JP2013125952A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device in which a circuit board and a semiconductor element are connected via a solder layer; which includes another layer between the circuit board and the solder layer to achieve favorable solder wettability; and which can inhibit accumulation of voids among layers thereby to achieve high connection strength between the solder layer and the other layer.SOLUTION: A semiconductor device 10 in which a circuit board 4 composed of Al or an Al alloy and a semiconductor element 1 are connected via a solder layer 3, comprises a metal powder layer 2 formed by lamination of metal powder composed of Ni, Cu, Ag, Au or an alloy of any of the metals, which is sandwiched between the circuit board 4 and the solder layer 3. The metal powder layer 2 includes groove strips 2b traversing the metal powder layer 2 on a surface 2a on the solder layer side.

Description

  The present invention relates to a semiconductor device characterized by a connection structure between a circuit board and a semiconductor element.

  The basic configuration of a semiconductor device (power module) mounted with a semiconductor element such as an IGBT (Insulated Gate Bipolar Transistor) is such that one side of the circuit board and the semiconductor element are connected via a solder layer, and the other side of the circuit board is, for example, An insulating substrate such as AlN (aluminum nitride) is connected by brazing or the like, and a heat sink or a cooler is connected to the insulating substrate by brazing or the like. There are various laminated structures such as a form in which the material stress relaxation plate is interposed between the insulating substrate and the heat sink. Further, there is a form in which these laminated structures are accommodated in a case and potted with a sealing resin body.

  The circuit board is generally formed of Al or Al alloy. For this reason, the surface of the circuit board has a problem that an oxide film having poor solder connectivity (solder wettability) is easily formed. Patent Document 1 discloses a technique in which a metal film made of Ni, Cu, Ag, or the like is formed on the surface of a circuit board to enhance connectivity, and a semiconductor element is mounted on the surface of the metal film via a solder layer. Yes.

  To describe the technique disclosed in Patent Document 1 in more detail, minute irregularities are formed on the surface of a metal coating made of Ni or the like so that the surface roughness Ra is 0.5 μm or more. This increases the surface area of the metal coating and improves the solder wettability, while suppressing the generation of voids that can occur inside the solder layer.

  However, if unevenness is simply formed on the surface of the metal film, or if this unevenness (roughness) is too large, voids tend to stay between the metal film and the solder layer, and the solder layer against the metal film As a result, the solderability of the solder deteriorates, causing a reduction in the connection strength at these interfaces.

JP 2011-29323 A

  The present invention has been made in view of the above-described problems, and relates to a semiconductor device in which a circuit board and a semiconductor element are connected via a solder layer, and a solder layer with a separate layer interposed between the circuit board and the solder layer. An object of the present invention is to provide a semiconductor device that can suppress the retention of voids between these layers while improving the wettability, and has high connection strength between a solder layer and a separate layer.

  In order to achieve the above object, a semiconductor device according to the present invention is a semiconductor device in which a circuit board made of Al or an Al alloy and a semiconductor element are connected via a solder layer, and Ni, Cu, Ag, or an alloy thereof. The metal powder layer formed by laminating the metal powder is interposed between the circuit board and the solder layer, and the metal powder layer is a groove strip that crosses the metal powder layer on the surface on the solder layer side. It is what has.

  The semiconductor device of the present invention has a good solder wettability, such as Ni, Cu, Ag, Au, or those in order to solve the problem of solder wettability when forming a solder layer on a circuit board made of Al or Al alloy. A metal powder layer formed by laminating metal powders made of the above alloy is disposed on the surface of the circuit board, and the metal powder layer is connected to the semiconductor element via the solder layer.

  And this metal powder layer has the groove | channel which cross | intersects a metal powder layer in the surface which becomes the solder layer side resulting from the formation method.

  Here, "crossing the metal powder layer" means any other planar shape (circular, elliptical, square or rectangular, other polygons, etc.) from any end point to any other arbitrary This means that a continuous groove extends over the end points of the metal powder layer, and one or more grooves parallel to either side of the metal powder layer having a square shape in plan view are provided in the metal powder layer. Or a shape in which one or two or more grooves having a diameter passing through the center of the circle are arranged in the metal powder layer with respect to the metal powder layer having a circular shape in plan view.

  In this way, voids that can be formed between the surface of the metal powder layer and the solder layer by providing grooves extending from any end point to any other end point on the surface of the metal powder layer having an arbitrary planar shape. Can be discharged to the outside through this groove. That is, the semiconductor device of the present invention is provided with grooves for removing voids on the surface of the metal powder layer, which is a component thereof, on the solder layer side, and these grooves are voids composed of relatively large bubbles. However, it has a size (groove height of the groove) that cannot be re-entered from the outside. Intrusion is prevented by taking into account the groove height of the groove and the surface tension around the groove.

  This is greatly different from the technique disclosed in Patent Document 1 described above in which the surface of the metal coating is simply provided with irregularities.

  In addition, “metal powder made of Ni, Cu, Ag, Au, or an alloy thereof” means any single metal powder of Ni, Cu, Ag, Au, Ni alloy, Cu alloy, Ag alloy. , Which means any one kind of alloy powder of Au alloy.

  In addition, the semiconductor device of the present invention has an arbitrary structure such as a heat sink, a cooler, an insulating substrate such as AlN, a stress relaxation plate, etc., except that the circuit board and a metal powder layer, a solder layer, and a semiconductor element are laminated. It is intended to include various forms in which these members are further added. Further, the semiconductor element indicates all elements such as an IC chip (silicon chip), a transistor, and a diode.

  According to the semiconductor device of the present invention described above, a metal powder layer formed by laminating metal powders made of Ni, Cu, Ag or alloys thereof having good solder wettability is interposed between the circuit board and the solder layer. Furthermore, since the metal powder layer has a groove that crosses the metal powder layer on the surface on the solder layer side, voids generated when the solder layer is formed on the surface of the metal powder layer are grooved. Thus, the semiconductor device is excellent in connectivity between the metal powder layer and the solder layer.

  Further, when the metal powder layer has a rectangular shape in plan view having a long side and a short side, the groove extends in a direction along the short side on the surface on the solder layer side. preferable.

  This is because the voids are easily discharged to the outside by extending the grooves in the direction along the short side.

  In addition, as a result of verification by the present inventors, it has been confirmed that the void ratio (ratio of the void area in the plane area of the metal powder layer) increases at the stage where the groove height of the groove exceeds 80 μm, For this reason, the groove height of the groove is preferably in the range of 80 μm or less.

  Further, in the form in which a plurality of the grooves are provided and the groove has a substantially triangular cross-sectional shape, the width of the bottom side is w, the height is h, and adjacent grooves are partially wrapped. In this case, it is preferable that the relational expression h (w + p) / 2w <80 μm is satisfied, where p is the distance between the two apexes.

  Here, “the cross-sectional shape is substantially triangular” means that the cross-sectional shape is not only triangular but also includes a shape with rounded corners without a corner and a shape close to a triangle as a whole.

  Further, the metal powder layer is preferably formed by a method of cold spraying the metal powder.

  As a forming method for realizing a “metal powder layer formed by laminating metal powders”, it is preferable to make the metal powder collide with a circuit board in a solid state in a supersonic flow without melting or gasifying the metal powder. As a method for realizing this, cold spray can be mentioned, and in a broad sense, spraying can be given as a concept including cold spray (except for thermal spraying that melts metal powder).

  In cold spray processing, grooves can be automatically formed when metal powder is sprayed in such a manner that a spray gun held by a manipulator such as a robot hand continuously meanders on the surface of a circuit board. For example, by moving the spray gun parallel to the short side of the rectangle in plan view and applying it by spraying, an array of metal powders with a substantially triangular cross section can be formed. Forming and then moving the spray gun in the opposite direction and spraying by moving the spray gun parallel to the short sides at intervals to the previously formed rows of metal powder and spraying. Triangular cross-sections can be formed with a predetermined spacing (spacing provided between the tops of substantially triangular shapes as described above). Then, by repeating this processing over the entire surface of the circuit board or over a desired area, a metal powder layer in which rows of metal powder having a substantially triangular cross section are arranged at a predetermined interval can be formed.

  According to the semiconductor device described above, the circuit board and the semiconductor element are indirectly connected to each other with a solder layer with a high connection strength through the metal powder layer. It is most suitable for application to inverters mounted on recent hybrid vehicles and electric vehicles that require durability.

  As can be understood from the above description, according to the semiconductor device of the present invention, the metal powder layer formed by laminating the metal powder having good solder wettability is interposed between the circuit board and the solder layer, Since the metal powder layer has a groove that crosses the metal powder layer on the surface that becomes the solder layer side, voids that may be generated when the solder layer is formed on the surface of the metal powder layer through the groove A semiconductor device that can be effectively discharged to the outside and has excellent connectivity between the metal powder layer and the solder layer can be provided.

It is a longitudinal cross-sectional view of one embodiment of a semiconductor device of the present invention. (A) and (b) are both II-II arrow line views of FIG. (A) is the schematic diagram explaining the formation method of the metal powder layer of the form shown by the arrow figure of FIG. 2a, (b) is a longitudinal cross-sectional view of the circuit board and the metal powder layer formed in this surface . It is the schematic diagram used when prescribing | regulating the optimal value of the groove height of the groove formed in a metal powder layer. It is a figure which shows the experimental result which calculated | required the relationship between the groove height of a groove, and a void ratio by the difference in the extending direction of a groove.

  Hereinafter, embodiments of a semiconductor device of the present invention will be described with reference to the drawings. Note that the stacked configuration of the semiconductor device illustrated is merely an example, and may be a semiconductor device to which other components such as an insulating substrate, a stress relaxation plate, a cooler, and the like are further added. It may be a semiconductor device housed in a case and sealed with a sealing resin body.

(Embodiment of semiconductor device)
FIG. 1 is a longitudinal sectional view of an embodiment of a semiconductor device, and FIGS. 2A and 2B are views taken along the line II-II in FIG. In the semiconductor device 10 shown in the figure, a circuit board 4 made of Al or Al alloy is brazed to the surface of a heat sink 5 made of Al or Al alloy, and a plurality of grooves 2b are formed on the surface of the circuit board 4 on the surface 2a on the solder layer side. The metal powder layer 2 is formed, and the metal powder layer 2 and the semiconductor element 1 (IC chip, transistor, diode, etc.) are connected via the solder layer 3 to constitute the whole.

  The solder layer 3 may be either Pb-based solder or Pb-free solder, but in order to reduce environmental impact load, Sn-Ag solder, Sn-Cu solder, Sn-Ag-Cu solder, Sn It is preferably made of Pb-free solder such as -Zn solder or Sn-Sb solder.

  The metal powder layer 2 is obtained by cold spraying any one kind of powder of Ni, Cu, Ag, Au, or any one of Ni alloy, Cu alloy, Ag alloy, Au alloy. Is formed on the surface of the circuit board 4.

  A metal powder layer 2 formed by laminating metal powders made of Ni, Cu, Ag, Au or an alloy thereof is formed on the surface of a circuit board 4 made of Al or an Al alloy, and the metal powder layer 2 and a semiconductor element 1 is connected through the solder layer 3 so that the wettability of the solder is improved, and the circuit board 4 and the semiconductor element 1 are indirectly connected with a high connection strength through the metal powder layer 2 and the solder layer 3. can do.

  The metal powder layer 2 may have various shapes in plan view, but as shown in FIG. 2a, a rectangular shape having a long side (length t2) and a short side (length t1) is shown in FIG. 2b. The planar shape of the circuit board and the semiconductor element such as a square shape in plan view, a square shape in plan view, a rectangular shape in plan view and a polygon other than a square, and an elliptical shape in plan view are also available. There are various shapes depending on the planar shape. Furthermore, the metal powder layer 2 may be provided over the entire surface of the circuit board 4.

  In any planar shape, the metal powder layer 2 has one or two or more grooves 2b across the metal powder layer 2 on the surface on the solder layer side.

  Since the metal powder layer 2 has the grooves 2b that cross the surface, voids that can stay between the metal powder layer and the solder layer can be effectively formed by providing a metal powder layer with good solder wettability. Can be discharged outside the interface. That is, the groove that crosses the surface of the metal powder layer 2 is a void removal groove that extends from the central region of the surface of the metal powder layer 2 to the end that leads to the outside.

Here, with reference to FIG. 3, the preferable formation method of the metal powder layer 2 is outlined.
FIG. 3A is a schematic diagram illustrating a method for forming a metal powder layer in the form shown by the arrow in FIG. 2A, and FIG. 3B is a longitudinal sectional view of a circuit board and the metal powder layer formed on the surface.

  In forming the metal powder layer 2 having a rectangular shape in plan view having a long side (length t2) and a short side (length t1), a spray gun (not shown) applied in cold spray processing is shown in FIG. 3a. As shown in FIG. 3 b, a plurality of grooves 2 b extending in the direction along the short side are defined by moving so as to meander continuously and parallel to the short side (X direction). Thus, the metal powder layer 2 which consists of a some metal powder row | line | column with which the metal powder was laminated | stacked is formed.

  The row of metal powder shown in FIG. 3b has a substantially triangular cross-section (the top is rounded), and adjacent rows wrap at a part thereof to form a groove 2b above the lap region. Has been.

  By forming the metal powder layer 2 so that the groove 2b extends in the direction along the short side, the discharge distance of voids interposed between the metal powder layer 2 and the solder layer 3 becomes as short as possible. (For example, the discharge distance from the center position of the metal powder layer 2 to its end side in a plan view is shortened), and voids are easily discharged.

Here, the optimum value of the groove height of the groove 2b is defined using FIG.
The triangle shown in the figure assumes that the cross-sectional shape of the metal powder row is a triangle, where the base is w, the height is h, and the distance between the tops of each row is p, the groove height d of the groove 2b. Is defined from these factors.

  As shown in the figure, the relational expression d = h (w + p) / 2w holds, but according to the present inventors, the metal powder layer 2 is formed so that the groove height d is 80 μm or less. The knowledge that it is good to do is obtained. The reason is that when the groove height of the groove exceeds 80 μm, the void ratio (the ratio of the void area to the plane area of the metal powder layer) increases.

[Experiments and results of determining the relationship between groove height and void ratio due to differences in groove extending direction]
In the metal powder layer having a rectangular shape in a plan view shown in FIG. 3a, the present inventors formed a metal powder layer so as to form a row in the short side direction and a metal powder layer so as to form a row in the long side direction. As shown in Table 1 below, regarding the two cases when formed, a metal powder layer was formed by varying the height of the groove, and the void ratio (metal) was formed when the solder layer was formed on the surface. The ratio of the void area to the plane area of the powder layer) was determined. The results are shown in Table 1 and FIG.

  From Table 1 and FIG. 5, it is demonstrated that the void ratio is significantly lower in the metal powder layer composed of the rows along the short side direction than the metal powder layer composed of the rows along the long side direction. Has been.

  As described above, it is preferable that the upper limit value of the groove height of the groove is defined as 80 μm. Regarding the lower limit value, from the graph regarding the short side direction in FIG. 50 μm can be defined as the lower limit.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor element, 2 and 2A ... Metal powder layer, 2a ... Solder layer side surface, 2b ... Groove, 3 ... Solder layer, 4 ... Circuit board, 5 ... Heat sink, 10 ... Semiconductor device

Claims (5)

A semiconductor device in which a circuit board made of Al or an Al alloy and a semiconductor element are connected via a solder layer,
A metal powder layer formed by laminating metal powders made of Ni, Cu, Ag, Au or alloys thereof is interposed between the circuit board and the solder layer,
The said metal powder layer is a semiconductor device which has the groove | channel which crosses a metal powder layer in the surface used as the solder layer side.   2. The semiconductor device according to claim 1, wherein the metal powder layer has a rectangular shape in plan view having a long side and a short side, and the groove extends in a direction along the short side on a surface on the solder layer side.   The semiconductor device according to claim 1, wherein a groove height of the groove is 80 μm or less.   A plurality of the grooves are provided side by side, and the cross-sectional shape of the grooves is substantially triangular, the width of the base is w, the height is h, and adjacent grooves are partially wrapped and both The semiconductor device according to claim 1, wherein a relational expression of h (w + p) / 2w <80 μm is satisfied, where p is a distance between the tops.   The semiconductor device according to claim 1, wherein the metal powder layer is formed by a method of cold spraying the metal powder.

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