Field of the Invention
[0001] The present invention is directed to indium electroplating compositions and methods
for electroplating indium on nickel layers where the indium deposit is uniform, substantially
void-free, whisker-free and has a smooth surface morphology. More specifically, the
present invention is directed to acid indium electroplating compositions and methods
of electroplating indium on nickel layers where the indium deposit is uniform, substantially
void-free, whisker-free and has a smooth surface morphology, wherein the indium electroplating
compositions are environmentally friendly and include select amino acids to provide
the uniform matte, substantially void-free, whisker-free and smooth surface morphology
indium deposit.
Background of the Invention
[0002] Electrolytic indium is very attractive in the connectors industry for press-fit applications.
Indium can be used as a replacement metal for tin. Tin usually grows whiskers under
stress conditions. As electronic components become smaller, it is important to eliminate
the risk of whisker formation which can create electrical short circuits. The advantage
of indium over tin is that indium is less susceptible to whisker formation even after
reflow.
[0003] Connector pins (copper alloy) for press-fit applications are initially coated with
nickel followed by indium flash adjacent to the nickel. The thickness of indium layer
is generally from 0.2-1 µm. The problem is that many electrolytic indium processes
are unable to plate such a thin layer with uniform thickness distribution and with
good adhesion on the nickel without using a strike layer (adhesion promotor coating).
Such strike layers can have a thickness of 1-100nm.
[0004] The ability to reproducibly plate void-free uniform matte indium of target thickness
and smooth surface morphology on nickel layers is challenging. Indium reduction occurs
at potentials more negative than that of proton reduction, and significant hydrogen
bubbling at the cathode causes increased surface roughness. Indium (1
+) ions, stabilized due to the inert pair effect, formed in the process of indium deposition
catalyze proton reduction and participate in disproportionation reactions to regenerate
Indium (3
+) ions. In the absence of a complexing agent, indium ions begin to precipitate from
solutions above pH > 2. Plating indium on nickel is challenging because nickel is
a good catalyst for proton reduction and is more noble than indium, nickel can cause
corrosion of indium in a galvanic interaction. Indium may also form undesired intermetallic
compounds with nickel. Another problem with indium plating is the generation of hydrogen
gas. Such hydrogen gas generation can result in rough and irregular indium deposits
unsuitable for electronic components and devices.
[0005] In addition, many conventional indium plating baths include environmentally unfriendly
additives required to enable acceptable indium plating performance, such as certain
suppressors, many levelers, grain refiners, certain buffers and compounds used to
inhibit hydrogen evolution during plating. Many governments around the world are passing
stricter environmental laws and regulations with respect to how chemical waste is
treated and the types of chemicals industries may use in development and manufacturing
processes. For example, in the European Union the regulation Registration, Evaluation,
Authorization and Restriction of Chemicals, known as REACh, has banned numerous chemicals
or is in the process of banning chemicals used in plating baths from substantial industrial
use.
[0006] Accordingly, there is a need for improved indium compositions for electroplating
indium metal layers on nickel substrates and which are environmentally friendly.
Summary of the Invention
[0007] The present invention is directed to an indium electroplating composition consisting
of water; one or more sources of indium ions; one or more acids selected from the
group consisting of inorganic acids, alkane sulfonic acids, and salts of the acids,
wherein the inorganic acids are selected from the group consisting of sulfamic acid
and sulfuric acid; and one or more amino acids selected from the group consisting
alanine, arginine, aspartic acid, asparagine, glutamic acid, glycine, glutamine, histidine,
leucine, lysine, threonine, isoleucine, serine, and valine; optionally one or more
alloying metal; and optionally one or more pH adjuster.
[0008] The present invention is also directed to a method of electroplating indium on nickel
comprising:
- a) providing a substrate comprising a nickel layer adjacent to a copper or copper
alloy layer;
- b) contacting the substrate comprising the nickel layer adjacent to the copper or
the copper alloy layer with an indium electroplating composition consisting of water;
one or more sources of indium ions one or more acids selected from the group consisting
of inorganic acids, alkane sulfonic acids, and salts of the acids, wherein the inorganic
acids are selected from the group consisting of sulfamic acid and sulfuric acid; and
one or more amino acids selected from the group consisting alanine, arginine, aspartic
acid, asparagine, glutamic acid, glycine, glutamine, histidine, leucine, lysine, threonine,
isoleucine, serine, and valine; optionally one or more alloying metal; and optionally
one or more pH adjuster; and
- c) electroplating an indium layer adjacent to the nickel layer of the substrate with
the indium electroplating composition.
[0009] The aqueous acid indium electroplating compositions and methods of the present invention
can be used to plate indium metal layers having a thickness of > 0.1 µm on nickel
without using a strike. The current efficiency for the aqueous acid indium electroplating
compositions is high, and the indium deposit is uniform and matte, substantially void-free,
whisker-free, has a smooth surface morphology and shows good adhesion on Nickel. Post
annealing of the substrates with the indium deposit shows minor to substantially no
dewetting. During indium electroplating hydrogen gas evolution is substantially inhibited
to enable smooth uniform matte indium deposits. The indium electroplating compositions
contain only registered and REACh compliant compounds.
Detailed Description of the Inventions
[0010] As used throughout the specification, the following abbreviations have the following
meanings, unless the context clearly indicates otherwise: ° C = degrees Centigrade;
g = gram; mg = milligram; L = liter; A = amperes; dm = decimeter; ASD = A/dm
2 = current density; µm = micron = micrometer; indium ion = In
3+; nm = nanometers = 10
-9 meters; µm = micrometers = 10
-6 meters; M = molar; min. = minute; IC = integrated circuits; XRF = X-ray fluorescence;
and e.g. = example.
[0011] The terms "depositing", "plating" and "electroplating" are used interchangeably throughout
this specification. The term "aqueous" means water based or the solvent of the composition
is water. The term "adjacent' means in direct contact or two separate surfaces or
planes having a common interface. The term "interface" means point(s) of contact between
two surfaces or planes. The term "plane" means a substantially flat surface such that
a straight line joining any two points on it lies wholly in it. The term "surface"
means outer area or upper most area of an article or structure. The term "copolymer"
is a compound composed of two or more different monomers or oligomers. The term "dewetting"
means the retraction of indium plating at some position on the nickel surface after
reflow, wherein this position of the nickel is called the non-wettable area and occurs
when adhesion is poor. The term "matte" means dull and flat in appearance without
shine. Unless otherwise noted all plating baths are aqueous solvent based, i.e. water
based, plating baths. All amounts are percent by weight and all ratios are by moles,
unless otherwise noted. All numerical ranges are inclusive and combinable in any order
except where it is logical that such numerical ranges are constrained to add up to
100%.
[0012] The aqueous acid indium compositions of the present invention include one or more
sources of indium ions which are soluble in an aqueous environment. Such sources include,
but are not limited to, indium salts of alkane sulfonic acids, such as methanesulfonic
acid, ethanesulfonic acid, and butane sulfonic acid, indium salts of sulfamic acid,
sulfate salts of indium, chloride and bromide salts of indium, nitrate salts, hydroxide
salts, indium oxides, fluoroborate salts, indium salts of carboxylic acids, such as
citric acid, acetoacetic acid, glyoxylic acid, pyruvic acid, glycolic acid, malonic
acid, hydroxamic acid, iminodiacetic acid, salicylic acid, glyceric acid, succinic
acid, malic acid, tartaric acid, hydroxybutyric acid, indium salts of amino acids,
such as arginine, aspartic acid, asparagine, glutamic acid, glycine, glutamine, leucine,
lysine, threonine, isoleucine, and valine. Preferably, the source of indium ions is
one or more indium salts of sulfuric acid, sulfamic acid, and alkane sulfonic acids.
More preferably, the source of indium ions is one or more indium salts of sulfuric
acid, sulfamic acid and methane sulfonic acid. Most preferably, the source of indium
ions is indium sulfate.
[0013] The indium ions from the water-soluble salts of indium are included in the compositions
in sufficient amounts to provide an indium deposit of desired thickness. Preferably,
the indium ions from the water-soluble indium salts are included in the compositions
in amounts of 5 g/L to 70 g/L, more preferably, from 10 g/L to 50 g/L, most preferably,
from 10 g/L to 40 g/L.
[0014] One or more amino acids selected from the group consisting of alanine, arginine,
aspartic acid, asparagine, glutamic acid, glycine, glutamine, histidine, leucine,
lysine, threonine, isoleucine, serine, and valine are included in the indium plating
compositions of the present invention. Preferably, the indium electroplating compositions
of the present invention are free of amino acids having sulfur and sulfur functional
groups. Preferably, the one or more amino acids are selected from the group consisting
of arginine, aspartic acid, asparagine, glycine, glutamine, lysine, serine and histidine,
more preferably, the one or more amino acids are selected from the group consisting
of arginine, asparagine, glycine, aspartic acid, lysine and serine, even more preferably,
the one or more amino acids are selected from the group consisting of glycine, lysine
and serine. Most preferably, the amino acid is glycine. Including one or more of the
amino acids in the indium electroplating compositions of the present invention inhibits
hydrogen gas evolution during indium electroplating and stabilizes indium ions such
that no substantial precipitation of the indium ions occurs at a relatively high pH
of >1.5.
[0015] One or more of the foregoing amino acids can be included in the indium plating compositions
of the present invention in amounts of 5 g/L or greater. Preferably, the one or more
amino acids of the present invention can be included in amounts of 10 g/l to 200 g/L,
more preferably, the amino acids can be included in amounts of 25 g/L to 150 g/L (e.g.
30 g/L to 120 g/L, 30 g/L to 100 g/L or 25 g/L to 75 g/L), even more preferably, the
amino acids can be included in amounts of 25 g/l to 100 g/L (e.g. 30 g/L to 100 g/L
or 40 g/L to 100 g/L), most preferably, the amino acids are included in amounts of
50 g/L to 100 g/L (e.g. 50 g/L to 90 g/L).
[0016] One or more acids selected from the group consisting of inorganic acids, alkane sulfonic
acids, and salts of the acids, wherein the inorganic acids are selected from the group
consisting of sulfamic acid and sulfuric acid. Alkane sulfonic acids include, but
are not limited to methanesulfonic acid, ethanesulfonic acid, and butane sulfonic
acid. Preferably, the one or more acids are selected from the group consisting of
sulfuric acid, sulfamic acid and methane sulfonic acid, more preferably, the one or
more acids are selected from the group consisting of sulfuric acid and sulfamic acid,
most preferably, the acid is sulfamic acid.
[0017] One or more of the foregoing acids or salts thereof are included in the indium electroplating
compositions of the present invention in amounts of 10 g/L or greater. Preferably,
the one or more acids are included in the indium plating compositions in amounts of
10 g/L to 300 g/L, more preferably, from 50 g/L to 250 g/L, even more preferably from
50 g/L to 200 g/L, most preferably from 50 g/L to 100 g/L.
[0018] The pH of the aqueous acid indium electroplating compositions of the present invention
range from 5 or less, preferably from 1-4, more preferably, from 1-3, even more preferably,
from 1.5-3, most preferably, from 1.5-2.5.
[0019] Optionally, one or more pH adjusters can be included in the indium electroplating
compositions to provide and maintain a desired acid pH. The pH adjuster can include
buffers which include an acid and the salt of its conjugate base. Acids are selected
from glyoxylic acid, pyruivic acid, hydroxamic acid, iminodiacetic acid, salicylic
acid, succinic acid, hydroxybutyric acid, acetic acid, acetoacetic acid, tartaric
acid, phosphoric acid, oxalic acid, carbonic acid, ascorbic acid, butanoic acid, thioacetic
acid, glycolic acid, malic acid, formic acid, heptanoic acid, hexanoic acid, hydrofluoric
acid, lactic acid, nitrous acid, octanoic acid, pentanoic acid, uric acid, nonanoic
acid, decanoic acid, sulfurous acid, sulfuric acid, alkane sulfonic acids and aryl
sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, benzenesulfonic
acid, toluenesulfonic acid, sulfamic acid. Bases such as potassium hydroxide and sodium
hydroxide can also be used as pH adjusters alone or combination with one or more of
the foregoing acids. Preferably, the one or more pH adjustors are selected from the
group consisting of sulfamic acid, sulfuric acid, potassium hydroxide and sodium hydroxide,
more preferably, the one or more pH adjusters are selected from the group consisting
of sulfamic acid, sulfuric acid and potassium hydroxide.
[0020] Optionally, the aqueous acid indium electroplating compositions can include one or
more alloying metal. Preferably, the one or more alloying metal is selected from the
group consisting of tin, copper, bismuth and silver, more preferably, the one or more
alloying metal is selected from the group consisting of tin, copper and silver, most
preferably, the alloying metal is tin. The alloying metals can be added to the indium
compositions as water soluble metal salts. Such water-soluble metal salts are well
known to those of skill in the art. Many are commercially available or can be prepared
from descriptions in the literature. One or more sources of alloying metal can be
added to the indium electroplating compositions in amounts such that the indium alloy
has from 1wt% to 3wt% of one or more alloying metals. Preferably, alloying metals
are excluded from the indium compositions. It is preferred that only indium metal
is plated.
[0021] Optionally, one or more sources of chloride can be added to the indium electroplating
compositions of the present invention. Sources of chloride include, but are not limited
to, sodium chloride and potassium chloride. Preferably, when one or more sources of
chloride is added to the indium electroplating composition, the concentration of chloride
can range from 1-50 g/L.
[0022] Conventional hydrogen gas suppressors, such as copolymers of epihalohydrin and nitrogen-containing
organic compounds, are excluded from the indium electroplating compositions of the
present invention. Preferably, many conventional additives, such as levelers, suppressors,
brighteners, grain refiners, alloying metals and surfactants are also excluded of
the indium electroplating compositions of the present invention.
[0023] Preferably, in the aqueous acid indium electroplating compositions of the present
invention, the water is at least one of deionized and distilled water to limit incidental
impurities.
[0024] Preferably, the aqueous acid indium electroplating composition of the present invention
consists of water; one or more sources of indium ions, including both indium (In
3+) cations and counter anions; one or more acids selected from the group consisting
of inorganic acids, wherein the inorganic acids are selected from the group consisting
of sulfamic acid and sulfuric acid, and alkane sulfonic acids, including salts of
sulfamic acid, sulfuric acid and alkanesulfonic acid; one or more amino acids selected
from the group consisting of alanine, arginine, aspartic acid, asparagine, glycine,
glutamine, histidine, leucine, lysine, threonine, isoleucine, serine, and valine;
optionally one or more sources of chloride; and optionally one or more pH adjusters.
[0025] More preferably, the aqueous acid indium electroplating composition of the present
invention consists of water; one or more sources of indium ions, including both indium
(In
3+) cations and counter anions; one or more acids selected from the group consisting
of sulfamic acid, sulfuric acid, methane sulfonic acid and salts of the foregoing
acids; one or more amino acids selected from the group consisting of arginine, aspartic
acid, asparagine, glycine, glutamine, lysine and serine; one or more sources of chloride;
and optionally one or more pH adjusters.
[0026] Most preferably, the aqueous acid indium electroplating composition of the present
invention consists of water; one or more sources of indium ions, including both indium
(In
3+) cations and counter anions; one or more acids selected from the group consisting
of sulfamic acid and sulfuric acid, wherein the most preferred acid is sulfamic acid;
one or more amino acids selected from the group consisting of arginine, asparagine,
glycine, lysine and serine, wherein glycine, lysine and serine are the more preferred
amino acids, and glycine is the most preferred; and optionally one or more pH adjusters.
[0027] Preferably, the aqueous acid indium electroplating composition of the present invention
can be used to electroplate indium metal or an indium alloy directly adjacent to a
nickel layer, wherein the nickel layer is directly adjacent to copper or a copper
alloy. More preferably, the aqueous acid indium electroplating composition of the
present invention can be used to electroplate indium metal directly adjacent to a
nickel layer, wherein the nickel layer is directly adjacent copper or a copper alloy.
Nickel layer thickness preferably ranges from 0.1-5µm. Conventional strike layers
of indium or silver having thickness values ranging from 1-100nm, more typically,
from 1-40nm are excluded from the nickel surface such that the indium metal or indium
alloy can be electroplated directly adjacent the nickel and provide a matte, uniform,
void-free and substantially whisker-free indium deposit of > 100nm which has good
adhesion to the nickel. Such adhesion can be tested by cross-hatch tests, pin bending
tests and reflow test followed by dewetting control.
[0028] The indium layers range in thickness from > 0.1 µm, preferably, from 0.2 µm to 10µm,
more preferably, from 0.2µm to 5µm, most preferably, from 0.2µm to 1µm.
[0029] Apparatus used to deposit indium metal or indium alloys directly adjacent to nickel
is conventional. Preferably, conventional soluble indium electrodes are used as the
anode. Current densities can vary depending on the concentration of indium ions in
the electroplating composition and bath agitation. Preferably, current densities range
from 0.1 ASD or greater (e.g. 0.1-50 ASD, 0.1-30 ASD or 0.1-20 ASD), more preferably,
0.5 ASD to 50 ASD (e.g. 0.5-40 ASD, 1-20 ASD or 1-10 ASD).
[0030] The temperatures of the indium compositions during indium metal or indium alloy electroplating
can range from room temperature to 60 °C. Preferably, the temperatures range from
room temperature to 55 °C, more preferably, from room temperature to 50 °C, most preferably,
from 30-45 °C.
[0031] The indium plating speed of the aqueous acid indium electroplating compositions of
the present invention can range from ≥ 0.2µm/min., ≥ 0.5µm/min., > 1µm/min., > 2.3µm/min.,
or > 3µm/min., at 1, 2, 4, 8 or 10 ASD, respectively.
[0032] Optionally, the indium or indium alloy plated nickel and copper or copper alloy substrates
are reflowed. Reflow tests are preferably done at temperatures of ≥ 150 °C, more preferably,
at temperatures of ≥ 200 °C, most preferably, from 200-350 °C. Reflow can be done
in conventional reflow ovens used for metal substrates. The reflowed indium plated
nickel substrates show minor to substantially no dewetting.
[0033] Although the aqueous acid indium electroplating compositions of the present invention
are preferably used to deposit indium metal or indium alloy directly adjacent a nickel
layer, wherein the nickel layer is directly adjacent copper or copper alloy, such
as for connector pins in IC electronic devices, it is envisioned that the aqueous
acid indium electroplating compositions of the present invention can be used to deposit
indium metal or indium alloys directly adjacent other metals, such as copper and copper
alloys. It is preferred that indium metal is deposited directly adjacent other metals,
such as nickel, copper or copper alloys, most preferably, indium metal is deposited
directly adjacent nickel, wherein the nickel is directly adjacent copper or copper
alloy.
[0034] The following examples are intended to illustrate the present invention, but are
not intended to limit the inventions scope.
Examples 1-10
Hull Cell Electroplating Performance of Aqueous Acid Indium Electroplating Compositions
of the Present Invention
[0035] The following aqueous, acid indium electroplating compositions were prepared:
Table 1
Example |
Indium Ion Concentration |
Amino Acid |
Acid |
pH |
Plating Temperature °C |
1 |
30 g/L Indium ions (from indium sulfate) |
Glycine 100 g/L |
Sulfamic acid 50 g/L |
2.1 |
30 |
2 |
30 g/L Indium ions (from indium sulfate) |
Glycine 50 g/L |
Sulfamic acid 100 g/L |
1.1 |
50 |
3 |
30 g/L Indium ions (from indium sulfate) |
Glycine 50 g/L |
Sulfamic acid 100 g/L |
2 |
50 |
4 |
30 g/L Indium ions (from indium sulfate) |
Glycine 100 g/L + Arginine 40 g/L |
Sulfuric acid 28 g/L |
2.4 |
40 |
5 |
30 g/L Indium ions (from indium sulfate) |
Glycine 120 g/L |
Methane Sulfonic acid 160 g/L |
2.2 |
30 |
6 |
30 g/L Indium ions (from indium sulfate) |
Lysine 100 g/L |
Sulfamic acid 50 g/L |
2.1 |
35 |
7 |
30 g/L Indium ions (from indium sulfate) |
Glutamine 100 g/L |
Sulfamic acid 50 g/L |
2.1 |
40 |
8 |
30 g/L Indium ions (from indium sulfate) |
Histidine 100 g/L |
Sulfamic acid 50 g/L |
2.1 |
35 |
9 |
30 g/L Indium ions (from indium sulfate) |
Serine 100 g/L |
Sulfamic acid 50 g/L |
2.1 |
35 |
10 |
30 g/L Indium ions (from indium sulfate) |
Asparagine 100 g/L |
Sulfamic acid 50 g/L |
2.1 |
35 |
The solvent of the foregoing indium electroplating compositions was water and the
pH of the indium electroplating compositions was adjusted with potassium hydroxide.
[0036] 250 mL of each indium composition was placed in separate Hull cells. A brass (copper-zinc
alloy) panel coated with nickel was used as the cathode. Indium metal was used as
a soluble anode. The rectifier was set as 2 A. During plating, the indium compositions
were agitated using a common laboratory paddle agitator. Indium electroplating was
done for 3 min. Current densities ranged from 0.1-10 ASD. The indium metal deposit
was measured at current densities of 1, 2, 3, 4, 6, 8 and 10 ASD using a Fischerscope
X-Ray XDV-SD XRF apparatus. The plating rate was determined by dividing the thickness
at each current density by the plating time in minutes.
[0037] As the current density increased, the plating rate of the indium deposition on the
nickel also increased. Plating rates ranged from a low of 0.5µm/min. at 1 ASD to a
high of 3.2µm/min. at 10 ASD. After electroplating was completed, the indium deposits
were examined for the quality of the deposits. All the indium deposits appeared smooth,
matte and uniform. No deposit defects were observed.
Examples 11-12
Reflow Test of Indium Metal on Nickel
[0038] The following aqueous, acid indium electroplating compositions were prepared:
Table 2
Example |
Indium Ion Concentration |
Amino Acid |
Copolymer |
Acid |
pH |
Plating Temperature °C |
11 |
30 g/L Indium ions (from indium sulfate |
Glycine 100 g/L |
----------- |
Sulfamic acid 50 g/L |
2.1 |
30 |
12 (comparative) |
30 g/L Indium (from indium sulfate) |
----------- |
Imidazole-epichlorohydrin1 130 g/L |
Methane sulfonic acid 4.4 g/L |
1.1 |
50 |
1LUGALVAN™ IZE, available from BASF (IZE contains 48-50wt% copolymer). |
[0039] Each aqueous, acid indium electroplating composition was used to plate indium on
nickel coated brass (copper-zinc alloy). The counter electrode was an indium soluble
anode. Plating of indium on the nickel of the substrate was done for 3 min. at a current
density of 5ASD. The indium electroplating compositions were agitated throughout plating.
[0040] After plating, the indium plated substrates were rinsed with DI water, dried and
observed for plating performance. The indium deposit on the nickel appeared uniform,
matte and smooth on both substrates.
[0041] The substrates were then reflowed/heated using a conventional reflow oven. Reflow
was done at 200 °C for 3 min. The reflowed substrates were removed from the oven and
the quality of their surfaces was analyzed. The substrate which was plated with the
indium composition of Example 11 showed no indication of dewetting. In contrast, the
substrate plated with the indium composition of Example 12 showed significant dewetting:
nickel was exposed on some areas which were covered by the indium before reflow.
Examples 13-14
Hull Cell Plating Performance of Aqueous Acid Indium Plating Compositions Containing
Amino Acid Cysteine or Amino Acid Glycine
[0042] The following aqueous acid indium electroplating compositions were prepared:
Table 3
Example |
Indium Ion Concentration |
Amino Acid |
Acid |
pH |
Plating Temperature °C |
13 (comparative) |
30 g/L Indium ions (from indium sulfate) |
L-cysteine 100 g/L |
Sulfamic Acid (sufficient amount to provide desired pH) |
2 |
35 |
14 |
30 g/L Indium ions (from indium sulfate) |
Glycine 100 g/L |
Sulfamic Acid (sufficient amount to provide desired pH) |
2 |
35 |
250 mL of each aqueous acid indium composition was placed in a Hull cell. A nickel
coated brass (copper-zinc alloy) substrate was used as a cathode. The plating was
done at a current of 2A for 3 min. under paddle agitation. The counter electrode was
a soluble indium anode. The coating appearance and thickness were evaluated at the
current density ranging from 0.1-10 ASD. For comparative Example 13 there was no indication
of indium plating as the lower current densities of 0.1-3 ASD. The indium deposit
was very thin (less than 0.4µm) and non-uniform at current densities above 3 ASD.
Substantial gas evolution was observed during plating (observed by gas bubbling from
the cathode with the naked eye).
[0043] In contrast, the indium deposit of Example 14 appeared uniform, matte and smooth
from 0.1-10 ASD. The plating speed was comparable to the plating speeds of Examples
1-5, above.
Examples 15-17
Hull Cell Plating Performance of Aqueous Acid Indium Plating Compositions The following
aqueous acid indium electroplating compositions were prepared:
[0044]
Table 4
Example |
Indium Ion Concentration |
Amino Acid |
Copolymer |
Acid |
pH |
Plating Temperature °C |
15 |
30 g/L Indium ions (from indium sulfate) |
Glycine 100 g/L |
----------- |
Sulfamic acid 50 g/L |
2 |
35 |
16 (comparative) |
30 g/L Indium ions (from indium sulfate) |
Glycine 100 g/L |
Imidazole-epichlorohydrin1 5 g/L |
Sulfamic acid 50 g/L |
2 |
35 |
17 (comparative) |
30 g/L Indium ions (from indium sulfate) |
Glycine 100 g/L |
Imidazole-epichlorohydrin1 15 g/L |
Sulfamic acid 50 g/L |
2 |
35 |
1LUGALVAN™ IZE, available from BASF (IZE contains 48-50wt% copolymer). |
[0045] 250 mL of each aqueous acid indium composition was placed in a Hull cell. A nickel
coated brass (copper-zinc alloy) substrate was used as a cathode. The plating was
done at a current of 2 A. Plating was done under paddle agitation for 3 min. The counter
electrode was an indium soluble anode. The indium coating appearances and thicknesses
were evaluated at current densities ranging from 0.1-10 ASD.
[0046] The substrate plated with indium from Example 15 had a uniform, matte and smooth
indium deposit. The plating rate was good and was substantially the same as in Examples
1-5 above over the current density range of 0.1-10 ASD. There were no observable defects.
[0047] In contrast, the substrates plated with the indium compositions of Examples 16-17
showed no substantial indium deposited on the substrate. XRF analysis of the substrates
from Examples 16-17 showed 0.1-0.6µm indium clusters at some areas of the substrates.
Substantial gas evolution was observed during the plating of the substrates of Examples
16-17. It was determined that the imidazole/epihalohydrin copolymer was not suitable
for indium metal electroplating.
Example 18
Hydrogen Gas Generation and Reflow Test of Indium on Nickel
[0048] The indium plating compositions of Examples 15, 16 and 17 of Table 4 above were added
to separate one liter glass beakers. Two indium soluble anodes were placed in each
beaker. A nickel coated brass coupon was used in each beaker as a cathode. The electrodes
were connected to a rectifier. A current density of 4 ASD was applied to each composition.
Plating was done over 2 min. The indium electroplating compositions were agitated
using a magnetic stirrer throughout plating. After plating, each coupon was removed
from the beaker and rinsed with DI water, dried and analyzed for indium plating performance.
[0049] The coupon from Example 15 had a uniform, matte and smooth indium deposit 2.2µm thick.
In contrast, the indium deposits from the plating compositions of Examples 16-17 were
very thin. XRF analysis measured an indium deposit of only 0.2µm thick for the coupon
plated with the indium composition from Example 16 and an indium deposit of 0.1 µm
thick from the composition of Example 17. Substantial gas evolution was observed during
plating for Examples 16-17.
[0050] The above experiment was repeated using a current density of 8 ASD with a plating
time of 1 min. 30 sec. The indium deposit from Example 15 was uniform, matte and smooth
in appearance with a 3.7µm thick indium deposit. The indium deposit from the compositions
of Examples 16-17 had indium thicknesses of 0.55µm and 0.35µm, respectively.
Examples 19-21
Hydrogen Gas Generation and Reflow Test of Indium on Nickel
[0051] The following aqueous acid indium electroplating compositions were prepared:
Table 5
Example |
Indium Ion Concentration |
Amino Acid |
Copolymer |
Acid |
pH |
Plating Temperature °C |
19 |
30 g/L Indium ions (from indium sulfate) |
Glycine 100 g/L |
----------- |
Sulfamic acid 50 g/L |
2 |
35 |
20 (comparative) |
30 g/L Indium ions (from indium sulfate) |
Glycine 100 g/L |
Imidazole-epichlorohydrin1 5 g/L |
Sulfamic acid 50 g/L |
2 |
35 |
21 (comparative) |
30 g/L Indium ions (indium sulfate) |
Glycine 100 g/L |
Imidazole-epichlorohydrin1 15 g/L |
Sulfamic acid 50 g/L |
2 |
35 |
1LUGALVAN™ IZE, available from BASF (IZE contains 48-50wt% copolymer). |
[0052] Each of the indium plating compositions of Examples 19-20 were added to separate
glass one liter beakers. Two indium anodes were placed in each beaker and a nickel
coated coupon was used in each beaker as a cathode. The electrodes were connected
to a rectifier. A current density of 4 ASD was applied for 2 min. of plating. The
plating compositions were agitated throughout plating. During indium plating substantial
hydrogen gas evolution was observed for Examples 20-21. In contrast, insignificant
hydrogen gas evolution was observed for Example 19.
[0053] After plating, the indium plated substrates were rinsed with DI water, dried and
observed for plating performance. The indium deposit on the nickel plated from the
indium compositions of Example 19 appeared uniform, matte and smooth. The average
indium thickness was 2.2µm.
[0054] In contrast, substantially no indium was deposited on the nickel from the indium
compositions of Examples 20 and 21. The average indium thickness on the nickel plated
with the indium composition of Example 20 was only 0.55µm and the average thickness
on the nickel plated with indium with the composition of Example 21 was only 0.35µm.
[0055] The substrates with the indium deposits adjacent the nickel were then reflowed using
a conventional reflow oven. Reflow was done at 200 °C for 3 min. The reflowed substrates
were removed from the oven and the quality of their surfaces was analyzed. The substrate
which was plated with the indium composition of Example 19 showed no indication of
dewetting. In contrast, the substrates plated with the indium compositions of Examples
20-21 showed several dewetting spots spread over the surface of the indium layer.
Examples 22-27
Aqueous Acid Indium Electroplating Composition Stability
[0056] The following aqueous acid indium electroplating compositions were prepared:
Table 6
Example |
Indium Ion Concentration |
Amino Acid |
Acid |
pH |
pH Adjuster |
22 (comparative) |
30 g/L Indium ions (from indium sulfate) |
----------- |
Sulfamic acid 50 g/L |
2 |
Potassium hydroxide |
23 |
30 g/L Indium ions (from indium sulfate) |
Glycine 25 g/L |
Sulfamic acid 50 g/L |
2 |
Potassium hydroxide |
24 |
30 g/L Indium ions (from indium sulfate) |
Glycine 50 g/L |
Sulfamic acid 50 g/L |
2 |
Potassium hydroxide |
25 |
30 g/L Indium ions (from indium sulfate) |
Glycine 75 g/L |
Sulfamic acid 50 g/L |
2 |
Potassium hydroxide |
26 |
30 g/L Indium ions (from indium sulfate) |
Glycine 100 g/L |
Sulfamic acid 50 g/L |
2 |
Sulfamic acid |
27 |
30 g/L Indium ions (from indium sulfate) |
Glycine 150 g/L |
Sulfamic acid 50 g/L |
2 |
Sulfuric acid |
[0057] After initial make-up at room temperature, all the foregoing indium plating compositions
appeared colorless. All the indium plating compositions idled at room temperature
for one day. The indium plating composition of Example 22 was significantly turbid.
White precipitate was observed at the bottom of the glass beaker. The white precipitate
indicated that an indium salt precipitated from the composition.
[0058] In contrast, the indium plating compositions of Examples 23-27 remained colorless
indicating good stability. The compositions of Examples 23-27 remained colorless indicating
stable indium compositions over several weeks. No turbidity or precipitation was observed
even after one month.
1. An indium electroplating composition consisting of water; one or more sources of indium
ions; one or more acids selected from the group consisting of inorganic acids, alkane
sulfonic acids, and salts of the acids, wherein the inorganic acids are selected from
the group consisting of sulfamic acid and sulfuric acid; and one or more amino acids
selected from the group consisting alanine, arginine, aspartic acid, asparagine, glutamic
acid, glycine, glutamine, leucine, histidine, lysine, threonine, isoleucine, serine,
and valine; optionally one or more alloying metal; and optionally one or more pH adjuster.
2. The indium electroplating composition of claim 1, wherein the one or more amino acids
are selected from the groups consisting of glycine, arginine, lysine, glutamine, serine,
histidine and asparagine.
3. The indium electroplating composition of claim 1, wherein the one or more amino acids
are in amounts of at least 5 g/L.
4. The indium electroplating composition of claim 3, wherein the one or more amino acids
are in amounts of 10 g/L to 200 g/L.
5. The indium electroplating composition of claim 1, wherein the one or more acids are
inorganic acids selected from the group consisting of sulfamic acid and sulfuric acid.
6. The indium electroplating composition of claim 1, wherein the one or more alloying
metals is selected from the group consisting of tin, silver, bismuth and copper.
7. A method of electroplating indium on nickel comprising:
a. providing a substrate comprising a nickel layer adjacent to a copper or copper
alloy layer;
b. contacting the substrate comprising the nickel layer adjacent to the copper or
the copper alloy layer with an indium electroplating composition consisting of water;
one or more sources of indium ions; one or more acids selected from the group consisting
of inorganic acids, alkane sulfonic acids, and salts of the acids, wherein the inorganic
acids are selected from the group consisting of sulfamic acid and sulfuric acid; and
one or more amino acids selected from the group consisting alanine, arginine, aspartic
acid, asparagine, glutamic acid, glycine, glutamine, histidine, leucine, lysine, threonine,
isoleucine, serine, and valine; optionally one or more alloying metal; and one or
more pH adjuster; and
c. electroplating an indium layer adjacent to the nickel layer of the substrate with
the indium electroplating composition.
8. The method of electroplating indium on nickel of claim 7, wherein the indium layer
is greater than 0.1µm.
9. The method of electroplating indium on nickel of claim 8, wherein the indium layer
is 0.2-1 µm.
10. The method of electroplating indium or indium alloy of claim 7, wherein the one or
more amino acids are selected from the groups consisting of glycine, lysine, glutamine,
histidine, serine, asparagine and arginine.