U.S. patent application number 13/314392 was filed with the patent office on 2013-04-25 for method for selective metallization on a ceramic substrate.
This patent application is currently assigned to VIKING TECH CORPORATION. The applicant listed for this patent is Chien-Hung Ho, Shen-Li Hsiao, Shih-Long Wei. Invention is credited to Chien-Hung Ho, Shen-Li Hsiao, Shih-Long Wei.
Application Number | 20130098867 13/314392 |
Document ID | / |
Family ID | 48101634 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130098867 |
Kind Code |
A1 |
Wei; Shih-Long ; et
al. |
April 25, 2013 |
Method for Selective Metallization on a Ceramic Substrate
Abstract
A method of selective metallization on a ceramic substrate
includes selectively forming an active brazing material on a
predetermined area of a surface of a ceramic substrate, attaching
the metal layer to the ceramic substrate with the active brazing
material, performing a brazing process on the active brazing
material, forming an etching stop layer on the metal layer and
performing an etching process, and removing the etching stop layer.
The method can be applied to a severe environment, and the
conchoidal fracture between the ceramic substrate and the metal
layer can also be avoided. The present invention not only
simplifies the process but also improves the product yield.
Inventors: |
Wei; Shih-Long; (Hsinchu
County, TW) ; Hsiao; Shen-Li; (Hsinchu County,
TW) ; Ho; Chien-Hung; (Hsinchu County, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wei; Shih-Long
Hsiao; Shen-Li
Ho; Chien-Hung |
Hsinchu County
Hsinchu County
Hsinchu County |
|
TW
TW
TW |
|
|
Assignee: |
VIKING TECH CORPORATION
Hsinchu Country
TW
|
Family ID: |
48101634 |
Appl. No.: |
13/314392 |
Filed: |
December 8, 2011 |
Current U.S.
Class: |
216/41 |
Current CPC
Class: |
C04B 2237/125 20130101;
C04B 2237/123 20130101; C04B 2237/127 20130101; C04B 2237/366
20130101; C04B 2237/343 20130101; C04B 2237/592 20130101; C04B
37/026 20130101; C04B 2237/365 20130101; C04B 2237/86 20130101;
C04B 2237/406 20130101; C04B 2237/402 20130101; C04B 2237/407
20130101 |
Class at
Publication: |
216/41 |
International
Class: |
C23F 1/00 20060101
C23F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 19, 2011 |
TW |
100137839 |
Claims
1. A method of selective metallization on a ceramic substrate,
comprising: forming an active brazing material on a predetermined
area of a surface of the ceramic substrate; attaching a metal layer
to the surface of the ceramic substrate with the active brazing
material, and performing a brazing process on the active brazing
material; forming an etching stop layer on the predetermined area
of the metal layer and etching the metal layer; and removing the
etching stop layer.
2. The method of claim 1, wherein the active brazing material is
nickel-based brazing material or silver-based brazing material.
3. The method of claim 1, wherein the active brazing material has
an active metal with a specific proportion.
4. The method of claim 1, wherein the active brazing material is
formed on the surface of the ceramic substrate by printing, spray
coating, or lamination.
5. The method of claim 1, wherein the etching stop layer
corresponds in position to the active brazing material on the
surface of the ceramic substrate.
6. The method of claim 1, wherein the metal layer is copper,
aluminum or stainless steel.
7. A method of selective metallization on a ceramic substrate,
comprising: performing a predetermined depth etching on a
predetermined area of a metal layer, so as for forming an etching
area and a reserved area on the metal layer; forming an active
brazing material on the reserved area of the metal layer; attaching
the metal layer with the active brazing material to the ceramic
substrate, and performing a brazing process on the active brazing
material; and etching the metal layer for removing the etching area
of the metal layer.
8. The method of claim 7, wherein the active brazing material is
nickel-based brazing material or silver-based brazing material.
9. The method of claim 7, wherein the active brazing material has
an active metal with a specific proportion.
10. The method of claim 7, wherein the active brazing material is
formed on the metal layer by printing, spray coating, or
lamination.
11. The method of claim 7, wherein the metal layer is copper,
aluminum or stainless steel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to methods for
selective metallization on a ceramic substrate, and, more
particularly, to a method of forming a metal layer within a
selected area of a ceramic substrate by a brazing process.
[0003] 2. Description of Related Art
[0004] Two methods are generally used for selective metallization
on a ceramic substrate. For the metal of copper, one is realized
with selectively etching a copper layer after a direct bonded
copper (DBC) process is performed, and the other is done with
selective copper deposition or by selectively etching a copper
layer after a direct plated copper (DPC) process is performed on
the whole substrate.
[0005] As shown in FIGS. 1A to 1E, cross-sectional views
illustrating a method for the metallization of a ceramic substrate
by using the DBC process according to the prior art are provided.
The method is performed under a high temperature and specific
oxygen content. As shown in FIG. 1A, a copper layer 1 is provided,
and the surface of the copper layer 1 is oxidized to form a cuprous
oxide layer 11. As shown in FIG. 1B, the copper layer 1 and a
ceramic substrate 2 are bonded by Cu--Al--O chemical bonds provided
by a eutectic layer 12 which is composed of the cuprous oxide layer
11 after cooling. A ceramic substrate 5 directly bonded with copper
is thus formed. As shown in FIGS. 1C and 1D, an etching resist 3 is
formed on the ceramic substrate 5, and a portion of the copper
layer 1 that is not covered by the etching resist layer 3 is etched
and removed. As shown in FIG. 1E, the etching resist 3 is removed,
so as to complete the selective metallization process of the
ceramic substrate 5.
[0006] However, the DBC process encounters problems. For example,
since the desired eutectic temperature for the bonding of copper
and ceramic is very close to the melting point of the copper
itself, the DBC process must work in a very narrow temperature
range, in order to prevent the copper from melting when the ceramic
substrate is bonded to the copper layer. Therefore, in a batch
production process it is difficult to keep the furnace in
inconsistent atmosphere and temperature at different positions,
which results in a yield issue on the product. Currently, the
metallized ceramic substrate with eutectic bonding is made of
aluminum oxide that has low thermal conductivity. This kind of
ceramic substrate is rarely made of aluminum nitride (AlN) or
silicon carbide (SiC) that have high thermal conductivity because
it is difficult to be bonded with the copper layer, due to the lack
of wettability or capability of forming Cu--Al--O bonds. Thus, the
application of the DBC metallized ceramic substrate for high
thermal conductivity or high heat dissipation is extremely
restricted. In addition, since the DBC process adopts Cu--Cu2O
eutectic bonding, such that no other metal material can be bonded
with the ceramic substrate except copper. On the other hand, the
conchoidal fracture exists between the ceramic substrate and the
copper layer in the conventional DBC process, which is not along
the lattice and is irregularly broken, mainly due to the internal
stress caused by the mismatch thermal expansion, and affects the
reliability and lifetime indirectly.
[0007] Referring to FIGS. 2A to 2E, cross-sectional views
illustrating a method of fabricating a copper plating substrate
according to the prior art are provided. The method of performing
selective metallization with DPC is as follows. As shown in FIG.
2A, an adhesion layer/seed layer 4 is formed on the ceramic
substrate 2. As shown in FIG. 2B, a resist layer 6 for the
prevention of metal deposition is formed on the adhesion layer/seed
layer 4. A metal layer 10 is deposited directly on the portion of
the adhesion layer/seed layer 4 that is not covered by the resist
layer 6 by a copper plating process, as shown in FIG. 2C. As shown
in FIGS. 2D and 2E, the resist layer 6 is removed, and a surface
micro-etching process is performed to complete the selective
metallization of the ceramic substrate.
[0008] FIGS. 3A to 3E are cross-sectional views illustrating
another method of fabricating a copper plating substrate according
to the prior art. As shown in FIG. 3A, an adhesion layer/seed layer
4 is formed on the ceramic substrate 2. As shown in FIG. 3B, a
copper plating process is performed on the surface of the ceramic
substrate 2, and a copper layer 1 is formed on the adhesion
layer/seed layer 4 to generate the DPC substrates 5. As shown in
FIG. 3C, an etching stop layer 3 is formed on the DPC 5. As shown
in FIG. 3D, a portion of the copper layer 6 and the adhesion
layer/seed layer 4 that is not covered by the etching stop layer 3
is etched and removed. Finally, the etching stop layer 3 is removed
and the selective metallization of the ceramic substrate is formed,
as shown in FIG. 3E.
[0009] However, the disadvantages exist in performing the selective
metallization in the DPC. For example, the copper layer and the
ceramic substrate are bonded with the adhesion layer, and the
adhesion layer is physically bonded by sputtering or evaporating
the titanium (Ti) or titanium tungsten (TiW), thus the adhesion
strength is not superior as chemical bonding, and can not be used
in the situation of high temperature or large temperature
difference. In addition, forming the copper layer (DPC process) by
plating will significantly affect the production capability due to
time-consuming for the plating deposition process. the obtained
thickness of copper layer formed by plating will vary
substantially. This is because the current density distribution is
significantly affected by the design of plating tank, the resist
pattern, and the edge effect of the ceramic substrate. Furthermore,
the materials used may be restricted in the plating field, only
copper or nickel can be used, and thereby the ceramic substrate can
not be bonded with other metals.
[0010] Therefore, how to provide a process of metallized ceramic
substrate with high bonding strength, capable of solving the
limitations to the applied environment and material selection of
the conventional ceramic substrate and metal layer, and reducing
the situation of conchoidal fracture caused by the inner stress
between the ceramic substrate and the metal layer, is the issue has
to be faced by persons skilled in the art.
SUMMARY OF THE INVENTION
[0011] In view of the above drawbacks of the prior art, the object
of the present invention is to provide a tightly bonding between
the ceramic substrate and the metal layer using brazing
technology.
[0012] To achieve the objects above and other objects, the present
invention provides a method of selective metallization on a ceramic
substrate, comprising: forming an active brazing material on a
predetermined area of a surface of the ceramic substrate; attaching
a metal layer to the surface of the ceramic substrate with the
active brazing material and performing a brazing process on the
active brazing material; forming an etching stop layer on the
predetermined area of the metal layer and etching the metal layer;
and removing the etching stop layer.
[0013] In the present invention, the active brazing material is
formed on the ceramic substrate, but not limited thereto. In
another embodiment, a layer of active brazing material can be also
selectively formed on the copper layer and then the copper layer is
attached to the ceramic substrate, and subsequent brazing and
etching process are performed.
[0014] In an embodiment of the present invention, the active
brazing material has active metal with a specific proportion.
[0015] In another embodiment of the present invention, the active
brazing material is formed on the surface of the ceramic substrate
by a printing, spray coating, or lamination.
[0016] In another embodiment of the present invention, the etching
stop layer corresponds to the active brazing material formed on the
surface of the ceramic substrate.
[0017] The present invention further provides a method of selective
metallization on a ceramic substrate, comprising: performing a
predetermined depth etching on a predetermined area of a metal
layer, so as for forming an etching area and a reserved area on the
metal layer; forming an active brazing material on the reserved
area of the metal layer; attaching the metal layer with the active
brazing material to the ceramic substrate and performing a brazing
process on the active brazing material; and etching the metal layer
for removing the metal on the etching area.
[0018] In an embodiment of the present invention, the metal layer
is copper, aluminum or stainless steel.
[0019] Compared to the prior art, the present invention provides a
method of selective metallization on the ceramic substrate. A
brazing process is performed with the active brazing material to
increase the bonding reliability between the ceramic substrate and
the metal layer. Also, since the electroplating or eutectic bonding
is not used in the present invention, materials of the ceramic
substrate and the metal layer will not be limited as in the prior
art and the process may be applied to the environment with high
temperature or large temperature difference. In addition, the
problem of conchoidal fracture or poor adhesion between the ceramic
substrate and the metal layer in the prior art can be avoided. The
present invention not only can simplify the process, but also can
improve product yield.
BRIEF DESCRIPTION OF DRAWINGS
[0020] FIGS. 1A to 1E are cross-sectional views illustrating a
method for the DBC process according to the prior art;
[0021] FIGS. 2A to 2E are cross-sectional views illustrating a
method of fabricating a DPC substrate according to the prior
art;
[0022] FIGS. 3A to 3E are cross-sectional views illustrating
another method of fabricating a DPC substrate according to the
prior art;
[0023] FIGS. 4A to 4E are cross-sectional views illustrating a
method of forming a selected metal on a ceramic substrate according
to a first embodiment of the present invention; and
[0024] FIGS. 5A to 5D are cross-sectional views illustrating a
method of forming a selected metal on a ceramic substrate according
to a second embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0025] It is to be understood that both the foregoing general
descriptions and the detailed embodiments are exemplary and are,
together with the accompanying drawings, intended to provide
further explanation of technical features and advantages of the
invention.
[0026] The following illustrative embodiments are provided to
illustrate the disclosure of the present invention, these and other
advantages and effects can be apparent to those skilled in the art
after reading the disclosure of this specification. The present
invention can also be performed or applied by other different
embodiments. The details of the specification may be on the basis
of different points and applications, and numerous modifications
and variations can be devised without departing from the spirit of
the present invention.
First Embodiment
[0027] Referring to FIGS. 4A to 4E, cross-sectional views
illustrating a method of forming a selected metal on a ceramic
substrate according to a first embodiment of the present invention
are provided. The method produces a selectively metallized
structure of a ceramic substrate with high reliability by a brazing
process.
[0028] As shown in FIG. 4A, a ceramic substrate 20 is provided. An
active brazing material 40 is selectively formed on a predetermined
area of the ceramic substrate 20. The active brazing material 40 is
selectively coated on some areas of the ceramic substrate 20. The
active brazing material 40 may be nickel-based or silver-based
brazing material, and the active brazing material 40 has an active
metal with a specific proportion, such as titanium (Ti), zirconium
(Zr) or niobium (Nb), which is helpful to increase the wettability
of the active brazing material 40 on the surface of the ceramic
substrate 20. In addition, the active brazing material 40 may be
brazing material, such as paste, powder or foil, and the coating
process may be performed by a printing, spray coating, or
lamination.
[0029] As shown in FIG. 4B, the metal layer 10 is attached to the
surface of the ceramic substrate 20 with the active brazing
material 40. Then, a brazing process is performed on the active
brazing material 40, such that the ceramic substrate 20 and the
metal layer 10 may produce highly reliable bonding at an area
having the active brazing material 40 to form a structure with the
metal covering on the ceramic substrate.
[0030] As shown in FIG. 4C, an etching stop layer 30 is formed on
the metal layer 10. The etching stop layer 30 corresponds in
position to the active brazing material 40 formed on the surface of
the ceramic substrate 20. In other words, one side of the metal
layer 10 has the active brazing material 40 and the etching stop
layer 30 is formed at the relative position of the other side of
the metal layer 10.
[0031] As shown in FIG. 4D, the metal layer 10 is selectively
etched. The etching stop layer 30 formed on the metal layer 10
works as a protective layer with specific patterns generated by dry
film and lithography process. Thus, an exposed portion of the metal
layer 10 unprotected by the etching stop layer 30 is etched and
removed. The etched and removed area is the area not coated by the
active brazing material 40.
[0032] As shown in FIG. 4E, the etching stop layer 30 is removed,
after the metal layer 10 is etched, to complete the selective
metallization of the ceramic substrate.
[0033] In addition to commonly used alumina, the foregoing ceramic
substrate 20 may also be used with aluminum nitride or silicon
carbide. In addition to the common copper, the metal layer 10 may
also be made of aluminum or stainless steel and the like. In the
DBC structure shown in FIGS. 1A to 1E, bonding for the metal layers
may be Cu--Cu2O eutectic bonding. Thus, except copper, no other
metal material can be used for bonding to the substrate. Also, for
the copper plating method shown in FIGS. 2A to 2E and 3A to 3E,
because the metal has to be produced by plating, material selection
may also be limited to the one that is capable of electroplating.
More common materials are only copper or nickel. Therefore, the
present invention performs brazing with the active brazing
material, such that the ceramic substrate 20 and the metal layer 10
are more flexible in selecting the material.
[0034] Further, because the active brazing material 40 is not
easily removed by etching, the present invention is characterized
in selectively coating the active brazing material 40 at a
particular area, such that the metal layer 10 at an area not coated
by the active brazing material 40 is removed. The ceramic substrate
20 having the removal of the metal layer 10 will not have brazing
material residue thereon, and the selective metallization of the
ceramic substrate is completed.
[0035] According to another embodiment of the present invention, as
shown in FIGS. 4A and 4B, the active brazing material 40 can also
be first coated on the metal layer 10, then the ceramic substrate
20 and the metal layer 10 are bonded, and the selective
metallization of the ceramic substrate is also completed.
Second Embodiment
[0036] Referring to FIGS. 5A to 5D, cross-sectional views
illustrating a method of forming a selected metal on a ceramic
substrate according to a second embodiment of the present invention
are provided.
[0037] As shown in FIG. 5A, a metal layer 10 having an etching area
102 and a reserved area 101 is provided. The metal layer 10 is
selectively etched through dry film, photoresist or other methods.
Thus, the etched etching area 102 has a certain depth, and the
reserved area 101 will be bonded to the ceramic substrate 20.
[0038] As shown in FIG. 5B, an active brazing material 40 is formed
on the reserved area 101 of the metal layer 10. The active brazing
material 40 may be nickel or silver-based active brazing material.
The active brazing material 40 containing an active metal with a
specific proportion, such as titanium, zirconium or niobium, may be
a brazing material in paste, powder or foil, and coated on the
reserved area 101 by printing, spray coating or lamination.
[0039] As shown in FIG. 5C, the metal layer 10 having the active
brazing material 40 is attached to the ceramic substrate 20, and
subsequently the active brazing material 40 is performed the
brazing process, such that the ceramic substrate 20 and the metal
layer 10 are bonded with high reliability at area having the active
brazing material 40.
[0040] As shown in FIG. 5D, the etching step of the metal layer 10
is performed. The metal layer 10 is etched to remove the etching
area 102 of the metal layer 10. The metal layer 10 is selectively
etched. The etched portion refers to the etching area 102 which is
not coated by the active brazing material 40, such that the surface
without the active brazing material 40 attached to the metal layer
10 is exposed, in order to complete the selective metallization of
the ceramic substrate.
[0041] The etching step of the metal layer 10 can also be
comprehensive etching to the metal layer 10. The etched portion
refers to the etching area 102 and the reserved area 101. As the
metal layer of the reserved area 101 is thicker for the bonding to
the ceramic substrate 20, under equal etching rate, the etching
area 102 will be fully removed after the comprehensive etching, and
the reserved area 101 bonded to the ceramic substrate 20 will
remain the metal layer 10 with a specific thickness. The selective
metallization of the ceramic substrate is thus completed.
[0042] Similarly, the aforementioned ceramic substrate 20 may be
alumina, aluminum nitride or silicon carbide, and the metal layer
10 may be copper, aluminum, stainless steel or other materials.
Compared to the conventional process, the present invention
performs brazing with the active brazing material, such that the
ceramic substrate 20 and the metal layer 10 are more flexible in
selecting the material.
[0043] In addition, according to another embodiment of the present
invention, as shown in FIGS. 5B and 5C, the active brazing material
40 can also be coated on the ceramic substrate 20, and the ceramic
substrate 20 and the metal layer 10 can be bonded to complete the
selective metallization of the ceramic substrate of the present
embodiment.
[0044] By the process described in the present invention, as the
operating range of the brazing temperature is greater, the yield of
the batch production is improved, and by using the brazing process,
the ceramic substrate and the metal layer are more flexible in
selecting the material, and thus will not have limitations as in
the prior art. In addition, the reliability is better by brazing
bonding and the problems of the conchoidal fracture between the
ceramic substrate and the metal layer or poor adhesion can be
solved, and thus also can be used under the environment of a high
temperature or large temperature difference. Finally, since the
metal layer with a specific thickness is bonded to the ceramic
substrate, the problem of uneven thickness will not occur.
[0045] In summary, the method of selective metallization on the
ceramic substrate of the present invention can tightly bond the
metal layer and the ceramic substrate by the brazing process.
Compared to the prior art, the better process of selective
metallization on the ceramic substrate and higher product yield are
provided.
[0046] The above embodiments are illustrated to disclose the
preferred implementation according to the present invention but not
intended to limit the scope of the present invention. Accordingly,
all modifications and variations completed by those with ordinary
skill in the art should fall within the scope of present invention
defined by the appended claims.
* * * * *