U.S. patent application number 16/737288 was filed with the patent office on 2020-07-30 for ceramic substrate component/assembly with raised thermal metal pad, and method for fabricating the component.
This patent application is currently assigned to ICP Technology Co., Ltd.. The applicant listed for this patent is ICP Technology Co., Ltd. Industrial Technology Research Institute, Hsinchu, (Taiwan). Invention is credited to Hsiao-Ming Chang, Jing-Yao Chang, Tao-Chih Chang, Chen-Cheng-Lung Liao, Chun-Yu Lin, Ho-Chieh Yu.
Application Number | 20200245456 16/737288 |
Document ID | 20200245456 / US20200245456 |
Family ID | 1000004639720 |
Filed Date | 2020-07-30 |
Patent Application | download [pdf] |
United States Patent
Application |
20200245456 |
Kind Code |
A1 |
Yu; Ho-Chieh ; et
al. |
July 30, 2020 |
Ceramic Substrate Component/Assembly with Raised Thermal Metal Pad,
and Method for Fabricating the Component
Abstract
A ceramic substrate component suitable for high-power chips
includes a ceramic substrate body and at least one raised metal
pad. The ceramic substrate body has an upper surface and a lower
surface opposite to the upper surface. The raised metal pad
includes a base portion and a top layer. The base portion, which is
attached to the upper surface of the ceramic substrate body, has a
thickness between 10 and 300 micrometers, and a thermal expansion
coefficient greater than the ceramic substrate body. The top layer
is formed on the base portion and adapted to install a high-power
chip thereon. The top layer extends an area less than the base
portion but greater than the high-power chip, and has a thermal
expansion coefficient greater than the ceramic substrate body. As
such, damages due to thermal stress occurring between the base
portion and the ceramic substrate body can be mitigated.
Inventors: |
Yu; Ho-Chieh; (Taoyuan City,
TW) ; Liao; Chen-Cheng-Lung; (Taoyuan City, TW)
; Lin; Chun-Yu; (Taoyuan City, TW) ; Chang;
Hsiao-Ming; (New Taipei City, TW) ; Chang;
Jing-Yao; (Hsinchu, TW) ; Chang; Tao-Chih;
(Hsinchu, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ICP Technology Co., Ltd.
Industrial Technology Research Institute, Hsinchu,
(Taiwan) |
Taoyuan City
Hsinchu |
|
TW
TW |
|
|
Assignee: |
ICP Technology Co., Ltd.
Industrial Technology Research Institute, Hsinchu,
(Taiwan)
|
Family ID: |
1000004639720 |
Appl. No.: |
16/737288 |
Filed: |
January 8, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05K 1/0306 20130101;
H05K 3/341 20130101; H05K 1/111 20130101; H05K 3/4015 20130101;
H05K 1/0271 20130101; H05K 3/4629 20130101 |
International
Class: |
H05K 1/03 20060101
H05K001/03; H05K 1/11 20060101 H05K001/11; H05K 1/02 20060101
H05K001/02; H05K 3/40 20060101 H05K003/40; H05K 3/34 20060101
H05K003/34; H05K 3/46 20060101 H05K003/46 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 29, 2019 |
TW |
108103286 |
Claims
1. A ceramic substrate component suitable for at least one
high-power chip that produces a lot of heat, comprising: a ceramic
substrate body having an upper surface and a lower surface opposite
to the upper surface; and at least one raised metal pad, which
includes: a base portion attached to the upper surface of the
ceramic substrate body, the base portion having a thickness between
10 and 300 micrometers and having a thermal expansion coefficient
greater than the ceramic substrate body; and a top layer formed on
the base portion and adapted to solder or braze a high-power chip
thereon, the top layer extending an area less than the base portion
but greater than the high-power chip, the top layer having a
thermal expansion coefficient greater than the ceramic substrate
body; whereby damages due to thermal stress occurring between the
base portion and the ceramic substrate body can be mitigated.
2. The ceramic substrate component of claim 1, wherein the base
portion is composed of a first thin layer and a second thin layer,
the first thin layer being attached to the upper surface of the
ceramic substrate body and having a thickness less than 0.5
micrometer, the second thin layer being formed on the first thin
layer and attached to the top layer.
3. The ceramic substrate component of claim 1, wherein the first
thin layer is formed of titanium and copper, while the second thin
layer and the top layer are formed of copper.
4. The ceramic substrate component of claim 1, further comprising a
protective layer formed on an outer surface of the raised metal
pad.
5. A ceramic substrate assembly, comprising: at least one chip that
produces a lot of heat; a ceramic substrate body having an upper
surface and a lower surface opposite to the upper surface; and at
least one raised metal pad, which includes: a base portion attached
to the upper surface of the ceramic substrate body, the base
portion having a thickness between 10 and 300 micrometers and
having a thermal expansion coefficient greater than the ceramic
substrate body; and a top layer formed on the base portion to
solder or braze the chip thereon, the top layer extending an area
less than the base portion but greater than the chip, the top layer
having a thermal expansion coefficient greater than the ceramic
substrate body; whereby damages due to thermal stress occurring
between the base portion and the ceramic substrate part can be
mitigated.
6. The ceramic substrate assembly of claim 5, wherein the base
portion is composed of a first thin layer and a second thin layer,
the first thin layer being attached to the upper surface of the
ceramic substrate body and having a thickness less than 0.5
micrometer, the second thin layer being formed on the first thin
layer and attached to the top layer.
7. The ceramic substrate assembly of claim 5, further comprising a
protective layer formed on an outer surface of the raised metal
pad.
8. In a method for fabricating a ceramic substrate assembly that
includes a ceramic substrate body having an upper surface and a
lower surface and provided with a raised metal pad suitable for
soldering or brazing at least one high-power chip thereon, the
method comprising: (a) forming a seed layer by sputtering a target
metal onto the upper surface of the ceramic substrate body such
that the seed layer has a thickness less than 1 micrometer; (b)
forming a build-up layer of metal on the seed layer such that the
seed layer and the build-up layer constitute a base portion having
a thickness between 10 and 300 micrometers and having a thermal
expansion coefficient greater than the ceramic substrate body, so
that damages due to thermal stress occurring between the base
portion and the ceramic substrate body can be mitigated; and (c)
forming a top layer of metal on the base portion to extend an area
less than the base portion such that the top layer and the base
portion constituting the raised metal pad, the top layer having a
thermal expansion coefficient greater than the ceramic substrate
body.
9. The method of claim 8, further comprising: (d) coating an outer
surface of combination of the base portion and the top layer with a
protective layer.
10. The method of claim 8, further comprising: (d) fixing the chip
onto the top layer and connecting metal wires between bond pads of
the chip and corresponding metal pads on the ceramic substrate
body; and (e) performing a sealing process over the chip and the
metal wires on the ceramic substrate body.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a ceramic substrate and,
more particularly, to a ceramic substrate component/assembly, and a
method for fabricating the component.
BACKGROUND OF THE INVENTION
[0002] Compared with traditional substrates for circuit boards,
ceramic substrates are excellent in heat dissipation, temperature
resistance, reliability, and capable of being made into a thin,
small-sized circuit board, and thus they are suitable for
high-power chips or dies in electronic products. Both DBC (direct
bounded copper) and DBA (direct bounded aluminum) substrates, made
of aluminum oxide (Al.sub.2O.sub.3), are the most commonly used
ceramic substrates, wherein the thickness of copper or aluminum
layer is generally between 200 and 300 micrometers; when the
thickness of copper or aluminum layer is greater than 300
micrometers, because the substrates are easy to suffer interfacial
breaks.
[0003] With increasing power of chips or dies, the electrical
circuit, including pads, traces and conductive layers, on a ceramic
substrate need to be thickened. Generally, there is a significant
difference between the thermal expansion coefficients of a metal
layer and a ceramic substrate. For example, the linear thermal
expansion coefficients of copper and aluminum are about 16.5 and 23
ppm/K (at 20 degree C.) respectively, while the liner thermal
expansion coefficients of aluminum oxide, aluminum nitride, silicon
nitride are about 7, 4.5, 3.5 ppm/K (at 20 degree C.) respectively.
The significant difference of thermal expansion coefficients often
causes thermal stress at the interface of the circuit layer and the
substrate. Under these circumstances, the circuit board easily
suffers interfacial breaks, bending or deformation.
[0004] To alleviate the problem of existing circuit boards, a
technical solution is provided in the present invention, which
employs at least one raised or thickened pad of a metal circuit
layer on a ceramic substrate for installing a high-power chip, so
that most of the temperature difference between the chip and the
ceramic substrate is applied across the thickened pad, so that the
temperature difference per unit height can be reduced, and thus the
thermal stress occurring at the interface between the metal circuit
layer and the substrate can be mitigated. Also, the pad can be
configured with various thicknesses according to customers'
demands.
SUMMARY OF THE INVENTION
[0005] One object of the present invention is to provide a ceramic
substrate component, which includes a ceramic substrate body
provided thereon with a metal circuit layer containing a raised
thermal metal pad composed of a top layer and a thinner base
portion, wherein the top layer has an area less than the thinner
base portion, so that breaks caused at the interface between the
metal circuit layer and the ceramic substrate body can be
mitigated.
[0006] Another object of the present invention is to provide a
ceramic substrate component with a raised thermal metal pad so that
the component is suitable for installing a high-power chip or
die.
[0007] A further object of the present invention is to provide a
ceramic substrate assembly, which includes a high-power chip or die
installed on a ceramic substrate component, which allows the heat
produced by the chip to be dissipated properly.
[0008] A still further object of the present invention is to
provide a method for fabricating a ceramic substrate assembly,
whereby a high-power chip can be installed onto a ceramic substrate
body so that interfacial damages between pads and the ceramic
substrate body can be mitigated while the chips works.
[0009] The ceramic substrate component is adapted for installing
thereon at least one chip that produces a lot of heat, which
generally comprises a ceramic substrate body and at least one
raised metal pad. The ceramic substrate body has an upper surface
and a lower surface opposite to the upper surface. The raised metal
pad includes a base portion and a top layer. The base portion,
which is attached to the upper surface of the ceramic substrate
body, has a thickness between 10 and 300 micrometers and has a
thermal expansion coefficient greater than the ceramic substrate
body. The top layer, which is formed on the base portion and
adapted to solder or braze a high-power chip thereon, extends an
area less than the base portion but greater than the chip. The top
layer has a thermal expansion coefficient greater than the ceramic
substrate body. As such, damages due to thermal stress occurring at
the interface between the base portion and the ceramic substrate
body can be mitigated.
[0010] The ceramic substrate assembly is obtained by installing a
high-power chip onto the ceramic substrate component. Accordingly,
the ceramic substrate assembly comprises at least one chip that
produces a lot heat, a ceramic substrate body, and at least one
raised metal pad. The ceramic substrate body has an upper surface
and a lower surface opposite to the upper surface. The raised metal
pad includes a base portion and a top layer. The base portion,
which is attached to the upper surface of the ceramic substrate
body, has a thickness between 10 and 300 micrometers and has a
thermal expansion coefficient greater than the ceramic substrate
body. The top layer is formed on the base portion, and the chip is
placed on the top layer and soldered or brazed in place. The top
layer extends an area less than the base portion but greater than
the chip, and has a thermal expansion coefficient greater than the
ceramic substrate body. As such, damages due to thermal stress
occurring at the interface between the base portion and the ceramic
substrate body can be mitigated.
[0011] The method for fabricating a ceramic substrate component
that includes a ceramic substrate body having an upper surface and
a lower surface and provided with a raised metal pad for soldering
at least one high-power chip thereon comprises the steps of: (a)
forming a seed layer by sputtering a target metal onto the upper
surface of the ceramic substrate body such that the seed layer has
a thickness less than 1 micrometer; (b) forming a build-up layer of
metal on the seed layer such that the seed layer and the build-up
layer constitute a base portion having a thickness between 10 and
300 micrometers, and having a thermal expansion coefficient greater
than the ceramic substrate body, so as to reduce damages caused by
thermal stress occurring between the base portion and the ceramic
substrate body; and (c) forming a top layer of metal on the base
portion to extend an area less than the base portion such that the
top layer and the base portion constituting the raised metal pad,
the top layer having a thermal expansion coefficient greater than
the ceramic substrate body.
[0012] Compared with conventional technology, the present invention
is featured in a raised thermal metal pad, including a thinner base
portion and a thicker top layer, on a ceramic substrate body,
wherein the base portion has an area greater than the top layer.
Therefore, the temperature difference per unit thickness of the
metal pad can be reduced, while the extensibility of the base
portion can be increased, so that the ceramic substrate body is
suitable for a high-power chip, and damages caused by thermal
stress occurring at the interface of the pad and the ceramic
substrate body can be mitigated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 shows a side view of a first embodiment of a ceramic
substrate component according to the present invention.
[0014] FIG. 2 shows a side view of an embodiment of a ceramic
substrate assembly according the present invention, wherein a
high-power chip is installed on a ceramic substrate component.
[0015] FIGS. 3A through 3K show side views of temporary products
during fabrication of the ceramic substrate assembly according to
the present invention.
[0016] FIG. 4 shows a side view of a second embodiment of the
ceramic substrate component according to the present invention.
[0017] The foregoing and other features and advantages of
illustrated embodiments of the present invention will be more
readily apparent from the following detailed description, which
proceeds with reference to the accompanying drawings.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0018] The foregoing and other technical contents, features and
advantages of the present invention will be illustrated in detail
by way of exemplary embodiments in the following paragraphs with
reference to the accompanying drawings.
[0019] The drawings accompanying with the specification show the
structural features of elements used in the present invention,
which may be depicted in a size or proportion to be easily
understood by those skilled in the art without changing the subject
matter of the present invention.
[0020] FIG. 1 shows a first embodiment of a ceramic substrate
component according to the present invention. The ceramic substrate
component, indicated by reference numeral 10, comprises a ceramic
substrate body 11 and a raised metal pad 12, wherein the ceramic
substrate body 11 has an upper surface 111 and a second surface 112
opposite to the upper surface 111; the raised metal pad 12 includes
a base portion 13 and a top layer 14. The base portion 13 can be
formed by sputtering copper onto the upper surface 111 of the
ceramic substrate body and subsequently performing an
electroplating process to reach a thickness of copper between 10
and 300 micrometers. Since copper has a linear thermal expansion
coefficient of about 17 ppm/K while general ceramic substrates,
such as aluminum oxides, aluminum nitrides or silicon nitrides,
have a thermal expansion coefficient of 4 to 7 ppm/K, the use of
the thinner base portion 13 leads to better extensibility or
ductility. Thereafter, the substrate product can be coated with a
photo-resist (a photo-sensitive material) and then exposed with
proper radiation so that unwanted portion of the photo-resist can
be removed to expose part of the base portion 13, which can be
further electroplated thereon with copper to form the top layer 14
that is thicker and extends an area less than the base portion 13.
On the top layer, a high-power chip can be soldered or brazed. As
such, the thicker top layer can take a significant portion of the
temperature difference existing between the chip and the substrate,
while the extensible base portion 13 can keep contact with the
ceramic substrate body without being damaged caused by thermal
stress.
[0021] The base portion and the top layer can be further processed
by general routines to form a metal circuit according to a design
pattern. The raised metal pad can work as a solder pad or a land
for attachment of an electronic component. Of course, other ways of
providing copper, such as evaporation or electroless plating,
and/or other metals suitable for the base portion and the top layer
can also be used.
[0022] FIG. 2 shows one embodiment of a ceramic substrate assembly
or package according the present invention. In this embodiment, a
high-power chip 25, which can produce a lot of heat, refers to an
IGBT (insulated gate bipolar transistor) device. The high-power
chip 25 can be soldered on the raised metal pad 22 via SMT
(surface-mount technology). As show, the raised metal pad 22
includes a base potion 23 and a top layer 24. The base portion 23
is composed of a first thin layer 232 (seed layer), and a second
thin layer 231 (build-up layer). The first thin layer 232 formed of
titanium/copper and having thickness less than 0.5 micrometer is
firstly attached on the upper surface of the ceramic substrate body
by sputtering technique. The second thin layer 231 can be formed on
the first thin layer 232 by electroplating technique. The top layer
24 can be formed on the second thin layer 231 by electroplating to
reach a thickness suitable for the high-power chip 25 according to
the specification thereof. Generally, the thickness of the top
layer 24 is greater than that of the base portion 23. After the
high-power chip 25 has been fixed onto the top layer 24 by
soldering or brazing, metal wires 26 can be connected between bond
pads (not shown) of the chip 25 and corresponding metal pads 27, so
that the chip 25 can work properly (in FIG. 2, only one metal wire
is shown).
[0023] Due to various advantages, such as high efficiency and fast
switching capability, IGBT devices are often used in electrical
equipment that performs heavy work, such as air conditioners,
refrigerators, stereos, and motor drives. In operation of such
equipment, the IGBT devices can produce a lot of heat. With the
thicker top layer 24, the raised metal pad 22 can take more heat
than ordinary pads. Also, since the thermal expansion coefficients
of the top layer 24 and the second thin layer 231 are approximately
equal, thermal stress resulting from different thermal expansion
coefficients is low, and thus does not cause damages between the
two layers. On the other hand, the base portion 23, composed of the
first thin layer 232 and the second thin layer 231, has a thinner
thickness than the top layer 24 and extends an area greater than
the top layer 24, which leads the base portion 23 to have better
extensibility or ductility than the top layer 24. Even though the
base portion 23 has a different thermal expansion coefficient than
the substrate body 21, the base portion 23 allows to be extended
over the substrate body 21 more freely to reduce the thermal stress
caused by thermal expansion, thus reducing interface breaks.
[0024] FIGS. 3A through 3K show a method for fabricating a ceramic
substrate assembly or package. The method is based on a process the
technique of DPC (direct plating copper), which is superior over
the technique of DBC (direct bonding copper) in designing a stable
substrate assembly. With the DPC technique, the flexibility of
designing a ceramic substrate assembly and the bonding strength
between the metal and the ceramic substrate body can be increased,
while the ratio of gaps existing between the metal and the ceramic
substrate body can be reduced.
[0025] FIG. 3A shows a ceramic substrate body 30 made of Aluminum
Oxide (Al.sub.2O.sub.3) or Aluminum Nitride (AlN). Firstly, the
ceramic substrate body 30 can be drilled to form a through hole 31,
as shown in FIG. 3B. Secondly, the ceramic substrate body 30 can be
sputtered with titanium/copper to form a first thin layer 32
thereon, as shown in FIG. 3C. Thirdly, a first layer 33 of
photo-resist can be applied on the first thin layer 32, as shown in
FIG. 3D, and then the photo-resist can be exposed under a radiation
lamp and then treated with a development process to remove unwanted
photo-resist and thus to form a first remained photo-resist layer
33, as shown in FIG. 3E. Fourthly, the first thin layer 32 can be
electroplated with copper to form a second thin layer 34, as shown
in FIG. 3F, wherein the first and second thin layers 32, 34 will
constitute a base portion of the raised metal pad.
[0026] Fifthly, a second layer 35 of photo resist can be applied on
top of the second thin layer 34 and the first remained photo resist
layer 33, as shown in FIG. 3G Sixthly, the second photo-resist
layer 35 can be exposed under a radiation lamp and then treated
with a development process to remove unwanted photo resist, thus
forming a second remained photo-resist layer and exposing the
second thin layer 34, as shown in FIG. 3H. Seventhly, a top layer
36 of copper can formed on the second thin layer 34 by
electroplating and extends an area less than the second thin layer
34, as shown in FIG. 3I. Eighthly, all of the remained photo resist
can be removed from the ceramic substrate body, and then portions
of the first thin layer 32 (uncovered by the second thin layer 34)
can be etched away, thus obtaining a ceramic substrate component
containing a circuit layer according to a design pattern, as shown
in FIG. 3J. Ninthly, a high-power chip 37 can be installed on to
the ceramic substrate component, wherein the chip's back (ground)
can be soldered or brazed onto the top layer 36 and fixed in place;
a metal wire 38 is soldered or brazed between one bond pad of the
chip (not shown) and a metal pad 39 of the circuit layer, as shown
in FIG. 3K. Finally, a sealing or encapsulation process can be
performed so as to protect the chip and metal wire on the ceramic
substrate component.
[0027] Of course, those skilled in the art can understand that
alternative steps can be performed to fabricate the ceramic
substrate assembly of the present invention. For example, the first
and second thin layers on the ceramic substrate body can be
replaced by a piece of copper foil. Alternatively, the ceramic
substrate body can be electroplated with copper so that an initial
copper layer having a thickness equal to the total thickness of a
top layer and a base portion is formed on the substrate, and then
unwanted portions of the initial copper layer can be removed
through imaging (light exposure), developing and etching process to
obtain a raised metal pad.
[0028] FIG. 4 shows a second embodiment of the ceramic substrate
component, which is the same as the one shown in FIG. 3J except for
the base portion and/or the top layer being coated with a
protective layer 42, which protects the copper of the raised metal
pad 41 and other pads from oxidation, thus improving solderability
and conductivity of the pads. The protective layer 42 can be formed
of gold, silver, palladium, or nickel by using hot gas over a layer
of solder paste containing protective metals (reflow technique),
organic coating technique, or electroless plating technique.
[0029] As a summary, the ceramic substrate component/assembly of
the present invention employs a raised thermal metal pad including
a thicker top layer to take a significant portion of temperature
difference existing between a high-power chip and a ceramic
substrate body, and a thinner base portion under the top layer. The
thickness of the top layer depends on the power or heat generation
of the chip. The base portion, which has an area greater than the
top layer, can be extended more easily than the top layer to reduce
the thermal stress caused by different thermal expansions of the
base portion and the ceramic substrate body, thus reducing
interfacial breaks.
[0030] While the invention has been described with reference to the
preferred embodiments above, it should be recognized that the
preferred embodiments are given for the purpose of illustration
only and are not intended to limit the scope of the present
invention and that various modifications and changes, which will be
apparent to those skilled in the relevant art, may be made without
departing from the scope of the invention.
* * * * *