U.S. patent application number 17/081547 was filed with the patent office on 2021-06-10 for method for reproducing plating solution.
The applicant listed for this patent is C. Uyemura & Co., Ltd.. Invention is credited to Daisuke HASHIMOTO, Toshikazu KANO, Masayuki KISO, Akira OKADA, Hironori SUGIURA, Keita TANIGUCHI.
Application Number | 20210172084 17/081547 |
Document ID | / |
Family ID | 1000005235523 |
Filed Date | 2021-06-10 |
United States Patent
Application |
20210172084 |
Kind Code |
A1 |
HASHIMOTO; Daisuke ; et
al. |
June 10, 2021 |
METHOD FOR REPRODUCING PLATING SOLUTION
Abstract
A plating solution containing a leveler is brought into contact
with silica particles with an average particle diameter of 500
.mu.m or less to remove impurities from the plating solution.
Inventors: |
HASHIMOTO; Daisuke; (Osaka,
JP) ; KISO; Masayuki; (Osaka, JP) ; OKADA;
Akira; (Osaka, JP) ; SUGIURA; Hironori;
(Osaka, JP) ; KANO; Toshikazu; (Osaka, JP)
; TANIGUCHI; Keita; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
C. Uyemura & Co., Ltd. |
Osaka |
|
JP |
|
|
Family ID: |
1000005235523 |
Appl. No.: |
17/081547 |
Filed: |
October 27, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D 3/30 20130101; C25D
21/16 20130101 |
International
Class: |
C25D 21/16 20060101
C25D021/16; C25D 3/30 20060101 C25D003/30 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 2019 |
JP |
2019-220573 |
Claims
1. A method for reproducing a plating solution comprising: bringing
a plating solution containing a leveler into contact with silica
particles with an average particle diameter of 500 .mu.m or less to
remove impurities from the plating solution.
2. The method of claim 1, wherein the plating solution is
circulated from a plating tank containing the plating solution and
the plating solution from which the impurities are removed by the
circulation is returned to the plating tank.
3. The method of claim 1, wherein the silica particles are
contained in an impurity removing device disposed in a circulating
path for the plating solution.
4. The method of claim 3, wherein the impurity removing device is a
bag filter.
5. The method of claim 4, wherein an average particle diameter of
the silica particles is larger than an opening of the bag
filter.
6. The method of claim 1, wherein the plating solution is an
electrolytic tin plating solution or an electrolytic tin alloy
plating solution.
7. The method of claim 1, wherein the leveler is indole.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of
Japanese Patent Application No. 2019-220573, filed on Dec. 5, 2019,
the entire disclosure of which as is incorporated by reference
herein in its entirety.
BACKGROUND
[0002] The present invention relates to a method for reproducing a
plating solution.
[0003] In integrated circuit (IC) packages, for example, solder
paste and solder balls have widely been used for connection with
ICs. In recent years, electrode areas have been microminiaturized,
and thus it has been difficult for the conventional solder paste
and the like to cope with the situation.
[0004] Given these circumstances, as a measure therefor, a method
is proposed which uses an electrolytic tin plating solution or an
electrolytic tin alloy plating solution for formation of bumps of
semiconductor chips. More specifically, a plating solution is
proposed which contains a soluble salt containing a stannous salt,
and an acid selected from an organic acid and an inorganic acid or
a salt thereof, two kinds of surfactants, namely, an amine-based
surfactant and a nonionic surfactant, and an additive such as
indole, for example. It is shown that use of such a plating
solution achieves height uniformity of solder bumps over a wide
current density range, and prevents or reduces occurrence of voids
during formation of the bumps (see, e.g., Japanese Unexamined
Patent Publication No. 2018-162512).
BRIEF SUMMARY
[0005] In the plating solution for bump formation, an additive such
as indole is used as in Japanese Unexamined Patent Publication No.
2018-162521 because a plated coating is required to be uniform and
to have a flat surface. Unfortunately, when electrolytic treatment
is performed on the plating solution, this additive changes to form
impurities (a water-insoluble substance as a byproduct accompanying
decomposition of the additive), and consequently, it is
disadvantageously impossible to prevent or reduce occurrence of
voids within the plated coating after reflow.
[0006] In view of the foregoing problems, it is therefore an object
of the present invention to provide a method for reproducing a
plating solution, the method including removing impurities from a
plating solution to prevent or reduce occurrence of voids within a
plated coating after reflow.
[0007] To achieve the above object, a method for reproducing a
plating solution according to the present invention includes
bringing a plating solution containing a leveler into contact with
silica particles with an average particle diameter of 500 .mu.m or
less to remove impurities from the plating solution.
[0008] The present invention can remove impurities from a plating
solution and can thus prevent or reduce occurrence of voids within
a plated coating after reflow.
BRIEF DESCRIPTION OF THE FIGURES
[0009] FIG. 1 is a schematic diagram for illustrating a method for
reproducing a plating solution of the present invention.
DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS
[0010] The following describes a method for reproducing a plating
solution of the present invention.
[0011] Plating Solution to be Treated
[0012] A plating solution to which the method of reproduction of
the present invention is applied is not limited to a particular
plating liquid. Examples thereof include an electrolytic tin
plating solution and an electrolytic tin alloy plating solution for
use in formation of connection bumps.
[0013] The electrolytic tin plating solution or the electrolytic
tin alloy plating solution can contain a tin salt as a compound as
a tin ion supply source. In one preferred embodiment, a stannous
salt (tin salt(II)) and a stannic salt (tin salt(IV)) are used.
[0014] The stannous salt (tin salt(II)) is not limited to a
particular stannous salt. Examples thereof include tin(II) alkane
sulfonates such as tin(II) methane sulfonate, tin(II) organic
sulfonates such as tin(II) alkanol sulfonates such as tin(II)
isethionate, tin(II) sulfate, tin(II) borofluoride, tin(II)
chloride, tin(II) bromide, tin(II) iodide, tin(II) oxide, tin(II)
phosphate, tin(II) pyrophosphate, tin(II) acetate, tin(II) citrate,
tin (II) gluconate, tin(II) tartrate, tin(II) lactate, tin(II)
succinate, tin(II) sulfamate, tin(II) formate, and tin(II)
silicofluoride.
[0015] The stannic salt (tin salt(IV)) is not limited to a
particular stannic salt. Examples thereof include sodium stannate
and potassium stannate. In one preferred embodiment, tin(II) alkane
sulfonates such as tin(II) methane sulfonate and tin(II) organic
sulfonates such as tin(II) alkanol sulfonates such as tin(II)
isethionate are used.
[0016] The concentration of the tin salt (the concentration as
Sn.sup.2+) is preferably 5 g/L or more, more preferably 10 g/L or
more in order to reduce the occurrence of burning and scorching in
the film. The concentration of the tin salt is preferably 120 g/L
or less, more preferably 90 g/L or less in order to improve the
stability of a plating bath and reduce the occurrence of
precipitates. Being such a concentration is advantageous also in
view of costs.
[0017] As the tin salt, a low-concentration lead tin salt with a
lead (Pb) concentration of 1.0 ppm or less can also be used. Use of
the low-concentration lead tin salt can achieve low-concentration
lead.
[0018] The electrolytic tin alloy plating solution can contain a
silver salt as a compound as a silver ion supply source. This
silver salt is not limited to a particular silver salt. Examples
thereof include silver organic sulfonates, silver sulfate, silver
borofluoride, silver chloride, silver bromide, silver iodide,
silver oxide, silver phosphate, silver pyrophosphate, silver
acetate, silver citrate, silver gluconate, silver tartrate, silver
lactate, silver succinate, silver sulfamate, silver formate, and
silver silicofluoride. Among these, in one particularly preferred
embodiment, silver organic sulfonates are used.
[0019] The concentration of the compound as the silver ion supply
source (the concentration as Ag.sup.+) is preferably 10 mg/L or
more, more preferably 20 mg/L or more in order to easily control
the plating solution. The concentration of the compound as the
silver ion supply source is 1,000 mg/L or less, more preferably 500
mg/L or less in view of costs.
[0020] The electrolytic tin alloy plating solution may further
contain a compound as a copper (Cu) ion supply source. Addition of
the compound as the copper ion supply source can form a film of a
Sn--Ag--Cu ternary alloy.
[0021] As the copper ion supply source, a copper salt can be used
and this copper salt is not limited to a particular copper salt.
Examples thereof include copper organic sulfonates, copper sulfate,
copper borofluoride, copper chloride, copper bromide, copper
iodide, copper oxide, copper phosphate, copper pyrophosphate,
copper acetate, copper citrate, copper gluconate, copper tartrate,
copper lactate, copper succinate, copper sulfamate, copper formate,
and copper silicofluoride. Among these, in one particularly
preferred embodiment, copper organic sulfonates are used.
[0022] The concentration of the compound as the copper ion supply
source (the concentration as Cu.sup.+) is preferably 10 mg/L or
more, more preferably 50 mg/L or more in order to easily control
the plating solution. The concentration of the compound as the
copper ion supply source is preferably 5,000 mg/L or less, more
preferably 2,000 mg/L or less in view of bath stability.
[0023] The electrolytic tin plating solution or the electrolytic
tin alloy plating solution contains a leveler in order to improve
the uniformity of a plated coating and the flatness of the surface
shape thereof. As this leveler, a nitrogen-containing aromatic
compound is used, for example. Examples of this nitrogen-containing
aromatic compound include indole, pyridine, pyrazine, pyrimidine,
pyridazine, triazine, tetrazine, acridine, quinoline, isoquinoline,
quinoxaline, quinazoline, cinnoline, indazole, imidazole,
benzimidazole, isoindole, benzothiazole, phenazine, iminostilbene,
quinaldine, purine, 1,10-phenanthroline, carbazole, acrinol,
benzotriazole, benzoxazole, and derivatives thereof.
[0024] The concentration of the nitrogen-containing aromatic
compound is preferably 0.001 g/L or more, more preferably 0.01 g/L
or more in order to improve the flatness of the surface shape of
the film. The concentration of the nitrogen-containing aromatic
compound is preferably 20 g/L or less, more preferably 10 g/L or
less in view of costs.
[0025] The electrolytic tin plating solution or the electrolytic
tin alloy plating solution may contain any of an inorganic acid, an
organic acid, and a water-soluble salt thereof. Addition of the
acid or water-soluble salt thereof allows the pH of the surface of
an object to be plated and a tin surface or Sn--Ag alloy surface
serving as the plated coating to be made uniform, thus achieving
uniform surface electric potential. This can reduce co-deposition
of lead.
[0026] The acid or water-soluble salt thereof is not limited to
particular one. Examples thereof include sulfuric acid,
hydrochloric acid, nitric acid, phosphoric acid, sulfamic acid,
organic sulfonic acids (alkane sulfonic acids such as methane
sulfonic acid and alkanol sulfonic acids such as isethionic acid),
and carboxylic acids (aromatic carboxylic acids, aliphatic
saturated carboxylic acids, and amino carboxylic acids).
Neutralization salts of these water-soluble salts can also be used
as needed. Among these, in one preferred embodiment, methane
sulfonic acid, which is easy to handle, is used.
[0027] The concentration of the acid or water-soluble salt thereof
is preferably 35 g/L or more, more preferably 50 g/L or more in
order to improve the stability of the plating solution and reduce
occurrence of precipitates. Such a concentration is advantageous
also in view of lead precipitation potential. The concentration of
the acid or water-soluble salt thereof is preferably 500 g/L or
less, more preferably 300 g/L or less, even more preferably 200 g/L
or less in view of costs.
[0028] The electrolytic tin plating solution or the electrolytic
tin alloy plating solution may contain a surfactant. As the
surfactant, one or more selected from an anionic surfactant, a
cationic surfactant, and a nonionic surfactant can be used. Among
these, in one preferred embodiment, the nonionic surfactant is
used, and in one more preferred embodiment, an alkylene oxide-based
one is used. Addition of the surfactant allows the current density
of the object to be plated and a tin crystal surface serving as the
plated coating to be made uniform, thus maintaining uniform
precipitation potential on the surface. This can reduce
co-deposition of lead.
[0029] The alkylene oxide-based surfactant is not limited to a
particular surfactant. Examples thereof include polyoxyethylene
alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene
alkyl amines, polyoxyethylene alkyl amides, polyoxyethylene
aliphatic esters, polyoxyethylene polyhydric alcohol ethers,
ethylene oxide-propylene oxide block copolymerized compounds,
ethylene oxide-propylene oxide random copolymerized compounds, and
propylene oxide polymerized compounds. Among these, in one
preferred embodiment, polyoxyethylene alkylphenyl ethers are
used.
[0030] The concentration of the surfactant is preferably 0.05 g/L
or more, more preferably 0.5 g/L or more. Being such a
concentration, even when plating is performed with a high current
density in order to reduce a plating time, can reduce occurrence of
burning and scorching in parts with a high current density. The
concentration of the surfactant is preferably 100 g/L or less in
order to reduce the occurrence of color unevenness caused by
blackening of the plated coating.
[0031] The electrolytic tin plating solution or the electrolytic
tin alloy plating solution contains an acid or water-soluble salt
thereof. The acid or water-soluble salt thereof is one or more
acids or water-soluble salts thereof selected from sulfuric acid,
hydrochloric acid, nitric acid, phosphoric acid, sulfamic acid,
organic sulfonic acids, and carboxylic acids or salts thereof.
[0032] The electrolytic tin plating solution or the electrolytic
tin alloy plating solution can contain an organic solvent, an
antioxidant, and a chelating agent. The organic solvent is not
limited to a particular organic solvent. Examples thereof include
monohydric alcohols such as methanol and 2-propanol and dihydric
alcohol such as ethylene glycol, diethylene glycol, and triethylene
glycol. The antioxidant is not limited to a particular antioxidant.
Examples thereof include catechol, hydroquinone, 4-methoxyphenol,
and ascorbic acid. The chelating agent is not limited to a
particular chelating agent. Examples thereof include oxalic acid,
succinic acid, malonic acid, glycolic acid, gluconic acid,
gluconolactone, glycine, ethylenediamine acetic acid,
pyrophosphoric acid, and tripolyphosphoric acid.
[0033] When the plated coating is formed using the electrolytic tin
plating solution or the electrolytic tin alloy plating solution, in
one preferred embodiment, the pH of the plating solution is
strongly acidic. Temperature when the plated coating is formed is
not limited to a particular temperature. In one preferred
embodiment, the temperature is 20.degree. C. or more and 40.degree.
C. or less. Current density when the plated coating is formed is
preferably 0.1 A/dm.sup.2 or more, more preferably 0.5 A/dm.sup.2
or more and is preferably 20 A/dm.sup.2 or less, more preferably 10
A/dm.sup.2 or less.
[0034] The electrolytic tin plating solution or the electrolytic
tin alloy plating solution can be used for formation of plated
bumps of semiconductor chips and package substrates, for example.
In forming the plated bumps, reflow treatment may be performed
after a plated coating with a certain size is formed at a certain
position. This reflow treatment is not limited to particular reflow
treatment and can be performed using a normal reflow apparatus.
[0035] Method for Reproducing Plating Solution
[0036] As described above, when electrolytic treatment is performed
using the electrolytic tin plating solution or the electrolytic tin
alloy plating solution containing the leveler such as indole, there
is a problem in that caused by decomposition of the leveler, the
impurities (the water-insoluble substance as a byproduct
accompanying decomposition of the leveler, for example) are
generated in the plating solution, and consequently, voids occur
within the plated coating after reflow.
[0037] Given these circumstances, the inventors of the present
invention have studied the above problem to find out that the
plating solution containing the impurities is circulated to be
brought into contact with silica particles (SiO.sub.2), whereby the
impurities can be removed from the plating solution.
[0038] The following specifically describes the method for
reproducing a plating solution of the present invention with
reference to the accompanying drawing. FIG. 1 is a schematic
diagram for illustrating the method for reproducing a plating
solution of the present invention.
[0039] As illustrated in FIG. 1, the method for reproducing a
plating solution of the present invention circulates a plating
solution 2 (that is, the electrolytic tin plating solution or the
electrolytic tin alloy plating solution containing the leveler such
as indole described above) contained in a plating tank 1 by a pump
3 and brings the plating solution 2 into contact with silica
particles 5 contained in an impurity removing device 4 disposed in
a circulating path of the plating solution 2 to remove impurities 6
from the plating solution 2.
[0040] More specifically, first, the plating solution 2 is
circulated to be brought into contact with the silica particles 5
to cause the leveler within the plating solution 2 to adsorb onto
the silica particles 5. Next, electrolytic treatment is performed
with the plating solution 2 in the plating tank 1 to form the
plated bumps described above, for example. In this process, as
described above, the impurities 6 are generated in the plating
solution 2 caused by decomposition of the leveler; the plating
solution 2 is constantly circulated, whereby as illustrated in FIG.
1, the impurities 6 are brought into contact with the silica
particles 5 and are adsorbed onto the silica particles 5 instead of
the leveler.
[0041] Consequently, the silica particles 5 can remove the
impurities 6 from the plating solution 2, and consequently, this
can prevent or reduce occurrence of voids within the plated coating
after reflow.
[0042] As illustrated in FIG. 1, the plating solution 2 from which
the impurities 6 are removed is circulated by the pump 3 to be
returned again to the plating tank 1.
[0043] The impurity removing device 4 is not limited to a
particular device. Examples thereof include a bag filter. An
opening of this bag filter is not limited to a particular value. In
one preferred embodiment, the opening is 4 .mu.m or less in order
to surely prevent an outflow of the silica particles contained in
the filter (that is, filter passing) caused by circulation of the
plating solution.
[0044] In the present invention, an average particle diameter of
the silica particles is 500 .mu.m or less in order to surely
perform adsorption of the impurities. When the average particle
diameter is larger than 500 .mu.m, the pore size of the silica
particles is large, and selective adsorptivity for the impurities
is lost. That is to say, this is because when the size of the
silica particles increases, matter other than the impurities is
also adsorbed and removed, which may make removal of the impurities
difficult (that is, reduce impurity removal performance).
[0045] In order to surely prevent the filter passing described
above, in one preferred embodiment, the lower limit value of the
average particle diameter of the silica particles is larger than
the opening of the bag filter described above; more specifically,
in one preferred embodiment, the lower limit value is 20 .mu.m or
more.
[0046] The "average particle diameter" referred to in this
specification indicates a 50% particle diameter (D50) and can be
measured with, e.g., a particle size distribution measurement
apparatus using the laser Doppler method (manufactured by Nikkiso
Co., Ltd., Nanotrac (registered trademark) particle size
distribution measurement apparatus UPA-EX150).
EXAMPLES
[0047] The following describes the invention according to the
present application more specifically based on examples and
comparative examples. The present invention is not limited to the
following examples at all.
Example 1
[0048] Formation of Plated Coating First, a base material was
subjected to electrolytic nickel plating (electrolytic nickel
plating solution: manufactured by C. Uyemura & Co., Ltd.,
product name: Thrunic AMT, liquid temperature: 50.degree. C.,
current density: 1 A/dm.sup.2, plating time: 10 minutes).
[0049] Next, mixing was performed so as to contain tin(II) alkane
sulfonate as a tin salt of 70 g/L as tin (Sn.sup.2+), methane
sulfonic acid as an organic acid of 100 g/L, polyoxyethylene
bisphenol A ether as a surfactant of 50 g/L, and indole of 5 g/L,
and the mixture was stirred to prepare an electrolytic tin plating
solution of the present example.
[0050] Next, this electrolytic tin plating solution was contained
in a plating tank. While the electrolytic tin plating solution was
circulated using a pump, using the electrolytic tin plating
solution, a tin plated coating was formed on the surface of nickel
as the base material with a liquid temperature of 30.degree. C. and
a current density of 4 A/dm.sup.2.
[0051] A bag filter as an impurity removing device (manufactured by
Eaton, product name: LCR-113-TO1E-401, opening: 4 .mu.m) was
disposed in a circulating path of the plating solution. Silica
particles with an average particle diameter of 50 .mu.m
(manufactured by Evonik Industries, product name: Sipernat 50) in
an amount of 1 kg was contained in the bag filter. A tin plated
coating was formed while the electrolytic tin plating solution was
circulated using a pump to bring the electrolytic tin plating
solution into contact with the silica particles.
[0052] Void Evaluation
[0053] After being reflowed at 260.degree. C., the obtained tin
plated coating was evaluated for the presence or absence of voids
with an X-ray nondestructive inspection apparatus (manufactured by
Nordson Dage, product name: XD7600NT Diamond FP). The X-ray
nondestructive inspection apparatus was set to give a tube voltage
of 60 kV and an output of 1.5 W. Table 1 lists a result of the
foregoing.
Example 2
[0054] A tin plated coating was formed, and void evaluation was
performed in a manner similar to Example 1 except that the average
particle diameter of the silica particles was changed to 120 .mu.m
(product name: CARPLEV XR manufactured by Evonik Industries was
used). Table 1 lists a result of the foregoing.
Example 3
[0055] A tin plated coating was formed, and void evaluation was
performed in a manner similar to Example 1 except that the average
particle diameter of the silica particles was changed to 300 .mu.m
(product name: Nipsil AQ manufactured by Tosoh Silica Corporation
was used). Table 1 lists a result of the foregoing.
Comparative Example 1
[0056] A tin plated coating was formed, and void evaluation was
performed in a manner similar to Example 1 except that the bag
filter containing the silica particles was not disposed in the
circulating path of the plating solution, and the plating solution
was not brought into contact with the silica particles. Table 1
lists a result of the foregoing.
Comparative Example 2
[0057] A tin plated coating was formed, and void evaluation was
performed in a manner similar to Example 1 except that silica
particles with an average particle diameter of larger than 500
.mu.m (manufactured by Fuji Silysia Chemical Ltd., product name:
Fuji silica gel ID40) was used in place of the silica particles
with an average particle diameter of 50 .mu.m. Table 1 lists a
result of the foregoing.
TABLE-US-00001 TABLE 1 Compar- Compar- ative ative Example 1
Example 2 Example 3 Example 1 Example 2 Presence or Present Present
Present Absent Present Absence of Silica Treatment Average 50 120
300 None >500 Particle Diameter of Silica Particles (.mu.m)
Occurrence Not Not Not Occurred Occurred of Voids Occurred Occurred
Occurred
[0058] As listed in Table 1, in Examples 1 to 3, the tin plated
coating was formed while the plating solution containing the
leveler was brought into contact with the silica particles with an
average particle diameter of 500 .mu.m or less, and it is thus
shown that the impurities in the plating solution were removed by
the silica particles, and consequently, no voids occurred within
the plated coating after reflow.
[0059] On the other hand, in Comparative Example 1, the plating
solution was not brought into contact with the silica particles,
and it is thus shown that the impurities were not removed from the
plating solution, and voids occurred within the plated coating
after reflow.
[0060] In Comparative Example 2, the average particle diameter of
the silica particles was larger than 500 .mu.m, and it is thus
shown that the impurities were not removed from the plating
solution, and voids occurred within the plated coating after
reflow.
[0061] The method for reproducing a plating solution of the present
invention is suitably used in plating solutions for use in
formation of plated bumps of semiconductor chips and package
substrates in particular.
* * * * *