thik film technology0 pages

R&D BULLETIN
THICK FILM TECHNOLOGY
Thick film technology is simply a technique for
applying a layer of material onto a substrate.
Layer thickness can be varied from 5 to several
hundred microns but typically are about 25.
Thick film technology is widely used in the
electronic industry for the preparation of hybrid
circuits.
Thick film layers are applied and processed in
powder form. The layer material is mixed with
polymer and glass binders, used to give the thick
film layer both strength and adhesion to the
substrate and temperature depending electric
properties. A heavy organic solvent is also added
to form a thick film ink of a viscosity suitable for a
screen printing process.
The ink is printed as an image through a mesh
screen onto the substrate, dried to remove most of
the organic medium (100°C-200°C) and fired
(450°-900°C) to form a continuous layer with
specific electrical behaviour and tolerances.
A layer containing Ag/Pd, Ni/Cr, Mo or C powders
printed in the form of a resistive track onto an
insulating substrate has potential applications as a
heating element.
The ink composition governs both the electric
(O/sq and TCR) and mechanical (adhesion, TCE)
behaviour of the thick film layer.
By changing the powder composition, dielectric or
conducting areas can be printed as well.
By selection of the binder material and processing
conditions it is possible to apply several thick film
layers onto many different substrates, including
300 and 400 series stainless steel, aluminium,
ceramics, glass and mica foils.
Printable shapes may be both flat and circular.
Cermet and polymer thick film heating elements
have several attractive properties including thin
section, direct application to the surface to be
heated, rapid response, high power density
support, flexible design and power pattern,
NTC/PTC control integration. Multiple heating
elements and varying power outputs can be
incorporated across a single substrate in order to
get the requested temperature distribution.
Max temperature of operation depends upon the
substrate and the dielectric thickness, ranging
from 200°C up to 600°C.
Different resistor paste formulations fix a wide
range of O/sq and TCR (Temperature Coefficient of
Resistance, in ppm/K) enabling several options in
terms of circuit design and product behaviour.
Pd/Ag
Ni/C r
Mo
C
O/sq
0.1 ..
0.2
0.2 ..
2.0
50 ..
1000
2 .. 200
ppm/K
300 ..
3500
400 ..
600
-400 ..
400
-500 ..
–1000
Depending on the heat transfer conditions the watt
densities on the hot track can be raised up until
100 watt/sqcm.
At the upper limit, in static air conditions, a Thick
Film heater provide a thermal response of about
300°C/sec.
Silver based terminations / pads are suitable for
soldering or mechanical contact.
Solderable pads for electronic component
attachment (SMD) can be built onto the substrate
as well.
All these features make Thick Film heaters a smart
solution for improving appliance performances and
efficiency while reducing the global cost of the host
application.
Applications include tea kettles, waffle irons,
clothes dryers, stove top burners, humidifiers,
water heaters, boilers, thermal print heads, glue
guns, ceiling heating panes, acquarium, fridge
defrosting, deicing or demisting devices, warming
tray, car reversing mirror, evaporators, plate
exchangers, just to list some of them.
Thick Film heaters offer a 2D-profile design that
can be fitted into appliance framework, hydraulic
and mechanical parts.
Due to low thermal mass and excellent heat
transfer, Thick Film heaters have proven to be
energy-efficient heat sources, leading to space,
time, energy and water savings.
Another advantage of Thick Film heaters deals with
quality issues. In fact, due to the heating element
structure, traditional failures due to moisture
adsorption and electrical leakage are avoided.
11/2003 - 07
All the Thick Film elements are designed and tested
to withstand 2000 V dielectric breakdown.
That value is achieved by appropriate insulating
layers depending on substrate properties and
working temperature.
The data presented in this brochure are in accordance with the present state of our knowledge. We reserve the right to change product data within
the scope of technical progress or new developments. The recommendations made in this brochure do not absolve the user from the obligation of
investigating the possibility of infringement of third parties’ rights and, if necessary, clarifying the position. Recommendations for use do not
constitute a warranty, either express or implied, of the fitness or suitability of the product for a particular purpose.