JPH0846111A - Lead frame and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] (Modified) [Objective] The present invention improves the close contact with the mold resin by specifying the material and method for coating,
Provided is a lead frame for obtaining a reliable resin-encapsulated semiconductor device that does not cause problems such as cracks during reflow mounting and practical use. According to the present invention, there is provided a lead frame 1 having a metal coating 14 of 1 to 20 μm on a front surface and a back surface of a die pad 3 surrounded by leads, and a manufacturing method thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is excellent in mountability in which a lead frame mounted with a semiconductor chip and used as a central part of a semiconductor device does not cause peeling from a resin during molding or resin cracks during reflow. And a method for manufacturing the same.

[0002]

2. Description of the Related Art In general, a lead frame has a die pad for mounting a semiconductor chip in the center by pressing or etching a thin metal made of a conductive material such as 42Ni alloy or Al, Cu. It is manufactured by molding into a shape in which a predetermined number of leads are arranged around it, and is used as a key part of a resin-sealed semiconductor device.

A resin-sealed semiconductor device is die-bonded to a semiconductor chip 2 with a bonding material 4 such as Ag paste on a die pad 3 in the center of a lead frame 1, as shown in FIG. , The electrode pad 5 on the chip and the inner lead 1a of the lead frame 1 are
The structure formed by bonding with a bonding wire 6 such as a u thin wire is inserted into a package and resin-sealed 7 to produce the structure. In the semiconductor device manufactured in this manner, the tip (outer lead) 1b of the lead frame 1 to which the solder 8 is attached is soldered by soldering by applying heat or heat in order to firmly fix the solder to the circuit board 9. It is subjected to a so-called reflow treatment in which it melts.

Generally, a sealing resin for a semiconductor device has a hygroscopic property and thus tends to absorb moisture over time. There is also moisture adhering to the components. Such contained water mainly destroys the interface with the resin, and the water accumulated in the gap causes rapid vaporization and expansion due to reflow heating, and causes resin destruction 10. On the other hand, it has been known that, at room temperature, potentially, strain occurs due to the difference in expansion between the resin and the component, especially the die pad, and shear peeling occurs at the interface, and this peeling occurs during reflow heating. Water vapor generated in the gap portion promotes peeling. In particular, peeling is large at the end of the die pad where stress concentration is likely to occur, and cracks 10 as shown in the figure occur in combination with the action of vapor pressure. Therefore, the sealing performance of the semiconductor device is deteriorated and the reliability is impaired.

For this reason, measures such as special packaging for preventing moisture when shipping semiconductor devices, requesting that the board mounting time be shortened, and baking the hygroscopic product before board mounting are taken. However, these methods are not preferable because they are extremely troublesome and need to be dealt with by the customer.

On the other hand, in order to prevent the peeling of the sealing resin and the die pad, for example, in Japanese Patent Laid-Open No. 58-199548, the back surface of the die pad (tab) 3 is uneven 11 as shown in the cross section in FIG. It is suggested to form. Further, Japanese Patent Application Laid-Open No. 55-4983 discloses that a die pad (island) 3 shown in FIG. 6 is provided with a partial cutout portion 12, and further, Japanese Patent Application Laid-Open No. 60-97645. In the publication, as shown in a cross section in FIG. 7, a semiconductor device in which a thermosetting or thermoplastic organic resin (polyimide type) 13 having a thermal expansion coefficient similar to that of a sealing resin is attached to the back surface of a die pad (tab) 3 is described. is suggesting.

[0007]

The above-mentioned conventional method is such that the die pad is mechanically processed to increase its surface area, or the die pad is made to have a large contact surface with the encapsulating resin so that shear peeling or Although it is intended to suppress the generation of cracks, the improvement of the bonding strength of the die pad itself with the sealing resin is not perfect, and when moisture is absorbed, the bond is broken and water pools are formed, causing a sudden buildup during reflow. Expansion occurs and the sealing resin is destroyed. Further, when a polyimide-based organic resin is used, the resin itself has a hygroscopic property, and thus a problem remains.

The present invention solves the above-mentioned conventional problems, increases the adhesive strength with the lead frame sealing resin, and does not cause problems such as cracks during reflow mounting and during practical use. It is an object of the present invention to provide a method for manufacturing a lead frame for obtaining a reliable resin-sealed semiconductor device.

[0009]

In order to achieve the above object, the present invention has the following structures. That is, (1) in a lead frame including a lead having a die pad in the center, one surface of the die pad and the lead has an elastic modulus of 1 × 10 ^{11 to} 3 × 10 ¹¹ Pa and a thickness of 0.1 μm.
A lead having a metal coating of about 30 μm, and a part or all of the die pad on the side facing the metal coating and the tip of the inner lead are plated with Ag having a thickness of about 5 μm. flame. (2) On the surface of the die pad and the lead on the side opposite to the surface having the metal coating on one surface, the elastic modulus is 1 × in a portion or all of the Ag-plated die pad and the portion excluding the tip of the inner lead. 10 ¹¹ ~ 3 x 10 ¹¹
The lead frame according to (1) above, which has a metal coating having a thickness of 0.1 μm to 30 μm at Pa.

(3) A lead characterized by dry-coating a metal coating on at least one surface of a strip-shaped lead frame material processed to a product thickness, and forming the material into a lead frame shape by a pressing method or an etching method. Frame manufacturing method. (4) Dry coating a metal coating on both sides of the strip-shaped lead frame material processed to the product thickness, removing the metal coating on a predetermined portion of the surface of the material, and then forming into a lead frame shape by an etching method. And a lead frame manufacturing method.

[0011]

According to the present invention, the surface of the lead frame, which is one of the constituents of the semiconductor device, is coated with a metal film to modify the surface. That is, in the resin-sealed semiconductor device using this lead frame, the interface having high adhesive strength can be formed by the following mechanism.

A natural oxide film formed on the surface of the coated metal film, that is, MO or M-OH (M =
(Metal) is effective as an intermediate layer for improving the substrate / resin adhesion. That is, the bonding mode of —C—O, which is a constituent molecule of the resin, is similar to the bonding mode of —M—O, M—OH, which are natural oxide films formed on the surface of the coated metal film. As a result, excellent adhesive strength can be realized.

The metal film covering the shear strain generated at the resin / substrate interface during reflow can be relaxed, and thus the true interface strain between the resin and the substrate can be reduced. In this way, it becomes possible to control the reflow crack by reducing the strain. The relaxation by the metal film at this time means elastic strain relaxation by the metal film having an elastic modulus intermediate between that of the lead frame base material (42Ni alloy or the like) and resin, or strain relaxation by the composition change of the metal film. . As described above, the metal coating film that is easily plastically changed is advantageous in terms of strain relaxation over the ceramic coating film that has high hardness but is inferior in deformation.

The present invention will be described in detail below. FIG. 1 shows a manufacturing process of a resin-sealed semiconductor device including a method for manufacturing a lead frame of the present invention. In the step (A), a strip-shaped material is dry-coated on one surface with a metal material, and then punched by a press method which is generally used in the past to form a lead frame. The material is the metal that has been conventionally used as described above, and is a band-shaped body processed to have a product thickness as a lead frame.

The metal forming the thin film coating in the present invention is Ni or Ni alloy, Co or Co alloy, Cr or Cr alloy, etc., and has an elastic modulus of 1 × 10 ^{11 to} 3 × 10 ^11.
It is a metal of Pa, and these are sprayed, PVD method, CVD
A single layer or a plurality of layers are coated by a generally used dry coating method such as a sputtering method, a sputtering method, or an ion plating method. It is sufficient that the film thickness is in the range of 100 Å to 30 μm. The reason why the above-mentioned metal is used is that it is excellent in corrosion resistance and heat resistance, and the adhesion to the sealing resin is extremely effective.

The elastic modulus of the metal coating is 1 × 10 ^{11 to} 3 × 10.
^The reason for limiting the pressure to ¹¹ Pa is that when the pressure is less than 1 × 10 ¹¹ Pa, the elastic modulus of the lead frame base material approaches and the effect of strain relaxation due to the metal coating cannot be sufficiently obtained.
This is because if it exceeds 10 ¹¹ Pa, the elastic modulus approaches that of the resin, and similarly the effect of strain relaxation due to the metal coating cannot be sufficiently obtained.

A material coated with such a metal is punched into a predetermined shape by the above-mentioned press working. FIG. 2A shows a cross-sectional view of the lead frame 1 that has been formed and processed.
The surface (lower surface) is coated with a metal coating 14.

This lead frame 1 is an inner lead 1
The tip portion and the die pad 3 are plated with Ag of about 5 μm to form the electrode pad 5 and the joint portion 4 of the semiconductor chip. Thereafter, a semiconductor chip is mounted on the die pad, die-bonded, wire-bonded in a predetermined process, introduced into a molding die and molded with an epoxy resin. After the molding, the metal coating 14 attached to the outer leads 1b is removed by etching, and the outer leads 1b are solder-plated 8 and connected to the base circuit 9 after cutting and molding. FIG. 3 shows a cross section of the semiconductor device manufactured in this manner.

In the step (B), both sides of the strip-shaped lead frame material are dry-coated with a metal film, and the metal of the portion corresponding to the inner lead electrode portion of the lead frame and the semiconductor chip die bonding portion of the die pad in this strip-shaped material is formed. The coating is removed by etching as described above, and then the material is processed by the commonly used pressing method as described above to form a lead frame. After the electrode part of the inner lead and the part of the die pad excluding the semiconductor chip die bonding part are masked and Ag plating is applied to the electrode part and the die bonding part,
The process is performed in the same process as the process (A). 2 (b) and 2 (c) show the lead frame 1 processed in the above process, and the metal film is coated on both surfaces other than the electrode 5 on the upper surface and the die bonding portion 4.

The lead frame and die pad are preferably dull-processed in advance in the process before metal coating. That is, by making the surface rough, the adhesiveness with the sealing resin or the bonding force of the metal coating can be improved. The rough surface can be formed by, for example, etching a necessary portion.
The roughness at that time is about 10 μm.

[0021]

EXAMPLE A semiconductor device sealed with a resin using the lead frame according to the present invention is left in an atmosphere kept at a temperature of 30 ° C. and a humidity of 95% for various times and then soldered to a circuit board under the same conditions. Heating was performed at 230 to 260 ° C. for 5 to 15 seconds. The lead frame material in this example was coated with a thin film of various metals to a film thickness of 10 nm to 1 μm by vacuum deposition, ion plating and sputtering. For comparison, the uncoated one was treated similarly. Table 2 shows the results of an examination of the state of cracking of the resin after heating by coating Cr among the coated metals Cr, Ti, Ni, Co under the conditions shown in Table 1. The test is carried out by examining the number of crack generation materials with respect to the standing time after heating. The denominator is the number of materials and the numerator is the number of crack generation materials. As can be seen from Table 2, no reflow crack occurred in the sample coated with the metal film.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

As described above, according to the present invention, a lead frame having one side or both sides coated with a metal by dry coating is manufactured and used in a resin-sealed semiconductor device, so that Adhesion is very strong, and even if moisture is absorbed, the adhesive does not peel off or break, and moisture does not accumulate at the interface. No cracks occur. Moreover, since no peeling of the adhesive occurs, stress concentration at the corners of the die pad does not occur, and a semiconductor device having extremely high reliability can be provided. Incidentally, the conventional method can also be applied to dry coating, and inexpensive manufacturing is possible.

[Brief description of drawings]

1A and 1B are views showing a manufacturing process of a resin-sealed semiconductor device including a method for manufacturing a lead frame of the present invention.

2A, 2B, and 2C are cross-sectional views of the lead frame of the present invention.

FIG. 3 is a cross-sectional view of a semiconductor device using the lead frame of the present invention.

FIG. 4 is an explanatory cross-sectional view showing an embodiment of a conventional semiconductor device.

FIG. 5 is a morphological view of a conventional die pad.

FIG. 6 is a configuration diagram of a conventional die pad.

FIG. 7 is a morphological view of a conventional die pad.

[Explanation of symbols]

 1: Lead frame 1a: Inner lead 1b: Outer lead 1c: Lead 2: Semiconductor chip 3: Die pad 4: Die bonding part (Ag plating) 5: Electrode pad (Ag plating) 6: Bonding wire 7: Resin sealing 8: Solder 9: Circuit board 10: Crack 11: Concavo-convex shape 12: Cutout portion 13: Organic resin 14: Dry coating film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Misao Hashimoto 1618 Ida, Nakahara-ku, Kawasaki City, Kanagawa Inside Nippon Steel Corporation Advanced Technology Research Laboratories (72) Yuji Kubo 1618 Ida, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Advanced Technology Research Laboratories, Nippon Steel Co., Ltd. 1618 Ida, Nippon Steel Corporation Advanced Technology Research Laboratories

Claims (4)

[Claims] 1. A lead frame comprising a lead having a die pad in the center thereof, wherein one surface of the die pad and the lead has a modulus of elasticity of 1 × 10 ^{11 to} 3 × 10 ¹¹ Pa and a metal coating having a thickness of 0.1 μm to 30 μm. A lead frame, characterized in that a part or all of the die pad on the side facing the metal coating and the tips of the inner leads are plated with Ag having a thickness of about 5 μm. 2. On the surface of the die pad and the lead on the side opposite to the surface having the metal coating on one surface, a part or all of the Ag-plated die pad and the portion excluding the tip of the inner lead have an elastic modulus. 1 x 10 ^{11 to} 3 x
The lead frame according to claim 1, further comprising a metal coating having a thickness of 10 ¹¹ Pa and a thickness of 0.1 μm to 30 μm. 3. A lead frame, characterized in that at least one surface of a strip-shaped lead frame material processed into a product thickness is dry-coated with a metal film and the material is formed into a lead frame shape by a pressing method and an etching method. Manufacturing method. 4. A lead frame material, which has been processed to a product thickness, is dry-coated on both sides with a metal coating, the metal coating on a predetermined portion of the surface of the material is removed, and then a lead frame shape is formed by an etching method. A method for manufacturing a lead frame, which comprises processing.