Datasheet SHT21
Users Guide SHT2x
1 Extended Specifications
2 Application Information
1.1 Operating Range
2.1 Soldering Instructions
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 “Recon-
ditioning Procedure” for eliminating the offset. Prolonged
exposure to extreme conditions may accelerate ageing.
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 lands9 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 6.
100
80
60
Max.
Range
Normal
Range
40
20
0
The solder mask10 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.
-40
-20
0
20
40
60
80
100 120
Temperature (°C)
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 58.
0.4
0.3
±5
±4
100
90
80
70
60
50
40
30
20
10
0
±6
±5
±5
±7
±8
2.4
±4
±6
±3 ±3
±3
±4
±6
±5
±4
±5
±7
1.0
1.0
±5
Figure 6 Recommended metal land pattern for SHT2x. Values
in mm. Die pad (centre pad) and NC pads may be left floating or
be connected to ground. The outer dotted line represents the
outer dimension of the DFN package.
0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Temperature (°C)
Figure 5 Maximal tolerance of relative humidity measurements
given in %RH for temperatures 0 – 80°C.
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
Please note that above values are maximal tolerances (not
including hysteresis) against a high precision reference
such as a dew point mirror. Typical deviations are at
±2%RH where maximal tolerance is ±3%RH and about
half the maximal tolerance at other values.
9
The land pattern is understood to be the metal layer on the PCB, onto which
the DFN pads are soldered to.
8
10
Details on how Sensirion is specifying and testing accuracy performance are
The solder mask is understood to be the insulating layer on top of the PCB
planned to be published on the Sensirion web page.
covering the connecting lines.
www.sensirion.com
Version 1.0 – January 2010
3/12
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