JP2011167713A - Connection material, method for producing the same, and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a connection material in which the joining temperature of a Zn/Al clad material is reduced, thus residual thermal stress in a using temperature region is reduced, and reliability of the joint can be improved. <P>SOLUTION: The connection material is composed of: an Mg-containing Al-based alloy layer 2; and Zn layers 3, 4 adjacent to both the sides of the Al based alloy layer 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a connection material technique, and more particularly to a structure and manufacturing method of the connection material, and a technique effective when applied to a semiconductor device, a power semiconductor device, a power module, and the like using the connection material. .

  As a technique studied by the present inventors, a semiconductor device using a connection material will be described with reference to FIGS. FIG. 3 is a diagram showing a structure of a conventional semiconductor device. FIG. 4 is a diagram for explaining flashing by remelted solder.

  As shown in FIG. 3, in the semiconductor device 30, a semiconductor element 31 is connected to a frame (die) 32 by solder 33, and an inner lead 36 of a lead 35 and an electrode of the semiconductor element 31 are wire-bonded by a wire 34. It is manufactured by being sealed with a sealing resin 37 or an inert gas.

  The semiconductor device 30 is reflow soldered to the printed circuit board with Sn-Ag-Cu-based medium temperature lead-free solder. The melting point of Sn-Ag-Cu-based lead-free solder is as high as about 220 ° C., and it is assumed that the connection portion is heated up to 260 ° C. during reflow connection. Therefore, high lead solder having a melting point of 290 ° C. or higher is used for die bonding of the semiconductor element 31 inside the semiconductor device 30 for the purpose of the temperature hierarchy. High-lead solder contains 85 mass% or more of lead as a constituent component and has a greater environmental impact than Sn-Pb eutectic solder prohibited by the RoHS Directive enforced in July 2006 . Therefore, development of an alternative connection material to replace high lead solder is eagerly desired.

  Currently developed Sn-Ag-Cu solders have a melting point of 260 ° C or lower, so when used for die bonding of semiconductor elements, the solder melts during secondary mounting (maximum temperature 260 ° C). Resulting in. When the periphery of the connecting portion is molded with resin (resin sealing), when the internal solder is melted, due to volume expansion at the time of melting, as shown in FIG. 4, the sealing resin 37 and the frame 32 are called flash. Solder 33 may leak from the interface. Alternatively, even if it does not leak, it acts to leak, and as a result, a large void 38 is formed in the solder after solidification, resulting in a defective product. As alternative material candidates, Au solder such as Au-Sn, Au-Si, Au-Ge, Zn, Zn-Al solder, and solder such as Bi-Cu, Bi-Ag are reported in terms of melting point. Is being studied all over the world.

  However, Au-based solder contains 80 mass% or more of Au as a constituent component, and is difficult to be versatile in terms of cost. Bi-based solder has a thermal conductivity of about 9 W / mK, which is lower than that of current high lead solder, and it can be estimated that application to power semiconductor devices and power modules that require high heat dissipation is difficult. In addition, Zn and Zn-Al solder have high thermal conductivity of about 100 W / mK, but they are difficult to wet (especially Zn-Al solder), the solder is hard, and the semiconductor is subjected to thermal stress during cooling after connection. There is a problem that the element is easily destroyed.

  In Patent Literature 1 and Patent Literature 2, Al: 1 to 7 mass%, Mg: 0.5 to 6 mass%, Ga: 0.1 to 20 mass%, P: 0.001 to 0.5 mass%, and the balance is Zn, Ge : 2-9 mass%, Al: 2-9 mass%, P: 0.001-0.5 mass%, the balance is Zn or Ge: 2-9 mass%, Al: 2-9 mass%, Mg: 0.01-0. By using 5 mass%, P: 0.001 to 0.5 mass%, and the balance being Zn, the wettability of the Zn-based solder alloy to Cu and Ni is improved and the melting point is lowered. However, since Al or Mg is used as a component, Al oxide and Mg oxide generate a film on the surface of the melted portion by heating during connection. Since these films inhibit wetting, there is a possibility that sufficient wetting may not be obtained unless the film is mechanically broken by scrubbing or the like. In addition, since no improvement has been made with respect to the hardness of the solder, it cannot be expected to improve the destruction of the semiconductor element due to the thermal stress during cooling after connection or during temperature cycling.

  In Patent Document 3, an In, Ag, and Au layer is provided on the outermost surface of a Zn—Al alloy, thereby suppressing oxidation of the Zn—Al alloy surface and improving wettability. However, in order to provide the In, Ag, and Au layers, it is indispensable to treat the surface of the Zn—Al-based alloy such as plating and vapor deposition, which leads to an increase in the process of manufacturing the material. Further, as described above, when In is added, the hardness can be reduced, but an effect that suppresses the destruction of the semiconductor element due to the thermal stress during cooling after connection cannot be expected.

  On the other hand, Patent Document 4 proposes a Zn / Al / Zn clad solder substitute material that improves the stress relaxation performance of a conventional Zn-Al solder.

JP 2002-358539 A JP 2004-358540 A JP 2002-261104 A JP 2008-126272 A

  However, the Zn / Al / Zn clad material has a melting point (liquidus temperature) of 382 ° C. when alloyed, compared with other high-temperature solders such as Pb—Sn high-temperature solder and Au—Sn solder. It is extremely hot. If the bonding temperature is high, the amount of thermal shrinkage of the bonded portion when it is cooled to room temperature after solidification becomes larger, so the thermal stress caused by the difference in thermal expansion coefficient between the bonded object and the bonded object increases, When the starting point of a crack is formed, the progress is promoted. When the crack progresses, the joint strength of the joint portion decreases, and the joint portion itself may be destroyed. At the same time, since the thermal resistance increases, the temperature of adjacent objects to be joined increases, and the system may not function.

  Accordingly, an object of the present invention is to reduce the residual thermal stress in the operating temperature range by lowering the bonding temperature of the Zn / Al clad material, and to improve the reliability of the joint, and a method for manufacturing the connection material And providing a semiconductor device.

  The present invention was devised to achieve the above object, and the invention of claim 1 is a connection comprising an Al-based alloy layer containing Mg and a Zn layer adjacent to both sides of the Al-based alloy layer. Material.

  Invention of Claim 2 is a connection material of Claim 1 whose Mg contained in the said Al type alloy layer is 2.0 mass% or more and 5.6 mass% or less.

  According to a third aspect of the present invention, there is provided a connection material manufactured by clad rolling, wherein an Al-based alloy layer containing Mg is stacked on a first Zn layer, and a second Zn layer is stacked on the Al-based alloy layer. It is a manufacturing method.

  The invention according to claim 4 is a connection manufactured by pressure forming by stacking an Al-based alloy layer containing Mg on the first Zn layer, and stacking a second Zn layer on the Al-based alloy layer. It is a manufacturing method of material.

  According to a fifth aspect of the present invention, there is provided a semiconductor device in which a semiconductor element is mounted on a frame via a connecting material, and electrodes of the semiconductor element are connected to inner leads by wire bonding, and then these are resin-sealed with a resin. The connecting material is a semiconductor device including an Al-based alloy layer containing Mg and Zn layers provided on both surfaces of the Al-based alloy layer.

  According to a sixth aspect of the present invention, a semiconductor element is mounted on a substrate, an electrode of the semiconductor element is connected to an inner lead by wire bonding, and then a metal cap is placed on the substrate via a cap connecting material to be hermetically sealed. In the stopped semiconductor device, the cap connection material is a semiconductor device including an Al-based alloy layer containing Mg and a Zn layer provided on the outermost surface of the Al-based alloy layer.

  According to a seventh aspect of the present invention, the semiconductor element is mounted on the substrate via an element connecting material, and the element connecting material includes an Al-based alloy layer containing Mg and both surfaces of the Al-based alloy layer. The semiconductor device according to claim 6, comprising a Zn layer provided on the semiconductor layer.

  The invention according to claim 8 is a semiconductor device in which a semiconductor element is mounted on a substrate having a bump on the lower surface through a connecting material, the connecting material comprising an Al-based alloy layer containing Mg and the Al-based alloy layer. This is a semiconductor device comprising a Zn layer provided on the outermost surface.

  According to the present invention, by reducing the bonding temperature of the Zn / Al clad material, the residual thermal stress in the operating temperature range can be reduced, and the reliability of the bonded portion can be improved.

It is sectional drawing which shows the connection material which concerns on one embodiment of this invention. It is sectional drawing which shows the joined body for evaluation using the connection material of FIG. It is a structural diagram showing a conventional semiconductor device. FIG. 4 is a diagram illustrating flashing by remelted solder in the semiconductor device of FIG. 3.

  As a result of intensive studies on a clad material composed of an Al-based alloy layer and a Zn layer, the inventors of the present invention can lower the bonding temperature than a conventional clad material by using an Al-based alloy layer containing Mg. I found out that I can.

  Hereinafter, preferred embodiments of the present invention completed based on this finding will be described with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view showing a connection material according to the present embodiment.

  As shown in FIG. 1, the connection material 1 according to the present embodiment is used when a semiconductor element is mounted on a frame or a substrate or when the semiconductor element is hermetically sealed, and an Al-based alloy containing Mg. It consists of the layer 2 and Zn layers 3 and 4 adjacent to both surfaces of the Al-based alloy layer 2.

  The connecting material 1 is formed by laminating an Al-based alloy layer 2 containing Mg on the first Zn layer 3 and laminating the second Zn layer 4 on the Al-based alloy layer 2, and performing clad rolling or pressure forming. Manufactured by.

  When clad rolling or pressure forming is performed, the Al-based alloy layer 2 and the Zn layers 3 and 4 come into contact with each other, and at the same time, large deformation occurs due to the pressure, and the Al-based alloy layer 2 and the Zn layers 3 and 4 are formed on the surfaces. The oxide film is broken and metal is bonded to the new surface. In addition, in the clad rolling or pressure forming, no heat load is applied to a temperature at which Al and Zn diffusion becomes significant. Therefore, Al does not diffuse into the Zn layers 3 and 4 on the surface and reach the outermost surface, and good wetting can be obtained at the time of connection.

  The operation of the connecting material 1 will be described together with the operation of the conventional clad material.

  In the case of a clad material composed of a conventional pure Al-based alloy layer and a Zn layer, when the material is heated and heated, the portion that becomes a liquid phase for the first time at 382 ° C., which is the eutectic temperature of the Zn—Al binary alloy, Arise. When the liquid phase occurs, the adjacent solid phase melts and diffuses at high speed into the liquid phase, and the entire brazing material layer melts. Furthermore, diffusion from the remaining Al-based alloy layer continues, and the liquidus point rises. As long as the Al-based alloy layer exists, the liquid phase point increases, the liquid phase decreases, and the solid phase is obtained.

  On the other hand, in the case of the connection material 1 according to the present embodiment, since an alloy containing Mg is used as the Al-based alloy layer 2, the diffusion reaction at the interface between the Al-based alloy layer 2 and the Zn layers 3 and 4 is performed. A Zn—Al—Mg ternary alloy is formed. As Mg is alloyed with Zn and Al, the liquidus temperature is lowered. At this time, the temperature drop range varies depending on the Mg concentration.

  Mg contained in the Al-based alloy layer 2 is preferably 2.0 mass% or more and 5.6 mass% or less. This is because when the Mg content is less than 2.0% by mass, the melting point of the connecting material 1 is 3 ° C. or less, and the liquidus temperature is not sufficiently lowered. This is because A5056 (5.6% by mass) containing the most Mg component in the Al alloy spreading material is exceeded, and it is necessary to separately cast and produce an Al alloy. The use of a special alloy as a constituent material of the clad material leads to an increase in cost, and the effect applied to the product is significantly reduced.

  Here, as a general-purpose Al alloy satisfying the above-mentioned conditions, A5052 (average Mg content 2.5 mass%), A5154 (average Mg content 3.5 mass%), A5082 (average Mg content 4.5 mass%) ), A5056 (average Mg content: 5.0% by mass), and the like.

  Since the connecting material 1 according to the present embodiment includes the Al-based alloy layer 2 containing Mg and the Zn layers 3 and 4 adjacent to both surfaces of the Al-based alloy layer 2, the pure Al-based alloy layer and the Zn layer The liquidus temperature can be lowered, that is, the bonding temperature can be lowered as compared with the conventional clad material composed of Therefore, it becomes possible to reduce the thermal stress which arises in a junction part.

  Moreover, in the connection material 1, since Mg contained in the Al-based alloy layer 2 is 2.0 mass% or more and 5.6 mass% or less, the liquidus temperature can be sufficiently lowered at low cost. it can.

  In short, according to the present invention, by reducing the bonding temperature of the Zn / Al clad material, the residual thermal stress in the operating temperature range can be reduced, and the reliability of the bonded portion can be improved.

  In this embodiment, the Zn layers 3 and 4 are provided on both surfaces of the Al-based alloy layer 2, but the Zn layer 3 may be provided on the outermost surface of the Al-based alloy layer 2.

  The connection material 1 can be effectively used for die bonding of semiconductor devices such as semiconductor devices, power semiconductor devices, and power modules, hermetic sealing materials, flip chip bonding, and the like.

  As an example, an application example of the connection material 1 to a semiconductor device will be described.

  Here, a semiconductor device (die bonding structure) for mounting a semiconductor element on a frame, a semiconductor device (hermetic sealing structure) for covering a metal cap on a substrate, and a semiconductor device (flip chip mounting structure) connected by bumps will be described. .

<Application example 1>
A die in which a semiconductor element is mounted on a frame (die) through a connecting material, electrodes of the semiconductor element are connected to inner leads by wire bonding, and then these semiconductor elements, frame, inner leads, and wires are resin-sealed with resin. In a semiconductor device having a bonding structure, the connection material 1 of the present invention can be used as a connection material used when a semiconductor element is mounted on a frame.

<Application example 2>
After mounting the semiconductor element on the substrate (module substrate) and connecting the electrode of the semiconductor element to the inner lead by wire bonding, the semiconductor element, the inner lead, and the wire are covered with a metal cap on the substrate via a connecting material for cap. In the hermetically sealed semiconductor device in which the metal cap is hermetically sealed, the connection material of the present invention in which the Zn layer 3 is provided on the outermost surface of the Al-based alloy layer 2 is used as the cap connection material for connecting the metal cap onto the substrate. be able to. Furthermore, the connection material 1 of the present invention can be used as a connection material used when the semiconductor element is mounted on the substrate.

<Application example 3>
In a semiconductor device in which a semiconductor element is mounted on a substrate having a bump on the lower surface via a connection material, a Zn layer 3 is formed on the outermost surface of the Al-based alloy layer 2 as a connection material used when the semiconductor element is mounted on the substrate. The provided connection material of the present invention can be used.

  Although the invention made by the present inventors has been specifically described based on the embodiment, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  That is, in the above description, the application of the present invention has been described by taking die bonding of a semiconductor device as an example. However, any semiconductor device that is die bonded can be applied to various semiconductor devices. These include, for example, alternator diodes, IGBT modules, front-end modules such as RF modules, automobile power modules, and the like.

  In the above description, the case where the semiconductor device is reflow-mounted on the module substrate has been described as an example. However, the present invention is naturally applicable to, for example, an MCM (Multi Chip Module) configuration.

  The numerical basis of the present invention will be described below.

  Each connection material used in Examples 1 to 12 and Comparative Examples 1 to 6 is clad rolled (working degree 80%) to the base plate obtained by stacking the Zn layers on both sides of the Al-based alloy layer, and then finished. Rolling was performed several times and processed to a predetermined product thickness. Table 1 shows the thickness structure of each of the produced connection materials.

The original plate thickness, the plate thickness after clad rolling, and the final plate thickness in each pattern of Table 1 are as follows.
・ Pattern 1
Original plate thickness = Zn: 0.2 mm, Al: 0.7 mm, Zn: 0.2 mm
Plate thickness after clad rolling = Zn: 0.04 mm, Al: 0.14 mm, Zn: 0.04 mm Final plate thickness = Zn: 0.02 mm, Al: 0.07 mm, Zn: 0.02 mm
・ Pattern 2
Original plate thickness = Zn: 0.2 mm, Al: 1.1 mm, Zn: 0.2 mm
Plate thickness after clad rolling = Zn: 0.04 mm, Al: 0.22 mm, Zn: 0.04 mm Final plate thickness = Zn: 0.02 mm, Al: 0.11 mm, Zn: 0.02 mm
・ Pattern 3
Original plate thickness = Zn: 0.45 mm, Al: 0.15 mm, Zn: 0.45 mm
Plate thickness after clad rolling = Zn: 0.09 mm, Al: 0.03 mm, Zn: 0.09 mm Final plate thickness = Zn: 0.045 mm, Al: 0.015 mm, Zn: 0.045 mm

  In Examples 1 to 12 and Comparative Examples 1 to 6, as shown in FIG. 2, a bonding clad material 21 is used for an evaluation bonded body that simulates a semiconductor device. The evaluation bonded body includes a semiconductor element 22 and a base plate 23 on which the semiconductor element 22 is mounted. The semiconductor element 22 and the base plate 23 are bonded with a bonding clad material 21.

  In the production of the evaluation bonded body, the bonding surface of the semiconductor element 22 was subjected to Ni / Au plating, and the bonding surface of the base plate 23 was subjected to Ni plating. The bonding was arranged between the semiconductor element 22 and the base plate 23 via a bonding clad material 21 having the same area as the bonding surface of the semiconductor element 22 and bonded by heat treatment in a nitrogen atmosphere. The size of the semiconductor element 22 was 0.5 mm × 5 mm square, and the size of the base plate 23 was 3 mm × 30 mm square. During the bonding heat treatment, 50 g of a stainless steel weight was placed on the semiconductor element 22 and heated in a nitrogen atmosphere.

  Examples 1 to 12 are examples in which JIS standards A5052, A5154, A5056, and A5082 were used as the Al-based alloys as the core material in the patterns 1, 2, and 3 of Table 1, respectively. Comparative Examples 1 to 6 are examples in which JIS standard A1050 and A1100 are used as the Al-based alloy as the core material.

  About these, the result evaluated about the wettability at the time of joining is shown in Table 2.

  The bonding temperatures were 400 ° C. and 380 ° C., and the bonding time was 5 minutes. Regarding the wettability, the case where 80% or more of the wettability with respect to the area of the semiconductor element 22 was obtained was evaluated as ◯, and the case where it was less than 80% was evaluated as x.

  As a result of this evaluation, 80% or more of wetness was obtained for any of the evaluation materials of Examples 1 to 12 and Comparative Examples 1 to 6 for a bonding temperature of 400 ° C.

  On the other hand, when the bonding temperature was 380 ° C., 80% or more of the evaluation materials of Examples 1 to 12 were obtained, but bonding using pure Al-based materials (A1050 and A1100) not containing Mg. In Comparative Examples 1 to 6 using the clad material, the melting point was not changed at 382 ° C., so that the wetness was less than 80% with respect to the base plate 23.

  Here, as a result of conducting a cross-sectional investigation of the joint portion of Examples 1 to 12 having a joining temperature of 380 ° C., the crack length generated in the joint portion is 1% of the cross-sectional length. On the other hand, as a result of conducting a cross-sectional investigation on those bonded at 400 ° C. among Comparative Examples 1 to 6, the crack length generated in the bonded portion was 5% or more with respect to the cross-sectional length. It was. The crack length is measured by observing the structure of the cut surface in the same direction as the side of the bonding clad material, and measuring the length of the crack. Was measured. The occurrence of these cracks occurred because the thermal stress generated by the difference in linear expansion coefficient between the semiconductor element 22 and the base plate 23 during cooling after bonding could not be relaxed, but Examples 1 to 12 lowered the bonding temperature. Since the temperature difference from room temperature can be reduced, compared with Comparative Examples 1 to 6, the progress of cracks in the use environment after bonding can be remarkably reduced, and the possibility of peeling of the bonded portion and destruction of the semiconductor element 22 is reduced. it can.

  By the above, according to Examples 1-12, by using the clad material for joining which uses the general purpose Al alloy which contains Mg 2.0 mass% or more and 5.6 mass% or less for die bonding joining of a semiconductor device Good wetting can be obtained at a lower bonding temperature. As a result, since the thermal stress remaining in the bonded portion at room temperature after bonding is reduced, high connection reliability can be obtained.

1 Connecting material 2 Al-based alloy layer 3, 4 Zn layer

Claims (8)

  A connection material comprising: an Al-based alloy layer containing Mg; and a Zn layer adjacent to both surfaces of the Al-based alloy layer.   The connection material according to claim 1, wherein Mg contained in the Al-based alloy layer is 2.0 mass% or more and 5.6 mass% or less.   An Al-based alloy layer containing Mg is stacked on the first Zn layer, and a second Zn layer is stacked on the Al-based alloy layer, and manufacturing is performed by clad rolling. Method.   A connection material characterized in that an Al-based alloy layer containing Mg is stacked on the first Zn layer, and a second Zn layer is stacked on the Al-based alloy layer, and is manufactured by pressure molding. Production method.   In a semiconductor device in which a semiconductor element is mounted on a frame via a connecting material, the electrodes of the semiconductor element are connected to inner leads by wire bonding, and then these are resin-sealed with a resin, the connecting material contains Mg A semiconductor device comprising: an Al-based alloy layer to be formed; and a Zn layer provided on both surfaces of the Al-based alloy layer.   In a semiconductor device in which a semiconductor element is mounted on a substrate, the electrode of the semiconductor element is connected to an inner lead by wire bonding, and then the substrate is covered with a metal cap via a cap connecting material and hermetically sealed. The cap connection material is composed of an Al-based alloy layer containing Mg and a Zn layer provided on the outermost surface of the Al-based alloy layer.   The semiconductor element is mounted on the substrate via an element connecting material, and the element connecting material includes an Al-based alloy layer containing Mg, and a Zn layer provided on both surfaces of the Al-based alloy layer. The semiconductor device according to claim 6, comprising:   In a semiconductor device in which a semiconductor element is mounted on a substrate having a bump on the lower surface via a connecting material, the connecting material includes an Al-based alloy layer containing Mg and Zn provided on the outermost surface of the Al-based alloy layer. A semiconductor device comprising a layer.

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