U.S. patent application number 15/770160 was filed with the patent office on 2018-10-25 for sensor element and method for producing a sensor element.
This patent application is currently assigned to EPCOS AG. The applicant listed for this patent is EPCOS AG. Invention is credited to Jan Ihle, Christl Lisa Mead, Anke Weidenfelder.
Application Number | 20180306647 15/770160 |
Document ID | / |
Family ID | 58545722 |
Filed Date | 2018-10-25 |
United States Patent
Application |
20180306647 |
Kind Code |
A1 |
Ihle; Jan ; et al. |
October 25, 2018 |
Sensor Element and Method for Producing a Sensor Element
Abstract
A sensor element and a method for producing a sensor element are
disclosed. In an embodiment the sensor element is configured to be
secured on a printed circuit board by pressure sintering, wherein a
structural form of the sensor element is designed such that an
exposure to pressure of the sensor element during the pressure
sintering is compensated.
Inventors: |
Ihle; Jan; (Raaba-Grambach,
AT) ; Weidenfelder; Anke; (Graz, AT) ; Mead;
Christl Lisa; (St. Martin Island, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EPCOS AG |
Munchen |
|
DE |
|
|
Assignee: |
EPCOS AG
Munchen
DE
|
Family ID: |
58545722 |
Appl. No.: |
15/770160 |
Filed: |
October 18, 2016 |
PCT Filed: |
October 18, 2016 |
PCT NO: |
PCT/EP2016/074966 |
371 Date: |
April 20, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01C 17/283 20130101;
G01K 7/18 20130101; H01C 7/008 20130101; H01C 17/075 20130101; G01K
7/22 20130101; H01C 7/043 20130101; H01C 17/08 20130101; H01C
17/281 20130101; B28B 3/02 20130101; B28B 11/243 20130101; H01C
17/12 20130101; G01K 7/16 20130101 |
International
Class: |
G01K 7/22 20060101
G01K007/22; H01C 17/28 20060101 H01C017/28; H01C 7/04 20060101
H01C007/04; B28B 3/02 20060101 B28B003/02; B28B 11/24 20060101
B28B011/24 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 2, 2015 |
DE |
102015118720.5 |
Jan 25, 2016 |
DE |
102016101247.5 |
Claims
1-14. (canceled)
15. A sensor element for temperature measurement, wherein the
sensor element is configured to be secured on a printed circuit
board by pressure sintering, and wherein a structural form of the
sensor element is designed such that an exposure to pressure of the
sensor element during the pressure sintering is compensated.
16. The sensor element according to claim 15, wherein the sensor
element has at least two electrodes, and wherein the sensor element
is designed such that a compressive loading occurring during the
pressure sintering is dissipated to the printed circuit board in an
intermediate region between the electrodes.
17. The sensor element according to claim 16, wherein the sensor
element has a ceramic main body, wherein the electrodes are
arranged on an outer area of the main body, wherein the main body
has a projection, and wherein the projection is arranged between
the electrodes.
18. The sensor element according to claim 17, wherein the
electrodes is arranged on a common outer area of the sensor
element, and wherein the common outer area represents an underside
of the sensor element.
19. The sensor element according to claim 17, wherein the
projection is designed as a base, and wherein the projection
protrudes between the electrodes out of the outer area of the
sensor element.
20. The sensor element according to claim 17, wherein the
projection forms an integral part of the main body.
21. The sensor element according to claim 16, wherein the sensor
element has a ceramic main body and comprises a ceramic carrier
material, wherein the main body is formed on the carrier material,
wherein the carrier material has a projection, and wherein the
projection is arranged between the electrodes.
22. The sensor element according to claim 21, wherein the
electrodes are arranged on different end faces of the sensor
element.
23. The sensor element according to claim 22, wherein the
electrodes are caps of the end faces.
24. The sensor element according to claim 21, wherein the
projection is designed as a base, and wherein the projection
projects between the electrodes out of an outer area of the sensor
element.
25. The sensor element according to claim 21, wherein the
projection forms an integral part of the carrier material.
26. The sensor element according to claim 15, wherein the sensor
element has a T-shaped structural form.
27. A method for producing a sensor element, the method comprising:
producing NTC powder to form a ceramic main body; pressing the NTC
powder using a pressing mold, wherein the pressing mold is designed
in such a way that the pressed main body has a projection;
sintering the pressed main body; and applying electrodes to an
underside of the main body, the electrodes being separated from one
another by the projection.
28. A method for producing a sensor element, the method comprising:
providing a ceramic carrier material, the carrier material having a
projection; at least partially printing the carrier material with
an NTC paste to form an NTC layer; and applying electrodes on
opposite end faces of the system comprising the NTC layer and the
carrier material, the electrodes being separated from one another
by the projection.
Description
[0001] This patent application is a national phase filing under
section 371 of PCT/EP2016/074966, filed Oct. 18, 2016, which claims
the priority of German patent application 10 2015 118 720.5, filed
Nov. 2, 2015 and German patent application 10 2016 101 247.5, filed
Jan. 25, 2016, each of which is incorporated herein by reference in
its entirety.
TECHNICAL FIELD
[0002] A sensor element is provided. The sensor element may be used
for measuring a temperature. It is, for example, an NTC sensor
element (negative temperature coefficient), that is to say an NTC
resistor. Methods for producing a sensor element are also
provided.
BACKGROUND
[0003] According to the prior art, for monitoring and controlling
temperatures in a wide variety of applications, they are mostly
measured by ceramic negative temperature coefficient thermistors
(NTC), silicon temperature sensors (KTY), platinum temperature
sensors (PTD) or thermocouples (TC). Of these, the NTC thermistors
are most commonly used, because of the low production costs.
Another advantage over thermocouples and metallic resistance
elements, such as, for example, Pt elements, is the significant
negative resistance temperature characteristic.
[0004] For use in power modules, SMD NTC temperature sensors that
are soldered on are mostly used. Also used as an alternative to
this in the case of control modules for low power levels are NTC
chips, which are mounted on the underside by means of Ag sintering,
soldering or adhesive bonding and the upper side of which is
contacted by means of a bonding wire.
[0005] For electrical contacting of the NTC ceramic, metallic
electrodes have to be applied. According to the prior art, for this
purpose thick-film electrodes are applied, mostly from silver or
gold pastes, by means of a screen printing process with subsequent
firing. The silver metallizations are particularly suitable for
Ag-sintered and soldered connections. As a result of the increasing
technological requirements with regard to new reliable ways of
establishing electrical contact in connections, such as bonding and
welding, another electrode is necessary, especially when bonding
with gold or aluminum or copper wires, because a connection to
silver does not have sufficient reliability.
[0006] In the case of gold metallizations, soldered connections
with terminal wires cannot be realized. For reasons of cost, only
thin gold wire is used for making bonded connections. Aluminum
bonding wire connections on gold electrodes do not meet the
reliability requirements.
[0007] At present, the temperature measurement in the case of power
modules is performed by soldered-on SMD NTC sensors. As a result of
the increasing requirements with respect to operating temperature
and reliability, there is the requirement for NTC temperature
sensors that can be applied to the mother board without soldered
mounting and have high long-term stability and also are suitable
for higher operating temperatures.
[0008] Suitable mounting is provided by Ag sintering with finely
dispersed silver pastes, which however is performed under pressure
by applying a load from above. For this purpose, sufficient
mechanical stability of the components in flip-chip mounting is
required, in order that the flexural stresses occurring do not lead
to rupturing and there is no superficial damage (cracks).
Conventional NTC sensor ceramics usually have a flexural strength
that is too low to withstand the loads occurring.
SUMMARY OF THE INVENTION
[0009] Embodiments provide a sensor element that has improved
properties.
[0010] According to one aspect, a sensor element for temperature
measurement is provided. The sensor element may comprise a ceramic
sensor material. The sensor material may be an NTC ceramic. For
example, the ceramic has a perovskite structure. In particular, the
ceramic may be based on the system Y--Ca--Cr--Al--O with various
dopings. Alternatively, the sensor element may comprise a ceramic
with a spinel structure. For example, the ceramic may be based on
the system Ni--Co--Mn--O with various dopings. The sensor element
may be an NTC sensor chip.
[0011] In various embodiments, the sensor element is intended to be
secured on a printed circuit board or a DCB board by means of Ag
pressure sintering. In particular, the sensor element may be
designed to be mounted on the printed circuit board by means of Ag
sintering. A structural form of the sensor element is designed such
that an exposure to pressure of the sensor element during the
pressure sintering is compensated.
[0012] The mechanical stability of the sensor element may be
increased by the structural form according to the invention. In
various embodiments, the pressure sintering of the component is
thereby made possible without inducing any damage such as micro
cracks or the like, or even bringing about a rupturing of the
component. Consequently, a particularly stable sensor element that
can be applied to the printed circuit board without soldered
mounting is provided.
[0013] According to an exemplary embodiment, the sensor element has
at least one electrode. Preferably, the sensor element has two
electrodes. In addition, the sensor element may also have a ceramic
reinforcement or a ceramic carrier. The electrodes are arranged on
the ceramic sensor material.
[0014] In further embodiments, the electrodes are spatially
separated from one another. This means that there is a distance
between the electrodes. For example, ceramic sensor material is
arranged between the electrodes. The sensor element is designed
such that compressive loading occurring during the Ag pressure
sintering is dissipated to the printed circuit board in an
intermediate region between the electrodes. In particular, the
forces acting during the Ag pressure sintering are compensated with
the aid of the intermediate region between the electrodes.
[0015] Consequently, an NTC temperature sensor with electrodes
suitable for Ag sintering is provided, the sensor being formed such
that the compressive loading during the Ag sintering is for the
most part dissipated to the mother board in the intermediate region
of the electrodes and instances of damage due to flexural loading
during mounting are avoided.
[0016] According to an exemplary embodiment, the sensor element has
a T-shaped structural form. In particular, the sensor element has a
portion that corresponds to a horizontal line or bar of a "T".
Furthermore, the sensor element has a portion that corresponds to a
vertical line or bar of a "T". The two portions are undetachably
connected to one another. The two portions are preferably made in
one piece.
[0017] The mechanical stability of the sensor element may be
increased by the T-shaped structural form. The Ag pressure
sintering of the component is thereby made possible without
inducing any damage such as micro cracks or the like, or even
bringing about a rupturing of the component.
[0018] According to an exemplary embodiment, the sensor element has
a ceramic main body. The ceramic main body comprises the ceramic
sensor material. The electrodes are arranged on an outer area of
the main body. The electrodes are preferably arranged on a common
outer area of the sensor element or of the main body. The common
outer area preferably represents an underside of the sensor element
or of the main body.
[0019] In various embodiments the main body has a projection. The
projection forms an integral part of the main body. In other words,
the projection and the main body are formed in one piece. In
particular, the projection comprises ceramic sensor material. The
projection is arranged between the electrodes. The projection forms
an intermediate region between the electrodes.
[0020] The projection may be designed in the form of a base. The
projection represents, for example, the vertical line of a "T",
while the rest of the main body represents the horizontal line or
bar of the "T". The projection protrudes between the electrodes out
of the main area or the underside of the sensor element.
[0021] The forces occurring during the Ag pressure sintering may be
dissipated to the printed circuit board through the projection or
base arranged in the intermediate region between the electrodes.
Damage to the sensor element due to flexural loading can
consequently be prevented.
[0022] According to an exemplary embodiment, the sensor element has
a ceramic main body. The ceramic main body comprises the ceramic
sensor material. The electrodes are arranged on different end faces
of the sensor element. The electrodes are arranged on opposite end
faces. Preferably, the electrodes are applied to the end faces as
caps.
[0023] The sensor element may also comprise a ceramic carrier
material. The main body may be formed on the carrier material.
Preferably, the main body covers an outer area of the carrier
material, for example, an upper side of the carrier material,
completely.
[0024] The carrier material may have a projection. The projection
forms an integral part of the carrier material. In other words, the
carrier material and the projection are formed in one piece. In
particular, the projection comprises ceramic carrier material. The
projection is arranged between the electrodes. The projection forms
an intermediate region between the electrodes. The projection is
designed in the form of a base. The projection projects between the
electrodes out of an outer area of the sensor element.
[0025] As described above, the sensor element may have a T-shaped
structural form. In particular, the sensor element has a projection
or base. The projection or base protrudes from a surface of the
sensor element. The projection or base is preferably formed between
the electrodes. The projection or base may comprise ceramic sensor
material and/or a material of the ceramic reinforcement. The
structural form of the sensor element is modified or designed such
that an exposure to pressure of the sensor element during the
production or mounting process is compensated. Furthermore,
mechanical flexural loading is reduced to a minimum.
[0026] According to one aspect, methods for producing a sensor
element are described. Preferably, the sensor element described
above is produced by the respective method. All of the properties
that are disclosed with reference to the sensor element or the
method are also correspondingly disclosed with reference to the
respective other aspects, and vice versa, even if the respective
property is not explicitly mentioned in the context of the
respective aspect.
[0027] The method has the following steps:
[0028] Producing NTC powder to form a ceramic main body.
[0029] Pressing the NTC powder. For this purpose, a pressing mold
is used. The pressing mold is designed in such a way that the
pressed main body has a projection. The pressing mold is designed
in such a way that the pressed main body has a T-shaped structural
form.
[0030] Sintering the pressed main body.
[0031] Applying electrodes to an underside of the main body. This
may be performed by means of thin-film or thick-film technology.
The electrodes are separated from one another by the
projection.
[0032] According to a further aspect, the method has the following
steps:
[0033] Providing a ceramic carrier material. The carrier material
has a projection.
[0034] At least partially printing the carrier material with an NTC
paste to form an NTC layer. Preferably, a surface of the carrier
material that is opposite from the base is printed with NTC paste.
For example, an upper side of the carrier material is printed with
NTC paste. For example, the projection is arranged on the opposite
side, that is to say the underside of the carrier material.
Alternatively, the projection of the carrier material may also only
be formed after the printing of the carrier material with the NTC
paste.
[0035] Sintering the system comprising the carrier material and the
NTC paste.
[0036] Applying electrodes. The electrodes are arranged on opposite
end faces of the system comprising the NTC layer and the carrier
material. The electrodes are separated from one another by the
projection. In order that an electrical contact is created between
the mounting areas of the carrier ceramic and the NTC layer, the
electrodes are designed as caps over the end faces.
[0037] According to one aspect, a sensor element for temperature
measurement is provided, the sensor element having a T-shaped
structural form, and the structural form of the sensor element
being designed such that an exposure to pressure of the sensor
element during the production process is compensated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] The sensor element and the method are explained in more
detail below on the basis of exemplary embodiments and the
associated figures.
[0039] The drawings described below should not be regarded as true
to scale. Rather, for better representation, individual dimensions
may be shown as increased or reduced in size or even distorted.
[0040] Elements that are the same as one another or perform the
same function are provided with the same designations.
[0041] FIG. 1 shows a sensor element in a first embodiment;
[0042] FIG. 2 shows a sensor element in a further embodiment;
[0043] FIG. 3 shows a sensor element in a further embodiment;
and
[0044] FIG. 4 shows an embodiment of the sensor element from FIG.
3.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0045] FIG. 1 shows a sensor element 1, in particular a sensor
chip. The sensor element 1 is preferably designed for measuring a
temperature. The sensor element 1 has two electrodes 2. The sensor
element 1 comprises a ceramic sensor material. The sensor element 1
has a ceramic main body 7. The main body 7 comprises the ceramic
sensor material.
[0046] The sensor material is an NTC (negative temperature
coefficient) ceramic. For example, the ceramic has a perovskite
structure. In particular, the ceramic may be based on the system
Y--Ca--Cr--Al--O with various dopings. Such a sensor element 1 is
particularly suitable for high-temperature applications.
Alternatively, in particular in the case of lower application
temperatures, the sensor element 1 may comprise a ceramic with a
spinel structure. For example, the ceramic may be based on the
system Ni--Co--Mn--O with various dopings.
[0047] The sensor element 1 is designed to be secured on a printed
circuit board under pressure, for example, by means of Ag
sintering. Ag sintering involving exposure to pressure is not
possible in the case of the conventional SMD NTC sensors and
alternative flip-chip structural forms because of the flexural
loads occurring that exceed the intrinsic strength of the
components. The flexural loading is caused by the component that
lies on the terminal pads on the mother board being pressed from
above. Especially in the case of DCB boards, between the terminal
pads there is a relatively deep trench, which corresponds to the
thickness of the electrode layer on the DCB board and is generally
several 100 .mu.m.
[0048] To compensate for the compressive loads occurring during Ag
sintering, the sensor element 1 from FIG. 1 has a base 3. The
sensor element 1 is designed in a T-shaped form. According to the
exemplary embodiment from FIG. 1, in particular the ceramic main
body 7 is designed in a T-shaped form. In this exemplary
embodiment, the horizontal line of the "T" forms an upper side of
the sensor element 1 or of the main body 7. The vertical line of
the "T" represents the base 3. The base 3 protrudes out of an
underside of the sensor element 1 or main body 7. The base 3 is an
integral part of the main body 7.
[0049] The sensor element 1 with the base 3 may either be produced
directly by pressing with a suitable pressing mold or be cut in a T
shape from a pressed blank or a substrate produced from NTC sheets.
This can be realized by sawing, grinding, laser cutting or other
suitable machining operations.
[0050] The metallization is applied as a thin-film or thick-film
electrode. The electrodes 2 are separated or spatially separated
from one another by the base 3.
[0051] The electrodes 2 are applied on the underside to the right
and left of the base 3, in particular by means of sputtering, vapor
deposition or screen printing. The electrodes 2 are arranged on the
same outer area (here the underside) of the sensor element 1.
[0052] To achieve good adhesive attachment in the Ag pressure
sintering process, an electrode that likewise consists of Ag is of
advantage. However, other electrode materials, such as, for
example, Au, Cu, Al, etc., may also be used, as long as they are
Ag-sinterable or can be processed by some other standard
process.
[0053] The production of thin-film electrodes may be performed by
sputtering or vapor deposition. In this case, in a first embodiment
the base electrode consists of a nickel layer, which may comprise
fractions of vanadium, or in a second embodiment of two layers, the
lower layer comprising chromium or titanium and the second layer
consisting of nickel, which likewise may comprise fractions of
vanadium.
[0054] The base electrode may be protected by a covering layer
consisting of an oxidation-inhibiting metal such as, for example,
silver, gold, copper, aluminum, etc. This covering electrode may
either just serve for protecting the nickel base electrode from
corrosion (oxidation) or else be advantageous or even necessary for
contacting. In the case of a connection by means of Ag sintering
with finely dispersed silver pastes, for example, a silver covering
electrode is indispensable.
[0055] The thickness of the base electrode is less than 10 .mu.m,
advantageously less than 3 .mu.m, ideally less than 0.5 .mu.m. The
thickness of the covering electrode may be up to 1 .mu.m, in
exceptional cases up to 20 .mu.m.
[0056] The production of thick-film electrodes may be performed by
a screen printing process with subsequent firing. The pastes used
may contain Ag or any admixtures.
[0057] The final geometry is produced by a cutting process. In the
case of very closely toleranced resistances, a trimming process may
be performed for setting the resistance at nominal temperature by
partial laser ablation. The contacting of the sensor element 1 with
respect to the DCB board or the printed circuit board or the mother
board may be performed by means of Ag sintering, soldering or
adhesive bonding.
[0058] According to this exemplary embodiment, the sensor element 1
(pressed blank) is produced, for example, in the following way:
[0059] In a first step, NTC powder is produced. This comprises, for
example, initial weighing, wet pre-grinding, drying, screening,
calcining, wet after-grinding and spraying. After that, the
pressing of the granular sprayed material is performed. The
pressing mold is in this case designed such that a T-shaped main
body is created during the pressing.
[0060] The decarburizing of the pressed blank follows in a further
step. After that, the pressed blank is sintered.
[0061] The application of Ni/Ag thin-film electrodes 2 to the
undersides to the right and left of the base 3 is performed by
means of sputtering technology, as described above. The electrodes
2 are separated from one another by the base 3.
[0062] To improve the long-term stability of the ceramic, in a
further step a thin, nonconducting protective layer, which
consists, for example, of ceramics, glasses, plastics or metal
oxides, may be applied over the unmetallized region. This can be
achieved by sputtering, vapor deposition, lithography or printing
and firing.
[0063] After that, the electrical measuring of the resistances of
the individual sensor elements 1 with base 3 at nominal temperature
is performed. For setting the resistance, the metalized substrates
are electrically measured in advance. The geometry of the NTC
sensor chips with base is defined on the basis of the measurement
data obtained in advance. Since the length is fixed, the width
remains as a variable setting parameter.
[0064] In a further step, a trimming of the individual sensor
element 1 with base 3 to the required resistance value is performed
by grinding the full surface area of one side.
[0065] For particularly closely toleranced resistances at nominal
temperature, the resistance of the individual components can be set
by the additional trimming process (also see in this respect FIG.
4). In this case, ceramic material or electrode material is
partially removed, for example, by laser cutting or grinding, in
such a way that the resistance is adapted by changing the
geometry.
[0066] A visual inspection and random control measurement follow in
a final step.
[0067] FIG. 2 shows a reinforced sensor element 1 with base 3. The
construction corresponds substantially to the sensor element 1 from
FIG. 1. However, the sensor element 1 has an additional ceramic
layer 4 on the upper side (the side opposite from the base 3). The
main body 7 is arranged on the ceramic layer 4. In particular, the
ceramic layer 4 covers the upper side of the main body 7 preferably
completely. The ceramic layer 4 serves as mechanical reinforcement
for processes with particularly high stresses. The construction is
realized by pressing granular material or stacked sheets. The NTC
ceramic is pressed either together with the ceramic layer 4 or one
after the other. The production of the sensor element 1 according
to FIG. 2 is otherwise performed as described in connection with
FIG. 1.
[0068] FIG. 3 shows a carrier material 5 with base 6 printed with
sensor material (NTC layers). In this exemplary embodiment, the NTC
layers represent the main body 7.
[0069] The NTC layers are printed onto the ceramic carrier material
5. The carrier material 5 is designed in a T-shaped form. In
particular, the carrier material 5 has the base 6, the base
representing the vertical line of the "T". The base 6 is an
integral part of the carrier material 5.
[0070] The ceramic carrier material 5 consists on the basis of, for
example, Al.sub.2O.sub.3, ZrO.sub.2, ATZ or ZTA materials or MgO.
The carrier material 5 may be brought into an appropriate form
before or after being printed with NTC paste and individually
separated after the sintering, or already take the form of a single
part.
[0071] The electrodes 2 are applied to the end faces or side faces.
In particular, the electrodes 2 are applied as caps. This allows
the contacting of this structural form on the printed circuit board
or mother board or the DCB board. Since the sensor material (the
NTC layer) is not however in direct contact with the pads, the cap
form of the electrodes 2 is required to ensure contacting of the
NTC layer.
[0072] FIG. 4 shows a trimmed NTC sensor on a carrier material 5
with base 6. Sensor material has been removed by the trimming
process for setting the resistance at nominal temperature. The
removal is performed by partial laser ablation, as already
described above.
[0073] According to all of the exemplary embodiments shown in FIGS.
1 to 4, the sensor element 1 has a T-shaped structural form. The
high forces acting on the component during the pressure sintering
are compensated by the structural form chosen, and the mechanical
flexural loading is reduced to a minimum. In particular, the
compressive loading during the Ag sintering is for the most part
dissipated to the mother board in the intermediate region of the
electrodes 2, whereby instances of damage due to flexural loading
during mounting are avoided.
[0074] The use of ceramic carrier materials on the basis of, for
example, Al.sub.2O.sub.3, ZrO.sub.2, ATZ or ZTA materials or MgO
can lead to a further increase in the mechanical stability.
[0075] For use on mother boards or DCB boards, the sensor elements
1 shown in FIGS. 1 to 4 may be sintered onto the conductor tracks.
This may be performed under pressure or without pressure. Mounting
by adhesive bonding or soldering continues to be applicable.
[0076] The description of the subjects specified here is not
restricted to the individual specific embodiments. Rather, the
features of the individual embodiments can--as far as technically
feasible--be combined with one another in any desired manner.
* * * * *