JPH03252148A - Bump structure of tab inner lead and its formation - Google Patents

Abstract

PURPOSE:To obtain a structure capable of attaining bonding to semiconductor elements with sufficient bonding strength and high reliability despite of dispersion in bump height in a simple process of forming bumps by inlaying the inner face of a hollow bump with a material whose melting point is higher than a temperature in bonding of an LSI chip and its bump. CONSTITUTION:A bump 15 formed in the vicinity of the tip of an inner lead 14 of a TAB tape carrier is structured in hollow, and the inner face of its hollow bump 15 is inlaid with a stopper material 16 whose melting point is higher than a temperature in bonding of an LSI chip and its hollow bump 15. In the case of forming the bump 15 in the vicinity of the tip of an inner lead 14 of the TAB tape carrier, the inner lead 14 is loaded with a sheet of material 13 whose melting point is higher than a temperature in bonding of an LSI chip and its hollow bump 15, and this material 13 is punched out by mechanical pressing using a punch 12 and a die 11, and the inner lead 14 is continuously press-molded into the bump 15.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is directed to a TAB (Ta
The present invention relates to the structure of a bump formed at the tip of an inner lead of a tape carrier for (Automated Bonding) and a method for forming the same.

(Prior Art) Generally, in order to mount a semiconductor element on a TAB tape carrier, it is necessary to form a protrusion that becomes a bump on either the electrode part of the semiconductor element or the inner lead tip of the tape carrier. For example, there are methods for forming bumps on the electrodes of semiconductor devices, as described in IBM Journal (
IBM Journal) Volume 8 (1964) 102
There is a method of forming protrusions that will become bumps directly on the electrode part using the plating method as described in the page, and a method of forming bumps directly on the electrode part,
IC Packaging & Production
), December 1984 issue, pages 33 to 39, the pedestal method using etching technology, that is, masking the part where the bump will be formed and half-etching the other inner lead parts, is used. ~4
There is a method of forming protrusions with a height of 0 pm. However, forming bumps using these methods not only requires expensive equipment such as exposure equipment and plating equipment, but also requires a photolithography process and an etching process for patterning, making the bump formation process long. There is a problem.

For this reason, a method has been proposed in which a pedestal is manufactured at the tip of the inner lead using a mechanical press forming technique using a mold, as described in Japanese Patent Publication No. 10094/1983. In this method, as shown in FIG. 4(a), a tape carrier 22 in which a film 21 and an inner lead 14 are integrated is attached to a lower die 23, and a convex portion 27 larger than the width of the inner lead 14 is formed from above. In this method, the upper die 24 is lowered, and as shown in FIG. 4(e), a four part 28 is formed at the tip of the inner lead 14 by press molding, and a pedestal 25, which becomes a bump, is formed at the tip of the inner lead. . In order to allow the material in the recess 28 of the inner node 14 pressed by the projection 27 of the upper mold 24 to escape, a notch 26 is provided in the radial direction as shown in FIG. 4(b).

(Problem to be Solved by the Invention) However, since the bump or pedestal 25 formed at the tip of the inner lead by such a press working method has a solid structure, it is difficult to bond the semiconductor element and the bump by thermocompression bonding. It acts as a rigid body in response to the compressive load applied to it. For this reason, if there is variation in the height of individual bumps, there is a problem that when bonding the bumps to the semiconductor element, it is not possible to bond all the bumps uniformly, resulting in electrical connection failures. In order to prevent connection failures, it is necessary to limit the variation in the height of the bumps to at least 0.5 pm or less, and it is required to form the bumps with extremely high precision. Further, there are also problems such as the need to process the four parts of the inner lead to provide notches in advance.

The purpose of the present invention is to solve these conventional problems, to simplify the bump formation process, to achieve sufficient bonding strength even with variations in bump height, and to achieve highly reliable bonding with semiconductor elements. An object of the present invention is to provide a bump structure for an inner node and a method for forming the same.

(Means for Solving the Problems) In the bump structure of the TAB inner lead of the present invention, the bump has a hollow structure, and the temperature at which the LSI chip and the hollow structure bump are bonded is set on the inner surface of the hollow structure bump. It is constructed by embedding a material with a higher melting point.

The method for forming bumps on TAB inner leads of the present invention is to place a thin plate-like material on the inner leads with a melting point higher than the temperature at which the LSI chip and the hollow structure bumps are bonded, and use a machine using a punch and a die. The thin plate-like material is punched out using a conventional pressing method, and the inner leads are continuously press-molded to form bumps.

(Function) The bump structure of the present invention is a hollow bump 15 formed in a dome shape smaller in width than the inner lead 14 as shown in FIG. Hollow structure bumps have the advantage of greatly simplifying the bump formation process by eliminating the need for pre-processing for bump formation.Moreover, the bump structure is more easily deformed by compressive force than solid structures, so it is possible to increase the height of the bump. Even if there is variation in the bump height, the bump is plastically deformed by the compressive load during thermocompression bonding, and the bump height can be corrected to a uniform height.

However, on the other hand, with hollow bumps, it is difficult to ensure sufficient bump height after thermocompression bonding because the bumps are crushed by a slight compressive load, and because the deformation resistance is low, There has been a problem in that sometimes it is not possible to bring the bumps and the electrodes on the LSI chip into close contact with each other with sufficient pressure, making it difficult to bond with sufficient strength. Therefore, in the bump structure of the present invention, the hollow structure bump 1
A stopper material 16 having a melting point higher than the temperature at the time of thermocompression bonding is embedded in the inner surface of 5. Therefore, as shown in FIG. 3, the bump having the hollow structure of the present invention easily starts plastic deformation as a hollow bump due to the compressive load during thermocompression bonding, but when the stopper material 16 comes into contact with the bonding tool 19, Since it acts as a substantially rigid bump like the solid bump, it is possible to bring the bump 15 and the electrode 18 of the LSI chip into close contact with each other with sufficient pressure. Further, the bump height can be easily adjusted by changing the thickness of the stopper material 16, making it possible to ensure a sufficient bump height even after thermocompression bonding.

In order to obtain a bump having a hollow structure as described above, a thin plate-shaped material serving as a stopper material is placed on the inner lead, and the thin plate-shaped material is punched out by a mechanical pressing method using a punch and a die. By press-molding the inner lead, the stopper material can be embedded in the inner surface of the hollow structure, and the inner lead can be easily formed.

(Example) The present invention will be described in detail below with reference to the drawings. 1st
The figure is a cross-sectional view showing an embodiment of the bump structure of the inner lead of the present invention, and FIGS. 2(a) and 2(b) are cross-sectional views showing an embodiment of the bump forming method of the present invention in the order of steps. .

First, as shown in FIG. 2(a), an inner lead 14 and a Cu foil 13 having a thickness of 30 μm were placed on the die 11, and the punch 12 was fixed so that the central axis of the die 11 and the axis coincided with each other. Here, the diameter of the die hole 17 was 70 pm, and the diameter of the punch was 50 pm. Next, Figure 2 (b
), the punch 12 was gradually moved downward to press-form the inner lead 14, the Cu foil 13 was punched out, and a hollow hole was formed on the inner lead 14 in which a stopper material 16 was embedded as shown in FIG. Structure bump 1
We were able to form 5. Note that the punched Cu foil 13 acts as the stopper material 16. Here, the inner lead has a width of 100 νm, a thickness of 30 pm, and a pitch of 2.
00 pm Cu foil plated with 1 pm of Au was used.

The formed hollow structure bump 15 had an outer diameter of 70 pm, an inner diameter of 50 μm, and a bump height of 30±lpm. Further, when observing the cross section of the hollow structure bump 15, the Cu foil 13, which is the stopper material 16 embedded in the inner surface of the bump, was slightly deep drawn as shown in FIG. 1, so its thickness was 25 pm. decreased to

As shown in FIG. 3, the hollow bumps 15 formed as described above and the AI electrodes 19 of the LSI chip 18 are bonded using a low temperature bonding method (element heating temperature = 275°C1 temperature of the pressure tool 20: 450°C1 pressure bonding). 60gf/lead, 1
As a result of bonding (tensile strength: 60g)
f/1 lead) and electrically, a good connection is achieved.
It was confirmed that it can be used satisfactorily as a bump for inner leads. The reason why we were able to achieve a good connection despite the ±lpm variation in bump height is that the bumps act as a hollow structure and are easily plastically deformed until the stopper material 16 comes into contact with the pressurizing tool 20. This is because all the bumps could be corrected to a uniform height.The reason why the bump height after bonding was 20 pm, which was a sufficient height, was that when the stopper material 16 came into contact with the pressure tool 20, the bumps This is because it acted almost as a rigid structure.

Finally, in order to evaluate the reliability of the bonding, after bonding the semiconductor element and the inner lead, the
A thermal shock test at 500 degrees Celsius (1 cycle/hour) was conducted to test the strength against thermal stress. As a result, it was confirmed that in the bump structure according to an embodiment of the present invention, no bonding failure occurred at all.

(Effects of the Invention) As explained above, with the bump structure of the TAB inner lead of the present invention, even if there are variations in the bumps, the bumps and the electrode portions of the semiconductor element can be bonded uniformly and with sufficient bonding strength. Furthermore, it is possible to realize highly reliable joining that does not cause a joining failure even if thermal stress or external force is applied after joining.

Furthermore, the TAB inner lead bump forming method of the present invention has the effect of easily forming a hollow bump in which a stopper material is embedded in the inner surface of the hollow bump.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the bump structure of the inner lead of the present invention, FIGS. 2(a) and 2(b) are schematic diagrams showing the bump forming method of the present invention in the order of steps, and FIG. 3 is a cross-sectional view showing the bump structure of the inner lead of the present invention. A cross-sectional view showing a state of bonding between a hollow bump formed in an example and an AI electrode part of an LSI chip,
FIGS. 4(a) to 4(e) are a sectional view, a plan view, and a side view, respectively, showing a conventional method for forming a solid bump. 11...Dice, 12...Punch, 13...Cu
Foil, 14... Inner lead, 15... Hollow structure bump, 16... Stopper material, 17... Dice hole, 18... LSI chip, 19... AI electrode, 20
...pressure tool, 21...film, 22...
Tape carrier, 23...lower mold, 24...upper mold, 2
5... Pedestal, 26... Notch, 27... Convex part, 28... Concave part

Claims (1)

[Claims] 1. In the structure of the bump formed near the tip of the inner lead of the TAB tape carrier, the bump has a hollow structure, and an LSI chip and the hollow structure bump are arranged on the inner surface of the hollow structure bump. A TAB characterized by being filled with a material whose melting point is higher than the bonding temperature of
Bump structure of inner lead. 2. In a method of forming a bump near the tip of an inner lead of a TAB tape carrier, a thin plate-like material having a melting point higher than the temperature at which the LSI chip and the hollow structure bump are bonded is placed on the inner lead, and a punch is formed. A method for forming bumps on a TAB inner lead, characterized in that the thin plate material is punched out by a mechanical pressing method using a die and a die, and the inner lead is continuously press-molded to form a bump.