U.S. patent application number 16/473072 was filed with the patent office on 2020-03-26 for bonding material and bonding method employing same.
This patent application is currently assigned to DOWA ELECTRONICS MATERIALS CO., LTD.. The applicant listed for this patent is DOWA ELECTRONICS MATERIALS CO., LTD.. Invention is credited to Keiichi ENDOH, Hideyuki FUJIMOTO, Tatsuro HORI, Satoru KURITA.
Application Number | 20200094318 16/473072 |
Document ID | / |
Family ID | 62844700 |
Filed Date | 2020-03-26 |
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United States Patent
Application |
20200094318 |
Kind Code |
A1 |
FUJIMOTO; Hideyuki ; et
al. |
March 26, 2020 |
BONDING MATERIAL AND BONDING METHOD EMPLOYING SAME
Abstract
The present invention aims at providing a bonding material
having both preferable dispensing properties and preferable bonding
properties, and also providing a bonding method employing the
bonding material. Provided are: a bonding material comprising fine
silver particles having an average primary particle diameter of
smaller than or equal to 130 nm, and a crosslinking-type
inter-particle distance keeping agent crosslinking between the fine
silver particles and keeping a distance between the fine silver
particles; and a bonding method employing the bonding material.
Inventors: |
FUJIMOTO; Hideyuki; (Tokyo,
JP) ; ENDOH; Keiichi; (Tokyo, JP) ; HORI;
Tatsuro; (Tokyo, JP) ; KURITA; Satoru; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DOWA ELECTRONICS MATERIALS CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
DOWA ELECTRONICS MATERIALS CO.,
LTD.
Tokyo
JP
|
Family ID: |
62844700 |
Appl. No.: |
16/473072 |
Filed: |
December 28, 2017 |
PCT Filed: |
December 28, 2017 |
PCT NO: |
PCT/JP2017/047171 |
371 Date: |
June 24, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 7/064 20130101;
B22F 7/08 20130101; B23K 35/0244 20130101; B23K 35/3006 20130101;
H01L 24/00 20130101; B22F 2301/255 20130101; B22F 1/0011 20130101;
B23K 35/365 20130101; H01L 2224/83203 20130101; B22F 1/00 20130101;
B23K 35/26 20130101; B22F 1/02 20130101; H01L 24/83 20130101; H01L
2924/10253 20130101; B22F 1/0059 20130101; H01L 2224/8384 20130101;
B22F 9/24 20130101; H01L 24/29 20130101; H01L 2224/29339 20130101;
B22F 1/0062 20130101; H01B 1/00 20130101; H01B 1/22 20130101; B22F
1/0018 20130101 |
International
Class: |
B22F 1/00 20060101
B22F001/00; B22F 7/06 20060101 B22F007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2016 |
JP |
2016-256400 |
Dec 27, 2017 |
JP |
2017-251767 |
Claims
1. A bonding material comprising fine silver particles having an
average primary particle diameter of smaller than or equal to 130
nm, and a crosslinking-type inter-particle distance keeping agent
crosslinking between the fine silver particles and keeping a
distance between the fine silver particles.
2. The bonding material according to claim 1, wherein the
crosslinking-type inter-particle distance keeping agent is a
compound .alpha. expressed by formula (I) below ##STR00007## (here,
in formula (I), R represents an organic group having a valence of 2
to 4, A and B represent a hydroxyl group, amino group, carboxyl
group, or thiol group, and in a case where two As are present, the
two As may be identical or different from each other and in a case
where two Bs are present, the two Bs may be identical or different
from each other, and assuming that in the longest straight-chain
moiety forming R, the longest moiety from among moieties between an
atom 1 bonding to A and an atom 2 bonding to B is a first main
chain, the number of chain-forming atoms of the first main chain is
10 to 180).
3. The bonding material according to claim 2, wherein at least one
from among A and B in the formula (I) is a hydroxyl group, amino
group, or thiol group, and the longest straight-chain moiety
forming R in the formula (I) has a side chain, and the number of
chain-forming atoms of the longest straight-chain moiety in the
side chain is smaller than or equal to 1/3 of the number of
chain-forming atoms of the first main chain.
4. The bonding material according to claim 2, wherein the longest
straight-chain moiety forming R in the formula (I) has a side
chain, the side chain is a hydrocarbon group having a carbon number
of 1 to 12, and A and B may bond to the side chain.
5. The bonding material according to claim 2, wherein assuming that
in the formula (I), the longest straight-chain moiety forming the
compound .alpha. is a second main chain, chain-forming atoms
(excluding atoms at a chain terminal) of the first main chain and
the second main chain form a group selected from --CH.sub.2--,
--CH(R.sup.a)--, --C(R.sup.a).sub.2--, --CX.sub.2--,
--CX(R.sup.a)--, --CH.dbd., --C(R.sup.a).dbd., .dbd.C.dbd., --CO--,
--NH--, --N(R')--, --N.dbd., --N(OH)--, --O--, --S--, and
--SO.sub.2-- (here, R.sup.a represents a side chain of the longest
straight-chain moiety forming R, and X represents halogen).
6. The bonding material according to claim 2, wherein the compound
.alpha. is any one of formulae (II) to (IV) below ##STR00008##
(here, in formula (II), v and y are each independently an integer
of 1 to 2, w is an integer of 0 to 10, and x is an integer of 14 to
40) ##STR00009## (here, in formula (III), the plurality of ks are
each independently an integer of 3 to 10, the plurality of is are
each independently an integer of 6 to 16, and m is an integer of 2
to 8) [Chemical formula 4]
C.sub.nH.sub.2n+1CH(OH)--(CH.sub.2).sub.p--CONH--(CH.sub.2).sub.q--NHCO---
(CH.sub.2).sub.r--CH(OH)C.sub.sH.sub.2s+1 (IV) (here, in formula
(IV), n and s are each independently an integer of 3 to 10, p and r
are each independently an integer of 6 to 18, and q is an integer
of 2 to 10).
7. The bonding material according to claim 1, wherein the bonding
material further comprises silver particles having an average
primary particle diameter of 0.3 to 10 .mu.m.
8. The bonding material according to claim 1, wherein the fine
silver particles are coated with an organic compound.
9. The bonding material according to claim 1, wherein the bonding
material further comprises a polar solvent.
10. The bonding material according to claim 1, wherein the bonding
material further comprises an acid-type dispersing agent.
11. A bonding method comprising: placing the bonding material
according to claim 1 between substances to be bonded and heating
the bonding material to form a bonding layer from the bonding
material; and bonding together the substances accordingly.
Description
TECHNICAL FIELD
[0001] The present invention relates to a bonding material and a
bonding method employing same, in particular to a bonding material
containing fine silver particles and a bonding method employing
this bonding material.
BACKGROUND ART
[0002] Metal, when having a size of a minute particle diameter, is
known to demonstrate physical properties that are peculiar to the
size. Nano-order particles in particular may demonstrate different
properties from those of a bulk material. Based on such
characteristics, there are proposed bonding materials in which
nanometal particles are used to bond different substances.
[0003] To cite an example, Patent Document 1, which aims at
ensuring adequate bonding strength with the simplest possible
constitution while also limiting unevenness in bonding strength,
discloses a bonding material that contains: fine silver particles
having an average primary particle diameter (D50 diameter) of 0.5
to 3.0 .mu.m (as measured with the particle size distribution
measurement device "Microtrac"); fine silver particles having an
average primary particle diameter of 1 to 200 nm (as measured with
"Microtrac") and being coated with a fatty acid having a carbon
number of 6; and a disperse medium for dispersing the fine silver
particles.
[0004] Further, Patent Document 2, which aims at enabling uniform
application on a bonding surface even with an increased silver
content and forming a dense bonding layer to achieve resistance to
repeated heat shock, discloses a bonding material constituted by:
fine silver particles being coated with a carboxylic acid that has
a carbon number of lower than or equal to 6 and having an average
primary particle diameter of 10 to 30 nm; fine silver particles
being coated with a carboxylic acid that has a carbon number of
lower than or equal to 6 and having an average primary particle
diameter of 100 to 200 nm; fine silver particles having an average
primary particle diameter of 0.3 to 3.0 .mu.m; and a dispersing
agent having a phosphoric ester group.
CITATION LIST
Patent Literature
Patent Document 1: Japanese Patent No. 5824201
Patent Document 2: Japanese Patent No. 5976684
SUMMARY OF INVENTION
Technical Problem
[0005] The inventors of the present invention continued intensive
studies on conventional bonding materials, which are represented by
the patent documents above, and as a result, found out that when
bonding materials containing fine silver particles are used, if
dispense-type printing is adopted, notable amount of fluctuation
occurs in the amount of bonding material being discharged through a
nozzle. Hereinbelow, such fluctuation in the bonding material
discharged amount will be referred to as "dispensing properties"
and the dispensing properties will be described as being preferable
when the fluctuation in the discharged amount is small. Further, in
this description, a printing method in which printing is performed
by applying shear force on a bonding material (ink or paste) so as
to discharge the bonding material from a nozzle will be referred to
as "dispense-type printing".
[0006] As set forth in the patent documents above, it is known to
use both minute, nano-sized fine silver particles and micron-sized
silver particles in combination in a bonding material. In these
documents, bonding properties are evaluated in terms of bonding
strength; however, a bonding material is required not only to bond
substances to be bonded with adequate strength but also to ensure
electrical continuity therebetween. If there are voids or cracks
when a bonding layer is formed by sintering a bonding material,
although a certain level of bonding strength may still be obtained,
it is conceivable that electrical continuity may be inadequate, and
it is also conceivable that such voids or cracks may become the
cause of a crack occurring in the process of processing a product.
The inventors of the present invention considered that, in order to
comprehensively evaluate the aforementioned matters, it would be
appropriate to evaluate whether voids or cracks are present in a
bonding layer. In this description, a condition in which there are
few or no voids or cracks in a bonding layer will be expressed as
the bonding properties being preferable. Studies conducted by the
inventors of the present invention have revealed that the minute,
nano-sized fine silver particles mentioned above are effective for
making the bonding properties preferable, but lead to degradation
in dispensing properties. It was also revealed that in order to
improve on the dispensing properties, it is effective to increase
the proportion of the fine silver particles that are described in
the patent documents above as having a relatively large particle
size or to increase the particle size itself. It was found,
however, that since such use of larger particles lead to a
reduction in the proportion of the minute fine silver particles,
the bonding properties of the formed bonding layer are
degraded.
[0007] In view of the above, the present invention aims at
providing a bonding material having both preferable dispensing
properties and preferable bonding properties, which are in a
trade-off relationship as described above, as well as providing a
bonding method employing the bonding material.
Solution to Problem
[0008] As a result of conducting intensive studies in order to
solve the problems described above, the inventors of the present
invention discovered that if a substance having a function to keep
the distances between fine silver particles appropriate is added to
the bonding material, both dispensing properties and bonding
properties can be obtained, and thus achieved the present
invention.
[0009] A first aspect of the present invention is
[0010] a bonding material comprising
[0011] fine silver particles having an average primary particle
diameter of smaller than or equal to 130 nm, and a
crosslinking-type inter-particle distance keeping agent
crosslinking between the fine silver particles and keeping a
distance between the fine silver particles.
[0012] A second aspect of the present invention is the invention as
set forth in the first aspect, wherein
[0013] the crosslinking-type inter-particle distance keeping agent
is a compound .alpha. expressed by formula (I) below
##STR00001##
[0014] (here, in formula (I), R represents an organic group having
a valence of 2 to 4,
[0015] A and B represent a hydroxyl group, amino group, carboxyl
group, or thiol group, and in a case where two As are present, the
two As may be identical or different from each other and in a case
where two Bs are present, the two Bs may be identical or different
from each other, and
[0016] assuming that in the longest straight-chain moiety forming
R, the longest moiety from among moieties between an atom 1 bonding
to A and an atom 2 bonding to B is a first main chain, the number
of chain-forming atoms of the first main chain is 10 to 180).
[0017] A third aspect of the present invention is the invention as
set forth in the second aspect, wherein
[0018] at least one from among A and B in the formula (I) is a
hydroxyl group, amino group, or thiol group, and
[0019] the longest straight-chain moiety forming R in the formula
(I) has a side chain, and the number of chain-forming atoms of the
longest straight-chain moiety in the side chain is smaller than or
equal to 1/3 of the number of chain-forming atoms of the first main
chain.
[0020] A fourth aspect of the present invention is the invention as
set forth in the second or third aspect, wherein
[0021] the longest straight-chain moiety forming R in the formula
(I) has a side chain, the side chain is a hydrocarbon group having
a carbon number of 1 to 12, and A and B may bond to the side
chain.
[0022] A fifth aspect of the present invention is the invention as
set forth in any one of the second to fourth aspects, wherein
[0023] assuming that in the formula (I), the longest straight-chain
moiety forming the compound .alpha. is a second main chain,
chain-forming atoms (excluding atoms at a chain terminal) of the
first main chain and the second main chain form a group selected
from --CH.sub.2--, --CH(R.sup.a)--, --C(R.sup.a).sub.2--,
--CX.sub.2--, --CX(R.sup.a)--, --CH.dbd., --C(R.sup.a).dbd.,
.dbd.C.dbd., --CO--, --NH--, --N(R.sup.a)--, --N.dbd., --N(OH)--,
--O--, --S--, and --SO.sub.2--
[0024] (here, R.sup.a represents a side chain of the longest
straight-chain moiety forming R, and X represents halogen).
[0025] A sixth aspect of the present invention is the invention as
set forth in the second aspect, wherein
[0026] the compound .alpha. is any one of formulae (II) to (IV)
below
##STR00002##
[0027] (here, in formula (II), v and y are each independently an
integer of 1 to 2, w is an integer of 0 to 10, and x is an integer
of 14 to 40)
##STR00003##
[0028] (here, in formula (III), the plurality of ks are each
independently an integer of 3 to 10, the plurality of 1s are each
independently an integer of 6 to 16, and m is an integer of 2 to
8)
[Chemical formula 4]
C.sub.nH.sub.2n+1CH(OH)--(CH.sub.2).sub.p--CONH--(CH.sub.2).sub.q--NHCO--
-(CH.sub.2).sub.r--CH(OH)C.sub.sH.sub.2s+1 (IV)
[0029] (here, in formula (IV), n and s are each independently an
integer of 3 to 10, p and r are each independently an integer of 6
to 18, and q is an integer of 2 to 10).
[0030] A seventh aspect of the present invention is the invention
as set forth in any one of the first to sixth aspects, wherein
[0031] the bonding material further comprises silver particles
having an average primary particle diameter of 0.3 to 10 .mu.m.
[0032] An eighth aspect of the present invention is the invention
as set forth in any one of the first to seventh aspects,
wherein
[0033] the fine silver particles are coated with an organic
compound.
[0034] A ninth aspect of the present invention is the invention as
set forth in any one of the first to eighth aspects, wherein
[0035] the bonding material further comprises a polar solvent.
[0036] A tenth aspect of the present invention is the invention as
set forth in any one of the first to ninth aspects, wherein
[0037] the bonding material further comprises an acid-type
dispersing agent.
[0038] An eleventh aspect of the present invention is a bonding
method comprising:
[0039] placing the bonding material as set forth in any one of the
first to tenth aspects between substances to be bonded and heating
the bonding material to form a bonding layer from the bonding
material; and bonding together the substances accordingly.
Advantageous Effects of Invention
[0040] According to the present invention, a bonding material
having both preferable dispensing properties and preferable bonding
properties and a bonding method employing the bonding material can
be provided.
BRIEF DESCRIPTION OF DRAWINGS
[0041] FIG. 1 is a set of photographs showing results of
observation with C-SAM of a bonded body obtained using a bonding
material, where (a) shows a result relating to Example 1 and (b)
shows a result relating to Comparative example 1.
[0042] FIG. 2 is a plot showing a result relating to a change over
time of viscosity when a shear strength (shear rate: 1/s) was
changed for the bonding material according to Example 1, where the
horizontal axis indicates time (s) and the vertical axis indicates
viscosity (Pas).
[0043] FIG. 3 is a plot showing a result relating to a change over
time of a recovery rate of viscosity obtained on the basis of FIG.
2, where the horizontal axis indicates time (s) and the vertical
axis indicates the recovery rate.
[0044] FIG. 4 is a plot showing a result relating to a change over
time of viscosity when a shear strength (shear rate: 1/s) was
changed for a bonding material according to Comparative example 2,
where the horizontal axis indicates time (s) and the vertical axis
indicates viscosity (Pas).
[0045] FIG. 5 is a plot showing a result relating to a change over
time of a recovery rate of viscosity obtained on the basis of FIG.
4, where the horizontal axis indicates time (s) and the vertical
axis indicates the recovery rate.
[0046] FIG. 6 is a plot showing a result relating to a change over
time of viscosity when a shear strength (shear rate: 1/s) was
changed for a bonding material according to Example 4, where the
horizontal axis indicates time (s) and the vertical axis indicates
viscosity (Pas).
[0047] FIG. 7 is a plot showing a result relating to a change over
time of a recovery rate of viscosity obtained on the basis of FIG.
6, where the horizontal axis indicates time (s) and the vertical
axis indicates the recovery rate.
[0048] FIG. 8 is a plot showing a result relating to a change over
time of viscosity when a shear strength (shear rate: 1/s) was
changed for a bonding material according to Example 5, where the
horizontal axis indicates time (s) and the vertical axis indicates
viscosity (Pas).
[0049] FIG. 9 is a plot showing a result relating to a change over
time of a recovery rate of viscosity obtained on the basis of FIG.
8, where the horizontal axis indicates time (s) and the vertical
axis indicates the recovery rate.
[0050] FIG. 10 is a plot showing a result relating to a change over
time of viscosity when a shear strength (shear rate: 1/s) was
changed for a bonding material according to Example 6, where the
horizontal axis indicates time (s) and the vertical axis indicates
viscosity (Pas).
[0051] FIG. 11 is a plot showing a result relating to a change over
time of a recovery rate of viscosity obtained on the basis of FIG.
10, where the horizontal axis indicates time (s) and the vertical
axis indicates the recovery rate.
[0052] FIG. 12 is a plot showing a result relating to a change over
time of viscosity when a shear strength (shear rate: 1/s) was
changed for a bonding material according to Example 7, where the
horizontal axis indicates time (s) and the vertical axis indicates
viscosity (Pas).
[0053] FIG. 13 is a plot showing a result relating to a change over
time of a recovery rate of viscosity obtained on the basis of FIG.
12, where the horizontal axis indicates time (s) and the vertical
axis indicates the recovery rate.
DESCRIPTION OF EMBODIMENTS
[0054] The present invention will be described in detail below.
Note: In this description, a range indicated by two boundary values
connected with the term "to" is inclusive of the boundary
values.
[0055] In this embodiment, description will be given in the
following order.
1 Bonding Material
[0056] 1-1 Fine Silver Particles
[0057] 1-2 Silver Particles
[0058] 1-3 Crosslinking-type inter-particle distance keeping
agent
[0059] 1-4 Solvent
[0060] 1-5 Dispersing Agent
[0061] 1-6 Others
[0062] 1-7 Bonding Material Production Method
2 Bonding Method employing Bonding Material
1 Bonding Material
[0063] Elements constituting a bonding material according to this
embodiment will be described (the bonding material being a silver
paste containing fine silver particles).
1-1 Fine Silver Particles
[0064] There are no particular limitations on the fine silver
particles to be used in this embodiment, given that the average
primary particle diameter thereof is smaller than or equal to 130
nm. A method known in the art may be used as a method for producing
the fine silver particles, and it is also possible to use fine
silver particles that are known in the art and have an average
primary particle diameter of smaller than or equal to 130 nm.
[0065] Fine silver particles having an average primary particle
diameter of smaller than or equal to 130 nm are preferable in terms
of bonding properties and, in particular, fine silver particles
having an average primary particle diameter of 1 to 40 nm superior
in bonding properties. From the viewpoint of bonding properties,
the average primary particle diameter of the fine silver particles
is more preferably 5 to 30 nm, yet more preferably 10 to 20 nm.
[0066] Although not as much as 40 nm or smaller fine silver
particles, fine silver particles having an average primary particle
diameter of greater than or equal to 41 nm are also preferable in
terms of bonding properties and, at the same time, allow for a
reduction in the viscosity of the bonding material (compared to
when 40 nm or smaller fine silver particles are added) so that the
bonding material can be printed more readily. From the viewpoint of
balance between such bonding properties and printing suitability,
the average primary particle diameter of the fine silver particles
is preferably 50 to 115 nm, more preferably 55 to 100 nm.
[0067] In this embodiment, taking bonding properties and printing
suitability into account, there may be used as the fine silver
particles a combination of fine silver particles having an average
primary particle diameter of 1 to 40 nm and fine silver particles
having an average primary particle diameter of 41 to 130 nm.
[0068] An average primary particle diameter of metal particles
(fine silver particles or silver particles (to be described later))
as referred to in this description means an average value of
primary particle diameters obtained on the basis of a transmission
electron microscopic photograph (TEM image) or scanning electron
microscopic photograph (SEM image) of the metal particles.
[0069] More specifically, such an average primary particle diameter
may be calculated from the primary particle diameters of any 100 or
more metal particles in an image (scanning electron microscope
(SEM) image or transmission electron microscope (TEM) image) (the
diameters being diameters of circles having the same areas as the
metal particles) that is obtained through observation of the metal
particles at a prescribed magnification using, for example, a TEM
(JEM-1011 (Japan Electron Optics Laboratory Ltd.)) or a SEM (S-4700
(Hitachi Hi-Technologies Corporation)). Image analysis software
(EIZOU KUN (registered trademark) (Asahi Kasei Engineering
Corporation)), for example, may be used for such a calculation of
an average primary particle diameter of metal particles.
[0070] The fine silver particles used in the present invention are
prone to aggregation because of the average primary particle
diameter thereof being as small as smaller than or equal to 130 nm,
so it is preferable that the particles be coated with an organic
compound. For such an organic compound, any known organic compound
that is able to coat fine silver particles can be used. A saturated
fatty acid, an unsaturated fatty acid, or an amine having a carbon
number of smaller than or equal to 8, preferably 2 to 6, is
preferable as the organic compound so that through low-temperature
(e.g., 170.degree. C. to 400.degree. C.) sintering, the organic
compound separates from the fine silver particles adequately and
does not hinder sintering of the fine silver particles. Examples of
such saturated fatty acid or amine include hexanoic acid, sorbic
acid, hexylamine, and octylamine.
[0071] The content of the fine silver particles described above in
the bonding material according to this embodiment is preferably 4%
to 97% by mass, more preferably 4% to 85% by mass, from the
viewpoint of demonstrating appropriate bonding strength.
1-2 Silver Particles
[0072] Silver particles having an average primary particle diameter
of 0.3 to 10 .mu.m may be added to the bonding material according
to this embodiment. Addition of silver particles allows for a
reduction in the viscosity of the bonding material and facilitates
printing of the bonding material (compared to when the metal
particles are constituted solely by fine silver particles without
the addition of silver particles). From the viewpoint of such
printing suitability, the average primary particle diameter of the
silver particles is more preferably 0.3 to 5 .mu.m, yet more
preferably 0.3 to 3 .mu.m.
[0073] The silver particles may be coated with an organic compound
for purposes such as attaining higher dispersibility, and when
doing so, it is preferable that an organic compound having a carbon
number of smaller than or equal to 20 (the carbon number of an
organic compound is usually greater than or equal to 2) be used to
coat the silver particles.
[0074] The content of silver particles in the bonding material
according to this embodiment is preferably 20% to 80% by mass from
the viewpoint of ensuring good printing suitability without
degradation in bonding properties due to a reduction in the amount
of fine silver particles blended.
[0075] When silver particles are to be used, then the total content
of fine silver particles and silver particles in the bonding
material according to this embodiment is preferably 85% to 97% by
mass, more preferably 87% to 95% by mass, from the viewpoint of
what has been described above.
1-3 Crosslinking-Type Inter-Particle Distance Keeping Agent
[0076] The bonding material according to this embodiment contains a
crosslinking-type inter-particle distance keeping agent that keeps
a distance between fine silver particles through crosslinking
between fine silver particles. Crosslinking between fine silver
particles allows a physical distance to be kept between the fine
silver particles so that aggregation of the fine silver particles
prior to use of the bonding material can be prevented and a
dispersed state of the fine silver particles can be maintained. At
the same time, with this crosslinking, the cross-link breaks or
weakens due to application of shear force, resulting in a decrease
in viscosity so that discharge in dispense-type printing is
facilitated, whereas when the printing has been completed and there
is no shear force, viscosity is recovered even in an ink having
ordinary thixotropy, and it is considered that the recovery of the
cross-link results in an earlier recovery of the viscosity (see the
examples described later). In this way, the crosslinking-type
inter-particle distance keeping agent is found to make the
dispensing properties of the bonding material preferable.
[0077] Moreover, the crosslinking-type inter-particle distance
keeping agent during sintering (being heated to, for example,
170.degree. C. to 400.degree. C.) volatilize due to being heated or
at least the molecular motion thereof becomes more active due to
being heated, thereby becoming more easily separable from the fine
silver particle, so the crosslinking-type inter-particle distance
keeping agent does not hinder sintering of the fine silver
particles, and thus preferable bonding properties can be achieved.
Note that if metal particles other than fine silver particles are
present in the bonding material, the crosslinking-type
inter-particle distance keeping agent may crosslink between such
metal particles or between such metal particles and fine silver
particles.
[0078] Any agent, without particular limitations, can be used for
the crosslinking-type inter-particle distance keeping agent as long
as the agent demonstrates a similar function to the aforementioned
by cross-linking (bonding) between fine silver particles. To cite
an example of such cross-link, a bond to silver per se may serve to
bond fine silver particles together through the crosslinking-type
inter-particle distance keeping agent.
[0079] The crosslinking-type inter-particle distance keeping agent
has a plurality of functional groups (e.g., a hydroxyl group, amino
group, thiol group, and carboxyl group) that have affinity for the
fine silver particles so as to crosslink between the fine silver
particles. Although the crosslinking-type inter-particle distance
keeping agent serves to keep a distance between fine silver
particles, if the distance is too long, a gap will be present
between the fine silver particles, which may result in the
formation of voids during sintering for the bonding and thus cause
cracks and the like; therefore, it is preferred that the
crosslinking-type inter-particle distance keeping agent have a
molecular length and a molecular structure according to which a
distance that is appropriate from the aforementioned perspective
can be kept between fine silver particles.
[0080] As a result of using such a crosslinking-type inter-particle
distance keeping agent, it is possible to achieve both preferable
dispensing properties and bonding properties in the bonding
material including the fine silver particles.
[0081] The crosslinking-type inter-particle distance keeping agent
may be, for example, a compound .alpha. expressed by formula (I)
below.
##STR00004##
[0082] In the formula (I), R represents an organic group having a
valence of 2 to 4, A and B represent a hydroxyl group, amino group,
carboxyl group, or thiol group, and assuming that in the longest
straight-chain moiety forming R, the longest moiety from among
moieties between an atom 1 bonding to A and an atom 2 bonding to B
is a first main chain, the number of chain-forming atoms of the
first main chain is 10 to 180. In a case where two As are present,
the two As may be identical or different from each other; the same
stands for B. Moreover, A and B may bond to any site in the longest
straight-chain moiety of R and may not bond to a terminal of the
straight-chain moiety.
[0083] Here, R may have a side chain. A and B may bond to this side
chain.
[0084] The definition of the first main chain is that in a case
where there are a plurality of As and/or Bs, observation is made
for the first main chain from the side of As and/or Bs that is
closest to the molecular terminal.
[0085] As a result of the number of the chain-forming atoms of the
first main chain being 10 to 180, A and B are separated to a
certain degree, and the function of the crosslinking-type
inter-particle distance keeping agent of keeping an appropriate
distance between the fine silver particles is demonstrated
preferably. From the viewpoint of this function, the number of
chain-forming atoms of the first main chain is preferably 20 to
120.
[0086] Note that for the first main chain, according to the
stipulation "the longest moiety from among moieties between an atom
1 bonding to A and an atom 2 bonding to B", the side chain in the
first main chain is not included in the count of the number of
chain-forming atoms.
[0087] The chain-forming atom is an atom that has a valence of
greater than or equal to 2 and that bonds to more than or equal to
2 atoms having a valance of greater than or equal to 2. It is
assumed that this chain-forming atom includes divalent atoms (e.g.,
O, N, C, and S) that form A and B. An increase in the number of
chain-forming atoms is assumed to indicate a longer chain.
[0088] It is preferable that at least one from among A and B in the
formula (I) be a hydroxyl group, amino group, or thiol group, the
longest straight-chain moiety forming R in the formula (I) have a
side chain, and the number of chain-forming atoms of the longest
straight-chain moiety in the side chain be smaller than or equal to
1/3 of the number of chain-forming atoms of the first main chain.
If so, in the recovery of the viscosity of the bonding material
indicated in the examples described later, the original viscosity
of the bonding material can be recovered within a short period of
time after start of the recovery. Further, it is preferable that
the number of chain-forming atoms of the longest straight-chain
moiety in the side chain at this time be greater than or equal to
1/100 of the number of chain-forming atoms of the first main chain.
It is assumed that the chain-forming atoms of the longest
straight-chain moiety in the side chain are equivalent to the
chain-forming atoms in the first main chain and include an atom
having a valence of greater than or equal to 2 and bonding to H at
the side chain terminal.
[0089] In the above example, it is particularly preferable that all
of A and B be hydroxyl groups, amino groups, or thiol groups from
the viewpoint of early recovery of the viscosity of the bonding
material and the viewpoint of the bonding properties thereof, and
from these viewpoints, it is most preferable that all of A and B be
hydroxyl groups.
[0090] In a case where the longest straight-chain moiety forming R
in the formula (I) has a side chain, examples of the side chain
include a hydrocarbon group having a carbon number of 1 to 12
(preferably 2 to 8). This hydrocarbon group may be saturated or
unsaturated and may have a branch.
[0091] Assuming that in the formula (I), the longest straight-chain
moiety forming the compound .alpha. is a second main chain, it is
preferable that the difference between the numbers of chain-forming
atoms of the second main chain and the first main chain be smaller
than or equal to 1/4 of the number of chain-forming atoms of the
second main chain. If so, A and B are at the molecular terminal of
the compound .alpha. (i.e. the difference is zero) or in the
vicinity thereof, and act more readily with the fine silver
particles. Note that while the second main chain indicates the
longest straight-chain moiety in the "compound .alpha." itself, the
first main chain indicates, as has already been described above,
the longest moiety from among moieties between an atom 1 bonding to
A and an atom 2 bonding to B in the longest straight-chain moiety
forming "R".
[0092] The chain-forming atom of the first main chain and the
second main chain is preferably C, N, O, or S, more preferably C,
N, or O. Preferably, the first main chain and the second main chain
are saturated or unsaturated.
[0093] To describe more specific examples of the first main chain
and the second main chain, the first main chain and the second main
chain may be such that the chain-forming atoms thereof form a group
selected from --CH.sub.2--, --CH(R.sup.a)--, --C(R.sup.a).sub.2--,
--CX.sub.2--, --CX(R.sup.a)--, --CH.dbd., --C(R.sup.a).dbd.,
.dbd.C.dbd., --CO--, --NH--, --N(R.sup.a)--, --N.dbd., --N(OH)--,
--O--, --S--, and --SO.sub.2--. Here, R.sup.a represents the
aforementioned side chain of R, and X represents halogen. Among
these, from the viewpoint of the function of the crosslinking-type
inter-particle distance keeping agent, preferable is a group
selected from --CH.sub.2--, --CH(R.sup.a)--, --C(R.sup.a).sub.2--,
--CH.dbd., --C(R.sup.a).dbd., --CO--, --NH--, --N(R.sup.a)--, and
--O--.
[0094] Specific examples of the compound .alpha. expressed by the
formula (I) that are particularly preferable will be listed
below.
[0095] The compound .alpha. is preferably a compound expressed by
any one of formulae (II) to (IV) below.
##STR00005##
[0096] Here, in formula (II), v and y are each independently an
integer of 1 to 2, w is an integer of 0 to 10 (preferably an
integer of 0 to 8 from the viewpoint of achieving both dispensing
properties and bonding properties), and x is an integer of 14 to 40
(preferably an integer of 18 to 36 from the viewpoint of achieving
both dispensing properties and bonding properties).
--(CH.dbd.CH)w-(CH.sub.2)x- may have a block structure in which w
(CH.dbd.CH)s bond contiguously and then x (CH.sub.2)s bond
contiguously, or may have a random structure in which these are
arranged randomly.
[0097] An example of a specific product name of the compound of
formula (II) is BYK-R606 (BYK Japan KK).
##STR00006##
[0098] Here, in formula (III), the plurality of ks are each
independently an integer of 3 to 10 (preferably an integer of 4 to
8 from the viewpoint of achieving both dispensing properties and
bonding properties), the plurality of is are each independently an
integer of 6 to 16 (preferably an integer of 8 to 12 from the
viewpoint of achieving both dispensing properties and bonding
properties), and m is an integer of 2 to 8 (preferably an integer
of 3 to 6 from the viewpoint of achieving both dispensing
properties and bonding properties).
[0099] An example of a specific product name of formula (III) is
HINOACT KF-1000 (Kawaken Fine Chemicals Co., Ltd.).
[Chemical formula 8]
C.sub.nH.sub.2n+1CH(OH)--(CH.sub.2).sub.p--CONH--(CH.sub.2).sub.q--NHCO--
-(CH.sub.2).sub.r--CH(OH)C.sub.sH.sub.2s+1 (IV)
[0100] Here, in formula (IV), n and s are each independently an
integer of 3 to 10 (preferably an integer of 4 to 8 from the
viewpoint of achieving both dispensing properties and bonding
properties), p and r are each independently an integer of 6 to 18
(preferably an integer of 8 to 14 from the viewpoint of achieving
both dispensing properties and bonding properties), and q is an
integer of 2 to 10 (preferably an integer of 2 to 6 from the
viewpoint of achieving both dispensing properties and bonding
properties).
[0101] An example of a specific product name of the compound of
formula (IV) is MA-WAX-O (KF TRADING CO., LTD.).
[0102] From among the compounds of formulae (II) to (IV) described
above, the compound expressed by formula (II) is particularly
preferable from the viewpoint of bonding properties and dispensing
properties.
[0103] Other preferable examples of the compound .alpha. include
polyhydroxycarboxylic acid ester (synthesized from
transesterification of dicarboxylic acid dimethyl ester with
alkanolamines) (the polyhydroxycarboxylic acid ester including
BYK-R606 (BYK Japan KK) mentioned above).
[0104] While not as preferable as the compounds of formulae (II) to
(IV) above for the compound .alpha., used as other examples of the
compound .alpha. may be hydrogenated castor oils (e.g. that
produced by KF TRADING CO., LTD.) or a dimer acid (a liquid fatty
acid, the main component of which is a dibasic of C36 dicarboxylic
acid obtained by dimerization of a vegetable oil-based C18
unsaturated fatty acid and which contains a monobasic and a
tribasic (e.g. product name: Tsunodyme 395 (TSUNO CO., LTD.)).
[0105] The content of the crosslinking-type inter-particle distance
keeping agent described above in the bonding material according to
this embodiment is preferably 0.01% to 2% by mass, more preferably
0.03% to 1% by mass, from the viewpoint of achieving both
preferable dispensing properties and preferable bonding
properties.
1-4 Solvent
[0106] A bonding material usually contains a solvent so that the
bonding material assumes an easily printable form. There are no
particular limitations on the solvent to be used in this
embodiment, given that, eventually, there can be obtained a bonding
material (silver paste) with which a bonding layer can be formed
through sintering of fine silver particles (and silver particles)
and which has a viscosity such that printing can be performed with
ease. One type of solvent may be used singly or two or more types
thereof may be used in combination.
[0107] The content of the solvent in the bonding material is
preferably 1% to 10% by mass, more preferably 2% to 8% by mass. A
polar solvent or a non-polar solvent may be used for this solvent,
and from the viewpoint of environmental load and miscibility with
other components in the bonding material, a polar solvent is
preferable. Used as such a polar solvent may be water, alcohol,
polyol, glycol ether, 1-methylpyrrolidinone, pyridine, terpineol,
butyl carbitol, butyl carbitol acetate, texanol, phenoxypropanol,
diethylene glycol monobutyl ether, diethylene glycol monobutyl
ether acetate, .gamma.-butyrolactone, ethylene glycol monomethyl
ether acetate, ethylene glycol monoethyl ether acetate,
methoxybutyl acetate, methoxypropyl acetate, diethylene glycol
monoethyl ether acetate, ethyl lactate, 1-octanol, and so on. It is
preferable to use, as such a polar solvent, 1-decanol, 1-dodecanol,
1-tetradecanol, 3-methyl-1,3-butanediol 3-hydroxy-3-methylbutyl
acetate, 2-ethyl-1,3-hexanediol, hexyl diglycol, 2-ethylhexyl
glycol, dibutyl diglycol, glycerin, dihydroxyterpineol,
dihydroterpinyl acetate, 2-methyl-butane-2,3,4-triol (isoprene
triol A (IPTL-A (Nippon Terpene Chemicals, Inc.))),
2-methyl-butane-1,3,4-triol (isoprene triol B (IPTL-B, Nippon
Terpene Chemicals, Inc.))), Terusolve IPG-2Ac (Nippon Terpene
Chemicals, Inc.)), Terusolve MTPH (Nippon Terpene Chemicals, Inc.),
Terusolve DTO-210 (Nippon Terpene Chemicals, Inc.), Terusolve
THA-90 (Nippon Terpene Chemicals, Inc.), Terusolve THA-70 (Nippon
Terpene Chemicals, Inc.), Terusolve TOE-100 (Nippon Terpene
Chemicals, Inc.), dihydroterpinyloxyethanol (Nippon Terpene
Chemicals, Inc.), terpinyl methyl ether (Nippon Terpene Chemicals,
Inc.), dihydroterpinyl methyl ether (Nippon Terpene Chemicals,
Inc.), and so on, and it is more preferable to use, as such a solar
solvent, at least one from among 1-decanol, 1-dodecanol,
2-ethyl-1,3-hexanediol, and 2-methyl-butane-1,3,4-triol (isoprene
triol B (IPTL-B)).
1-5. Dispersing Agent
[0108] In this embodiment, a dispersing agent may be added to the
bonding material for the purpose of keeping the dispersed state of
the fine silver particles more reliably. Any dispersing agent, with
no particular limitations, may be used that can maintain dispersion
of the fine silver particles and that, during sintering, separates
from the fine silver particles through, for example, volatilization
from the particles. For the dispersing agent, various
commercially-available dispersing agents may be used, among which
use of acid-type dispersing agents and phosphoric ester-type
dispersing agents is preferable. Examples of the acid-type
dispersing agent include butoxyethoxy acetic acid. One type from
among such dispersing agents may be used singly or two or more
types therefrom may be used in combination.
[0109] The content of the dispersing agent in the bonding material
is preferably 0.01% to 3% by mass, more preferably 0.03% to 2% by
mass.
1-6 Others
[0110] Components known in the art may be included, as appropriate,
in the bonding material according to this embodiment, in addition
to the constituents mentioned above. Specific examples of such
components include viscosity modifiers, organic binders, inorganic
binders, pH adjusters, buffers, antifoaming agents, leveling
agents, and volatilization inhibitors.
[0111] A preferable viscosity of the bonding material according to
this embodiment is 5 to 40 Pas as a general index, although the
preferable viscosity varies according to the printing method in
question in which the bonding material is adopted. In this
description, unless specifically noted otherwise, the viscosity is
measured using a rotary dynamic viscoelasticity measurement device
under the condition of 25.degree. C. and 5 rpm.
1-7 Bonding Material Production method
[0112] Next, a bonding material production method according to this
embodiment will be described. The bonding material may be produced
by, for example, separately preparing the components forming the
bonding material and mixing the same in an arbitrary order using
ultrasonic dispersion, disper, 3-roll mill, ball mill, beads mill,
twin-screw kneader, revolving stirrer, or the like.
2. Bonding Method Employing Bonding Material
[0113] The technical concept of the present invention is applicable
to a bonding method that employs the bonding material described
above. To cite an example, the technical concept may be applied to
a bonding method including: placing the bonding material described
above between substances to be bonded and heating the bonding
material to form a bonding layer from the bonding material; and
bonding together the substances accordingly.
[0114] A method known in the art may be used as a specific bonding
method, and the following shows some examples.
[0115] The bonding material (silver paste) described above may be
applied onto at least one of two substances to be bonded by
dispense-type printing; the bonding material may be disposed so as
to be interposed between the substances; and heating may be carried
out at 170.degree. C. to 400.degree. C., preferably at 200.degree.
C. to 300.degree. C., in order to sinter the fine silver particles
(and silver particles) in the bonding material, thereby forming a
bonding layer, so that the substances are bonded through this
bonding layer. Alternatively: the bonding material may be applied
to one of two substances to be bonded; heating may be carried out
at 60.degree. C. to 160.degree. C., preferably 80.degree. C. to
150.degree. C., to dry the bonding material and form a pre-dried
film; the other one of the substances to be bonded may be placed on
the pre-dried film; and thereafter heating may be carried out at
170.degree. C. to 400.degree. C., preferably at 200.degree. C. to
300.degree. C., in order to sinter the fine silver particles (and
silver particles) in the bonding material, thereby forming a
bonding layer, so that the substances are bonded through this
bonding layer. When carrying out heating, pressure may be applied
on the substances to be bonded, although such application of
pressure is not essential. The substances to be bonded can be
bonded through heating in an inert atmosphere such as nitrogen
atmosphere but can also be bonded through heating in the
atmosphere.
[0116] For the bonding method according to this embodiment, the
bonding material according to the present invention has been
described as being printed using a dispense-type printing method;
however, the bonding material may be printed using other methods
such as metal mask printing. Examples of the substances to be
bonded in the bonding method include: a substrate and a
semiconductor element; a substrate and another substrate (which may
be formed from different materials); etc.
[0117] The technical scope of the present invention is not limited
to the embodiments described above, and encompass embodiments to
which a variety of modifications or improvements are made within a
scope in which it is possible to derive specific effects that can
be obtained from the constituents of the present invention or from
the combination of the constituents.
EXAMPLES
[0118] The present invention will be described in further detail
below using examples and comparative examples, although the present
invention is not limited by the examples and comparative
examples.
Example 1
Production of First Fine Silver Particles
[0119] First, 3400 g of water was poured into a 5 l reaction
vessel. Then, nitrogen was introduced into the water in the
reaction vessel through a nozzle provided at the bottom part of the
reaction vessel at a flow rate of 3000 ml/min for 600 seconds to
remove dissolved oxygen. Next, the temperature of the water in the
reaction vessel was adjusted to 60.degree. C., while supplying
nitrogen into the reaction vessel through the top part of the
reaction vessel at a flow rate of 3000 ml/min so as to create a
nitrogen atmosphere inside the reaction vessel and performing
stirring using a stirring bar provided in the reaction vessel and
equipped with stirring blades.
[0120] 7 g of ammonia water containing 28% by mass of ammonia was
added to the water in the reaction vessel, followed by stirring for
1 minute to create a homogeneous solution. 45.5 g of hexanoic acid
(Wako Pure Chemical Corporation) (mole ratio to silver=1.98), which
is a saturated fatty acid, was added to the solution in the
reaction vessel as an organic compound (for coating fine silver
particles), and stirring was carried out for 4 minutes to dissolve
the same. Thereafter, 50% by mass of hydrazine hydrate (Otsuka
Chemical Co., Ltd.) was added as a reducing agent in the amount of
23.9 g (mole ratio to silver=4.82) to create a reducing agent
solution.
[0121] A silver nitrate aqueous solution obtained by dissolving
33.8 g of silver nitrate crystal (Wako Pure Chemical Corporation)
in 180 g of water was prepared as a silver salt aqueous solution,
and the temperature of the silver salt aqueous solution was
adjusted to 60.degree. C. Then, 0.00008 g of copper nitrate
trihydrate (Wako Pure Chemical Corporation) (1 ppm in terms of
copper relative to silver) was added to the silver salt aqueous
solution. The addition of copper nitrate trihydrate was carried out
such that an aqueous solution obtained by diluting an aqueous
solution with a comparatively high concentration of copper nitrate
trihydrate was added so that an intended copper addition amount
would be achieved.
[0122] Next, the silver salt aqueous solution described above was
added at once to the reducing agent solution described above and
mixed, and stirring the mixture, reduction reaction was initiated.
Change in color of the slurry as the reaction solution terminated
about 10 seconds after initiation of the reduction reaction. The
slurry was aged for 10 minutes while being stirred, after which the
stirring was stopped and the slurry was subjected to solid-liquid
separation based on suction filtration. The solid obtained by the
solid-liquid separation was washed with pure water and vacuum-dried
at 40.degree. C. for 12 hours, thereby obtaining a dry powder of
the first fine silver particles (coated with hexanoic acid).
[0123] The proportion of silver in the first fine silver particles
was calculated to be 97% by mass from the weight after removal of
the hexanoic acid through heating. The average primary particle
diameter (particle size) of the first fine silver particles was 17
nm, as measured using a transmission electron microscope (TEM).
Production of Second Fine Silver Particles
[0124] Further, 180.0 g of pure water was poured into a 300 ml
beaker and 33.6 g of silver nitrate (TOYOKAGAKU, INC.) was added
thereto and dissolved to prepare a silver nitrate aqueous solution
as a raw material solution.
[0125] In addition, 3322.0 g of pure water was poured into a 5 l
beaker, and while the pure water was aerated with nitrogen for 30
minutes to remove dissolved oxygen, the temperature thereof was
raised to 40.degree. C. Added to this pure water was 44.8 g of
sorbic acid (Wako Pure Chemical Corporation) as an organic compound
(for coating the fine silver particles) and then 7.1 g of 28%
ammonia water (Wako Pure Chemical Corporation) as a stabilizer.
[0126] While stirring the aqueous solution to which the ammonia
water had been added, 14.91 g of 80%-pure hydrous hydrazine (Otsuka
Chemical Co., Ltd.) was added to the solution as a reducing agent
after the lapse of 5 minutes from the time point at which the
ammonia water had been added (reaction initiation time point) to
prepare a reducing agent-containing aqueous solution as a reducing
solution. After the lapse of 9 minutes from the reaction initiation
time point, the raw material solution (silver nitrate aqueous
solution), the temperature of which had been adjusted to 40.degree.
C., was added at once to the reducing solution (reducing
agent-containing aqueous solution) to allow reaction therebetween
and the resultant was further stirred for 80 minutes, after which
the temperature of the same was raised from 40.degree. C. to
60.degree. C. at the temperature-raising speed of 1.degree. C./min,
then the stirring was terminated.
[0127] After an aggregate of fine silver particles coated with
sorbic acid was formed in this way, the solution containing the
aggregate of fine silver particles was filtered using a No. 5C
filter paper, and the substance recovered through the filtration
was washed with pure water to obtain an aggregate of fine silver
particles. This aggregate of fine silver particles was dried in a
vacuum drier at 80.degree. C. for 12 hours to obtain a dry powder
of the aggregate of fine silver particles. The thus obtained dry
powder of the aggregate of fine silver particles was subjected to
comminution and the size of the secondary aggregate was adjusted;
thus, the second fine silver particles were obtained. The average
primary particle diameter (particle size) of the second fine silver
particles was 85 nm, as measured using a scanning electron
microscope (SEM).
Production of Bonding Material
[0128] Next, what are listed below were kneaded and the substance
thus obtained through kneading was passed through a 3-roll machine
to obtain a bonding material constituted by a silver paste.
[0129] 14.60% by mass of the dry powder of the fine silver
particles (coated with hexanoic acid) with a particle size of 17
nm, produced as the first fine silver particles as described
above
[0130] 26.94% by mass of the dry powder of the fine silver
particles (coated with sorbic acid) with a particle size of 85 nm,
produced as the second fine silver particles as described above
[0131] 51.04% by mass of silver particles (AG2-1C (DOWA Electronics
Materials Co., Ltd.)) with a particle size of 0.6 .mu.m
[0132] 1.49% by mass of octanediol (2-ethyl-1,3-hexanediol (Wako
Pure Chemical Corporation)) as a first solvent
[0133] 0.85% by mass of 1-dodecanol (Tokyo Chemical Industry Co.,
Ltd.) as a second solvent
[0134] 3.48% by mass of 2-methyl-butane-1,3,4-triol (isoprene triol
B (IPTL-B)) (Nippon Terpene Chemicals, Inc.) as a third solvent
[0135] 0.50% by mass of butoxyethoxy acetic acid (BEA) (Tokyo
Chemical Industry Co., Ltd.) as the dispersing agent
[0136] 0.99% by mass of another acid-type dispersing agent
[0137] 0.10% by mass of polyhydroxycarboxylic acid ester (BYK-R606
(BYK Japan KK)) as the crosslinking-type inter-particle distance
keeping agent
[0138] Table 1 below shows the aforementioned constituents and the
contents thereof. The constituents and the contents thereof for
Examples 2 and 3 and Comparative examples 1 and 2 described below
are also shown in Table 1.
TABLE-US-00001 TABLE 1 Comparative Comparative Example 1 Example 2
Example 3 example 1 example 2 First fine silver 14.60 14.61 14.48
14.63 14.62 particles Second fine silver 26.94 26.97 26.72 27.00
26.99 particles Silver particles: 51.04 51.09 50.62 51.16 51.13
AG2-1C First solvent: 2- 1.49 1.49 1.48 1.50 1.50 ethyl-1,3-
hexanediol Second solvent: 0.85 0.80 2.66 0.73 1.77 dodecanol Third
solvent: 3.48 3.49 3.45 3.49 3.49 IPTL-B Dispersing Agent: 0.50
0.50 0.49 0.50 0.50 butoxyethoxy acetic acid Other acid-type 0.99
1.00 0 1.00 0 dispersing agent Crosslinking-type 0.10 0.05 0.10 0 0
inter-particle distance keeping agent: BYK-R606
Viscosity of Bonding Material
[0139] The viscosity of this bonding material (silver paste) at
25.degree. C., as measured with a rheometer (rotary dynamic
viscoelasticity measurement device) (HAAKE RheoStress 600 (a cone
with a cone diameter of 35 mm and a cone angle of 2.degree. was
used) (Thermo Fisher Scientific)), was 24 (Pas) at 5 rpm. The
viscosity at 1 rpm was 65 (Pas).
[0140] Table 2 below shows these viscosities. Table 2 also shows
viscosities and the evaluation results therefor (will be described
in detail below) for Examples 2 and 3 and Comparative examples 1
and 2 described below.
TABLE-US-00002 TABLE 2 Comparative Comparative Example 1 Example 2
Example 3 example 1 example 2 Viscosity 1 rpm 65 64 86.3 55 56 5
rpm 24 24 25 25 25 Dispensing Weight <.+-.10 <.+-.10
<.+-.10 <.+-.10 >.+-.10% properties fluctuation (%)
Bonding Void, crack None None None Crack None properties
Example 2
[0141] A bonding material (silver paste) was produced using an
equivalent method to Example 1, except that the amount of each
constituent blended in the bonding material was changed as in Table
1 above (the amount of each constituent blended is adjusted so that
the viscosity would be substantially the same; same below). The
measured viscosity of the bonding material at 25.degree. C. was 64
(Pas) at 1 rpm and 24 (Pas) at 5 rpm.
Example 3
[0142] A bonding material (silver paste) was produced using an
equivalent method to Example 1, except that the amount of each
constituent blended in the bonding material was changed as in Table
1 above. The measured viscosity of the bonding material at
25.degree. C. was 86.3 (Pas) at 1 rpm and 25 (Pas) at 5 rpm.
Comparative Example 1
[0143] A bonding material (silver paste) was produced using an
equivalent method to Example 1, except that polyhydroxycarboxylic
acid ester (BYK-R606 (BYK Japan KK)) as the crosslinking-type
inter-particle distance keeping agent in the bonding material was
not used and that the amount of each constituent blended was
changed as in Table 1 above. The measured viscosity of the bonding
material at 25.degree. C. was 55 (Pas) at 1 rpm and 25 (Pas) at 5
rpm.
Comparative Example 2
[0144] A bonding material (silver paste) was produced using an
equivalent method to Example 1, except that polyhydroxycarboxylic
acid ester (BYK-R606 (BYK Japan KK)) as the crosslinking-type
inter-particle distance keeping agent in the bonding material was
not used, that butoxyethoxy acetic acid (BEA) (Tokyo Chemical
Industry Co., Ltd.) was used alone as the dispersing agent, and
that the amount of each constituent blended was changed as in Table
1 above. The measured viscosity of the bonding material at
25.degree. C. was 56 (Pas) at 1 rpm and 25 (Pas) at 5 rpm.
[Evaluation]
Evaluation of Dispensing Properties
[0145] The bonding materials obtained in the Examples and
Comparative examples above were used to evaluate the dispensing
properties. The following evaluation method was employed to
evaluate the dispensing properties.
[0146] The bonding material (silver paste) above was loaded into a
syringe. A needle (0.58 mm .PHI.) was attached to the syringe and a
23 mm-long line pattern was drawn (printed) using a dispenser
(ML-5000XII (Musashi Engineering Inc.)).
[0147] As for the procedure, first, the line pattern was singly
printed (so-called "purging") on a glass plate. Then, printing was
halted for 3 minutes, whereafter 10 line patterns were printed on
another glass plate. An interval between printing one line pattern
and starting to print the next line pattern was 1 second.
[0148] Thereafter, 10 line patterns were printed on yet another
glass plate. An interval between printing the last line pattern on
the previous glass plate and starting to print the first line
pattern on the next glass plate was 2 seconds. In this way, 15 such
glass plates on which 10 line patterns were printed were
prepared.
[0149] For these glass plates on which line patterns were printed,
the weight of the 10 patterns on the first glass plate was assumed
to be 100%, and in relation to this, the degree of fluctuation in
the weight of the 10 patterns in each of the other, second to
fifteenth, glass plates was ascertained. The results showed that
variations were within .+-.10% for Examples 1 to 3 and Comparative
example 1, whereas for Comparative example 2, weight fluctuation
exceeded .+-.10%.
[0150] It should be noted that although the result for Comparative
example 1 in terms of dispensing properties was not unfavorable,
there would be a significant difference between Example 1 and
Comparative example 1 in terms of bonding properties, which
constitute the other item of evaluation.
Evaluation of Bonding Properties
[0151] Next, bonding test was conducted. For the substrate, there
was used a 10 mm square copper plate on which gold plating had been
applied. Onto this copper plate, the bonding material (silver
paste) of the examples and comparative examples was applied in the
shape of a 3 mm square-equivalent snow star (asterisk) using the
dispenser (ML-5000XII), and a onto this, a semiconductor element
having been subjected to 3 mm square gold plating was mounted.
Thereafter, in a state where no pressure was applied, the
temperature of the copper plate, the semiconductor element, and the
bonding material therebetween was raised in an inert oven to
210.degree. C. at 0.05.degree. C./sec and was maintained thus for
60 minutes to sinter the fine silver particles and silver
particles, thereby forming a silver bonding layer. For the bonded
body obtained in this way, an image (C-SAM image) obtained using an
ultrasonic microscope (C-SAM: D9500 (SONOSCAN, INC.)) was used to
observe whether there were voids in the silver bonding layer
(within the silver bonding layer and also on the boundary between
the silver bonding layer and the substrate and the boundary between
the silver bonding layer and the Si chip).
[0152] Results for Example 1 and Comparative example 1 are shown in
FIG. 1 as representative examples. In FIG. 1, (a) shows an
observation result for a silver bonding layer in which the bonding
material of Example 1 was used, and (b) shows an observation result
for a silver bonding layer in which the bonding material of
Comparative example 1 was used.
[0153] If the entirety of a C-SAM image was black, there would be
no voids, and bonding was assessed as being preferable, whereas if
there were white portions in a C-SAM image, there would be voids or
cracks, and a bonding state was assessed as not being
preferable.
[0154] From the results of the evaluation of bonding properties, no
cracks or voids were observed and bonding was preferable in the
cases in which the bonding materials of Examples 1 to 3 and
Comparative example 2 were used. Meanwhile, in the case in which
the bonding material of Comparative example 1 was used, there were
cracks as shown in FIG. 1 (b) and bonding was not preferable.
[0155] According to the above, a bonding material having both
preferable dispensing properties and preferable bonding properties,
and a bonding method employing the bonding material, could be
provided in the case of Examples 1 to 3.
[Verification of Quick Viscosity Recovery in Examples]
[0156] As indicated above, dispensing properties and bonding
properties were preferable in the Examples. As a reason for which
such results were obtained, a section of the embodiments of the
present invention has stated that there is demonstrated an effect
that viscosity recovers quickly in the bonding material when shear
force ceases to be applied. In this section, how quickly viscosity
recovers in relation to the presence or absence of shear force and
the progress thereof with time is verified for Example 1 and
Comparative example 2 serving as representative examples.
[0157] First, the viscosities of the bonding materials produced in
Example 1 and Comparative example 2 were measured over time using
the aforementioned rheometer (rotary dynamic viscoelasticity
measurement device) (HAAKE RheoStress 600 (Thermo Fisher
Scientific)). Specifically, the temperature of the bonding material
was adjusted to 25.degree. C., and measurement was carried out at
the shear rate of 10 (1/s) for 120 seconds, after which the shear
rate was reduced to 1 (1/s) and measurement was carried out for 600
seconds. Here, the viscosity at each timepoint after the shear rate
was reduced to 1 (1/s) was divided by the viscosity at the
timepoint at which measurement was ended (the timepoint at which
600 seconds (during which the reduced shear rate of 1 (1/s) was
maintained) elapsed) and the resulting value was defined to be the
recovery rate. FIGS. 2 to 5 show the results of the same.
[0158] FIG. 2 is a plot showing the result relating to a change
over time of viscosity when the shear strength (shear rate: 1/s)
was changed for the bonding material according to Example 1, where
the horizontal axis indicates time (s) and the vertical axis
indicates viscosity (Pas). FIG. 3 is a plot showing the result
relating to a change over time of the recovery rate obtained on the
basis of FIG. 2, where the horizontal axis indicates time (s) and
the vertical axis indicates the recovery rate. 0th second in FIG. 3
corresponds to the timepoint of the 120th second in FIG. 2.
[0159] FIG. 4 is a plot showing the result relating to a change
over time of viscosity when the shear strength (shear rate: 1/s)
was changed for the bonding material according to Comparative
example 2, where the horizontal axis indicates time (s) and the
vertical axis indicates viscosity (Pas). FIG. 5 is a plot showing
the result relating to a change over time of the recovery rate
obtained on the basis of FIG. 4, where the horizontal axis
indicates time (s) and the vertical axis indicates the recovery
rate. 0th second in FIG. 5 corresponds to the timepoint of the
120th second in FIG. 4.
[0160] In Example 1 (FIG. 2), viscosity recovers very quickly after
the shear rate is reduced to 1 (1/s) at once. As an evidence
thereof, in FIG. 3, the recovery rate at the measurement starting
timepoint is higher than or equal to 0.90.
[0161] In contrast, in Comparative example 2 (FIG. 4), the speed of
viscosity recovery is very slow. As an evidence thereof, in FIG. 5,
considerable amount of time is required for the recovery rate to
even reach, for example, 0.90. This slowness in recovery leads to
fluctuations in the discharged amount and, eventually, to the
problem with dispensing properties.
[0162] Meanwhile, in the case of the Examples, viscosity can be
recovered quickly, and not only the dispensing properties but also
the bonding properties can be made preferable. As can be seen from
the results described above, it is preferable that the recovery
rate of the bonding material as defined above be high:
Specifically, the same at the measurement starting timepoint is
preferably higher than or equal to 0.80, more preferably higher
than or equal to 0.85.
Examples 4 to 7
[0163] In Examples 4 to 7, HINOACT KF-1000 (Example 4), MA-WAX-O
(Example 5), Tsunodyme 395 (Example 6), and hydrogenated castor oil
(Example 7) were used in place of BYK-R606 used in Examples 1 to 3
as the crosslinking-type inter-particle distance keeping agent, the
test was conducted accordingly. The method for producing the first
and second fine silver particles are the same as for Example 1, and
also for other matters, the same matters as those in Example 1 are
adopted unless specifically noted otherwise.
Production of Bonding Material
[0164] Next, what are listed below were kneaded and the substance
thus obtained through kneading was passed through a 3-roll machine
to obtain a bonding material constituted by a silver paste.
[0165] 14.61% by mass of the dry powder of the fine silver
particles (coated with hexanoic acid) with a particle size of 17
nm, produced as the first fine silver particles as described
above
[0166] 26.97% by mass of the dry powder of the fine silver
particles (coated with sorbic acid) with a particle size of 85 nm,
produced as the second fine silver particles as described above
[0167] 51.09% by mass of silver particles (AG2-1C (DOWA Electronics
Materials Co., Ltd.)) with a particle size of 0.6 .mu.m
[0168] 1.49% by mass of octanediol (2-ethyl-1,3-hexanediol (Wako
Pure Chemical Corporation)) as a first solvent
[0169] 0.80% by mass of 1-dodecanol (Tokyo Chemical Industry Co.,
Ltd.) as a second solvent
[0170] 3.49% by mass of 2-methyl-butane-1,3,4-triol (isoprene triol
B (IPTL-B)) (Nippon Terpene Chemicals, Inc.) as a third solvent
[0171] 0.50% by mass of butoxyethoxy acetic acid (BEA) (Tokyo
Chemical Industry Co., Ltd.) as the dispersing agent
[0172] 1.00% by mass of another acid-type dispersing agent
[0173] 0.05% by mass of the crosslinking-type inter-particle
distance keeping agent according to Examples 4 to 7
[0174] Table 3 below shows the aforementioned constituents and the
contents thereof. The constituents and the contents thereof for the
examples described below are also shown in Table 3.
TABLE-US-00003 TABLE 3 Exam- Exam- Exam- ple 4 ple 5 ple 6 Example
7 First fine silver particles 14.61 14.61 14.61 14.61 Second fine
silver particles 26.97 26.97 26.97 26.97 Silver particles: AG2-1C
51.09 51.09 51.09 51.09 First solvent: 2-ethyl-1,3- 1.49 1.49 1.49
1.49 hexanediol Second solvent: dodecanol 0.8 0.8 0.8 0.8 Third
solvent: IPTL-B 3.49 3.49 3.49 3.49 Dispersing Agent: butoxyethoxy
0.5 0.5 0.5 0.5 acetic acid Other acid-type dispersing agent 1 1 1
1 Crosslinking-type inter-particle 0.05 0 0 0 distance keeping
agent: HINOACT KF-1000 Crosslinking-type inter-particle 0 0.05 0 0
distance keeping agent: MA-WAX-O Crosslinking-type inter-particle 0
0 0.05 0 distance keeping agent: Tsunodyme 395 Crosslinking-type
inter-particle 0 0 0 0.05 distance keeping agent: Hydrogenated
castor oil
Viscosity of Bonding Material
[0175] The viscosity of this bonding material (silver paste) at
25.degree. C. was measured with a rheometer (rotary dynamic
viscoelasticity measurement device) (HAAKE RheoStress 600 (a cone
with a cone diameter of 35 mm and a cone angle of 2.degree. was
used) (Thermo Fisher Scientific)). The viscosity and thixotropy
(Ti=viscosity (1 rpm)/viscosity (5 rpm)) of each of the above are
shown in Table 4 below. The viscosity and Ti for the examples
described below are also shown in Table 4.
TABLE-US-00004 TABLE 4 Example 4 Example 5 Example 6 Example 7
Viscosity 1 rpm 65.41 60.62 53.49 67.95 5 rpm 26.79 26.03 25.63
27.02 Ti 2.44 2.33 2.09 2.51
[Evaluation]
Evaluation of Dispensing Properties
[0176] As stated above, a reason for which the dispensing
properties of the bonding material are preferable is that viscosity
recovers quickly in the bonding material when shear force ceases to
be applied. Accordingly, in Examples 4 to 7, the evaluation of
dispensing properties is based on how quickly viscosity recovers.
Specifically, the method used in the [Verification of Quick
Viscosity Recovery in Examples] section above was adopted to carry
out the measurements. FIGS. 6 to 13 show results for Examples 4 to
7.
[0177] FIG. 6 is a plot showing a result relating to a change over
time of viscosity when a shear strength (shear rate: 1/s) was
changed for a bonding material according to Example 4 (HINOACT
KF-1000), where the horizontal axis indicates time (s) and the
vertical axis indicates viscosity (Pas). FIG. 7 is a plot showing a
result relating to a change over time of a recovery rate obtained
on the basis of FIG. 6, where the horizontal axis indicates time
(s) and the vertical axis indicates the recovery rate. 0th second
in FIG. 7 corresponds to the timepoint of the 120th second in FIG.
6.
[0178] Results for Example 4 correspond to FIGS. 6 and 7, and
likewise, results for Example 5 (MA-WAX-O) correspond to FIGS. 8
and 9, results for Example 6 (Tsunodyme 395) correspond to FIGS. 10
and 11, and results for Example 7 (hydrogenated castor oil)
correspond to FIGS. 12 and 13.
[0179] In all these Examples, viscosity recovered quickly after the
shear rate was reduced to 1 (1/s) at once, compared to Comparative
example 2. As an evidence thereof, in all these Examples, the
recovery rate at the measurement starting timepoint is higher than
or equal to 0.78. It should be noted that for Examples 6 and 7, as
compared to Examples 4 and 5 (and Example 1), viscosity recovery is
slower (for example, the time until the viscosity recovery rate
reaches 0.95 is longer), and the bonding materials of Examples 4
and 5 are superior in terms of dispensing properties.
[0180] In addition, in Example 4 (HINOACT KF-1000) and in Example 5
(MA-WAX-O) in particular among Examples 4 to 7, viscosity recovered
quickly.
Evaluation of Bonding Properties
[0181] Next, bonding test was conducted using an equivalent method
to Examples 1 to 3 and Comparative examples 1 and 2 above.
[0182] From the results of the evaluation of bonding properties, in
cases in which the bonding materials of Examples 4 to 7 were used,
bonding was favorable, but compared to Examples 1 to 3, a small
amount of voids or cracks were observed.
[0183] According to the above, a bonding material having both
preferable dispensing properties and preferable bonding properties,
and a bonding method employing the bonding material, could be
provided in the case of examples 4 to 7. The existence of
differences between these examples in terms of dispensing
properties and the inferiority of these examples compared to
examples 1 to 3 in terms of bonding properties are as described
above.
Synopsis
[0184] As can be seen from the above results, in the bonding
materials in all of the Examples, a crosslinking-type
inter-particle distance keeping agent was added and the dispensing
properties and bonding properties were preferable.
[0185] Meanwhile, Comparative examples 1 and 2 in which no
crosslinking-type inter-particle distance keeping agent was added
gave either a result with unfavorable dispensing properties in
terms of weight fluctuation in the discharged amount in the
dispenser exceeding .+-.10% or a result with unfavorable bonding
properties in terms of occurrence of cracks or voids.
* * * * *