Handling Instructions
For SCD4x CO2 Sensors
PrefaceFor taking advantage of the SCD4x outstanding
performance, some precautions must be taken duringstorage, assembly and packaging. Please read thefollowing instructions carefully - preferably during designin phase and before production release of the respectivedevice.

1

ESD protection

Protection against ESD is mandatory.

2

Mechanical handlingAs the SCD4x is an optical system, it must not be
exposed to extreme mechanical forces at any time. Wearclean gloves or finger cots while handling the sensor andavoid touching the white protection membrane.
Furthermore, no excessive force must be applied to theprotection membrane on top of the metal cap. Damage
to the protection membrane such as partial removal or aminor cut will make the sensor irreversibly defective.
Finally, the sensor must not be exposed to strong air
blasts from an air-pistol.
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3

The sensor shall be protected from ESD (ElectrostaticDischarge) and only be handled in ESD protected areas(EPA) under protected and controlled conditions (groundall personnel with wrist-straps, ground all non-insulating
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 protection membrane on top of the metal
cap must not be removed or damaged.
No excessive shear force must be applied to themetal cap.
The sensors in SMD packages are classified as
Moisture Sensitivity Level 3.
Prolonged exposure to high concentrations ofvolatile organic compounds such as solventsshould be avoided.

Exposure to Chemicals

Some solvents might cause the protection membrane topeel off the metal cap which results in an irreversible
defect of the SCD4x sensor. Furthermore, the SCD4xcomprises a best-in-class Sensirion relative humidity(RH) and temperature (T) sensor that must be protectedfrom pollutants. While ambient environments are usually
not critical for the sensor, pollutants are known to occur
in manufacturing environments and may occur duringstorage and by packaging materials. Please carefully
follow the guidelines in this application note to ensurethat the performance of the built-in RH/T sensor is notcompromised. Note that preserved accuracy of the RH/Tsensor is required to ensure precise CO2 readings overthe entire relative humidity and temperature range –even if the RH and T output is not used in the application.
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 thehumidity reading – irreversibly in most of the cases.
Please note that such chemicals are integral part ofepoxies, glues, adhesives, etc. and outgas during baking
and curing. These chemicals are also added asplasticisers into plastics, used for packaging materials,
and do out-gas for some period.
Acids and bases may affect the sensor irreversibly andshall be avoided: HCl, H2SO4, HNO3, NH3 etc. Alsoozone in high concentration or H2O2 have the same
effect and therefore shall be avoided. Please note thatabove examples represent not a complete list of harmful
substances.
The sensor shall not get in contact with cleaning agents(e.g., PCB board wash after soldering). Applying
cleaning agents to the sensor may lead to drift of thereading or complete breakdown of the sensor.

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Ensure good ventilation (fresh air supply) to avoid highconcentrations of volatile chemicals (solvents, e.g.
ethanol, isopropanol, methanol, acetone, cleaning
solutions, detergents…).

4Packing and Storage

The SCD4x is classified as Moisture Sensitivity Level 3(IPC/JEDEC J-STD-020). Therefore, the sensor shouldbe mounted and reflowed within 1 week of exposure toambient room conditions (30° C / 60% RH maximum).

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 colour); bevery careful with bubble foils and foams. Be careful about
stickers present inside the packaging (e.g., on the
housing of the device).

Prior to assembly or use of the sensors it is strongly
recommended to store the sensors in the original sealed
bag with temperatures in the range of 10°C – 50°C.

SCD40 – 600pcs

Do not use polyethylene antistatic bags (light blue,pink or rose colour). Do not use adhesive tapes
inside packaging.

Inspected

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 storing the individual sensors as well
as devices with assembled sensors in antistatic shielded
ESD bags at normal pressure (i.e. bag should not beevacuated). In particular, it is recommended not to use
any adhesive or adhesive tapes to reseal the sensor bag
after opening. The following ESD bags can berecommended (no polluting effect on humidity sensor):
ESD Bag
Manufacturer
Stroebel

Product"Topshield" Bags

Sensors as a component or mounted into the final
product shall not be packaged in outgassing plasticmaterials. Please note that many packaging materials
may be contain additives (plasticizers) which may havea polluting effect on the sensor. Generally speaking, if amaterial emits a strong odour you should not use it.

For guidance on simple and straight-forward testing of
SCD4x CO2 sensors please consult the corresponding“Testing Guide”. Furthermore, the humidity sensor
handling instruction lists some encapsulants andadhesives that do not contaminate the integrated
humidity sensor1.

5

Assembly

Before fixing the assembly process parameters, please
read the datasheet carefully.

5.1

Pick and place process

The SCD4x footprint, landing pads and the tape & reeldimension are illustrated in the SCD4x datasheet. Notethat pins are numbered according to IPC standard withpin 1 having a rounded edge. Subsequent pins arecounted upwards counter-clockwise (top view). On thefront side of the SCD4x, an edge of the membrane
serves as the polarity mark, indicating pin 1.
To avoid damage, the SCD4x should be picked in thecentre of protection membrane with a nozzle that has aplastic contact area (see schematic below). The touch
down force of the nozzle should be tuned to a value suchthat the nozzle leaves no permanent mark on the1 Humidity sensor handling instructions:www.sensirion.com/file/handling_instructions_rht
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membrane (typically < 5 N). Finally, the outer diameterof the nozzle should be smaller than 4.4 mm.

applied to the metal cap or the protection membrane
during rework process.
Do not apply board wash after the sensor is assembled
onto the PCB. Furthermore, be particularly careful whenusing strong cleaning agents (e.g. detergents, alcohols,brominated or fluorinated solvents) during rework
processes as they might compromise the membrane
adherence.

SCD4x P&P nozzle contact area. The edge in theprotection membrane serves as a polarity markindicating the pin 1 mark on the backside of the PCB.

5.2

XXXSensor reflow soldering (SMT)Standard reflow soldering ovens are recommended forthe soldering process. A soldering profile is illustrated in
the SCD4x datasheet. Make sure that maximum
temperatures and exposure times are respected. In case
the PCB passes through multiple solder cycles (as is thecase for e.g. PCBs that are assembled on top andbottom side), the SCD4x must be assembled in the lastsolder cycle. Subsequent manual soldering of other PCB
components (e.g. through-hole soldering) has no impact
as long as the SCD4x is not exposed to temperatureshigher than 200 °C. The sensor shall be mounted into
the device, if possible, after all materials that are used in
the assembly process have completely cured or driedout. Otherwise ensure good ventilation (fresh air supply)in curing ovens and assembly lines. Not respecting theseguidelines can result in non-reversible and / or reversible
change of calibration (i.e. offset of the CO2 signal, which
can be corrected by applying a FRC). See SCD4x
Datasheet 2 and Testing Guide Application Note 3 formore information on recalibration procedure).

Do not apply board wash.

6

Conformal Coating

Active components of the SCD4x are shielded fromenvironmental influences by the metal cap and theprotection membrane. Therefore, conformal coating of
the SCD4x is not necessary for most applications.
If a conformal coating is applied anyways, there aresome important aspects that must be respected toprevent sensor failure or diminished performance.

The SCD4s is not compatible with vapour phase reflow
soldering.

5.3

Rework process

Manual hand soldering / de-soldering of the SCD4x must
only be done with solder equipment that allows precise
temperature control. Temperatures higher than thespecified peak temperature in the SCD4x datasheet canresult in a sensor defect or can compromise SCD4x
sensor performance, even if heat exposure is very local
and limited in time. Furthermore, no force must be

If conformal coating is applied, the top surface of thesensor (protection membrane) must remain free ofcoating.

2 www.sensirion.com/file/datasheet_scd4x

3 www.sensirion.com/file/scd4x_testing_guidewww.sensirion.com

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Most importantly, covering the protection membrane (topof the sensor) with any kind of coating must be avoided.
This is because the membrane must remain permeable
to air molecules to ensure coupling to ambient. Note thata thin layer of conformal coating is already enough tofully block the sensors opening and thus destroying thesensor. Furthermore, the membrane must not beremoved after the coating process.
The SCD4x is not compatible with spray coating and dipcoating. Manual coating with a brush, dispensing andjetting can be used to apply conformal coating on thePCB while ensuring that no coating is applied to themembrane.

7

Application in extreme environment

Some applications require the exposure to harshenvironments. Even though the sensor is uncritical to beused in most cases, some precautions must be taken.
Regarding limits of exposure to extreme humidity andtemperature conditions please consult the SCD4x
datasheet.
If the SCD4x is used in condensing environments, it isrecommended to operate the sensor continuously in thehigh performance mode. The induced temperature offset
reduces risk of condensation inside the optical cavity.
Exposure to volatile organic compounds at highconcentration and long exposure time is critical as this
could result in pollution of the built-in humidity sensor
resulting in offset of RH readings. Inaccurate RH
readings can compromise the CO2 output accuracy due
to the built-in RH-compensation algorithm.
Exposure to acids or bases may be critical too. Etching
substances such as H2O2, NH3, etc. at highconcentrations are critical to the sensor as well. Suchapplication needs to be carefully tested and qualified.

Do not apply spray to unprotected sensor.
Finally, a suitable coating should be selected that does
not contaminate the built-in humidity sensor. The
following table lists conformal coatings which have beentested regarding pollution of the humidity sensor and are
known to be suitable if applied and fully cured undergood ventilation (fresh air supply) and according to therespective datasheet.
Conformal Coatings
Manufacturer
ProductPeters
Elpeguard SL 1301 ECO-FLZ
Dow Corning
1-2577 Low Voc Conformal Coating
Electrolube
AFA (Aromatic Free Acrylic ConformalCoating)Disclaimer
The above given restrictions, recommendations,materials, etc. do not cover all possible cases and items.
The material recommendations are given regarding topollution of the built-in humidity sensor and assume
optimal processing for avoiding VOCs. The materials
were not tested regarding other properties like reliability,performance, usability or mechanical properties. The
material recommendations have been compiled with ourbest knowledge at the time of writing. Manufacturers maychange the compounds without notice, which can lead to
reduced Sensor performance due to outgassing.
This document is not to be considered complete and issubjected to changes without prior notice.

Revision History
DateJanuary 2021

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1Page(s)AllChanges
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Important Notices
Warning, Personal Injury
Do not use this product as safety or emergency stop devices or in any other application where failure of the product could resultin personal injury. Do not use this product for applications other than its intended and authorized use. Before installing,handling, using or servicing this product, please consult the data sheet and application notes. Failure to comply with these
instructions could result in death or serious injury.
If the Buyer shall purchase or use SENSIRION products for any unintended or unauthorized application, Buyer shall defend, indemnify andhold harmless SENSIRION and its officers, employees, subsidiaries, affiliates and distributors against all claims, costs, damages andexpenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such
unintended or unauthorized use, even if SENSIRION shall be allegedly negligent with respect to the design or the manufacture of theproduct.
ESD Precautions
The inherent design of this component causes it to be sensitive to electrostatic discharge (ESD). To prevent ESD-induced damage and/ordegradation, take customary and statutory ESD precautions when handling this product.
See application note “ESD, Latchup and EMC” for more information.
Warranty
SENSIRION warrants solely to the original purchaser of this product for a period of 12 months (one year) from the date of delivery that thisproduct shall be of the quality, material and workmanship defined in SENSIRION’s published specifications of the product. Within suchperiod, if proven to be defective, SENSIRION shall repair and/or replace this product, in SENSIRION’s discretion, free of charge to theBuyer, provided that:notice in writing describing the defects shall be given to SENSIRION within fourteen (14) days after their appearance;such defects shall be found, to SENSIRION’s reasonable satisfaction, to have arisen from SENSIRION’s faulty design, material, orworkmanship;the defective product shall be returned to SENSIRION’s factory at the Buyer’s expense; andthe warranty period for any repaired or replaced product shall be limited to the unexpired portion of the original period.
This warranty does not apply to any equipment which has not been installed and used within the specifications recommended bySENSIRION for the intended and proper use of the equipment. EXCEPT FOR THE WARRANTIES EXPRESSLY SET FORTH HEREIN,SENSIRION MAKES NO WARRANTIES, EITHER EXPRESS OR IMPLIED, WITH RESPECT TO THE PRODUCT. ANY AND ALL
WARRANTIES, INCLUDING WITHOUT LIMITATION, WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULARPURPOSE, ARE EXPRESSLY EXCLUDED AND DECLINED.
SENSIRION is only liable for defects of this product arising under the conditions of operation provided for in the data sheet and proper useof the goods. SENSIRION explicitly disclaims all warranties, express or implied, for any period during which the goods are operated orstored not in accordance with the technical specifications.
SENSIRION does not assume any liability arising out of any application or use of any product or circuit and specifically disclaims any andall liability, including without limitation consequential or incidental damages. All operating parameters, including without limitation
recommended parameters, must be validated for each customer’s applications by customer’s technical experts. Recommended
parameters can and do vary in different applications.
SENSIRION reserves the right, without further notice, (i) to change the product specifications and/or the information in this document and(ii) to improve reliability, functions and design of this product.
Copyright © 2021, by SENSIRION. CMOSens® is a trademark of Sensirion. All rights reserved

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