Datasheet

CAPACITIVE HUMIDITY SENSOR KFS140-MSMD
Released 01/2007 Rights reserved for change in technical data! HYGROSENS INSTRUMENTS GmbH Postfach1054 D-79839 Löffingen Tel: [phone] Fax: [phone]
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Soldering paste
The component is suitable for both lead based and
lead free pastes.
If a lead free paste is to be used, then it should be
noted that it has a high silver content and hence is
likely to have a low melting point (generally 217°
C).
The paste should have a low content of fluxing
agent. The processing should be done as per
manufacturer's guidelines. Paste in proper
proportion (Dispenser) must be manually activated
after the assembly (i.e. pre-dried), in order to
evaporate the liquid components.
For example, one of the recommended soldering
pastes is the NoClean Paste OMNIX OM 338 (alloy
of Sn96.5 Ag3 Cu0.5), manufacturer Alpha Metals.
Contact through bonding
In principle, the metallising zones are also suitable
for gold wired bonds. By bonded connection
technique the humidity sensitive layer of the
sensor can face upwards, which brings
advantages with respect to the response
behaviour. The sensor can be adhered on the
backside to the carrier substrate with hot curing
SMD adhesive. Please contact us if you need
further information about this production
technology.
Cleaning
The sensor may be blown off with oil free and
filtered pure air (for drying or removing dust
particles).
A cleaning of the populated circuit board is not
necessary in general, but it is recommended
according to application conditions (for example
high humidity values). The sensor may be cleaned
in Isopropanol at 23°C. Since the dirt materials
accumulate in the cleaning agent, the bath should
be regularly changed. It should be repeatedly
cleaned many times, either in Isopropyl alcohol or
pure water with max. 15 µS conductance.
Subsequently, the circuit board is blown with
cleaned compressed air and dried in oven at 60°C
for 24 hours.
The application of ultrasound is possible, but
however, it is not recommended.
Calibration
The calibration may be done after the process
steps - soldering, cleaning and drying. Between
the cleaning process (followed by drying) and
calibration, there should always be a time gap of at
least 48 hours during which the populated circuit
board should be stored under normal room
conditions so that the residual water content in
carrier substrate can come into an equilibrium
state.
ESD protection
Like most components, the capacitive humidity
sensor KFS 140 should be protected from
electrostatic discharges, since the thin polymer
layer can permanently get damaged.
Mechanical damage
The active sensor surface should not be damaged,
touched or contaminated.
The SMD sensor can be placed from the rear side
of the component with usual Pick & Place tools.
Alternatively, the sensor can also be held at the
outer edge. The sensitive layer side may not be
touched! Through contact with sharp-edged tools
on the layer side, the polymer insulation can get
pierced and the sensor can permanently get
damaged!
During soldering, special care should be taken to
ensure that the fluxing agent or solder does not
reach the active surface.
The sensor should not be subjected to
mechanically rough conditions, for example
bending or touching with sharp edged objects.
Patent rights caution
We would like to inform you as a precaution, that
we take no liability for any patent infringements,
which result from use of protected third party
printed circuit board designs and board layouts.
Specially, the use of edge sealant for hygroscopic
circuit board materials in the vicinity of humidity
sensors is a third party patented item.
Moreover, there is also a third party patent with
respect to improvement of heat conduction
between sensor surface and a nearby temperature
sensor.
The infringement of such and similar layout patents
is to be avoided by suitable design technical
measures, for example, by use of suitable circuit
board materials or good air circulation in the
sensor area. Also the sensor area should be
isolated from rest of the circuit board with the help
of special housing design with respect to humidity
or thermal behaviour.
Individual problem solutions
If you have questions regarding the production
processes, you may please discuss with our
research/development department, contact person,
Mr Friedrich. We would like to share with you, our
experiences from other projects. We will be able to
certainly to help you further regarding your
questions or production technology problems.