JPH01184840A - Wireless bonding and equipment therefor - Google Patents

Abstract

PURPOSE:To improve reliability, by pressing the bonding pad of a semiconductor chip at the tip of an inner lead by pressure, connecting a bump and the bonding pad by heating, and connecting at the same time the inner lead and all bonding pads. CONSTITUTION:The tip of an inner lead 4 of a lead frame RF1 for semiconductor device is formed sufficiently thinner than the thickness of material of the lead 4. A semiconductor chip(m) is moved nearer to the lead frame RF1, and bonding pad 8 is brought into contact with a bump 6. While the bump 6 of the lead 4 and the pad 8 of the chip (m) are pressed by a necessary pressure P, the boundary surface between the bump 6 and the pad 8 is heated by applying heat H at a necessary temperature, from the rear of the bonding surface of the lead 4. Eutectic bonding is formed on the boundary surface between the bump 6 and the pad 8, which are electrically connected. Thereby the reliability is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a wireless bonding method and a wireless bonding device.

<Prior Art> Wire bonding method and wireless bonding method are known as typical conventional methods for bonding a semiconductor chip to a lead frame for a semiconductor device.

The former wire bonding method is shown in FIG. 7(A).

As shown in (B), the pad 31 of the lead frame RF
A semiconductor chip m is fixed to the bonding pad 3 of the semiconductor chip m by thermocompression bonding or a conductive adhesive, etc.
2 and the tips of the inner leads 33 of the lead frame RF are electrically connected one by one using bonding wires 34 such as gold wires.

In the latter wireless bonding method, as shown in FIG. 8, a tape carrier-type lead frame 41 is formed by etching copper foil pasted on a polyimide tape 44, and a layer is attached to the tip of the inner lead. Bonding pad 4 of semiconductor chip m to bump 42
For example, JP-A-60-130
Publication No. 147 (Title of invention: “Method for manufacturing a semiconductor device”)
describes a technique related to the width of the inner lead in such a wireless bonding method.

Unlike the former wire bonding method, the latter wireless bonding method uses the bonding wires 34 to perform bonding one by one sequentially. Since all of the bumps 42 can be connected at the same time, bonding time can be significantly shortened.

<Problems to be Solved by the Invention> However, in the wireless bonding method, when bonding the bump 42 at the tip of the inner lead to the bonding pad 43 of the semiconductor chip m, it is difficult to prevent the inner lead from absorbing the heat for bonding. It is required to make the inner lead thinner so that the inner lead flexibly corresponds to the shape at the time of bonding, and the lead frame 41 has been formed using W4 foil as a base material. Therefore, since such a lead frame alone has a problem in handling strength, it has been supported by being attached to a polyimide tape 44. However, since polyimide tape is very expensive, there is a problem in that the cost is high.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a wireless bonding method and a wireless bonding device that are advantageous in improving bonding productivity and reliability and reducing costs. purpose.

Means for Solving the Problems> A wireless bonding method according to the present invention includes forming the tips of inner leads of a lead frame for a semiconductor device to be sufficiently thinner than the thickness of the material of the inner leads, and attaching a semiconductor chip to the lead frame. The method is characterized in that the interface between the lead frame and the semiconductor chip is heated from the back side of the bonding surface of the lead frame while pressing the lead frame and the semiconductor chip.

Further, the wireless bonding apparatus according to the present invention includes a lead frame conveying means for step-feeding a semiconductor device lead frame in which the tip of the inner lead is sufficiently thinner than the thickness of the material of the inner lead, with its bonding surface facing downward. , a semiconductor chip supporting means on which the semiconductor chip is placed with the electrode forming surface facing upward, and the semiconductor chip is raised to supply the semiconductor chip to the lead frame;
By descending, the lower end surface contacts the back surface of the bonding surface of the lead frame, and presses the lead frame and the semiconductor chip between them with the semiconductor chip support means, and also presses the lead frame and the semiconductor chip from the back surface of the bonding surface of the lead frame. It is equipped with a pressing heating means for heating.

Effect〉 The effects of the present invention are as follows.

That is, pressing the bonding pad of the semiconductor chip against the tip of the inner lead in the lead frame, and
The tip of the inner lead and the bonding pad are bonded by heating. That is, all the inner lead tips and all the bonding pads are simultaneously connected by just one press and heat.

The thickness of the tip of the inner lead is made sufficiently thinner than the thickness of the material of the inner lead, ensuring the thinness required for directly bonding the bonding pad of the semiconductor chip to the tip of the inner lead. Also, the lead frame as a whole can be thick enough to have the required strength required for its handling, making the above-mentioned direct bonding feasible. Therefore, there is no need to attach and support the lead frame to expensive polyimide tape.

<Example> Hereinafter, an example of the present invention will be described in detail based on the drawings.

First, the process of forming a bumped pattern at the tip of the inner lead will be described with reference to FIG. 1.

FIG. 1A shows a semi-finished state of a quad-shaped lead frame as an example of a lead frame for a semiconductor device. As shown in the figure, the lead frame material RF o
4 immediately inside the tip of the inner lead, which is to be formed in a later process, by punching with a press.
Two slit-shaped relief windows 1 and an outer lead 2 are formed at the same time.

Next, the area corresponding to the tip of the inner lead where a bumped pattern is to be formed in the later process (hatched area)
Then, the thin portion 3 is formed by coining. This state is shown in FIG. 1(B).
It is an enlarged view of a cross section taken along the line E. The escape window 1 is provided to ensure a space for the lead frame material RF to stretch during coining.

Next, as shown in FIGS. 1(C) and 1(D), after forming the inner leads 4 on the lead frame material RF0 by punching with a press, the semiconductor chip is formed in the thin wall portion 3 at the tip of the inner leads 4. A bump 6 for bonding is formed by etching at a position to be bonded to the bonding pad. That is, by etching, the hatched portion 3a in FIG. 1(D) is removed, and a convex portion, that is, a bump 6 is formed at the tip thereof.

Note that the inner lead 4 formed by etching
There is a close relationship between the spacing between the tips of the plate and the thickness of the plate to be etched. For something that is directly connected to the bonding pad of the semiconductor chip, such as the bump 6 at the tip of the inner lead 4, for example, it is about 2 to 3 times the diameter of the bonding wire (25 μm) in the case of the wire bonding method. A plate thickness of approximately 50 to 75 μm is desirable.

For handling purposes, if the lead frame RF is too thin, it will not be possible to secure the required strength.
A lead frame material with a thickness of 0 μm is used.

However, when using lead frame material of this thickness,
This creates a problem in directly connecting the bump at the tip of the inner lead to the bonding pad of the semiconductor chip.
For this reason, as described above, the portion corresponding to the tip of the inner lead is made thin in advance by coining.

Next, after gold plating is applied to the bumps 6 at the tips of the inner leads 4, the central pad 7 of the lead frame material RF0 is removed.

Through the above steps, the production of the lead frame RFI is completed.

Next, the procedure of the bonding work will be explained based on FIG. 2.

As shown in FIG. 2(A), the lead frame RF is fixed at the bonding location with the bumps 6 facing downward. Next, the semiconductor chip m is mounted on the lead frame RF with the electrode forming surface facing upward (face up).
, is supplied to.

The supply is first performed with the bonding pad 8 of the semiconductor chip m separated from the bump 6 by a microscopic dimension 2.Next, the bonding pad 8 of the semiconductor chip m and the lead are separated using a microscope. The relative positional relationship of the frame RF with the bump 6 is imaged and displayed on a monitor display. Then, all the bonding pads 8 are aligned with all the bumps 6 while watching the monitor display. This positioning may be performed by moving the semiconductor chip m, or by moving the lead frame RF, and the movement may be performed manually, or by moving the lead frame RF. It may be done automatically.

After completing this alignment, the semiconductor chip m is moved closer to the lead frame RF, and the semiconductor chip m is moved closer to the lead frame RF, as shown in FIG.
), the bonding pad 8 is brought into contact with the bump 6.

Next, as shown in FIG. 2(C), the inner lead 4
While pressing the bumps 6 and the bonding pads 8' on the semiconductor chip m with the required pressure P, heat H at the required temperature is applied from the back side of the bonding surface of the inner lead 4.
is applied to heat the interface between the bump 6 and the bonding pad 8. By this pressing and heating, a eutectic bond is formed at the interface between the bump 6 and the bonding pad 8, so that the two are bonded and electrically connected.

In addition, as a lead frame, as shown in Fig. 3,
The bumps 6 may be formed to be sharp, and the bonding may be made stronger by piercing the bonding pads 8 with the sharp bumps 6.

Further, in the above embodiment, the semiconductor chip m is bonded in a face-up state, but the bonding may be performed in a face-down state.

Further, in the above embodiment, the lead frame RF.

The inner lead 4 is a bumped inner lead in which a bump 6 is formed at the bonding position with the bonding pad 8 of the semiconductor chip m at the tip thereof, but a bumpless inner lead in which the bump 6 is not formed is used. You can also use it as

4 is a front view of the wireless bonding device, and FIG. 5 is a sectional view of the guide rail portion at the bonding location.

The cross section is almost L-shaped, and the top surface of the stepped part is the lead frame R.
Guide rails 10, which serve as guide surfaces 10a for guiding the FI at i1, are provided facing each other on the left and right (see Figure 5), and the longitudinal center of both guide rails 10 is located at the bonding point BP ( (See Figure 4). This bonding point BP is located at the center of both guide rails 10 in the Y direction (left-right direction), and is located at the same height as the guide surface 10a of the guide rail 10 in the vertical direction.

As the lead frame RF, one having a structure similar to the lead frame RF described above is used. However, whereas the previous lead frame RF had a quad shape, the lead frame RF of this embodiment has a rectangular shape. The guide rail IO connects this strip-shaped lead frame RF to its bonding surface, that is, the bump 6.
Guide the placement so that it faces down.

Lead frame RF,
A lead frame conveying means A for feeding the lead frame RFt in steps is provided on the upper side in the conveying direction X of the lead frame RFt.

Below the bonding point BP, a semiconductor chip support is placed on which a semiconductor chip m is placed with the electrode formation surface, that is, the bonding pad 8 facing upward (face up), and which rises to supply the semiconductor chip m to the lead frame RF. Means B is provided.

Furthermore, by descending above the bonding point BP, the lower end surface is a lead frame RF.

in contact with the back side of the bonding surface of lead frame RF8
A pressing/heating means C is provided for sandwiching and pressing the semiconductor chip m and the semiconductor chip supporting means B, and for heating from the back side of the bonding surface of the lead frame RF t.

First, the lead frame conveying means A will be explained.

Below the guide rail IO, a vertical lifting air cylinder 13 is installed upright on a movable base 12 that is attached to a stepping motor 11 for step feeding via a ball screw and moves back and forth along the X direction, and its piston rod A horizontal feed plate 14 is fixed to the
Taper pins 15 are erected upward at two locations at the ends of the. Each of these taper pins 15 is inserted into a long hole 10b formed vertically through the guide surface 10a of both guide rails 1O.

The tapered pin 15 is configured such that a tapered portion of its upper end is inserted from below into the pair of left and right perforations 30 of the lead frame RFz placed on the guide surfaces 10a of both guide rails 10. ing.

Stepping motor 11 and lifting air cylinder 13
■ Advancement of the taper pin 15 due to normal rotation of the stepping motor 11, ■ Lowering of the taper pin 15 due to contraction of the lifting air cylinder 13, ■ Retraction of the taper pin 15 due to reverse rotation of the stepping motor 11, ■ Advancement of the taper pin 15 due to the contraction of the lifting air cylinder 13, ■ The tapered pin 15 is sequentially controlled in the order in which the taper pin 15 is raised due to the elongation of the pin.

When the lifting air cylinder 13 is at the end of its contraction stroke, a portion of the taper of the taper pin 15 is located below the guide surface 10a of the guide rail 10, and when the lifting air cylinder 13 is at the end of its extension stroke. teeth,
A portion of the taper is configured to be located above the guide surface 10a of the guide rail 10.

Through the above-described sequence control, the tapered portion of the taper pin 15 is configured to perform tact movement drawing a rectangular locus, thereby feeding the lead frame RF2 in steps.

A notch 10c is formed in the guide rail lO at the bonding point BP, and the notch 10c is moved up and down in conjunction with the up and down movement of the feed plate 14, and when it is lowered, both side edges of the lead frame RF2 are connected to the guide surface of the guide rail 10. A pair of left and right lead frame holding plates 16 are provided to be clamped and fixed to the lead frame 10a. As for the mechanism for this interlocking, any suitable mechanism may be adopted, and illustration and description thereof will be omitted.

Next, the semiconductor chip support means B will be explained.

An X table 18 that reciprocates in the X direction by an X direction stepping motor 17; a Y table 20 that is provided on the X table 18 and that reciprocates in the Y direction by a Y direction stepping motor 19; A stage box 21, an X-direction stepping motor 22 provided in the stage box 21, and a
It is composed of a bonding stage 23 and the like that are moved up and down by a directional stepping motor 22. The bonding stage 23 has a vacuum suction path opened on its upper surface, and is configured to suction and hold the semiconductor chip m placed on the upper surface.

X direction stepping motor 17. The Y-direction stepping motor 19 is configured to be driven by an X-Y twisttake (not shown).

The pressing and heating means C includes a pressing air cylinder 24 provided vertically above the bonding location BP, and a tool holding block 2 attached to the piston rod.
5, a bonding tool 26 provided on the lower surface of the tool holding block 25, a heater 27 built into the bonding tool 26, and a reaction force against the downward movement of the tool holding block 25 due to the extension of the pressing air cylinder 24. It is composed of a tension spring 28 and the like for cushioning. The bonding tool 26 is configured to have approximately the same size as the semiconductor chip m, and is located directly above the vacuum suction port of the bonding stage 23.

Note that the inner lead 4 in the lead frame RF
A microscope (not shown) for photographing the relative positional relationship between the bump 6 of the semiconductor chip m and the bonding pad 8 of the semiconductor chip m on the bonding stage 23, and a monitor display (not shown) for displaying the image photographed by this microscope. (not shown) is provided.

Next, the operation of the wireless bonding apparatus of this embodiment will be explained.

When the elevating air cylinder 13 is extended and a part of the taper of the taper pin 15 is projected above the guide surface 10a of the guide rail 10, the lead frame holding plate 16 is moved upward from the guide surface 10a in conjunction with this. Separate. Note that the heater 27 in the press heating means C is constantly energized, and the bonding tool 26 is controlled to a predetermined temperature.

In this state, a pair of left and right perforations 30 in the first unit lead frame portion of lead frame RF
is first manually engaged with the taper portion of the taper pin 15.

Next, the stepping motor 11 in the lead frame transport means A is driven to rotate in the normal direction, and the movable base 12.degree. lifting air cylinder 13. The feed plate 14 and the pair of taper pins 15 move forward together in the X direction. Each taper pin 15 moves within the long hole 10b of the guide rail 10, and when it reaches the bonding location BP, the stepping motor 11 is stopped. As a result, the first unit lead frame portion is transported to the bonding location BP.

Next, the lifting air cylinder 13 contracts, and the feeding plate 14
．． The tapered bins 15 descend together.

Due to this lowering, a part of the taper of the taper pin 15 retires below the guide surface 10a of the guide rail 10. When the taper pin 15 is retired downward, the lead frame holding plate 16 lowers in conjunction with the lead frame holding plate 16 to clamp both side edges of the lead frame RF between the guide surface 10a of the guide rail 10 and fix the lead frame RFI. (See Figure 5).

Next, the stepping motor 11 is driven in reverse, and the feed plate 14. The taper pins 15 move backward together, reach the origin position, stop, and wait until the next step feed (see FIG. 4).

Pre-alignment in the X direction, Y direction and θ direction is completed in a pre-alignment section (not shown), and the semiconductor chip m
is sucked and transported by a traverse arm (not shown), and as shown in FIG. 6(A), the semiconductor chip m is placed on the vacuum suction port on the top surface of the bonding stage 23, and the semiconductor chip m is suction-held on the bonding stage 23 in a face-up state.

Next, the bonding stage 23 is raised by normal rotation driving of the Z-direction stepping motor 22, and the bonding pad 8 of the semiconductor chip m thereon is moved downward from the bump 6 of the inner lead 4 as shown in FIG. 6(B). When the Z-direction stepping motor 22 comes to a position separated by a minute distance l (for example, 0.5 mm), the Z-direction stepping motor 22 is stopped.

Next, the bump 6 at the tip of the inner lead 4 in the lead frame RF photographed with a microscope.
The relative positional relationship between the semiconductor chip m and the bonding pad 8 is displayed on the monitor display.
Operate the joystick to drive the X direction stepping motor 17
．． The Y-direction stepping motor 19 is driven to align each bump 6 and each bonding pad 8 in both the X and Y directions.

After this alignment is completed, when a start switch (not shown) is turned on, the Z-direction stepping motor 22 of the semiconductor chip support means B is again driven in normal rotation, the bonding stage 23 is raised again, and the bonding pad 8 of the semiconductor chip m is The Z-direction stepping motor 22 is stopped when the bump 6 of the inner lead 4 comes into contact with the bump 6 of the inner lead 4 (the sixth
(See figure (C)).

Next, the pressing air cylinder 24 of the pressing heating means C is extended, the tool holding block 25 is lowered, and the heater 27
The bonding tool 26, which has been heated to a predetermined temperature, joins the bump 6 and the bonding pad 8, as shown in FIG. 6(D).

In this case, as the pressing air cylinder 24 expands, the buffering tension spring 28 gradually expands and acts as a reaction force against the expansion force of the pressing air cylinder 24, and the lowering speed of the bonding tool 26 gradually decreases. This avoids impact on the semiconductor chip m.

When a predetermined period of time has elapsed since the pressing air cylinder 24 reached the end of its extension stroke, the pressing air cylinder 24 is contracted and the bonding tool 26 is raised. At the same time, the negative pressure applied to the vacuum suction port of the bonding stage 23 is released, and the suction and holding of the semiconductor chip m by the bonding stage 23 is released. After this suction holding is released, the Z direction stepping motor 22 is driven in reverse, and the bonding stage 23
descends.

Next, when the elevating air cylinder 13 in the lead frame conveying means A is extended, the taper pin 15 that has been waiting at the origin position rises, and the predetermined perforation 30 in the unit lead frame portion that is the next bonding target is lifted. A part of the taper of the taper bottle 15 is engaged with the taper.

With the above steps, one cycle of bonding work for the unit lead frame portion is completed.

Thereafter, operations similar to those described above are repeated.

<Effects of the Invention> According to the present invention, the bump and the bonding pad are connected by pressing and heating the bonding pad of the semiconductor chip on the tip of the inner lead. Productivity can be improved because all inner leads and all bonding pads are connected simultaneously. Furthermore, the number of connection points is the same as the number of bonding pads on the semiconductor chip, which is half that of the wire bonding method, so that the reliability of bonding can be improved.

Further, since it is not necessary to use expensive polyimide tape, cost reduction can be promoted.

[Brief explanation of the drawing]

1 to 3 illustrate an embodiment of the wireless bonding method according to the present invention, in which FIG. 1 is an explanatory diagram of the lead frame manufacturing process, FIG. 2 is an explanatory diagram of the bonding process, and FIG. 3 is an explanatory diagram of the bonding process. FIG. 3 is a diagram showing another aspect of the lead frame. 4 to 6 explain an embodiment of the wireless bonding device according to the present invention, FIG. 4 is a partially cutaway front view of the wireless bonding device, FIG. 5 is a sectional view of the guide rail portion, FIG. 6 is an explanatory diagram of the operation. FIGS. 7 and 8 are explanatory diagrams of conventional examples. 4... Inner lead 6... Bump 8... Ponding pad 27... Heater A... Lead frame conveying means B... Semiconductor chip supporting means C... Pressing heating means m... Semiconductor chip RF,,RF,...Lead frame applicant Mitsui Hytic Co., Ltd. Applicant Dainippon Screen Mfg. Co., Ltd. Agent Patent attorney Tsutomu Sugitani Figure 1 CB) Figure 1 (D) Figure 3 Figure 4 Figure 5■

Claims (2)

[Claims] (1) The tip of the inner lead of a lead frame for a semiconductor device is formed to be sufficiently thinner than the thickness of the material of this inner lead, and a semiconductor chip is supplied to the lead frame, and while pressing the lead frame and the semiconductor chip, . A wireless bonding method, characterized in that the interface between the lead frame and the semiconductor chip is heated from the back side of the bonding surface of the lead frame. (2) A lead frame transport means for step-feeding a lead frame in which the tip of the inner lead is sufficiently thinner than the thickness of the material of the inner lead with its bonding surface facing downward; and a lead frame transporting means for transporting a semiconductor chip with its electrode forming surface facing upward. A semiconductor chip supporting means is placed and raised to supply the semiconductor chip to the lead frame, and by lowered, the lower end surface thereof comes into contact with the back surface of the bonding surface of the lead frame, and the semiconductor chip is connected to the lead frame and the semiconductor chip. A wireless bonding device comprising: a pressing/heating means that presses the lead frame by sandwiching it between the chip support means and heats the lead frame from the back side of the bonding surface of the lead frame.