JPH10303206A - Method and device for manufacturing very small bump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a very small bump used for mounting an element on a substrate with high accuracy. SOLUTION: A very small bump is transferred onto a substrate 6 by punching a ribbon-like bonding metal 3 put on a die 2 with a very small punch 1 having a recess on its front end face. The very small bump 3-1 punched with the punch has a protrusion. When an optical element 5 is temporarily mounted on the bump, the metallic pad 4 of the element 5 comes into contact with the protrusion of the bump 3-1, and burrs 3-3 formed on the outer peripheral edge of the bump 3-3 do not come into contact with the element 5 except the metallic pad. Therefore, a symmetrical bump shape which is only bonded to the metallic pad is obtained, because the burrs are not protruded outward from the metallic pad, but melted. Therefore, the optical element 5 can be positioned and fixed with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for manufacturing minute bumps for fixing an optical element or the like used in an optical module for optical communication or the like to a substrate.

[0002]

2. Description of the Related Art In optical communications, active and passive elements such as semiconductor laser LDs, photodiodes, photodiodes, and optical modulators, as well as optical fibers, optical switches, optical isolators, optical waveguides, etc., have been improved in performance and function. Is expanding the range of applications.

[0003] In recent years, application to general subscriber systems has been considered as one of the application ranges of optical communication.
There is a demand for higher precision and lower cost of modules equipped with optical elements and the like.

As an effective means for reducing the cost of a module for mounting an optical element or the like, a non-adjustable element mounting method in which an element is mounted on a substrate without adjustment via a metal pad bonded by a plurality of minute bonding bumps. Is attracting attention. This is because there is a feature that the element can be positioned at the bonding position specified by the pad position by the self-alignment effect at the time of melting the bump.

[0005] A conventional method for forming a small bonding bump used for mounting a non-adjustable element is to transfer a small bonding bump onto a substrate by a punching machine for punching a ribbon-shaped bonding metal foil using a small punch and a die. A method using a highly reliable AuSn bump as a micro junction bump is described in Japanese Patent Application Laid-Open No. 4-152682 (Ito et al., "Method for Manufacturing Sub-Substrate for Array Optical Device").

[0006]

In order to improve the positioning accuracy by the self-alignment effect due to the surface tension at the time of melting the bump, it is important that the bump shape after fixing is symmetrical with respect to the center of the pad. is there.

[0007] The method of forming the minute bumps is to punch a ribbon-shaped bonding metal on a substrate using a minute punch and a die. However, the minute bumps punched by such a method have burrs formed on the outer periphery. You. In general, the diameter of a punched bump is larger than the metal pad of the device, and burrs protrude from the surface of the bump. For this reason, the burr of the bump comes into contact with the outside of the metal pad of the element and is melted and protrudes outside the metal pad. As a result, there is a problem that the bump shape becomes irregular and the positioning accuracy is reduced.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing a fine bump for forming a fine bonding bump for mounting an optical element or the like on a substrate by punching a ribbon-like bonding metal using a fine punch and a die. It is characterized in that a recess is provided at the tip of the micro punch.

By providing a depression at the tip of the micro punch, the stamped bump has a convex shape. When an element in which a metal pad is formed on such a bump is temporarily mounted, the protruding protrusion contacts the metal pad of the element. For this reason, the burrs formed around the micro bumps do not come in contact with the outside of the metal pad, and therefore, when the bump is melted, the burrs do not protrude outside the metal pad, and the bump shape is symmetric with respect to the center of the pad. Become.

Since the shape of the bump is symmetrical with respect to the center of the pad, a sufficient self-alignment effect is generated when the bump is melted, and the element is positioned with high accuracy. Product quality and productivity can be improved by high-precision positioning.

[0011]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an embodiment of the present invention.

As shown in FIG. 1 (a), the structure and arrangement of each part of the manufacturing apparatus according to the present embodiment include a substrate 6, a die 2 having an opening for punching the substrate 6, and an upper part of the die 2. A bonding metal foil 3 in the form of a ribbon and a bonding metal foil 3
And a micro-punch 1 having a depression 1-1 at the top end of the punch. Hereinafter, the operation of the method or the apparatus for manufacturing a micro bump on a substrate according to the present embodiment will be described.

In a state where the ribbon-shaped joining metal foil 3 is inserted between the small punch 1 and the die 2 ((a) in the drawing), the punch 1 is hit on the joining metal foil 3 and the minute opening is formed in the die 2. The bump 3-1 is punched, and the bump 3-1 is transferred onto the substrate 6. The punched-out bump 3-1 is formed into a depression 1-1 provided on the punch 1 at the time of transfer onto the substrate 6.
As a result, a convex shape on the upper portion of the bump is formed (b in the figure).

When an optical element 5 having a metal pad 4 formed on such a convex bump 3-1 is temporarily mounted, the protrusion 3-2 of the convex bump comes into contact with the metal pad 4 and the bump 3-
The burr portion 3-3 formed around 1 can be prevented from contacting the outside of the metal pad 4 (c in the figure). In this state,
When the bump 3-1 is heated and melted, the burr portion 3-3 does not protrude out of the metal pad and has a symmetrical shape with respect to the pad center (d in the figure).

As a result, a sufficient and accurate self-alignment effect due to the surface tension at the time of melting the bump occurs, and high-accuracy positioning of the element can be realized.

In the above-described embodiment, an example in which one micro punch is used has been described. However, the present invention is not limited to this, and a large number of micro punches may be used according to the number of metal pads of a mounted element. It is needless to say that a plurality of minute bumps can be formed simultaneously. In addition, the depression at the tip of the micro punch can have an appropriate height, size, and shape depending on the material of the bonding metal, the metal pad, and the like.

[0017]

Next, an example of this embodiment will be described in detail. This embodiment has the same basic configuration and operation as those of FIG.

In the present embodiment, a ribbon-shaped AuSn foil having a thickness of 50 μm is used as the bonding metal foil 3. The micro punch 1 uses a super steel micro punch having an outer diameter of 50 μm, and the die 2 uses a stainless steel die having a hole diameter of 60 μm. Then, the tip of the micro punch has a hole diameter of 20 μm and a depth of 10 μm.
and m depressions 1-1.

The optical element 5 is a semiconductor laser in which the diameter of a metal pad 4 made of Au having a diameter of 40 μm is formed, and the substrate is a Si substrate.

Based on such a configuration or specifications, the punched bump 3-1 has a projection 3-2 having a diameter of about 20 μm, a height of about 10 μm, and a burr 3-3 having a height of about 20 μm. 5
μm and the outer diameter is about 50 μm. The outer diameter of the bump 3-1 is set to be larger than that of the metal pad 4.
Since the shape of -1 is convex, the burr 3-3 is melted without contacting the outside of the metal pad 4 from the state where the optical element is temporarily mounted, and the bump shape is symmetrical with respect to the center of the pad. Become.

In this embodiment, a high-precision bonding accuracy of 1 μm or less was obtained as the positioning accuracy of the optical element 5.

In this embodiment, Au is used as the bonding metal material.
Although Sn was used, the present invention is not limited to this. For example, PbSn, Au, or the like can be used. In the present embodiment, the diameter of the minute bump is set slightly larger than the diameter of the element as a preferred example. However, the diameter of the minute bump may vary depending on the shape of the metal pad, the shape of the projection of the minute bump, and other conditions. It is apparent that the relationship between the diameter of the element and the diameter of the metal pad of the element can be arbitrarily set so as to obtain the best positioning effect.

[0023]

According to the present invention, a minute bump having a convex portion can be punched out from a bonding metal on a substrate by a minute punch and a die.

For this reason, when an optical element or the like is mounted on the substrate, the projecting portion of the convex portion of the minute bump comes into contact with the metal pad of the element, and the burr formed on the outer periphery of the minute bump does not contact the outside of the metal pad. Therefore, at the time of joining, the burrs of the minute bumps are melted without protruding outside the metal pad, and a symmetrical bump shape joined only to the metal pad can be formed.

As a result, it is possible to realize highly accurate positioning of the element by a sufficient self-alignment effect. In addition, the quality of the product is improved by high-precision positioning, and the elements can be mounted on the substrate without adjustment, so that the productivity can be improved.

[0026]

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Micro punch 1-1 Depression 2 Die 3 Bonding metal foil (AuSn foil) 3-1 Convex bump 3-2 Protrusion 3-3 Burr 4 Metal pad 5 Optical element 6 Si substrate

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Masataka Ito 5-7-1 Shiba, Minato-ku, Tokyo Within NEC Corporation

Claims (5)

[Claims] 1. A method of manufacturing a micro-bump for forming a micro-bump on a substrate by punching a bonding metal, comprising the steps of: Forming a minute bump having a projection to be formed on a substrate. 2. The micro-punch having a diameter larger than a diameter of a metal pad of an element to be mounted, and forming a minute bump having a diameter larger than a diameter of a metal pad of the element mounted on a substrate. Item 4. A method for producing a micro bump according to Item 1. 3. A micro-bump manufacturing apparatus for forming a micro-bump on a substrate by punching a bonding metal in a ribbon shape using a micro-punch and a die, wherein a recess is provided at a tip end of the micro-punch. Manufacturing equipment for small bumps. 4. The apparatus according to claim 3, wherein the small punch has a diameter larger than a diameter of a metal pad of an element mounted on the substrate. 5. The apparatus according to claim 3, wherein the element mounted on the substrate is an optical element having a metal pad.