U.S. patent application number 13/348072 was filed with the patent office on 2012-05-03 for low temperature bonding material and bonding method.
Invention is credited to Hiroshi Hozoji, Eiichi Ide, Toshiaki Ishii, Toshiaki Morita, Yusuke Yasuda.
Application Number | 20120104618 13/348072 |
Document ID | / |
Family ID | 39640120 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120104618 |
Kind Code |
A1 |
Yasuda; Yusuke ; et
al. |
May 3, 2012 |
LOW TEMPERATURE BONDING MATERIAL AND BONDING METHOD
Abstract
A bonding material comprising metal particles coated with an
organic substance having carbon atoms of 2 to 8, wherein the metal
particles comprises first portion of 100 nm or less, and a second
portion larger than 100 nm but not larger than 100 .mu.m, each of
the portions having at least peak of a particle distribution, based
on a volumetric base. The disclosure is further concerned with a
bonding method using the bonding material.
Inventors: |
Yasuda; Yusuke; (Hitachi,
JP) ; Morita; Toshiaki; (Hitachi, JP) ; Ide;
Eiichi; (Hitachi, JP) ; Hozoji; Hiroshi;
(Hitachiota, JP) ; Ishii; Toshiaki; (Hitachi,
JP) |
Family ID: |
39640120 |
Appl. No.: |
13/348072 |
Filed: |
January 11, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13099394 |
May 3, 2011 |
|
|
|
13348072 |
|
|
|
|
11964827 |
Dec 27, 2007 |
7955411 |
|
|
13099394 |
|
|
|
|
Current U.S.
Class: |
257/772 ;
257/E23.023 |
Current CPC
Class: |
B22F 1/0062 20130101;
H01L 2924/15165 20130101; H01L 2224/2919 20130101; H01L 2224/45124
20130101; H01L 2924/01024 20130101; H01L 2924/3512 20130101; H01L
24/32 20130101; H01L 2224/37147 20130101; H01L 2924/01047 20130101;
Y10T 428/12028 20150115; H01L 2224/2919 20130101; H01L 2224/45015
20130101; H01L 2224/85205 20130101; H01L 2224/29371 20130101; H01L
2224/29101 20130101; H01L 2924/01044 20130101; H01L 2924/181
20130101; H01L 2924/01013 20130101; B23K 35/22 20130101; H01L
2924/01028 20130101; H05K 2201/0266 20130101; H01L 2224/371
20130101; B23K 35/3013 20130101; H01L 2924/01006 20130101; H01L
2924/01079 20130101; H05K 3/321 20130101; H01L 24/40 20130101; H01L
2224/32225 20130101; H05K 2201/0257 20130101; H01L 2924/01073
20130101; H01L 2224/29101 20130101; H01L 2924/15787 20130101; H01L
2224/8384 20130101; H01L 2924/01027 20130101; H01L 2924/09701
20130101; H01L 2924/181 20130101; H05K 2201/0224 20130101; B23K
35/40 20130101; B22F 2003/145 20130101; H01L 24/37 20130101; H01L
2224/29355 20130101; H01L 2224/48247 20130101; H01L 2224/49175
20130101; Y10T 428/8305 20150401; H01L 2924/00011 20130101; H01L
24/33 20130101; H01L 2224/40225 20130101; H01L 2224/73265 20130101;
H01L 2924/0665 20130101; H01L 2924/19043 20130101; H01L 2924/10253
20130101; H01L 2924/01077 20130101; H01L 24/45 20130101; Y10T
428/2991 20150115; H01L 2924/19105 20130101; H01L 2924/01033
20130101; H01L 2224/3754 20130101; B22F 1/0014 20130101; H01L
2924/01029 20130101; B22F 3/14 20130101; H01L 2224/29339 20130101;
H01L 2924/0665 20130101; H01L 2224/29366 20130101; H01L 2924/01019
20130101; H01L 2224/49175 20130101; H01L 2924/01045 20130101; H01L
2924/15787 20130101; H01L 2924/00 20130101; H01L 2224/48247
20130101; H01L 2924/00 20130101; H01L 2924/00012 20130101; H01L
2924/00 20130101; H01L 2224/48247 20130101; H01L 2224/32245
20130101; H01L 2924/00 20130101; H01L 2924/00 20130101; H01L 24/29
20130101; H01L 2224/29344 20130101; H01L 2224/29364 20130101; H01L
2224/32245 20130101; H01L 2224/45124 20130101; H01L 2224/48247
20130101; H01L 2224/73265 20130101; H01L 2924/014 20130101; H01L
2924/15153 20130101; H01L 2224/48247 20130101; H01L 2924/00
20130101; H01L 2224/8584 20130101; H01L 2224/40095 20130101; H01L
2924/01005 20130101; B23K 35/302 20130101; H01L 25/072 20130101;
H01L 2224/29311 20130101; H01L 2924/00011 20130101; H01L 2924/01016
20130101; H01L 2224/2936 20130101; H01L 2224/29324 20130101; H01L
2224/83801 20130101; H01L 2924/01075 20130101; H01L 2224/29369
20130101; H01L 2224/45015 20130101; H01L 2924/01046 20130101; H01L
2924/01074 20130101; H01L 2924/19041 20130101; Y10T 428/12181
20150115; H01L 2924/01049 20130101; H01L 2924/13091 20130101; H01L
2924/01076 20130101; H01L 24/83 20130101; H01L 2224/29007 20130101;
H01L 2224/84801 20130101; H01L 2924/0103 20130101; H01L 2924/01078
20130101; H01L 2224/73265 20130101; B23K 35/3006 20130101; H01L
2924/0105 20130101; H01L 2924/01014 20130101; H01L 2924/01082
20130101; H01L 2924/2076 20130101; H01L 2924/2076 20130101; H01L
2924/00014 20130101; H01L 2924/13091 20130101; H01L 2924/00
20130101; H01L 2924/00 20130101; H01L 2224/32225 20130101; H01L
2924/0665 20130101; H01L 2224/83205 20130101; H01L 2924/014
20130101 |
Class at
Publication: |
257/772 ;
257/E23.023 |
International
Class: |
H01L 23/488 20060101
H01L023/488 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2006 |
JP |
2006-353649 |
Claims
1. A semiconductor device comprising: a semiconductor element one
of the surfaces thereon having an electrode; a ceramic substrate
having wiring; and a bonding layer for electrically bonding the
electrode and the wiring, wherein the bonding layer is a sintered
layer of metal particles, wherein the metal particles comprise a
first portion having a particle size of 100 nm or less, and a
second portion of an aggregate having a particle size larger than
100 nm but not larger than 100 .mu.m, said aggregate being
constituted by the particles having 100 nm or less, and each of the
portions having at least one peak of a particle distribution, based
on a volumetric base.
2. The semiconductor device according to claim 1, wherein the
bonding layer is made of the sintered layer of a bonding material,
before sintering, comprising the metal particles, which are coated
with an organic substance having carbon atoms of 2 to 8.
3. The semiconductor device according to claim 1, wherein the metal
particles are selected from the group consisting of gold, silver
and copper.
4. The semiconductor device according to claim 1, wherein the
semiconductor element has a connecting terminal on the surface
opposite to the electrode.
5. The semiconductor device according to claim 3, wherein the
wiring is constituted by copper, and the surface thereof is plated
with nickel.
6. The semiconductor device according to claim 3, wherein the
connecting terminal is made of copper, and the surface thereof is
plated with nickel.
7. The semiconductor device according to claim 3, wherein the
connecting terminal has a large wiring width.
8. The semiconductor device according to claim 1, wherein a
periphery of the ceramic substrate is provided with a water
repellent film on the surface opposite to the surface where the
electrode is formed.
9. The semiconductor device according to claim 1, which further
comprises a base plate connected with the opposite surface of the
ceramic substrate where the semiconductor element is mounted by
means.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of U.S.
application Ser. No. 13/099,394 filed May 3, 2011, which is a
divisional application of U.S. application Ser. No. 11/964,827,
filed Dec. 27, 2007, now U.S. Pat. No. 7,955,411, the contents of
which are incorporated herein by reference.
CLAIM OF PRIORITY
[0002] The present application claims priority from Japanese
application serial No. 2006-353649, file on Dec. 28, 2006, the
content of which is hereby incorporated by reference into this
application.
FIELD OF THE INVENTION
[0003] The present invention relates to a low temperature bonding
material for bonding electronic parts and a method for bonding the
electronic parts using the bonding material.
RELATED ART
[0004] In non-insulated type semiconductor devices such as power
semiconductor devices that are used for inverters, etc, a member
for fixing the semiconductor tips is an electrode through which
electric current of several amperes or more flows heat at the time
the semiconductor device is in operation so that the semiconductor
chip generates. Recently, since a current capacity of the
semiconductor device is increasing, an amount of heat at the
mounting portion of the semiconductor device, i.e. die-bonding
portion is increasing.
[0005] In order to stably operate the semiconductor chip while
avoiding reduction in life and instability of characteristics due
to the heat, it is necessary to secure heat dissipation at soldered
portions and long-term reliability (heat resistance) of the
semiconductor chip mounting portions. Accordingly, a bonding
material which is excellent in high heat dissipation and heat
resistance is needed.
[0006] On the other hand, in insulated type semiconductor devices
it is necessary to effectively dissipate heat generating at the
time of operation of the semiconductor devices to outside thereof
and to secure bonding reliability of the soldered portions.
[0007] Patent document No. 1 discloses a bonding method wherein
metal particles coated with organic substance and having a particle
size of 100 nm or less is used, and the organic substance covering
the metal particles is decomposed at the time of heating and
pressurizing to thereby effect sintering phenomenon among the metal
particles. In this technology, the metal particles after bonding
transform into bulk metal and at the same time metallic bonding in
the bonding interface of bonding takes place.
[0008] Patent document No. 2 discloses that in a bonding method
using metal particles having a particle size of 100 nm or less, the
metal particles having the particle size of 100 nm or less is mixed
with particles having a particle size of 1 to 100 .mu.m thereby to
secure a thickness of the bonding layer.
[0009] Nowadays a change from solder material containing lead to
lead-free solder has been urged; however, substituents for high
temperature solder have not been provided so far. Since it is
necessary to utilize hierarchy solders to perform package of
electronic parts, a bonding material for substituents of the high
temperature solder has been desired. Accordingly, the bonding
technology utilizing the metal particles having the particle size
of 100 nm or less is expected to be substituents for the high
temperature solders. [0010] Patent document No. 1: Japanese patent
laid-open 2004-107728 [0011] Patent document No. 2: Japanese patent
laid-open 2005-136375
SUMMARY OF THE INVENTION
[0012] The present invention is featured by a bonding material
comprising metal particles coated with an organic, wherein the
metal particles comprises (1) particles having a particle size of
100 nm or less and (2) metal particles having a particle size
larger than 100 nm but not larger than 100 .mu.m, and wherein there
is at least one peak in each of particle distributions of the metal
particles (1) and (2) in a volumetric unit.
[0013] A bonding material according to another aspect of the
present invention comprises metal particles having a particle size
of 1 nm to 100 nm and aggregates of the metal particles, wherein
aggregates have a grain size of 10 nm to 100 .mu.m.
[0014] A still another aspect of the present invention is featured
by a method of bonding electrodes of an electronic part and winding
circuits of a wiring board, which comprises coating a bonding
material comprising metal particles coated with an organic
substance and having a particle size of 100 .mu.m, wherein the
metal particles comprises (1) particles having a particle size of
100 nm or less and (2) metal particles having a particle size more
than 100 nm to 100 .mu.m, and wherein there is at least one peak in
each of particle distributions of the metal particles (1) and (2)
in a volumetric unit on a bonding face between the circuits and the
electrodes, and heating and pressurizing the circuits, electrodes
and the bonding material to thereby bond the circuits and the
electrodes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 shows a relationship between heating temperatures and
residual weight;
[0016] FIG. 2 shows a relationship between bonding temperatures and
shearing strength;
[0017] FIG. 3 shows a relationship between the number of carbon
atoms in the organic substances used for coating silver particles
and shearing strength;
[0018] FIG. 4 shows s structure of a non-insulated type
semiconductor device according to an embodiment of the present
invention, wherein FIG. 4(a) a plan view of the device and FIG.
4(b) is a cross sectional view along line A-A' in FIG. 4(a);
[0019] FIG. 5 shows a sub-assembly of the insulated type
semiconductor device shown in FIG. 4;
[0020] FIG. 6 shows a cross sectional view of a sub-assembly of the
insulated type semiconductor device shown in FIG. 5, before
bonding;
[0021] FIG. 7 shows a perspective view of a non-insulated type
semiconductor device according to another embodiment;
[0022] FIG. 8 shows a cross sectional view of the semiconductor
device shown in FIG. 7, before bonding;
[0023] FIG. 9 shows an embodiment of a non-insulated type
semiconductor device similar to that of example 3 in which FIG.
9(a) is a plan view of the semiconductor device and FIG. 9(b) is a
cross sectional view of the semiconductor device shown in FIG.
9(a);
[0024] FIG. 10 shows a cross sectional view of the insulated type
semiconductor device; and
[0025] FIG. 11 shows a cross sectional view of the mini-molded type
non-insulated semiconductor device according to an example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] In the bonding technologies disclosed in Patent document
Nos. 1 and 2, which use metal particles having a particle size of
100 nm or less, bonding at the bonding interface is performed by
metallic bonding. As a result, high heat resistance, reliability
and high heat dissipation are expected. On the other hand, the fine
metal particles having a particle size of 100 nm or less tend to
aggregate. Therefore, it is necessary to coat the metal particles
with an organic material to stabilize the fine metal particles. In
the conventional technologies, in order to stabilize the metal
particles more stable organic materials such as alkylcarboxylic
acid having a long chain have been used as a coating material. The
protecting coating of the organic material must be removed at the
time of bonding; however, the protecting coating is not removed
completely by low temperature heating, which leads to insufficient
shear strength. Accordingly, in order to obtain sufficient shear
strength the heating temperature is elevated or the heating time
must be extended. However, it is necessary to lower the temperature
for heat treatment and shorten the heating time so as to avoid
damage to the electronic parts during the bonding process. In the
bonding process using the metal particles having a particle size of
100 nm or less, low temperature and short time bonding have not
been investigated.
[0027] The present invention aims at providing a bonding material
and a bonding method that are capable of lowering the heating
temperature and shortening the heating time during the bonding
process, and also providing a semiconductor package free from
deterioration of long term reliability under a high temperature
atmosphere.
[0028] In the following the embodiments of the present invention
will be explained in detail.
[0029] The present invention utilizes a phenomenon that sintering
of fine metal particles having a particle size of 100 nm or less
takes place. The bonding material of the present invention
comprises metal particles having a particle size of 100 nm or less,
the particles being coated with organic substance having carbon
atoms of 2 to 8, wherein there are a first particle group of 100 nm
or less and a second particle of 100 nm to 100 .mu.m each having at
least one peak of a particle size distribution based on volumetric
unit.
[0030] In the present invention, the organic substance for coating
the metal particles has carbon atoms of 2 to 8. FIG. 1 shows a
relationship between heating temperatures and residual weight
according to thermal weight measurement with respect to organic
substances including hexyl amine having 6 carbon atoms, octyl amine
having 8 carbon atoms, decyl amine having 10 carbon atoms, laulyl
amine having 12 carbon atoms. According to FIG. 1, it is apparent
that the smaller the number of carbon atoms of the organic
substances, the lower the thermal weight loss starting temperature
becomes. Accordingly, it is possible to lower the decomposition
temperature for decomposition by using the organic substance having
a short chain of the small number of carbon atoms. Therefore, by
coating the metal particles with the organic substances having 2 to
8 carbon atoms, the decomposition and removal of the organic
substance can be done at lower temperatures. That is, the bonding
temperature can be lowered.
[0031] If the number of carbon atoms of the organic substance is
smaller than 2, the metal particles aggregate at room temperature;
the metal particles are not coated in a stable state. If the number
of carbon atoms exceeds 8, the decomposition temperature is too
high, and sintering of the metal particles is suppressed at the
bonding process to thereby lower the shear strength. Accordingly,
the number of carbon atoms in the organic substance is 2 to 8.
[0032] Since the organic substance for coating the metal particles
becomes a component that suppresses sintering of the metal
particles after the bonding, it is necessary to make an amount of
residue of the organic substance in the bonding layer as small as
possible. Therefore, it is necessary to make the amount of organic
substance as small as possible so as to sufficiently decompose and
remove it under low temperature.
[0033] The present inventors have found that after investigation on
the metal particles coated with the organic substance containing
carbon atoms of 2 to 8, the metal particles comprise not only
particles having a particle size of 100 nm or less (first
particles) but also particles having 100 nm to 100 .mu.m (second
particles), wherein the first and second particles have particle
size distributions based on volumetric unit each having at least
one peak. The metal particles having the particle size of 100 nm to
100 .mu.m should preferably be coated with the organic substance
because dispersing capability of the metal particles having the
particle size of 100 nm to 100 .mu.m with the metal particles
having the particle size of 100 nm or less is better than the case
where the metal particles having the particle size of 100 nm to 100
.mu.m that is not coated with the organic substance is admixed with
the metal particles having the particle size of 100 nm or less.
[0034] The metal particles having the particle size of 100 nm to
100 .mu.m can be particles that are aggregated metal particles
having the particle size of 100 nm or less. In this case, because
the organic substance coated on the metal particles having the
particle size of 100 nm or less and the coated metal particles
having the particle size of 100 nm to 100 .mu.m is the same one, a
better dispersing capability in an organic solvent is expected.
[0035] Shapes of the aggregates of the metal particles may have
different shapes such as globular, elliptic, triangle, rectangular
forms, etc, which are formed by random unification of metal
particles. The shapes of the aggregates are not limited to the
above ones. The aggregates of metal particles having the particle
size of 1 nm to 100 nm should preferably have a particle size of 10
nm to 100 .mu.m.
[0036] As described above, by employing metal particles having
peaks in the range of a particle size of 100 nm or less and a range
of a particle size larger than 100 nm, a shear strength can be
increased. Although the detailed mechanism for increasing the shear
strength is not elucidated yet, it is considered that the metal
particles of 100 nm or less fill gaps among metal particles of 100
nm or more in the bonding material to effect sintering at low
temperatures thereby to enhance sintering of the metal particles of
a particle size of 100 nm or more. Further, a combination of the
metal particles having a peak in a range of 100 nm or less and a
peak in a range of 100 nm or more reduces an amount of the organic
substance in the bonding material, which leads to better sintering
of the bonding material to reduce a residue of the organic
substance. As a result, a high shear strength is obtained.
[0037] A mixing ratio (% by weight) of the metal particles of 100
nm or less to the metal particles of 100 nm or more is preferably
more than 0.1% by weight, but less than 100%. If the amount of the
metal particles of 100 nm or less is 0.10 or less, the gaps among
the metal particles of 10 nm or more would not be filled with the
metal particles of 10 nm or less. As a result, the shear strength
will be lowered.
[0038] The metal particles used in the present invention and having
a particle size of 100 nm or less are selected from the group of
gold, silver, copper, platinum, palladium, rhodium, osmium,
ruthenium, iridium, iron, tin, zinc, cobalt, nickel, chromium,
titanium, tantalum, indium, silicon, aluminum, etc or alloys
thereof. Particularly, Au or Au alloys, Ag or Ag alloys are
preferably used singly or combinations thereof.
[0039] The metal particles having a particle size of 1 to 100 .mu.m
are selected from Au, Au alloys, Ag, Ag alloys, nickel metal core
metal plated with Au or Au alloys, Ag or Ag alloys, or copper core
metal plated with Au, Au alloys, Ag, Ag alloys, etc.
[0040] The organic substance having carbon atoms of 2 to 8 for
coating the metal particles contains radicals that are capable of
forming coordination with the metal elements and include oxygen
atoms, nitrogen atoms or sulfur atoms. For example, there are
exemplified an amino group, alcohol group, carboxylic group,
sulfanyl group, carbonyl group, aldehyde group, etc.
[0041] Alkyl amines are useful compounds. For example, there are
butyl amine, pentyl amine, hexyl amine, heptyl amine and octyl
amine. The amine compounds may have a branched structure; for
example, there are 2-ethylhexyl amine, 1,5-dimethylhexyl amine,
etc. In addition to primary amines, secondary amines and tertiary
amines are usable. The organic substance may have a cyclic
structure.
[0042] Carboxylic compounds such as alkyl carboxylic acids are
useful compounds. For example, there are butanoic acid, pentanoic
acid, hexanoic acid, heptanoic acid and octanoic acid. In addition
to the primary carboxylic acids, secondary carboxylic acids and
tertiary carboxylic acids, dicarboxylic acids, cyclic carboxylic
acids are usable.
[0043] Alcohol group containing compounds such as alkyl alcohols
are usable. For example, there are ethanol, propyl alcohol, pentyl
alcohol, heptyl alcohol and octyl alcohol. In addition to the
primary alcohols, secondary alcohols, tertiary alcohols, alkane
diols, cyclic alcohols are usable. Further, citric acid, ascorbic
acid are usable.
[0044] Sulfanyl group containing compounds such as alkylthiols are
useful compounds. For example, there are 1-thylthiol, 1-propyl
thiol, 1-butylthiol, 1-pentylthiol, 1-hexylthiol, 1-heptylthiol and
1-ocylthiol. Secondary thiols and tertiary thiols may be used.
[0045] In addition to the above compounds, compounds containing
carbonyl group, aldehyde group and ester group and having carbon
atoms of 2 to 8 can be used as a protecting film. The compounds can
be used singly or in combination.
[0046] The bonding material according to the present invention may
be used in a form of paste wherein the metal particles coated with
the organic substance are dispersed in an organic solvent. Examples
of the organic solvents are alcohols such as methanol, ethanol,
octyl alcohol, ethylene glycol, triethylene glycol,
.alpha.-terpineol, etc, and hexane, heptane, octane, decane,
dodecane, cyclopentane, cyclohexane, benzene, toluene, xylene,
ethylbenzene, water, etc.
[0047] The bonding materials comprising the metal particles having
the particle size of 100 nm or less, wherein the metal particles
having the particle size of 100 nm or less and the metal particles
having the particle size larger than 100 nm to 100 .mu.m
respectively have peaks in a volumetric base is prepared by
aggregating the metal particles having the particle size of 100 nm
or less. The metal particles having the particle size of 100 nm or
less can be prepared by any conventional methods in which the metal
particles having the particle size are synthesized in a solution.
The metal particles coated with the organic substance and having
the particle size of 100 nm or less, produced in the methods,
subjected to removing a solvent with an evaporator. As a result,
aggregation of the metal particles takes place to thereby form the
bonding material comprising the metal particles of 100 nm or less
and metal particles larger than 100 nm to 100 .mu.m, the metal
particles having peaks in the volumetric base.
[0048] In order to aggregate the metal particles having the
particle size of 100 nm or less to impart a particle size
distribution, the metal particles coated with the organic substance
having carbon atoms of 2 to 8 can be heated, the organic substance
is removed with an organic solvent, or ultraviolet ray is
irradiated on the metal particles to vaporize the organic
substance, in addition to the above mentioned-method. The method
for aggregation of the metal particles are not limited to the
above.
[0049] The bonding material can be admixed with flake form silver
metal and a thermosetting resin such as epoxy resin, polyimide
resin, etc. The resins are not limited to the above ones. In order
to obtain strong bonding by the bonding material, an amount of the
metal particles should preferably be larger than 50 parts by
weight, but lower than 99 parts by weight, based on the total
weight of the bonding material.
[0050] Next, a bonding method using the bonding material of the
present invention will be explained.
[0051] In a method of bonding electrodes with circuit wiring of a
wiring board, the above-described bonding material was coated at
bonding faces of the circuit wiring and electrodes, and electronic
elements were mounted on the circuit wiring. Followed by heating
and pressuring the bonding faces to perform bonding.
[0052] A heating temperature was preferably 40.degree. to
400.degree. C. The heating temperature of 40.degree. C. or higher
was necessary to remove the organic substance coated on the metal
particles within a reasonable time period. A pressuring time was 60
minutes or less. If the pressure time is longer than 60 minutes, it
takes too much time to produce a product, which is not proper for
mass production.
[0053] When the bonding material is used as a paste material for
brazing, there are various methods exemplified below.
(1) An ink-jet method wherein the paste is coated on the bonding
portion or the electrodes on a substrate by jetting the paste
through a fine nozzle. (2) A method for coating the paste through a
metal mask or mesh-form mask, having a necessary opening. (3) A
method of coating the paste using a dispenser. (4) A method of
coating the water repellent resin through an opening of a metal
mask or a mesh-form mask. (5) A method of coating a photosensitive
resin on a surface including the bonding portion, followed by
exposing and developing the bonding portion. Then, the exposed
portion is coated with the paste. (6) A method of coating a water
repellent resin on the surface including the bonding portion of a
substrate or the electronic elements, followed by removing the
water repellent resin on an unnecessary part to form openings.
Then, the paste is coated in the openings.
[0054] The coating method is selected in accordance with area to be
bonded and shapes of the bonding portions.
[0055] In the following, examples according to the present
invention will be explained.
Examples 1-2, Comparative Examples 1-2
[0056] In example 1 Ag particles were coated with hexyl amine; in
example 2 Ag particles were coated with octyl amine; in comparative
example1 1 Ag particles were coated with decyl amine; and in
comparative example 2 Ag particles were coated with lauryl
amine.
[0057] The Ag particles coated with hexyl amine in example 1 has
peaks of particle size at 7.6 nm and 15.2 nm in a range of 100 nm
or less, and a peak of particle size at 0.3437 .mu.m in a range of
100 nm or more. The Ag particles coated with octyl amine in example
2 has peaks of particle size at 7.6 nm and 15.2 nm in a range of
100 nm or less, and a peak of particle size at 2.75 .mu.m in a
range of 100 nm or more.
[0058] The Ag particles coated with decyl amine in comparative
example 1 has peaks of particle size at 7.6 nm and 15.2 nm in a
range of 100 nm or less. The Ag particles coated with lauryl amine
in comparative example 2 has a peak of particle size at 18.1
nm.
[0059] The above-mentioned 4 kinds of Ag particles were subjected
to particle distribution measurement by dispersing the Ag particles
in toluene. The particle distribution measurement was conducted by
a micro-track ultra fine particle distribution meter 9340-UPA150
manufactured by Nikkiso, Ltd. Measurement was repeated three times
and an average value was determined.
[0060] On the other hand, thermogravimetric analysis on 4 kinds of
organic substances for coating the Ag particles, i.e. hexyl amine,
octyl amine, decyl amine and lauryl amine was conducted. For
measurement of the thermogravimetry, TG/DTA6200 manufactured by
Seiko Instruments was used. A temperature rise was 10.degree.
C./min and measurement was carried out in air.
[0061] As shown in FIG. 1, hexyl amine having 6 carbon atoms in
example 1 and octyl amine having 8 carbon atoms in example 2
exhibited lower thermogravimetric decrease temperatures than those
of decyl amine having 10 carbon atoms in comparative example 1 and
lauryl amine having 12 carbon atoms in comparative example 2. From
these results, the smaller the number of carbon atoms of the
organic substance, the lower the sintering temperature of the metal
powder becomes.
[0062] The Ag particles coated with hexyl amine in example 1 having
a particle size of 100 .mu.m was prepared by dispersing Ag
particles in 200 mL of toluene solvent together with 4.0 g of
silver nitrate and 5 g of hexyl amine and the solution was stirred.
Then, 4 g of ascorbic acid was added, followed by stirring for 1
hour and a half to thereby prepare Ag particles having a particle
size of 100 nm or less and coated with hexyl amine. Thereafter,
filteration of the solution was conducted using quantitative filter
paper (No. 5) to remove unreacted ascorbic acid and silver
nitrate.
[0063] Further, added was about 200 mL of acetone solvent to the
toluene solution of the filtered product of silver particles whose
surface was coated with hexyl amine and has a particle size of 100
nm or less so as to precipitate the silver particles. After
removing the supernatant, purification was conducted by removing
excess hexyl amine and by-products produced at the reaction. These
processes were repeated three times. The repetition of the
processes removes the organic substance covering silver particles
and aggregation of the silver particles of the particle size of 100
nm or less proceeds to produce silver particles having a particle
size of 100 nm or more.
[0064] As the number of carbon atoms of the organic substance
covering the surface of the silver particles decreases, a distance
among the silver particles becomes small so that silver particles
may directly contact with each other. Further, because the low
carbon atom organic substances have low volatile temperatures, and
because the low carbon atom organic substance may separate from the
silver particles, the silver particles tend to aggregate more
easily than high carbon atom organic substances.
[0065] After evaporating the organic solvent of the resulting
silver particles with an evaporator having 40.degree. C. water
bath, 2.5 g of silver particles was obtained. It is possible to
effect aggregation of silver particles by changing a liquid state
to a powder state.
[0066] Thereafter, the silver particles were re-dispersed in
toluene solvent to thereby produce a dispersion wherein silver
particles coated with hexyl amine are dispersed. In example 2,
octyl amine was used to produce silver particles covered with octyl
amine, which are dispersed in toluene solvent in the same manner as
in example 1.
[0067] On the other hand, silver particles dispersed in toluene
solvent were obtained in comparative examples 1 and 2 using decyl
amine and lauryl amine in the same manner as in example 1.
[0068] Measurement of particle distribution of the silver particles
obtained in examples 1 and 2 and comparative examples 1 and 2 was
conducted. The results are shown in Table 1. The four kinds of the
silver particles had the particle distributions shown in Table 1
and had the organic substance carried on the surface of silver
particles that have thermal decomposition characteristics shown in
FIG. 1.
TABLE-US-00001 TABLE 1 Comparative Comparative Example 1 Example 20
Example 1 example 2 Hexyl amine Octyl amine Decyl amine Lauryl
amine *1 7.6 7.6 7.6 18.1 15.2 15.2 15.2 *2 0.344 2.75 No peak No
peak *1; Particle size (nm) at peaks in a range of 100 nm or less
*2; Particle size (nm) at peaks in a range of 100 nm or more
[0069] Next, shearing strength tests of bonded portions were
conducted wherein a paste material dispersing the silver particles
in toluene was used. Test pieces were made of copper. An upper
member had a diameter of 5 mm and a thickness of 2 mm; a lower
member had a diameter of 10 mm and a thickness of 5 mm. After the
paste material was coated on the test pieces, drying at 60.degree.
C. for 5 minutes was conducted to remove toluene, followed by
bonding. Bonging temperatures were selected as 250.degree. C.,
300.degree. C., 350.degree. C. and 400.degree. C. Bonding time was
2 minutes 30 seconds. A pressure was 2.5 MPa.
[0070] Using the test pieces obtained in the above bonding methods,
shear strength under a single shearing stress was measured. In the
shearing test Bond Tester-SS-100 KP (maximum load; 100 kg)
manufactured by Seishin Trade Corp. was used. A shearing speed was
30 mm/min, and the test pieces were ruptured by a shearing tool to
measure the maximum load at rupture. The maximum load was divided
by a bonding area to obtain the sharing strength. The bonding
temperatures in FIG. 2 were 250.degree. C., 300.degree. C.,
350.degree. C. and 400.degree. C.
[0071] The shearing strength of the bonding portion using
laurylamine for treating the silver particles of the paste was
100%, and ratios of shearing strengths of the bonding portions
using decylamine, octylamine and hexylamine to the shear strength
of the bonding portion using laurylamine.
[0072] In FIG. 3 there is shown a relationship between the number
of carbon atoms in the organic substances used for coating silver
particles and shearing strength. As the number of carbon atoms
coated on the silver particles deceases, and the particle size
distribution based on a volumetric base has a peak in a particle
size of 100 nm or more, the shear strength becomes large. When the
number of carbon atoms is 8 or less, and when a bonding material
wherein aggregation of silver particles progresses is used, residue
of the organic substance in the sintered layer decreases after
bonding and the shear strength starts to increase. When the number
of carbon atoms is 6, sufficient sintering progresses to produce a
strong bonding.
Example 3
[0073] FIG. 4 shows s structure of a non-insulated type
semiconductor device according to an embodiment of the present
invention, wherein FIG. 4(a) a plan view of the device and FIG.
4(b) is a cross sectional view along line A-A' in FIG. 4(a).
[0074] After the semiconductor (MOSFET) 301 is mounted on ceramic
insulating substrate 302, which is mounted on base 301, epoxy resin
case 304, bonding wire 305 and epoxy resin cover 306 were arranged.
Silicone gel 307 was filled in the case 304. The ceramic insulating
substrate 302 on the base 303 was bonded with a bonding layer 308
formed by the paste of example 1. The paste comprises silver
particles having the particle size of 100 .mu.m or less, which were
coated with hexylamine, and have peaks at 7.6 nm and 15.2 nm when
the volumetric base particle distribution is 100 nm or less, and at
0.3437 .mu.m when the volumetric base particle distribution is 100
nm or more. The silver particles were dispersed in toluene in a
concentration of 80% by weight to form the bonding layer 308.
[0075] 8 of Si MOSFETs were bonded by the bonding layer 309 formed
from the above-mentioned paste on copper plate 302a of the ceramic
insulating substrate 302. Bonding was carried out by the bonding
layers 308, 309 formed from the above-mentioned paste, wherein the
paste was coated on the copper plate 302a (Ni plated) on the
ceramic insulating substrate 302, and was coated on the base
material 303.
[0076] The semiconductor elements 301 and the ceramic insulating
substrate 302 were placed on the coated paste. The bonding portions
were heated at 300.degree. C. for 5 minutes under a pressure of 0.5
MPa.
[0077] Electrodes 302b formed on the insulating substrate and
terminals 310 formed to the epoxy resin case 304 were connected by
aluminum bonding wire having a diameter of 300 .mu.m, bonded by
ultrasonic bonding. A thermistor element 311 for detecting
temperature has a bonding layer 309 formed from the paste.
Electrode 302 and terminal 310 are connected by aluminum bonding
wire 305 having a diameter of 300 .mu.m to be connected to
outside.
[0078] The epoxy resin case 304 and the base material 303 were
fixed with silicone resin adhesive (not shown). The thick portion
of the epoxy resin cover 306 has a cavity 306', and the terminal
310 has a hole 310'; a screw (not shown) for connecting the
insulated type semiconductor device 1000 to an outer circuit can be
disposed. The terminal 310 was punched into a desired shape in
advance. The shaped copper plate was Ni plated, which was fixed to
the epoxy resin case 304.
[0079] FIG. 5 shows a sub-assembly of the insulated type
semiconductor device shown in FIG. 4, wherein the ceramic substrate
and the semiconductor element were mounted on the base material 303
as a composite material. The base material 303 is provided with
fixing holes 303A in the periphery of thereof. The base material is
formed of copper, the surface of which is plated with Ni.
[0080] The base material 303 was coated with the paste used in
example 1. The paste comprises silver particles coated with
hexylamine; the silver particles having the particle size of 100 nm
or less have particle size distribution peaks at 7.6 nm and 15.2 nm
and in a particle size of 100 nm or more the silver particles have
a peak of the particle size distribution at 0.344 .mu.m. The silver
particles having the above particle distribution peaks were
dispersed in toluene at a concentration of 80% by weight. MOSFET
301 was mounted on the ceramic insulating substrate 302 by the
paste.
[0081] FIG. 6 shows a cross sectional view of a sub-assembly 1000
of the insulated type semiconductor device shown in FIG. 5, before
bonding. As shown in FIG. 6, it is possible to use the paste
material in which the bonding material in example 1 is dispersed in
toluene in a concentration of 80% by weight. For preventing flowing
out of the paste at the time of coating, a water repellent film 322
was formed in correspondence to the mounting area of the ceramic
insulating substrate 302 on the base material 303.
(Experiment 4)
[0082] FIG. 7 shows a perspective view of a non-insulated type
semiconductor device according to another embodiment.
[0083] The semiconductor element 701 and ceramic insulating
substrate 703 were bonded by the paste used in example 1 wherein
the paste comprises silver particles coated with hexylamine; the
silver particles having the particle size of 100 nm or less have
particle size distribution peaks at 7.6 nm and 15.2 nm and in a
particle size of 100 nm or more the silver particles have a peak of
the particle size distribution at 2.75 .mu.m. The silver particles
having the above particle distribution peaks were dispersed in
toluene at a concentration of 80% by weight.
[0084] The emitter electrode of the semiconductor element and the
copper wiring plated with nickel, formed on the ceramic insulating
substrate, were bonded by the paste.
[0085] FIG. 8 shows a cross sectional view of the semiconductor
device shown in FIG. 7, before bonding. Connecting terminal 731 was
copper plate plated with nickel and gold on nickel plating. After
mounting the semiconductor element 701 on the wiring 702a of the
insulating substrate, the paste material (710) was coated on the
emitter electrode (upper side). Then, a gold plated portion of the
copper wiring 702b formed on the insulating substrate 702 the
surface of which was nickel-plated and a portion between the
emitter electrode and the terminal 731 were coated with the paste
(709). The connecting terminal 731 was placed on electrode above
the paste material and bonding between the semiconductor 701 and
the insulating substrate 702b was conducted at 250.degree. C. under
a pressure of 1.0 MPa for 5 minutes. In the insulated type
semiconductor device, since large current flows through not only
the collector electrode, but also the emitter electrode, it is
possible to increase bonding reliability at the emitter electrode
side by using a connecting terminal 731 having a large wiring
width.
Example 5
[0086] FIG. 9 shows an embodiment of a non-insulated type
semiconductor device similar to that of example 3. FIG. 9(a) is a
plan view of the semiconductor device and FIG. 9(b) is a cross
sectional view of the semiconductor device shown in FIG. 9(a). In
this example, a connecting terminal 505 was used instead of the
bonding wire in example 3.
[0087] The electrodes 302a, 302b on the insulating substrate and
terminal 310 formed on epoxy resin casing 304 were bonded by using
a paste used in example 1. The paste was coated on the electrodes.
The bonding was conducted by heating at 250.degree. C. for 2
minutes under a pressure of about 0.5 MPa towards the clip 505.
[0088] The paste comprises silver particles coated with hexylamine;
the silver particles having the particle size of 100 nm or less
have particle size distribution peaks at 7.6 nm and 15.2 nm and in
a particle size of 100 nm or more the silver particles have a peak
of the particle size distribution at 2.75 .mu.m. The silver
particles having the above particle distribution peaks were
dispersed in toluene at a concentration of 80% by weight.
Example 6
[0089] In this example there is explained an insulated type
semiconductor device for a high frequency amplification apparatus
used in a transmitter of cellular telephones, etc.
[0090] The insulated type semiconductor device (size: 10.5
mm.times.4 mm.times.1.3 mm) in this example has a following
constitution. FIG. 10 shows a cross sectional view of the insulated
type semiconductor device. MOSFET element 1 (size: 2.4 mm.times.1.8
mm.times.0.24 mm), chip resistor 101 (temperature coefficient about
7 ppm/.degree. C.) and chip condenser 102 (temperature coefficient
about 11.5 ppm/.degree. C.) were mounted on a multi-glass ceramic
substrate 100 as a substrate (size: 10.5 mm.times.4 mm.times.0.5
mm; three layered wiring; thermal expansion coefficient 6.2 ppm;
thermal conductivity 2.5 W/mK; bending strength 0.25 Gpa; Young's
modulus 110 Gpa; specific dielectric constant 5.6 (at 1 MHz)).
[0091] An intermediate metal member 103 such as Cu--Cu2O composite
material is disposed between MOSFET element 1 and the multi-layered
glass ceramic substrate 100. There are formed inside of the
multi-layered glass ceramic substrate 100 a thick film inner wiring
layer (Ag-1 wt % Pt, diameter 140 .mu.m), a thick film through-hole
conductor for electric connection between the multi-layered wirings
(Ag-1 wt % Pt, diameter 140 .mu.m) and a thermal via hole for heat
dissipation (Ag-1 wt % Pt, diameter 140 .mu.m).
[0092] A thick film wiring pattern 104 (Ag-1 wt % Pt, thickness 15
.mu.m) was formed on one of the main faces of the multi-layered
glass ceramic substrate 100. Chip components including the chip
resistor 101 and chip condenser 102 were coated with the paste used
in example 2. The paste comprises silver particles coated with
hexylamine; the silver particles having the particle size of 100 nm
or less have particle size distribution peaks at 7.6 nm and 15.2 nm
and in a particle size of 100 nm or more the silver particles have
a peak of the particle size distribution at 2.75 .mu.m. The silver
particles having the above particle distribution peaks were
dispersed in toluene at a concentration of 80% by weight. The paste
was coated on the thick film pattern, followed by bonding at
300.degree. C. for 5 minutes under a pressure of 0.5 MPa towards
the chip components. As a result, the wiring pattern and the chip
components were electrically connected by sintered silver layer
105.
[0093] MOSFET 1 (Si, temperature constant 3.5 ppm/.degree. C.) was
mounted In the cavity formed in one main face of the multi-layered
glass ceramic substrate 100 by means of an intermediate member 103.
Bonding was conducted in a vacuum of 10.sup.-3. The size of the
intermediate member 103 was 2.8 mm.times.2.2 mm.times.0.2 mm. The
sintered silver layer 105 for connecting MOSFET 1 and the
intermediate metal member 103 and the bonding layer 106 for
connecting the intermediate metal member 103 and the multi-layered
glass ceramic substrate are formed by using the paste in example 2
wherein the bonding materials are dispersed in toluene in the
concentration of 80% by weight.
[0094] The clip type connecting terminal 107 made of copper is
bonded between MOSFET 1 and the thick film wiring pattern 104. The
clip was pressed at 0.1 MPa at 300.degree. C. for 2 minutes.
[0095] A thick film exterior electrode 104' (Ag-1 wt % Pt,
thickness; 15 .mu.m) was formed on the other main face of the
multi-layered glass ceramic substrate 100. The thick film exterior
electrode 104' is electrically connected to the thick film through
the inner wiring layer disposed in the ceramic substrate 100 or
through-hole wiring. The epoxy resin layer 108 is formed on the
other main face of the multi-layered glass ceramic substrate 100 to
seal the mounted chip components.
Example 7
[0096] In this example non-insulated type semiconductor device to
which lead frame for a mini-molded type transistor was used is
explained.
[0097] FIG. 11 shows a cross sectional view of the mini-molded type
non-insulated semiconductor device according to this example.
[0098] Silicon transistor element 1 (size; 1 mm.times.1
mm.times.0.3 mm) as a semiconductor element was bonded to the lead
frame 600 (thickness 0.3 mm) made of Cu--Cu.sub.2O composite
material by a sintered silver layer 601 formed from the paste. The
paste comprises silver particles coated with hexylamine; the silver
particles having the particle size of 100 nm or less have particle
size distribution peaks at 7.6 nm and 15.2 nm and in a particle
size of 100 nm or more the silver particles have a peak of the
particle size distribution at 2.75 .mu.m. The silver particles
having the above particle distribution peaks were dispersed in
toluene at a concentration of 80% by weight.
[0099] A collector of the transistor element 1 was placed at the
bonding side. The emitter and the base electrode were disposed at
the opposite side of the bonding side. The paste was coated on the
portion between the clip terminal 602 and lead frame 600, and the
bonding was conducted at 250.degree. C. for 2 minutes under a
pressure of 1.0 MPa towards the clip terminal. The main portion of
the semiconductor device including the transistor element 1 and the
clip terminal 602 was molded with epoxy resin 603 by transfer
molding. The tips of the lead frame 600 are separated from the lead
terminals after the molding with epoxy resin is finished.
Example 8
[0100] LED was packaged on a substrate using the bonding material
according to the present invention. Better heat dissipation is
expected than those of the conventional solder bonding or thermal
conductive adhesives.
* * * * *