JP2000232187A - Manufacture of lead frame - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent disconnections of a support bar and a dam bar caused by a vibration when ultrasonically bonded. SOLUTION: In the case of bonding a radiation plate 8 to backsides of pads 3 of a lead frame 1 by an ultrasonic bonding, the frame 1 is ultrasonically bonded in a state of being pressed by a support plate 13a and a retaining plate 19 mounting elastic materials 18a, 18b at contact surface sides of the frame 1. When ultrasonically bonded, the frame 1 is bonded in a state such that parts except the pads 3 of the frame 1 are pressed by elastic materials 18a, 18b. Thus, since the vibration when ultrasonically bonded is absorbed by the materials 18a, 18b, transmission of the ultrasonic vibration to the frame can be suppressed, and hence a disconnection due to the vibration when bonded can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a lead frame for a semiconductor device, and more particularly to a method for manufacturing a lead frame in which a heat radiating plate is bonded to the back surface of a pad by ultrasonic bonding. .

[0002]

2. Description of the Related Art In recent years, as semiconductor integrated circuits have become more multifunctional and highly integrated, an increase in power consumption of a semiconductor element and an increase in heat generation due to the increase in power consumption have become a serious problem as a cause of impairing the reliability of a semiconductor device. Is coming. As a countermeasure against such an increase in the amount of heat generated by the semiconductor element, the back surface of the semiconductor element mounting surface of the lead frame which is the base material of the semiconductor device is
A lead frame equipped with a heat sink made of a high thermal conductor is used.

Now, an example of a lead frame will be described. As shown in FIG. 4, a lead frame 1 has a pair of connecting strips 2 arranged in parallel, and a semiconductor arranged substantially at the center between the connecting strips 2. Pad 3 for mounting elements
And a support bar 4 supporting the pad 3, one end of which is connected to the pad 3 and the other end of which is connected to the connecting strip 2.
And an inner lead 5 arranged around the pad 3 and extending radially outward, and a dam bar 6 connecting the adjacent inner leads 5 and connecting a root portion to the connecting strip 2.
And an outer lead 7 connected to each of the inner leads 5. As described above, the heat radiating plate 8 having an outer diameter substantially equal to the outer diameter of the pad 3 is mounted on the back surface side of the semiconductor element mounting surface of the pad 3.

As shown in FIG. 5, a semiconductor element 9 is then mounted on the lead frame 1 on which the heat radiating plate 8 is mounted, as shown in FIG. After connecting the electrode of the semiconductor element 9 and the inner lead 5 with the bonding wire 10, the sealing resin 11 is formed.
A necessary region including the semiconductor chip 9 and the bonding wire 10 is sealed with a resin, and the outer lead 7 is formed into a desired shape.
2 is obtained.

[0005] By the way, when joining the lead frame 1 and the heat sink 8 described above, joining with an insulating adhesive tape, welding, or joining by caulking has been used so far. Due to the thermal history and mechanical shock at the time of joining, the reliability of the lead frame, and eventually the semiconductor device, may be reduced.
Further, when an adhesive material such as an insulating adhesive tape is used, there is a problem that the cost is increased by the material.

Therefore, in recent years, as disclosed in Japanese Patent Application Laid-Open No. 8-125092, the use of ultrasonic bonding when attaching a heat sink to a lead frame has attracted attention.

Here, an example of the ultrasonic bonding method will be described. First, the lead frame 1 and the heat radiating plate 8 are separately formed, and as shown in FIG. 3A, the heat radiating plate 8 is placed in the concave portion 14 provided on the upper surface of the support base 13. Here, the outer diameter of the recess 14 is substantially equal to the outer diameter of the radiator plate 8, and a number of small projections 15 are formed on the bottom surface of the recess 14 in contact with the radiator plate 8.

Next, the heat radiating plate 8 and the pad 3 of the lead frame 1 are aligned with each other, and the support base 13 is placed so that the rear surface side of the semiconductor element mounting surface of the pad 3 and the heat radiating plate 8 abut and overlap. The lead frame 1 is placed thereon. Note that a pressing tool 16 is disposed above the pad 3.
The pressure tool 16 is connected to an ultrasonic horn (not shown). Also, a large number of small projections 17 are formed on the contact surface of the tip of the pressure tool 16 with the pad 3.

Then, as shown in FIG. 3B, the pressing tool 16 is lowered to bring its tip into contact with the pad 3, and the small projection 17 is cut into the surface of the pad 3. At this time, the small projection 15 formed on the bottom surface of the concave portion 14 bites into the back surface of the contact surface of the heat sink 8 placed on the concave portion 14 of the support plate 13 with the pad 3. In this case, the portion of the lead frame 1 other than the pad 3 is free from any pressure. Then, while the pad 3 is pressurized by the pressurizing tool 16 in this way, an ultrasonic electric signal is transmitted by an ultrasonic oscillator (not shown), and this is converted into mechanical vibration by an ultrasonic vibrator. Then, the mechanical vibration is applied to the pressing tool 16 through the ultrasonic horn, and the lead frame 1 is
Ultrasonic vibration is applied to the pad 3 of FIG. Then, at the contact surface between the pad 3 and the heat radiating plate 8, the oxide film covering each surface is broken, and an activated metal surface appears. Further, since the temperature of the pole portion at the boundary increases due to friction, the distance between the active atoms is reduced and metal bonding is performed. As a result, the pad 3 of the lead frame 1 and the heat sink 8 are solid-phase bonded. is there.

According to such a bonding method utilizing ultrasonic vibration, heat is hardly generated at the time of bonding, so that no heat history is generated in the lead frame, and the lead frame is not exposed to mechanical shock. As a result, the reliability of the semiconductor device can be improved. Further, since no joining material is required, the manufacturing cost can be reduced.

[0011]

However, in ultrasonic bonding, since ultrasonic vibrations at the time of bonding are transmitted to the entire lead frame 1, as a result, the portion of the lead frame 1 where the strength is weak, specifically, usually The stress caused by the ultrasonic vibration is concentrated on the connecting portion between the support bar 4 and the dam bar 6 which are formed narrower than the other lead portions and the connecting strip 2, and as a result, a disconnection occurs at this portion. There was a problem that it would occur.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to perform ultrasonic bonding while pressing a lead frame by using a member that absorbs vibration generated during ultrasonic bonding. Thus, transmission of ultrasonic vibration to each part of the lead frame is suppressed, and disconnection of each part of the lead frame due to vibration at the time of ultrasonic bonding is prevented.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a lead frame, wherein a heat sink is bonded by ultrasonic bonding to a back surface of a semiconductor element mounting surface of a pad of the lead frame.
At the time of ultrasonic bonding, bonding is performed in a state where a portion of the lead frame other than the pad is pressed with an elastic material.

As the material of the elastic material, any material can be used as long as it can absorb vibrations, such as rubber materials such as synthetic rubber and natural rubber, as well as elastic plastics, fluorine-based and urethane-based resins.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. First, a copper-based material such as A194 or an iron-based material such as A42 is punched or etched by a press to shape the lead frame 1 as shown in FIG.

In addition to the shape processing of the lead frame 1, the shape processing of the heat sink 8 is performed. Here, as the material of the heat radiating plate 8, a metal having good thermal conductivity such as copper and copper alloy, aluminum, nickel, chromium, zinc and their alloys, or various ceramics is used. In this embodiment, the heat radiating plate 8 is a pad 3 of the lead frame 1.
Are formed in individual pieces having substantially the same outer diameter as.

Next, the lead frame 1 and the heat radiating plate 8, which are separately formed, are ultrasonically bonded. In this embodiment, joining is performed using a tool as shown in FIG. First, a support plate 13 for mounting the lead frame 1
a will be described. Lead frame 1 of support plate 13a
A concave portion 14 for mounting the heat sink 8 is provided substantially at the center of the mounting surface.
The elastic member 18a made of silicone rubber is attached to a portion excluding the concave portion 14a. Here, the outer diameter of the concave portion 14a is substantially equal to the outer diameter of the heat sink 8, and a number of small projections 15a are formed on the bottom of the concave portion 14 in contact with the heat sink 8. Further, in the present embodiment, the sum of the depth of the concave portion 14a of the support plate 13a and the thickness of the elastic member 18a is formed so as to be approximately the same as or slightly smaller than the height of the heat radiating plate 8.

Further, in the present embodiment, a pressing plate 19 for holding the lead frame 1 in pair with the support plate 13a is used at the time of ultrasonic bonding. This holding plate 19
A through-hole 20 is provided at a position substantially corresponding to the pad 3 of the lead frame 1 at the center of the lead frame 1.
An elastic member 18b made of silicone rubber is attached to a portion except for. A pressing tool 16 a corresponding to the outer diameter of the pad 3 and having an outer diameter smaller than the outer diameter of the through hole 20 is disposed above the pressing plate 19.

Next, a joining method using these tools will be described. First, as shown in FIG. 2A, a concave portion 1 formed on the mounting surface of the lead frame 1 of the support plate 13a.
A heat radiating plate 8 is placed on 4a, the heat radiating plate 8 is aligned with the pad 3 of the lead frame 1, and the back surface of the semiconductor element mounting surface of the pad 3 is in contact with the heat radiating plate 8 so as to overlap. The lead frame 1a is placed on the elastic member 18a of the support 13a.

The pressing plate 1 is provided on the entire surface of the lead frame 1 except for the pads 3 on the side opposite to the heat radiating plate 8 mounting surface.
The surface of the elastic material 18b of No. 9 is brought into contact with and pressed. In this embodiment, the pressing force is increased by using the spring 21 for pressing.

Next, the pressing tool 16a disposed above the holding plate 19 is lowered through the through hole 20 of the holding plate 19. The pressure tool 16a is connected to an ultrasonic horn (not shown), and a number of small projections 17a are formed on the contact surface of the pressure tool 16a with the pad 3 at the tip.

Then, as shown in FIG. 2B, the tip of the lowered pressing tool 16a is brought into contact with the pad 3, and the small projection 17a is cut into the surface of the pad 3. At this time, a small projection 15a formed on the bottom surface of the concave portion 14a cuts into the back surface of the contact surface of the heat radiating plate 8 placed on the concave portion 14a of the support plate 13a. Then, while the pad 3 is pressurized by the pressurizing tool 16a, an ultrasonic electric signal is transmitted by an ultrasonic oscillator (not shown), and this is converted into mechanical vibration by an ultrasonic vibrator. Then, the mechanical vibration is applied to the pressing tool 16a through the ultrasonic horn, and the ultrasonic vibration is applied to the pad 3 of the lead frame 1 via the pressing tool 16a. 8 is solid-phase bonded.

Thereafter, the pressing of the holding plate 19 is released,
The lead frame 1 on which the heat radiating plate 8 is mounted is sent to the subsequent process, and the semiconductor element 9 is mounted on the surface of the pad 3 of the lead frame 1 opposite to the surface on which the heat radiating plate 8 is mounted, using an adhesive such as silver paste. After the electrodes of the semiconductor element 9 and the inner leads 5 are connected by the bonding wires 10, a necessary area including the semiconductor chip 9 and the bonding wires 10 is resin-sealed with the sealing resin 11.
To separate the outer leads 7 and separate the support bar 4 from the connecting strip 2. Then, by forming the outer lead 7 into a desired shape,
The semiconductor device 12 as shown in FIG. 5 is obtained.

In this embodiment, the elastic members 18a and 18b are mounted on both the support plate 13a and the pressing plate 19 on the contact surfaces of the lead frame 1, but the elastic members 18a and 18b are mounted on only one of the sides. It may be. Although the spring 21 is used to increase the pressing force of the holding plate 19, this may be performed by, for example, a fluid pressure mechanism. Further, when a sufficient pressing force can be secured by the weight of the holding plate 19, the pressing is particularly performed. There is no need to add a mechanism to increase the pressure.

[0025]

The present invention is embodied in the form described above and has the following effects.

At the time of ultrasonic bonding, the bonding is performed in a state where a portion of the lead frame other than the pad is pressed with an elastic material, so that the elastic material absorbs vibration at the time of ultrasonic bonding. The transmission of ultrasonic vibration to the substrate can be suppressed, thereby making it possible to prevent disconnection due to vibration during ultrasonic bonding.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing a conventional example.

FIG. 4 is a view showing a lead frame.

FIG. 5 illustrates a semiconductor device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lead frame 2 Connecting strip 3 Pad 4 Support bar 5 Inner lead 6 Dam bar 7 Outer lead 8 Heat sink 9 Semiconductor element 10 Bonding wire 11 Sealing resin 12 Semiconductor device 13, 13a Support base 14, 14a Recess 15, 15a Small protrusion 16, 16a Pressure tool 17, 17a Small protrusion 18a, 18b Elastic material 19 Pressing plate 20 Through hole 21 Spring

Claims (1)

[Claims] In a method for manufacturing a lead frame, a heat sink is bonded to a back surface of a pad of a lead frame on a semiconductor element mounting surface by ultrasonic bonding. A method of manufacturing a lead frame, wherein the bonding is performed in a state where the lead frame is pressed.