Sensirion Humidity Handling Instructions V4

Sensirion Humidity Handling Instructions V4
Handling Instructions
For SHTxx Humidity and Temperature Sensors
Preface
Sensirion SHTxx are relative humidity and temperature
sensors of high quality. For taking advantage of their
outstanding performance some precautions must be
taken during storage, assembly and packaging.
Therefore, please read the following instructions
carefully - preferably during design-in phase and before
production release of the respective device. Special
attention is required regarding the exposure to volatile
organic compounds, i.e. high concentration and long
exposure time to respective gases shall be avoided.
Such conditions are known to occur in manufacturing
environment and/or during storage. Therefore proper
handling and choice of materials are crucial. Applying
sensors in the field in ambient environment is not
critical.
Applicability
critical, pollutants are known to occur in manufacturing
environments and during storage. Please carefully
follow the guidelines in this application note to ensure
that you can benefit of the sensor’s outstanding
performance.
This document is applicable to all Sensirion SHTxx
humidity and temperature sensors.
ESD protection
The sensor shall be protected from ESD (Electrostatic
Discharge) and only be handled in ESD protected areas
(EPA) under protected and controlled conditions
(ground all personnel with wrist-straps, ground all noninsulating and conductive objects, exclude insulating
materials from the EPA, operate only in grounded
conductive floor, etc.). Protect sensor outside the EPA
using ESD protective packaging.
The sensor shall not get in close contact with volatile
chemicals such as solvents or other organic
compounds. Especially high concentration and long
exposure must be avoided. Ketenes, Acetone, Ethanol,
Isopropyl Alcohol, Toluene, etc. are known to cause
drift of the humidity reading – irreversibly in most of the
cases. Please note that such chemicals are integral
part of epoxies, glues, adhesives, etc. and outgas
during baking and curing. These chemicals are also
added as plasticisers into plastics, used for packaging
materials, and do out-gas for some period.
Acids and bases may affect the sensor irreversibly and
shall be avoided: HCl, H2SO4, HNO3, NH3 etc. Also
Ozone in high concentration or H2O2 have the same
effect and therefore shall be avoided. Please note, that
above examples represent no complete list of harmful
substances.
The sensor shall not get in contact with cleaning agents
(e.g. PCB board wash after soldering) or strong air
blasts from an air-pistol (not oil-free air). Applying
cleaning agents to the sensor may lead to drift of the
reading or complete breakdown of the sensor.
Protection against ESD is mandatory.
Exposure to Chemicals
Humidity and Temperature sensors are highly accurate
environmental sensors and as such they are not
ordinary electronic components. The opening in the
package exposes the sensor to the environment and
makes it susceptible to pollutants. While applying
sensors in the field in ambient environment is not
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Ensure good ventilation (fresh air supply) to avoid high
concentrations of volatile chemicals (solvents, e.g.
ethanol, isopropanol, methanol, acetone, cleaning
solutions, detergents…).
Packing and Storage
Prior to assembly or use of the sensors it is strongly
recommended to store the sensors in the original
sealed ESD bag at following conditions: Temperature
shall be in the range of 10°C – 50°C (0 – 125°C for
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SHTxx Handling Instructions
limited time) and humidity at 20 – 60%RH (sensors that
are not stored in ESD bags).
Store sensors in original, unopened ESD bag. Place
additional stickers only on the outside of the ESD
bag.
Once sensors have been removed from the original
ESD bag we recommend to store the individual sensors
as well as devices with assembled sensors in metal-in
antistatic shielded ESD bags. In particular, it is
recommended not to use any adhesive or adhesive
tapes to reseal the sensor bag after opening. Therefore
reclosable bags with zipper are preferred.
For a recommendation on specific ESD bags please
contact Sensirion.
Sensors as a component or mounted into the final
product shall not be packaged in outgassing plastic
materials which could cause sensor pollution. Besides
metal-In antistatic shielded ESD bags, paper or
cardboards based packaging, deep drawn plastic trays
(PE, PET, PP) may be considered. Do not use antistatic
polyethylene bags (light blue, pink or rose color); be
very careful with bubble foils and foams.
Be careful about stickers present inside the packing
(e.g. on the housing of the device). Sticker size should
be kept to a minimum, and the sticky side shall fully
adhere onto a surface.
Please note that many packaging materials may be
provided with additives (plasticizers) which may have a
polluting effect on the sensor. Generally speaking, if a
material emits a strong odor you should not use it.
Additives may also be added to materials which are
listed for recommended use. For high safety, device
housing and shipment packaging must be qualified.
Such a qualification test may contain exposure of the
final device with sensor in its shipment packaging to
temperature ≥65°C for at least 168 hours. (If shipping
or storage conditions are expected to be harsh, the
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qualification test conditions for the packing material
have to be customized.) The sensor reading then shall
show no changed deviation against a reference
compared to same measurements before the exposure.
Do not use polyethylene antistatic bags (light blue,
pink or rose color). Do not use adhesive tapes
inside packaging.
For guidance on simple and straight-forward testing of
humidity sensors please consult the Testing Guide for
humidity sensors.
Assembly
Sensors in SMT packages are classified as Moisture
Sensitivity Level 1 (IPC/JEDEC J-STD-020). It is
recommended to process the sensors within 1 year
after date of delivery.
Before developing the assembly process please read
the User’s Guide of the Datasheets carefully. In the
following, crucial items are underlined plus additional
items are given:
For soldering please read carefully the corresponding
Section in the User’s Guide of respective Datasheet.
Make sure that maximum temperatures and exposure
times are respected. In case the PCB passes through
multiple solder cycles (as is the case for e.g. PCB that
are assembled on top and bottom side), it is
recommended to assemble the SHTxx only in the last
solder cycle. This is to reduce risks of sensor pollution.
It is important that “no-clean” solder paste is used and
no board wash is applied once the sensor is assembled
to the PCB.
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SHTxx Handling Instructions
In any case, covering the humidity sensor opening with
any kind of coating must be avoided. Therefore, the top
surface of the sensor should remain free of coating.
The following table lists conformal coatings which have
been tested regarding pollution of the humidity sensor
and are known to be suitable if applied and fully cured
under good ventilation (fresh air supply) and according
to respective datasheet.
Conformal Coatings
Manufacturer
Product
Peters
Elpeguard SL 1301 ECO-FLZ
Dow Corning
1-2577 Low Voc Conformal Coating
XXX
Do not apply board wash.
No mechanical force shall be applied to any part of the
sensor during assembly or usage. Especially, after
soldering no force shall be applied to the sensor cap
(SHT1x) to prevent weakening of the adhesive joint
between cap and PCB.
For application in corrosive environment – such as
condensed water or corrosive gases – it may be
necessary to protect the electronic assembly including
the soldered contacts of the sensor with a passivation.
Such passivation may be achieved by conformal
coating or by applying adhesive.
Low viscose conformal coatings or potting materials
may flow into the inside the sensor cap (SHT1x,
SHT7x), cover the sensor element and thus make the
humidity sensor inoperative. Use only high viscose
conformal coatings or potting materials, or seal the
interface between sensor cap (SHT1x, SHT7x) and
sensor PCB before applying conformal coating. Make
sure that used conformal coating is not outgassing.
Do not apply spray to unprotected sensor.
Whenever using spray coating techniques (e.g. to apply
varnish or conformal coating, etc.) the SHTxx sensor
has to be covered by the adhesive tape to prevent
coating of the humidity sensor opening. The following
table lists adhesive tapes which have been tested
regarding pollution of the humidity sensor and are
known to be suitable.
Adhesive Tapes
Manufacturer
3M
Product
Electrical Tape 92
Do not apply any other adhesive tapes such as Scotch
Tape, Sello Tape, Tesa Film, etc.
If conformal coating is applied, the top surface of
the sensor must remain free of coating.
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SHTxx Handling Instructions
PUR (Polyutherane) Casting Compounds
Manufacturer
Product
Peters
VU 4457-61
Hot melts may absorb water and thus may have an
impact on the response time of the sensor in the
device. Therefore hot melt shall be applied sparingly.
The sensor shall be mounted into the device, if
possible, after all materials that are used in the
assembly process have completely cured or dried out.
Otherwise ensure good ventilation (fresh air supply) in
curing ovens and assembly lines.
In conjunction with the sensor, use only
recommended Kapton® tape Electrical Tape 92 by
3M™.
Regarding adhesives and encapsulants the material in
the following tables may be used – according to
respective datasheets, applied and fully cured in well
ventilated environment (fresh air supply). Materials and
brands not listed in the following tables may be harmful
and shall be tested carefully before applying.
Epoxy Adhesives
Manufacturer
EPO-TEK
EPO-TEK
EPO-TEK
Lord
Eccobond
Ablebond
Product
H70E/S
T6067
93-86
MD-130
E3503-1
84-3
Prevent any dust or particles from entering the sensor
opening (sensor performance may be affected).
Wear clean gloves or finger cots while handling the
sensor and avoid touching the sensor opening.
Ensure recommendations in this application note are
equally considered during repair and rework of
assemblies containing sensors. During repair and
rework it may be recommendable to cover Kapton tape
(specific recommendation see above).
Be particularly careful when using strong cleaning
agents (e.g. detergents, alcohols, brominated or
fluorinated solvents). Cleaning any part of a product
might lead to high concentration of cleaning agents on
the sensor. Please remove any sensors or devices
containing sensors before cleaning the production area
and tools. Ensure good ventilation (fresh air supply)
and that any solvents have evaporated before resuming
production.
Epoxy Glob Top Encapsulants
Manufacturer
Product
Stycast
50300 / 50400 series
Hysol
EO1061/EO1062
Silicone Adhesives
Manufacturer
Product
RTV
6424 (Momentive)
Dow Corning
732
Silicone Glob Top Encapsulants
Manufacturer
Product
Stycast
S 7503
Instant Adhesives
Manufacturer
Product
Loctite
401
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Prevent sensor from exposure to cleaning agents.
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SHTxx Handling Instructions
Application in extreme environment
Some applications require the exposure of humidity and
temperature sensors to harsh environments. In many of
the cases the sensor is uncritical to be used. However,
some precautions must be taken.
For exposure to extreme conditions with regards to
humidity and temperature please consult the User’s
Guide of respective product. Please make sure that
exposure time of the sensor to maximum range of
operating conditions is limited as given in the User’s
Guide. Exposure to volatile organic compounds at high
concentration and long exposure time is critical not only
in assembly but also in the field. Such application
needs to be carefully tested and qualified.
The material recommendations are given with regard to
pollution of SHTxx sensors and assume optimal
processing for avoiding VOC in process – the materials
were not tested regarding other properties like
reliability, performance, usability or mechanical
properties. The material recommendations have been
compiled with our best knowledge at the time of writing.
Manufacturers may change the compounds without
notice, which can lead to reduced Sensor performance
due to outgassing.
This document is not to be considered complete and is
subject to change without prior notice.
Exposure to acids or bases may be critical, too. In order
to be critical, the concentration must be such that
polymers are attacked. For bases there is a rule of
thumb that pH<9 are uncritical. Etching substances
such as H2O2, NH3, etc. at high concentrations are
critical to the sensor, too.
Corrosive substances at very low concentrations are
not critical to the sensor itself. However, they may
attack the solder contacts. Therefore, the contacts must
be well protected (passivated) in case of an application
to such environment – compare also Section
“Assembly”.
Application of Sensirion humidity and temperature
sensors to harsh environment must be carefully tested
and qualified. Sensirion qualifies its humidity and
temperature sensors to work properly within ambient
clean air – qualification for use in harsh environment is
duty of the user of the sensor.
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 1.
Disclaimer
The above given restrictions, recommendations,
materials, etc. do not cover all possible cases and
items.
1
75%RH can conveniently be generated with saturated NaCl solution.
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SHTxx Handling Instructions
Revision History
Date
29 June 2007
7 January 2009
18 March 2010
28 June 2012
18 November 2013
22. May 2014
Revision
0.1 (Preliminary)
1.0
1.1
2.0
3
4
Changes
Initial revision
Complete rework.
New format, implementation of pictograms.
Moisture Sensitivity Level adapted.
Document partially restructured and clarifications added.
ESD bag recommendation changed, reconditioning procedure added.
Copyright© 2014, SENSIRION.
CMOSens® is a trademark of Sensirion
All rights reserved
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phone: +41 44 927 11 66
info@sensirion.com
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To find your local representative, please visit www.sensirion.com/contact
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