JPH11121673A - Lead frame - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lead frame, made of copper alloy which can prevent the occurrence of delaminations due to the generation of an oxide film on the surface of the lead frame, even if the temperature at IC assembly is relatively high, and which does not spoil wire-bonding capability. SOLUTION: A die pad 221 constituted of a copper alloy member and on which a semiconductor element is loaded, an inner lead 223 which is provided at the periphery of the die pad 221 and which is connected with a connection pad on the semiconductor element and an outer lead which continues from the inner lead 223 and is connected with an outer circuit, are provided. The resin encapsulated-type lead frame for a semiconductor device 210, in which partial silver plating 250 is applied on the tip part of the inner lead 223 and a die pad face through copper strike plating 240, is provided. A Cu2 O oxide film is formed on the entire face of copper strike plating, except for a partial silver plating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-sealed lead frame used for a semiconductor integrated circuit device and the like, and more particularly, to a lead frame made of a copper alloy and having improved bonding strength with a sealing resin. About.

[0002]

2. Description of the Related Art Normally, a lead frame incorporated in a semiconductor device is made of a metal having excellent conductivity such as 42 alloy (42% by weight of nickel, iron alloy being the balance iron), copper alloy or Kovar, It is formed by a press method using a mold, a photo etching method, or the like.

One type of lead frame is a resin-sealed (plastic package) type lead frame. FIG. 7 shows QFP (Qua) which is a general form of a resin-encapsulated (plastic package) type lead frame.
FIG. 4 is a diagram schematically illustrating a (Flat Page) type lead frame. As shown in FIG. 7, the QFP type lead frame 120 is connected to a die pad 121 which is a portion on which a semiconductor element (IC chip) is mounted, and a connection pad formed on the semiconductor element mounted on the die pad 121. The plurality of inner leads 123 provided around the die pad 121 are connected to an external circuit. The outer leads 122 continuous from the inner leads 123 and the sealing resin are sealed when the lead frame 120 is sealed with the resin. Dam bar 124 that becomes a dam
And a frame (frame) section 125 for holding the entire lead frame 120.

As shown in FIG. 6 schematically showing a cross section of a semiconductor device, after a semiconductor element 110 is mounted on a die pad 121, terminals (connection pads 111) formed on the semiconductor element 110 and inner leads 123 are formed. The tip and
Connection (wire bonding) is performed with a thin wire (wire 130) such as gold (Au). Next, after sealing the inside of the dam bar 124 with resin so as to cover the semiconductor element 110 with the resin 140, the semiconductor device 100 is obtained through processes such as cutting the dam bar 124 portion and forming the outer lead 122 portion into a predetermined shape. Things.

The lead frame 120 shown in the above example
At the time of wire bonding and the die pad 12
In order to obtain a strong coupling force and conductivity with the lead frame when mounting the semiconductor element 110 on the inner lead 123, as shown in FIG.
And at least a noble metal plating is applied to the surface of the die pad 121 on the side where the semiconductor element is mounted. As the noble metal plating, silver plating is generally performed, and in the example of FIG. 5, 250 silver plating portions are shown. In addition, the tip portion of the inner lead 123,
Silver plating performed on the die pad 121 on the side on which the semiconductor element is mounted is hereinafter referred to as partial silver plating.

Conventionally, in performing a partial silver plating process on a lead frame 120 made of a copper alloy, a copper strike plating 240 is applied on the lead frame 120 as shown in FIG. The partial silver plating 250 is formed on the die pad 121 and the tip of the inner lead 123. An example of the partial silver plating process is described below.

First, as shown in the process diagram of FIG. 4, a pre-processing step such as degreasing and acid cleaning is performed on the lead frame 120 whose outer shape has been processed by a known method such as a press method or a photo-etching method.

[0008] Next, a base plating serving as a base for the partial silver plating is applied to the lead frame 120. Copper (Cu) strike plating is usually used for the base plating,
It is common to use copper (Cu) strike plating having a thickness of about 0.2 μm.

Next, a predetermined region (for example, a tip portion of the inner lead 123 and a die pad 121 surface on which a semiconductor element is mounted) is subjected to partial silver plating with a thickness of about 1.5 to 10 μm. In addition, as means of partial silver plating,
A masking jig having a predetermined opening is brought into close contact with the lead frame, or an electrodeposition resist having a predetermined opening is formed on the lead frame, and thereafter, the lead frame is subjected to silver plating, so that the lead frame is silver-plated. A method of selectively performing silver plating on an exposed portion is known.

Next, after the partial silver plating, an electrolytic peeling process is performed to remove the silver adhering to the lead frame portion which should not be subjected to the silver plating by, for example, leaking the plating solution. Next, a discoloration prevention treatment is performed to prevent discoloration of the silver plating due to oxidation and hydroxylation. As a means of the discoloration prevention treatment, for example, it is common to form a thin silver (Ag) organic film on the silver plating surface.

In the case of a lead frame made of a copper alloy and partially plated with silver through an undercoat (copper strike plating), mounting of a semiconductor element, wire bonding, and resin sealing are performed after the lead frame is manufactured. In a semiconductor device manufacturing process and a semiconductor device mounting process, the underlying plating (copper strike plating) does not peel off, and the underlying plating (copper strike plating) does not peel off when using the semiconductor device. Is required.

However, even in a lead frame made of a copper alloy which has been subjected to the above-mentioned plating process, the delamination of the sealing resin caused by the lead frame in a semiconductor device manufacturing process and a semiconductor device mounting process. Peeling)
Has occurred.

When delamination (peeling) occurs in the sealing resin, moisture enters through a gap between the lead frame and the sealing resin, which causes problems such as lowering the durability and reliability of the semiconductor device. .

As a cause of delamination (peeling) occurring at the interface between the sealing resin and the lead frame (for example, the back surface of the die pad), electrolytic peeling and discoloration prevention treatment are performed after partial silver plating is performed via copper strike plating. In a lead frame made of a copper alloy as a raw material, a copper strike plating or an oxide film is formed on a copper alloy surface in a heating step of the lead frame in a semiconductor device manufacturing process, and an oxide film and a metal (copper strike plating, or , Copper alloy) is estimated to be insufficient.

For this reason, the following proposals have been made as a method for improving the adhesion strength at the interface between the sealing resin and the lead frame (for example, the back surface of the die pad) and preventing the occurrence of delamination (peeling). is there. That is, Japanese Patent Application No. 5-512688 proposes a lead frame in which the entire surface is covered with a mixture of chromium and zinc or a thin film of chromium and zinc alone. However, in the lead frame proposed above, the partial silver plating part is also covered with a metal coating such as chromium and zinc.
There is a problem that wire bonding performance using gold (Au) wire is inferior.

Japanese Patent Application Laid-Open No. 9-116065 proposes a lead frame which is entirely plated with zinc flash plating or copper strike plating as a base plating for partial silver plating. However, even in the lead frame of this proposal, a tin (Sn) needle-like crystal is formed at the time of exterior plating, which may cause a short circuit between the outer leads, and it can be said that there is a problem in reliability.

In the method of forming a silver (Ag) organic film to prevent discoloration of copper by oxidation or hydroxylation as in the conventional lead frame plating process shown in FIG. If the heating temperature for the lead frame is increased during the manufacture of the semiconductor device, the effect of preventing delamination cannot be obtained.

[0018]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has been described in connection with a semiconductor device manufacturing method in which a lead frame is heated at a relatively high temperature (for example, about 300 ° C.). Oxide film on the frame surface (CuO
An object of the present invention is to provide a lead frame made of a copper alloy which can prevent the occurrence of delamination due to the formation of an oxide film and does not impair the wire bonding property.

[0019]

In order to achieve the above object, the present invention first provides a die pad made of a copper alloy material on which a semiconductor element is mounted, and a die pad provided around the die pad. An inner lead for connecting to a connection pad on the semiconductor element, and an outer lead that is continuous from the inner lead and connects to an external circuit, and is provided with a tip of the inner lead via copper strike plating. A resin-encapsulated lead frame for a semiconductor device in which a part and a die pad surface on which a semiconductor element is mounted are subjected to partial silver plating, wherein a Cu ₂ O oxide film is formed on a copper strike plating surface excluding the partial silver plating part. The lead frame is characterized in that a lead frame is formed.

According to a _second aspect of the present invention, there is provided the lead frame according to the first aspect, wherein the thickness of the Cu ₂ O oxide film is 0.002 μm or more and 0.020 μm or less.

That is, as described above, when the temperature is increased during the manufacture of a semiconductor device, an oxide film (CuO oxide film) is formed on the copper strike plating surface, and this oxide film (CuO oxide film) is formed.
It is presumed that the oxide film) weakens the bond between the sealing resin and the surface of the lead frame including the back surface of the die pad, and causes delamination (peeling) at the interface between the surface of the lead frame and the sealing resin. Therefore, the present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, as shown in FIG. 1, formed a Cu ₂ O oxide film 230 on the surface of the copper strike plating 240 except for the portion where the partial silver plating 250 is to be applied. By doing so, even if the heating temperature to the lead frame 210 is increased during the manufacture of the semiconductor device, the generation and growth of the CuO oxide film from the copper strike plating 240 are suppressed, and the surface of the lead frame 210 and the sealing resin The present inventors have found that delamination (peeling) at the interface can be prevented and the bonding property is not impaired, and this is proposed.

Here, as a means for forming the Cu ₂ O oxide film 230 on the surface of the copper strike plating 240, a copper sulfate aqueous solution or a sodium chlorite-based aqueous solution (sodium chlorite, sodium hydroxide, trisodium phosphate) is used. (A mixed aqueous solution) or the like. As a result, the Cu ₂ O oxide film 230 is formed on the surface of the copper strike plating 240, and the oxide film (CuO oxide film) is generated at all the interfaces between the lead frame surface and the sealing resin including the die pad back surface. Delamination (peeling) can be prevented.

[0023] When subjected to partial silver plating 250 on Cu ₂ O oxide film 230, for adhesion between the Cu ₂ O oxide film 230 and the partial silver plating 250 is weak, partial silvered 2
50 may peel off. Therefore, in the present invention, the partial silver plating 250 is applied on the copper strike plating 240,
The Cu ₂ O oxide film 230 is formed on the surface of the copper strike plating 240 excluding the portion where the partial silver plating 250 is applied.

[0024] Then, the present inventors have found that the appropriate thickness of the Cu ₂ O oxide film effect of preventing the delamination (peeling) can be obtained, 0.002 .mu.m thickness of Cu ₂ O oxide film
As described above, it is proposed that the thickness be 0.020 μm or less.

That is, when the thickness of the Cu ₂ O oxide film 230 is thinner than 0.002 μm, the concentration of copper ions diffused into the Cu ₂ O oxide film by copper strike plating when heating the lead frame in the semiconductor device manufacturing process. Becomes large, and it becomes insufficient to suppress the generation and growth of the CuO oxide film, so that the occurrence of delamination (peeling) cannot be prevented. If the thickness of the Cu ₂ O oxide film is larger than 0.02 μm, the external appearance of the lead frame is discolored, and the strength of the Cu ₂ O oxide film, which is weak in strength, is increased, resulting in insufficient strength. ). Accordingly, the thickness of the Cu ₂ O oxide film is set to be 0.002 μm or more and 0.020 μm or less.
Even if the temperature of the lead frame 210 is set to a relatively high temperature, for example, about 300 ° C., it is possible to prevent the occurrence of delamination (peeling) of the sealing resin due to the growth of the oxide film (CuO oxide film).

In the lead frame of the present invention,
Is very thin copper acid on the surface of copper strike plating 240
Film (Cu_TwoSince only the O-oxide film 230) is formed,
Wire bonding properties are equivalent to conventional lead frames
Is obtained. Also, Cu _TwoFormation of O oxide film 230
Except for the steps, the lead frame of the present invention
Can be manufactured in the same process as the frame, and
Various post-processes performed after manufacturing the frame are also the same
The same processing as that for the frame can be used._TwoO oxide film shape
Except for the production process, no special manufacturing process or processing is required.
No.

[0027]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an embodiment of a lead frame according to the present invention.

<Embodiment 1> A lead frame 210 according to Embodiment 1 is made of a copper alloy and is formed by a press method or a photo-etching method in the same manner as the conventional lead frame shown in FIG. It is composed of a lead, an outer lead, a dam bar, a frame (frame) portion, a suspension bar, and the like. Further, a copper strike plating 240 is applied to the entire surface of the lead frame 210, and the tip portion of the inner lead where wire bonding is performed and the die pad surface on the side on which the semiconductor element is mounted are partially silver plated 250 through the copper strike plating 240.
Has been given.

Here, as a feature of the lead frame 210 of the present invention, as shown in FIG. 1, a Cu ₂ O oxide film 230 is formed on the entire surface of the copper strike plating 240 except for the portion where the partial silver plating 250 is applied. Is what you are doing.
FIG. 1 is a cross-sectional view schematically showing a main part of an embodiment of a lead frame 210 according to the present invention.
50 shows the die pad 221 portion and the tip portion of the inner lead 223 to which 50 is applied.

The lead frame 210 of the first embodiment is made of a copper alloy material having a thickness of 0.125 mm (made by Furukawa Electric Co., Ltd.).
After processing into the external shape of FIG. 5 by a known photo-etching method using a product name “EFTEC64T-1 / 2H material”), the copper strike plating 240 is applied to the lead frame 21.
0, and then a partial silver plating 250 is applied.

Here, in the first embodiment, the copper strike plating 24 excluding the portion to be subjected to the partial silver plating 250 is used.
A Cu ₂ O oxide film 230 is formed on the surface 0 by a treatment using a chemical solution such as an aqueous solution of copper sulfate or an aqueous solution of sodium chlorite (a mixed aqueous solution of sodium chlorite, sodium hydroxide and trisodium phosphate). And then Cu
Copper strike plating 24 exposed from ₂ O oxide film 230
0 is provided with partial silver plating 250.

The Cu ₂ O oxide film 23 is previously formed on the surface of the copper strike plating 240 excluding the portion where the partial silver plating 250 is to be applied.
The formation of a CuO film by the copper strike plating 240 can prevent Cu ₂ O from being generated even if the heating temperature of the lead frame 210 is increased to, for example, about 300 ° C. during the manufacture of the semiconductor device. The oxide film 230 is to suppress.

Next, a plating process for the lead frame 210 in the first embodiment will be described with reference to FIG. FIG. 2 shows a die pad 221 to which a partial silver plating 250 is applied and an inner lead 223 similarly to FIG.
Is shown.

First, the surface of the lead frame 210 whose outer shape was processed by a known photoetching method was degreased with an aqueous alkali solution, and then washed with water. Next, an acid activation treatment for removing an oxide film formed on the surface of the lead frame 210 with an acidic solution is performed to activate the surface of the lead frame 210, followed by washing with water again to obtain FIG. 2A. .

Next, copper plating is performed on the entire surface of the lead frame 210 with a plating solution (copper cyanide solution) at a solution temperature of 50 ° C. for about 20 seconds, and a copper strike plating 2 having a thickness of 0.2 μm is performed.
40 were formed, and FIG. 2B was obtained.

Next, after the surface of the lead frame 210 on which the copper strike plating 240 is formed is washed with water and washed, the entire surface of the lead frame 210 is replaced so that silver is not deposited on unnecessary portions of the lead frame 210 when performing partial silver plating. Prevention treatment was performed. The anti-replacement treatment uses thin silver (A
g) An organic film is formed on the surface of the lead frame 210. Then, after covering the lead frame 210 with a masking jig having a predetermined opening so that the surface of the die pad 221 on the surface side on which the semiconductor element is mounted and the tip region of the inner lead 223 are exposed, the lead frame is used as a cathode. A 3 μm-thick partial silver plating was applied to a predetermined area of the lead frame 210 by a plating method of spraying a plating solution from a nozzle onto the lead frame.

Next, after the lead frame 210 is washed with water, the surface of the die pad 221 and the inner leads 22 are removed.
Ag plating (for example, Ag plating leaked from a masking jig) attached to a lead frame portion where silver should not be attached other than the tip portion of No. 3 was removed by electrolytic peeling.
Next, the lead frame 210 is immersed in a sodium chlorite-based aqueous solution (a mixed aqueous solution of sodium chlorite, sodium hydroxide and trisodium phosphate) at a liquid temperature of 60 ° C. for about 30 seconds, and then the lead frame is washed with water. Thereafter, the lead frame was dried with warm air. As a result, as shown in FIG. 2 (c), a 0.002 μm thick Cu ₂
Lead frame 2 of the first embodiment having O-oxide film 230
10 was obtained.

Next, another embodiment of the present invention will be described. <Embodiment 2> In Embodiment 2, the Cu ₂ O oxide film 2
A lead frame 210 was obtained in the same process as in the first embodiment except that the forming process of the lead frame 30 was changed. That is, similarly to the first embodiment, after the partial silver plating, Ag plating adhered to the part of the lead frame 210 to which silver should not adhere except the surface of the die pad 221 and the tip part of the inner lead 223 (moling from the masking jig). A
g plating) is electrolytically peeled off, and as a chemical treatment for forming the Cu ₂ O oxide film 230, a lead frame is placed in a copper sulfate aqueous solution for about 1 minute using a 3 to 10% by weight aqueous solution of copper sulfate at a liquid temperature of 50 ° C. It is immersed. Thus, a lead frame 210 having a 0.018 μm-thick Cu ₂ O oxide film 230 on the surface of the copper strike plating 240 excluding the portion where the partial silver plating 250 was applied was obtained.

Next, the first and second embodiments described above
Of the lead frame according to the present invention and the lead frame of each comparative example described below were evaluated by the methods described below, respectively. In this evaluation, as a material to be plated, a solid plate-shaped special frame for evaluating sealing resin adhesion strength (trade name “EFTEC64T-1 / 2H” manufactured by Furukawa Electric Co., Ltd.)
Material ”, plate thickness 0.125 mm).

Subsequently, the same plating steps as those of the above-mentioned first and second embodiments were performed on the above-mentioned dedicated frames. That is, a copper strike plating 24 of 0.2 μm thickness
A dedicated frame corresponding to the first embodiment having a 0.32 μm thick partial silver plating 250 and a 0.002 μm thick Cu ₂ O oxide film 230 on the surface of the copper strike plating 240 excluding the partial silver plating 250; 0.2 μm thick copper strike plating 240, 3 μm thick partial silver plating 250,
And a 0.018 μm thick Cu ₂ O oxide film 2 on the surface of the copper strike plating 240 except for the 250 parts of the partial silver plating.
A dedicated frame corresponding to the second embodiment having the number 30 is obtained.

As Comparative Example 1, the same plating treatment as that performed on the conventional lead frame shown in FIG.
0.2μm thick copper strike plating 240 and 3μm
A dedicated frame having a thick partial silver plating 250 is obtained. Note that the plating process in Comparative Example 1 is the same as that in FIG.
Are performed according to the process chart shown in FIG. Next, as Comparative Example 2, a special frame having a copper strike plating 240 having a thickness of 0.2 μm and a partial silver plating 230 having a thickness of 3 μm was obtained by performing the same plating treatment as that of Comparative Example 1 except that no discoloration treatment was performed. Was.

The thicknesses of the oxide films of Comparative Examples 1 and 2 were measured. As a result, the thickness of the Cu ₂ O oxide film of Comparative Example 1 was 0.0015 μm, and the thickness of the CuO oxide film was 0.0007 μm.
m, and the thickness of the Cu ₂ O oxide film of Comparative Example 2 was 0.3.
[0015] The thickness of the CuO oxide film was 0.0020 µm.
The thickness of the oxide film was measured by a reduction potential method (trade name “QC-100 Surface-Scan” manufactured by ECI Technology Co., Ltd.).

Next, after performing a surface treatment under the same conditions on each of the dedicated frames of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, the wire bonding is performed by ordinary wire bonding.
After heating each dedicated frame for 5 minutes at a temperature of 320 ° C., which is 50 ° C. higher than a heating temperature of 270 ° C., a sealing resin having a fixed area was molded on the surface of each dedicated frame. Thereafter, the shear strength was used to measure the adhesion strength of the sealing resin molded on the surface of each dedicated frame. In addition, the determination of the adhesion strength by the shear method is 3.0 N / mm ² or more as “good”, and 2.0 N / mm ² or more 3.0
A value of less than N / mm ² was judged as “acceptable” and a value of less than 2.0 N / mm ² was judged as “impossible”. Next, after measuring the adhesion strength, the adhesion state of the oxide film adhered to the sealing resin peeled from the dedicated frame was observed, and the peeling of the oxide film from the dedicated frame as a material was evaluated. The measured adhesion strength of the sealing resin and the peeling state of the oxide film in each dedicated frame are shown in Table 1 below.

[0044]

[Table 1]

As shown in the above (Table 1), the first and second embodiments in which the Cu ₂ O oxide film 230 was formed on the surface of the copper strike plating 240 were different in the point of the sealing resin adhesion strength and the oxide film peeling. It can be seen that in Comparative Example 1 was superior to Comparative Example 1 in which silver plating was performed in the same manner as in the related art.
Comparative example 2 is comparative example 1 in terms of sealing resin adhesion strength.
It can be seen that, although better, the peeling of the oxide film was inferior to Examples 1 and 2 as in Comparative Example 1.

From the above, it can be seen that the first embodiment of the present invention is used.
When the lead frame of the second embodiment is used in a semiconductor device, the lead frame is caused by the oxidized state of the copper oxide film as compared with the case where the lead frame obtained by the same plating process as in the related art shown in FIG. It is determined that the occurrence of delamination of the IC package can be effectively suppressed.

[0047]

As described above, according to the present invention, the oxidation of the copper oxide film on the surface of the lead frame can be performed irrespective of the manufacturing conditions of the semiconductor device (even if the heating temperature of the lead frame is high at the time of manufacturing the semiconductor device). A lead frame made of a copper alloy can be obtained which prevents delamination of the sealing resin due to the state and does not impair the wire bonding property.

[0048]

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing a main part of an embodiment of a lead frame according to the present invention.

FIGS. 2A to 2C are cross-sectional explanatory views showing a main part of an example of a manufacturing process of a lead frame according to the present invention in the order of steps.

FIG. 3 is an explanatory sectional view showing a main part of an example of a conventional lead frame.

FIG. 4 is a process chart showing an example of a plating process for a lead frame.

FIG. 5 is an explanatory plan view showing an example of partial silver plating applied to a lead frame.

FIG. 6 is an explanatory cross-sectional view illustrating a main part of an example of a semiconductor device.

FIG. 7 is an explanatory plan view showing an example of a lead frame.

[Explanation of symbols]

Reference Signs List 100 semiconductor device 110 semiconductor element 111 connection pad 120, 210 lead frame 121, 221 die pad 122 outer lead 123, 223 inner lead 124 dam bar 125 frame portion 130 wire 140 resin 230 Cu ₂ O oxide film 240 copper strike plating 250 silver plating

Claims (2)

[Claims] 1. A die pad made of a copper alloy material on which a semiconductor element is mounted, an inner lead provided around the die pad for connecting to a connection pad on the semiconductor element, and a continuous lead from the inner lead. A resin-encapsulated semiconductor having at least an outer lead for connection to an external circuit, and a partial silver plating applied to a tip portion of the inner lead and a die pad surface on which a semiconductor element is mounted via copper strike plating. A lead frame for an apparatus, wherein a Cu ₂ O oxide film is formed on a copper strike plating surface excluding the partial silver plating portion. 2. The lead frame according to claim 1, wherein the thickness of the Cu ₂ O oxide film is 0.002 μm or more and 0.020 μm or less.