JPH0997794A - Bump of flip chip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a bump from increasing in contact resistance and to protect it against a contact failure caused by cracking induced in it by a method wherein the upside of the bumps is set rugged. SOLUTION: A recess 1b (conical hole) is provided in the upper plane 1a of a bump. The recess 1b is formed through such processes that a ball is bonded, a wire is cut, a cut surface is flattened by a hammer, and a recess 1b is formed. The recess 1b is formed through such a manner that a flattened cut surface is hit by a hammer with a projection. By this setup, a bump is enhanced in adhesion to die paste, prevented from increasing in contact resistance due to thermal stress, and protected against a contact failtare caused by cracking induced in it.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD This application relates to flip-chip bumps.

[0002]

2. Description of the Related Art FIG. 5 is a cross-sectional view showing a bump of a conventional flip chip and its vicinity. 1 is a gold bump, 2 is a semiconductor substrate on which a semiconductor element is formed, 3
Is an electrode formed on the semiconductor substrate 2 and 4 is passivation. The gold bump 1 is formed by cutting a ball formed by a ball bonding technique from the root, and the cut surface is struck with a hammer to be flat in order to make the height of the ball uniform.

FIG. 6 shows a state in which a flip chip using the gold bump 1 is mounted on a printed board or the like. The conductive pattern 6 formed on the ceramic substrate 5 and the gold bump 1 of the flip chip are connected using a die paste 7. An epoxy-based silver paste is generally used as the die paste 7.

[0004]

Since the height of the bump depends on the mechanical accuracy, a variation of about ± 10 μm usually occurs. Therefore, when the flip chip is mounted on the substrate using the die paste, the thickness of the die paste becomes non-uniform as shown in FIG. The thermal decomposition temperature of die paste (epoxy silver paste) is usually 300.
The solder reflow furnace (maximum temperature 230 ~
The stress concentrates between the bumps and the die paste when it is passed through a temperature of about 255 degrees c. As a result, there are problems that contact resistance increases and open defects occur due to cracks. When the height variation of the bumps is about ± 10 μm or more, the contact resistance increases by about several percent to several tens of percent and the open failure occurs.

In order to solve the above problems, it is possible to use palladium instead of silver as a metal mixed in the die paste, but it is not suitable because it is expensive. Also,
Although there is a resin whose heat resistance is improved by using a polyimide resin instead of an epoxy resin, it is not suitable for flip-chip mounting because it is weak against stress.

An object of the present application is to provide a flip-chip bump capable of preventing an open defect caused by an increase in contact resistance and cracks.

[0007]

The bumps of the flip chip according to the present invention are characterized in that the upper surfaces of the bumps are uneven.

[0008]

1A and 1B show a first embodiment of a bump according to the present invention. FIG. 1A is a top view of the bump, and FIG. 1B is a sectional view of the bump. Is. That is, by providing a concave portion 1b (conical hole, depth is about 0.1 μm to several tens of μm depending on the ball diameter, usually about several μm) on the upper plane 1a of the bump, the bump and die The adhesiveness with the paste (adhesiveness) is improved to prevent an increase in contact resistance due to thermal stress and the occurrence of open defects due to cracks. The forming method is a modification of the conventional bump forming method. Specifically, ball bonding, wire cutting (cutting the ball), and flattening the cut surface by a hammer (to make the height of the ball uniform, Flatten with a hammer.),
It is formed in the process of forming a recess. The concave portion is formed by striking a flattened cut surface with a hammer having a convex protrusion portion. Of the above steps, both the flattening of the cut surface with a hammer and the formation of the recess may be common (after the wire cutting step, the cut surface is directly struck by a hammer having a convex projection) to form the recess. To form).

2A and 2B show a second embodiment of a bump according to the present invention. FIG. 2A is a top view of the bump and FIG. 2B is a sectional view of the bump. This is because by providing a plurality of recesses 1c (conical holes, the depth is about 0.1 μm to several tens of μm depending on the ball diameter, usually about several μm) on the upper plane 1a of the bump, The contact area between the bump and the die paste is increased, and the adhesion (adhesiveness) between the bump and the die paste is further improved as compared with the case of the first embodiment.
The method of forming the bumps is basically the same as that of the first embodiment, and the cut surface flattened by using a hammer having a convex or needle-shaped protrusion or the cut surface after wire cutting is tapped. To form a recess.

3A and 3B show a third embodiment of a bump according to the present application. FIG. 3A is a top view of the bump and FIG. 3B is a sectional view of the bump. This is a recess 1d on the upper plane 1a of the bump (a groove having a triangular cross section formed vertically and horizontally, and the depth is 0.1 μm to 0.1 μm depending on the ball diameter.
The contact area between the bump and the die paste is increased by providing the thickness of about several tens of μm, but usually about several μm), and the adhesion (adhesiveness) between the bump and the die paste is increased according to the first embodiment. It is designed to be improved further than in the case of. The bump forming method is the same as the first method described above.
Similar to the above-described embodiment, a concave portion is formed by hitting a flattened cut surface or a cut surface after wire cutting with a hammer in which convex portions are formed vertically and horizontally.

FIG. 4 shows a bump according to a fourth embodiment of the present invention. This is an improvement of the second embodiment described above. A plurality of recesses 1e (conical holes) are provided on the upper plane 1a of the bump, and the recesses 1f ( It has a conical hole).

In the first, second and fourth embodiments described above, the hole of the recess has a conical shape, but it may have a pyramidal shape, a cylindrical shape, a prismatic shape or the like. Further, in the third embodiment, the groove has a triangular cross section, but the cross section may be rectangular, trapezoidal, or the like.

Further, although the case of gold bumps has been described in the first to fourth embodiments, it is also applicable to the case of fixing solder bumps with a die paste.

Further, in the above-mentioned first to fourth embodiments, the case of using the ball bonding method has been described, but it is also applicable to the case of using the plating method used for solder bumps or the like.

[0015]

By adopting the bump according to the present invention, it becomes possible to prevent an increase in contact resistance and the occurrence of open defects due to cracks.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment according to the present application.

FIG. 2 is a diagram showing a second embodiment according to the present application.

FIG. 3 is a diagram showing a third embodiment according to the present application.

FIG. 4 is a diagram showing a fourth embodiment according to the present application.

FIG. 5 is a diagram relating to a conventional technique, showing a state of a bump of a flip chip and its vicinity.

FIG. 6 is a diagram related to a conventional technique, showing a state in which a flip chip having bumps is mounted on a printed circuit board or the like.

[Explanation of symbols]

 1 ... Bump 1b, 1c, 1d, 1e ... Recess

Claims (5)

[Claims] 1. A flip-chip bump in which the upper surface of the bump is uneven. 2. A flip-chip bump, characterized in that a recess is provided on the upper surface of the bump. 3. The bump of the flip chip according to claim 2, wherein the recess is a single hole. 4. The bump of the flip chip according to claim 2, wherein the recess is a plurality of holes. 5. The bump of the flip chip according to claim 2, wherein the recess is a groove formed vertically and horizontally.