JP2015000986A - Joining material and joint structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joint structure in which a low melting point phase having 200°C or lower solid phase temperature can be eliminated in a short time at the process temperature equal to the conventional temperature and by such a heating process that shorter-time compression is not necessitated and consequently which has high heat resistance.SOLUTION: Since the joint structure is joined by using a joining material, which comprises a Sn-Bi alloy, Cu and Zn and satisfies relationships: 0.6Y≤X, 0.2Z≤Y, and 0.03X≤Z≤0.1X when the content of the Sn-Bi alloy is X wt.%, that of Cu is Y wt.% and that of Zn is Z wt.%, the low melting point phase having 200°C or lower solid phase temperature can be eliminated in the short time and consequently the joint structure has high heat resistance.

Description

  The present invention relates to a bonding material that requires heat resistance, such as wiring connection in a power semiconductor device.

  In the power semiconductor device, the connection between the electrode of the semiconductor element and the external conductor has been replaced with the solder bonding from the solid phase bonding by the aluminum wire. For example, Sn-Ag solder is used as a bonding material for this solder bonding.

  However, semiconductor elements that can operate in high-temperature environments such as GaN and SiC are beginning to be used as semiconductor elements in power semiconductor devices. These semiconductor elements using GaN or SiC are required to have a heat resistance of, for example, 200 ° C. to 250 ° C. for connection between the electrode of the semiconductor element and the external conductor. However, Sn—Ag solder, which is an example of lead-free solder, cannot achieve such heat resistance because it cannot ensure a melting point difference with respect to operating temperature.

  In order to realize a lead-free solder material that ensures heat resistance, for example, in Patent Document 1, a bonding material in which an alloy layer is formed is formed. 6 (a) and 6 (b) are diagrams showing a process of forming a bonding material disclosed in Patent Document 1. FIG.

  In patent document 1, as shown to Fig.6 (a), after preparing Sn-Bi type alloy particle 51 and Cu particle 52, it heats for 90 minutes or more at the process temperature more than the melting | fusing point of Sn-Bi type metal particle 51. Thereby, as shown in FIG. 6B, the bonding material 53 in which the outer periphery of the Cu particles 52 is covered with the alloy layer 54 is formed.

  In such a bonding material 53, since the interlayer connection is performed by bonding the alloy layers 54 having a solid phase temperature of 250 ° C. or higher, the alloy layer 54 does not melt even in a reflow resistance test (for example, 230 ° C.), and has high heat resistance. Have sex.

JP 2002-94242 A

  However, the bonding material 53 of Patent Document 1 requires heating for 90 minutes or more in order to form the alloy layer 54. The reason why the heating for a long time is necessary is that the interdiffusion speed of Cu and Sn is slow. As means for solving this problem, in order to increase the diffusion rate, it is conceivable that the process temperature is increased to, for example, 300 ° C. or higher, or heating is performed while pressurizing at 1 MPa or higher. This is not desirable because a load is applied to the Bi-based alloy particles 51 and the Cu particles 52.

  An object of this invention is to implement | achieve the joining structure which has high heat resistance by the heating process which does not require high process temperature and does not require pressurization.

  In order to solve the above problems, the bonding material according to the present invention is composed of Sn—Bi alloy and Cu and Zn, excluding inevitable impurities, and the content ratio of Sn—Bi alloy is X wt%, and the Cu content is When Ywt% is set and the Zn content is Zwt%, the relationship of 0.6Y ≦ X, 0.2Z ≦ Y, 0.03X ≦ Z ≦ 0.1X is satisfied.

  According to the bonding material of the present invention, it is possible to realize a bonded structure having high heat resistance by a heating process that does not require high process temperature and does not require pressurization.

(A) Schematic of the junction structure of Embodiment 1 of the present invention, (b) Flow chart of the method for manufacturing the junction structure of Embodiment 1 of the present invention. Sn-Bi binary phase diagram The figure which shows the relationship of Sn-Bi alloy, Cu, and Zn discovered in Embodiment 1 of this invention Schematic sectional view of the bonded structure according to Embodiment 1 of the present invention. The figure which shows the table | surface for comparing the effect of the structure of this Embodiment 1, and a prior art example. (A), (b) The figure which shows the formation process of the joining material disclosed by patent document 1

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
The joined structure according to the first embodiment of the present invention is obtained by joining a first conductor 1 and a second conductor 3 with a joining material 2 as shown in FIG.

  First, the configuration of the bonding material according to the first embodiment of the present invention will be described. The bonding material 2 according to the first embodiment is used, for example, for wiring connection corresponding to a large current in a power semiconductor device, component mounting on an electronic circuit board, or wiring formation. The bonding material 2 of the first embodiment is mainly composed of an alloy, a solvent, and an activator. The bonding material 2 of the first embodiment is prepared by preparing these alloys, solvents, and activators, and adjusting the viscosity according to the shape of the bonding member, but adding rosin or a thixotropic agent as necessary, The bonding material may be thixotropic.

  The alloy in the bonding material 2 of the first embodiment is composed of Sn—Bi alloy, Cu, and Zn metal powder, excluding inevitable impurities. As will be described in detail later, the alloy in the bonding material 2 of the first embodiment specifically has a Sn-Bi alloy content of Xwt%, a Cu content of Ywt%, and a Zn content of In the case of Zwt%, one of the characteristics is that the relationships of 0.6Y ≦ X, 0.2Z ≦ Y, and 0.03X ≦ Z ≦ 0.1X are satisfied.

  As will be described in detail later, in the bonding material 2 of the first embodiment, the particle size of the Sn—Bi alloy is 0.1 μm or more and 30 μm or less, and the particle size of Cu is 0.5 μm or more and 30 μm. One of the features is that the particle size of Zn is 0.005 μm or more and 10 μm or less.

  The solvent in the bonding material 2 of the first embodiment is, for example, octanol or terpineol.

  The activator in the bonding material 2 of the first embodiment is, for example, an organic acid such as diglycolic acid or sebacic acid.

  Then, the manufacturing method of the joining structure using the joining material of this Embodiment 1 is demonstrated using FIG.1 (b).

  In FIG. 1B, first, in step S01, the bonding material 2 is supplied to the first conductor 1 at room temperature. In this step, as a method for supplying the bonding material 2, for example, dispensing or a printing method is used.

  Next, in step S02, the second conductor 3 is mounted on the bonding material 2 at room temperature.

  Next, in step S03, the first conductor 1 and the second conductor 3 are heated in a state in which the bonding material 2 is wet at a temperature equal to or higher than the liquid phase temperature of Sn—Bi contained in the bonding material 2, and bonded. The mutual diffusion reaction of each alloy in the material 2 is promoted. Specifically, for example, the mutual diffusion reaction of each alloy in the bonding material 2 is promoted by heating at 230 ° C. for 30 minutes. At this time, the atmosphere may be air, but in order to ensure good wettability of the bonding material 2, a mixed atmosphere of hydrogen and nitrogen, or a reducing atmosphere such as a hydrogen atmosphere is desirable. Furthermore, a reduced pressure atmosphere is desirable in order to reduce voids due to volatilization of the solvent and activator during bonding. Thereafter, in the same manner, in step S03, the bonding material 2 in which the mutual diffusion reaction of each alloy is promoted is cooled, and the first conductor 1 and the second conductor 3 are bonded by the bonding material 2, whereby a bonded structure is manufactured. Is done.

  Here, the alloy composition of Sn—Bi contained in the bonding material 2 will be described with reference to FIG. In the first embodiment, the process temperature is set to 230 ° C. or lower, which is the minimum temperature at which Sn—Ag solder (for example, Sn—3.0 wt% Ag—0.5 wt% Cu having a melting point of 217 ° C.) can be melted. Targeted. Further, considering the temperature variation of 10 ° C. in the bonding process, the lower limit value of Bi with respect to Sn was set to 21 wt%, and the upper limit value was set to 58 wt% which is a eutectic composition.

  Subsequently, the inventors have obtained a bonding material 2 that can produce a bonded structure having high heat resistance by a heating process that does not require high process temperature and does not require pressurization (in a non-pressurized state). The composition was verified. The results found from this demonstration are shown in FIG. FIG. 3 shows the relationship regarding the composition of the Sn—Bi alloy (Sn-21 wt% Bi) and Cu and Zn, which was found by the inventors' verification. FIG. 3 shows that the composition of the Sn—Bi alloy with respect to Cu is 0 wt% to 100 wt% from the lower left to the lower right, and the composition of Cu with respect to Zn is 0 wt% to 100 wt% from the lower right to the upper. It indicates that the composition of Zn with respect to the Sn—Bi alloy is 0 wt% to 100 wt% from the top to the bottom left.

  In FIG. 3, first, the relationship between the Sn—Bi alloy and Cu will be described. The inventors conducted various demonstrations, and in order for the Cu particles to come into surface contact with each other due to the wettability of the bonding material 2 itself in a non-pressurized state, the composition of the Sn—Bi alloy with respect to Cu is 60 wt% or more. I found it necessary. In other words, it has been found that in order to bring Cu particles into surface contact with each other in a non-pressurized state, it is necessary to be within the range of the arrow A1 shown in FIG.

  Next, the relationship between Zn and Cu will be described. The inventors have found that the composition of Cu with respect to Zn needs to be 20 wt% or more in order to ensure the wettability of the bonding material 2 in a non-pressurized state by performing various demonstrations. That is, it has been found that in order to ensure the wettability of the bonding material 2 in a non-pressurized state, it is necessary to be within the range of the arrow A2 shown in FIG.

  Next, the relationship between the Sn—Bi alloy and Zn will be described. The inventors have conducted various experiments to form an intermetallic compound of Cu—Zn and Cu—Sn—Zn at the joint in a non-pressurized state in order to form a composition of Zn with respect to the Sn—Bi alloy. Was found to be 3 wt% or more. In addition, by conducting various experiments, it was found that the composition of Zn with respect to the Sn—Bi alloy needs to be 10 wt% or less in order to ensure the wettability of the bonding material 2 in a non-pressurized state. . That is, in order to form an intermetallic compound of Cu—Zn and Cu—Sn—Zn at the joint portion without applying pressure, and to ensure the wettability of the joining material 2, the composition of Zn with respect to the Sn—Bi alloy It has been found that it is necessary that the content be 3 wt% or more and 10 wt% or less within the range of the arrow A3 shown in FIG.

  From the above-described verification results, the bonding material 2 capable of producing a bonded structure having high heat resistance by a heating process that does not require high process temperature and does not require pressurization (in a non-pressurized state). The inventors have found that the composition is in the range indicated by region B1 in FIG. Specifically, in the region B1, when the content rate of the Sn—Bi alloy is Xwt%, the Cu content rate is Ywt%, and the Zn content rate is Zwt%, 0.6Y ≦ X, 0.2Z ≦ Y and 0.03X ≦ Z ≦ 0.1X.

  Note that metals such as Zn and Cu are easily oxidized at a relatively high temperature. Therefore, it is not desirable for the bonding material 2 to contain Zn or Cu in an excessive ratio (for example, 80 wt% or more) with respect to the wettability of the bonding material 2 itself.

  Next, a detailed configuration of the bonded structure using the bonding material 2 described above will be described. FIG. 4 is a schematic cross-sectional view showing a bonded structure manufactured by bonding a conductor or the like with the bonding material 2 described above.

  If the composition ratio of the Sn—Bi alloy, Cu, and Zn contained in the bonding material 2 in the first embodiment is in the range of the region B1 in FIG. 3, the first surface 1f that corresponds to the bonding surface of the first conductor 1 and A joint portion having high heat resistance can be formed between the second surfaces 3f corresponding to the joint surface of the second conductor 3. Specifically, the first surface 1f and / or the second surface 3f, which are Cu, interdiffuse with Sn contained in the bonding material 2 in step S03 of FIG. A second metal region 12 is formed in a part of the second surface 3 f, and the first conductor 1 and the second conductor 3 are joined by the second metal region 12.

  Here, the bonding material 2 is composed of a first metal region 11 indicated by dots in FIG. 4, a second metal region 12 indicated by hatching in FIG. 4, and a third metal region 13 indicated by horizontal lines in FIG. Yes. Here, the 1st metal area | region 11 is an area | region containing the coupling body of Cu particle | grains which forms the path | route which electrically connects the 1st surface 1f and the 2nd surface 3f. The second metal region 12 is a region mainly composed of at least two kinds of metals selected from the group consisting of a Sn—Cu intermetallic compound, a Cu—Zn intermetallic compound, and a Cu—Sn—Zn intermetallic compound. . The third metal region 13 is a region containing Bi as a main component. In the first metal region 11, the Cu particles are in surface contact with each other to form a surface contact portion. Further, at least a part of the second metal region 12 is in contact with the first metal region 11, and at least a part of the third metal region 13 is in contact with the second metal region 12.

  The joining member 2 according to the first embodiment configured as described above has a high heat resistance in which the low melting point phase having a solid phase temperature of 200 ° C. or less has disappeared and the solid phase temperature is 250 ° C. or more. A joined portion can be formed. Specifically, the bonding material 2 is at least selected from the group consisting of Cu having a melting point of 1080 ° C., an Sn—Cu intermetallic compound having a melting point of 415 ° C. or higher, a Cu—Zn intermetallic compound, and a Cu—Sn—Zn intermetallic compound. It is composed of two metals, Bi having a melting point of 270 ° C.

  Note that a device such as Si, GaN, or SiC may be used for either the first conductor 1 or the second conductor 3. For example, when a Si device is used for the first conductor 1, Cu, Ag, Ni, or Au, which is a metal that interdiffuses with Sn contained in the bonding material 2, needs to be formed on the first surface 1 f. There is. These metals can be joined by interdiffusion with Sn to form a Cu—Sn intermetallic compound, an Ag—Sn intermetallic compound, a Ni—Sn intermetallic compound, or an Au—Sn intermetallic compound. it can. Since any intermetallic compound has a melting point of 250 ° C. or higher, high heat resistance can be maintained.

  Next, the particle size of the alloy contained in the bonding material 2, the ratio other than the above, and the additive elements will be described.

  As described above, in the first embodiment, the particle size of the alloy is such that the particle size of the Sn—Bi alloy is 0.1 μm or more and 30 μm or less, and the particle size of Cu is 0.5 μm or more and 30 μm. The Zn particle size is 0.005 μm or more and 10 μm or less.

  The reason for defining the particle size of Zn as described above will be described. In step S03 of FIG. 1, in order to increase the mutual diffusion rate of Sn, Zn and Cu, by increasing the diffusion area, that is, by reducing the particle size of Zn or Cu existing as a solid during heating, It is necessary to increase the specific surface area. Here, when Zn having a large particle size of, for example, 11 μm to 58 μm is used, it does not sufficiently undergo mutual diffusion reaction with Sn and Cu, and remains as a single element, and thus the Cu—Sn—Zn intermetallic compound as described above. Is not formed, and the disappearance rate of the low melting point phase having a solid phase temperature of 200 ° C. or lower is lowered. Thus, since Cu has a relatively slow mutual diffusion rate with Sn, it is easy to maintain a substantially spherical shape before melting and heating, so that the first surface 1f and the second surface 3f at the joint are electrically connected. It is easy to take a role to form a route. However, if the Cu particle size is reduced too much, the gap between the first surface 1f and the second surface 3f is not maintained, and it becomes difficult to form a matrix by the first metal region 11, and the first surface at the joint is formed. It is difficult to form a path that electrically connects 1f and the second surface 3f. Therefore, in Embodiment 1, these problems are solved by reducing the particle size of Zn.

  There are various methods for reducing the metal particle size in both the gas phase method and the liquid phase method. In the first embodiment, the laser evaporation method is used. The reason for using the laser evaporation method is to reduce the particle size of Zn in a desired solvent by preventing participation. The laser evaporation method can reduce the particle size of Zn in a high boiling point solvent, so that the state covered with the solvent is maintained until the bonding temperature is reached, and oxidation is prevented by suppressing contact with oxygen. be able to. This is because Zn itself is a metal that is relatively easy to oxidize among metals, and when the particle size is reduced, the specific surface area becomes large, so that it becomes easy to be combined with oxygen in the high temperature environment in step S03 in FIG. This is because the interdiffusion rate with Sn or Cu tends to decrease.

  As a solvent, octanol having a boiling point of around 195 ° C. was selected for an assumed process temperature of 150 ° C. to 230 ° C. As the solvent, terpineol at around 215 ° C. may be selected.

  In the above description, the ratio of the Sn—Bi alloy has been described using a Bi ratio of 21 wt% in the alloy. However, the Bi ratio in the alloy may be 21 wt% or more and 58 wt% or less. . When the ratio of Bi in the alloy increases from 21 wt% to 58 wt%, the composition approaches the eutectic composition, so that the wettability of the bonding material 2 itself is improved. Further, since the Sn ratio in the alloy is reduced from 79 wt% to 42 wt%, the intended disappearance time of the low melting point phase is also accelerated, and there is no problem due to the Bi ratio in the alloy increasing from 21 wt% to 58 wt%. Therefore, if the ratio of Bi is 21 wt% or more and 58 wt% or less, the range of the region B1 in FIG. 3 is not reduced and no problem occurs.

  Note that the Sn—Bi alloy has an alloy ratio of 0.001 wt% or more and 3 wt% or less of Ag and / or an alloy ratio of 0. 0% for the purpose of improving the wettability of the bonding material 2 by lowering the melting point. 001 wt% or more and 3 wt% or less of Ni may be included as a trace additive element. In the Sn—Bi alloy, when the content ratio of Ag and Ni is high (for example, when Ag is 3 wt% and Ni is 3 wt%), it may be referred to as an Sn—Bi alloy. Then, Sn—Bi alloys including Sn—Bi alloys are used.

  Next, the effects of the configuration of the first embodiment and the conventional example when the Sn-58Bi alloy is used will be compared. FIG. 5 shows a table for comparing the effects. Here, Cu is used as the material of the first conductor 1 and the second conductor 3.

  As shown in FIG. 5, levels 1 to 3 in which the process time is changed for the bonding material corresponding to the conventional example are set, and the process time is changed for the bonding material corresponding to the first embodiment. Levels 4 to 5 were set to 0, the peak temperature of the joint obtained at each level was measured twice by differential scanning calorimetry (DSC), and the solid phase temperature was measured. As a result, the following was found.

  When the process time is 5 minutes as in level 1 and level 4, a low melting point phase (Sn—Bi alloy) of 200 ° C. or lower is detected at the initial stage of the bonding process in step S03 of FIG.

  On the other hand, in Level 3, a low melting point phase is detected even at a process time of 60 minutes, whereas in Level 5, a low melting point phase is not detected even if it is 30 minutes shorter than Level 3, and the solid phase temperature at the junction is It is 270 ° C., which is the melting point of Bi. That is, by comparing the level 3 and the level 5, it is suggested that all Sn is replaced by a Cu—Sn intermetallic compound or a Cu—Zn—Sn intermetallic compound by containing a predetermined amount of Zn. The From this result, the bonding material according to the first embodiment exhibits a low melting point phase having a solid phase temperature of 200 ° C. or lower in a heating process that does not require pressurization for a short time at the same process temperature as the conventional example. It can be eliminated in a short time, and it is thereby possible to provide a bonded structure with high heat resistance.

  The present invention can be used as, for example, a bonding material used for a bonding portion in a power semiconductor device.

DESCRIPTION OF SYMBOLS 1 1st conductor 1f 1st surface 2 Joining material 3 2nd conductor 3f 2nd surface 11 1st metal area | region 12 2nd metal area | region 13 3rd metal area | region

Claims (7)

Consists of Sn-Bi alloy and Cu and Zn, excluding inevitable impurities,
When the Sn-Bi alloy content is Xwt%, the Cu content is Ywt%, and the Zn content is Zwt%, 0.6Y≤X, 0.2Z≤Y, 0.03X≤Z ≦ 0.1X is satisfied,
Bonding material. The Sn—Bi alloy has a Bi ratio of 21 wt% or more and 58 wt% or less in the alloy.
The bonding material according to claim 1. The particle size of the Sn—Bi alloy is 0.1 μm or more and 30 μm or less, the particle size of the Cu is 0.5 μm or more and 30 μm or less, and the particle size of the Zn is 0.005 μm or more and 10 μm. Is
The bonding material according to claim 1 or 2. The Sn—Bi alloy contains Ag of 0.001 wt% or more and 3 wt% or less in the alloy, and one or more kinds of Ni in the alloy of 0.001 wt% or more and 3 wt% or less,
The bonding material according to any one of claims 1 to 3. The joint portion between the first conductor and the second conductor is joined by the joining material according to any one of claims 1 to 4.
Bonding structure. The joint includes a first metal region including a combination of Cu particles that form a path that electrically connects the first surface of the first conductor and the second surface of the second conductor; A second metal region composed mainly of at least two metals selected from the group consisting of an Sn intermetallic compound, a Cu—Zn intermetallic compound, or a Cu—Sn—Zn intermetallic compound; and a third composed mainly of Bi. Composed of metal regions,
In the first metal region, the Cu particles are in surface contact with each other to form a surface contact portion, at least a part of the second metal region is in contact with the first metal region, and at least a part of the third metal region is formed. Is in contact with the second metal region,
The joint structure according to claim 5. When the second conductor is made of Cu or a Cu alloy, and the first conductor is made of Si, GaN, or SiC, Cu, Ag, Ni, or Au is formed on the surface of the first surface of the first conductor. Been formed,
The joining structure according to claim 5 or 6.

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