U.S. patent application number 14/289879 was filed with the patent office on 2015-12-03 for method of manufacturing nickel-based alloy barrier layer of wiring connection terminal.
This patent application is currently assigned to NATIONAL CHUNG SHAN INSTITUTE OF SCIENCE AND TECHNOLOGY. The applicant listed for this patent is National Chung Shan Institute of Science and Technology. Invention is credited to CHI-HAW CHIANG, REN-RUEY FANG, YANG-KUAO KUO, CHUN-YU LEE, CHIH WANG, YU-PING WANG.
Application Number | 20150345040 14/289879 |
Document ID | / |
Family ID | 54701079 |
Filed Date | 2015-12-03 |
United States Patent
Application |
20150345040 |
Kind Code |
A1 |
CHIANG; CHI-HAW ; et
al. |
December 3, 2015 |
METHOD OF MANUFACTURING NICKEL-BASED ALLOY BARRIER LAYER OF WIRING
CONNECTION TERMINAL
Abstract
A method of manufacturing a nickel-based alloy barrier layer of
a wiring connection terminal includes providing a substrate having
a metal wiring; electroplating a nickel or a nickel-based alloy to
the metal wiring at a deposition rate of 15-30 .mu.m/hr to form a
first layer thereon, wherein the first layer is of a thickness of
0.5 .mu.m-5 .mu.m, and the nickel-based alloy layer has nickel
content of at least 50%; and plating a gold layer to the first
layer to form thereon a second layer of a thickness of 0.03
.mu.m-0.3 .mu.m. The surface of the nickel-based alloy
electroplated layer features a crystalline-phase structure full of
micro-protuberances, and the thickness of the gold plated layer is
reduced to 0.03 .mu.m.
Inventors: |
CHIANG; CHI-HAW; (LONGTAN,
TW) ; WANG; CHIH; (LONGTAN, TW) ; WANG;
YU-PING; (LONGTAN, TW) ; LEE; CHUN-YU;
(LONGTAN, TW) ; FANG; REN-RUEY; (LONGTAN, TW)
; KUO; YANG-KUAO; (LONGTAN TOWNSHIP, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
National Chung Shan Institute of Science and Technology |
Longtan Township |
|
TW |
|
|
Assignee: |
NATIONAL CHUNG SHAN INSTITUTE OF
SCIENCE AND TECHNOLOGY
LONGTAN TOWNSHIP
TW
|
Family ID: |
54701079 |
Appl. No.: |
14/289879 |
Filed: |
May 29, 2014 |
Current U.S.
Class: |
205/103 ;
205/104; 205/117; 205/149 |
Current CPC
Class: |
C25D 3/562 20130101;
C25D 7/0607 20130101; C25D 5/12 20130101 |
International
Class: |
C25D 3/56 20060101
C25D003/56; C25D 5/48 20060101 C25D005/48; C25D 7/06 20060101
C25D007/06; C25D 5/18 20060101 C25D005/18 |
Claims
1. A method of manufacturing a nickel-based alloy barrier layer of
a wiring connection terminal, the method comprising the steps of:
(1) providing a substrate having a metal wiring; (2) electroplating
one of a nickel layer and a nickel-based alloy layer to the metal
wiring at a deposition rate of 15-30 .mu.m/hr to form a first layer
thereon, wherein the first layer is of a thickness of 0.5 .mu.m-5
.mu.m, and the nickel-based alloy layer has nickel content of at
least 50%; and (3) plating gold to the first layer to form a second
layer thereon, the second layer being of a thickness of 0.03
.mu.m-0.3 .mu.m, so as to form a nickel-based alloy barrier layer
of the wiring connection terminal by controlling the thickness of
the first and second layers and the deposition rate.
2. The method of claim 1, wherein the metal wiring is made of one
of a copper and a copper-based alloy.
3. The method of claim 1, wherein a main constituent element of the
nickel-based alloy is nickel, and a minor constituent element of
the nickel-based alloy is one of cobalt, molybdenum, tungsten, and
a combination thereof.
4. The method of claim 1, wherein the electroplating of one of the
nickel layer and the nickel-based alloy layer to the metal wiring
to form the first layer thereon is performed by one of brush
electroplating and tank electroplating.
5. The method of claim 1, wherein the first layer is formed by a
power selected from one of a direct current (DC), a reciprocating
electric power, and a pulsed electric power.
6. The method of claim 5, wherein the power is of a current density
of 0.1.about.15 Amp/dm.sup.2 (ASD).
7. The method of claim 1, further comprising (4) soldering one of a
tin layer and a tin-based alloy layer to the second layer.
8. The method of claim 1, wherein the substrate of the metal wiring
is a connection terminal or a pin of one of a semiconductor
package, a printed circuit board, and an electrical connector.
Description
FIELD OF TECHNOLOGY
[0001] The present invention relates to wiring connection terminal
manufacturing methods, and more particularly, to a method of
electroplating nickel and the like to a metal wiring layer and thus
forming a multi-element alloy layer thereon to reduce the thickness
of a gold layer thereon.
BACKGROUND
[0002] According to the prior art, regarding an interposer
substrate or an integrated circuit substrate (IC substrate) for use
in semiconductor packaging, its wiring (usually made of copper or
copper alloy) connects a connection pad, a terminal, and a pin of
components with a view to maintaining a contact resistance value.
The connection terminal undergoes surface treatment, such as
electroless nickel/gold or electro nickel/gold, so as to form a
barrier layer, which is applicable to package-related connection
processes, such as soldering and wire bonding, to reduce solder
diffusion between solder bumps when tin copper alloy is involved.
Surface treatment of the connection pad, the terminal, and the pin
surface during the wiring connection processes are disclosed in the
prior art. US2008/0257742 A1 discloses a method of manufacturing a
printed circuit board for a chip scale package (CSP), including the
steps of performing surface treatment on the pads of a surface
mount device (SMD) and a printed circuit board wiring, and
performing electroless nickel immersion gold (ENIG) to form pads
for use with an electroless nickel/gold plated layer on a copper
wiring. Taiwan Patent I419275 is directed to a substrate with a
plurality of electrical contact pads and wirings and discloses a
method for forming a surface treatment-related layer on electrical
contact pads and subsequent processes.
[0003] Taiwan Patent I420753 discloses a terminal for use with an
electrical connector. But Taiwan Patent I420753 has a drawback,
that is, if a gold plated layer for use with a terminal contact
portion and a soldering portion of the electrical connector is
overly thin, there will be deterioration of the electrical
conduction, corrosion inhibition, and resistance to wear and tear
of a terminal of the electrical connector. If the gold plated layer
is too thick, the production cost of the electrical connector
terminal will increase. To avoid the aforesaid disadvantageous
situations, Taiwan Patent I420753 discloses that the soldering
portion gold layer is of a thickness of 0.05 .mu.m-0.15 .mu.m, and
the gold layer of the contact portion is of a thickness of at least
0.076 .mu.m. To achieve reduction of contact impedance, enhancement
of corrosion inhibition, and enhancement of slidability of the
electrical connector, the electrical connector terminal is plated
fully with nickel to prevent terminal oxidation and then the
nickel-plated electrical connector terminal is plated with gold to
enhance the corrosion inhibition and enhance the electrical
conductivity of the electrical connector terminal.
[0004] Application of electroless nickel/gold to the surface
treatment of a conventional wiring connection terminal of a printed
circuit board or a connector is confronted with the following
problems: [0005] 1. The electroless nickel/gold process is carried
out with an electrolyte at a temperature of 80.degree.
C.-90.degree. C. and thus is likely to compromise precise
components therein. Moreover, photoresists for use in defining
connection terminal points and wiring patterns fail to remain
intact when they come into contact with the extremely hot chemical
electrolyte and thus the photoresists are susceptible to
degradation, deformation, and detachment. [0006] 2. The gold layer
has a thickness of 0.05 .mu.m-0.5 .mu.m. Considering the high
prices of the raw materials for use in this process, the thickness
of the gold layer formed by the technique for performing the
aforesaid surface treatment is of vital importance. To address the
aforesaid concern, related improvements are being made, and
alternative solutions have been developed, namely electroless
nickel palladium gold plating. [0007] 3. As regards the application
of a conducting wire to a connection terminal, with its plugging
and unplugging being carried out repeatedly, considerations must be
given to related physical properties of the surface treatment layer
(such as the ENIG layer), that is, resistance to wear and tear.
[0008] The descriptions above and below are intended to illustrate
the techniques and means of fulfilling the objectives of the
present invention and the anticipated advantages thereof. The other
objectives and advantages of the present invention are also
described below.
SUMMARY
[0009] To overcome the aforesaid drawbacks of the prior art, the
present invention provides a method of manufacturing a nickel-based
alloy barrier layer of a wiring connection terminal to reduce the
thickness of a gold plated layer formed on the nickel alloy
electroplated layer and cut the manufacturing costs.
[0010] The method of the present invention is characterized in
that: an anti-oxidation layer is formed by means of electroplating,
using nickel or any other appropriate metal, to enhance resistance
to wear and tear and thus reduce the thickness of the gold plated
layer to 0.03 .mu.m. The method of the present invention is
applicable to the surface treatment of a wiring connection
terminal, such as a wiring connection pad and a pin, of a
semiconductor package or a printed circuit board, so as to provide
a barrier layer for the copper wiring, the copper-based alloy
wiring, and the connection terminal of the semiconductor package or
the printed circuit board.
[0011] With an electroplating process being cherished for its role
in surface quality modification, it involves treating an object as
a cathode, immersing the cathode in an electrolyte which contains
the ions of a metal intended to be electroplated to the cathode,
providing an appropriate anode opposite to the cathode, applying
direct current (DC) to both the cathode and the anode such that the
metal ions in the electrolyte are deposited on the surface of the
cathode. In doing so, the resultant plated layer is crystalline and
delicate, and its physical properties, appearance, and dimensions
are advantageously different from pre-electroplating ones so as to
add economic values to the object. Depending on what metal is
electroplated to the object, the electroplated layer serves a
decorative purpose (when the metal is one of the conventional noble
metals) and features enhanced surface hardness, enhanced resistance
to wear and tear, enhanced corrosion inhibition, and enhanced
electrical conductivity of the object. The other important factors
in the electroplating process include the color, hardness,
uniformity, coverage, thickness, and solderability of the
electroplated layer.
[0012] Electroless plating, also known as chemical or
auto-catalytic plating, involves either turning the surface of an
object into one capable of undergoing a catalytic reaction or
providing an object whose surface is inherently catalytic, and
reducing the metal ions of electrolyte to the metal. The advantages
of electroless plating include high uniformity of the plated layer,
uniform thickness of every part of the plated layer regardless of
the shape of the object, dispensing with any electroplating
apparatus, wide applications (such as glass, plastics, and
ceramics), and the plated layer has a smaller pore size than the
electroplated layer.
[0013] Before undergoing electroplating or chemical electroplating,
the material to be plated must undergo a series of pre-treatment
processes, including de-greasing (removing oils from surfaces),
rinsing (washing the surfaces with cold water or hot water to
remove stains or residuals of a de-greasing agent used in the above
de-greasing process), acid cleaning (removing scaling or oxidized
layers), activation (activating the surfaces of the object by an
acid to promote the adhesion of the plated layer), and beaching
(removing residuals of the acid). Unsatisfactory electroplating
pre-treatment compromises the binding force between the plated
layer and the object, thereby causing the plated layer to detach
from the object. The binding force between the plated layer and the
object will be strong, if the crystallites of the plated layer are
small and impurity-free. The other factors in the binding force
between the plated layer and the object include the constituents of
the electroplating bath and the current density. The crystallites
of the plated layer will be small in the event of a low
concentration of the electroplating bath and low current
density.
[0014] The present invention provides a method of manufacturing a
nickel-based alloy barrier layer of a wiring connection terminal,
including: providing a substrate having a metal wiring;
electroplating a nickel or a nickel-based alloy to the metal wiring
at a deposition rate of 15-30 .mu.m/hr to form a first layer
thereon, wherein the first layer is of a thickness of 0.5 .mu.m-5
.mu.m, and the nickel-based alloy layer has nickel content of at
least 50%; and plating a gold layer to the first layer to form
thereon a second layer of a thickness of 0.03 .mu.m-0.3 .mu.m. The
surface of the nickel-based alloy electroplated layer features a
crystalline-phase structure full of micro-protuberances, and the
thickness of the gold plated layer is reduced to 0.03 .mu.m.
[0015] In an embodiment of the present invention, the gold plated
layer is made of gold in the form of pure gold, gold cobalt alloy,
or gold nickel alloy, wherein tin or a tin-based alloy is soldered
to the gold plated layer.
[0016] The process of electroplating an alloy plated layer is
usually speeded up by carrying out the process at a high current
density and thus a high deposition rate. However, in the event of
an overly high current density, there is a lack of metal ions in
the vicinity of the cathode immersed in the electrolyte, and thus
the cathode produces hydrogen gas faster and thereby increases the
pH value of the electrolyte in the vicinity of the surface of the
plated layer. As a result, any alkaline salts or hydroxides
produced are likely to be adsorbed to the plated layer and thus
deposited thereon in a powder-like or spongy form, thereby
compromising the physical properties of the plated layer.
[0017] Furthermore, composite electroplating entails uniformly
distributing and depositing one or more solid particles insoluble
in a plating solution or a specific metallic alloy in the plating
solution on a substrate to form a compact flat plated layer,
wherein the secondary metal content of the plated layer equals at
least 1%, such that two or more metals undergo a co-plating process
also known as alloy deposition. The alloy deposition involves
performing co-deposition on two or more metals by chemical
electroplating, wherein co-deposition includes co-deposition of
non-metals. The alloy plated layer which results from the
co-deposition of two metal ions is known as a binary alloy plated
layer, and the alloy plated layer which results from the
co-deposition of three metal ions is known as a ternary alloy
plated layer. The main (i.e., the most numerous) constituent of the
nickel-based alloy of the present invention is nickel, but a minor
constituent element of the nickel-based alloy is cobalt,
molybdenum, tungsten, or a combination thereof, such that a binary
alloy, a ternary alloy, or a multi-element alloy can be
electroplated to the metal wiring. The commonest form of alloys is
a solid solution, which generally comes in two categories, namely a
substitutional solid solution and an interstitial solid solution.
In the substitutional solid solution, which consists of two
elements, solute atoms substitute for solvent atoms of the crystal
lattice in a manner that the crystalline structure of the solvent
atoms remains unchanged, but it is possible that the lattice gets
distorted just because of the presence of the solute atoms. The
aforesaid lattice distortion will be readily observable in the
event of a large difference in the atomic radius between the solute
and the solvent. The interstitial solid solution is characterized
in that: the solute atoms occupy the interstices between the
solvent atoms; and the solute differs from the solvent in terms of
atomic size.
[0018] In the event of a high tungsten content (say, higher than 43
wt %) in the nickel tungsten alloy, the nickel tungsten alloy will
be amorphous and thus will lack a translation cycle in the
arrangement of atoms, thereby being free of crystal-related
defects, say, dislocation, twin, and grain boundary. Nonetheless,
the amorphous nickel tungsten alloy has its own drawback, that is,
high internal stress, which will crack the amorphous nickel
tungsten alloy if the plated layer is thick, thereby reducing the
industrial applicability of the amorphous nickel tungsten alloy. On
the contrary, low internal stress and thus crack reduction is
manifested by a composite alloy plated layer which is produced by
the co-deposition of a metal and solid particles of high hardness.
Last but not least, variation of current density has a marked
effect on the composition of a plated layer formed by alloy
deposition.
BRIEF DESCRIPTION
[0019] FIG. 1 is a schematic view of a wiring connection terminal
barrier layer according to the embodiment of the present invention;
and
[0020] FIG. 2 is a flow chart of manufacturing a wiring connection
terminal barrier layer according to the embodiment of the present
invention.
DETAILED DESCRIPTION
[0021] In the embodiment of the present invention, dents or cracks
occur to the surface of a nickel tungsten alloy plated layer in
response to an increase in current density, because current density
is proportional to deposition rate. In case of an overly high
current density, consumed ions in the vicinity of the cathode will
not be replaced in time and thus the deposition rate decreases. As
mentioned before, the surface of the nickel tungsten electroplated
layer is coarse as a result of the overly high current density
during the electroplating process. On the contrary, when the
current density is not overly high, the resultant nickel tungsten
electroplated layer has a shiny surface and manifests high
compactness. Tungsten atoms occupy the lattice points of the nickel
lattice to form a face-centered cubic nickel lattice which comes in
the form of a substitutional solid solution, wherein tungsten
enhances the hardness of the nickel tungsten alloy. Tungsten
increases the binding force between the atoms in the plated layer,
decreases the porosity of the plated layer, increases the
compactness of the plated layer, and enhances the corrosion
inhibition of the plated layer.
[0022] In an embodiment of the present invention, the
electroplating of a nickel layer or a nickel-based alloy layer is
performed by brush electroplating or tank electroplating, wherein a
nickel tungsten alloy plated layer is produced by a power, such as
a direct current (DC), a reciprocating electric power, or a pulsed
electric power, and the power is of a current density of
0.1.about.15 Amp/dm.sup.2 (ASD).
[0023] Pulse electroplating is in wide use for performing the
surface treatment of an alloy plated layer. Alloys manufactured by
pulse electroplating and pulse reverse electroplating are different
from alloys manufactured by direct current (DC) electroplating in
terms of characteristics. Plated layers manufactured by pulse
electroplating manifest satisfactory electrical conductivity, low
impurity content, high hardness, and high corrosion inhibition.
When pulse electroplating enhances the electrical potential and
thus causes the operating electrodes to generate a large current,
the large current phenomenon of the operating electrodes results in
quick deposition of an alloy plated layer. On the contrary, the
large current generated in the course of manufacturing the plated
layer by the operating electrodes causes the operating electrodes
to generate a large amount of Joule heat, thereby charring the
alloy plated layer. The heat thus generated can be dissipated by a
vigorous blend, so that the plated layer is charred to a minimum
extent.
[0024] Referring to FIG. 1, there is shown a schematic view of a
wiring connection terminal and a barrier layer thereon according to
the embodiment of the present invention. A connection terminal
formed from a copper wiring 10 and adapted for use in semiconductor
packaging is provided. The copper wiring 10 is electroplated with a
nickel molybdenum tungsten ternary alloy layer 20 of a thickness of
0.5 .mu.m-5 .mu.m approximately. Then, the nickel molybdenum
tungsten ternary alloy layer 20 is plated with a gold layer 30 of a
thickness of 0.03 .mu.m-0.3 .mu.m. Finally, a tin ball 40 is
soldered to the gold layer 30, thereby finalizing the manufacturing
of the connection terminal barrier layer.
[0025] Referring to FIG. 2, there is shown a flow chart of a method
of forming a barrier layer of a wiring connection terminal
according to the embodiment of the present invention. The process
flow of the method comprises the steps of: providing a substrate
having a copper wiring (step 110); electroplating a nickel tungsten
binary alloy layer to a copper wiring (step 120) at a deposition
rate of 15-30 .mu.m/hr and with a 65% nickel content of the nickel
tungsten binary alloy; plating a gold layer to the nickel tungsten
binary alloy layer (step 130); and soldering tin to the gold layer
(step 140) to form the barrier layer of the wiring connection
terminal.
[0026] The embodiment of the present invention discloses
electroplating a nickel-based alloy to a copper (or copper alloy)
wiring so as to form a barrier layer on a connection terminal. The
main constituent element of the nickel-based alloy is nickel, and
the nickel content of the nickel-based alloy is higher than 50 wt.
%. The nickel-based alloy also contains cobalt (Co), tungsten (W),
or molybdenum (Mo), so as to form a binary alloy, a ternary alloy,
or a multi-element alloy. As compared to an electroless nickel/gold
(ENIG) plated layer, the surfaces of the electroplated and plated
layers of the present invention are advantageously characterized in
that: first, the surface of the nickel-based alloy electroplated
layer manifests a high degree of hardness of 500.about.600 HV,
whereas the surface of an electroless nickel/gold plated layer has
a hardness of 400.about.450 HV, thereby opening to a wider range of
process tolerance and materials applicable to an ensuing wire
bonding process; second, the nickel-based alloy plated layer
manifests a high degree of resistance to wear and tear, reduction
in the loss of the gold plated layer, and suitability for use in
plugging and unplugging a connection terminal repeatedly.
[0027] The present invention is disclosed above by preferred
embodiments. However, persons skilled in the art should understand
that the preferred embodiments are illustrative of the present
invention only, but should not be interpreted as restrictive of the
scope of the present invention. Hence, all equivalent modifications
and replacements made to the aforesaid embodiments should fall
within the scope of the present invention. Accordingly, the legal
protection for the present invention should be defined by the
appended claims.
* * * * *