U.S. patent application number 10/913370 was filed with the patent office on 2005-03-17 for thermosetting flux and solder paste.
This patent application is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Komatsu, Izuru, Matsumoto, Kazutaka, Tadauchi, Masahiro.
Application Number | 20050056687 10/913370 |
Document ID | / |
Family ID | 34269041 |
Filed Date | 2005-03-17 |
United States Patent
Application |
20050056687 |
Kind Code |
A1 |
Matsumoto, Kazutaka ; et
al. |
March 17, 2005 |
Thermosetting flux and solder paste
Abstract
The invention aims to provide a thermosetting flux suitable for
solder bonding of a semiconductor element and an electronic part
and making solder bonding with a high bonding strength and a high
heat resistant strength at a high temperature possible and a paste
containing the flux and a non-lead type solder paste and with
respect to the thermosetting flux, an epoxy resin, a hardening
agent, and at least one of rosin derivatives having functional
groups reactive on the epoxy resin and selected from maleic
acid-modified rosin, a fumaric acid-modified rosin, and acrylic
acid-modified rosin are used. The flux can be used in form of a
solder paste while being mixed and kneaded with the non-lead type
solder alloy powder.
Inventors: |
Matsumoto, Kazutaka;
(Kanagawa-ken, JP) ; Tadauchi, Masahiro;
(Kanagawa-ken, JP) ; Komatsu, Izuru;
(Kanagawa-ken, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Kabushiki Kaisha Toshiba
Tokyo
JP
|
Family ID: |
34269041 |
Appl. No.: |
10/913370 |
Filed: |
August 9, 2004 |
Current U.S.
Class: |
228/248.1 |
Current CPC
Class: |
H05K 3/3485 20200801;
B23K 2101/40 20180801; B23K 35/025 20130101; H05K 2201/10977
20130101; B23K 35/3618 20130101; B23K 35/3613 20130101; B23K 35/36
20130101; B23K 35/262 20130101; B23K 35/0244 20130101; H05K 3/3489
20130101; B23K 35/3612 20130101; B23K 35/0222 20130101 |
Class at
Publication: |
228/248.1 |
International
Class: |
B23K 031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 8, 2003 |
JP |
2003-289645 |
Claims
What is claimed is:
1. A thermosetting flux comprising an epoxy resin, a hardening
agent, and at least one of rosin derivatives having functional
groups reactive on the epoxy resin, selected from maleic
acid-modified rosin, a fumaric acid-modified rosin, and acrylic
acid-modified rosin.
2. The flux according to the claim 1, wherein the ratio of the
rosin derivative is 5 to 50% by weight in the thermosetting
flux.
3. The flux according to the claim 1, wherein the equivalent ratio
of the epoxy group of the epoxy resin and the reactive group of the
hardening agent is 0.5 to 1.5.
4. The thermosetting flux according to the claim 3, wherein the
equivalent ratio of the epoxy groups of the epoxy resin and the
reactive groups of the hardening agent 0.8 to 1.2.
5. The thermosetting flux according to the claim 1, wherein the
rosin derivative is maleic acid-modified rosin.
6. The thermosetting flux according to the claim 1, wherein the
hardening time of the epoxy resin is within 30 minutes at the
soldering temperature.
7. A solder paste comprising a thermosetting flux containing an
epoxy resin, a hardening agent, and at least one rosin derivative
having a functional group reactive on the epoxy resin and selected
from a maleic acid-modified rosin, a fumaric acid-modified rosin,
and acrylic acid-modified rosin and a non-lead type solder alloy
powder as well.
8. The solder paste according to the claim 7, wherein the addition
amount of the thermosetting flux to the solder paste is not more
than 5 parts by weight and not less than 15 parts by weight to 100
parts by weight of the solder paste.
9. The solder paste according to the claim 7, wherein melting
points of the epoxy resin and the hardening agent are the melting
point of the non-lead type solder alloy or lower.
10. The solder paste according to the claim 7, wherein the
hardening temperature of the epoxy resin in the solder paste is the
melting point of the non-lead type solder alloy or higher.
11. The solder paste according to the claim 7, wherein hardening
time of the epoxy resin is within 30 minutes at the soldering
temperature.
12. The solder paste according to the claim 7, wherein the non-lead
type solder alloy has a melting point in a range of 150 to
300.degree. C.
13. The solder paste according to the claim 12, wherein the
non-lead type solder alloy has a melting point in a range of 180 to
280.degree. C.
14. The solder paste according to the claim 7, wherein solder paste
contains at least one of an antioxidant and an anti-corrosion
agent.
15. A soldering method comprising at least steps of applying a
solder paste comprising a thermosetting flux containing an epoxy
resin, a hardening agent, and at least one rosin derivative having
a functional group reactive on the epoxy resin and selected from a
maleic acid-modified rosin, a fumaric acid-modified rosin, and
acrylic acid-modified rosin and a non-lead type solder alloy powder
to an object part of a substrate having an electrode to be bonded
and then mounting an object part to be bonded on the substrate;
pre-heating the substrate and the mounted part at 150 to
180.degree. C. for 0.1 to 10 minutes; and heating the resulting
substrate and the mounted part at 200 to 300.degree. C. for 0.1 to
30 minutes.
16. The soldering method according to the claim 15, wherein the
object part to be bonded is a power semiconductor element.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.2003-289645,
filed on Aug. 8, 2003; the entire contents of which are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to a thermosetting flux suitable for
solder bonding of electronic parts of a semiconductor device and a
solder paste using the flux.
DESCRIPTION OF THE RELATED ART
[0003] In assembly of a semiconductor device, a mounting step of
mounting a semiconductor element at a prescribed part on a
leadframeoraresinsubstr- ateisoneofimportantstepsaffecting the long
term reliability of elements. Conventionally, as a mounting method,
a solder mounting method using a low melting point alloy (solder)
and a resin mounting method using a resin paste containing mainly a
thermosetting resin such as an epoxy resin have been employed.
Especially, in the case of a semiconductor element such as a power
element required to have a heat releasing property, a solder
mounting method using a high temperature solder mainly containing
90% or more lead has been employed.
[0004] However, in recent years, along with increase of the
concerns of global environmental issues, non-lead type solders have
been drawing attention. With respect to electronic apparatuses,
production of products using lead-type ones and their import and
export become subjects to legal regulation and accordingly, urgent
countermeasure is needed.
[0005] Under such a situation, as non-lead type high temperature
solder materials to be used for electronic apparatuses, Zn--Al--Mg
type solders (reference to Japanese Patent Application Laid-Open
No. 11-172354), Zn--Al--Ge type solder (reference to Japanese
Patent Application Laid-Open No. 11-172353) and the like have
proposed. However, any compositions are unsatisfactory in the
processibility and further the compositions contain elements easy
to be oxidized, so that they are inferior in the wettability and
unsuitability for practical uses.
[0006] On the other hand, Sn--Cu type solders as a non-lead type
high temperature solder material have been supposed possible. The
Sn--Cu type solders have no problem in oxidation and are excellent
in wettability, however they have a problem in the brittleness and
are thus unsuitable for practical use. In such a manner, presently,
there is no usable non-lead type solder material as a high
temperature solder.
[0007] To solve the above-mentioned problem, it has been discussed
whether it is possible or not to use a conductive adhesive as a
substituting material for the high temperature solder. On the other
hand, not only as a solder mounting material, but also as a
solder-substituting bonding material, it has been tried to use the
conductive adhesives for assembly of general electron apparatus
substrates (reference to Japanese Patent Application Laid-Open No.
2000-290617).
[0008] The conductive adhesive is produced by mixing conductive
filler such as silver, gold, copper, nickel, carbon or the like and
a binder such as an epoxy resin, a phenolic resin, a polyester
resin, an acrylic resin or the like at a prescribed ratio and
kneading them.
[0009] However, in order to attain conductivity by the conductive
adhesive as high as that by conventional soldering, those
containing nickel or carbon as the conductive filler are
unsatisfactory and presently, those containing a noble metal powder
of such as silver, gold or the like as the conductive filler have
to be used. However, silver and gold cost very high as compared
with the cost of a general solder material (mainly containing tin)
and that becomes an obstacle to use of the conductive adhesive
besides the technical problems. Also, to use the conductive
adhesive as the mounting material for a power element, there is
another problem that the thermal conductivity is insufficient.
Nevertheless, soldering is best for bonding a semiconductor device
or an electronic part.
[0010] As known well, a flux is used for soldering. The main
functions of the flux are to clean the solder-bonding part, to
prevent oxidation of a metal, and to improve the wettability of a
solder. A conventional flux is anauxiliary agent for making the
soldering easy by such functions and it does nothing to do with the
adhesion of the soldered part after the soldering and accordingly,
the bonding strength is exclusively depending on the fusion bonding
of the solder metal. In the solder bonding using a common non-lead
type solder material with a melting point of 250.degree. C. or
lower, the heat resistant strength and the bonding strength are not
necessarily sufficient. Particularly, with respect to a
semiconductor element, in the wire bonding after mounting the
semiconductor element or the second time or later soldering of a
double-mounted type substrate bearing parts, the solder material
may be re-melted when it is heated to 250.degree. C. or higher to
result in an undesirable consequence that the bonded part of the
semiconductor element or the electronic part is separated or
dropped.
[0011] Accordingly, in the case of carrying out solder bonding of
the semiconductor element or the electronic part, it is needed to
strengthen the bonding strength of the element or the electronic
part.
[0012] To strengthen the bonding of the electronic part at the time
of above-mentioned soldering, a flux for thermosetting solder
obtained by adding a thermosetting resin to a rosin type flux is
disclosed (reference to Japanese Patent Application Laid-Open No.
2001-219294). The flux can firmly strengthen an electronic part by
owing to hardening of the thermosetting resin in the flux at the
time of soldering and combination of the bonding by the solder and
the bonding of the thermosetting resin. However, this technique is
based only on addition of a conventional rosin to the thermosetting
resin and the resin is not reacted with the thermosetting resin but
simply mixed with and exists in the thermosetting resin and
therefore, the heat resistant strength is not sufficient, so that
in the case of carrying out soldering at a high temperature for a
non-lead type solder, the bonding part is separated to result in
deterioration of the reliability of the electronic apparatuses.
SUMMARY OF THE INVENTION
[0013] The invention has been accomplished in consideration of the
above-mentioned problems and aims to provide a thermosetting flux
suitable for solder bonding of a semiconductor element and an
electronic part and capable of firmly bonding an electronic part to
a part-mounted substrate simultaneously with soldering and
maintaining stably bonding for a long duration and a non-lead type
solder paste using the thermosetting flux.
[0014] The first aspect of the invention provides a thermosetting
flux containing as indispensable components, an epoxy resin, a
hardening agent, and a rosin derivative having a functional group
reactive on the epoxy resin and which is at least one compound
selected from a maleic acid-modified rosin, fumaric acid-modified
rosin, and acrylic acid-modified rosin.
[0015] The second aspect of the invention provide a solder paste
comprising a thermosetting flux containing as indispensable
components, an epoxy resin, a hardening agent, and a rosin
derivative having a functional group reactive on the epoxy resin
and which is at least one compound selected from a maleic
acid-modified rosin, a fumaric acid-modified rosin, and acrylic
acid-modified rosin and a non-lead type solder alloy powder as
well.
DETAILED DESCRIPTION OF THE INVENTION
[0016] A thermosetting flux according to an embodiment of the
invention contains thermosetting resin components comprising an
epoxy resin and a hardening agent and a rosin derivative having the
flux function as indispensable components, so that excellent
solderability can be provided and since the epoxy resin in the flux
functions as an adhesive while being hardened at the time of
soldering, an element or a part can firmly be fixed.
[0017] Further, since the rosin derivative in form of this
embodiment has two or more carboxyl groups reactive on the epoxy
resin, it can directly react on the epoxy resin and accordingly
increase the heat resistant strength and the bonding strength of
the bonding part after the soldering. Therefore, the rosin
derivative can prevent separation or dropping of the element or the
part and improve the reliability of the solder bonding in a wire
bonding step after a semiconductor element is mounted or in the
second time or later soldering step of a double-mounted type
substrate bearing parts.
[0018] As the semiconductor element suitable for solder bonding
using the flux of the embodiment of the invention, a power element
such as an intelligent power device, a power IC, and a power
transistor; other independent semiconductor elements; and IC can be
exemplified.
[0019] As the electronic part suitable for solder bonding using the
flux of the embodiment of the invention, a surface-mounting type
small electronic part for directly mounting on the a substrate
bearing parts and for example, a solder bump-bonding type
semiconductor package such as a flip chip, a CSP or the like; and a
chip part such as a resistor, a coil, a capacitor, and a transistor
can be exemplified.
[0020] In the case of solder bonding by using a flux according to
this embodiment, the flux may be used solely by applying it to a
soldering part, however it is more preferable to use the flux in
such a manner that the flux is mixed and kneaded with a solder
alloy powder and used in form of a solder paste. After the solder
paste is applied to the solder bonding part, a semiconductor
element or an electronic part is mounted on the part and
solder-bonded.
[0021] In the case of applying the flux according to this
embodiment solely to the solder bonding part separately from a
solder to carry out soldering, it is suitable for solderbonding
using solder balls or reflow of a solder-precoated electrode or a
preform solder.
[0022] In the case of applying the flux solely to the solder
bonding part to carry out soldering, the flux function in the
soldering and fixation owing to the hardening of the epoxy resin in
the surrounding of the solder can simultaneously be
accomplished.
[0023] In the case of carrying out solder bonding of an element or
a part by using the flux in form of a paste containing a solder
alloy powder kneaded with the flux, at the time of heating, the
flux in the paste enters into gaps between a substrate to be bonded
and either the element or the part and on completion of the
soldering, the epoxy resin hardened substance fixes the element or
the part.
[0024] Hereinafter, the respective components of the embodiment of
the invention will be described in details.
[0025] As the epoxy resin to be used in the embodiment of the
invention, those which have two or more epoxy groups in each
molecule may be used without any particular limit. Practical
examples are a bisphenol A type epoxy resin, a bisphenol F type
epoxy resin, a phenol novolak type epoxy resin, a cresol novolak
type epoxy resin, a naphthol type novolak epoxy resin, a novolak
type epoxy resin of bisphenol A, a naphthalene diol type epoxy
resin, an alicyclic type epoxy resin, an epoxy compound derived
from tri or tetra(hydroxyphenyl)alkane, a bishydroxybiphenyl type
epoxy resin, an epoxy compound of a phenol aralkyl resin and the
like. These epoxy resins may be used alone or two or more of them
are used in form of a mixture.
[0026] As the hardening agent to be used in the embodiment of the
invention, those which are used commonly as a hardening agent for
epoxy resins may be used any particular limit. Practical examples
of the agent are an acid anhydride such as phthalic anhydride,
hexahydrophthalic acid anhydride, tetrahydrophthalic acid
anhydride, and trimellitic acid anhydride; a novolak type phenolic
resin such as a phenol novolak resin, acresol novolak resin, a
tert-butylphenol novolak resin, a nonylphenol novolak resin, and a
novolak resin of bisphenol A; a dicyclopentadiene-phenolic polymer;
a polyfunctional phenolic resin such as a
tris(bisphenoxyphenyl)alkane; a phenolic resin having a terpene
skeleton structure; and an aromatic amine such as a
diaminodiphenylmethane, diaminodiphenylsulfone and the like. Among
them, the acid anhydride and the phenol novolak resin are
particularly preferableto beused. These hardeningagents
maybeusedalone or tow or more of them may be used in
combination.
[0027] The mixing ratio of the hardening agent is not particularly
limited, however it is preferable adjust the equivalent ratio of
the epoxy group of the above-mentioned epoxy resin and the reactive
group of the hardening agent to be in a range of about 0.5 to 1.5,
more preferably in a range of about 0.8 to 1.2. The reason for that
is because if the ratio is out of the above-mentioned range, it
becomes difficult to sufficiently cause the hardening reaction to
result in decrease of the heat resistant strength and the bonding
strength after the soldering.
[0028] In the embodiment of the invention, in addition to the
hardening agent, a hardening accelerator can be added. As the
hardening accelerator, those which are commonly used may be used
without any particular limit and for example, a basic catalyst can
be used. Practical examples of it are an organic phosphine compound
such as trimethylphosphine, triethylphosphine, tributylphosphine,
triphenylphoshine, tri(p-methylphenyl)phosphine,
methyldiphenylphosphine, and tri(2,6-dimethoxyphenyl)phosphine; an
imidazole compound and its derivatives such as 2-ethylimidazole,
2,4-dimethylimidazole, 2-ethyl-4-methylimidazole,
2-phenylimidazole, and 2-heptadecylimidazole; DBU
(1,8-diazabicycloundec-7-ene) or its phenolic salt, and
6-dibutylamino-1,8-diazabicycloundec-7-ene.
[0029] The mixing amount of the hardening accelerator is not
particularly limited, however it is preferably about 0.01 to 10% by
weight in the total of the epoxy resin and the hardening agent.
[0030] The melting points of the epoxy resin to be used in the
embodiment of the invention and the hardening agent are preferably
the soldering temperature or lower. That is because if the melting
points exceed the soldering temperature, the hardening reaction of
the epoxy resin hardly occurs at the soldering temperature and
accordingly the epoxy resin cannot work as an adhesive to result in
decrease of the bonding strength of the element or the part.
[0031] The combination of the epoxy resin, the hardening agent, and
a hardening accelerator is preferably selected so as to harden the
epoxy resin at a temperature not lower than the liquid phase line
temperature of the solder alloy to be used. That is because if the
epoxy resin is hardened before the solder is melted, the solder
bonding is inhibited.
[0032] Further, the gelation time of the epoxy resin (the time to
be taken for hardening) is preferably set within 30 minutes at the
soldering temperature. That is because if the gelling time of the
epoxy resin exceeds 30 minutes, the semiconductor element, a frame,
a part electrode, and a substrate electrode may possibly be
oxidized to result in deterioration of the function. In general, in
order to shorten the assembly time of an electronic apparatus, it
is required to harden the epoxy resin as quick as possible and at
the soldering temperature, it is preferable to set the gelling time
for the epoxy resin to be several seconds to several minutes. To
shorten the gelling time of the epoxy resin, it may be possible to
add the above-mentioned hardening accelerator or increase the
soldering temperature to further higher.
[0033] The soldering temperature using the solder paste of the
embodiment of the invention is preferably in a range of 200 to
300.degree. C. If the soldering temperature is lower than the
range, it is not desirable since the hardening time of the epoxy
resin is prolonged and on the other hand, if the soldering
temperature exceeds the above-mentioned range, the probability of
considerably damaging the substrate to be subjected to the
soldering and the parts mounted on the substrate by heat could be
increased and therefore it is not preferable.
[0034] The total addition amount of the above-mentioned epoxy resin
and the hardening agent in the embodiment of the invention is not
particularly limited, however it is preferably 50 to 95% by weight
in the entire flux. That is because if it is less than 50% by
weight, the heat resistant strength and the bonding strength after
soldering is insufficient and if it exceeds 95% by weight, the
solderability is decreased.
[0035] The rosin derivative to be used in the embodiment of the
invention is a compound selected frommaleic acid-modified rosin,
fumaric acid-modified rosin, and acrylic acid-modified rosin. These
modified rosins are obtained by addition reaction (Diels Alder
reaction) of rosins to be raw materials with maleic anhydride,
fumaric acid, or acrylic acid. They have two or more carboxyl
groups in each molecule and can be reacted with the epoxy resin by
cross-linking reaction. As the rosins to be raw materials, natural
rosins such as gum rosin, wood rosin, and tall rosin;
disproportionated rosin, hydrogenated rosin, polymerized rosin,
glycolic acid-modified rosin, a high purity refined rosin and the
like can be exemplified. Commercialized products of such rosins are
KR-85, KR-604, KR-610, KR-612, and AG-100 manufactured by Arakawa
Chemical Industries, Ltd.
[0036] The addition amount of the rosin derivatives in the
embodiment of the invention is not particularly limited, however it
is preferably 5 to 50% by weight in the entire flux. That is
because if it is less than 5% by weight, the solderability is
decreased and if it exceeds 50% by weight, the heat resistant
strength and the bonding strength after soldering is
insufficient.
[0037] In the embodiment of the invention, other than the
above-mentioned rosin derivatives, various rosin derivatives having
functional groups reactive on the epoxy resinmayproperly be added
to the extent that they do not interfere the functions of the
hardenable flux such solderability and hardenability. Examples of
such rosin derivatives are an epoxylated rosin, a rosin amine, a
rosin amide, a rosin skeleton-containing diol compound,
rosin-modified phenol resin and the like.
[0038] The epoxylated rosin is a rosin glycidyl ester obtained by
reaction of rosins and glycidyl ether.
[0039] The rosin amine and rosin amide are obtained from rosins by
modifying the carboxyl groups of the rosins to amino groups or
amido groups.
[0040] The rosin skeleton-containing diol compound is obtained by
ring-opening and addition reaction of a diepoxy compound and a
rosin in 1:2 by mol ratio at 120 to 200.degree. C. in the presence
of a catalyst to adjust the acid value 5 or lower. Examples of such
a diepoxy compound are ethylene glycol diglycidyl ether, diethylene
glycol diglycidyl ether, triethylene glycol diglycidyl ether,
polyethylene glycol diglycidyl ether, propylene glycol diglycidyl
ether, dipropylene glycol diglycidyl ether, neopentyl glycol
diglycidyl ether, 1,6-hexanediol diglycidyl ether, bisphenol A
diglycidyl ether, bisphenol F glycidyl ether, and the like.
Examples of such a catalystmayinclude amine type catalysts such as
trimethylamine, triethylamine, tributylamine, benzyl dimethylamine,
pyridine, 2-imidazole and the like; quaternary ammoniums such as
benzyl trimethylammonium chloride; Lewis Acid; boric acid esters;
organometal compounds; organometal salts. Examples of
commercialized products of the rosin skeleton-containing diol
compounds obtained in such a manner are KE-601, KE-615, and KE-624
manufactured by Arakawa Chemical Industries, Ltd.
[0041] The rosin-modified phenolic resin is produced by mixing a
rosin and a phenol formaldehyde initial condensate, heating the
mixture at a temperature as high as 200 to 300.degree. C., and
esterifying the carboxyl groups in the rosin by glycerin,
pentaerythritol, or ethylene glycol. Examples of commercialized
products produced in such a manner are Tamanol 135 and 145
manufactured by Arakawa Chemical Industries, Ltd.
[0042] In addition to the above-mentioned indispensable components,
the flux of the embodiment of the invention may contain additives
such as an activation agent, a solvent, and a thixotropic agent
based on the necessity.
[0043] Examples of the activation agent are amine halogen salts
such as aniline hydrogen bromic acid salt, isopropylamine
hydrochloric acid salt, ethylamine hydrochloric acid salt,
diethylamine hydrogen bromic acid salt, diphenylguanidine hydrogen
bromic acid salt, and cyclohexylamine hydrochloric acid salt; amine
organic acid salts; organic monocarboxylic acids such as formic
acid, acetic acid, myristic acid, palmitic acid, stearic acid, and
benzoic acid; organic dicarboxylic acids and their anhydrides such
as oxalic acid, malonic acid, succinic acid, adipicacid,
fumaricacid, and maleic acid; organic amines such as hexylamine,
dioctyl amine, and triethylamine; and halogenated hydrocarbons. The
addition amount of the activation agent is preferably in a range of
0 to 10% by weight in the entire flux.
[0044] As the solvent, alcohols, ketones, esters, and aromatic
solvents can be used and practical examples of the solvent to be
used are benzyl alcohol, ethanol, isopropyl alcohol, butanol,
acetic acid cellosolve, ethyl cellosolve, butyl cellosolve, butyl
cellosolve acetate, butyl carbitol, terpineol, toluene, xylene,
propylene glycol monophenyl ether, diethylene glycol monohexyl
ether, and diethylene glycol monobutyl ether. The addition ratio of
the solvent may properly be adjusted so as to have a concentration
and a viscosity proper for making the flux usable for the uses, in
consideration of the properties of the epoxy resin and the
hardening agent and in general, it is preferably in a range of 0 to
40% by weight in the entire flux.
[0045] As the thixotropic agent, cured castor oil, hydrogenated
castor oil, bees wax, carnauba wax, stearic acid amide, and
hydroxystearic acid ethylene bisamide can be used. In general, the
mixing ratio of the thixotropic agent is preferably 0 to 10% by
weight in the entire flux.
[0046] The solder paste of the embodiment of the invention is
obtained by kneading the above-mentioned flux and a non-lead type
solder alloy powder.
[0047] The solder alloy to be used in the embodiment of the
invention is not particularly limited if it is a non-lead type
solder alloy and has proper characteristics as a solder. The solder
alloy can be selected from alloys of Sn, Ag, Cu, Zn, Bi, In, and Sb
and representative examples are Sn--Ag type, Sn--Cu type, Sn--Zn
type, Sn--Bi type, and Zn--Al--Mg--Sn type alloys.
[0048] As the above-mentioned solder alloy, those having a melting
point (the liquid phase line temperature) in a range of 150 to
300.degree. C. are preferable and those having a melting point (the
liquid phase line temperature) in a range of 180 to 280.degree. C.
are more preferable. That is because in the case the melting point
is too low, the solder is melted by heat generated in the power
element during the use to probably result in deterioration of the
reliability. On the other hand, if the melting point exceeds
300.degree. C., since the soldering temperature is increased, the
epoxy resin may not stand for the temperature in some cases.
[0049] A powder obtained by powdering such a solder alloy into a
particle diameter of 4 to 100 .mu.m, preferably 10 to 50 .mu.m is
kneaded with the above-mentioned flux to obtain a solder paste. The
mixing ratio of the solder powder is preferably adjusted to be 85
to 95 parts by weight of the solder alloy powder and 5 to 15 parts
by weight of the flux in 100 parts by weight in total of the solder
powder and the flux.
[0050] The paste in the embodiment of the invention may contain
additives such as an antioxidant, an anti-corrosion agent, or the
like based on the necessity.
[0051] The antioxidant suppresses the reaction with oxygen
attributed to an anti-oxidation function and a function as a
radical collecting agent. In the solder paste, it takes in oxygen
and thereby increases the storage stability of the paste. Further,
in the reflow step, it collects the oxygen in the surrounding to
prevent oxidation of the solder paste and suppress deterioration of
the wettability and spreading property. On the other hand, the
anti-corrosion agent has a chelating agent-like function in the
paste and forms a chelating complex with the metal on the solder
powder surface to protect the solder powder surface. Accordingly,
increase of the viscosity attributed to the reaction of the metal
component easy to be oxidized in the solder alloy with the
activation agent in the flux can be prevented and thus
deterioration of the storage stability of the solder paste can be
prevented. During there flow, it is effective to prevent oxidation
with oxygen in the surrounding.
[0052] Organic compounds to be used for the antioxidant can be
classified broadly into polymeric phenolic compounds, phosphorus
compounds, and sulfur compounds. Further, organic compounds to be
used for the anti-corrosion agent can be classified broadly into
nitrogen compounds and sulfur compounds and the nitrogen compounds
include triazole type, imidazole type, and guanidine type and
sulfur compounds include thiazole type thiuram type, and
dithiocarbamic acid salts. These antioxidants and anti-corrosion
agents may be used alone or in combination.
[0053] The polymeric phenolic compounds to be used for the
antioxidant may include, for example, triethylene glycol
bis[3-(3-tert-butyl-5-methyl-4-h- ydroxyphenyl)propionate],
1,6-hexanediol bis[3-(3,5-di-tert-butyl-4-hydrox-
yphenyl)propionate], pentaerythrityl
tetrakis[3-(3,5-di-tert-butyl-4-hydro- xyphenyl)propionate],
octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propi- onate, and
1,3,5-trimehtyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzy
l)benzene. The phosphorus compounds may include triphenyl
phosphite, trisnonyl phenyl phosphite,
tris(2,4-di-tert-butylphenyl)phosphite, distearylpentaerythritol
diphosphite, diphenylisodecyl phosphite and the like. The sulfur
compounds may include dilauryl-3,3'-thiodipropoionate,
dimyristyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate,
dilauryl sulfide, 2-mercaptobenzimidazole,
and2-mercaptomethylbenzimidazo- le.
[0054] The respective antioxidants may be used alone and two or
more of them are more preferably used in combination. Particularly,
combination use of the polymeric phenolic compounds and phosphorus
compounds and combination use of the polymeric phenolic compounds
and the sulfur compounds give profoundly efficient synergetic
effects. The addition amount of the antioxidant is properly in a
range o 0.5 to 20% by weight in the entire flux and further
preferably in a range of 1 to 10% by weight. In the case of using a
plurality of antioxidants in combination, it is preferable to keep
the total amount in the above-mentioned range.
[0055] The nitrogen compounds to be used as the anti-corrosion
agent may include triazole compounds such as benzotriazole and
methylbenzotriazole; imidazole type compounds such as imidazole,
methylimidazole, and 2,4,5-triphenylimidazole; and guanidine
compounds such as 1,3-diphenylguanidine. Further, the sulfur
compounds may include thiazole compounds such as
2-mercaptobenzothiazole and dibenzothiazyl disulfide; thiuram
compounds such as tetraethylthiuram disulfide, tetrabutylthiuram
disulifide, and tetrakis(2-ethylhexyl)thiuram disulfide; thiourea
type compounds such as N,N'-diphenylthiourea; and dithiocarbamic
acid salt.
[0056] These anti-corrosion agents may be use alone or two or more
of them may be used in combination. The addition amount of the
anti-corrosion agent is properly in a range of 0.1 to 10% by
weight, more preferably in a range of 0.5 to 5% by weight, in the
entire flux.
[0057] However, the total of the above-mentioned antioxidant and
anti-corrosion agent is properly in a range of 1 to 30% by weight
in the entire flux. If the addition amount is too low, the
oxidationprevention effect and the storage stabilization effect are
not so sufficient and if it is excess, the protection for the
solder metal particles is so firm as to possibly inhibit the
activation power and deteriorate wettability and the spreading
property.
[0058] The solder paste of the embodiment of the invention can be
obtained by preparing the flux by evenly mixing the above-mentioned
flux composing components in a common manner and further kneading
the flux with the solder alloy powder. In the flux preparation, if
the epoxy resin and the hardening agent are liquid at a
roomtemperature, mixing can be carried out easily by adding only
the indispensable components, however if the epoxy resin or the
hardening agent are solids in a room temperature and difficult to
be mixed, a proper solvent may be added to make the mixing
easy.
[0059] The flux and the solder paste of the embodiment of the
invention can be used efficiently by a normal method as a solder
for reflow type soldering at the time of producing a solder-mounted
material and an electronic part of a semiconductor element, an
electronic module, and a printed circuit substrate.
[0060] Hereinafter, a method for carrying out soldering using the
above-mentioned solder paste will be described. A wiring substrate
such as a glass epoxy resin composite substrate on whose surface
printed wiring is formed is made ready and the solder paste is
applied to a part of the substrate where the solder bonding is
carried out, that is an electrode part of the like where solder
bonding is carried out with a terminal of a part to be disposed in
the substrate. As described above, the solder paste is preferably a
solder paste comprising a thermosetting flux containing an epoxy
resin, a hardening agent, and at least one kind of rosin
derivatives selected from maleic acid-modified rosin, a
fumaricacid-modified rosin, and acrylic acid-modified rosin having
functional groups reactive with the epoxy resin and a non-lead type
solder alloy powder.
[0061] The solder paste application can be carried out by employing
a known method such as a screen printing method or the like.
[0062] The solder paste is applied to the object part of a
substrate having an electrode to be bonded and then mounting an
object part to be bonded on the substrate.
[0063] Next, the substrate and the mounted part are pre-heated at
150 to 180.degree. C. for 0.1 to 10 minutes. Further, they are
heated at 200 to 300.degree. C. for 0.1 to 30 minutes. In these
steps, the epoxy resin contained in the solder paste is hardened to
stick the substrate and the mounted part and simultaneously carry
out solder bonding and accordingly the substrate in which the part
is mounted mechanically and electrically firmly can be
obtained.
[0064] As described above in details, a flux of an embodiment make
it possible to firmly bond a semiconductor element or an electronic
part simultaneously with soldering when it is used at the time of
soldering of the semiconductor element or the electronic part and
also can provide a solder paste having good soldering ability,
suitable for solder bonding of the semiconductor element or the
electronic part, and excellent in the bonding strength and the heat
resistant strength at a high temperature. Further, the solder paste
of the invention can be used as a substituting bonding material for
the solder paste and is provided with a profoundly desirable
industrial value.
[0065] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
EXAMPLES
[0066] Hereinafter, the invention will be described more in
details. The invention is not limited to these examples. Examples 1
to 6 and Comparative Examples 1 to 3
[0067] [Preparation of Fluxes]
[0068] The following components were used as the raw material of
fluxes.
[0069] Epoxy resin A: Bisphenol A type epoxy resin (Epikote 828,
epoxy equivalent 190, liquid phase; manufactured by Japan Epoxy
resin Co., Ltd.)
[0070] Epoxy resin B: o-Crosol novolak type epoxy resin (ESCN-195
XL, epoxy equivalent 197, solid phase, manufactured by Sumitomo
Chemical Co., Ltd.)
[0071] Hardening agent A: Methyltetrahydrophthalic acid anhydride
(MH-700, acid anhydride equivalent 168, liquid phase, manufactured
by New Japan Chemical Co., Ltd.)
[0072] Hardening agent B: Phenol novolak resin (BRG-556, hydroxyl
equivalent 104, solid phase, manufactured by Showa Highpolymer Co.,
Ltd.)
[0073] Hardening accelerator: 2-Heptadecylimidazole (C17Z,
manufactured by Shikoku Chemicals Corp.)
[0074] Rosin derivative A: Maleic acid (anhydride)-modified rosin
(acid value 366) .
[0075] Rosin derivative B: Fumaric acid-modified rosin (acid value
362)
[0076] Rosin derivative C: Acrylic acid-modified rosin (acidvalue
265)
[0077] Rosin derivative D: Rosin ester (KE-100, having no
functional group; manufactured by Arakawa Chemical Industries,
Ltd.)
[0078] Rosin: Polymerized rosin
[0079] Solvent: Propylene glycol monophenyl ether
[0080] Activation agent: Diethylamine hydrogen bromic acid salt
[0081] Thixotropic agent: Hydrogenated castor oil
[0082] Antioxidant A: Pentaerythrityl
tetrakis[3-(3,5-di-tert-butyl-4-hydr- oxyphenyl)propionate]
[0083] Antioxidant B: tris(2,4-di-tert-butylphenyl)phosphite
[0084] Anti-corrosion agent: methylbenzotriazole
[0085] These components were mixed at ratios (% by weight) as
described in the following Table 1 and Table 2, loaded into
containers, and stirred and kneaded to obtain fluxes.
[0086] [Preparation of Solder Pastes]
[0087] As non-lead type solder alloy powders, powders of Sn-3.0
Ag-0.5 Cu alloy (melting point: 220.degree. C.), Sn-0.7 Cu alloy
(melting point: 229.degree. C.) , and Sn-9 Zn alloy (melting point:
199.degree. C.) with particle diameters of 20 to 40 .mu.m were used
and the solder alloy powders 90 parts by weight and the
above-mentioned fluxes 10 parts by weight were mixed and stirred by
a kneader to produce solder pastes.
[0088] [Evaluation of Solder Pastes]
[0089] Nine types of solder pastes of Examples 1 to 6 and
Comparative Examples 1 to 3 produced in the above-mentioned manner
were subjected to the following evaluation tests.
[0090] (1) Evaluation of Solder Spreading Ratio
[0091] The solder spreading ratio was measured according to JIS Z
3197. A common copper plate was used for the evaluation.
[0092] (2) Evaluation of Bonding Strength
[0093] Each solder paste was applied to an electrode potion formed
at prescribed position of a glass epoxy substrate by a screen
printing method and a 2,125 type chip part was mounted. Next, in a
reflow furnace, preheating was carried out at 170.degree. C. for 1
minute and then reflow was carried out by heating at a temperature
of 200.degree. C. or higher, at highest 240.degree. C., for 40
seconds to complete the soldering.
[0094] The load (gf) at the moment when the part was separated by
applying the force to the part in the transverse direction was
determined to be a bonding strength. The bonding strength
measurement was carried out by using a fixative strength
tester.
[0095] (3) Evaluation of Heat Resistant Strength at High
Temperature
[0096] A silicon chip of 2.times.2 mm was mounted on a copper frame
using each solder paste and further mounted on a hot plate heated
to 250.degree. C. and after it was confirmed that the solder alloy
was melted, the chip was slightly pushed to complete the soldering.
After that the hot plate was heated to 300.degree. C. to carry out
hot temperature treatment simulating the wire bonding and
occurrence of separation in the bonded part was observed. In the
case the bonded part was separated, NG was marked and in the case
no separation was observed and bonding was found good, OK was
marked.
[0097] (4) Evaluation of Thermal Conductivity
[0098] After the soldering, the solder bonded body in the bonded
part was cut and the thermal conductivity was measured by a laser
flash method.
[0099] The obtained evaluation results were shown in the following
Table 1 and Table 2.
1 TABLE 1 Example 1 2 3 4 5 6 Flux Epoxy resin A 45 45 40 -- -- --
composition Epoxy resin B -- -- -- 42 40 40 (wt. %) Hardening agent
A 36 36 32 -- -- -- Hardening agent B -- -- -- 19 18 18 Hardening
accelerator 1 1 1 1 1 1 Rosin derivative A 17 -- -- 17 -- -- Rosin
derivative B -- 17 -- -- 13 -- Rosin derivative C -- -- 26 -- -- 17
Solvent -- -- -- 20 20 20 Activation agent 1 1 1 1 1 1 Antioxidant
A -- -- -- --5 -- Antioxidant B -- -- -- -- 2 -- Anti-corrosion
agent -- -- -- -- -- 3 Flux (parts by weight) 10 10 10 10 10 10
Solder powder Sn--3.0Ag--0.5Cu 90 90 -- -- -- -- (parts by weight)
Sn--0.7Cu -- -- 90 90 -- -- Sn--9Zn -- -- -- -- 90 90 Evaluation
results Solder spreading ratio (%) 92 91 91 90 92 92 Bonding
strength (gf) 1000 1200 1100 1000 1200 1000 Heat resistant strength
at high OK OK OK OK OK OK temperature Thermal conductivity (W/mK)
32 30 32 35 34 32
[0100]
2 TABLE 2 Comparative Example 1 2 3 4 Flux Epoxy resin A -- 50 45
50 composition Epoxy resin B -- -- -- -- (wt. %) Hardening agent A
-- 48 36 48 Hardening agent B -- -- -- -- Hardening accelerator --
2 1 2 Polymerized rosin 59 -- -- -- Rosin derivative A -- -- -- --
Rosin derivative B -- -- -- -- Rosin derivative C -- -- -- -- Rosin
derivative D (having -- -- 17 -- no functional group) Solvent 35 --
-- -- Activation agent 1 -- 1 -- Thixotropic agent 5 -- -- -- Flux
(parts by weight) 10 10 10 10 Solder powder Sn--3.0Ag--0.5Cu 90 90
90 -- (parts by Sn--0.7Cu -- -- -- -- weight) Sn--9Zn -- -- -- --
Silver powder (parts by weight) -- -- -- 90 Evaluation Solder
spreading ratio (%) 92 60 90 -- results Bonding strength (gf) 400
1200 800 1200 Heat resistant strength at NG OK NG OK high
temperature Thermal conductivity 64 25 30 10 (W/mK)
[0101] As shown in Table 1, the solder pastes using the fluxes in
the invention were found showing good wettability and spreading
property and having high bonding strength of the elements or the
parts to the bonded substrate. Further, no separation in the bonded
part took place by the high temperature treatment, showing the high
bonding strength.
[0102] On the other hand, as shown in Table 2, the bonding strength
and heat resistant strength were low in the case of using a
conventional rosin type flux (Comparative Example 1) and the
wettability and spreading property were insufficient in the case of
using no rosin derivative (Comparative Example 2). Further, in the
case of using the rosin derivative having no reactivity on the
epoxy resin (Comparative Example 3), the heat resistant strength
was inferior, so that the bonded part was separated at the high
temperature. Further, in the case of using a conductive adhesive of
the Comparative Example 4 (as the conductive particle, a silver
powder with a particle diameter of 5 to 15 .mu.m was used), the
thermal conductivity was insufficient and in the case of using it
for bonding a power element, it was found that heat generated in
the power element could not efficiently be released.
* * * * *