Electroless nickel deposition from methane sulfonate bath

Article abstract of DOI:10.1016/j.jallcom.2009.06.178

Electroless plating is a controlled autocatalytic chemical reduction process for depositing metals. The process involves a continuous build up of a nickel coating on a substrate by immersion of the substrate in a suitable nickel plating under appropriate

Full text of DOI:10.1016/j.jallcom.2009.06.178

Journal of Alloys and Compounds 486 (2009) 447–450
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Electroless nickel deposition from methane sulfonate bath
∗
K.N. Srinivasan , S. John
Central Electrochemical Research Institute, Karaikudi 630006, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 June 2009
Received in revised form 23 June 2009
Accepted 28 June 2009
Available online 4 July 2009
Electroless plating is a controlled autocatalytic chemical reduction process for depositing metals. The
process involves a continuous build up of a nickel coating on a substrate by immersion of the substrate in
a suitable nickel plating under appropriate conditions. In this paper the authors have studied the effect of
pH and temperature on the rate of deposition and phosphorous content from nickel methane sulfonate
bath. Effect of phosphorous content on hardness, wear resistance and corrosion resistance were also
studied. SEM and XRD measurements show nodular and amorphous character of the deposits. As the
bath is free from sulfate ions the bath can be operated for more number of turn overs and orthophosphite
formed during the process can be removed easily.
Keywords:
Electroless nickel
Methane sulfonate
Nickel–phosphorous
Chemical plating
©
2009 Elsevier B.V. All rights reserved.
1
. Introduction
a reducing agent. When we use hypophosphite as reducing agent
during the process it is oxidized to orthophosphate ions and the
nickel cations are reduced to form Ni–P alloy on the substrate sur-
face. As the reaction proceeds the level of orthophosphite ions in the
bath increases and often precipitated as insoluble metal orthophos-
phates. Most electroless nickel solutions use sulfate as the source
of nickel ions in solutions and so the sulfate anions also increases
during the process. At some critical concentration of these two, i.e.
sulfate and orthophosphite ions the electroless nickel solution pro-
duces deposits that are rough with variable amount of occluded
phosphorous. Martyak [7] has studied the replacement of sulfate
ions by methane sulfonate ions and evaluated the various proper-
ties of the coatings.
Electroless nickel process based on nickel methane sulfonate
show many advantages over the conventional nickel sulfate baths
[8]. The solubility of Ni2+ in methane sulfonic acid is high >100 g/L
and although the methane sulfonate anions increases in concentra-
tion with age of the bath the addition of calcium to aged solution
allows for the selective removal of orthophosphite thus increas-
ing electroless nickel bath life [9]. This study examines the effect
of time, pH and temperature on the rate of deposition in nickel
methane sulfonate bath. Effect of phosphorous content on hard-
ness, wear resistance and corrosion resistance was also carried out.
Structural investigations were carried out using SEM and XRD mea-
surements.
Electrolessplatingofmetalsandprocesstechnologyhaveimpor-
tant role along with other methods of plating. Today, sophisticated
electroless plating systems are in use for many electronic appli-
cations. The term electroless plating is defined as autocatalytic
deposition of metals/alloys from an aqueous solution of its ions by
interaction with a chemical reducing agent. The reducing agent pro-
vides electrons for the metal ions to be neutralized. The reduction
is initiated by the catalysed surface of the substrate and continues
by the self-catalytic activity of the deposited metal/alloy as long
as the substrate is immersed in the electroless bath and the oper-
ating conditions are maintained. The history of electroless plating
began in 1946 when Brenner and Riddel [1] discovered that sodium
hypophosphite added as an anti-oxidant to the nickel electroplat-
ing bath produced a nickel coating even without passing current.
Further investigations revealed that the coating contained phos-
phorous also. Their discoveries lead to the first commercially usable
electroless nickel bath in 1950. Later years witnessed the evolution
of electroless copper [2], cobalt [3] silver [4] gold [5] and spec-
trum of electroless baths capable of producing deposits of improved
quality. In 1970 there was an upsurge in electroless deposition of
poly-alloys based on nickel–phosphorous, cobalt–phosphorous and
nickel–boron. In 1980s a large number of composite coatings with
varying engineering properties are being introduced [6]. Electroless
plating baths generally comprise nickel salt, complexing agent and
2. Experimental
2
.1. Electrode preparation
∗ Corresponding author. Tel.: +91 4565 227550/227559;
fax: +91 4565 227779/227713.
Mild steel panels of size 10 cm × 10 cm were mechanically polished, degreased,
alkaline cleaned, washed, and dipped in 10% HCl for 2 min, washed, rinsed in deion-
ized water and electroless nickel-plated. These specimens were used for structural
E-mail address: knsvasan@gmail.com (K.N. Srinivasan).
0
925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2009.06.178

4
48
K.N. Srinivasan, S. John / Journal of Alloys and Compounds 486 (2009) 447–450
investigations. For analyzing the phosphorous content, stainless steel panels of the
same was used. These panels were etched in hydrochloric acid, washed and activated
in a solution containing 0.5 g/L of palladium chloride. After the activation treatment
the panels were washed well, rinsed and plated with electroless nickel. Copper pan-
els were used for finding out the rate of deposition, cleaned in sulfuric acid, washed
and activated in palladium chloride solution before electroless nickel deposition.
2.7. Scanning electron microscopic studies (SEM)
The morphology of the electroless deposits was examined under high magnifica-
tion to assess the grain size, deposit nature, heterogeneities and pores present in the
deposits using a scanning electron microscope. The scanning electron microscope,
which makes use of reflected primary electrons and secondary electrons, enable one
to obtain information from regions that cannot be examined by others. The electro-
less nickel-plated specimens were cut into 1 cm × 1 cm size and mounted suitably
and examined under the microscope. The SEM photographs were taken with the
magnification range of 1000.
2.2. Bath preparation
Nickel methane sulfonate solution Ni(CH3SO3)2 was formulated by dissolving
150 g/L of nickel carbonate into approximately 200 mL distilled water. This slurry
was adequately mixed with 70% methane sulfonic acid (MSA) until all the carbonate
was removed. Then it was made up to 1 L and used as a stock solution. This stock
solution contains 75 g/L of nickel.
3. Results and discussion
Following is the bath composition selected for further studies:
3.1. Effect of temperature on the rate of deposition and
phosphorous content in the deposit
1
. Nickel as methane sulfonate: 6 g/L.
2
3
4
. Sodium hypophosphite: 25 g/L.
. Tri ammonium citrate: 30 g/L.
. Stabilizer: 1 ppm.
Table 1 shows the effect of temperature on the rate of deposition
and phosphorous content. It is seen from the table, as the tem-
perature increases rate of deposition also increases. Temperature
is the most important parameter affecting the rate of deposition.
Most of the oxidation and reduction reaction involved in the over-
all process required energy in the form of heat and this is true for all
Required amount of chemicals were weighed and dissolved in distilled water.
Then filtered the solution through fine filter of 1 ␮m size and made into 1 L. The pH
of the solution was adjusted using ammonium hydroxide solution. After proper con-
ditioning pretreatment, parts to be electroless nickel-plated are simply immersed
in a bath after attaining the operating temperature. Mechanical agitation was used.
The temperature of the bath was maintained by using temperature controller. The
content in the bath was analyzed by EDTA method for every half an hour and replen-
ished.
baths and at all pH values. While the higher temperature more than
◦
9
0 C makes the deposition rate very attractive there is a danger
due to possible decomposition of the bath at these temperatures.
Hence further experiments were carried out at a temperature of
◦
9
0 C.
2.3. Effect of bath variables on the rate of deposition
Apart from the deposition rate, temperature also affects the
phosphorous content of the deposit and hence its properties. It is
noticed from the table there is a slight increase in phosphorous con-
tent as the temperature increases. Hence for these reasons accurate
temperature control of the electroless nickel bath is essential to get
constant phosphorous in the deposit. In the present study constant
temperature controller has been used which maintains the bath
2
.3.1. Effect of temperature on the rate of deposition
Copper panels were etched in 10% sulfuric acid washed with water, dried and
weighed. These copper panels were activated and placed in a 250 mL beaker con-
taining electroless bath solution whose pH was 5 and heated for half an hour at 40,
5
◦
0, 60, 70, 80 C in a magnetic stirrer.
After half an hour these panels were removed, washed, dried and weighed.
From the difference, the weight of nickel deposited was calculated. From the weight
of nickel deposited, area of copper panel and density of the deposit, the rate of
deposition was calculated.
◦
temperature with a variation of ± 2 C. Mechanical agitation with
a rotation set-up was used to maintain the bath constituents and
temperature uniformly through the rotation.
4
weight of Ni deposit in g × 10
Rate of deposition (␮m/h) =
2
area of copper panel (cm ) × density
3.2. Effect of pH on the rate of deposition and phosphorous
content
2.3.2. Effect of pH on the rate of deposition
The pH of electroless bath was changed to 5, 6, 7, 8, 10 using ammonia solution.
Activated copper panels were placed in electroless bath at pH values of 5, 6, 7, 8 and
Table 2 shows the effect of pH on the rate of deposition and
phosphorous content at a bath temperature of 90 C. It is seen from
the table as the bath pH increases the rate of deposition increases
and phosphorus content decreases in the deposit. The following is
◦
10 at 40, 50, 60, 70, 80 and 90 C, respectively for half an hour. Then these panels
◦
were removed, washed, dried and weighed. From the weight of the deposit, the rate
of deposition was calculated.
2.4. Anodic polarization measurements
Table 1
Anodic polarization measurements were carried out galvanostatically by expos-
Effect of bath temperature on the rate of deposition and phosphorous content at a
pH of 5.
ing 1 cm2 of the plated specimens using constant current regulator. Platinum was
used as an auxiliary electrode and saturated calomel electrode as a reference elec-
trode and varied the current from 0 to 100 mA and the corresponding change in the
potential was measured against SCE using digital voltmeter. The electrolyte used in
the study was 3% NaCl. Graph was drawn between potential and current density.
◦
S. No.
Temperature ( C)
Rate of deposition (␮m/h)
Phosphorous content
1
2
3
4
5
6
7
40
50
60
70
80
3.5
5.3
6.6
6.8
7.2
7.0
7.5
8.2
8.5
9.0
2
.5. Abrasion measurements
8.2
10.9
11.5
18.2
Abrasion measurements were carried out using Taber Abraser. The panels were
90
100
weighed before and after the experiments. 1 kg load was applied in the abrading
wheels. Weight loss was found out for 1000 cycles. The experiment was repeated
for the second 1000 cycles, the average value was taken. The value gives indication
of abrasion resistance of the coating.
Table 2
weight loss in g
Effect of pH on rate of deposition and phosphorous content at a bath temperature
Abrasion index =
◦
1000 cycles
of 90 C.
S. No.
pH
Rate of deposition (␮m/h)
% of phosphorous content
2
.6. X-ray diffraction studies
1
2
3
4
5
6
4
5
6
7
8
10
10
9
8.5
6.5
6.4
5
11.5
12.5
15
18.62
22.53
The X-ray diffraction is widely used to determine the structure and composition
of the materials. Diffraction patterns contain information showing various phases
of a material and also residual stresses present within the coating material. The X-
ray diffraction pattern for the electrolessly deposited nickel specimen obtained from
MSA bath was recorded using XRD instrument (make-Panalytical, USA) instruments.
10

K.N. Srinivasan, S. John / Journal of Alloys and Compounds 486 (2009) 447–450
449
Table 4
Wear resistance of electroless nickel coatings deposited at various pH values.
S. No.
pH
Weight loss in grams for
first 1000 cycles
Weight loss in grams for
second 1000 cycles
1
2
3
4
5
4
5
6
7
8
0.007
0.015
0.024
0.033
0.04
0.012
0.024
0.026
0.045
0.72
3.3. Anodic polarization studies
Fig. 1 shows the anodic polarization behavior of Ni–P deposits
obtained at various pH ranges. It is seen from the figure that there
is an increase in anodic polarization as the pH of the bath decreases
or P content increases in the deposit. Thus there is an increase in
corrosion resistance behavior of the deposit with increase in P in
the deposit.
Fig. 1. Anodic polarization behavior of electroless nickel deposited at various bath
pHs.
the overall reaction in the hypophosphite reduction of nickel ions:
3
.4. Effect of phosphorous on hardness and wear resistance of the
0
Ni(CH SO ) + 3NaH PO + 3H O → Ni (P) + 3NaH PO + H
3
3
2
2
2
2
2
3
2
deposit
+
2NaH SO3
(1)
3
Tables 3 and 4 show the hardness and wear resistance values of
the deposits. It is clear from the tables that both wear resistance
and hardness of the deposits increases with increase in phospho-
−
Also producing H PO3 and methanesulfonate CH SO3
The same reaction has been written as
.
2
3
−
−
0
2
H PO + Ni2+ + 2H O → 2H PO + H + 2H+ + Ni
(2)
(3)
2
2
2
2
3
2
or
Ni2 + H PO + H O → Ni + H PO + 2H
+
0
−
2
2
2
2
3
It is seen from the equations that the H+ ion concentration
increased as nickel ions are reduced to form the metal. The practical
implications of this are that pH will drop as the process proceeds.
−
Because of the OH ions must be supplied by controls dosing
with NH OH to maintain the pH of the bath. pH of the solution
4
has great effect on the rate of deposition and phosphorous content.
There are three competing reactions in the electroless processes
hydrogen evolution, nickel reduction, and phosphorous reduction
as per the following partial reactions
catalytic
H PO + H O −→ H PO + 2H+ + 2e
−
−
(4)
2
2
2
2
3
energy
0
Ni2 + 2e → Ni
+
(5)
(6)
(7)
+
2
H
+ 2e → H2
Fig. 2. SEM photomicrograph of electroless nickel deposit (1000×).
−
−
H PO + e → 2OH +P
2
2
With increase in acidity of the bath probability of interaction
of protons with electrons is increased leading to the reduction of
coefficient of utilization of hypophosphite. So the rate of reduction
of nickel decreases (5) and there will be more hydrogen evolution
(
(
6). Further hydrogen ion present in the electrolyte favors reaction
7) leading to the formation of more phosphorus content in the
deposit.
Table 3
◦
Effect of pH, hardness and phosphorous content at a temperature of 90 C.
S. No.
pH
Hardness Hv load 100 g
1
2
3
4
5
6
4
5
6
7
8
581
500
449
449
431
400
10
Fig. 3. XRD pattern of electroless nickel deposit obtained at a pH of 5.

4
50
K.N. Srinivasan, S. John / Journal of Alloys and Compounds 486 (2009) 447–450
rous content in the deposit which is in agreement with polarization
behavior.
duces uniform and high quality coatings. Following is the optimum
concentration of bath and operating conditions to get quality nickel
deposits:
3.5. SEM and XRD studies
Nickel methanesulfonate: 6 g/L (as Ni).
Ammonium citrate: 30 g/L.
Sodium hypophosphite: 25 g/L.
Stabilizer: 1 ppm.
Figs. 2 and 3 show the SEM and XRD pattern of the deposits
◦
obtained from MSA bath at a pH of 5 and at a temperature of 90 C.
It is seen from the XRD pattern there is broadening of XRD lines
which indicates amorphous nature of the deposits. SEM micrograph
shows that the deposits are nodular in nature.
pH (ammonia): 5.
Phosphorous content: 9%.
◦
Temperature: 90 C.
4
. Conclusions
Acknowledgement
A new electroless bath has been formulated based on nickel
methanesulfonate as the source of metal ions. The absence of sulfate
ions increases the bath life of the electroless nickel solution. Only
little nickel sulfonate is required for replenishments due to higher
solubility of nickel sulfonate. Electroless nickel process based on
Authors wish to convey their thanks to the Director, CECRI,
Karaikudi for his kind permission to publish this paper.
References
nickel methane sulfonate show many advantages over the conven-
tional nickel sulfate baths. The solubility of Ni2+ in methane sulfonic
[1] A. Brenner, G. Riddell, J. Res. Nat. Bur. Std. 37 (1946) 31.
[
[
2] K.F. Blurton, Plat. Surf. Finish. 73 (1986) 1.
3] M. Paunovic, Plating 55 (1968) 1161.
acid is high. Although the methane sulfonate anions increases in
concentration with age of the bath, the addition of calcium to the
aged solution allows for the selective removal of orthophosphite
thus increasing electroless nickel bath life. Further replenishments
of the solutions require only little nickel sulfonate due to higher
solubility of nickel sulfonate. The small replenishment volume
maintains a constant operating temperature, which in turn pro-
[4] Y. Okinaka, Plating 57 (1970) 914.
[
[
[
5] P. Bindra, J. Tweedie, J. Electrochem. Soc. 130 (1983) 1112.
6] Parker, Plating 61 (1974) 61.
7] N.M. Martyak, Plat. Surf. Finish. 89 (2002) 42–46.
[8] F.I. Nobe, European Patent Applications EP 0693577A1 (1995).
[9] S.E. George, US Patent 20030232148 (2003).