JPH0555635A - Flip chip connection structure of electronic part - Google Patents

Abstract

PURPOSE:To simply form a bump and also connect bumps with each other at a low temperature by a method wherein one of the bumps is a bump mainly containing tin while the other mainly contains gold or silver. CONSTITUTION:A gold bump 18 is formed on an LED array 4, while a tin bump 20 is formed on a glass substrate 2. The formation is done by supplying gold or tin wires from a capillary and pressing the LED array 4 or the glass substrate 2 while they are heated. This heat and friction heat due to ultrasonic oscillation at this time and pressure cause the metal wire or tin wire to be bonded to the LED array 4 or the glass substrate 2 to be a ball. If the metal wire or the tin wire is cut above the ball immediately after the bonding, the bump 18 or 20 can be obtained. Since gold or silver and tin form an eutectic compound at approximately 20 deg.C, bumps can be easily interconnected by means of thermocompression bonding, ultrasonic bonding or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flip chip connection structure for electronic parts, which is used for flip chip connecting electronic parts to a substrate. The invention is particularly applicable to LEDs
It is used when flip-chip connecting an array of light emitting / receiving elements such as an array to a transparent substrate such as glass.

[0002]

2. Description of the Related Art In a conventional flip-chip connection structure, bumps are formed on an electronic component and a substrate, then the electronic component is bonded to the substrate by a shrinkable adhesive, and the bumps are connected by the shrinking force of the adhesive. Known (Japanese Patent Laid-Open No. 2-155,257)
issue). It is also well known that the combination of bump materials is solder and gold, or solder and solder, and the bumps are connected in a reflow furnace (for example, Japanese Patent Publication No. 2-26,780).
issue). Furthermore, Nikkei Microdevices, December 1990, page 15, proposes to form gold bumps by a method similar to wire bonding. In this method, a gold thin wire is wire-bonded to form a gold ball, and then the gold wire is cut at the upper part of the ball to form a gold bump. In this proposal, a solder bump is used for the other bump, and heat treatment is performed in a reflow furnace to connect the gold bump and the solder bump.

In forming solder bumps, Japanese Patent Publication No. 26-26,
As shown in Japanese Patent No. 780, first, a barrier film such as chromium or molybdenum is formed on a substrate or an electronic component, and a conductive metal film such as gold, nickel or copper is formed on the barrier film. Next, mask the area other than the bump formation area with a resist,
Bumps are formed by solder plating. After forming the bumps, a step of removing the resist and etching the conductive metal film or the barrier film is required. As is clear from this, the bump forming process is long, and there is a problem of contamination due to the barrier film or the conductive metal film and contamination due to diffusion of solder to the portion masked with the resist. Another problem with solder bumps is that the solder eats the gold plating of the electrodes underlying the bumps, which can easily lead to connection failures. After all, the solder bump has a complicated forming process and may contaminate the IC or the like, and easily reacts with the gold plating of the electrode at the time of connection. Therefore, a flip chip connection structure that does not use solder bumps is required.

[0004]

An object of the present invention is to provide a flip-chip connection structure that does not use solder bumps, and (1) facilitates the formation of bumps, and (2) facilitates the mutual connection of bumps, and (3) The purpose is to prevent contamination of electronic components in the bump forming process.

[0005]

According to the present invention, in a flip chip connection structure of an electronic component in which a bump provided on an electronic component and a bump provided on a substrate are connected, one bump is a bump whose main component is tin and the other bump is a bump. Is a bump having gold or silver as a main component, and is in a flip-chip connection structure for electronic parts.

[0006]

In the present invention, one of the bump materials has gold or silver as a main component and the other has tin as a main component. Tin forms a eutectic compound with gold or silver at low temperature, and bumps can be easily connected to each other. For example, the eutectic temperature of gold and tin is 217 ° C, and that of silver and tin is 227 ° C.
Next, gold or silver can be easily drawn into a thin wire, and a bump can be easily formed by a method similar to wire bonding. Similarly, with tin, it is easy to obtain a thin tin wire, and it is easy to form bumps. The tin wire is softer than the gold wire and the silver wire, and is easy to cut after the ball is formed and the bump is particularly easy to form.

Therefore, if one of the bumps is made of gold or silver and the other is made of tin, these fine wires are bonded to a substrate or an electronic component to form a ball, and then the wire is cut at the upper part of the ball to form the bump. Can be formed. 20 for gold, silver and tin
Since the eutectic compound is formed at about 0 ° C., bumps can be easily connected to each other by thermocompression bonding or ultrasonic pressure bonding.

[0008]

EXAMPLE An example will be described by taking a flip chip connection of a light emitting and receiving element array to a glass substrate as an example, but a flip chip connection of a general IC chip can be similarly performed. The glass substrate is taken as an example because glass is vulnerable to thermal shock, and the surface is smooth, so that the adhesion strength of electrodes under the bumps is low and flip-chip connection is particularly difficult. Another reason for using the glass substrate is to align the light receiving and emitting surface of the light emitting and receiving element array with the glass substrate, perform light reception and emission through the glass substrate, and align the surface height of the light receiving and emitting element array with the glass substrate as a reference. This is to prevent a decrease in focus accuracy due to a variation in surface height of the light emitting / receiving element array. Except for such a point, flip-chip connection of an IC chip to an alumina substrate or the like can be similarly performed.

In FIG. 1, 2 is a transparent substrate such as glass,
4 is a GaAs LED array. The same applies when a light receiving element array such as a CCD or a photocell array is used instead of the GaAs LED array 4. Reference numeral 6 denotes a light-emitting body in which impurities such as Zn are injected into GaAs, and the bottom of the light-emitting body 6 and the GaAs of the substrate.
The interface with the layer serves as a light emitting surface. Reference numeral 8 denotes a common lead connected to the LED array 4, and for example, the lead frame is thermocompression-bonded to the common electrode on the back surface of the LED array 4, and then the base portion of the lead frame is cut. Reference numeral 10 is an insulating layer such as a polyimide resin on the glass substrate 2, and 12 is a common electrode on the glass substrate 2. 14 is an electrode provided on the LED array 4,
For example, an Al electrode is provided, and 16 is an electrode provided on the glass substrate 2. For example, gold is plated on the Al electrode or gold is laminated by vapor deposition or sputtering, but the gold coating may not be provided. When the gold coating is provided, it may be provided only on the bump forming portion.

Reference numeral 18 denotes a gold bump which has gold as a main component, and may contain silver, palladium, nickel, tin or the like in a range of, for example, 10% by weight or less. Instead of the gold bumps 18, silver bumps may be used, and in that case, silver may be replaced with gold, palladium, tin or the like in a range of, for example, 10% by weight or less. Reference numeral 20 denotes a tin bump as long as it has tin as a main component, and may contain nickel, lead, gold, silver or the like in a range of 10% by weight or less. The substitution range for the tin bumps 20 and the gold bumps 18 is a range that does not make drawing a fine wire difficult and does not hinder the formation of a eutectic crystal of gold or silver and tin. The gold bumps 18 are provided on the LED array 4 and the tin bumps 20 are provided on the glass substrate 2 because the tin wire used for forming the tin bumps 20 is soft, and the tin balls can be easily formed during the bump formation. This is because it is easy to cut the tin wire later. This is particularly suitable for the glass substrate 2 which is fragile and has low adhesion strength of the electrode 16. Further, the reason why the surface of the electrode 16 on the glass substrate 2 side is coated with gold is to facilitate the ball formation during the formation of the bump 20 by utilizing the alloy formation reaction of tin and gold. Apart from these points,
Gold bumps may be provided on the glass substrate 2 side and tin bumps may be provided on the LED array 4 side.

In FIG. 2, gold bumps 18 on the LED array 4 are shown.
Shows the arrangement of. The electrode 14 was formed so as to vertically cut the light emitting body 6, and gold bumps 18 were provided on both sides of the light emitting body 6. Figure 3
The arrangement of the tin bumps 20 on the glass substrate 2 is shown in FIG. For example, about 40 arrays of LED arrays 4 are linearly arranged on the glass substrate 2, and the electrodes 16 are arranged so that each LED array 4 is folded back. The electrode 16 is the LED array 4
In order not to interfere with the light emission from, the light emitting body 6 is not provided in the portion, and this portion is bypassed by the electrode 14 of the LED array 4. For this reason, each light emitting body 6 is flip-chip connected using the gold bumps 18 and the tin bumps 20 at the two upper and lower positions in the drawing.

The process of flip-chip connection will be described with reference to FIG. The electrodes 16 are formed on the glass substrate 2 and the electrodes 14 are formed on the LED array 4. Gold bumps 18 are formed on the LED array 4, and tin bumps 20 are formed on the glass substrate 2. These bumps are formed by supplying fine wires of gold or tin from the capillary and heating the LED array 4 or the glass substrate 2 with ultrasonic vibration, for example, by applying ultrasonic vibration to the fine wires of gold or tin.
In addition to the space between the ED array 4 and the glass substrate 2, a thin wire of gold or tin is pressed against the LED array 4 and the glass substrate 2. The gold wire and the tin wire are bonded to the LED array 4 and the glass substrate 2 by the heat at this time and the frictional heat and the applied pressure due to the ultrasonic vibration. The bonding may use only heat or only ultrasonic vibration. By bonding, the tip of the gold wire or tin wire is bonded to the LED array 4 or the glass substrate 2 into a ball shape, and if the gold wire or tin wire is cut above the ball immediately after bonding, the bumps 18, 20
Is obtained. The gold wire or the tin wire may be cut, for example, by moving the capillary while applying ultrasonic waves to cut by ultrasonic vibration, or by locally heating the tip of the capillary, or cutting with a laser or the like. Although the bump forming method itself is the same as that described in Nikkei Microdevice, the tin wire is soft, and the ball 16 can be easily formed even on the electrode 16 on the fragile glass substrate 2, and the cutting after the ball is formed. Is easy. Further, unlike solder, tin is easy to draw into a fine wire, cheaper than gold wire, and soft, so that the temperature during ball formation can be lowered, ultrasonic vibrations can be weakened, and pressure can be reduced. For example, the eutectic point of gold and tin is 217 ° C., and the contact surface between the gold and tin wire on the surface of the electrode 16 is heated to about 200 ° C. by ultrasonic waves or heat.
A eutectic can be formed to form a ball.

By thus forming the gold bumps 18 and the tin bumps 20 by a method similar to wire bonding, the sizes of the gold bumps 18 and the tin bumps 20 can be made constant. This is because the diameter of the gold wire or the tin wire determines the size of the bumps 18 and 20. Next, the bump formation process is similar to wire bonding, and the number of processes is smaller than that of solder bump formation. Further, the electrodes 16 on the LED array 4 and the glass substrate 2 due to formation of a barrier film or a conductive metal film, solder plating, etc.
Therefore, the LED array 4 is not wasted when bumps are formed.

After the bumps 18 and 20 are formed, the LED array 4 is picked up by, for example, a collet 22, and the gold bump 18 is thermocompression bonded to the tin bump 20 by a die mounter. Therefore, for example, the glass substrate 2 is heated to about 200 ° C. by a die mounter (not shown), and the collet 22 is used to drive the LED array 4
Should be lowered to the connection position. By doing this, the pressure from the collet 22 and the heating by the die mounter
The gold bump 18 forms a eutectic crystal with the tin bump 20 and can be connected to each other. The formation of the eutectic does not have to proceed to the depths of the bumps 18 and 20, but only the surface portion. The heating temperature may be lower than the eutectic point of 217 ° C., and the contact surface between the gold bump 18 and the tin bump 20 may be heated by ultrasonic vibration instead of being uniformly heated by the die mounter. The eutectic point of silver and tin is 227 ° C, which is as low as that of the eutectic of gold and tin.
Silver bumps may be used instead of the gold bumps 18.

Since the gold bump 18 and the tin bump 20 can be connected at a low temperature, no load is applied to the LED array 4 and the glass substrate 2. Further, unlike the case of the solder bump, since the treatment in the reflow furnace is not required, the gold layer on the surface of the electrode 16 is attacked by the diffusion of the solder, or the solder is diffused and the light emitting member 6 is emitted.
Is never contaminated. Then, one LED array 4 as a whole can be flip-chip connected by thermocompression bonding by a die mounter, and bumps can be formed by a simple process. Therefore, the yield when connecting the bumps to each other is high, and the loss of the expensive LED array 4 is small.

[0016]

As described above, the present invention has the following advantages. (1) Since the bumps are formed using tin wires, gold wires, or silver wires, the bumps can be easily formed and uniform bumps can be obtained. (2) The bump forming process is simple, and there is no contamination or waste of electronic components or substrates during bump formation. (3) Since gold bumps and silver bumps can be connected to tin bumps at about 200 ° C, the bumps can be easily connected to each other, and there is no connection failure or reduction in yield at the time of connection. (4) The tin bumps used are extremely inexpensive.

[Brief description of drawings]

FIG. 1 is a side view of an embodiment.

FIG. 2 is a plan view showing a gold bump on an LED array used in an example.

FIG. 3 is a plan view showing tin bumps on a glass substrate used in Examples.

FIG. 4 is a side view showing a thermocompression bonding process in an example.

[Explanation of symbols]

 2 glass substrate 4 LED array 6 light emitter 14 electrode 16 electrode 18 gold bump 20 tin bump 22 collet

Claims (1)

[Claims] 1. In a flip-chip connection structure of an electronic component in which a bump provided on an electronic component and a bump provided on a substrate are connected, one bump is a bump containing tin as a main component and the other bump is gold or silver. A flip-chip connection structure for electronic parts, characterized in that it is a bump whose main component is.