JPH0652822B2 - Bonding material for mounting semiconductor element and mounting method using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor element mounting bonding material for mounting an optical semiconductor element or the like used in the fields of optical communication, optical information processing and the like, and a mounting method using the same.

[0002]

2. Description of the Related Art In recent years, the demand for semiconductor lasers has increased in many fields, and GaAs-based and InP-based semiconductors have been actively commercialized. And, these have realized high performance, high reliability, and low cost by the progress of crystal growth, process technology, and package technology, and have expanded the application range. It can be said that the packaging technology has contributed most to the realization of low cost by mass production. Moreover, the final performance and reliability of the device are greatly influenced by the packaging technology, and have been greatly improved and devised up to the present day.

An optical semiconductor device such as a semiconductor laser has a structure shown in FIG. 1 in order to reduce thermal resistance when it is assembled into a package.
The configuration shown in 0 is often adopted. A material having excellent heat conduction such as copper is used for the heat sink 1, and in order to reduce mechanical strain caused by the difference in thermal expansion coefficient between the semiconductor element 50 and the heat sink 1, indium 2 which is a soft metal is used as a solder material. It is used. Usually, the heat sink 1 has a simple structure in which it is brazed integrally with the stem 8, and this mounting method is called direct bonding. For example, in the case of a semiconductor laser, a package assembled by this method is 4
A low thermal resistance of about 0 ° C./W can be easily obtained.

However, in the direct bonding, the film thickness controllability and flatness of the solder by the indium 2 are required. That is, if the indium 2 serving as the solder layer is too thin, the bonding strength is reduced, and if it is too thick, the creeping up of the indium 2 on the side surface of the semiconductor element 50 covers the pn junction 9, as shown in FIG. , Electrical shorts or leaks may occur. Therefore, in order to satisfy these requirements, it is necessary to form the indium 2 by controlling the film thickness to 2-3 μm by vacuum vapor deposition. However, since the heat sink 1 which is the vapor deposition section is integrated with the stem 8 as described above, the portions other than the vapor deposition section such as the wiring posts 7 are masked one by one,
It has a drawback that indium must be prevented from adhering and the process becomes complicated.

In order to solve the above problems, Japanese Patent Laid-Open No.
Japanese Patent Laid-Open No. 2-143496 proposes a method for forming the mounting bonding material shown in FIG. According to this method, the indium 2 is once vapor-deposited on the Teflon film 20, and is pressed from the Teflon film 20 side with the iron 6 while applying ultrasonic waves to the heated heat sink 1, and the indium 2
By making the transfer as shown in FIG. 13, it is possible to simplify the process, and it is expected that the cost of the product will be significantly reduced. In FIG. 13, 2d is the transferred indium.

[0006]

However, in the above-mentioned direct bonding, the material for the transfer film is, for example, Teflon film 20.
Generally, Teflon (polytetrafluoroethylene) is used, but this material has a small bending elastic modulus, and when a strong ultrasonic wave is applied at the time of transfer, the surface of the indium 2 in contact with the heat sink 1 is melted to form a heat sink with the heat sink 1. Unless the adhesion was made stronger, the transfer could not be done cleanly. FIG. 14 shows the result of analysis of the surface of the transferred indium 2d by Auger Electron Spectroscopy (AES). According to this, it can be seen that fluorine or carbon is attached to the surface of the transferred indium 2d. This is because fluorine-based copolymers such as Teflon generally tend to decompose when the temperature rises,
It is considered that the application of ultrasonic waves locally decomposed the film material, and the fluorine and carbon contained in the Teflon film 20 adhered to the surface of the indium 2d.
Then, there is a problem that the fluorine or carbon dissociated from the surface of the Teflon film 20 causes defective adhesion between the indium 2d and the semiconductor element (not shown).

Further, as shown in FIG. 15, it is difficult to mount the semiconductor element 5 having an uneven surface. This is because the film thickness of the indium 2 must be 2 to 3 μm as described above, and when the unevenness is large, the gap 15 is generated and the semiconductor element 5 as a whole cannot be adhered, and the adhesion strength is insufficient. Because it will be. A first object of the present invention is a bonding material for mounting a semiconductor element, which can be easily transferred to a heat sink without using ultrasonic waves, has a clean surface after transfer, and provides stable adhesion strength of a semiconductor element. And to provide an implementation method using it.

A second object is that transfer can be easily performed to a heat sink without using ultrasonic waves, the surface after transfer is clean, and stable adhesion strength can be obtained even with a semiconductor element having unevenness on the surface. A bonding material for mounting a semiconductor element and a mounting method using the same.

[0009]

A bonding material for mounting a semiconductor device according to claim 1 is characterized in that a metal containing indium which becomes a solder layer is provided on a tetrafluoroethylene-ethylene copolymer film. To do. The bonding material for mounting a semiconductor device according to claim 2, wherein two layers of indium and a metal layer having a melting point between the two layers of indium and having a melting point exceeding the mounting temperature are soldered on a tetrafluoroethylene-ethylene copolymer film. It is characterized by being provided as a layer.

A mounting method using the bonding material for mounting a semiconductor element according to claim 3 is different from the bonding material for mounting a semiconductor element according to claim 1 or 2 in that it is different from a tetrafluoroethylene-ethylene copolymer film. Place on a heat sink so that the surfaces are in contact, press the soldering iron from the tetrafluoroethylene-ethylene copolymer film side to transfer the solder layer onto the heat sink, and transfer the semiconductor element to the heat sink via the transferred solder layer. It is to join.

[0011]

According to the bonding material for mounting a semiconductor element of claim 1, since the tetrafluoroethylene-ethylene copolymer film has an appropriate flexural modulus, the solder layer can be easily transferred onto the heat sink. can do. Further, claim 2
According to the bonding material for semiconductor element mounting described, most of the irregularities on the surface of the semiconductor element are absorbed by the deformation of the lower layer indium, the thickness of the upper layer indium does not change, and the entire semiconductor element is adhered. Can be made.

According to the mounting method using the bonding material for mounting a semiconductor element according to the third aspect, the solder layer is transferred onto the heat sink only by pressurizing with a trowel without using ultrasonic waves. There is no local temperature rise of the ethylene-ethylene copolymer film, and it is possible to suppress the migration of impurities to the solder layer surface due to thermal decomposition.

[0013]

EXAMPLES First, in the following first and second examples, a tetrafluoroethylene-ethylene copolymer (hereinafter referred to as "ETFE") was used as a material of a film of a bonding material for mounting a semiconductor element.
I will explain the background that led to the use. Teflon has been used as a film of a conventional bonding material as disclosed in JP-A-62-143496. However, in mounting a bonding material using a Teflon film, it is necessary to apply ultrasonic waves to transfer indium, which is a bonding metal, and thus impurities such as fluorine and carbon are also transferred from the Teflon film. Therefore, we decided to find a film that could transfer the joining metal without applying ultrasonic waves. If the film has a large thickness, it cannot be transferred well because the force from the iron, which is a pressing member, is not transmitted, so the film must be thin. However, if it is thin, it has the drawback of stretching when the film is pulled, so we decided to use a film with a certain degree of tensile strength.

In the experiment, tetrafluoroethylene-hexafluoropropylene copolymer (hereinafter referred to as "FEP"), which is the same fluororesin as Teflon, and tetrafluoroethylene-perfluoroalkyl vinyl ether (hereinafter referred to as "PFA"). ，
Four films of EFTE and a polyimide that is a thermoplastic were used. First, Table 1 shows a comparison of the physical properties of these substances and Teflon. The heat resistant temperatures of these substances are all higher than the mounting temperature, and there is no problem in mounting.

[0015]

[Table 1]

(1) The experimental results when FEP and PFA are used as a film will be described. FIG. 8 is a cross-sectional view when transferring indium by applying pressure to the film with a trowel. As shown in FIG. 8, when the film 21 is pressed by the iron 6, the film 21 jumps up so as to warp. At this time, film 2
Since the upper surface of 1 directly hits the iron 6, the shape of the iron 6 is reflected on the film 21. However, the bending elastic modulus of the film 21 is small, and even the lower surface of the film 21 in contact with the heat sink 1 which is the base is the iron. Because the power of 6 is difficult to transmit,
The lower surface bends with a curvature. Therefore, indium 2
However, the size of the iron 6 is not cut and more indium 2b is transferred than necessary. This is considered to be because FEP and PFA have properties similar to Teflon in both tensile strength and flexural modulus (see Table 1). F
It was found that when EP or PFA was used as a film, it could be transferred by using ultrasonic waves in the same manner as in the case of a Teflon film.

(2) The experimental results when polyimide is used as a film will be described. Taking advantage of the experimental results when the above FEP and PFA were used as a film, an experiment was carried out using polyimide as a film, which is a thermoplastic resin having both higher tensile strength and flexural modulus than Teflon.
FIG. 9 is a sectional view when indium is transferred by applying pressure to the film with a trowel. As shown in Table 1, since polyimide is a material that is considerably harder than Teflon, it has the feature that the force pressed by the iron 6 is transmitted to the lower surface of the film 31 as it is. As shown in FIG. 9, if the bottom surface of the iron 6 does not become parallel to the heat sink 1 and hits the film 31 at a slight angle, the film 31 becomes hard and the iron 6
Only the indium 2c corresponding to the portion hit by the iron 6 could be transferred because it did not absorb the force.

(3) From the experimental results of (1) and (2) above, an experiment was conducted using ETFE, which has a tensile strength and a flexural modulus both larger than Teflon and smaller than polyimide, as a film. This will be described below as an example. [First Embodiment] A first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a transfer process diagram using a bonding material for mounting a semiconductor element according to the first embodiment of the present invention. As shown in FIG. 1, the bonding material A for mounting a semiconductor element according to the present invention is
The indium 2 having a thickness of 2 μm is vapor-deposited on the ETFE film 10 having a thickness of 50 μm.

The mounting method using the semiconductor element mounting bonding material A will be described below. The bonding material A is pressed against the heat sink 1 from the ETFE film 10 side while applying an acceleration of about 0.5 m / sec ² and a static pressure of 300 g to the iron 6. At this time, the bottom of the iron 6 is circular and has a bottom area of 5
× 10 ^-3 cm ² and almost half of it is heat sink 1
Contact with. The heat sink 1 is heated to 80 ° C. Then, as shown in FIG. 2, ETFE
The film 10 is deformed by the impact when the iron 6 hits,
The vapor-deposited surface of the indium 2 extends and can be separated from the ETFE film 10 and transferred to the heat sink 1.

FIG. 3 shows a state of the transferred indium 2a. The shape of the bottom of the pressed iron 6 is beautifully transferred. In this way, it is possible to easily transfer an arbitrary shape to an arbitrary place on the heat sink 1. The result of the Auger electron spectroscopy analysis of the surface of the transferred indium 2a is shown in FIG. According to this, it is found that a clean surface of indium 2a free of fluorine and carbon can be obtained.

After that, a semiconductor element (not shown) may be placed on the indium 2a. As described above, according to this embodiment, since the ETFE film 10 has an appropriate flexural modulus, the bonding material A can be transferred only by pressing without using ultrasonic waves, and the ETFE film 10 can be transferred. The surface of the indium 2a can be cleaned without dissociating fluorine or carbon contained in the surface of the indium 2a to obtain stable adhesion strength of the semiconductor element (not shown). You can

In this embodiment, the acceleration and the static pressure corresponding to the bottom area of the iron 6 are set, but by changing these settings, it is possible to transfer a larger area. [Second Embodiment] A second embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a transfer process diagram using the semiconductor element mounting bonding material of the second embodiment of the present invention.

Bonding material B for mounting a semiconductor device according to the present invention
As shown in FIG. 5, the first indium 12, the gold 13, and the second indium 14 are sequentially formed on the ETFE film 10 having a thickness of 50 μm by vapor deposition.
The film thickness is 4 μm, 0.5 μm, and 2 μm, respectively. The mounting method using the bonding material B for mounting the semiconductor element is the same as that of the first embodiment, and FIG. 6 shows the ETFE while applying a static pressure to the iron 6.
The state of the bonding material B (12, 13, 14) transferred by being pressed against the heat sink 1 from the film 10 side is shown. According to this, similarly to the first embodiment, it is understood that the transferred image is formed in the shape of the bottom surface of the pressed iron 6 neatly.

Further, FIG. 7 shows a state in which the semiconductor element 5 having unevenness on the bonding portion is mounted. A ridge stripe 5a having a height of 3 μm is formed on the bonding surface of the semiconductor element 5. The ridge stripe 5a on the surface of the semiconductor element 5
Are absorbed mainly by the sinking of the first indium 12. The gold 13 is deformed due to the unevenness of the semiconductor element 5, but it does not melt and does not break at the mounting temperature, so that the first indium 12 and the second indium 14 can be separated, and the second indium. 1
In No. 4, the original film thickness is maintained even if it is deformed as shown in FIG.
Therefore, the extra creep of indium to the side surface of the semiconductor element 5 is reduced, the pn junction 9 is not covered, and defects such as electrical leakage or short circuit do not occur.

As described above, according to this embodiment, even when the semiconductor element 5 having irregularities on the bonding portion is mounted, the first
Similar to the embodiment of the above, since the ETFE film 10 has an appropriate flexural modulus, the bonding material B can be transferred only by pressurization, and the surface of the second indium 14 can be cleaned. it can. Further, while maintaining the film thickness of the second indium 14 that adheres to the semiconductor element 5, the unevenness on the surface of the semiconductor element 5 is easily absorbed mainly by the sinking of the first indium 12, so that it is stable. The adhesion strength can be obtained.

Although gold 3 is used as the intermediate layer in this embodiment, it goes without saying that a metal such as platinum or silver whose melting point exceeds the mounting temperature may be used.

[0028]

According to the bonding material for mounting a semiconductor device and the mounting method thereof of the present invention, since the tetrafluoroethylene-ethylene copolymer film has an appropriate flexural modulus, it is possible to use a soldering iron without using ultrasonic waves. It is possible to transfer the solder layer onto the heat sink just by applying pressure, and there is no local temperature rise of the tetrafluoroethylene-ethylene copolymer film, and the movement of impurities to the solder layer surface due to thermal decomposition is suppressed. You can As a result, the surface of the solder layer after transfer is cleaned, and stable adhesion strength of the semiconductor element is obtained.

Further, by interposing a metal layer having a melting point exceeding the mounting temperature between the two layers of indium, a stable adhesion strength can be obtained even in a semiconductor element having an uneven surface, and electrical leakage or short-circuit can occur. Nor.

[Brief description of drawings]

FIG. 1 is a transfer process diagram using a bonding material for mounting a semiconductor element in a first embodiment of the present invention.

FIG. 2 is a sectional view of a transfer process in the example.

FIG. 3 is a perspective view showing a bonding material after transfer in the example.

FIG. 4 is an AES of the surface of the bonding material after transfer in the example.
It is a figure which shows the elemental analysis result by.

FIG. 5 is a transfer process diagram using a semiconductor element mounting bonding material according to a second embodiment of the present invention.

FIG. 6 is a perspective view showing a bonding material after transfer in the example.

FIG. 7 is a view showing a state in which a semiconductor element having irregularities is mounted in the example.

FIG. 8 is a cross-sectional view of a transfer process when using FEP and PFA films.

FIG. 9 is a cross-sectional view of a transfer process when a polyimide film is used.

FIG. 10 is a conventional direct bonding configuration diagram.

FIG. 11 is a diagram showing a state in which an electrical failure has occurred due to an excessive thickness of the bonding material layer.

FIG. 12 is a transfer process diagram using a conventional bonding material for mounting a semiconductor element.

FIG. 13 is a perspective view showing a conventional bonding material after transfer.

FIG. 14 is a diagram showing a result of elemental analysis by AES of the surface of the bonding material after the conventional transfer.

FIG. 15 is a diagram showing a state in which a semiconductor element having irregularities is mounted on a conventional bonding material.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Heat sink 2 Indium 6 iron 10 ETFE (tetrafluoroethylene-ethylene copolymer) film 12 1st indium 13 Gold 14 2nd indium A, B Bonding material for semiconductor device mounting

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-143496 (JP, A) JP-A-59-231825 (JP, A) JP-A-60-3132 (JP, A)

Claims (3)

[Claims] 1. A semiconductor element mounting bonding material for directly bonding a semiconductor element to a heat sink, characterized in that a metal containing indium which forms a solder layer is provided on a tetrafluoroethylene-ethylene copolymer film. A bonding material for mounting semiconductor devices. 2. A semiconductor element mounting bonding material for directly bonding a semiconductor element to a heat sink, comprising: 2 on a tetrafluoroethylene-ethylene copolymer film.
A bonding material for mounting a semiconductor element, comprising a layer of indium and a metal layer interposed between the two layers of indium and having a melting point exceeding the mounting temperature as a solder layer. 3. The semiconductor element mounting bonding material according to claim 1 or 2 is placed on a heat sink so that the surface different from the tetrafluoroethylene-ethylene copolymer film is in contact with the tetrafluoroethylene. -Mounting method using a bonding material for semiconductor element mounting, in which a solder layer is transferred onto the heat sink by pressing with a trowel from the ethylene copolymer film side and the semiconductor element is bonded to the heat sink via the transferred solder layer. .