Note: Descriptions are shown in the official language in which they were submitted.
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Specification
Plating Apparatus, Plating Method and Manufacturing Methodfor
Semiconductor Device
Technical Field of the Invention
The present invention relates to a plating apparatus,
a plating method and a manufacturing method for a semiconductor
device wherein at least two plating film layers are formed on
leads and a lead frame having a main material of Cu or an Fe-Ni
alloy.
Prior Art
A lead member wherein the surface of a conductive material
made of , for example, simple Cu, a Cu alloy or an Fe-Ni alloy,
is covered with a plating layer made of, for example, simple
Sn or an Sn alloy, has excellent conductance and mechanical
strength provided by simple Cu or a Cu alloy. In addition, such
a lead member is a high performance conductor that has bath
resistance to corrosion as well as excellent solderability
provided by simple Sn or an Sn alloy. Therefore, such members
are widely used in the field of electrical and electronic
apparatuses , such as in a variety of terminals , connectors and
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leads as well as in the field of power cables.
In addition, in the case that a semiconductor chip is
mounted on a circuit substrate, hot-dip plating or electrical
plating is carried out on outer lead parts of the semiconductor
chip using an Sn alloy and, thereby, solderability of the outer
lead parts is increased. A representative example of such an
Sn alloy is solder (Sn-Pb alloy) which has excellent
solderability and resistance to corrosion and, therefore, is
widely utilized in industrial plating of electrical and
electronic industrial members such as connectors and lead
frames .
Fig. 7 is a cross sectional view showing the basic
configuration of a lead member, being the A-A cross section
of the semiconductor lead frame shown in Fig. 6. A conductive
material 21 is formed of, for example, Cu, a Cu-based alloy
having Cu as a primary component or an Fe-Ni-based alloy having
Fe-Ni as a primary component. Then, two plating film layers
made of differing metal materials are placed on the surface
of such a conductive material 21. A first plating film 22 made
of Sn and a second plating film 23 made of Sn-Bi, for example,
are formed, in this order. Here, it is known that when the
thickness of first plating film 22 is denoted as tl and the
thickness of second plating film 3 is denoted as tz, it is
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preferable for tl to be set at approximately 3 ~Zm to 15 um,
for t2 to be set at approximately 1 um to 5 um and for t2/tl
to be set at approximately 0.1 to 0.5 because performance in
the lead member can be improved from the point of view of cost,
solderability and resistance to heat, and there are excellent
properties concerning junction strength with solder as well
as welding strength of the welded portion with an aluminum wire ,
or the like.
Fig. 8 is a layout of the entirety of an automatic plating
apparatus. First, an organic pollutant, such as fats and oils,
that hinders the adhesion and solderability of solder plating
film on the surface of conductive material 21 is removed in
an alkaline electrolytic washing bath 1. Next, the conductive
material is washed in a water washing bath 2 and, after that,
a chemical etching process (essentially a process utilizing
an oxidation-reduction reaction) is carried out in a chemical
etching bath 3 so that the surface of conductive material 21 ,
which has become uneven due to the existence of grain interfaces ,
inclusion, or the like, is made uniform.
Next, the conductive material is washed in a water washing
bath 4 and, after that, an oxide film that has become attached
to the conductive material in water washing bath 4 is removed
in an acid activation bath 5. Next, the conductive material
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is washed in a water washing bath 6 and, after that, plating
is carried out in a solder plating apparatus 7 . Since the solder
plating liquid is strongly acidic, the surface after plating
becomes acidic. The color of the film changes on such a surface
astime elapses and the solderability deteriorates. Therefore,
the acid that remains on the plating surface is neutralized
and the attached organic substance is removed in a water washing
bath 8 and in a neutralization process bath 9. After that, the
conductive material is washed in a water washing bath 10 and
in a hot water washing bath 11 and the plated conductive material
21 is dried in a drying apparatus 12.
Fig. 9 is a cross sectional view in the B-B direction
of chemical etching bath 3 of the plating apparatus of which
the entirety is shown in Fig. 8.
The reaction in this chemical etching bath 3 is as described
above. Here, the mechanism of this plating apparatus is described.
Lateral transfer-type pushers 13 and a conveyance rail 14 are
both moveable in the upward and downward directions in this
plating apparatus . Then, the upper limit positions and the lower
limit positions of these moveable ranges are determined so that
the above repeatedly move between those limit positions . Hooks
15 for hanging are hung from conveyance rail 14 at appropriate
intervals in accordance with the purpose of work. The intervals
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are usually set at intervals corresponding to the distance
between the centers of adjacent baths. Then, auxiliary plating
racks 16 for hanging conductive materials 21 to be plated are
hung from these hooks 15 for hanging and are set in this plating
apparatus. Next,lateraltransfer-type pushersl3are described.
The distance between lateral transfer-type pushers 13 is
basically the same as the distance between the centers of
adjacent baths. Then, these lateral transfer-type pushers 13
are installed in single arms so that, when a hook 15 for hanging
is transferred by one span in the direction of work, a pusher
is returnedby the same amount . Then, these lateral transfer-type
pushers 13 are transferred by one span at the upper limit
positions and are returned by the same amount at the lower limit
positions . In addition, conveyance rail 14 moves in the upward
and downward directions and does not move in the direction of
progress . These actions are repeated and, thereby, this plating
apparatus functions.
The above described plating apparatus has one pre-plating
process line and one solder plating line. There are cases wherein,
for example, a plating film of Sn is formed as first plating
film 22 and a plating film of Sn-Bi is formed as second plating
film 23 on conductive material 21, and wherein a plating film
of Sn is formed as first plating film 22 and a plating film
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of Sn-Ag is formed as second plating film 23 on conductive
material 21. In both cases the same Sn plating liquid can be
utilized for the formation of the first plating film while
different plating liquids must be utilized for the formation
of the second plating film. Therefore, after formation of the
first plating film on conductive material 21 is completed, the
plating apparatus is once stopped and the plating liquid in
the bath is switched to the plating liquid for the second plating
film and, then, the plating film is formed on the next conductive
material 21.
In addition, according to the above described solder
platingmethod, the plating bath in the plating line has a plating
liquid for forming a plating film on conductive material 21
and an electrode for supplying current to conductive material
21 in the plating apparatus used in this method. Here, the
electrode installed within this plating bath is used primarily
as an anode in electrical plating. Then, conductive material
21 is immersed in this plating bath and, at this time, conductive
material 21 works as a cathode and, thereby, a plating film
is formed. At this time, the plating work is carried out by
placing conductive material 21 on a rectangular auxiliary
plating rack 16 formed of two main pillars . There are conductive
materials 21 having, for example, different package sizes,
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different package designs and different properties. Then,
plating work is carried out by applying a strong current density
to the plating liquid when a thick plating film is formed on
such conductive materials 21. A plating film having a variety
of thicknesses is formed primarily by adjusting the current
density in such a manner.
In addition, it is known that in electrical plating, the
closer to the edge the position of application of current in
conductive material 21 becomes , the greater the current density
becomes and the thicker the formedplating film becomes . Moreover,
the upper limit of the range of current density that is
appropriate for the plating liquid is referred to as the maximum
current density. By utilizing this maximum current density,
high speed plating can be achieved and plating time can be reduced .
However, in the case that this maximum current density is
exceeded, the plating surface becomes fogged and, furthermore,
burn deposits or powder deposits are formed. Moreover, it is
also known that when the limit current density is reached, no
plating film can be formed.
Problem to be Solved by the Invention
As for the first problem, the above described solder
plating apparatus has one plating pre-processing line and one
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solder plating line. Therefore, in the case that a plurality
of combined plating films is formed on conductive material 21,
a problem arises wherein work cannot be sequentially carried
out when combinations of plating films are switched. In other
words, this plating apparatus allows sequential formation of
plating films wherein the same plating films are combined by
sequentially immersing conductive material 21 in the prepared
plating liquid. However, a plurality of combined plating films
cannot be sequentially formed on conductive material 21 in
accordance with usage applications wherein the plated
conductive material 21 is utilized. That is to say, there is
a problem wherein excessive time and effort must be spent to
replace the plating liquid in the solder plating line.
In addition to the above description, a great effort must
be made in order to manage the solder plating line. There is
a case wherein one type of plating liquid is utilized in one
plating bath and, after that, another type of plating liquid
having different plating liquid components is utilized. At this
time the liquid components of the latter plating liquid are
changed, unless the formerplating liquid is completely removed.
In addition, in the case that the utilized plating liquid
components differ, the anodes utilized in the plating bath also
differ and the anodes must be changed. That is to say, there
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is a problem wherein great effort must be made concerning
maintenance, such as management of the plating liquid and
management of the plating bath.
As for the second problem, according to the above described
solder plating method, the plating bath in the plating line
has a plating liquid for forming a plating film on conductive
material 21 and an electrode for supplying current to conductive
material 21 in the plating apparatus used in the method. Then,
a plating film is formed using such a plating apparatus . However,
a variety of types of conductive material 21 exist according
to the size of the surface area or design . Therefore, all portions
of the surface of conductive material 21 , which work as a cathode ,
do not necessarily allow a uniform current to pass through when
current f lows from the anode to the cathode . In other words ,
the respective portions of conductive material 21 are not
necessarily located at equal distances from the anode. Then,
plating work is carried out by placing conductive material 21
on rectangular auxiliary plating rack 16 formed of two main
pillars in this plating apparatus. Therefore, conductive
material 21 has one surface to receive current density from
the anode and, therefore, the closer to the edge of conductive
material 21 the portion on which the current dens ity concentrates
is located, the greater the current densitybecomes concentrated
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and the thicker the plating film formed so that a thinner plating
film is formed on the center portions of conductive material
21 , in comparison with the edge . In addition, there is a problem
wherein, when a plating film is formed on conductive material
21 , plating is carried out on portions having a high current
density so that optimization and uniformity of the plating film
thickness and of plating film composition distribution are not
obtained.
Means for Solving the Problem
The present invention is provided in view of the above
described problems with the prior art and a plating apparatus
of the present invention is a plating apparatus having a plating
pre-processing line and a plating line, characterized in that
the above described plating line has a plurality of plating
baths and a plating liquid containment bath is provided in a
desired plating bath from among the above described plating
baths.
The plating apparatus of the present invention preferably
has a plurality of plating baths underneath the conveyance rail
in the plating line. Then, plating liquid containment baths
are installed corresponding to these plating baths and are
provided with a function of making plating liquid shift between
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two baths . Alternately, a plurality of plating baths and plating
liquid containment baths corresponding to the respective
plating baths are installed underneath the conveyance rail and
the function of making a plating liquid shift between two baths
is provided. Thereby, a plurality of combined plating films
of a single layer, or of two or more layers, can be sequentially
formed on a conductive material using one conveyance rail.
In addition, the present invention is provided in view
of the above described problem with the prior art and a plating
method of the present invention is a plating method for forming
a plating film by placing an electrode for supplying current
and a conductive material on which the plating film is formed
within a plating bath containing a desired plating liquid and
by applying electricity, characterized in that the current
density flowing from the above described electrode is set within
the optimal range of current density of the above described
plating liquid and the above described conductive material is
placed on an auxiliary plating rack and, after that, the plating
film is formed on the above described plating material.
According to the plating method of the present invention,
preferably the above described conductive material and the above
described auxiliary plating rack are integrally utilized as
the other electrode of the pair and the above described auxiliary
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plating rack is positionedbetween the above described electrode
and the above described conductivematerial so that the thickness
of the plating film and the distribution of the composition
of the plating film can be adjusted.
In addition, a plating apparatus of the present invention,
which is provided in view of the above described problem with
the prior art, is a plating apparatus for forming a plating
film from a desired plating liquid, an electrode for supplying
current and a conductive material placed on an auxiliary plating
rack within a plating bath, characterized in that the plating
film is formed by installing the above described conductive
material within the above described auxiliary plating rack
formed of members of a conductive material.
The auxiliary plating rack is preferably a rectangular
parallelepiped formed of four main pillars, and the above
described conductive material is placed within the above
described auxiliary plating rack, and the plating film is formed
in the plating apparatus of the present invention. Thereby,
uniform current density can be applied to all of the portions
of the above described conductive material , even when the surface
area, the design, or the like, of the above described conductive
material differ.
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Preferred Embodiments of the Invention
First, a plating apparatus according to the first
embodiment, which is a plating apparatus having a plating
pre-processing line and a plating line characterized by having
plating baths for forming a plating film layer of a plurality
of patterns in the plating line and by providing plating liquid
containing baths in the respective plating baths is described
in reference to Figs. 1, 2 and 7.
Fig. 1 is a layout schematically showing the function
of the solder plating line for implementing the plating apparatus
of the present invention. A pre-dip bath 43, a first plating
bath 44, a second plating bath 45, a third plating bath 46 and
a water washing bath 47 are installed underneath a conveyor
rail 42 in this solder plating line. Then, conductive materials
21 are transferred in unison by the same pitch by means of lateral
transfer-type pushers 41 and plating films are formed on
conductive materials 21 using these baths (see Fig. 7) in the
same manner as in the prior art.
According to the first embodiment of the present invention,
as many plating liquid containment baths as necessary are
installed in correspondence with the plating baths . As shown
in Fig. 1, for example, a plating liquid containment bath is
not installed in firstplatingbath 44 while firstplating liquid
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containment bath 49 is installed in second plating bath 45 and
second plating liquid containment bath 50 is installed in third
plating bath 46, respectively. In this case, the plating liquid
containment baths are installed underneath the plating baths
so that the work space can be efficiently utilized and so that
the plating liquids can be contained for a short period of time
when the plating liquid is contained. Thereby, this solder
plating line is characterized in that a plurality of combined
plating films can be sequentially formed on conductive material
21 using one conveyance rail in accordance with the usage
application.
Fig. 2 is also a layout schematically showing the function
of a solder plating line for implementing a plating apparatus
of the present invention in the same manner as in the above
described Fig. 1. A pre-dip bath 53, a first plating bath 54,
a second plating bath 55 , a third plating bath 56 and a water
washing bath 57 are installed underneath a conveyance line 52
in this solder plating line. Then conductive materials 21 are
transferred in unison by the same pitch by means of lateral
transfer-type pushers 51 and plating films are formed on
conductive materials 21 using these baths.
Then, according to the second embodiment plating liquid
containment baths are installed for all of the plating baths .
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As shown in Fig. 2, for example, a first plating liquid
containment bath 59 is installed in first plating bath 54, a
second plating liquid containment bath 60 is installed in second
plating bath 55 and a third plating liquid containment bath
61 is installed in third plating bath 56, respectively. In this
case, also, the plating liquid containment baths are installed
underneath the plating baths in the same manner as in the above
described first embodiment. Thereby, this solder plating line
is characterized in that a plurality of combined plating films
can be sequentially formed on conductive material 21, which
allows plating, using one conveyance rail in accordance with
the usage application.
Concretely, with respect to the first embodiment, the
conveyance mechanism of this solder plating line is the same
as in the above described Fig. 9. In the solder plating line
of this Fig. 1, for example, a plating liquid of Sn is contained
in first plating bath 44, a plating liquid of Sn-Bi is contained
in second plating bath 45 and a plating liquid of Sn-Ag is
contained in third plating bath 46 . Then, the necessary plating
baths from among these plating baths are selected in accordance
with the usage applications of conductive material 21 to be
plated and the plating liquids in the plating baths that are
unused are shifted to plating liquid containment baths . In this
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embodiment, however, a plating liquid is always contained in
first plating bath 44, for containing a plating liquid of Sn,
and conductive material 21 is immersed in this plating liquid
of Sn. As a result, a single plating film layer of Sn is formed
on conductive material 21 or a plating film having a first layer
of Sn and a second layer of Sn-Bi or Sn-Ag is formed. Here,
the structure of the lead member is the same as Fig. 7 and the
same symbols are used.
First, a case is described wherein first plating film
22, which is a single Sn layer, is formed alone on conductive
material 21 . A plating liquid of Sn is always contained in first
plating bath 44, for containing a plating liquid of Sn, and
a plating film of Sn is formed on conductive material 21 . First,
the hydroxide film on the surface is removed in pre-dip bath
43 and, then, conductive material 21 that has been processed
in the above described pre-plating process line is immersed
in the plating liquid of Sn in first plating bath 44. Then,
no plating films are formed on conductive material 21 during
this time in second plating bath 45 and third plating bath 46
and, therefore, plating liquids in the baths are shifted to
first plating liquid containment bath 49 and second plating
liquid containment bath 50. Conductive material 21, on which
a plating film of Sn has been formed in first plating bath 44,
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is conveyed to second plating bath 45 and to third plating bath
46 and those plating baths do not contain any plating liquid
and, therefore, no plating films are formed. Next, the surface
of conductive material 21, on which a plating film has been
formed, is cleaned in water washing bath 47. As a result, a
single plating film layer of Sn is formed on conductive material
21.
Second, a case is described wherein two layers, first
plating film 22 and second plating film 23, are formed on
conductive material 21 . The process for forming a plating film
on conductive material 21 is the same as described above . First,
first plating bath 44 always contains a plating liquid of Sn
and, therefore, first plating film 22 of Sn is formed on
conductive material 21 . Then, the plating bath for forming second
plating film 23 is selected in accordance with the usage
application of this conductive material 21. Here, in the case
that second plating film 23 of Sn-Bi is formed, first, a plating
liquid of Sn-Ag in third plating bath 46 is moved to second
plating liquid containment bath 50. Next, in the case that a
second plating film of Sn-Ag is formed, a plating liquid of
Sn-Bi in second plating bath 45 is shifted to first plating
liquid containment bath 49 and a plating liquid of Sn-Ag is
returned from second plating liquid containment bath 50 to third
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plating bath 46. As a result, two plating film layers of Sn
and of Sn-Bi, or of Sn and of Sn-Ag, are formed on conductive
material 21.
Here , in the plating apparatus of Fig . 1 , the metal material
of the plating liquid in first plating bath 44 is Sn, the metal
material of the plating liquid in second plating bath 45 is
Sn-Bi and the metal material of the plating liquid in third
plating bath 46 is Sn-Ag. In addition, the solutions from which
these metals and solvents for solving these metals have been
removed have the same liquid constitutions and, therefore,
plating films can be sequentially formed on conductive material
21. In some cases, however, plating films are formed on
conductive material 21 using plating liquids having different
liquid constitutions. At this time, plating baths containing
pure water are prepared between plating baths having plating
liquids of differing constitutions so that the surface of
conductive material 21 , which has been plated, is washed and,
thereby, these plating liquids having different liquid
constitutions are prevented from mixing with each other. In
addition, in the case that this pure water is not necessary,
the pure water is contained in the plating liquid containment
baths . Thereby, a plurality of combined plating films can be
sequentially formed on conductive material 21 using one
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conveyance rail, regardless of the liquid constitutions of the
plating liquids.
Concretely, with respect to the second embodiment, the
plating method in this solder plating line is the same as in
the above described first embodiment. In the solder plating
line of the above Fig. 2, a plating liquid of Sn is contained
in first plating bath 54, a plating liquid of Sn:Bi = 98 (wt.%)
2 (wt.%) is contained in second plating bath 55 and plating
liquid of Sn:Bi = 43 (wt.%): 57 (wt.%) is contained in third
plating bath 56 . Then, necessary plating baths from among these
plating baths are selected in accordance with the usage
application of conductive material 21 to be plated and the
plating liquids in the plating baths that are unused are shifted
to plating liquid containment baths. As a result, a single
plating film layer of Sn:Bi = 98 (wt. %) : 2 (wt. %) may be formed
on conductive material 21, two plating film layers having a
first layer of Sn and a second layer of Sn : Bi = 43 (wt . % ) : 57
(wt . % ) may be formed on conductive material 21 or two plating
f film layers having a f first layer of Sn : Bi = 98 (wt . % ) : 2 (wt . % )
and a second layer of Sn : Bi = 43 (wt . % ) : 57 (wt . % ) may be formed
on conductive material 21.
In this second embodiment, a plating liquid of Sn:Bi =
98 (wt. %) : 2 (wt. %) can be utilized in order to form first plating
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film 22 on conductive material 21. At this time, approximately
several o of Bi may be included in the plating liquid and, thereby,
whiskers (crystal in a needle form) can be prevented to a
significant extent from being formed on first plating film 22 .
Accordingly,the presentinvention providesplating baths
containing a plurality of plating liquids of differing
constitutions, and plating liquid containment baths are
installed in all of these plating baths, or in the necessary
plating baths . Thereby, plating liquids can be shifted between
each of these pairs of baths in accordance with the usage
application of conductive material 21 . As a result, a plurality
of combined plating films can be sequentially formed using one
conveyance rail.
That is to say, a plurality of combined plating films
can be sequentially formed on conductive material 21 using one
conveyance rail. Thereby,it becomesunnecessary to temporarily
stop the plating apparatus in order to replace the plating
liquids in the baths according to the combinations of the plating
films. As a result, working time can be greatly shortened, and
time and effort necessary to replace the plating liquids can
be eliminated. In addition, in the case that one plating liquid
is replaced with another in the same bath, the respective plating
liquids can be prevented from mixing with each other and, thereby,
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management of the plating liquids and effort necessary for
maintenance of plating baths or other plating equipment can
be greatly reduced.
There are other plating methods that allow the sequential
formation of a plurality of combined plating films using one
conveyance rail. For example, there are methods for forming
plating films in the second and third plating baths while
shifting the plating liquids in the first plating bath to the
first plating liquid containment bath, and for forming a single
plating film layer solely in the third plating bath while
shifting the plating liquids in the first and second plating
baths to the first and second plating liquid containment baths .
In addition, a thick plating film can be formed on conductive
material 21 by using adjacent plating baths to contain plating
liquids of the same composition.
In any case, as described above, it is possible to
sequentially form a plurality of combined plating films using
one conveyance rail by shifting the plating liquids between
each of the pairs of baths according to the present invention.
Though a case of solder plating is described above as
an example, this plating apparatus can be utilized without
limitation in solder plating. For example, there are Sn plating,
Cu plating, Ni plating, and the like . This plating apparatus
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can be used in these cases so that a plurality of combined plating
films can be sequentially formed on conductive material 21 using
one conveyance rail.
Next, an auxiliary plating rack having a rectangular
parallelepiped structure with four main pillars and a plating
method wherein this auxiliary plating rack is used are described
in reference to Figs. 3, 4 and 7 as the second embodiment.
Fig. 3 is a layout schematically showing an auxiliary
plating rack used in the implementation of a plating method
of the present invention. Then, Fig. 4 is a layout, as viewed
from above, of conductive material 21 (see Fig. 7) placed in
auxiliary plating rack 72 shown in Fig. 3 being plated in plating
bath 71. Here, conductive material 21 is, in most cases, used
as a cathode in electrical plating and, therefore, a case is
described wherein the electrode is used as anode 73.
The present invention is characterized in that a
rectangular parallelepiped auxiliary plating rack 72 formed
of four main pillars is used when a plating film is formed on
conductive material 21 and, thereby, uniform current density
is applied to all portions of conductive material 21, being
any of a variety of types of different surface areas, or the
like.
Concretely, an appropriate range ofcurrent density exists
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for each plating liquid when plating work is carried out wherein
a high quality plating film can be formed by carrying out plating
work only within this range. Then, according to this plating
method, conductive material 21 is placed in a rectangular
parallelepiped auxiliary plating rack 72 formed of four main
pillars and is immersed in the plating liquid in plating bath
71 together with this auxiliary plating rack 72 . This auxiliary
plating rack 72 is formed of conductive members so as to
integrally form a cathode with conductive material 21. Then,
as shown in Fig. 2, conductive material 21 is placed so as to
be positioned at the center of auxiliary plating rack 72 and,
therefore, the main pillars of auxiliary plating rack 72 are
positioned between anode 73 and conductive material 21 . Thereby,
the main portion of the current of high density is directed
to the main pillars of auxiliary plating rack 72 while the
remaining current density is applied to conductive material
21 so as to form a plating film. As a result, a plating film
having a uniform thickness and having a uniform composition
distribution can be formed on a variety of conductive materials
21, such as conductive material 21 having a large surface area
and conductive material 21 having a small surface area.
There is a case, for example, wherein a plating film is
formed on conductive material 21 having a large surface area .
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Here, an appropriate range of current density exists for the
plating liquid. In addition, different levels of current density
are applied to the center portion and to the edge portion of
conductive material 21 because the surface area thereof is large .
In such a case, as described above, the main pillars of auxiliary
plating rack 72 are positioned between conductive material 21
and anode 73 and, thereby, electrolysis in the plating liquid
is adjusted will assistance in the same manner such that the
majority of the high current density can be avoided. As a result,
the difference in current density between the portion at the
center of conductive material 21 close to anode 73 and the edge
portion of conductive material 21 distant from anode 73 becomes
small so that a plating film of a uniform film thickness and
of a uniform plating composition is formed on the surface of
this conductive material 21.
In addition, there is a case wherein a plating film having
a first layer of Sn, which is Pb-free plating, and a second
layer of Sn-Bi is formed. At this time, a second plating film
layer of Sn-Bi is plated to have a range of thickness of
approximately 1 um to 5 um. Here, when plating is carried out
without utilizing auxiliary plating rack 72, dispersion in
plating film thickness or a portion wherein the plating film
is not formed may occur, particularly at the edge portion and
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center portion of conductive material 21 when a thin plating
film of Sn-Bi is formed, due to the above described electrical
plating characteristics. However, by using auxiliary plating
rack 72, a plating film of a uniform film thickness and of a
uniform plating composition can be formed on the surface of
conductive material 21 without the occurrence of a portion
wherein the plating film is not formed.
Here, the plating apparatus used according to the plating
method of the present invention is described. In this plating
apparatus, auxiliary plating rack 72 formed of conductive
members is used. This auxiliary plating rack 72 is in a
rectangular parallelepiped shape formed of four main pillars.
Then, auxiliary plating rack 72 is positioned between conductive
material 21 and anode 73 when conductive material 21 is placed
at the center and, thereby, assists in the formation of a plating
film. At this time, auxiliary plating rack 72 integrally forms
a cathode with conductive material 21 and adjusts the
electrolysis in the plating liquid so that a plating film of
a uniform film thickness and of a uniform plating composition
is formed.
Therefore, according to the above described plating method,
auxiliary plating rack 72 , of a rectangular parallelepiped shape
formed of four main pillars made of conductive members, is
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utilized when a plating film is formed on conductive material
21 in the plating apparatus used therein. Thereby, auxiliary
plating rack 72 integrally forms a cathode with conductive
material 21 and the four main pillars of auxiliary plating rack
72 are positioned between conductive material 21 and anode 73
and, thereby, the formation of a plating film can be avoided
as a result of direct application of a high current density
to conductive material 21. As a result, the electrolysis in
the plating liquid is adj usted with the assistance of auxiliary
plating rack 72 so that a uniform current density is applied
to the entirety of the surface of conductive material 21.
That is to say, a plating film is formed on conductive
material 21 using auxiliary plating rack 72 and, thereby, the
thickness of the plating film and the plating composition
distribution are optimized so that a uniform plating film can
be formed.
Though a case of solder plating is described above as
an example, this plating apparatus can be utilized without
limitation to solder plating. There are, for example, Snplating,
Cu plating, Ni plating, and the like. In these cases, a plating
film can be formed on a variety of types of conductive materials
21 under conditions suitable for the plating liquid by means
of a plating apparatus used according to this plating method.
26
CA 02467037 2004-05-13
In addition, though an embodiment of a case wherein
electrode 73 is anode 73 is described above, a plating film
can be formed on conductive material 21 according to the same
plating method in the case wherein electrode 73 is cathode 73 .
Finally, a plating method for a lead used for a
semiconductor device is described in reference to Figs . 5 through
7 as the third embodiment.
First, in a case, in particular, where first plating film
22 , such as of a simple Cu, a Cu alloy or an Fe-Ni alloy which
is plated on the surface of conductive material 21 , is formed
using a plating liquid having a main metal material of simple
Sn, a smooth film is formed on the surface of first plating
film 22. In a case that two types of metals, such as Sn-Bi,
are plated as first plating film 22, the first plating film
is characterized in that Bi, havinga greater ionization tendency,
has priority of deposition. As a result phenomenon, the surface
of first plating film22 is formed as a rough film made of deposited
grains.
As a result, in a case that the lead frame is contacted
during work, the problem described below occurs. During the
process of bending, for example, the above described grains
forming the rough surface, which have had priority of deposition,
come off, and the grains that have come off become attached
27
CA 02467037 2004-05-13
between leads and, thereby, defects are caused during the process
of determining whether or not an IC is a good product by making
the electrical terminals make contact with the lead frame. In
addition, there is a case wherein the grains that have come
off stay on the conveyance means that makes contact with the
lead frame in order to reduce the friction between the surfaces
when the lead frame is conveyed.
Here, a problem that occurs during the bending process
is concretely described. Fig. 5 is a schematic view of a metal
mold for bending a lead frame. Then, as illustrated, a lead
frame 82 of a semiconductor device 81 is cut or bent by means
of a punch 83 when a problem occurs.
First, plated lead frame 82 is placed on supports 84A
and 84B, and the mold as well as lead frame 82 of semiconductor
device 81 are secured by means of support 84A and a lead support
means 85. At this time, the tip of lead frame 82 is placed on
support 84B and, then, lead frame 82 is cut by means of punch
83 while the remaining portion is bent. At this time, the bottom
of punch 83 and the surface of lead frame 82 make contact with
each other wherein a phenomenon occurs such that enlarged
deposited grains adhere to the bottom of punch 83 as waste
material or adhere to lead frame 82.
In addition,leadframespresently used have approximately
28
CA 02467037 2004-05-13
200 pins and the pitch of the pins becomes as narrow as 0.4
mm. Moreover, semiconductor devices, themselves, have become
greatly reduced in size and, therefore, it is assumed that the
above described attached waste material easily causes defects.
Therefore, it is preferable for a semiconductor device to be
plated using a plating liquid having a main metal material of
simple Sn, or the like, in a manufacturing process as described
above.
On the other hand, it is shown that a microscopic amount
of Bi is mixed according to the manufacturing method described
below in a plating film having a main metal material of simple
Sn.
As described in the first embodiment, it is possible to
freely select the plating liquid in the plating apparatus of
the present invention and it is possible to form first plating
film 22 of simple Sn on the surface of conductive material 21.
As described in the second embodiment, however, auxiliary
plating rack 72 is utilized at the time of plating on conductive
material 21 and, therefore, a plating film is formed on the
surface of auxiliary plating rack 72. Then, auxiliary plating
rack 72 is cleaned in the subsequent step so that the plating
film on auxiliary plating rack 72, itself, is removed and
auxiliary plating rack 72 is repeatedly utilized in one
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CA 02467037 2004-05-13
conveyance line. Therefore, mixing into the plating liquid
containing a metal material of simple Sn of a microscopic amount
of Bi cannot be avoided. In addition, a microscopic amount of
Bi, as an impurity, is mixed into the anode used as electrode
73. Accordingly, a certain amount of Bi relative to Sn is mixed
into the plating liquid of simple Sn. There is a possibility
that even when first plating film 22 is designed as a plating
film made of simple Sn, the semiconductor device is practically
formed to have a microscopic amount of Bi in the plating film.
Therefore, the amount of Bi mixed into first plating film
22 that causes a problem is examined. In a case that 0 wt.%
to 0.5 wt.% of Bi is included in Sn, no deposition of grains
occurs. In addition, in a case that 0.5 wt.% to 1.0 wt.% of
Bi is included in Sn, almost no enlargement of deposited grains
occurs while a microscopic amount of deposition at a level that
does not cause problems may occur. However, in a case that 1.0
wt.% to 3.0 wt.% of Bi is included, a problematic level of
enlargement of deposited grains occurs . Then, in a case wherein
the enlargement of the deposited grains occurs on the surface
of the first plating film, enlargement of the deposited grains
on the surface of second plating film 23 naturally occurs.
It is understood from the above description that grain
enlargement does not occur when first plating film 22 is formed
CA 02467037 2004-05-13
as a plating film of simple Sn or of Sn having 1 wt. %, or less
(particularly 0 wt . % to 0 . 5 wt . % ) , of Bi , even in the case of
the formation thereon of an Sn-Bi plating film 23 of any
concentration.
In the following, a semiconductor device utilizing a lead
frame is described wherein a semiconductor chip is mounted on
a lead frame and wiring is carried out using fine metal wires .
After that, the semiconductor chip is sealed in a mold and the
leads that are exposed from the mold are bent. Then, this
semiconductor device, which has become a single product, is
supplied to the user after electrical measurement via the leads .
Then, the user fixes the semiconductor device on the electrodes
of a mounting board via a brazing material.
Here, it is possible to carry out a plating process before
the semiconductor chip is mounted as well as after the
semiconductor chip has been sealed in a mold. In a case that
a plating process is carried out before the semiconductor chip
is mounted, it is necessary to process the connection portions
of the fine metal wires so that no plating film is formed on
the connection portions. On the other hand, in a case that a
process is carried out after molding, it is possible to immerse
metal conductive portions exposed from the mold in plating
chemicals and, therefore, there is an advantage wherein
31
CA 02467037 2004-05-13
selective coating is unnecessary. Here, though a semiconductor
chip is described as the circuit device, a passive element or
a composite of elements may be sealed in a mold. In addition,
as for the molding material, a thermoplastic resin, a
thermosetting resin, a ceramic, or the like, can be processed
as an object.
In addition, the present invention can be applied to the
electrodes of a CSP, or the like, wherein semiconductor chips
are secured on electrodes on a support board in a matrix and
are separated after molding. In this case, a means for applying
electricity to all of the electrodes is necessary.
Effects of the Invention
As is clear from the above description, the following
effects are obtained in the plating apparatus of the present
invention.
As for the first effect, this plating apparatus has a
function of shifting the plating liquid between the two baths
in the solder plating line and, thereby, a single plating film
layer or a plurality of combined plating films can be
sequentially formed using one conveyance rail. Therefore, it
becomes unnecessary to replace the plating liquid with another
plating liquid whenever the type of plating film formed on the
32
CA 02467037 2004-05-13
conductive material is switched, and it is not necessary to
temporarily stop the plating apparatus. Thereby, a plurality
of combined plating films can be sequentially formed on the
conductive material us ing one conveyance rail and time and ef fort
necessary to replace the plating liquids can be eliminated.
In addition, when one plating liquid is replaced with another
in the same bath, the respective plating liquids can be prevented
from mixing with each other and, thereby, management of the
plating liquids and effort necessary for maintenance of plating
baths or other plating equipment can be greatly reduced.
As for the second effect, by carrying out plating work
according to the plating method of the present invention, the
maj ority of high current density that is otherwise applied to
the conductive material, which is of a variety of types having
different surface areas, or the like, can be avoidedwhenplating
is carried out. Thereby, a uniform current density is applied
to the entire surface of the conductive material, which is of
a variety of types having different surface areas and designs,
while the current density is in an appropriate range for the
utilized plating liquid and electrolysis in the plating liquid
is also controlled. As a result, the thickness of the plating
film and the plating composition distribution can be optimized
so that a uniformplating film is formed on a variety of conductive
33
CA 02467037 2004-05-13
materials.
As for the third effect, a plating film of high quality
can be formed on a variety of conductive materials different
surface areas, or the like, by utilizing the plating apparatus
used according to this plating method, that is to say, by
utilizing the auxiliary plating rack in a rectangular
parallelepiped shape formed of four main pillars made of
conductive members.
As for the fourth effect, according to a manufacturing
method for a semiconductor device wherein a plurality of plating
film layers is formed on the surface of a conductive material,
such as a simple Cu, a Cu alloy or an Fe-Ni alloy, a plating
film is formed using a plating liquid having a main metal material
of Sn-Bi, in particular, Sn into which a microscopic amount
of Bi is mixed, as the first plating film and deposition of
grains does not occur on the surface of the first plating film
and, even when they occur, they are microscopic deposited grains
and, thereby, a manufacturing method for a semiconductor device
having an excellent plating film can be implemented.
34
CA 02467037 2004-05-13
grief ~escript,_c~. O= the Drawin gs
FW :, . ~ =s a (i'_a'gram 1Cr I~C~Crl~ii:C( a pl at~iZ~~ ~ ~ WC L::~CCi
in G pl Gt~.lWj GppGrGtL:s o ~ the presen t lnventlon ;
Fig. 2 is a diagram for describing a plating line used
in the plating apparatus of the present invention;
Fig. 3 is a diagram for describing an au:~iliary pl ating
rack used in the plating apparatus of the present invention;
Fig. 4 is a layout, as viewed from above, of plating work
on a plating bath used in a plating apparatus of the present
invention';
Fig. 5 is a diagram for describing a manufacturing method
for a semiconductor device of the present invention;
Fig. 6 is a diagram for describing lead frames to which
semiconductor chips, which have been plated according to the
present invention or according to a prior art, are secured;
Fig. 7 is a diagram for describing a cross section, as
viewed in the A-A direction , of a semiconductor lead frame formed
of two plating film layers shown in Fig. 6 according to the
present invention or according to the prior art;
Fig. 8 is a diagram for describi ng a layout of the entirety
of an automatic plating apparatus according to the present
invention or according to the prior art; and
Fig. 9 is a diagram for describing a cross section, as
vi owed in the B-B directi on, of chemical etching baths included
in the entirety of the automatic plating apparatus shown in
Fig. 7 according to the present invention or according to the
prior art.
