JP2879629B2 - Lead frame and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead frame and a method of manufacturing the same, and more particularly, to a lead frame structure for mounting a semiconductor integrated circuit chip.

[0002]

2. Description of the Related Art In the field of high-output type semiconductor integrated circuits, in order to use high power, a lead for current supply uses a power plate instead of a bonding wire in order to prevent an increase in inductance at a connection portion with a wire. In many cases, a method of connecting to a bonding pad of a chip through a chip is used. In addition, in order to reduce the number of leads in accordance with high integration, when a plurality of pads are dropped on a ground line, a method of providing a ground plate and connecting all of them to the ground line has become effective.

[0003] Further, since the calorific value is large, a large heat radiating plate made of a metal plate having good heat radiating properties tends to be required instead of the die pad.

In such a power device, as shown in FIG. 4, one example is a ground plate 1 for grounding.
The power plate 2 and the power plate 14 are electrically connected to the lead frame main body 15 by welding via tongues provided at predetermined positions, respectively, to form a lead frame structure. Here, reference numeral 13 denotes an insulating film interposed for mutual electrical insulation.

[0005] For this reason, there is a case where each component is distorted due to the influence of the bending accuracy of the tongue piece and the accuracy of the welding position, and the welding portion is peeled off.

The ground plate 12, the power plate 14, and the lead frame body 15 are usually made of copper or a copper alloy, and copper has a low electric resistance. There is a problem that not only the welding itself is difficult, but also the welding strength is weak, so that reliable welding is difficult.

[0007] Furthermore, if welding is to be performed, expensive welding equipment is required, which raises the problem of increasing production costs.

[0008]

As described above, in the conventional power device, the connection between the grounding ground plate, the power plate, and the like and the lead frame main body is established through the tongue pieces provided at predetermined portions. Since welding is performed, welding strength is weak and reliable welding is difficult, and connection failure and deformation are apt to occur, which has caused a decrease in reliability as a device.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a highly reliable lead frame in which a conductive plate such as a ground plate or a power plate is securely connected to a lead frame body. I do.

[0010]

Therefore, in the lead frame of the present invention, at least one conductive plate is laminated and fixed to a lead frame main body in which a plurality of leads are arranged via an insulating layer. Electrical connection is achieved by joining the conductive plate and at least one lead of the lead frame body via a bump formed by metal plating. Desirably, metal plating made of the same metal as the bumps is formed in a region where the bumps are not formed on the conductive plate and the side of the lead frame body where the bumps are not formed.

Preferably, the noble metal plating formed on the conductive plate and the lead frame body is gold plating.

In the method for manufacturing a lead frame according to the present invention, a bump is formed on one of the conductive plate and the corresponding region of the lead of the lead frame main body, and the conductive plate and the lead frame main body are heated via the bump. Crimping is performed, and the conductive plate is laminated on the lead frame body so as to be connected to at least one lead of the lead frame body.

Preferably, a plating layer of the same metal is formed not only on the bump but also on a region corresponding to the bump.

[0014]

According to the above configuration, since the electrical connection between the conductive plate and the constituent metal of the lead frame main body is achieved by thermocompression bonding via the bumps, it is easy to join, extremely strong and reliable electrical connection is possible. Becomes

Further, since the bumps are formed by the metal plating step, the steps are simplified and the cost is reduced.

In addition, by using a conductive plate made of a low-resistance copper foil having good workability and flexibility and bonding via bumps formed by gold plating, fine and highly accurate connection can be achieved. In addition, the tongue piece used in the lead frame of the conventional example shown in FIG. 4 is not required, so that the bending process is not required, the displacement does not easily occur, and no mechanical stress is applied. There is no peeling or distortion.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing a main part of a power device formed by the method of the first embodiment of the present invention.

In this device, a lead frame is formed of a copper plate serving as a ground plate via a gold bump 3P formed in a predetermined region of a lead frame main body 5 mainly composed of copper. The conductive plate 2 and a second conductive plate 4 laminated on the upper layer, connected to a power supply line and connected to a power supply line and serving as a power plate made of a copper plate are thermocompressed to achieve an electrical connection therebetween. It is a feature. That is, this device
A first conductive plate 2 on which a semiconductor chip 1 is mounted and which also functions as a ground plate, and a first conductive plate 2 as a power plate fixed to an upper layer via an insulating layer 11 made of a polyimide film and connected to a power supply line. 2 conductive plate 4
And a lead frame main body 5 similarly fixed to the upper layer via an insulating layer 11 and provided with a plurality of inner leads so as to surround the semiconductor chip mounting portion of the first conductive plate 2. It is sealed by a sealing resin P.

A gold plating layer 3 and a gold bump 3P are formed at the tip of the corresponding inner lead of the lead frame body 5, and the first or second conductive plate is formed via the gold bump 3P. The electrical connection is achieved by thermocompression-bonding the tongue pieces provided in the corresponding areas and having the gold plating layer 3 formed thereon. Furthermore, each inner lead is connected via a bonding wire so as to connect to each bonding pad on the semiconductor chip.

Next, the manufacturing process of this device will be described.

First, as shown in FIG. 2 (a), a strip material is processed by a normal stamping method, and an inner lead 6, an outer lead 7, and a tie bar 8 facing the semiconductor chip mounting area a. It is molded into a normal lead frame shape including the above. 9 is a sidebar. Next, a coining process is performed to secure a flat width at the tip of the inner lead. Then, the tip is plated with gold, and then a predetermined area of the inner lead 6 is further plated with gold to form a bump 3P.
To form M indicates a gold plating area. At this time, if necessary, an insulating tape may be attached and fixed so as to avoid the bonding area at the tip of the inner lead.

On the other hand, as shown in FIG. 2 (b) and FIG. 2 (c), a copper plate having good heat dissipation is processed by a normal stamping method, and a first plate serving as a ground plate is formed. A conductive plate 2 and a second conductive plate 4 as a power plate connected to a power supply line are formed. After punching the first and second conductive plates 2 and 4 so as to have a tongue 4T, a gold plating layer 3 is formed on the surface of the tongue, and the surface excluding the joining area is formed. Is covered with an insulating polyimide film 11.

Then, as shown in FIG. 2 (d), the semiconductor chip 1 is fixed to the center of the first conductive plate 2 with an adhesive, and the first conductive plate and the second conductive plate are fixed. Then, the lead frame main bodies 5 are sequentially laminated, and the tongue pieces of the first and second conductive plates are electrically connected to the gold bumps 3P of the inner leads of the lead frame main body 5 by thermocompression bonding. The temperature of the thermocompression bonding is 400 to 600 ° C.

Thereafter, wire bonding and resin sealing are performed to complete the device as shown in FIG.

In the device thus formed, the lead and the conductive plate are welded via the gold bump 3P formed on the lead by plating, so that the welding operation is easy, there is no peeling, the cost is low and the cost is high. Accurate connection can be performed reliably.

In the above embodiment, the gold bumps are formed on the inner leads in the bonding region. However, bumps may be formed on the conductive plate side. Other metal plating layers such as a Pd plating layer and a Sn plating layer may be used. The formation of the bump is not limited to the plating method, but may be an adhesion method or the like.

In the above embodiment, the power plate and the ground plate are formed of a single conductive plate, but may be formed by forming a desired pattern on an insulating substrate such as a film carrier. good. At this time, the pattern of the signal line and the ground line is formed by patterning a copper thin film formed by sputtering and electrolytic plating by a photolithography method, after performing a surface treatment on the resin film surface, and directly pressing a thin copper foil. A copper thin film was formed by forming a copper thin film by fixing it via an adhesive or by patterning it, or by applying an insulating resin such as a polyimide resin on the surface of a thin copper foil and curing it. Thereafter, a method of patterning by a photolithography method or the like can be similarly employed.

Embodiment 2 Next, a second embodiment of the present invention will be described in which the ground plate and the power supply plate are made of copper foil.

This lead frame is characterized in that the first and second conductive plates are made of copper foil, and a gold bump layer 3P is formed on the lead frame main body in a region where the first and second conductive plates are joined. It is.

That is, as shown in FIG. 3, a first chip made of a copper foil having a thickness of about 0.02 to 0.1 μm, on which the semiconductor chip 1 is mounted and serves as a ground plate.
And a second conductive plate 24 made of a copper foil having a thickness of about 0.02 to 0.1 μm as a power plate connected to a power supply line and laminated on the conductive layer 22 with the insulating layer 11 interposed therebetween. And a lead frame main body 5 having a plurality of inner leads arranged so as to surround the semiconductor chip mounting portion of the first conductive plate 2 and laminated on the upper layer with an insulating layer 11 interposed therebetween. .

The other parts are formed in the same manner as in the first embodiment.

In the device thus formed, in addition to the effects of the first embodiment, since the conductive plate is formed by attaching a polyimide film to a flexible copper foil,
The connection with the lead can be satisfactorily achieved without causing distortion or peeling, and the inductance can be reduced because of low resistance.

In the second embodiment, the power plate and the grounding plate are formed by attaching a copper foil to a polyimide film and performing punching. However, the copper foil is attached to an insulating substrate such as a film carrier. After that, the copper foil may be selectively removed by etching to form a desired pattern. Further, a bump may be formed by forming a copper foil so as to be thick only in a bonding region with the inner lead, and plating a noble metal such as gold on the upper layer. In this case, bumps on the lead frame body are not required.

[0035]

As described above, according to the present invention, at least one conductive plate is laminated on a lead frame main body having a plurality of inner leads arranged thereon via an insulating layer to establish electrical connection. In doing so, the noble metal plating layer is formed in the corresponding area of the conductive plate and the lead frame body, and a bump is formed on either side, and thermocompression bonding is performed through this bump,
Bonding is easy, extremely strong and reliable electrical connection is possible, and a low-cost and highly reliable lead frame can be obtained.

[Brief description of the drawings]

FIG. 1 is a view showing a semiconductor device using a lead frame formed by a method according to a first embodiment of the present invention;

FIG. 2 is a manufacturing process diagram of the semiconductor device.

FIG. 3 is a diagram showing a semiconductor device using a lead frame formed by a method according to a second embodiment of the present invention;

FIG. 4 is a diagram showing a conventional semiconductor device.

[Explanation of symbols]

 Reference Signs List 1 semiconductor chip 2 first conductive plate 3P bump 3 gold plating layer 4 second conductive plate 5 lead frame main body P sealing resin a semiconductor chip mounting area 6 inner lead 7 outer lead 8 tie bar 9 side bar T Tongue piece 11 Polyimide film.

Claims (4)

(57) [Claims] A conductive plate; and a lead frame body laminated on the conductive plate via an insulating layer and having a plurality of leads disposed on a surface of the semiconductor chip such that a tip of the lead frame comes to a periphery of a semiconductor chip. The lead frame according to claim 1, wherein at least one corresponding region between the conductive plate and the lead of the lead frame main body is joined via a bump formed by metal plating. A conductive plate forming step of forming a conductive plate; and a step of forming a plurality of leads on a surface of the semiconductor chip so that the plurality of leads are stacked on the conductive plate via an insulating layer so that a tip of the lead comes to a periphery of a semiconductor chip. A lead frame main body forming step of forming a lead frame main body disposed in the conductive plate and a plating step of forming a bump by a metal plating method on one of the conductive plate and a corresponding region of a lead of the lead frame main body; The conductive plate and the lead frame body are thermocompression bonded via the bumps, and the conductive plate is
Assembling the lead frame main body so as to connect to at least one lead of the lead frame main body. 3. The method for manufacturing a lead frame according to claim 2, wherein the noble metal plating layer covering the bump, the conductive plate, and the area corresponding to the lead of the lead frame body is a gold plating layer. 4. The method according to claim 2, wherein the plating step is a step of forming a plating layer of the same metal as the bumps on both corresponding regions together with the formation of the bumps.
The method for manufacturing the lead frame described in the above.