JP2007260695A - Joining material, joining method, and joined body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a joined body which can maintain satisfactory mechanical strength even under high temperature conditions by using a joining material substantially not containing lead. <P>SOLUTION: The joining material is obtained by focusing on silver which is a metallic material excellent in heat conduction/electric resistance/malleability and further in corrosion resistance as joining material to replace a metallic alloy having the melting temperature of the metallic material of ≥260°C, and composed of lead and gold as principal components, combining the same with tin which is the metallic material promising for high temperature system solder in terms of the melting point/oxidation resistance/workability, and increasing the amount of the silver, and further, adding copper thereto. Namely, the joining material is the one composed of ≥15 to ≤40 mass% silver, ≥15 to ≤15 mass% copper, and the balance tin. The metallic composition is made applicable under industrial practical conditions by employing a metallic film forming process like a vapor deposition process. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention is particularly suitable for joining electronic device parts, for joining metal materials, non-metal materials and metal materials whose surfaces are metallized, and non-metal materials whose surfaces are metallized. The present invention relates to a bonding material, a bonding method, and a bonded body using the bonding material.

  Solder bonding technology, which is a bonding technology using a certain object and a material having a lower melting point than that object, has been used for a long time, and semiconductors such as microprocessors, memories, resistors, and capacitors have also been used for bonding electronic devices. Widely used for joining devices and electronic components to mounting boards. Solder bonding not only mechanically fixes a component to a substrate, but also has an advantage of being electrically bonded by including a conductive metal in the solder.

  Today, as personal devices such as personal computers and mobile phones are rapidly spreading, the selection of bonding materials and bonding methods in electronic component mounting technology is becoming increasingly important.

  Conventionally, tin-lead eutectic solder has been frequently used because it is extremely suitable for practical use. However, since the lead contained in the tin-lead eutectic solder is harmful to the human body, there is an urgent need to develop a so-called lead-free solder that does not contain lead.

  On the other hand, as bonding materials for power devices, for example, among current semiconductor devices, a low-temperature solder (tin-lead eutectic solder) mainly having a melting point of about 183 ° C. or lower and a high-temperature solder having a melting point of about 300 ° C. ( Lead-5 tin solder) is frequently used, and is used depending on the process.

  Among these, for low-temperature solders, those centered on tin-silver-copper alloys have reached the stage of practical application, and in the next few years, many set manufacturers will replace lead-free eutectic solders. It is scheduled to be completed.

  However, for a high-temperature solder, that is, a bonding material that forms a bonding portion that maintains good mechanical strength even at a high temperature condition of 260 ° C., for example, a gold-based alloy containing gold as a main component other than a high-lead-containing material is used. Although it is mentioned, it is a difficult material to use for general purposes because it uses a precious metal gold, and the material price increases significantly. Further, metal alloys mainly composed of metal materials other than lead and gold have not yet been put into practical use as high-temperature solders.

  Up to now, as a metal alloy having a melting point of around 300 ° C. mainly composed of a metal material other than lead and gold, a tin-based alloy mainly composed of tin having a melting point of 232 ° C., and zinc mainly composed of zinc having a melting point of 420 ° C. Base alloys and bismuth-based alloys mainly composed of bismuth having a melting point of 271 ° C. are promising candidates. In particular, it has been reported that tin-based alloys have been used as bonding materials in the past and have excellent characteristics in terms of price, bondability, workability, and bonding reliability ( Non-patent document 1).

  However, tin-based alloys have a problem in terms of heat resistance because they are mainly composed of tin, which is a low melting point element, as a high-temperature solder, and are still in practical use as a substitute material for lead-containing high-temperature solder. It has not reached (see Non-Patent Document 2).

Materia, 38 (1999), 919. Proc. Of the 17th Electronics Packaging Conference, 2003, 147.

The present invention uses a bonding material that does not substantially contain lead and gold, and a bonded body that can form a bonded portion capable of maintaining good mechanical strength even under high temperature conditions in a short time, a bonding method, and a substantial Joint material that does not contain lead, and can maintain good mechanical strength at the joint between the semiconductor element and the lead frame even under high temperature conditions, its joining method, and its joined body Another object of the present invention is to provide a semiconductor device including the bonding material.

  The present invention has a metal material having a melting temperature of 260 ° C. or higher, and is a metal having excellent thermal conductivity, electrical resistance, ductility and corrosion resistance as a joining material that substitutes for a metal alloy mainly composed of lead and gold. Focusing on the material silver, it was developed to realize a material combined with tin, which is a promising metal material for high-temperature solders in terms of melting point, oxidation resistance, and workability. By doing so, it has been made paying attention to the fact that such a material can be realized.

  The bonding material according to the first aspect of the present invention is a metal material containing silver, wherein silver is 15% or more and 40% or less, copper is 4% or more and 15% or less, and the balance is tin. .

  The bonding method of the second aspect of the present invention is the step of forming the bonding material layer on the surface of the first bonded body using the bonding material of the first aspect of the invention, and then the bonding temperature of the first step. It has the process of joining the said bonding material surface and a 2nd to-be-joined body at the above temperature.

  The joined body according to the third aspect of the present invention is a metallic material containing silver, and uses a joining material in which silver is 15% or more and 40% or less, copper is 4% or more and 15% or less, and the balance is tin. It is a joined body joined together.

In the present invention, a bonding material containing a tin-silver alloy as a main component and added with copper can satisfy heat resistance characteristics required for high-temperature solder without using lead or gold substantially.

The joined body of the present invention has sufficient joint strength without substantially using harmful lead and expensive gold, and can maintain mechanical strength even under high temperature conditions.

[First Embodiment: Bonding Material]
Hereinafter, the bonding material of the present embodiment will be described.
The bonding material of the present embodiment is a metal material containing silver, and is an alloy having a mass composition ratio of 15% to 40% silver, 4% to 15% copper, and the balance being tin. The alloy material does not exclude components such as gold, nickel, cobalt, bismuth, platinum palladium, and aluminum that are inevitably mixed.
Specific alloy materials such as tin-10 silver-10 copper, tin-15 silver-10 copper, and tin-20 silver-10 copper are suitable as the bonding material of the present invention.
In this alloy, when the amount of the silver and copper components is less than the above range, there is a problem that the amount of intermetallic compound having a high melting point is reduced and the heat resistance of the joint is lowered, while silver and copper When the amount of the copper component exceeds the above range, there is a problem that the liquidus temperature rises and it becomes difficult to bond at a practical bonding temperature.

This bonding material can be in a sheet form, a wire form, a solder paste form, or the like. When used as a solder paste, the alloy material can be prepared by mixing particles having an average particle diameter of 1 to 10 μm with commonly used solder paste material constituent components.
It can also be used for bonding by forming a thin layer on the surface of the solder-bonded member. When used as this thin layer, the bonding material can be used for bonding by forming it as a thin layer by means of plating or physical vapor deposition such as vapor deposition or sputtering. The thickness of the thin layer is not particularly limited, but the thickness of the thin layer bonding material should be not less than 1 μm and not more than 500 μm, more preferably not less than 310 μm and not more than 300 μm in order not to significantly increase the bonding time. Is desirable. If the thickness of the thin-layer bonding material is too thick, the material to be bonded will not sufficiently diffuse into the bonding material during the bonding time, and heat resistance may not be improved. There is a possibility that the bonding strength cannot be secured.

[Second Embodiment: Joining Method]
Hereinafter, the bonding method of the present embodiment will be described.

FIG. 1 is a cross-sectional view showing the bonding method of the present embodiment.
As shown to Fig.1 (a), the laminated body 4 is formed by laminating | stacking the 1st metal to-be-joined material 1, the joining material 5, and the 2nd metal to-be-joined material 2 first. At this time, pressurization may be performed.

  Next, the laminated body 4 is heated so that the first metal bonded material 1 and the second metal bonded material 2 are bonded via the bonding layer 3 as shown in FIG. Is obtained.

  When obtaining the laminated body 4, as shown in FIG. 2, the thin layer bonding material 5 is metallized in advance on the surface of the second metal bonded material 2, and the thin layer bonding material 5 is formed on the surface of the second metal bonded material 2. The laminated body 4 may be formed by laminating the first metal-bonded material 1 on a state in which is deposited. Conversely, the surface of the first metal bonded material is metallized in advance, and a laminated body is formed by laminating the first metal bonded material surface with a thin layer bonded material and the second metal bonded material. May be.

  The first metal bonded material or the second metal bonded material is metallized on the surface of another member made of metal, ceramics, semiconductor, etc., and used as a member for bonding the member to another member. Are also included in the scope of the present invention.

FIG. 3 is a cross-sectional view showing still another embodiment of the bonding method.
In this embodiment, the first metal bonded material 1 is metallized on the surface of the base material 7, and the second metal bonded material 2 is metalized on the surface of the base material 8. A thin layer bonding material 5 is disposed between the metallized layers to form a laminate 9. Thereafter, bonding is performed by heating the laminated body 9. The base material 7, the metallized layer 1, or the base material 8, and the metallized layer 2 are all selected from the group consisting of gold, nickel, silver, copper, palladium, platinum and aluminum, or a metal alloy using these metal materials. In this case, the laminate of the base material 7 and the metallized layer 1 is the first metal-bonded material, or the laminate of the base material 8 and the metallized layer 2 is the second metal-bonded material.

  FIG. 3 shows an example in which the first material to be bonded and the second material to be bonded are both metallized on the surface of the other base material, but only the first metal material to be bonded is metalized on the surface of the other base material. The second metal bonded material is also included in the scope of the present invention even when it is not metallized on another base material. On the contrary, the case where only the second metal bonded material is metallized on the surface of another base material and the first metal bonded material is not metallized on the other base material is also included in the scope of the present invention.

  Examples of means for metallizing the first and second metal bonded materials on the surface of another member include vapor deposition, plating treatment, and electron beam treatment.

Hereinafter, the member used for the said joining method is further demonstrated.
As the first metal bonded material 1 and the second metal bonded material, a metal material is usually used. The metal material can be selected depending on the application and is not particularly limited. However, when dissolved and diffused in a molten tin-silver alloy under high temperature conditions, the metal material dissolves in the tin-silver alloy, and the metal alloy formed is solidified. It is desirable that the material does not significantly decrease the phase line temperature. Specifically, a joint having excellent heat resistance is preferably a material selected from the group consisting of gold, nickel, silver, copper, palladium, platinum and aluminum, or a metal alloy using these metal materials. Can be formed. Further, metals other than those described above, for example, metals such as germanium, beryllium, niobium and manganese are also suitable.

  The thickness (average thickness) of the first metal bonded material and the second metal bonded material is desirably in the range of 0.1 μm to 500 μm.

  For example, when the metallized layer 2 is formed on the base material 8 as shown in FIG. 3, the laminate of the base material 8 and the metallized layer 2 is regarded as the second metal bonded material 2, and the metallized layer 2 and the base metal The total of the material 8 and thickness should just be the range of 0.1 micrometer or more and 500 micrometers or less.

  The thin-layer bonding material is desirably 1 μm or more and 500 μm or less, more preferably 30 μm or more and 300 μm or less in order not to significantly increase the bonding time. If the thickness of the thin-layer bonding material is too thick, the material to be bonded will not sufficiently diffuse into the bonding material during the bonding time, and heat resistance may not be improved, and if it is too thin, the wettability of the bonding material will decrease. There is a possibility that the bonding strength cannot be secured.

  Examples of the supply means in the form of a thin layer include plating treatment, solder paste, sheet solder, wire solder, or solder pre-coating by a super-jafit method-super solder method, physical vapor deposition methods such as vacuum deposition and ion plating, and the like. It is done.

  When solder paste is used, the solder paste thickness will increase to a high melting point if the solder paste thickness is extremely large, and the material to be joined will not sufficiently diffuse into the main tin layer layer during the joining time of several seconds. It is thought that it is not realized. Therefore, in order to appropriately satisfy both sides of realizing a high melting point in a short time, in order to make the solder paste thickness as small as possible, it is desirable to set it within the range of 50 to 100 μm, preferably 50 to 80 μm.

  When using a sheet solder material, if the sheet thickness is made extremely large, the material to be bonded will not sufficiently diffuse into the tin main component layer part in a bonding time of several seconds, and a high melting point will not be realized. It is done. Therefore, in order to appropriately satisfy both sides of realizing a high melting point in a short time, it is desirable to make the sheet thickness as small as possible within the range of 30 to 50 μm.

The joining method of the present invention will be further described.
The heating temperature at the time of heating the laminate is in the range of 265 ° C. or more and 450 ° C. or less. Within this range, the thin-layer bonding material mainly composed of a tin-silver alloy melts and can be bonded. The heating temperature is preferably 300 ° C. or higher.

  The heating time is desirably 0.1 seconds or more, and it is more preferable to perform heating so that the heating time at the peak temperature is 0.5 seconds or more. The heating time may be 30 seconds or less at the longest, and the heating may be performed so that the heating time at the peak temperature is 10 seconds or less.

  According to the bonding method of the present invention, since a bonding layer having a melting point equal to or higher than the solidus temperature of the tin-silver alloy is formed, as a 260 ° C guarantee required as a high temperature system mounting material, Also, the heat resistance of the bonding layer can be maintained. In the thin layer bonding material, the first metal bonded material or the second metal bonded material constituting element is formed in the bonding layer formed by diffusion of the first metal bonded material or the second metal bonded material. In addition to the phase in which tin is dissolved in the tin-silver alloy, an intermetallic compound phase composed of a tin-silver alloy and at least a constituent element of the second metal bonded material may be formed. As a result, a bonded body having good mechanical strength can be obtained in a short time even under high temperature conditions.

  The joined body and joining method according to the present invention may be used in any field, but in particular, components in electronic devices, semiconductor devices, particularly power semiconductor devices, which are placed under high temperature conditions during the manufacturing process or product use. It is used suitably for joining. In particular, it is particularly preferably used for joining a semiconductor element and a lead frame.

[Third embodiment: joined body]
FIG. 1B is an enlarged cross-sectional view showing an embodiment of the joined body of the present invention in which the first metal workpiece 1 is joined to the second metal workpiece 2 via the bonding material 3. is there.

In this embodiment, a metal material is used as the first metal bonded material 1 and the second metal bonded material 2.
The metal material that is the material to be joined can be selected depending on the application and is not particularly limited. However, when the material is dissolved and diffused in the molten joining material 3 under high temperature conditions, it is formed as a solid solution in the joining material 3. It is desirable that the material does not significantly reduce the solidus temperature of the alloy.
Specifically, it is preferably selected from the group consisting of gold, nickel, silver, copper, palladium, platinum and aluminum, or a metal alloy using these metal materials, similarly to the second metal bonded material described later. Material. When these metals are used, a joint having excellent heat resistance can be formed. In addition to these metals, germanium, beryllium, niobium, manganese and the like are preferable materials.

  The bonding layer 3 is mainly composed of tin having a melting point of 232 ° C., and a tin-silver alloy using silver, which is a metal material excellent in heat conduction, electrical resistance, spreadability, and corrosion resistance, and contains copper. It is a bonding material characterized by having heat resistance of 260 ° C. or higher.

  In the bonding layer 3, an intermetallic compound formed by dissolving and diffusing the constituent metal elements of the first bonded body 1 or the second bonded body may exist.

A preferred example of the joined body is a semiconductor device.
The semiconductor device according to the present embodiment includes a semiconductor element having at least one surface metalized with a metal thin film, a metal lead frame on which at least the semiconductor element is mounted, a surface of the semiconductor element on which the metal thin film is metalized, and the metal lead. A semiconductor comprising: a bonding layer formed between the frames, bonding the semiconductor element and the metal lead frame, and made of the bonding material; and a sealing resin for sealing the semiconductor element and the lead frame. Device.

  In the semiconductor device, the metal frame is preferably made of a material selected from the group consisting of gold, nickel, silver, copper, palladium, platinum, and aluminum, or a metal alloy using these metal materials.

In the semiconductor device, the metal thin film is preferably made of a material selected from the group consisting of gold, nickel, silver, copper, palladium, platinum, and aluminum, or a metal alloy using these metal materials.

  Hereinafter, the present invention will be described in detail by way of examples.

Example 1
The semiconductor element and the lead frame in the power semiconductor device were joined. FIG. 4 is a cross-sectional view showing a bonding configuration between the semiconductor element and the lead frame. In this power semiconductor module, a 10 mm square silicon semiconductor element 17 is metallized by vapor deposition of gold as a first metal bonded material to form a thin gold layer 18 made of 0.05 μm thick gold. Yes. Further, a nickel thin layer 20 having a thickness of 0.5 μm is applied to the lead frame 19 made of copper as a second metal bonded material by a sputtering process, and further, a thin layer bonding material having a thickness of 5 μm and tin-20 mass. % Silver-10 mass% copper alloy thin layer 21 was applied by electroless plating. The silicon semiconductor element 17 having the metal layer 18 deposited thereon and the lead frame 19 having the tin-silver-copper alloy thin layer 21 deposited on the nickel thin plating layer 20 are combined with the metal layer 18 and the tin-silver-copper alloy thin film. Lamination was performed so that the layer 21 was in contact, and then heating was performed for bonding. The heating was performed on a hot plate in a forming gas (nitrogen + hydrogen) atmosphere having an oxygen concentration of 100 ppm or less. The heating conditions were 350 ° C. and 5 seconds.

  From the SEM observation of the cross section of the bonded interface after bonding, no significant voids were observed, indicating good bonding properties.

  Finally, the joined lead frame and the semiconductor element were sealed with a resin to obtain a power semiconductor device having heat resistance of 260 ° C.

(Example 2)
In this embodiment, a power semiconductor device is obtained in the same manner as in Embodiment 1 except that a thin nickel layer 20 is applied to the lead frame 19 by electroless plating and a thin layer bonding material 21 is formed thereon by solder paste printing. It was.

  Using a tin-silver-copper alloy composed of 20% by mass of silver, 10% by mass of copper, and the balance tin, an approximately 5 μm solder powder was prepared. The solder powder material and the components of the flux were thoroughly mixed at a weight ratio of about 10% of the whole to prepare a solder paste. The flux component is a solvent, a rosin, an activator, an organic halogen, a thickener, and the like. The solder paste was stirred for about 20 minutes until reaching a viscosity suitable for printing of about 500,000 cps. This solder paste is printed on the nickel thin layer 19 by electroless plating so as to have a thickness of about 80 μm, and the semiconductor element 21 to which the metal layer 17 made of gold formed by vapor deposition is applied is mounted on the solder paste. Heating was performed on a hot plate in a forming gas (nitrogen + hydrogen) atmosphere having an oxygen concentration. The heating conditions were 350 ° C. and 5 seconds.

  From the SEM observation of the cross section of the bonded interface after bonding, no conspicuous voids were generated and good bonding properties were shown.

  Finally, the joined lead frame and the semiconductor element were sealed with a resin to obtain a power semiconductor device having heat resistance of 260 ° C.

(Example 3)
In this embodiment, the power semiconductor device is formed in the same manner as in Embodiment 1 except that the thin layer bonding material 20 is formed by supplying a sheet solder material to the lead frame 18 to which the nickel thin layer 19 is applied by electroless plating. Obtained. The sheet solder material is a sheet having a thickness of about 50 μm using a tin-silver-copper alloy composed of 20% by mass of silver, 10% by mass of copper, and the remainder of tin. This sheet solder material is placed on a lead frame 18 made of copper, and a silicon semiconductor element subjected to gold vapor deposition is mounted thereon, and a hot plate in a forming gas (nitrogen + hydrogen) atmosphere having an oxygen concentration of 100 ppm. Heated above. The heating conditions were 350 ° C. and 5 seconds.

  From the SEM observation of the cross section of the bonded interface after bonding, no conspicuous voids were generated and good bonding properties were shown.

  Finally, the joined lead frame and the semiconductor element were sealed with resin to obtain a power semiconductor device.

(Examples 4-7, Comparative Examples 1-4)
A joined body was obtained as follows. The joined bodies of Examples 4 to 9 were prepared by heating 0.5 and 1 μm thick nickel thin layers formed by electroless plating on a 300 μm thick copper plate and a 300 μm tin plate.

Table 1 describes the thin-layer bonding material, the bonding material supply method, and the heating conditions (peak temperature × peak temperature holding time) of each example. As an evaluation test, regarding the bondability, the bonded area of the obtained bonded body is measured by a fluorescent solution penetration test, the bonded area of Example 1 is set to 1.0, and the bonded area below that is expressed as a relative value. Moreover, regarding heat resistance, the joining degree in 260 degreeC was measured using the high temperature shear apparatus, the joining strength of Example 1 was set to 1.0, and the joining strength below it is shown by the relative value.

  In Examples 4-7, as Table 1 shows, it has a joining layer with favorable heat resistance. Moreover, it is clear that the joined bodies of Examples 4 to 9 having such a joining layer are excellent in joining strength at high temperatures.

  The bonded bodies of Comparative Examples 1 to 4 were prepared by using a tin-silver-copper alloy having a composition shown in Table 1 having a thickness of 10 μm and a 10 mm square silicon semiconductor element metallized by 300 μm thick gold vapor deposition. It was created by heating under the conditions shown.

(Examples 8 to 10)
In the same manner as in Example 1, a 10 mm square silicon semiconductor element was metallized by gold vapor deposition. Separately, samples were prepared in which palladium, platinum, and aluminum, which are the second metal bonded materials, were formed on a lead frame made of copper so as to have a thickness of 0.5 μm by electron beam treatment. Next, a tin-20 mass% silver-10 mass% copper alloy thin layer 21 was formed on the second metal-bonded material of these samples by electroless plating so as to have a thickness of 5 μm. Thereafter, the metallized surface of the silicon semiconductor element was bonded to the tin layer forming surface of the lead frame under the same conditions as in Example 1.
In all the samples, no significant voids were observed, and good bondability was exhibited.

[Application field of the present invention]
The joined body and joining method according to the present invention can be used in a wide range of fields, but are particularly suitable for joining parts in electronic devices, semiconductor devices, particularly power-based semiconductor devices that are placed under high temperature conditions during the manufacturing process or product use. In particular, it is more preferably used for joining a semiconductor element and a lead frame.

Process sectional drawing which shows one Embodiment of the joining method of this invention. Sectional drawing which shows other embodiment of the joining method of this invention. Sectional drawing which shows other embodiment of the joining method of this invention. Sectional drawing which shows the joining form of the semiconductor element and lead frame in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ......... 1st metal to-be-joined material 2 ......... 2nd metal to-be-joined material 3 ......... Joint layer 4 ......... Laminated body 5 ......... Thin layer joining material 6 ......... Joint body 7,8 ... ...... Base material 9... Laminated body 17 ...... Silicon semiconductor element 18 ...... Gold thin layer 19 ...... Copper lead frame 20 ...... Nickel thin layer 21 ...... Tin-silver-copper alloy layer

Claims (3)

  A bonding material characterized in that silver is 15% to 40% in mass composition ratio, copper is 4% to 15%, and the balance is tin. Using a metal alloy having a metal component of 10% to 40%, copper of 4% to 15%, and the balance of tin as a bonding material in terms of mass composition ratio, A first step of forming a bonding material layer;
And a step of forming a bond with a second object to be bonded on the surface of the bonding material layer at a temperature higher than the temperature of the first step. A joined body characterized in that a semiconductor material and a metal material are joined using a joining material in which silver is 15% or more and 40% or less, copper is 4% or more and 15% or less, and the balance is tin.

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