U.S. patent application number 13/660758 was filed with the patent office on 2013-02-21 for manufacturing method thereof and a semiconductor device.
This patent application is currently assigned to FUJITSU SEMICONDUCTOR LIMITED. The applicant listed for this patent is FUJITSU SEMICONDUCTOR LIMITED. Invention is credited to Takahiro Yurino.
Application Number | 20130043577 13/660758 |
Document ID | / |
Family ID | 29706739 |
Filed Date | 2013-02-21 |
United States Patent
Application |
20130043577 |
Kind Code |
A1 |
Yurino; Takahiro |
February 21, 2013 |
MANUFACTURING METHOD THEREOF AND A SEMICONDUCTOR DEVICE
Abstract
In a semiconductor device, a lead frame made of a copper alloy
prevents exfoliation occurring near the surface of the lead frame.
A copper oxide layer is formed on the base material made of a
copper alloy by immersing the base material into a solution of a
strong oxidizer. The copper oxide layer serves as an outermost
layer and consists of a copper oxide other than a copper oxide in
the form of needle crystals.
Inventors: |
Yurino; Takahiro; (Yokohama,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJITSU SEMICONDUCTOR LIMITED; |
Yokohama-shi |
|
JP |
|
|
Assignee: |
FUJITSU SEMICONDUCTOR
LIMITED
Yokohama-shi
JP
|
Family ID: |
29706739 |
Appl. No.: |
13/660758 |
Filed: |
October 25, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12856730 |
Aug 16, 2010 |
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13660758 |
|
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|
10336716 |
Jan 6, 2003 |
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12856730 |
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Current U.S.
Class: |
257/676 ;
257/E23.041 |
Current CPC
Class: |
H01L 2224/73265
20130101; H01L 2224/48465 20130101; H01L 2224/05599 20130101; H01L
23/49586 20130101; H01L 2924/181 20130101; H01L 2224/49171
20130101; H01L 2224/85439 20130101; H01L 2924/01029 20130101; H01L
2224/48091 20130101; H01L 2924/00 20130101; H01L 2224/49171
20130101; H01L 2224/48247 20130101; H01L 2224/48247 20130101; H01L
2924/00014 20130101; H01L 2924/00 20130101; H01L 2924/00014
20130101; H01L 2924/00 20130101; H01L 2224/48091 20130101; H01L
2224/45015 20130101; H01L 2224/48465 20130101; H01L 2924/207
20130101; H01L 2924/00 20130101; H01L 2224/45099 20130101; H01L
2924/00 20130101; H01L 2224/48247 20130101; H01L 2224/32245
20130101; H01L 2224/32245 20130101; H01L 2224/48465 20130101; H01L
2924/00014 20130101; H01L 2224/48465 20130101; H01L 2924/00014
20130101; H01L 2924/01078 20130101; H01L 24/48 20130101; H01L
2224/85439 20130101; H01L 24/49 20130101; H01L 2224/05599 20130101;
H01L 2924/01019 20130101; H01L 2224/48091 20130101; H01L 2924/181
20130101; H01L 2224/73265 20130101; H01L 2224/49171 20130101; H01L
2224/45099 20130101; H01L 2224/48247 20130101; H01L 2924/00014
20130101; H01L 23/3142 20130101; H01L 2924/00014 20130101; H01L
2924/00012 20130101 |
Class at
Publication: |
257/676 ;
257/E23.041 |
International
Class: |
H01L 23/495 20060101
H01L023/495 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 7, 2002 |
JP |
2002-166898 |
Claims
1. A semiconductor device, comprising: a lead frame comprising a
base material made of a copper alloy, a first copper oxide layer
formed on the base material and a second copper oxide layer formed
on the first copper oxide layer, a total thickness of the first
copper oxide layer and the second copper oxide layer being from 10
Angstroms to 1000 Angstroms; a semiconductor element mounted on the
lead frame; a bonding wire connecting to the lead frame and the
semiconductor element; and a seal resin encapsulating the
semiconductor element.
2. The semiconductor device according to claim 1, wherein the first
copper oxide layer is made of Cu.sub.2O and the second copper oxide
layer is made of CuO.
3. The semiconductor device according to claim 1, further
comprising: an inner lead as a part of the base material; and a
metal located on a tip of the inner lead.
4. A lead frame, comprising: a base material made of a copper
alloy; a first copper oxide layer formed on the base material; and
a second copper oxide layer formed on the first oxide layer, a
total thickness of the first copper oxide layer and the second
copper oxide layer being from 10 Angstroms to 1000 Angstroms.
5. The lead frame according to claim 4, wherein the first copper
oxide layer is made of Cu.sub.2O and the second copper oxide layer
is made of CuO.
6. The lead frame according to claim 4, further comprising: an
inner lead as a part of the base material; and a metal located on a
tip of the inner lead.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Continuation Application of U.S. Ser.
No. 12/856,730, filed Aug. 16, 2010, which is a Divisional
Application of U.S. Ser. No. 10/336,716, filed Jan. 6, 2003, which
is based upon and claims the benefit of priority from the prior
Japanese Patent Application No. 2002-166898, filed Jun. 7, 2002,
the entire contents of which are hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to semiconductor
devices and, more particularly, to a semiconductor device which is
formed by encapsulating a semiconductor element mounted on a lead
frame by a seal resin.
[0004] 2. Description of the Related Art
[0005] FIG. 1 is a cross-sectional view of a semiconductor device
using a conventional lead frame. The semiconductor device 1 shown
in FIG. 1 has a so-called lead type package, which is provided with
many lead terminals extending from a resin seal part which
encapsulates a semiconductor chip.
[0006] In FIG. 1, a semiconductor chip 2 is fixed on a die stage 4
of a lead frame 3 by a die-bonding material 5. Electrodes of the
semiconductor chip 2 are connected to inner leads 7.by bonding
wires 6, and the semiconductor chip 2, the die stage 4, the bonding
wires 6 and the inner leads 7 are encapsulated by a seal resin 8.
From the seal resin 8, outer leads 9 extend as terminals for
external connection.
[0007] Generally, a lead frame is formed by processing and
patterning a copper alloy plate by stamping, etching, etc. After
patterning the copper alloy plate, silver (Ag) plating is applied
at the end of each inner lead so as to facilitate wire bonding. If
necessary, an organic discoloration preventing agent is applied to
the whole lead frame. Zinc (Zn), lead (Pb), chromium (Cr), etc. are
contained as additives in the copper (Cu) alloy forming the lead
frame.
[0008] In a manufacturing process of the above-mentioned
semiconductor device 1, the surface of the lead frame 3 is oxidized
thermally in a heating process such as a wire-bonding process. That
is, heating of the lead frame 3 forms a thin film of copper oxide
on the surface. In such a case, a phenomenon occurs in which a very
small amount of additive elements in the copper alloy is separated
and condensed near a boundary between a copper oxide layer and a
base material. Such a part into which the additive elements are
condensed has a comparatively brittle characteristic. That is,
thermal oxidation of the base material of the copper alloy forms a
brittle layer between the copper oxide layer on the surface and the
inner base material.
[0009] Additionally, the discoloration-preventing agent applied to
the surface of the lead frame 3 also forms a brittle layer when a
thermal oxidation film is formed in a heating process such as a
wire-bonding process. That is, a part of elements contained in the
discoloration preventing agent may form a brittle layer near the
boundary between the copper base and the copper oxide film.
[0010] If a semiconductor device is heated in a solder reflow
process in a case in which the semiconductor device, which is
formed by encapsulating the lead frame 3 in which the
above-mentioned brittle layer is formed, is mounted onto a mounting
substrate, etc., a crack may occur in the brittle layer. If a
moisture in the seal resin turns into steam and enters such a
crack, as shown in FIG. 2, exfoliation may occur between the lead
frame 3 (a copper alloy which is the material of the die stage 4)
and the seal resin 8 (copper oxide layer of the surface of the die
stage 4), and there may occur a problem of package cracking or
internal cracking. Such a problem tends to appear more notably, if
a mounting temperature rises due to use of a lead-free solder.
[0011] Additionally, an effect similar to the effect of the present
invention may be obtained in a blackening treatment which forms
needle crystals of cupric oxide (CuO) on a surface of a copper
alloy process. However, depending on the state of formation of
copper dioxide, exfoliation may occur between the copper oxide and
the base material of the copper alloy when the completed
semiconductor device is subjected to a solder reflow process, and
there is no way to distinguish them by their appearance.
SUMMARY OF THE INVENTION
[0012] It is a general object of the present invention to provide
an improved and useful semiconductor device in which the
above-mentioned problems are eliminated.
[0013] A more specific object of the present invention is to
provide a lead frame made of copper alloy which can prevent
exfoliation occurring near the surface of the lead frame and a
semiconductor device using such a lead frame.
[0014] In order to achieve the above-mentioned objects, there is
provided according to one aspect of the present invention a lead
frame comprising: a base material made of a copper alloy; and a
copper oxide layer formed by contacting the lead frame with a
solution of a strong oxidizer, the copper oxide layer serving as an
outermost layer and consisting of a copper oxide other than a
copper oxide in the form of needle crystals.
[0015] According to the above-mentioned invention, since the copper
oxide layer is previously formed on the base material of the lead
frame, the base material of the lead frame is not oxidized
thermally and there is no brittle layer formed in the base material
in a manufacturing process of a semiconductor device. Thus, even if
the semiconductor device is heated after a resin encapsulation, the
package of the semiconductor device is prevented from being swollen
or cracked.
[0016] Additionally, the copper oxide layer can be formed by merely
immersing the lead frame into the solution of the strong oxidizer,
which reduces an increase in the manufacturing cost of the
semiconductor device.
[0017] Additionally, in the lead frame according to the present
invention, a thickness of the copper oxide layer is preferably 10
to 1000 Angstroms. Since the copper oxide layer is very thin, the
copper oxide layer does not change into a needle crystal layer.
Thus, the copper oxide layer can be formed as a stable single layer
on the surface of the base material.
[0018] Additionally, there is provided according to another aspect
of the present invention a manufacturing method of a lead frame,
comprising: configuring a base material made of a copper alloy into
a predetermined pattern; applying plating to a part of the base
material; and forming a copper oxide layer as an outermost layer on
a surface of the base material by immersing the base material into
a solution of a strong oxidizer, the copper oxide layer consisting
of a copper oxide other than a copper oxide in the form of needle
crystals.
[0019] In the manufacturing method according to the present
invention, a time period for immersing the base material into the
solution of the strong oxidizer may be adjusted so as to take the
base material out of the solution of the strong oxidizer before the
copper oxide changes to a needle crystal state.
[0020] Additionally, there is provided according to another aspect
of the present invention a semiconductor device comprising: a lead
frame having a copper oxide layer formed on a base material made of
a copper alloy, the copper oxide layer formed by contacting the
lead frame with a solution of a strong oxidizer and serving as an
outermost layer, the copper oxide layer consisting of a copper
oxide other than a copper oxide in the form of needle crystals; a
semiconductor element mounted on a predetermined portion of the
lead frame; and a seal resin encapsulating the semiconductor
device.
[0021] In the semiconductor device according to the present
invention, a thickness of the copper oxide layer may be 10 to 1000
Angstroms.
[0022] Other objects, features and advantages of the present
invention will become more apparent from the following detailed
description when read in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a cross-sectional view of a semiconductor device
using a conventional lead frame;
[0024] FIG. 2 is a cross-sectional view of the semiconductor device
shown in FIG. 1, which shows exfoliation occurring between a die
stage and a seal resin;
[0025] FIG. 3 is a plan view of a lead frame used in a
semiconductor device according to an embodiment of the present
invention;
[0026] FIG. 4 is an enlarged cross-sectional view of a die stage of
the lead frame shown in FIG. 3;
[0027] FIG. 5 is a plan view of the lead frame showing a state
where wire-bonding is performed after mounting a semiconductor chip
2 on a die stage;
[0028] FIG. 6 is an enlarged side view showing the semiconductor
chip mounted on the die stage; and
[0029] FIGS. 7A and 7B are illustrations for explaining a processes
of forming a copper oxide layer according to the present invention
in comparison with a process of a conventional blackening
treatment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] A description will now be given, with reference to the
drawings, of embodiments of the present invention.
[0031] FIG. 3 is a plan view of a lead frame 10 used in a
semiconductor device according to an embodiment of the present
invention. FIG. 4 is an enlarged cross-sectional view of a die
stage 11 of the lead frame 10 shown in FIG. 3. The lead frame 10
used in the semiconductor device according to the present invention
is formed, similar to the conventional lead frame, by processing
and patterning a copper alloy plate as a base. Generally, the
copper alloy for lead frames contains a very small amount of zinc
(Zn), lead (Pb), chromium (Cr), etc. as additive elements. The
patterning of the copper alloy plate is performed by a known
technique such as stamping and etching, as usual. After patterning
the copper alloy plate so as to form the configuration of the lead
frame 10, silver (Ag) plating is applied to the end of each of
inner leads 12. Thus far, the same process is performed as the
conventional lead frame.
[0032] Although an organic discoloration preventing agent may be
applied after the silver plating in the conventional lead frame,
the lead frame 10 according to the present invention omits the
discoloration preventing agent on the surface, and a thin layer of
copper oxide is formed on the surface of the lead frame 10. That
is, the conventional lead frame is completed after applying a
discoloration preventing agent onto the surface of the copper alloy
plate, while in the lead frame 10 according to the present
invention, the copper alloy, which is a base material, is oxidized
by a special method mentioned later so as to form a copper oxide
layer 14 as an outermost layer on the surface of the lead frame 10
(refer to FIG. 4).
[0033] As mentioned above, the lead frame 10 is completed after the
copper oxide layer 14 is formed on the surface of the lead frame
10, especially the surface of a die stage 11. Then, the lead frame
10 is used for manufacture of a semiconductor device.
[0034] Fundamental composition of the semiconductor device
according to the embodiment of the present invention is the same as
the semiconductor device shown in FIG. 1 except for the copper
oxide layer 14 being formed in the lead frame 10. FIG. 5 is a plan
view of the lead frame 10 showing a state where wire-bonding is
performed after mounting the semiconductor chip 2 on the die stage
11. FIG. 6 is an enlarged side view showing the semiconductor chip
2 mounted on the die stage 11.
[0035] In the production process of the semiconductor device, the
semiconductor chip 2 is first mounted onto the die stage 11 of the
lead frame 10 with a die-bonding material 5 provided therebetween.
Then, electrodes of the semiconductor chip 2 and the silver-plated
parts of the inner leads 12 are connected by bonding wires 6.
Thereafter, the die stage 11, the semiconductor chip 2, the bonding
wires 6 and the inner leads 12 are encapsulated by a seal resin
8.
[0036] The semiconductor device according to the present embodiment
uses the lead frame 10 in which the copper oxide layer 14 is formed
on the surface of the base material. For this reason, even if the
lead frame 10 is heated in a wire-bonding process, the copper in
the base material of the lead frame 10 is not oxidized thermally.
Therefore, there is no brittle layer, which may be formed between
the copper alloy as the base material and the copper oxide layer
due to condensation of the additive elements during the thermal
oxidation process, thereby preventing package selling or cracking
caused by the brittle layer.
[0037] A description will now be given, with reference to FIGS. 7A
and 7B, of a formation process of the copper oxide layer 14
according to the present embodiment. FIGS. 7A and 7B are
illustrations for explaining a process of forming the copper oxide
layer 14 in comparison with a case where the copper oxide layer 14
is not formed. FIG. 7A shows the change of state near, the surface
of the lead frame in the case where the copper oxide layer is not
formed, and FIG. 7B shows the change of state near the surface of
the lead frame in the case where the copper oxide layer 14
according to the present embodiment is formed.
[0038] First, a base material 21, which constitutes a copper alloy
plate, is patternized so as to from the plate into the
configuration of the lead frame. In this state, as shown in FIG.
7A-(a) and FIG. 7B-(a), the copper alloy of the base material 21 is
exposed on the surface of the lead frame.
[0039] Next, an oxidation treatment is applied to the lead frame 10
according to the present embodiment as shown in FIG. 7B-(b). This
treatment is not applied in the case of FIG. 7A where the copper
oxide layer is not formed. The oxidation treatment is performed by
immersing the lead frame 10 into a solution of a strong oxidizer.
Consequently, the copper in the base material 21 is oxidized by the
strong oxidizer, and the copper oxide layer 14 is formed. Although
the copper oxide layer 14 mainly consists of cuprous
oxide(Cu.sub.2O), the copper oxide layer 14 also contains cupric
oxide (CuO).
[0040] In the oxidization by the solution of a strong oxidizer,
there is no separation of additive elements between the copper
oxide layer 14 and the copper alloy of the base 21, and, thus, the
brittle layer due to condensation of the additive elements is not
formed. Additionally, even if the discoloration preventing agent is
applied on the surface of the base material, a component of the
discoloration preventing agent is not contained in the base
material since the component is dissolved into the solution of the
strong oxidizer, and, thus, a brittle layer is not formed.
[0041] Here, there is a so-called blackening treatment as a process
for forming a copper oxide layer by immersing a copper alloy into a
solution of a strong oxidizer. The blackening treatment is a
process for forming a needle crystal layer of cupric oxide (CuO) on
the surface of a copper alloy, and is called as a blackening
treatment since the color of the needle crystal layer of cupric
oxide (CuO) is black. Generally, the blackening treatment is a
process to improve adhesion between a seal resin and a lead frame
by configuring the surface of the lead frame into needle-like
shape.
[0042] The solution of the strong oxidizer used for the blackening
treatment is, for example, a mixed solution of sodium chlorite,
sodium hydroxide and potassium peroxydisulfate. The needle crystal
layer of cupric oxide (CuO) is formed by immersing the copper alloy
into such a mixed solution for 3-10 minutes at a temperature of
around 100.degree. C.
[0043] Although the copper oxide layer 14 formed on the base
material 21 in the present embodiment can also be formed using the
mixed solution of the strong oxidizer for the above-mentioned
blackening treatment, the copper oxide layer 14 is not a needle
crystal layer. Namely, in the conventional blackening treatment,
chemical reactions are continued until a copper oxide layer of the
surface becomes a needle crystal layer of cupric oxide (CuO). On
the other hand, the copper oxide layer 14 according to the present
embodiment mainly consists of cuprouse oxide (Cu.sub.2O), which is
formed by taking the lead frame out of the mixed solution of a
strong oxidizer prior to the formation of cupric oxide (CuO) which
turns to the needle crystal layer.
[0044] Therefore, the time of oxidation treatment according to the
present embodiment must be remarkably shorter than the time
required by the conventional blackening treatment. Additionally,
although the outermost layer of the lead frame, which has been
subjected to the blackening treatment, is the needle crystal layer
of cupric oxide (CuO), the lead frame 10 according to the present
embodiment has the copper oxide layer 14 as the outermost layer
which is not the needle crystal layer. Further, the thickness of
the copper oxide layer 14 according to the present embodiment is
remarkably smaller than the thickness of the needle crystal layer
formed by the blackening treatment, and is sufficient in the order
of about 10 to 1000 .ANG..
[0045] As mentioned above, since the copper oxide layer 14
according to the present embodiment can be formed by merely
immersing the lead frame into a solution of a strong oxidizer for a
very short tine, the copper oxide layer 14 can be easily formed
without increasing the manufacturing cost of the lead frame.
Moreover, the copper oxide layer 14 can be very thin, and can be
formed as a stable cuprous oxide (Cu.sub.20) layer.
[0046] Next, when the semiconductor device is formed using the lead
frame, the lead frame is heated in a wire-bonding process. At this
time, as shown in FIG. 7A-(c), a copper oxide layer 22 is formed as
shown in FIG. 7A-(c) due to thermal oxidation of copper of the
exposed base material 21 in the case where the copper oxide layer
14 is not formed as shown in FIG. 7. On the other hand, in the case
where the copper oxide layer 14 is formed in the above-mentioned
oxidation treatment process, another copper oxide layer is not
newly formed since the surface of the base material 21 is already
covered by the copper oxide layer 14.
[0047] Here, in the case of FIG. 7A where the copper of the exposed
base material 21 is oxidized thermally and the copper oxide layer
22 is formed, the additive elements in the base material 21
separate and condense between the copper oxide layer 22 and the
base material 21, thereby forming a condensation layer 23. This
condensation layer 23 corresponds to the above-mentioned brittle
layer. On the other hand, in the case shown in FIG. 7A where the
copper oxide layer 14 is formed, a copper oxide layer due to
thermal oxidation is not formed, and, thus, the condensation layer
23 is not formed.
[0048] After the wire-bonding process, the semiconductor chip 2 is
encapsulated by the seal resin 8. The semiconductor chip 2 is
mounted and fixed onto the die stage 11 of the lead frame 10, and
the die stage 11 is also encapsulated together with seal resin 8.
Therefore, in the process of FIG. 7A, the copper oxide layer 22 is
covered by the seal resin 8 as shown in FIG. 7A-(d). On the other
hand, in the process of FIG. 7B, the copper oxide layer 14, which
is forcibly formed by the oxidation process is covered by the seal
resin 8 as shown in FIG. 7B-(d).
[0049] The formation of the semiconductor device is completed after
the resin encapsulation is completed. At this time, the
semiconductor device functions normally both in the case of FIG. 7A
and the case of FIG. 7B. Accordingly, the semiconductor device is
stored until it is used. During the time period of storage, the
seal resin of the semiconductor device may absorb moisture from a
surrounding atmosphere.
[0050] Then, when a product is manufactured using the semiconductor
device, the semiconductor device is mounted onto a mounting
substrate etc. In many cases, solder mounting is used for mounting
the semiconductor device. Especially, a lead terminal type
semiconductor device is mounted by soldering the outer leads to the
electrode pads of the mounting substrate. In such a mounting
process, the semiconductor device is subjected to the heat of the
solder reflow. Since a lead-free solder has a high-melting point,
the heating temperature reaches about 230-240.degree. C.
[0051] When the semiconductor device is heated at such a
temperature, a thermal stress generated in the semiconductor device
(seal resin) is increased, which may cause a small crack formed in
the brittle condensation layer 23. If the moisture, which the seal
resin absorbed, enters such a crack and turns into steam
exfoliation may occur in the condensation layer 23, as shown in
FIG. 7A-(e), and a problem arises in that the seal resin is swollen
or broken.
[0052] On the other hand, in the case of FIG. 78 where the
semiconductor device is provided with the copper oxide layer 14 so
as to prevent the formation of the condensation layer 23, there is
no crack or breakage occurs near the boundary between the lead
frame 10 and the seal resin 8 since there is no brittle layer, and,
thus, there is no problem such as package swelling or cracking.
[0053] The inventors produced the base material 21 having the
copper oxide layer 14 according to the present embodiment (in the
case of FIG. 7B) and also produced the base material 21 having the
copper oxide layer 22 which is formed by thermal oxidation (in the
case of FIG. 7A), and performed tape pealing tests on both the
copper oxide layers 14 and 22. The lead frames were placed on a
heater block heated at 250.degree. C. for 3 minutes, and then the
copper oxide layers 14 and 22 are attached to tapes and pealed from
the read frames. As a result, the copper oxide film 22, which is a
thermal oxidation film, is exfoliated from the base material 21 in
all of five test pieces. On the other hand, exfoliation did not
occur in the copper oxide layer 14 according to the present
embodiment in all of five test pieces. Therefore, it was proved
that the copper oxide layer 14 according to the present embodiment
is joined to the base material 21 of the lead frame more firmly
than the copper oxide layer 22 formed by thermal oxidation.
[0054] As mentioned above, by using the lead frame 10 in which the
copper oxide layer 14 according to the present embodiment is
formed, package swelling or cracking due to heating of the
semiconductor device in a mounting process can be prevented.
Especially, even when a solder reflow is performed at
230-240.degree. C. as in a mounting process using a lead-free
solder, the semiconductor device can be prevented from being
swollen or cracked.
[0055] The present invention is not limited to the specifically
disclosed embodiments, and variations and modifications may be made
without departing from the scope of the present invention.
[0056] The present application is based on Japanese priority
application No. 2002-166898 filed Jun. 7, 2002, the entire contents
of which are hereby incorporated by reference.
* * * * *