Figures
are of typical nature and the variance is considerable.
8
7
6
5
4
3
2
1
0
0
20
40
60
80
100
120
Temperature (°C)
Normal
Range
Max.
Range
Figure 6
Dependency of supply current (sleep mode) versus
temperature at VDD = 3.0V. Please note the variance of the
displayed data may exceed ±25%.
20
18
16
14
12
10
8
6
2.1
2.3
2.5
2.7
2.9
3.1
3.3
3.5
Supply Voltage (VDD)
Figure 4
Operating Conditions
1.2 RH accuracy at various temperatures
Maximal tolerance for RH accuracy at 25°C is defined in
Figure 2. For other temperatures maximal tolerance has
been evaluated to be within limits displayed in Figure 5.
100
90
80
±5
±5
±5
±5
±4
±4
±4
±4
±4
±4
±4
±4
±4
±4
±4
±4
±4
±5
±8
±8
±12
±5
±5
±5
±4
±4
±4
±4
±4
±3
±2
±2
±2
±2
±3
±3
±4
±4
±4
±5
±8
±12
±5
±5
±4
±4
±4
±4
±4
±3
±3
±2
±2
±2
±2
±3
±3
±3
±4
±4
±5
±8
±12
±5
±4
±3
±3
±3
±3
±3
±3
±2
±2
±2
±2
±2
±2
±2
±2
±3
±3
±4
±6
±8
±5
±4
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±3
±5
±5
±4
±3
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±3
±4
±5
±4
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±2
±3
±5
±5
±5
±4
±3
±3
±3
±3
±3
±2
±2
±2
±2
±2
±2
±2
±2
±2
±3
±3
±4
±5
±5
±5
±4
±3
±3
±3
±3
±3
±3
±2
±2
±2
±2
±2
±2
±2
±2
±3
±3
±4
±5
±6
±5
±4
±3
±3
±3
±3
±3
±3
±2
±2
±2
±2
±2
±2
±2
±2
±3
±3
±4
±5
±6
±5
±4
±3
±3
±3
±3
±3
±3
±2
±2
±2
±2
±2
±2
±2
±2
±3
±3
±4
±5
±6
±5
±4
±4
±4
±3
±3
±3
±3
±2
±2
±2
±2
±2
±2
±2
±2
±3
±3
±4
±5
±6
±5
±4
±4
±4
±3
±3
±3
±3
±2
±2
±2
±2
±2
±2
±2
±2
±3
±4
±4
±5
±6
±5
±5
±4
±4
±4
±3
±3
±3
±3
±3
±3
±3
±3
±3
±3
±3
±3
±4
±4
±5
±8
±6
±5
±5
±5
±4
±4
±4
±4
±3
±3
±3
±3
±3
±3
±3
±3
±3
±4
±5
±6
±10
±8
±6
±6
±6
±5
±5
±5
±5
±4
±4
±4
±4
±4
±4
±4
±4
±4
±4
±6
±8
±12
±10
±8
±8
±8
±6
±6
±6
±6
±5
±5
±5
±4
±4
±4
±4
±4
±4
±5
±8
±10
±12
Relative Humidity (%)
70
60
50
40
30
20
10
0
Figure 7
Typical dependency of supply current (sleep mode)
versus supply voltage at 25°C. Please note the variance of the
displayed data may exceed ±25%.
0
10
20
30
40
50
60
70
80
Temperature (°C)
Figure 5
Maximal tolerance of relative humidity measurements
given in %RH for temperatures 0 – 80°C
.
www.sensirion.com
Version 2 – December 2011
Supply Current IDD (nA)
Supply Current IDD (μA)
3/14
Datasheet SHT25
2 Application Information
2.1 Soldering Instructions
The
DFN’s die pad
(centre pad) and
perimeter I/O pads
are fabricated from a planar copper lead-frame by over-
molding leaving the die pad and I/O pads exposed for
mechanical and electrical connection. Both the I/O pads
and die pad should be soldered to the PCB. In order to
prevent oxidation and optimize soldering, the bottom side
of the sensor pads is plated with Ni/Pd/Au.
On the PCB the
I/O lands
8
should be 0.2mm longer than
the package I/O pads. Inward corners may be rounded to
match the I/O pad shape. The I/O land width should match
the DFN-package I/O-pads width 1:1 and the land for the
die pad should match 1:1 with the DFN package – see
Figure 8.
The
solder mask
9
design
for the land pattern preferably is
of type Non-Solder Mask Defined (NSMD) with solder
mask openings larger than metal pads. For NSMD pads,
the solder mask opening should be about 120μm to
150μm larger than the pad size, providing a 60μm to 75μm
design clearance between the copper pad and solder
mask. Rounded portions of package pads should have a
matching rounded solder mask-opening shape to minimize
the risk of solder bridging. For the actual pad dimensions,
each pad on the PCB should have its own solder mask
opening with a web of solder mask between adjacent
pads.
0.2
0.4
0.3
centered on the thermal land area. It can also be split in
two openings.
Due to the low mounted height of the DFN, “no clean”
type 3 solder paste
10
is recommended as well as Nitrogen
purge during reflow.
T
P
t
P
Temperature
T
L
T
S
(max)
t
L
preheating
critical zone
Time
Figure 9
Soldering profile according to JEDEC standard. T
P
<=
260°C and t
P
< 30sec for Pb-free assembly. T
L
< 220°C and t
L
<
150sec. Ramp-up/down speeds shall be < 5°C/sec.
It is important to note that the diced edge or side faces of
the I/O pads may oxidise over time, therefore a solder fillet
may or may not form. Hence there is no guarantee for
solder joint fillet heights of any kind.
For soldering SHT2x, standard
reflow soldering
ovens may
be used. The sensor is qualified to withstand soldering
profile according to IPC/JEDEC J-STD-020 with peak
temperatures at 260°C during up to 30sec for Pb-free
assembly in IR/Convection reflow ovens (see Figure 9).
For manual soldering contact time must be limited to 5
seconds at up to 350°C
11
.
IMPORTANT: After soldering, the devices should be
stored at >75%RH for at least 12h to allow the sensor
element to re-hydrate. Otherwise the sensor may read an
offset that slowly disappears if exposed to ambient
conditions. Alternatively the re-hydration process may be
performed at ambient conditions (>40%RH) during more
than 5 days.
In no case, neither after manual nor reflow soldering, a
board wash shall be applied. Therefore, and as mentioned
above, it is strongly recommended to use “no-clean” solder
paste. In case of applications with exposure of the sensor
to corrosive gases or condensed water (i.e. environments
with high relative humidity) the soldering pads shall be
sealed (e.g. conformal coating) to prevent loose contacts
or short cuts.
2.2 Storage Conditions and Handling Instructions
Moisture Sensitivity Level (MSL) is 1, according to
IPC/JEDEC J-STD-020. At the same time, it is
10
0.75
2.4
1.0
1.0
Figure 8
Recommended metal land pattern for SHT2x. Values
in mm. Die pad (centre pad) and NC pads shall be left floating.
The outer dotted line represents the outer dimension of the DFN
package.
For
solder paste printing
a laser-cut, stainless steel stencil
with electro-polished trapezoidal walls and with 0.125mm
stencil thickness is recommended. For the I/O pads the
stencil apertures should be 0.1mm longer than PCB pads
and positioned with 0.1mm offset away from the centre of
the package. The die pad aperture should cover about 70
– 90% of the pad area – say up to 1.4mm x 2.3mm
8
The land pattern is understood to be the metal layer on the PCB, onto which
the DFN pads are soldered to.
9
The solder mask is understood to be the insulating layer on top of the PCB
covering the connecting lines.
0.2
≤1.4
≤2.3
1.5
0.4
Solder types are related to the solder particle size in the paste: Type 3 covers
the size range of 25 – 45 µm (powder type 42).
11
260°C = 500°F, 350°C = 662°F
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Version 2 – December 2011
4/14
Datasheet SHT25
recommended to further process the sensors within 1 year
after date of delivery.
It is of great importance to understand that a humidity
sensor is not a normal electronic component and needs to
be handled with care. Chemical vapors at high
concentration in combination with long exposure times
may offset the sensor reading.
For this reason it is recommended to store the sensors in
original packaging including the sealed ESD bag at
following conditions: Temperature shall be in the range of
10°C – 50°C and humidity at 20 – 60%RH (sensors that
are not stored in ESD bags). For sensors that have been
removed from the original packaging we recommend to
store them in ESD bags made of metal-in PE-HD
12
.
In manufacturing and transport the sensors shall be
prevented of high concentration of chemical solvents and
long exposure times. Out-gassing of glues, adhesive tapes
and stickers or out-gassing packaging material such as
bubble foils, foams, etc. shall be avoided. Manufacturing
area shall be well ventilated.
For more detailed information please consult the
document
“Handling Instructions”
or contact Sensirion.
2.3 Reconditioning Procedure
As stated above extreme conditions or exposure to solvent
vapors may offset the sensor. The following reconditioning
procedure may bring the sensor back to calibration state:
Baking:
Re-Hydration:
100 – 105°C at < 5%RH for 10h
20 – 30°C at ~ 75%RH for 12h
13
.
10% of the time – e.g. maximum two measurements per
second at 12bit accuracy shall be made.
Figure 10
Top view of example of mounted SHT2x with slits
milled into PCB to minimize heat transfer.
2.5 Light
The SHT2x is not light sensitive. Prolonged direct
exposure to sunshine or strong UV radiation may age the
sensor.
2.6 Materials Used for Sealing / Mounting
Many materials absorb humidity and will act as a buffer
increasing response times and hysteresis. Materials in the
vicinity of the sensor must therefore be carefully chosen.
Recommended materials are: Any metals, LCP, POM
(Delrin), PTFE (Teflon), PEEK, PP, PB, PPS, PSU, PVDF,
PVF.
For sealing and gluing (use sparingly): Use high filled
epoxy for electronic packaging (e.g. glob top, underfill),
and Silicone. Out-gassing of these materials may also
contaminate the sensor (see Section 2.2). Therefore try to
add the sensor as a last manufacturing step to the
assembly, store the assembly well ventilated after
manufacturing or bake at >50°C for 24h to outgas
contaminants before packing.
2.7 Wiring Considerations and Signal Integrity
Carrying the SCL and SDA signal parallel and in close
proximity (e.g. in wires) for more than 10cm may result in
cross talk and loss of communication. This may be
resolved by routing VDD and/or VSS between the two
SDA signals and/or using shielded cables. Furthermore,
slowing down SCL frequency will possibly improve signal
integrity. Power supply pins (VDD, VSS) must be
decoupled with a 100nF capacitor – see next Section.
2.4 Temperature Effects
Relative humidity reading strongly depends on
temperature. Therefore, it is essential to keep humidity
sensors at the same temperature as the air of which the
relative humidity is to be measured. In case of testing or
qualification the reference sensor and test sensor must
show equal temperature to allow for comparing humidity
readings.
If the sensor shares a PCB with electronic components
that produce heat it should be mounted in a way that
prevents heat transfer or keeps it as low as possible.
Measures to reduce heat transfer can be ventilation,
reduction of copper layers between the sensor and the
rest of the PCB or milling a slit into the PCB around the
sensor – see Figure 10.
Furthermore, there are self-heating effects in case the
measurement frequency is too high. To keep self heating
below 0.1°C, SHT2x should not be active for more than
12
For example, 3M antistatic bag, product “1910” with zipper.
13
75%RH can conveniently be generated with saturated NaCl solution.
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Version 2 – December 2011
5/14
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