JP2008147469A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device which uses a lead-free material as a joining material, assures sufficient performance, connection strength and resistance to thermal fatigue under a high temperature environment during use, and does not have a Si chip damaged by thermal stress. <P>SOLUTION: Ag nano paste which is slightly poor in resistance to thermal fatigue but is excellent in heat resistance is employed as joining materials 4 and 5 for joining the Si chip 1 and buffer plates 2 and 3. Sn-Cu-based solder which is slightly poor in the heat resistance but excellent in the resistance to thermal fatigue is employed as joining materials 8 and 9 for joining the buffer plates 2 and 3 and the electrodes 6 and 7. Use of the materials suitable for the place of the joining materials can assure the sufficient performance, connection strength and resistance to thermal fatigue and also achieve a lead-free semiconductor device which does not have the Si chip damaged by thermal stress. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a diode used for an alternator of a semiconductor device, particularly an automobile.

  The alternator for automobiles is a three-phase AC generator that generates electric power from the rotational force obtained by the engine and feeds the battery, and the alternator diode is used to supply the three-phase AC obtained by the generator to the battery. Has the function of rectifying to direct current. The alternator diode is composed of a Si chip having a rectifying function, a lead electrode and a base electrode having a current-carrying function, and solder for joining them, and a resin such as silicone rubber is filled inside the base electrode.

  At the time of alternator operation, since a large current flows through the alternator diode, the Si chip generates heat due to loss, and the Si chip, peripheral solder, lead electrode and base electrode reach a high temperature of 200 ° C. or more at the maximum. When the alternator stops, the current stops and the alternator diode is cooled to the ambient temperature. Since the alternator repeats operation and stop for a long time, the alternator diode repeats expansion by heating and contraction by cooling. At this time, since the thermal expansion amounts differ because the linear expansion coefficients of the Si chip, the lead electrode, and the base electrode are different, thermal stress is generated in the solder that joins them, and the solder is fatigued due to this thermal stress. There is a risk of destruction.

  For this reason, for example, as shown in Patent Document 1, between the Si chip and the lead electrode, between the Si chip and the base electrode, the linear expansion coefficient is larger than the linear expansion coefficient of Si, and the lead electrode and the base electrode material A diode provided with a stress buffer plate made of a material having a smaller coefficient of linear expansion has been proposed.

JP-A-56-50542

In recent years, as the impact of lead on the environment has become clear, there is an increasing tendency to restrict the use of lead in electronic components. In July 2006, the RoHS regulations were enforced in Europe. In order to comply with this RoHS regulation and eliminate lead from electronic parts, Sn-Ag series,
A wide variety of lead-free solders such as Sn-Bi solders have been developed.

  However, in the alternator diode, the temperature may reach a high temperature of 200 ° C. or higher. For this reason, a solder with a low melting point cannot be used as a bonding material. Furthermore, in order to ensure the characteristics and reliability of the alternator diode, the bonding material is required to have conductivity, thermal conductivity, connection strength, heat fatigue resistance, and low yield stress / hardness. However, no lead-free solder has been found that has all these required characteristics.

  The present invention has been made to solve the above-described problems, and its purpose is to use a lead-free material as a connection material and to provide sufficient performance and connection even in a high-temperature environment at the time of use. An object of the present invention is to provide a semiconductor device that ensures strength and thermal fatigue resistance and that does not cause damage to the Si chip due to thermal stress.

  In the present invention, in order to achieve the object, the bonding material on the upper side of the upper stress buffer plate and the bonding material on the lower side of the lower stress buffer plate are used at a higher temperature during use than the bonding material on the upper and lower sides of the Si chip. It was noted that the temperature was about 20 ° C. lower. The semiconductor device has a structure in which stress buffer plates are provided above and below the Si chip. As the bonding material above and below the Si chip, a bonding material composed of a mixture of silver nanoparticles and an organic material having a melting point of 200 ° C. or higher is used. The bonding material on the upper side of the buffer plate and the bonding material on the lower side of the lower stress buffer plate are made of a part or all of an alloy composed of Sn and Cu having sufficient connection strength and heat fatigue resistance at about 180 ° C. A bonding material is used. On the other hand, a stress buffer plate having a linear expansion coefficient closer to that of the Si chip than that of the lead electrode or the base electrode is used. As a result, the linear expansion coefficient between the Si chip and the stress buffer plate is relatively small, so that a bonding material composed of a mixture of silver nanoparticles having a relatively high yield stress and hardness and an organic material can be used. In addition, the coefficient of linear expansion between the stress buffer plate and the lead electrode base electrode is relatively large, but the Sn—Cu solder that joins the stress buffer plate and the lead electrode base electrode has sufficient connection strength.

  According to the present invention, there is provided a semiconductor device that uses a lead-free material as a connection material, does not cause damage to the Si chip due to thermal stress during use, and has sufficient connection strength and heat fatigue resistance. Obtainable.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a cross section of a semiconductor device according to an embodiment of the present invention. In this embodiment, stress buffer plates 2 and 3 are provided above and below the Si chip 1, and the Si chip and the stress buffer plate are bonded by a bonding material 4 and a bonding material 5 having a thickness of 0.05 mm. Cu lead electrodes 6 and Cu base electrodes 7 are provided above and below the stress buffer plates 2 and 3, and the thickness between the stress buffer plates 2 and 6 and between the stress buffer plates 3 and the base electrode 7 is 0. It is joined with a joining material 8 and a joining material 9 of 2 mm. The inner side of the base electrode is sealed with a sealing resin 10. The bonding materials 4 and 5 are made of a mixture of silver nanoparticles and an organic material, and the bonding materials 8 and 9 are made of Sn—Cu solder. It is preferable that the stress buffer plates 2 and 3 have a linear expansion coefficient close to that of a Si chip (3 × 10 ⁻⁶ / ° C.). Here, Mo (molybdenum, linear expansion coefficient 4.9 × 10 ⁻⁶ / ° C.) is used. Used. In addition, W (tungsten, linear expansion coefficient 4.5 × 10 ⁻⁶ / ° C.), Fe-42% Ni alloy (common name 42 alloy, linear expansion coefficient 5 × 10 ⁻⁶ / ° C.), CIC (Cu-Invar-Cu Laminated material, Invar (Fe—Ni alloy) linear expansion coefficient 2.8 × 10 ⁻⁶ / ° C., Cu linear expansion coefficient 16.5 × 10 ⁻⁶ / ° C.), Cu—Mo alloy, Cu—Mo sintered body (Equivalent linear expansion coefficient 7.3 × 10 ⁻⁶ / ° C.) or the like can be used to obtain the same effect.

Here, the reason why the present invention uses the above-described joining member will be described. In recent years, as the impact of lead on the environment has become clear, there is an increasing tendency to restrict the use of lead in electronic components,
In July 2006, the RoHS regulations were enforced in Europe. A wide variety of lead-free solders such as Sn-Ag series and Sn-Bi series solders have been developed so far in order to eliminate lead from electronic components in response to this RoHS regulation.

These lead-free solders are effective as solders for weak electrical devices used at relatively low temperatures. However, in the alternator diode, the temperature may reach 200 ° C. or more because the calorific value is large for flowing a large current and the ambient temperature is high because it is mounted near the engine of an automobile. For this reason, lead-free solders such as Sn—Ag and Sn—Bi, which have a low melting point, cannot be used, and conventionally high melting point solders such as Pb-5Sn have been used. That is, the joining material of the alternator diode is required to have a melting point of at least 200 ° C. or higher.
Furthermore, in order to ensure the characteristics and reliability of the alternator diode, the bonding material is required to have low conductivity, thermal conductivity, connection strength, heat fatigue resistance, and yield stress / hardness.

  In general, a lead-free solder having a high melting point such as zinc or silver has high yield stress and hardness, and there is a risk that the Si chip may be damaged by thermal stress during mounting or use. There are also lead-free solders with high melting points and low yield stress and hardness, such as Bi-Ag solders, but they have all the required characteristics such as low connection strength at low temperatures. No high melting point lead-free solder has been found. Therefore, a lead-free alternator diode has not been put into practical use.

  FIG. 2 shows the relationship between the specifications required for the bonding material and the characteristics of each material in realizing a lead-free alternator diode. None of the bonding materials meet any of the items, and it can be seen that the lead-free semiconductor device cannot be realized with a currently known single material.

  Next, the specifications required according to the position of the bonding material in the semiconductor device will be considered separately. FIG. 3 shows the relationship between the specifications required for the upper and lower Si chip bonding materials and the characteristics of each material. FIG. 4 shows the upper bonding material for the upper stress buffer plate and the lower bonding material for the lower stress buffer plate. The relationship between the specifications and the characteristics of each material is shown.

  In FIG. 3, compared with FIG. 2, the items of thermal fatigue resistance and relaxation of the force from the electrode are deleted. The bonding materials 4 and 5 above and below the Si chip 1 are sandwiched between the Si chip 1 and the stress buffer plates 2 and 3, and the difference in linear expansion coefficient between the Si chip 1 and the stress buffer plates 2 and 3 is the stress buffer plate 2. 3 is smaller than the linear expansion coefficient difference between the electrode 6 and the electrode 7, and a large thermal stress is not applied, so that the item of heat fatigue resistance becomes unnecessary. In addition, since the electrodes 6 and 7 are not in direct contact with each other, an item for reducing the force from the electrodes 6 and 7 is not necessary. Therefore, the bonding material formed from Ag nanopaste, which is a mixture of silver nanoparticles and an organic material, is suitable for all items.

  In FIG. 4, the heat resistance is lowered from 200.degree. C. to 180.degree. C. as compared with FIG. Since the bonding material 8 on the upper side of the upper stress buffer plate 2 and the bonding material 9 on the lower side of the lower stress buffer plate 3 are separated from the Si chip 1, the temperature during use becomes relatively low, and the required heat resistance The nature is also lowered. Sn-Cu solder has heat resistance to 180 ° C., and as a result, it is suitable in terms of heat resistance. In addition, since it is not in direct contact with the Si chip 1, the item for preventing Si chip cracking is also unnecessary. Therefore, Sn—Cu based solder is suitable for all items.

  3 and 4, a mixture of silver nanoparticles and an organic material is used for the bonding material above and below the Si chip, and the bonding material on the upper side of the upper stress buffer plate and the lower side of the lower stress buffer plate. It turns out that Sn-Cu type solder is suitable.

  Here, the mixture of silver nanoparticles and organic material is, for example, an independently dispersed nanoparticle in which the surface of silver nanoparticles is coated with a protective layer of organic matter, and the organic matter is removed by heating and the silver particles are combined. Plays the role of bonding material. For this reason, the bonding temperature is about 300 ° C. from which organic substances are removed, whereas the melting temperature after bonding has a characteristic of being 900 ° C. or more which is the same as the melting point of silver. In other words, joining with a mixture of silver nanoparticles and an organic material can ensure the same high heat resistance as silver solder, and the mounting temperature is low, so that the Si chip can be bonded to the stress buffer plate. It also has the effect of reducing thermal stress.

It is sectional drawing which shows the semiconductor device which becomes one Embodiment of this invention. It is a figure which shows the relationship between the specification requested | required of a joining material, and the characteristic of each material in the implementation | achievement of the alternator diode which does not contain lead. It is a figure which shows the relationship between the specification requested | required of the bonding material 4 on Si chip | tip and the bonding material 5 under Si chip | tip, and the characteristic of each material in one Embodiment of this invention. It is a figure which shows the relationship of the specification requested | required of the stress buffer board upper joining material 8 and the stress buffer board lower joining material 9, and the characteristic of each material in one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Si chip 2 Stress buffer plate of Si chip upper side 3 Stress buffer plate of Si chip lower side 4 Si chip upper side bonding material 5 Si chip lower side bonding material 6 Lead electrode 7 Base electrode 8 Stress buffer plate upper bonding material 9 Stress buffer plate Lower bonding material 10 Sealing resin

Claims (3)

A semiconductor chip having a rectifying function;
An upper stress buffer plate bonded via a first bonding material on the semiconductor chip;
A lead electrode joined to the upper stress buffer plate via a second joining material;
A lower stress buffer plate bonded via a third bonding material under the semiconductor chip;
A base electrode joined via a fourth joining material under the lower buffer plate,
The semiconductor device, wherein the first bonding material and the third bonding material are different in material from the second bonding material and the fourth bonding material. A semiconductor chip having a rectifying function;
An upper stress buffer plate bonded via a first bonding material on the semiconductor chip;
A lead electrode joined to the upper stress buffer plate via a second joining material;
A lower stress buffer plate bonded via a third bonding material under the semiconductor chip;
A base electrode joined via a fourth joining material under the lower buffer plate,
The difference in linear expansion coefficient between the semiconductor chip and the upper stress buffer plate is smaller than the difference in linear expansion coefficient between the upper stress buffer plate and the lead electrode,
The difference in linear expansion coefficient between the semiconductor chip and the lower stress buffer plate is smaller than the difference in linear expansion coefficient between the lower stress buffer plate and the base electrode,
The first bonding material and the third bonding material are bonding materials formed from silver nanopaste, and the second bonding material and the fourth bonding material are Sn-Cu based. A semiconductor device. The upper stress buffer plate and the lower stress buffer plate are Mo, W, Fe—Ni alloy, Fe—
The semiconductor device according to claim 2, wherein the semiconductor device is a laminated plate made of Ni alloy and Cu, or an alloy or sintered body made of Mo and Cu.

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