JPH04363039A - Manufacture of composite lead frame provided with large bonding strength - Google Patents

Abstract

PURPOSE:To provide a composite lead frame wherein its bonding method is improved, its bonding strength is enhanced, its irregularity is eliminated, its reliability is high and its high pin counts are realized when an outer lead for a TAB tape is thermocompression-bonded to an inner lead for a lead frame. CONSTITUTION:When an outer lead 8 for a TAB tape is overlapped with and thermocompression-bonded to an inner lead 7 for a lead frame, the outer lead 8 for the TAB tape is pushed into a U-shaped groove 12a formed on the surface of the inner lead 7 for the lead frame after the outer lead has been plastic- deformed. A bonding part which is not stripped and which is not irregular is formed. A composite lead frame provided with the bonding part whose bonding strength is high and whose reliability is high can be manufactured.

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 composite lead frame with high bonding strength used for packaging semiconductor devices in the semiconductor electronics industry.

0002

BACKGROUND OF THE INVENTION In recent years, as semiconductor devices have become more highly integrated and highly functional, packages have been increasing in number of pins, and lead frames are required to have even higher precision and finer pitches. This demand is particularly strong in application-specific integrated circuits (AISCs) and the like. Currently, there are press working methods and etching methods as lead frame processing methods, but with these processing methods, it is said that the limit for achieving fine pitch is that the lead width is about 70 to 80% of the plate thickness. In order to make it narrower, it is necessary to reduce the plate thickness. However, as the plate thickness decreases, the strength becomes insufficient, and problems such as lead bending are likely to occur during handling or joining. The limit is plate thickness 0.1-0.15mm
The maximum number of pins is about 200. Note that although the etching method allows finer pitch formation with higher precision than the pressing method, there is a problem in that the manufacturing cost is several times higher than that of the pressing method.

On the other hand, as one measure against increasing the number of pins, TAB technology has been applied. However, T
In the case of AB tape, since the leads are made of Cu foil, its strength is low and problems with alignment etc. tend to occur during external wiring, so it cannot be used in the same way as conventional lead frames.

[0004] On the other hand, as a measure to realize a large number of pins, for example, as disclosed in Japanese Patent Laid-Open No. 62-232948, an insulating film alone or a metal island formed on an insulating film is used. A composite lead frame in which the outer lead part of TAB tape with a pad part is joined to a semiconductor lead frame, and
As described in Japanese Patent No. 2850, the outer lead part of TAB tape is joined to the inner lead part of a semiconductor lead frame, and the TAB tape and Si chip are connected to TAB tape.
A composite lead frame that is collectively joined by AB joining has been proposed.

[0005] In the production of these composite lead frames that have already been proposed, the inner leads of the lead frame and the outer leads of the TAB tape are joined by soldering, or by combining gold-plated TAB leads and tin-plated lead frames. This is done using an alloy method that heats and presses the metal to form a gold-tin alloy on the bonding surface, but especially in lead bonding with a multi-pin structure, it is difficult to bond uniformly and firmly to each lead. This is difficult and causes problems such as yield loss and productivity decline due to poor bonding.

[0006] In other words, since conventional thermocompression bonding is a plane-to-plane bond, only physical surface bonding strength can be obtained, and a new surface is generated by plastic deformation and creep deformation on the normally oxidized lead surface. Furthermore, in order to cause sufficient diffusion and obtain high bonding strength, high bonding temperature, long bonding time, and high bonding load are required. Moreover, due to variations in the thickness of the Cu foil of the lead frame and TAB tape, and deviations in parallelism between the bonding tool and the stage,
The pressure applied during thermocompression bonding tends to be uneven, and in particular, the amount of plastic deformation of the lead is small when crimped with a flat tool, so if the lead thickness varies, it is difficult to apply pressure to thin leads, and it is difficult to apply sufficient pressure. It may not be possible to obtain sufficient bonding strength. Therefore, poor bonding occurs in subsequent steps, reducing reliability.

On the other hand, for thermocompression bonding, it is preferable that the bonding temperature be high, but from the viewpoint of productivity, the bonding time should be short. However, with the method of simply pressing from above the TAB tape with a conventional heating tool, heat conduction to the bonding surface is not very good, so the bonding time may be longer than the conditions sufficient for actual bonding, or the tool temperature may be higher. It is necessary to perform the bonding at Therefore, in any case, these causes a decrease in productivity.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems by improving the structure of the overlapping portion of the inner lead of the lead frame with the outer lead of the TAB tape, and by thermocompression bonding. We developed a manufacturing method for composite lead frames that provides high bonding strength in a short time and uniform bonding, enables a large increase in the number of pins compared to conventional pins, and has a high yield and reliability. The purpose is to provide

[0009]

[Means for Solving the Problems] In order to achieve the above object, the gist of the present invention is as follows. That is, (1) In manufacturing composite lead frames, TAB
When overlapping and joining the outer leads of the tape and the inner leads of the lead frame, grooves are formed on the surface of the inner leads of the lead frames to be joined, and the outer leads of the TAB tape are plastically molded into the grooves using a heating tool. A method for manufacturing a composite lead frame with high bonding strength, characterized by performing thermocompression bonding while deforming, and (2) attaching an outer TAB tape to a groove shape formed in the inner lead of the lead frame on the pressing surface of a heating tool. The method for manufacturing a composite lead frame with high bonding strength as described in item 1 above, characterized in that a pressing protrusion is formed in a shape that allows the lead to be pushed and deformed easily. In the above invention, the processed groove provided on the inner lead pressing (pressing) surface of the lead frame is formed into a groove (groove) in a V-shape, U-shape, circular arc shape, etc., or these grooves are formed in a wavy shape. Any type of material may be used as long as the outer leads of the TAB tape are pushed in while plastically deforming or creeping under pressure to be joined by thermocompression. For this purpose, a protrusion is provided on the pressure surface of the heating tool.
It is preferable that the outer lead of the B tape be easily pushed into the groove formed in the lead frame.

0010

[Operation] The present invention will be explained in detail below. Figure 1(a),
(b) schematically shows an example of a composite lead frame to which the present invention is applied. The composite lead frame 1 includes a lead frame 2 made of a thin plate of Fe-Ni alloy or Cu alloy by photo-etching or press punching, and a lead 4 made of Cu foil or the like on the surface of an insulating resin film 3 of polyimide or the like. Formed TAB tape 5
The TAB tape 5 has a chip window 6 in its center. This composite of lead frame 1 and TAB tape 5 is applied to the inner lead 7 of lead frame 1.
This is done by overlapping the outer leads 8 of the TAB tape and joining them by thermocompression bonding.

FIG. 2 schematically shows an example of a situation in which bonding is attempted by thermocompression bonding. That is, the lead frame 2 is placed on the stage 10, and the TAB
The outer leads 8 of the tapes 5 are aligned and overlapped. Then, the overlapped portions are heated and compressed using a tool 9 having a built-in heater. That is, the overlapping portions of the inner lead 7 and the outer lead 8 are heated and pressed by the pressing part 12 of the tool 9 heated to about 200 to 600° C. to join them. At this time, bonding performance can be improved by plating each bonding portion of the inner lead 7 and outer lead 8 with silver or gold.

Conventionally, as shown in the enlarged partial view of FIG.
A joint surface 11 between the TAB outer lead 8 and the inner lead 7 of the lead frame is a flat surface. but,
As described above, the thermocompression bonding of the bonded portion using such a flat surface is not necessarily uniform. 3 to 5 show an embodiment of the method of the present invention, and FIG. 3 shows an inner lead 8 with a U-shaped groove 12a formed on the surface when the outer lead 8 of the TAB tape and the inner lead 7 of the lead frame are overlapped and bonded. This is an enlarged partial cross-sectional view of the overlapping portion of the TAB tape, which is pressed by a tool 9 heated to the above temperature to give plastic deformation that pushes the outer lead 8 of the TAB tape into the groove 12a. There is. That is, in FIG. 3, the outer lead 8 is plastically deformed and bit into the U-shaped groove 12a provided in the inner lead 7 by the pressing force of the tool 9, and is joined with great mechanical strength. At this time, the pressure surface 13 of the tool 9 is provided with the concave groove 1 of the inner lead 7.
It is effective to provide a protrusion 13a similar to 2a. In FIG. 4, an arc-shaped concave groove 12b is formed on the joint surface of the inner lead 7 of the lead frame, and a tool 9 is formed.
The pressure surface 13 of the inner lead 7 and the tool 9 have a convex shape 13b with notches on both sides, and FIG.
3 form a chevron-shaped groove 12c and a protrusion 13c. In the example illustrated above, the tip of the protrusion does not need to be sharp, and may be arcuate. Moreover, the present invention is not limited only to each example.

The present invention provides a heating tool 9 in which grooves 12 as shown in FIGS. 3 to 5 are formed on the inner lead 7 of a lead frame by etching or press processing, and a pressing surface 13 is processed as necessary. By pressing the TAB lead 8 while plastically deforming it using the TAB and thermocompression bonding, (2) a large plastic deformation is applied, so a new surface is generated over a wide range, and a large thermocompression bonding strength is obtained. In addition, at the joint, mechanical strength is provided by the reed biting against tensile and shear deformation;
and ■ Because the amount of tool movement in the direction of lead thickness is large due to pushing, uneven bonding due to variations in lead thickness is less likely to occur. Furthermore, the contact area between the TAB tape lead and the heating tool during the pushing process is large, and the thickness is reduced due to lead plastic deformation, which improves heat conduction and provides great bonding strength in a short time. do.

[0014] The shape of the groove and the shape of the tool are not particularly limited.

[0015]

[Example] Examples are shown in Table 1. The tip pressurizing part of the tool is processed into the shape shown in FIGS. 3 to 5 (Examples 1 to 4),
The outer lead 8 of the TAB tape and the inner lead 7 of the lead frame were overlapped and thermocompression bonded according to the present invention. Further, as a comparative example, thermocompression bonding was performed using a conventional tool shown in FIG.

The bonding strength of each example was measured by a push test, and the average bonding strength and the probability of generating a lead with a bonding strength of 50 g or less, which represents the variation in bonding strength, were determined and are also listed in Table 1.

As is clear from Table 1, Examples 1, 3,
Regarding No. 4, the TAB lead part was broken due to the high bonding strength, and the bonding strength could not be determined. however,
T.A.

[0018]

[Table 1]

Since the breaking strength of the B lead is about 200 g, it can be said that the bonding strength is 200 g or more. In Example 2, the bonding strength was inferior due to the low bonding temperature, but the variation was very small and all the leads were 135 g or more, and there were no leads of 50 g or less. On the other hand, in the comparative example in which bonding was performed under the same conditions as Examples 1 and 4, the average bonding strength was not only low but also highly variable, with 11% of leads weighing less than 50 g. As described above, the bonding according to the present invention exhibits extremely superior characteristics, such as a larger average value of bonding strength and smaller variations in bonding strength compared to conventional methods.

[0020]

As described above, by the method of the present invention, the TAB leads are deformed and pushed into the grooves formed in the outer part of the lead frame by thermocompression bonding of the overlapping parts of the leads.
Furthermore, by joining using a tool crimping part with an irregularly shaped tip, a composite lead frame with high joint strength and little variation can be obtained, which can significantly reduce the defective rate and greatly increase productivity. can be improved.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are schematic plan views of a composite lead frame of the present invention.

FIG. 2 is an explanatory diagram showing an example of a joining situation of the present invention.

FIG. 3 is an enlarged cross-sectional explanatory diagram showing an example of a joining situation of the present invention.

FIG. 4 is an enlarged cross-sectional explanatory view showing another example of the joining situation of the present invention.

FIG. 5 is an enlarged cross-sectional explanatory view showing another example of the joining situation of the present invention.

FIG. 6 is an enlarged cross-sectional explanatory view showing a conventional joining situation.

[Explanation of symbols]

1: Composite lead frame 2: Lead frame 3: Insulating resin film 4: Cu foil lead of TAB tape 5: TAB tape 6: Chip window 7: Inner lead of lead frame 8: Outer lead of TBA tape 9: Tools 10: Stage 11: Joint surface 12: Groove 13: Tool pressure surface

Claims (2)

[Claims] [Claim 1] In manufacturing a composite lead frame,
When overlapping and joining the outer leads of the TAB tape and the inner leads of the lead frame, grooves are formed on the surface of the inner leads of the lead frames to be joined, and the outer leads of the TAB tape are inserted into the grooves using a heating tool. A method for manufacturing a composite lead frame with high bonding strength, which is characterized by performing thermocompression bonding while plastically deforming it. 2. Claim 1, characterized in that a pressurizing protrusion is formed on the pressurizing surface of the heating tool so that the outer lead of the TAB tape can be easily pressed and deformed into the groove shape formed in the inner lead of the lead frame. The method for manufacturing the composite lead frame with high bonding strength as described above.