U.S. patent application number 10/489064 was filed with the patent office on 2004-11-25 for electrode attachment to anode assembly.
Invention is credited to White, Tamara L.
Application Number | 20040231978 10/489064 |
Document ID | / |
Family ID | 33452517 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040231978 |
Kind Code |
A1 |
White, Tamara L |
November 25, 2004 |
Electrode attachment to anode assembly
Abstract
The invention relates to electroplating. In particular, the
invention relates to an improved anode for electroplating metals
onto substrates, and to a method of electroplating metals onto
substrates utilizing the anode. The anode has a solid metal
portion, and a metal electrode shaft having one or more barbs
projecting outwardly from a periphery of the shaft at one end of
the shaft. The barbs are fixed through the body extend a distance
therethrough.
Inventors: |
White, Tamara L; (Spokane,
WA) |
Correspondence
Address: |
Richard S Roberts
Roberts & Mercanti
P O Box 484
Princeton
NJ
08542-0484
US
|
Family ID: |
33452517 |
Appl. No.: |
10/489064 |
Filed: |
March 9, 2004 |
PCT Filed: |
September 19, 2001 |
PCT NO: |
PCT/US01/29172 |
Current U.S.
Class: |
204/280 ;
204/286.1; 204/288; 204/289; 204/292; 204/293; 29/825 |
Current CPC
Class: |
Y10T 29/49117 20150115;
C25B 9/65 20210101; C25D 17/10 20130101; C25C 7/02 20130101 |
Class at
Publication: |
204/280 ;
204/286.1; 204/288; 204/289; 204/292; 204/293; 029/825 |
International
Class: |
C25B 011/00; C25B
011/04; C25C 007/02; C25D 017/10 |
Claims
What is claimed is:
1. An anode comprising a shaped, substantially solid, metal body; a
metal electrode shaft having one or more barbs projecting outwardly
from a periphery of the shaft at one end of the shaft; the one or
more barbs being fixed within the body.
2. The anode of claim 1 wherein the shaft comprises a plurality of
barbs which are fixed within the body.
3. The anode of claim 1 wherein the one or more barbs are fixed
within the body by casting the body around the one or more
barbs.
4. The anode of claim 1 wherein the portion of the shaft outside of
the body is absent of barbs.
5. The anode of claim 1 wherein the body comprises tin, lead,
copper, aluminum, silver, bismuth, indium, antimony, tin-lead
alloy, tin-silver-copper alloy, silver-bismuth alloy, or
combinations thereof.
6. The anode of claim 1 wherein the body comprises from about 0% to
about 100% tin and from about 0% to about 100% lead.
7. The anode of claim 1 wherein the body comprises from about 5% to
about 63% tin and from about 37% to about 95% lead.
8. The anode of claim 1 wherein the shaft and one or more barbs
comprise titanium, copper, silver, platinum, tantalum, stainless
steel, gold or combinations thereof.
9. The anode of claim 1 wherein the shaft and one or more barbs
comprise nickel plated titanium.
10. The anode of claim 1 comprising a plurality of barbs projecting
outwardly from a periphery of the shaft at one end of the shaft,
said barbs being fixed within the body and wherein the body
comprises from about 5% to about 63% tin and from about 37% to
about 95% lead; and wherein the shaft and one or more barbs
comprise nickel plated titanium.
11. The anode of claim 1 wherein the body has a solid rectangular,
square, circular, oval, trapezoidal, triangular, ring or irregular
shape, and either with or without apertures therein.
12. An anode comprising a metal electrode shaft and a shaped,
substantially solid metal body cast around one end of the
shaft.
13. The anode of claim 12 comprising a metal electrode shaft having
one or more barbs projecting outwardly from a periphery of the
shaft at one end of the shaft, a substantially solid, metal body
cast around the barbs.
14. A method for producing an anode which comprises: a) providing a
metal electrode shaft having one or more barbs projecting outwardly
from a periphery of the shaft at one end of the shaft; b) providing
a shaped, substantially solid, metal body; c) fixing the one or
more barbs through the metal body.
15. The method of claim 14 comprising a plurality of barbs
projecting outwardly from a periphery of the shaft at one end of
the shaft, said barbs being fixed within the body and wherein the
body comprises from about 5% to about 63% tin and from about 37% to
about 95% lead; and wherein the shaft and one or more barbs
comprise nickel plated titanium.
16. A method for producing an anode which comprises: a) providing a
metal electrode shaft; b) casting a molten metal around one end of
the shaft and cooling the molten metal to thus form an anode
comprising a solid metal body enveloping said end of the shaft; and
c) subsequently removing the anode from the mold.
17. The method of claim 16 which comprises: a) providing a metal
electrode shaft; b) placing one end of the electrode into a
fixture; c) placing the fixture and the end of the electrode within
the fixture into a casting mold; d) casting a molten metal into the
casting mold and cooling the molten metal to thus form an anode
comprising a solid metal body enveloping said end of the shaft; and
f) subsequently removing the anode from the mold.
18. The method of claim 16 which comprises: a) providing a metal
electrode shaft; b) applying a flux composition to one end of the
shaft; c) placing the flux applied end of the electrode into a
fixture; d) placing the fixture and the flux applied end of the
electrode into a casting mold; e) casting a molten metal into the
casting mold and cooling the molten metal to thus form an anode
comprising a solid metal body enveloping the flux applied end of
the shaft; and f) subsequently removing the anode from the
mold.
19. The method of claim 16 wherein the flux applied end of the
shaft has one or more barbs projecting outwardly from a periphery
of the shaft at one end of the shaft, which one or more barbs are
fixed within the body.
20. The method of claim 16 comprising a plurality of barbs
projecting outwardly from a periphery of the shaft at one end of
the shaft, said barbs being fixed within the body and wherein the
body comprises from about 5% to about 63% tin and from about 37% to
about 95% lead; and wherein the shaft and one or more barbs
comprise nickel plated titanium.
21. The anode produced by the method of claim 16.
22. The anode produced by the method of claim 17.
23. The anode produced by the method of claim 18.
24. The anode produced by the method of claim 19.
25. The anode produced by the method of claim 20.
26. An electrolytic arrangement which comprises: a) a vessel
containing an electrically conductive fluid; and b) the anode of
claim 1 in the electrically conductive fluid, which anode is
connected to an electric circuit; and c) a cathode in the
electrically conductive fluid, which cathode is connected to an
electric circuit.
27. The electrolytic arrangement of claim 26 wherein the
electrically conductive fluid comprises water and at least one
ionic species.
28. The electrolytic arrangement of claim 26 wherein the
electrically conductive fluid comprises an ionic species derived
from the anode material.
29. The electrolytic arrangement of claim 26 wherein the cathode
comprises a material selected from the group consisting of
semiconductors, ceramics, silicon and combinations thereof.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to electroplating. In particular, the
invention relates to an anode for electroplating metals onto
substrates, and to a method of electroplating metals onto
substrates utilizing the anode.
[0003] 2. Description of the Related Art
[0004] In the production of microelectronic devices, a metal may be
plated onto a substrate for a variety of purposes. Typically, metal
is plated onto a substrate in a cell or reservoir that holds a
plating solution which is a metal ion containing bath for plating
the metal onto the substrate surface.
[0005] In the manufacture of semiconductor chips, printed circuit
boards and other circuit components and devices, the conductors of
the devices are electroplated with a solder material comprising tin
and/or lead to improve solderability of the device. The step of
electroplating is typically performed while several semiconductor
devices are mounted on a lead frame suspended by hooks on a cathode
rack placed in an electroplating bath or before devices have been
singulated (i.e, in wafer form). The bath contains an anode which
conducts an electrical current that passes to the cathode and lead
frames to deposit metal on the leads of the devices. After
electroplating, the lead frames are severed and the individual
semiconductor chips are separated.
[0006] The uniformity of the deposited metal is a function of the
current density, the purity of the plating bath and the purity of
the anode. Composition of plating baths and conditions within the
plating bath must be carefully controlled to produce deposition of
a desired quality of desired metal(s) on a substrate. Plating rate,
uniformity, and deposit quality may be affected by a variety of
factors. For example, among the parameters that may affect rate,
uniformity, and deposit quality of plating are concentration of
chemicals in the plating bath, nature and distribution of
electrical contacts and voltage within the plating system. The
physical design of an electroplating system may affect the
conditions within the system and the plating carried out in the
system.
[0007] The anode in the plating bath conducts the current into the
plating solution and produces an electric field between the anode
and the cathode workpiece. During routine plating operations, as
electroplating proceeds, the anode is consumed, and any anode
impurities may generate particles called anode fines. As the amount
of anode fines increases, they form a sludge. As electroplating
continues and the anode continues to be consumed, the anode sludge
continues to thicken. A number of problems are associated with
anode sludge. For example, the anode sludge may cause a voltage
drop in the electroplating cell because ions migrate through the
sludge to the plating solution and the plating voltage may rise. A
rising plating voltage may effect the deposit uniformity. The
effects of the anode sludge depend on cell design and plating
parameters, among other factors. Additionally, the anode sludge can
be incorporated into the structure of the plated metal and
contaminate a workpiece being plated.
[0008] As a result of anode sludge formation and the degradation in
plating, such as degraded plating uniformity that may result, anode
maintenance typically is required in electroplating systems. Anode
maintenance may include removal of the anode from the cell, removal
of excess sludge by scraping, etching in a suitable solution to
remove remaining sludge and then be subjecting to one or more
lengthy anode reconditioning steps. The reconditioning steps may
last for about 5 to about 16 hours. Impurities may also form gas
bubbles, such as air bubbles, which may interfere with electric
field lines between the anode and the wafer or workpiece.
Interference with the electrical field within the electroplating
system may result in overpotential. The overpotential may cause the
plating voltage to rise in an erratic manner until the power supply
reaches its set compliance voltage and shuts off. Disturbance in
the electrical operation caused by gas bubbles may also effect the
uniformity of electrodeposits. The thickness of plated films tends
to be thinner in the region adjacent to the bubbles. A
concentration gradient of plating ions may develop in the anode
assembly. The concentration of plating ions may be high close to
the anode and low in the vicinity of the wafer or workpiece being
plated. The concentration gradient may result in a concentration
polarization. The polarization may also cause the plating voltage
to rise. While the concentration gradient may affect not only
uniformity of wafers plated under such conditions, the
concentration gradient may cause plating voltage to rise and reach
its compliance value, again resulting in shut down of the plating
cell. The air or gas bubbles may not only cause undesirable cell
polarization, but may also distort the uniformity of the plated
film. This is because the electric field has to bend around the air
or gas bubbles before the field arrives at the workpiece. This
causes distortion from the preferred parallel field lines and
produces undesirable metal deposit uniformly on the workpiece.
[0009] To make plating more uniform across the workpiece, it is
necessary to produce a plating bath which is substantially free of
extraneous impurities. The improved solution purity helps to
eliminate the concentration gradient, concentration polarization,
and improving plating and the overall operation of the plating
cell. The present invention also makes it possible to dramatically
improve plating cell productivities. One source of plating bath
impurities is the anode assembly. Typically the anode comprises the
anode structure itself plus a metal handle which is used to
introduce and maintain the anode in the plating solution.
Typically, the handle is soldered to the anode. A joint is
typically formed using a solder composition, however, the solder
composition itself tends to introduce metal impurities into the
plating bath. It would be desirable to fixedly attach an anode to a
handle without the need for a solder joint. The present invention
provides an improved anode and holder. Among the features of an
anode and holder according to the present invention are at least
one barbed end to the holder. A mechanical joint may allow for
preferential corrosion and intermittent or inconsistent electrical
contact. The barbed end is fixed through a hole in the anode, thus
eliminating or reducing the need for a solder composition
therebetween.
[0010] The present invention also includes methods of
electroplating a metal on a substrate. A substrate may be arranged
in the electroplating composition and current supplied to the
substrate from the improved anode, resulting in the plating of the
metal from a purer plating solution onto the substrate.
SUMMARY OF THE INVENTION
[0011] The invention provides an anode comprising a shaped,
substantially solid, metal body; a metal electrode shaft having one
or more barbs projecting outwardly from a periphery of the shaft at
one end of the shaft; the one or more barbs being fixed within the
body.
[0012] The invention also provides an anode comprising a metal
electrode shaft and a shaped, substantially solid metal body cast
around one end of the shaft.
[0013] The invention further provides a method for producing an
anode which comprises:
[0014] a) providing a metal electrode shaft having one or more
barbs projecting outwardly from a periphery of the shaft at one end
of the shaft;
[0015] b) providing a shaped, substantially solid, metal body;
[0016] c) fixing the one or more barbs through the side wall of the
body.
[0017] The invention still further provides a method for producing
an anode which comprises:
[0018] a) providing a metal electrode shaft;
[0019] b) casting a molten metal around one end of the shaft and
cooling the molten metal to thus form an anode comprising a solid
metal body enveloping said end of the shaft; and
[0020] c) subsequently removing the anode from the mold.
[0021] The invention also provides an electrolytic arrangement
which comprises:
[0022] a) a vessel containing an electrically conductive fluid;
and
[0023] b) the anode of claim 1 in the electrically conductive
fluid, which anode is connected to an electric circuit; and
[0024] c) a cathode in the electrically conductive fluid, which
cathode is connected to an electric circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 shows metal electrode shaft having barbs projecting
outwardly from a periphery of the shaft at one end of the
shaft.
[0026] FIG. 2 shows an anode according to the invention having a
metal body and the metal electrode shaft with the barb end fixed
through the side wall of the metal body.
[0027] FIG. 3 is a schematic representation of the anode and a
workpiece wafer cathode suspended within an electroplating
bath.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] FIG. 2 shows an anode 2 according to the invention. It has a
metal body 4 and a metal electrode shaft 6 fixed through a side
wall 8 of the metal body 4. It has a top edge 8, an outside wall
surface 12, and a lower edge 16. The upper edge 8 and the lower
edge 16 are preferably in parallel planes. Although the anode
portion 4 has been shown to have a disc shape, it may have any
shape or cross section suitable for forming an anode. Such include
those which are rectangular, square, cubic, circular, oval,
trapezoidal, wedged, tubular, triangular, ring shaped, irregular
shaped, spherical, cylinders among others. They may be solids or
have apertures.
[0029] As better seen in FIG. 1, the metal electrode 6 comprises a
shaft 18 having one or more barbs 20 projecting radially outwardly
from a periphery of the shaft at one end of the shaft. In the
construction of the anode 2, the barbs 20 are fixed through the top
edge 8 of the metal body 4 and extending a distance through the top
edge 8 toward the lower edge 16 such that the barbs are positioned
in the body 4. In the preferred embodiment, all of the barbs are
within the body of the anode. In one embodiment of the invention,
the shaft portion within the body does not have any barbs.
[0030] The metal body comprises a metal or metal alloy capable of
conducting electricity and dissociating into ionic species under
electrolytic plating conditions. Non-exclusive examples of such
metals include tin, lead, copper, aluminum, silver, bismuth,
indium, antimony, or combinations thereof. Preferred body metals
non-exclusively include tin, tin-lead alloys, tin-silver-copper
alloys, silver-bismuth alloys, and combinations thereof.
[0031] In a more preferred embodiment, the metal body comprises
from about 0% to about 100% tin and from about 0% to about 100%
lead and still more preferably an alloy which comprises from about
5% to about 63% tin and from about 37% to about 95% lead.
[0032] The shaft 18 and barbs 20 preferably comprise a metal or
metal alloy capable of conducting electricity but not significantly
dissociating into ionic species under the electrolytic plating
conditions which cause the metal body to dissociate into ionic
species. Non-exclusive examples of such metals include titanium,
copper, silver, platinum, tantalum, stainless steel, gold and
combinations thereof. More preferably, the shaft and one or more
barbs comprise nickel plated titanium.
[0033] The metal electrode 6 may be formed by machining a shaft 18
with a suitable tool, such as a lathe to provide one or more barbs
20 projecting radially outwardly from a periphery of the shaft at
one end of the shaft. Any suitable method of producing such a shaft
with barbs, such as casting, may be used.
[0034] The anode may be produced by providing the metal electrode
shaft having one or more barbs projecting outwardly from a
periphery of the shaft at one end of the shaft; providing a metal
body and then fixing the one or more barbs through the metal body.
One way of assembling the anode may be by drilling a hole into the
metal body and then pressing the barbed end into the body. However,
the preferred method is by casting the body metal around the barbed
end of the shaft.
[0035] One may produce the anode by providing the metal electrode
shaft having one or more barbs; applying a flux composition to the
one or more barbs; placing the barbs of the electrode into a
fixture; placing the fixture and the electrode into a casting mold;
casting a molten metal into the casting mold and cooling the molten
metal to thus form the anode with subsequent removing of the anode
from the mold. Such casting methods are well known to the skilled
artisan. In this embodiment it is preferred that the selection of
the metal for the shaft and body is such that they are compatible
for casting one around the other for a true metallurgical bond.
Alternatively the shaft may have its end plated with a metal which
easily wets both the shaft and the solid body metals during
casting.
[0036] In another aspect of the invention, there is also provided a
method of electroplating a workpiece. A cathode workpiece and the
anode are immersed in an electroplating bath, and current flow from
the anode to the cathode deposits the anode material on the
workpiece.
[0037] FIG. 3 shows an electrolytic arrangement which comprises a
vessel 22 containing an electrically conductive fluid 24. The anode
2 is disposed in the electrically conductive fluid. The anode is
connected to an electric circuit via shaft 6. A cathode workpiece
26 is also disposed in the electrically conductive fluid 24. The
cathode 26 is connected to an electric circuit via a suitable
support 28.
[0038] The cathode workpiece 26 is conveniently a wafer, on which
materials, such as at least one metal or and or at least one alloy
are to be electroplated. It may conveniently comprise a material
such as semiconductors, ceramics, silicon and combinations thereof.
Any cathode which can be plated using prior art baths may be coated
in accordance with the present invention. For example, good
deposits may also be produced upon articles of copper, nickel,
iron, steel, etc. The best results are obtainable with these baths
if relatively pure anodes of the metals are employed, and either
tin/lead alloy anodes or separate tin anodes and lead anodes may be
used. It should be noted that the composition of the anode has a
significant effect upon the composition of the deposit, and that it
is generally desirable to employ an anode having a proportion of
metals approximating that desired in the plated alloy. The
composition of the deposit may also be controlled by use of
separate anodes of tin and lead, to which the current may be
proportioned appropriately.
[0039] The electrically conductive fluid may be comprised of water
and at least one ionic species, preferably an ionic species derived
from the dissociation of the anode material. Typical plating baths
are known from U.S. Pat. Nos. 4,118,289 and 4,440,608.
Electrodeposited tin/lead alloys of different compositions are
especially valuable in a number of applications including the
provision of bearing contact surfaces for which a 7/93 tin/lead
alloy is typically used and the provision of surfaces for soldering
such as on printed circuit boards and the like for which alloys of
60/40 tin/lead are desired. Suitable aqueous acid plating baths for
the electrodeposition of tin/lead alloys comprise about 5 to 80,
and preferably about 45 to 65 grams per liter of stannous ion;
about 85 to 10, and preferably about 35 to 15 grams per liter of
lead ion; and at least about 100, and preferably at least about
150, grams per liter of radical selected from the group consisting
of fluoborate, fluosilicate, and sulfamates. When the bath utilizes
the fluoborate radical, as is preferred, it desirably also contains
at least about 50 grams per liter of free fluoboric acid and at
least about 10 grams per liter of free boric acid. Preferably, the
amount of stannous ion will exceed the lead ion and will be in the
range of about 45 to 65 grams per liter, with the amount of lead
ranging from about 35 to 15 grams per liter. A most desirable
feature of the invention is that it enables the formation of
electrodeposits of solder having a composition at or near the
eutectic point for tin/lead alloys, and the most desirable range of
the ions in the bath therefore is about 53 to 57 grams of stannous
ion per liter and about 27 to 23 grams of lead ion per liter. The
fluoborate baths are preferred and, to be satisfactory, must
contain at least about 100 grams per liter of the fluoborate
radical; preferably the amount of the radical will not be less than
about 150 grams per liter. Such a bath should contain at least
about 50 grams per liter of fluoboric acid and at least about 10
grams per liter of boric acid. The bath preferably has a pH of less
than about 3 and desirably below about 1. It is common practice in
tin-lead plating to use refined peptone as an additive.
[0040] The baths are operable over a fairly wide range of cathode
current density, depending upon other factors such as temperature,
agitation, etc. More specifically, the operable range is about 10
to 200 amperes per square foot and preferably about 20 to 120
amperes per square foot, with a narrower range of 25 to 35 amperes
per square foot being most desirable for the production of deposits
having a substantially eutectic composition. The plating efficiency
is generally quite high and will range up to about 95 percent under
optimum conditions, based upon the theoretical rate of deposition,
and bright deposits of excellent quality can best be produced at a
bath efficiency in excess of 70 percent. The applied voltage should
be about 0.2 to 5 volts and preferably 0.5 to 4 volts.
[0041] The baths should be operated at a temperature of at least
about 50.degree. F., and preferably from about 60 to 90.degree. F.
Operation below about 50.degree. F. tends to be inefficient and to
produce undesirable deposits, whereas temperatures higher than
about 90.degree. F. tend to cause oxidation of the tin ion to the
stannic state and to produce dull, rough and generally unacceptable
deposits; furthermore, the bath is consumed at an excessive rate at
temperatures that are unduly high.
[0042] Some agitation is desirable to obtain high quality, uniform
deposits and to avoid development of sludge or film, and plating at
high current densities and temperatures may be improved by more
intense agitation. However, excessively high rates of agitation are
undesirable because they can cause excessive consumption of the
bath and impose limitations upon the current densities at which
brightness is achieved. Not only is agitation of the bath itself
desirable but agitation of the cathode may be beneficial in
obtaining a uniform plate and enabling extension of the range of
satisfactory current density.
[0043] The process is adapted to still plating and barrel plating
apparatus with equal efficacy, and may be used for strip, wire and
connector strip. Use of the bath and process is particularly
significant with respect to connector strip, printed circuit
boards, and the like because of the excellent solderability of the
plate produced. Filtration of the bath is not essential but will
normally be beneficial when contamination of the bath is
encountered due to air-borne impurities and carryover from other
finishing operations; preferably, it will be effected on a
continuous basis. Various filtering media may be utilized including
fabrics, such as a polypropylene, and other conventional filtering
materials.
[0044] The depletion of the various components of the bath is best
corrected by analysis for the several components on a periodic
basis which can be established for a given facility. To determine
the amounts of stannous salt required, an iodine titration
technique may be used; the lead content may be checked by
precipitation with dilute sulfuric acid. Tin-lead alloys are
electrolytically deposited in thicknesses typically ranging from
about 0.2 to about 2 mils when used in printed and other circuitry
to provide a solderable finish, a contact material, or an etchant
resistant.
[0045] Although the present invention has general applicability in
the field of manufacturing and assembly of integrated circuits, and
specifically in the electroplating of the solder bumps or under
bump metallurgy for flip chip electrical interconnect, it is to be
understood that the present invention is also applicable for use
with any electroplating apparatus and process in which achieving a
uniform plating thickness is desired. Although the anode as been
herein described has a anode, it also find use as any electrode
such as a cathode.
[0046] While the present invention has been particularly shown and
described with reference to preferred embodiments, it will be
readily appreciated by those of ordinary skill in the art that
various changes and modifications may be made without departing
from the spirit and scope of the invention. It is intended that the
claims be to interpreted to cover the disclosed embodiment, those
alternatives which have been discussed above and all equivalents
thereto.
* * * * *