JP5077536B2 - Manufacturing method of semiconductor device - Google Patents

Description

  The present invention relates to a method of manufacturing a semiconductor device in which a power semiconductor module is an object of implementation, and more particularly to a method of solder bonding between members constituting the module.

First, an assembly structure of a conventional semiconductor device is shown in FIGS. 6 and 7, taking the power semiconductor module described above as an example. FIG. 6 shows a semiconductor chip mounted on an insulating substrate (copper-clad laminate) applied to a printed wiring board or the like. Reference numeral 1 denotes an insulating layer 1a in which an inorganic filler such as SiO2, Al2O3 or AIN is added to an epoxy resin, for example. An insulating substrate having a copper foil circuit pattern 1b and a copper base 1c laminated on both the front and back sides of the substrate, 2 is a semiconductor chip (for example, IGBT (Insulated Gate Bipolar Transistor)), and 3 is a solder layer. On the other hand, the module shown in FIG. 7 is obtained by superposing an insulating substrate 5 on a heat radiating metal base plate 4 and soldering it, and mounting the semiconductor chip 2 on the insulating substrate 5 by soldering. Plate) 5a, and a copper foil circuit pattern 5a and a back copper foil 5c are laminated on both front and back surfaces.

Although not shown, in order to improve the heat dissipation of the semiconductor chip, a heat spreader made of a copper material or the like is stacked on the copper foil circuit pattern of the insulating substrates 1 and 5 and soldered, and this heat spreader is used. There is also a structure in which the semiconductor chip 3 is solder-mounted on top.
In the module assembly structure described above, in order to solder-bond the copper foil circuit pattern 1b / semiconductor chip 2, copper base plate 4 / insulating substrate 5, insulating substrate 5 / semiconductor chip 2 of the insulating substrate 1 to the bonding surface area. In general, the joining members are stacked one above the other with the applied cream solder or plate solder interposed therebetween, and in this state, the members are soldered together through a solder reflow process.

  By the way, in the solder joining method described above, when the solder is melted in the course of the solder reflow process, the members stacked on the upper side are joined while being inclined as shown in the figure due to unbalance of the amount of solder applied and the weight of the member. There is. In such a solder joint state, the layer thickness of the solder layer 3 is non-uniform, the heat conductivity between the members becomes non-uniform, and joint defects such as solder protrusion and solder voids are likely to occur. Further, when a thermal cycle is repeatedly applied due to ON / OFF of the semiconductor chip 2, cracks are generated and grow in a thin portion of the solder layer 3, and heat dissipation and conductivity are deteriorated. Decreases.

On the other hand, in order to deal with the above problem and to make the thickness of the solder layer joining the members uniform, the upper surface of the metal base plate 4 shown in FIG. 7 or the surface of the back surface copper foil 5c of the insulating substrate 5 is used. In addition, protrusions having a height corresponding to the appropriate thickness of the solder layer 3 are previously distributed and formed by a mechanical processing method such as pressing or cutting, and the protrusions are used as a support for maintaining a gap between members. A structure of a semiconductor device in which a solder layer 3 having a uniform thickness is formed between 4 and an insulating substrate 5 and reflow soldering is performed without tilting the member, and a manufacturing method (projection forming method) is known. (For example, see Patent Document 1 and Patent Document 2).
Japanese Patent Laid-Open No. 10-50928 JP 2000-277876 A

As described above, among the members to be soldered in the upper and lower layers, the metal base plate / insulating substrate is not tilted by forming protrusions aligned at the same height in advance at multiple locations on the surface of one member. Reflow soldering can be performed with a uniform layer thickness.
However, in the conventional manufacturing methods disclosed in Patent Document 1 and Patent Document 2 described above,
Since projections are engraved on the surface of the members that make up the module by mechanical processing methods such as pressing and cutting, special machining facilities and press dies are required to form the projections. In addition, it takes time and effort for processing, and the product becomes expensive.

  The present invention has been made in view of the above-mentioned points, and compared with the conventional machining method, the projection for holding the gap is formed on the surface of the member to be soldered easily and in a short time with high accuracy. It is an object of the present invention to provide a method for manufacturing a semiconductor device with an improved method so that reflow soldering can be performed with a uniform thickness.

In order to achieve the above object, according to the present invention, a semiconductor device having an assembly structure in which module components such as a metal base plate for heat dissipation, an insulating substrate, a semiconductor chip, and a heat spreader are stacked and soldered between the members is an object. In addition,
A laser beam is irradiated on the joining surface area of one of the first member and the second member that are superposed on each other and soldered together, and the thickness of the solder joint layer is increased at a plurality of locations on the surface of the member. After forming concavo-convex craters with corresponding projection heights in a dispersed manner, the first and second members are superposed on the joint surface area with cream solder or plate solder sandwiched between them, and each member is passed through a solder reflow process. It shall joining, in particular to form a crater by irradiating a laser beam on the surface of the member in a manner such as: Symbol.
(1) In a method for manufacturing a semiconductor device having an assembly structure in which a semiconductor chip is stacked on a copper foil of the insulating substrate and the copper foils of the insulating substrate are stacked on each side of the insulating layer, and the members are soldered together. The copper foil is a thick copper foil having a thickness of 0.5 mm or more, and is irradiated with laser light so as not to penetrate the thick copper foil, and corresponds to the layer thickness of the solder bonding layer at a plurality of locations on the surface. After forming uneven craters having protrusion heights, cream solder or plate solder is sandwiched between the joint surface areas, the semiconductor chip is overlaid on the thick copper foil, and they are joined to each other through a solder reflow process.
(2) In a method of manufacturing a semiconductor device having an assembly structure in which an insulating substrate in which copper foils are laminated on both front and back surfaces of an insulating layer and a metal base plate for heat dissipation are stacked and the members are soldered together, The thickness of the copper foil is 0.5 mm or more, and laser light is irradiated so as not to penetrate the thick copper foil, so that the protrusion height corresponding to the layer thickness of the solder bonding layer is applied to a plurality of locations on the surface. After forming uneven craters in a dispersed manner, cream solder or plate solder is sandwiched between the joining surface areas, the heat-dissipating metal base plate is overlaid on the thick copper foil, and they are joined together through a solder reflow process.
(3) In the preceding item (1) or (2), the laser light output, irradiation time, and irradiation angle are set to be the same, and craters are formed at a plurality of locations.
(4) In the preceding item (1) or (2), craters are dispersed and formed in at least three locations in the surface area to be soldered .

According to the above manufacturing method, without preparing a dedicated machining facility, the surface of the solder joint surface area of one member is irradiated with laser light for a very short time on a member to be soldered on top and bottom. By simply forming a crater, a projection having a desired height corresponding to the thickness of the solder joint layer can be easily and accurately formed on the joint surface of the member.
In other words, when the surface of a metal member such as copper is irradiated with a laser beam focused in a spot shape, the irradiated metal is melted and melted, and the molten metal (solution) is generated at the laser irradiation point. An uneven crater (laser machining trace) is formed which is pushed away by (metal vapor) and concentrically protrudes around the laser irradiation point. In this case, the height of the protrusions formed around the crater can be adjusted using the laser beam output, irradiation time, and irradiation angle as parameters, and the laser beam irradiation conditions can be adjusted to the appropriate solder layer thickness. By setting, crater protrusions of the same height can be formed with high accuracy at a plurality of locations on the surface of the joining member.

Then, by reflow soldering between the joining members that are vertically stacked as a support for holding the gap between the members, the insulating substrate and the heat dissipating metal base plate are provided between the copper foil of the insulating substrate and the semiconductor chip. A solder layer having a uniform thickness can be formed between them and soldered with high reliability.

  Hereinafter, embodiments of the present invention will be described based on the examples shown in FIGS. In the drawings of the embodiment, members corresponding to those in FIGS. 6 and 7 are denoted by the same reference numerals and description thereof is omitted.

<Example 1>
First, the construction method of the embodiment of the present invention in which the semiconductor chip is soldered by applying to the insulating substrate of FIG. 6 will be described with reference to FIGS. In this embodiment, a copper foil circuit pattern 1b laminated on the upper surface side of an insulating layer 1a of an insulating substrate 1 on which a semiconductor chip 2 is solder mounted has a thickness d of 0.6 mm (a copper foil formed on a normal insulating substrate). The thickness of the circuit pattern is about 200 to 250 μn), and laser light is applied to a plurality of locations (four corners of the copper foil circuit pattern in the illustrated example) defined within the bonding surface area where the semiconductor chip 2 is solder mounted. Irradiation was performed (see FIG. 1A), and an uneven crater 1d (laser irradiation trace) as shown in FIG. 1B was formed on the surface of the copper foil circuit pattern 1b. 2 (a) and 2 (b) are schematic enlarged views of the crater 1d. As shown in the figure, the copper foil surface has a recess 1d having a diameter slightly larger than the beam diameter of the laser light, centered on the laser light irradiation point. -1 and a ring-shaped protrusion 1d-2 that is raised at the periphery of the recess 1d-1.

  Here, the output of the laser beam is 500 W, the diameter of the optical fiber that guides the laser beam toward the irradiation point is 0.6 mm, the irradiation time is 5 msec, and obliquely to the copper foil surface (irradiation angle: 60 °) When the laser beam was irradiated in a spot shape, the height h of the ring-shaped protrusion 1d-2 raised on the periphery of the crater 1d was about 160 μm. In the schematic diagram shown in the drawing, the height h of the crater 1d is drawn at the same height all around, but in reality, the projection 1d-2 is formed slightly offset when irradiated with laser light from an oblique direction. The

  In this case, the height d of the protrusion 1d-2 formed on the periphery of the crater 1d can be adjusted by using the laser light output, the irradiation angle, and the irradiation time as parameters, and particularly effectively by changing the laser light output. The height can be adjusted. In this embodiment, the irradiation condition of the laser beam is set as described above according to the appropriate thickness of the solder layer 3 that joins between the insulating substrate 1 and the semiconductor chip 2, and the same irradiation condition as shown in FIG. When the craters 1d are formed at the four corners of the surface of the copper foil circuit pattern 1b shown in FIG. 2), it is confirmed that the protrusions 1d-2 are formed at the same height (h = 160 μm) in each crater 1d. . Note that, when laser light is irradiated on the copper foil surface from the vertical direction, the reflected light reflected by the copper foil surface may enter the optical fiber and cause a failure of the laser device. The laser beam was irradiated from an oblique direction by setting the angle to °.

Then, as described above, an appropriate amount of cream solder is applied to the solder joint surface area of the insulating substrate 1 in which the solder joint surface of the copper foil circuit pattern 1b is irradiated with laser light and a plurality of craters 1d are dispersedly formed. Alternatively, the semiconductor chip 2 is overlaid on the insulating substrate 1 with the plate solder placed thereon, and the insulating substrate 1 / semiconductor chip 2 is soldered through a solder reflow process.
FIG. 1C shows the assembled state after reflow soldering. As can be seen from this figure, the protrusions 1d-2 of the crater 1d, which are distributed and formed in advance at the four corners of the surface of the copper foil circuit pattern 1b of the insulating substrate 2, function as a spacing support between the semiconductor chip 2 and solder. During the reflow process, the semiconductor chip 2 placed on the insulating substrate 1 is held in a horizontal posture. As a result, the solder layer 3 having a uniform thickness is formed in the bonding area between the insulating substrate 1 and the semiconductor chip 2 without tilting the posture of the semiconductor chip 2 as described in FIG. Can be soldered.

  In order to hold the semiconductor chip 2 in a horizontal position on the insulating substrate 1 via the protrusion 1d-2 of the crater 1d as described above, the uneven crater 1d is dispersed in at least three locations of the solder joint surface area. It may be formed and supported at three points. In addition, if the copper foil thickness of the copper foil circuit pattern 1d is thin, the crater 1a may penetrate the copper foil and reach the ceramic insulating layer 1a due to laser light irradiation. Is 0.5 mm or more.

<Reference example>
Next, FIG. 3 (a) ~ (c) a reference example of the present invention applied to the solder bonding of the metal base plate 4 and the insulating substrate 5 in the module structure of Fig. In this reference example, the upper surface of the metal base plate (copper plate) 4 is irradiated with laser light on the solder joint surface area in the same manner as in the first embodiment (see FIG. 2A), and a plurality of locations ( The craters 4a are formed by aligning the protrusions described in FIG. 2 at the same height at three or more locations (see FIG. 2B).

Thereafter, an appropriate amount of cream solder is applied to the upper surface of the metal base plate 1 or the plate solder is placed thereon, and the insulating substrate 5 is placed and held thereon. After the solder reflow process, the metal base plate 4 / insulating substrate 5 Join between. This makes it possible to solder bonding of a metal base plate 4 / insulating solder layer 3 between the uniform thickness of the substrate 5, as shown in FIG. 3 (c).

<Example 2>
Next, the second embodiment shown in FIG. 4 (a) ~ (c) . In this embodiment, the insulating substrate 5 is irradiated with laser light on the solder joint surface area on the upper surface side copper foil circuit pattern 5b and the back surface copper foil 5c in the same manner as in the previous embodiment (FIG. 4). (See (a)), the crater 5d is formed by aligning the protrusion height at a plurality of locations (three or more locations) on the front surface of the copper foil circuit pattern 5b and the back surface copper foil 5c (see FIG. 4B). The copper foil circuit pattern 5b and the back copper foil 5c of the insulating substrate 5 have a thickness of 0.5 mm or more so that the crater 5d formed by laser light irradiation does not penetrate the copper foil. Keep it.

  In the subsequent solder bonding step, is an appropriate amount of cream solder applied to the upper surface of the metal base plate 3 on which the insulating substrate 5 is mounted and the solder bonding surface area of the copper foil circuit pattern 5b of the insulating substrate 5 on which the semiconductor chip 2 is mounted? After the plate solder is placed, the insulating substrate 5 and the semiconductor chip 2 are sequentially placed on the metal base plate 4, and in this state, the metal base plate 4 / insulating substrate 5 / semiconductor chip 2 is subjected to a solder reflow process. Solder together.

  FIG. 4C shows the state after the solder joint, and as described in the previous embodiments, the protrusions of the crater 5d formed on the copper foil surfaces on both the front and back surfaces of the insulating substrate 5 (see FIG. 4). 2) is used as a support for maintaining a distance, and the metal base plate 4 / insulating substrate 5 / semiconductor chip 2 can be joined with the solder layer 3 having a uniform thickness.

<Reference example>
FIGS. 5A to 5C are reference examples in which a semiconductor chip is mounted on an insulating substrate through a heat spreader in order to enhance the heat dissipation of the semiconductor chip. In the figure, reference numeral 6 is a copper plate. Heat spreader.
In this reference example, the heat spreader 6 is first irradiated with laser light in the same manner as described in the previous embodiments on the front and back solder joint areas (see FIG. 5 (a)), and the surface thereof. The crater 6d is formed by aligning the projection height at a plurality of locations (three or more locations) (see FIG. 5B).

  Next, after applying an appropriate amount of cream solder or placing sheet solder on the solder joint surface area of the copper foil circuit pattern 5b of the insulating substrate 5 on which the heat spreader 6 is mounted and the upper surface of the heat spreader 5 on which the semiconductor chip 2 is mounted. The heat spreader 6 and the semiconductor chip 2 are placed in this order on the copper foil circuit pattern 5b of the insulating substrate 5, and in this state, the insulating substrate 5 / heat spreader 6 / semiconductor chip 2 are soldered together through a solder reflow process. To do.

  FIG. 5 (c) shows the state after the solder joint, and the projections (see FIG. 2) of the crater 6d formed on the front and back surfaces of the heat spreader 6 are maintained at intervals as described in the previous embodiments. As a support, the insulating substrate 5 / heat spreader 6 / semiconductor chip 2 can be joined with the solder layer 3 having a uniform thickness.

BRIEF DESCRIPTION OF THE DRAWINGS It is manufacturing process explanatory drawing of the semiconductor device concerning Example 1 of this invention, (a) is the state which irradiates a laser beam to the copper foil circuit pattern of an insulated substrate, (b) was formed in the copper foil circuit pattern by laser irradiation. Concave and convex crater, (c) is a diagram showing a state where a semiconductor chip is reflow soldered on an insulating substrate, and (d) is a plan view of the main part in (c). It is a model enlarged view of the crater formed in the copper foil circuit pattern in FIG. 1, (a) is a plan view, (b) is an AA cross-sectional view of (a). It is explanatory drawing of the manufacturing process concerning the reference example of this invention, (a) is the state which irradiates a laser beam to the upper surface of a metal base board, (b) is the uneven crater formed in the surface of the metal base board by laser irradiation, (C) is a figure showing the state which carried out the reflow soldering of the semiconductor chip to the insulating substrate on the metal base plate. It is explanatory drawing of the manufacturing process concerning Example 2 of this invention, (a) is the state which irradiates a laser beam to the copper foil circuit pattern and back surface copper foil of an insulated substrate, (b) is the surface of an insulated substrate by laser irradiation. , Uneven craters formed on copper foils on both sides, (c) is a diagram showing a state where an insulating substrate and a semiconductor chip are mounted on a metal base plate and reflow soldered BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing of the manufacturing process concerning the reference example of this invention, (a) is the state which irradiates a laser beam on the front and back both surfaces of a heat spreader, (b) is the uneven | corrugated shape formed in the front and back both surfaces of a heat spreader by laser irradiation. Crater, (c) is a diagram showing a state in which a heat spreader and a semiconductor chip are mounted on an insulating plate and reflow soldered. Conventional structure of a module in which a semiconductor chip is solder-mounted on a copper foil circuit pattern on an insulating substrate Conventional structure of a module in which an insulating substrate and a semiconductor chip are mounted in order on a metal base plate and soldered

DESCRIPTION OF SYMBOLS 1 Insulating substrate 1a Insulating layer 1b Copper foil circuit pattern 1d Crater 2 Semiconductor chip 3 Solder layer 4 Metal base board 4a Crater 5 Insulating substrate 5a Insulating layer 5b Copper foil circuit pattern 5c Back surface copper foil 5d
5d crater 6 heat spreader 6a crater

Claims (4)

In a method of manufacturing a semiconductor device having an assembly structure in which a semiconductor chip is stacked on a copper foil of the insulating substrate and the copper foil of the insulating substrate is stacked on the front and back surfaces of the insulating layer and the members are soldered together.
The copper foil is a thick copper foil having a thickness of 0.5 mm or more,
Irradiate a laser beam so as not to penetrate the thick copper foil, and form a concavo-convex crater with projection heights corresponding to the layer thickness of the solder bonding layer at a plurality of locations on the surface, and then in the bonding surface area. look clamping solder cream solder or plate, wherein the semiconductor chip overlay the thick copper foil, a method of manufacturing a semiconductor device, characterized in that bonding the phase互間through a solder reflow process. In a manufacturing method of a semiconductor device having an assembly structure in which an insulating substrate in which copper foils are laminated on both front and back surfaces of an insulating layer and a metal base plate for heat radiation are stacked and soldered between the members.
The copper foil is a thick copper foil having a thickness of 0.5 mm or more,
Irradiate a laser beam so as not to penetrate the thick copper foil, and form a concavo-convex crater with projection heights corresponding to the layer thickness of the solder bonding layer at a plurality of locations on the surface, and then in the bonding surface area. A method of manufacturing a semiconductor device, characterized in that cream solder or plate solder is sandwiched, the heat dissipating metal base plate is superposed on the thick copper foil, and the two are joined together through a solder reflow process . 3. The method of manufacturing a semiconductor device according to claim 1 , wherein the laser light output, irradiation time, and irradiation angle are set to be the same, and craters are formed at a plurality of locations . The method of manufacture according to claim 1 or 2, the method of manufacturing a semiconductor device, and forming dispersed craters on the surface area of the solder joint in at least three places.

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