U.S. patent application number 15/730244 was filed with the patent office on 2018-05-17 for barrel plating or high-speed rotary plating using a neutral tin plating solution.
This patent application is currently assigned to Rohm and Haas Electronic Materials LLC. The applicant listed for this patent is Rohm and Haas Electronic Materials LLC. Invention is credited to Makoto Kondo, Yoko Mizuno.
Application Number | 20180135195 15/730244 |
Document ID | / |
Family ID | 60480138 |
Filed Date | 2018-05-17 |
United States Patent
Application |
20180135195 |
Kind Code |
A1 |
Kondo; Makoto ; et
al. |
May 17, 2018 |
BARREL PLATING OR HIGH-SPEED ROTARY PLATING USING A NEUTRAL TIN
PLATING SOLUTION
Abstract
A barrel plating or high-speed rotary plating method for
electronic components, and a neutral tin plating solution used
therein. A plating solution that includes (A) stannous ions, (B) an
acid or a salt, (C) a complexing agent, and (D) a diamine that has
a polyoxyalkylene chain, and that has a pH in a range between 4 and
8 is used. The use of this neutral tin plating solution prevents
the electronic components from coupling together during the barrel
plating, enabling an improvement in manufacturability in barrel
plating.
Inventors: |
Kondo; Makoto; (Niigata,
JP) ; Mizuno; Yoko; (Shibata-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rohm and Haas Electronic Materials LLC |
Marlborough |
MA |
US |
|
|
Assignee: |
Rohm and Haas Electronic Materials
LLC
Marlborough
MA
|
Family ID: |
60480138 |
Appl. No.: |
15/730244 |
Filed: |
October 11, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D 3/32 20130101; C25D
7/00 20130101; C25D 17/16 20130101; C25D 17/20 20130101 |
International
Class: |
C25D 3/32 20060101
C25D003/32; C25D 17/20 20060101 C25D017/20; C25D 7/00 20060101
C25D007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 2016 |
JP |
2016-220435 |
Claims
1. A barrel plating or high-speed rotary plating method for
electronic components, including a step for barrel plating or
high-speed rotary plating of an electronic component using a tin
plating solution that includes (A) stannous ions, (B) an acid or a
salt, (C) a complexing agent, and (D) a diamine that has a
polyoxyalkylene chain, and wherein the pH is in a range between 4
and 8.
2. The method as set forth in claim 1, wherein barrel plating is
carried out with a current density between 0.05 and 0.
3. The method as set forth in claim 1, wherein the electronic
component is selected from a capacitor, an inductor, a thermistor,
and a varistor.
4. A neutral tin plating solution for barrel plating or high-speed
rotary plating comprising: (A) stannous ions; (B) an acid or a
salt; (C) a complexing agent; and (D) a diamine having a
polyoxyalkylene chain, wherein a pH is in a range between 4 and
8.
5. The neutral tin plating solution for barrel plating or
high-speed rotary plating as set forth in claim 4, wherein the
diamine having the polyoxyalkylene chain has a molecular weight
between 200 and 1100.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a barrel plating or
high-speed rotary plating method for electronic components using a
neutral tin plating solution, and to the neutral tin plating
solution used therein. More specifically, it relates to a barrel
plating or high-speed rotary plating method, and to a neutral tin
plating solution used therein, which is capable of improving the
coverage of plating onto electronic components while preventing
electronic components from coupling to each other when barrel
plating or high-speed rotary plating is performed.
BACKGROUND OF THE INVENTION
[0002] Tin plating is carried out broadly for the purpose of
improving solderability of electronic components. The method for
tin plating electronic components can be selected from various
different methods, such as barrel plating, rack plating, and the
like, depending on the shape, the structure of the plating
location, and the like. Barrel plating is generally used as a
method for plating small electronic components such as chip
resistors, chip capacitors, and the like. Moreover, in recent
years, high-speed rotary plating has been carried out through
flow-through platers, and the like, as a plating method for small
electronic components.
[0003] Normally, when performing barrel plating, electronic
components that are to be plated, and conductive metal (dummy
balls) for improving the conductivity during plating, are loaded
into a cage-shaped container that is known as a barrel, and the
electronic components are plated through applying an electric
current while rotating or vibrating the barrel in a state wherein
it is immersed in a plating solution. However, in recent years, as
the sizes of electronic components have grown smaller, there has
been a tendency for the electronic components to couple to each
other, or the dummy balls to clump together, or for the electronic
components and the dummy balls to stick together, during barrel
plating, producing a problem in that there is an adverse effect on
manufacturability of electronic components in the barrel plating.
Moreover, depending on the type of plating solution, foaming may
occur at the solution surface, producing a problem with an adverse
effect on the plating operations. In high-speed rotary plating, the
electronic components that are the objects to be plated are
inserted into a disk-shaped cell, and plating is performed while
the cell is rotated at a high speed, and the same problems can
occur as with barrel plating.
[0004] Japanese Unexamined Patent Application Publication
2009-299123 discloses a tin electroplating solution for chip
components with a pH of 1 or less, including stannous ions, oxygen,
dipolyoxyalkylene alkyl amine or amine oxide, and a bonding
inhibitor. However, when electronic component ceramic members that
are the objects to be plated are inserted, the ceramic members are
damaged through the use of a plating solution with a pH of 1 or
less, which is not preferred.
[0005] Japanese Unexamined Patent Application Publication
2003-293186 discloses a neutral tin plating bath that includes a
soluble stannous salt, an acid or salt, a complexing agent selected
from an oxycarboxylic acid, or the like, and a quaternary amine
polymer. However, in research by the present inventors, a neutral
tin plating solution that uses a quaternary amine polymer is not
adequately effective in preventing coupling between the objects to
be plated, and further improvements are desired.
SUMMARY OF THE INVENTION
[0006] Consequently, the object of the present invention is to
enable suppression of coupling between the electronic components
even when using barrel plating or high-speed rotary plating of
electronic components that have been miniaturized in recent years,
to provide an electronic component plating method, and a neutral
tin plating solution used therein, wherein the foaming of the
plating solution is extremely little when performing barrel plating
or high-speed rotary plating.
[0007] The present inventors arrived at the present invention
through discovering that it is possible to improve
manufacturability in barrel plating or high-speed rotary plating
through preventing the objects being plated from coupling together,
and through having little foaming in the plating solution, through
the addition, to the neutral tin plating solution, of a diamine
that has a polyoxyalkylene chain.
[0008] That is, one aspect of the present invention provides an
electronic component barrel plating or high-speed rotary plating
method that includes a step that carries out barrel plating or
high-speed rotary plating on electronic components using a tin
plating solution that includes (A) stannous ions, (B) an acid or a
salt, (C) a complexing agent, and (D) a diamine that includes a
polyoxyalkylene chain, and wherein the pH is in a range between 4
and 8.
[0009] Moreover, one aspect of the present invention provides a
neutral tin plating solution for barrel plating or high-speed
rotary plating that includes (A) stannous ions, (B) an acid or a
salt, (C) a complexing agent, and (D) a diamine that includes a
polyoxyalkylene chain, and wherein the pH is in a range between 4
and 8.
DETAILED DESCRIPTION OF THE INVENTION
[0010] Abbreviations used throughout this Specification have the
following meanings, unless defined otherwise: g=grams;
mg=milligrams; .degree. C.=degrees Celsius; min=minutes; m=meters;
cm=centimeters; L=liters; mL=milliliters; A=amperes; and
dm.sup.2=square decimeters. All numeric values include the boundary
values thereof, and can be combined in arbitrary sequencing.
Throughout the present specification, the terms "plating solution"
and "plating bath," have identical meanings, and can be used
interchangeably. Moreover, unless stated specifically, throughout
this Specification, percent (%) indicates percent by weight.
[0011] The barrel plating or high-speed rotary plating method for
electronic components according to the present invention has, as a
distinctive feature, the use of a plating solution that includes
(A) stannous ions, (B) an acid or a salt, (C) a complexing agent,
and (D) a diamine that includes a polyoxyalkylene chain, and
wherein the pH is in a range between 4 and 8. This plating solution
will be explained sequentially below.
(A) Stannous Ions
[0012] In the plating solution used in the present invention, the
stannous ions are included as a required structural requirement.
Stannous ions are double-oxidized tin ions. In the plating
solution, an arbitrary compound may be used insofar as it is a
compound that is able to supply stannous ions. Generally, a tin
salt of an inorganic acid or an organic acid that is used in a
plating solution is preferred. For example, as tin salts of
inorganic acids there are stannous salts of sulfuric acid and of
hydrochloric acid, and as tin salts of organic acids there are, for
example, stannous salts of substituted or non-substituted alkane
sulfonic acids and alkanol sulfonic acids, such as, for example,
methane sulfonic acid, ethane sulfonic acid, propane sulfonic acid,
2-hydroxy ethane-1-sulfonic acid, 2-hydroxy propane-1-sulfonic
acid, and 1-hydroxy propane-2-sulfonic acid. Particularly preferred
sources for supplying stannous ions are stannous sulfonate salts
for salts of inorganic acids, or stannous methane sulfonate salts
for salts of organic acids. These compounds able to supply these
ions may be used singly or in mixtures of two or more thereof.
[0013] The inclusion proportion of the stannous ions within the
plating solution may be, for example, between 5 g/L and 30 g/L, as
tin ions, or, preferably, between 8 g/L and 25 g/L, or more
preferably, between 10 g/L and 20 g/L.
(B) Acids or Salts
[0014] The plating solution used in the present invention can use
an arbitrary acid or salt, insofar as the acid or salt has a
function that provides conductivity to the plating solution. Any
organic acid, inorganic acid, or salt thereof may be used. As
organic acids there are, for example, substituted or
non-substituted alkane sulfonic acids or alkanol sulfonic acids,
such as, for example, methane sulfonic acid, ethane sulfonic acid,
propane sulfonic acid, 2-hydroxy ethane-1-sulfonic acid, 2-hydroxy
propane-1-sulfonic acid, and 1-hydroxy propane-2 sulfonic acid.
Methane sulfonic acid is preferred. For inorganic acids, sulfuric
acid or hydrochloric acid, for example, may be used, and sulfuric
acid is preferred. As salts thereof, an arbitrary salt may be used,
such as an alkaline metal salt, an alkaline earth metal salt, an
ammonium salt, an amine salt, or the like. The acids and salts may
be used singly or in combinations of two or more. While use of the
inorganic acid or organic acid, or salt thereof, used for the
stannous ion salt, as described above, is preferred, there is no
limitation thereto.
[0015] Note that, so that the plating solution that is used in the
present invention will be a neutral plating solution, when an
organic acid or inorganic acid, as described above, is used for the
conductive substance, any of a variety of bases may be added, as a
pH adjusting agent, to the plating solution to adjust the pH into a
range of between 4 and 8.
[0016] The inclusion proportion of the acid or salt in the plating
solution is, for example, between 30 g/L and 300 g/L, and
preferably between 50 g/L and 200 g/L, and more preferably between
80 g/L and 150 g/L.
(C) Complexing Agent
[0017] The plating solution used in the present invention includes
a complexing agent as a required structural condition. Typically a
double-ionized tin ion in a tin plating solution is stable in a
strong acid, but becomes unstable when near neutral, and tends to
segregate out as a tin metal, so the plating solution tends to
decompose. For the tin plating solution of the present invention to
have a pH in a range between 4 and 8, a complexing agent must be
included. There is no particular limitation on the complexing agent
insofar as it has the effect of stabilizing the plating solution.
The complexing agent may be, for example, gluconic acid, citric
acid, malonic acid, succinic acid, tartaric acid, or a salt
thereof. Of these, gluconic acid or a salt thereof is preferred,
and sodium gluconate is most preferred.
[0018] The inclusion proportion of the complexing agent in the
plating solution is, for example, between 80 g/L and 250 g/L, and
preferably between 100 g/L and 200 g/L, and more preferably between
125 g/L and 175 g/L.
(D) Diamene that has a Polyoxyalkylene Chain
[0019] The plating solution used in the present invention includes,
as a required structural condition, a diamene that has a
polyoxyalkylene chain. The inclusion of this compound prevents the
objects being plated from coupling together, enabling an
improvement in manufacturability in barrel plating. Preferably the
diamene that includes a polyoxyalkylene alkylene chain is a
compound described by the following chemical formula:
##STR00001##
[0020] Here, in the equation above, R.sub.1 is a straight-chain or
branched-chain alkylene group with a carbon number between 1 and
10, and preferably is a straight-chain or branched-chain alkylene
group with a carbon number between 1 and 6, and more preferably is
a straight-chain or branched-chain alkylene group with a carbon
number between 1 and 4. Each of R.sub.2 through R.sub.5 is,
independently, a straight-chain or branched-chain alkylene group
with a carbon number between 1 and 10, and preferably is a
straight-chain or branched-chain alkylene group with a carbon
number between 1 and 6, and more preferably is a straight-chain or
branched-chain alkylene group with a carbon number between 1 and 4.
Each of n, m, o, and p is an integer between 0 and 15, where n, m,
o, and p are not all 0. Preferably, each of n, m, o, and p is an
integer between 1 and 12, and more preferably, an integer between 1
and 8. Note that the total of n, m, o, and p is between 1 and 60,
and preferably between 2 and 30, and more preferably between 4 and
25.
[0021] The present inventors discovered that a plating solution
that includes the compounds set forth above is able to reduce
coupling of electronic components when performing barrel plating or
high-speed rotary plating, and enables plating operations to be
performed stably with little production of bubbles that would be a
problem when performing plating.
[0022] The weight-average molecular weight of the diamene that has
the polyoxyalkylene chain is preferably between 200 and 1100, and
more preferably between 300 and 600. Here the weight-average
molecular weight is a value that is measured using the GPC
method.
[0023] The diamene with the polyoxyalkylene chain may use that
which is commercially available, and, for example, may use Adeka
Polyether EDP-450, Adeka Polyether BM-54 (manufactured by Adeka
Co., Ltd.), or the like.
[0024] The inclusion proportion of the diamene with a
polyoxyalkylene chain in the plating solution is, for example,
between 0.1 g/L and 30 g/L, and preferably between 0.5 g/L and 20
g/L, and more preferably between 1 g/L and 5 g/L.
(E) pH Adjusting Agent
[0025] The pH of the neutral tin plating solution used in the
present invention is in a range between 4 and 8, and preferably
between 5 and 7. A base or an acid may be added to the plating
solution to adjust the pH into this range. Acids that may be used
include, for example, methane sulfonic acid, ethane sulfonic acid,
propane sulfonic acid, hydrochloric acid, sulfuric acid, and the
like. As bases that can be used there are, for example, sodium
hydroxide, potassium hydroxide, and aqueous ammonia.
[0026] The neutral tin plating solution used in the present
invention may include, as other arbitrary components, components
that are typically added to plating solutions. For example,
oxidation inhibiting agents, brightening agents, smoothing agents,
conductive salts, anode solvents, corrosion inhibiting agents,
wetting agents, and the like, may be used.
(F) Oxidation Inhibiting Agents
[0027] In the plating solution according to the present invention,
an oxidation inhibiting agent may be used as appropriate. The
oxidation inhibiting agent is used to prevent the tin ions from
being oxidized from 2+ to 4+, where, for example, hydroquinone,
catechol, resorcin, phloroglucin, pyrogallol, hydroquinone,
sulfonic acid, a salt thereof, or the like, may be used.
[0028] The oxidation inhibiting agent may be used suitably in a
concentration, in the plating bath, of, for example, between 100
mg/L and 50 g/L, or preferably between 200 mg/L and 20 g/L, and
more preferably, between 0.5 g/L and 5 g/L.
[0029] There is no particular limitation on the sequence with which
the various components are added when initially making up the
electrolytic plating bath; however, from the point of view of
safety, the acids and salts are added after adding water, the tin
salt is then added after thorough mixing, after which the other
chemicals are added as necessary after thorough dissolution.
[0030] There are no particular limitations on the electronic
components that are the objects to be plated in the present
invention, and they may be, for example, resistors, capacitors,
inductors (or inductive transformers), thermistors, varistors,
variable resistors, variable capacitors, or other passive
components, or crystal oscillators, LC filters, ceramic filters,
delay lines, SAW filters, or other functional components, or
switches, connectors, relay fuses, optical connectors, or other
connecting components. In particular, capacitors, inductors,
thermistors, and varistors have ceramic portions within the
components, meaning that strong acid plating solutions cannot be
used, and thus plating using the neutral plating bath of the
present invention is preferred.
Plating Method
[0031] A method for carrying out barrel plating using the plating
solution according to the present invention will be explained. As
described above, normally, when performing barrel plating, the
electronic components that are the objects to be plated are loaded
together with dummy balls and, in a state wherein they are immersed
in a plating solution, an electric current is applied as the barrel
is rotated, but the barrel plating method according to the present
invention includes the case of placing, into the barrel, only the
objects to be plated, without addition of the dummy balls. The
barrel plating method may use an arbitrary apparatus, such as of a
horizontal or an inclined rotating barrel type, a pivoting barrel
type, a vibrating barrel type, or the like. The barrel plating may
be carried out with the temperature of the plating solution
between, for example, 10 and 50.degree. C., and preferably between
20 and 40.degree. C. Moreover, the cathode current density may be
selected as appropriate in a range that is, for example, between
0.01 and 10 A/dm.sup.2, and preferably between 0.05 and 5
A/dm.sup.2, and more preferably between 0.1 and 0.5 A/dm.sup.2. A
method may be selected wherein, for example, the plating bath is
not stirred during the plating process, or, for example, may be
stirred using a stirrer, or the method may have a fluid flow using
a pump.
[0032] Moreover, when performing high-speed rotary plating using
the plating solution according to the present invention, the
plating may be carried out using, for example, a flow-through
plater, or the like, under conditions of between 10 and 50.degree.
C., with a cathode current density between 0.01 and 10 A/dm.sup.2,
with small electronic components, which are the objects to be
plated, being plated during high-speed rotation.
Embodiment 1
[0033] An electrolytic bath of a tin plating solution with the
following composition was prepared:
(A) Stannous Methane Sulfonate: 39 g/L (15 g/L as Tin Ions)
(B) Sodium Methane Sulfonate: 100 g/L
(C) Sodium Gluconate: 145 g/L
(D) Adeka Polyether EDP-450 (Molecular Weight: 450): 2 g/L
[0034] (E) Sodium Hydroxide: Enough to cause the pH of the plating
solution to be 6
(F) Sodium Erythorbate: 2 g/L
(G) Water: Balance
Structure of the Adeka Polyether EDP-450
##STR00002##
[0036] Two liters of the tin plating solution of the electrolytic
bath that was prepared were used to carry out barrel tin plating,
under the following conditions, on chip resistors that had been
subjected to nickel plating, and various evaluations were
performed. The results are presented in Table 1.
Barrel Plating Conditions 1
[0037] Barrel: Yamamoto Mini Barrel (Capacity: Approximately 140
mL)
[0038] Objects Subjected to Plating: Chip Resistors: 5 g
[0039] Dummy Balls: Steel Balls, Diameter: 0.71 through 0.85 mm, 60
g
[0040] Current Density: 0.2 A/dm.sup.2
[0041] Plating Time: 50 min
[0042] Plating Solution Temperature: 35.degree. C.
[0043] Speed of Rotary: 6 rpm
(Solder Wettability Test)
[0044] Two liters each of plating solutions according to the
embodiments and the comparative examples were prepared, and tin
electroplating was carried out for 50 min. with a bath temperature
of 35.degree. C. at 0.2 A/dm.sup.2, to deposit a 5-.mu.m tin
plating coating on the external electrodes of the chip resistors.
On each of the tin plating coatings produced, a damp heat testing
procedure was performed (a PCT procedure with a temperature of
105.degree. C., humidity of 100%, for four hours), and the solder
wettability of the plating coating before and after the damp
heating testing was evaluated using a multi-solderability tester
SWET-2100, manufactured by Tarutin, to measure the zero-cross time
("ZCT") through a solder paste equilibrium method. The measurement
conditions were as follows:
Zero-Cross Time Measurement Conditions
[0045] Solder Paste: Sn:Ag:Cu=95.75:3.5:0.75 [0046] Test
Temperature: 245.degree. C. [0047] Immersion Depth: 0.15 mm [0048]
Test Speed: 2 mm/s [0049] Holding Time: 8 s
[0050] The solder wettability was measured both before and after
the PCT process, and the results are given in Table 1.
[0051] The coupling proportions (the proportion by weight of the
adhered chips, relative to the total chip weight), and the clumping
proportions (the proportion by weight of the dummy balls that were
clumped together, relative to the total weight of dummy balls) were
calculated, and, similarly, are given in Table 1.
External Appearance of Plating and Particle Size (Grain Size) of
Plating
[0052] Hull cell testing was carried out using the plating
solutions of the electrolytic baths that were prepared, and the
external appearances of the plating coatings that were produced
were observed with the naked eye, and the plating grain sizes were
measured using SEM (at 2000.times.).
Comparative Example 1
[0053] An electrolytic bath of a tin plating solution was prepared
with the same composition as in the first embodiment, except for
the use of 2 g/L of lauryl dimethylaminoacetate betaine (Amphitol
20BS, manufactured by Kao Corp.) instead of the (D) Adeka Polyether
EDP-450 in the first embodiment. The foamability of the plating
solution was high, and thus unsuitable for barrel plating.
Comparative Examples 2 to 4
[0054] An electrolytic bath of a tin plating solution was prepared
with the same composition as in the first embodiment, except for
the use of 2 g/L of a quaternary ammonium salt polymer (Papiogen
P-113 (Comparative Example 2)), SenkaFix 401 (Comparative Example
3), and a quaternary ammonium salt (Eretat M-65 (Comparative
Example 4)), respectively, instead of the (D) Adeka Polyether
EDP-450 in the first embodiment. The plating solution produced in
Comparative Example 4 had high foamability, so was not suitable for
barrel plating. For the plating solutions produced in Comparative
Example 2 and Comparative Example 3, the same procedures were
performed for each as in the first embodiment. The external
appearance of the plating coating obtained in the Hull cell testing
for the plating solution produced in Comparative Example 2 was
white, with an excellent result, but in the barrel plating test the
coupling rate was high, at 81.3%. For the plating solution obtained
in Comparative Example 3, the external appearance of the plating
coating produced in the Hull cell testing was grayish-black, which
was undesirable.
TABLE-US-00001 TABLE 1 Embodiment Comparative Example 1 1 2 3 4 (D)
Adeka 2 -- -- -- -- component Polyether (d/L) EDP-450 Anphitol -- 2
-- -- -- 20BS Papiogen -- 2 -- -- P-113 SenkaFix 401 -- -- -- 2 --
Eretat M-65 -- -- -- -- 2 Foamability Low High Low Low High
External Okay -- Okay No Good -- Appearance (White) (White)
(Grayish Black) Grain size 2 through 7 -- 5 through 10 -- --
(.mu.m) Coupling Chip 25.0 -- 81.3 -- Rate (%) Clumping Dummy Balls
2.4 -- 2.62 -- -- Rate (%) Solder Zero-Cross 1.87/1.93 -- -- -- --
Wettability Time (Units: Test Minutes)
Embodiment 2
[0055] Testing was carried out in the same way as in the first
embodiment, with the exception of changing Barrel Plating
Conditions 1 to Barrel Plating Conditions 2, below, and the
coupling rate and clumping rate were measured. The result was that
the chip coupling rate was 0.1%, and the dummy ball clumping rate
was 0%. Moreover, there was little foaming of the plating
solution.
[0056] Barrel Plating Conditions 2
[0057] Barrel: Yamamoto Mini Barrel (Capacity: Approximately 140
mL)
[0058] Objects Subjected to Plating: Chip Resistors: 5 g
[0059] Dummy Balls: Steel Balls, Diameter: 0.71 through 0.85 mm, 60
g
[0060] Current Density: 0.2 A/dm.sup.2
[0061] Plating Time: 50 min
[0062] Plating Solution Temperature: 35.degree. C.
[0063] Speed of Rotary: 12 rpm
* * * * *