JP4160889B2 - Manufacturing method of semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a heat dissipation plate for releasing heat generated from a semiconductor element to the outside, and a method for manufacturing the same.

  In recent years, semiconductor devices tend to increase in power consumption as the density increases and the amount of heat generated by the semiconductor devices also increases. For this reason, a heat sink is provided in a semiconductor device on which a semiconductor element is mounted, and heat generated by the semiconductor element is efficiently released to the outside through the heat sink.

  Generally, in a semiconductor device having a heat sink, the heat sink is fixed to a wiring board using an adhesive. The semiconductor element is directly mounted on the heat sink, and the heat sink is configured to be exposed on the upper surface of the semiconductor device. Therefore, the heat generated in the semiconductor element is directly transmitted to the heat sink and released from the heat sink to the outside. Thereby, a semiconductor element can be cooled efficiently.

  However, in the semiconductor device in which the heat radiating plate is fixed to the wiring board using an adhesive as described above, the heat radiating board may be peeled off from the wiring board due to deterioration of the adhesive over time. For this reason, there exists a possibility that the reliability of a semiconductor device may fall resulting from use of an adhesive agent. Further, when manufacturing a semiconductor device, a semiconductor device in which a heat sink is fixed to a wiring board using an adhesive requires a step of applying the adhesive to the heat sink or the wiring board in the manufacturing process. The adhesive application process is difficult to automate, and the manufacturing cost of the semiconductor device increases.

  Therefore, in order to solve the above-described problems, a metal joint is formed on the wiring board, and the metal heat sink is welded to the joint using laser welding or the like. The structure which connects a circuit board is proposed (for example, refer patent document 1).

  FIG. 1 shows a cross-sectional view of the semiconductor device in which the heat sink and the circuit board are connected by welding as described above. The semiconductor device shown in FIG. 1 generally includes a semiconductor element 11, a printed wiring board 12 (circuit board), a heat spreader 13 (heat sink), a sealing resin 14, and solder balls 15. The heat spreader 13 has a recess in the center, and the semiconductor element 11 is accommodated in the recess. The back surface of the semiconductor element 11 is fixed to the bottom surface of the recess of the heat spreader 13 with a die bond material 16.

  In the center of the circuit board 12, an opening is provided at a position corresponding to the recess of the heat spreader 13, and each electrode of the semiconductor element 11 is made of a conductive layer formed on the circuit board 12 through the opening of the circuit board 12 by a bonding wire 17. It is electrically connected to the pattern wiring 18. The circuit board 12 includes a core material 19 made of glass-epoxy or the like, and a pattern wiring 18 made of a conductive layer formed on the core material 19. Further, resist layers 20 and 21 for insulation protection are provided on both surfaces of the circuit board 12.

  In the semiconductor device having the above-described configuration, as shown in FIG. 2, a welded portion 22 is formed on the circuit board 12, and the heat spreader 13 is welded to the welded portion 22 by laser welding. The welded portion 22 is formed on the side opposite to the side on which the pattern wiring 18 of the core material 19 is formed, and the periphery of the welded portion 22 is covered with a resist layer 20.

  FIG. 3 is an enlarged view of a portion surrounded by a dotted circle A in FIG. The state shown in FIG. 3 is a state before the heat spreader 13 is welded to the welded portion 22. The side surface and the peripheral portion of the welded portion 22 are covered with a resist 21, and the surface of the welded portion 22 faces the surface of the heat spreader 13 through a gap 23 formed by the opening of the resist 21. In this state, the heat spreader 13 and a part of the welded portion 22 are welded (welded) by irradiating the laser from the heat spreader 13 side. The purpose of covering the periphery of the welded portion 22 with the resist 21 is to fix the welded portion 22 having a diameter of about 1.2 mm so as not to peel from the core material 19.

When the heat spreader 13 is welded by the above-described welding method, the heat spreader 13 is connected to the circuit board 12 by metal welding, so that heat is easily transmitted and the heat dissipation effect of the heat spreader 13 can be improved. Further, the heat spreader 13 can be reliably and firmly connected to the circuit board 12 by metal welding. That is, when connected by an adhesive, the heat spreader 13 and the substrate may be peeled at the bonding surface, but when connected by metal welding, there is no fear of peeling.
JP 2001-168244 A (page 4-9, FIG. 2)

  As described above, if the heat spreader 13 and the welded portion 22 are well joined by laser welding, there is no fear of peeling as described above. However, if there are variations in the size of the gap 23, there is a risk that problems may occur in laser welding. That is, one of the factors that determine the intensity of the laser to be irradiated in laser welding is the size of the gap 23. If the size of the gap 23 is too large, the laser energy does not reach the welded portion 22 sufficiently and welding is insufficient. There is a risk of becoming. On the other hand, if the gap 23 is too small, the energy of the laser applied to the welded portion 22 is too large, and the lower core member 19 may be damaged by penetrating the welded portion 22.

  The dimension of the gap 23 corresponds to the thickness of the resist 21 covering the periphery of the welded portion 22, but it is difficult to control the thickness of the resist 21 with high accuracy, and therefore it is unavoidable that the dimension of the gap 23 varies to some extent. Absent. Therefore, there is a possibility that the problem at the time of laser welding as described above may occur.

  Further, there is a possibility that a phenomenon occurs in which the air in the gap 23 expands during welding and the surface of the heat spreader 13 rises. When such a phenomenon occurs, there is a risk that the laser irradiation side surface of the heat spreader 13 swells greatly and a mass (usually referred to as a nugget) is formed on the surface of the heat spreader 13.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a semiconductor device that can stably and reliably weld a heat radiating plate to a welded portion of a substrate even with a small energy laser.

According to the present invention, there is provided a method for manufacturing a semiconductor device including a heat sink welded to a welded portion of a circuit board, the circuit board being placed on a floating portion of a set jig, and the heat sink being Placed on the circuit board, pressing a welding mask from above the heat sink, sandwiching the circuit board and the heat sink between the floating part and the welding mask, provided on the welding mask There is provided a method of manufacturing a semiconductor device, wherein a laser is irradiated to a recess formed in the heat sink by etching through the through-hole, and the heat sink is laser welded to the welded portion of the circuit board. .

  According to the present invention, since the thickness of the welded portion of the heat sink is reduced, the heat sink can be stably and reliably welded to the welded portion of the substrate even with a small energy laser. Further, laser welding can be performed more reliably by providing a protrusion on the surface of the heat sink opposite to the weld and performing laser welding in a state where the protrusion is in contact with the weld.

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

  First, a semiconductor device according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a cross-sectional view of a heat spreader and circuit board used in the semiconductor device according to the first embodiment of the present invention. FIG. 5 is an enlarged view of a portion surrounded by a dotted circle B in FIG. In the semiconductor device according to the first embodiment of the present invention, the components other than the heat spreader are the same as the components of the semiconductor device shown in FIG. 1, and illustration and description thereof are omitted. Further, the state shown in FIG. 4 is a state before the heat spreader 30 is welded to the welded portion 22.

  A heat spreader 30 (heat radiating plate) shown in FIG. 4 is used instead of the heat spreader 13 shown in FIG. The heat spreader 30 is formed of a metal plate such as a copper plate. The thickness of the heat spreader 30 is, for example, 0.25 mm, which is larger than that of the heat spreader 13 shown in FIG. Therefore, the rigidity of the heat spreader 30 is larger than the rigidity of the heat spreader 13, and the heat spreader 30 can be prevented from being deformed or bent when assembled as a semiconductor device.

  However, when the thickness of the heat spreader 30 is increased, more energy is required for the laser for welding or welding, making it difficult to obtain stable welding. Therefore, as described above, the instability due to the thickness of the heat spreader is added to the instability of laser welding due to the variation in the gap 23, and it becomes more difficult to perform reliable laser welding.

  Therefore, in the heat spreader 30 shown in FIG. 4, a recess 30 a is provided in the portion of the heat spreader 30 where the laser is irradiated. That is, the thickness of the heat spreader 30 at the portion to be laser-welded is reduced so that reliable laser welding can be performed even with a small energy laser.

  The recess 30a provided in the heat spreader 30 is preferably formed by partially removing the heat spreader 30 by etching. For example, with respect to the heat spreader 30 having a thickness of 0.25 mm (250 μm), the depth of the recess 30 a is about 0.1 mm (100 μm). The recess 30a is preferably circular with a diameter of about 2 mm. That is, if the diameter of the welded portion 22 provided on the circuit board 12 is about 1.2 mm, the diameter of the recessed portion 30 a may be slightly larger than the diameter of the welded portion 22.

  The thickness of the heat spreader 30 in the portion where the recess 30a is formed is about 0.15 mm (150 μm). With this thickness, stable and reliable welding can be performed even when a relatively small energy laser is irradiated. Can be done.

  In addition, when the heat spreader 30 and the welding part 22 are formed with copper, it is preferable to give nickel (Ni) plating to the surface of the welding part 22, and to give gold (Au) plating on it. The surface of the heat spreader 30 facing the welded portion 22 is preferably plated with nickel (Ni) having a thickness of about 5 μm. Although it is difficult to laser weld copper and copper, by performing nickel plating or gold plating in this manner, a copper heat spreader can be easily laser welded to a copper weld.

  Next, the process of connecting the heat spreader 30 and the circuit board 12 by laser welding will be described with reference to FIGS. FIG. 6 is a diagram showing a process of arranging the substrate and the heat spreader on the jig. FIG. 7 is a view showing a state in which the substrate and the heat spreader are arranged on the jig. FIG. 8 is a diagram showing a process of welding the heat spreader and the welded portion of the substrate by irradiating a laser.

  First, as shown in FIG. 6, the circuit board 12 on which the welded portion 22 is formed is placed on the setting jig 40 with the surface where the welded portion 22 is exposed facing upward, and then the concave portion 30a is raised upward. The heat spreader 30 is placed on the circuit board 12 in the state of being directed. The setting jig 40 has a floating portion 41 at a portion where the circuit board 12 is placed. The bottom of the floating portion 41 is supported by a spring 42 and can move up and down. By providing the floating portion 41 on the setting jig 40, the heat spreader 30 can be uniformly pressed against the circuit board 12 as described later in the laser welding process.

  After placing the circuit board 12 on the floating portion 41 of the setting jig 40, the heat spreader 30 is placed on the circuit board 12. At this time, the heat spreader 30 is positioned with respect to the circuit board 12 so that the welded portion 22 of the circuit board 12 and the recess 30a of the heat spreader 30 are aligned in the vertical direction. FIG. 7 shows a state where the circuit board 12 and the heat spreader 30 are placed on the setting jig.

  Next, as shown in FIG. 8, the welding mask 43 is pressed from above the heat spreader 30 to press the heat spreader 30 and the circuit board 12 against the setting jig 40. The welding mask 43 has a concave portion 43 a at the center, and a portion forming a concave portion at the center of the heat spreader 30 (a convex portion when viewed from the opposite side) is accommodated in the concave portion 43 a of the welding mask 43. Further, the welding mask has a welding through-hole 43 b at a position corresponding to the recess 30 a of the heat spreader 30.

  After the welding mask 43 is disposed on the heat spreader 30, the laser beam is sequentially irradiated into the recesses 30 a of the heat spreader 30 through the welding through holes 43 b while pressing the heat spreader 30 against the circuit board 12 by the welding mask 43. The bottom of the recess 30a and the welded portion 22 of the circuit board 12 are melted and solidified immediately by the irradiated laser beam, and laser welding is performed.

  At this time, since the circuit board 12 is placed on the floating portion 41 that can move up and down, even if the welding mask 43 is slightly inclined or the thickness of the circuit board 12 is not uniform, the circuit board 12 is floated. By tilting the portion 41, the heat spreader 30 can be pressed against the circuit board 12 with a uniform pressing force as a whole.

  As described above, by providing the recess 30a in the welded portion of the heat spreader 30, even if the thickness of the heat spreader 30 is increased, laser welding can be reliably performed with a small energy laser.

  Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 9 is a cross-sectional view of a heat spreader and circuit board used in the semiconductor device according to the second embodiment of the present invention. FIG. 10 is an enlarged view of a portion surrounded by a dotted circle C in FIG. In the semiconductor device according to the second embodiment of the present invention, the components other than the heat spreader are the same as those of the semiconductor device shown in FIG. The state shown in FIG. 10 is a state before the heat spreader 50 is welded to the welded portion 22.

  The heat spreader 50 shown in FIG. 9 has a recess 50a in a portion irradiated with a laser, like the heat spreader 30 shown in FIG. The dimensions of each part of the heat spreader 50 are the same as those of the heat spreader 30, and a description thereof will be omitted. The difference between the heat spreader 50 and the heat spreader 30 is that a protrusion 50 b is formed on the heat spreader 50.

  The protrusion 50b is formed so as to protrude to the opposite side of the portion where the recess 50a is formed. Therefore, when the heat spreader 50 is placed on the circuit board 12 for laser welding, the protrusion 50b is disposed in the gap 23 where the welded portion 22 of the circuit board 12 is exposed. The protrusion dimension of the protrusion 50b is, for example, about 30 μm to 50 μm so that the tip of the protrusion 50b is in contact with the weld 22 when laser welding is performed. That is, since the thickness of the resist 21 covering the periphery of the welded portion 22 is about 30 μm to 50 μm, if the protruding dimension of the protruding portion 50 b is set to 30 μm to 50 μm, the tip of the protruding portion 50 b is reliably brought into contact with the welded portion 22. be able to. However, the above dimensions vary depending on the dimension of the gap 23 defined by the resist 21, and are not limited to the specifically shown dimensions.

  As described above, by performing laser welding in a state where the protrusion 50b is in contact with the welded portion 22, laser welding can be reliably performed, and the laser welding defect rate can be greatly reduced. As a reason why laser welding is ensured, it is conceivable that the laser energy is easily transmitted to the welded portion 22 through the protruding portion 50b when the protruding portion 50b directly contacts the welded portion 22.

  Next, an example of a method for forming small protrusions such as the above-described protrusions 50b on a metal plate such as the heat spreader 50 will be described with reference to FIGS. FIG. 11 is a diagram for explaining a process of forming the protrusion on the metal plate, and FIG. 12 is an enlarged cross-sectional view showing the vicinity of the protrusion formed in FIG.

  The protrusion forming method shown in FIG. 11 is a method of forming a protrusion by deforming a metal plate with a die press. In FIG. 11A, a metal plate 54 (corresponding to a heat spreader) on which the protrusion 54 a is formed is placed on the table 51 a of the lower mold 51. In the table 51a, a recess 51b is formed at a position corresponding to a portion where the protrusion 54a is formed. An upper mold 52 is provided above the lower mold so as to be movable with respect to the lower mold 51.

  The upper mold 52 is provided with leg portions 52b that come into contact with the base 51c of the lower mold 51 when the mold is closed. The leg 52b is attached to the base 52a of the upper mold 52 via a shim 52c, and the distance from the base 52a to the tip of the leg 52b can be adjusted by adjusting the thickness of the shim 52c.

  A press-fit pin 52 d is attached to the surface of the base 52 a of the upper mold 52 that faces the table 51 a of the lower mold 51. The press-fit pins 52d are provided corresponding to positions where the protrusions 54a of the metal plate 54 are formed. Accordingly, the press-fit pin 52d of the upper mold 52 is arranged in a state of being aligned in the vertical direction with the concave portion 51b of the lower mold 51.

  After the metal plate 54 is arranged at a predetermined position on the table 51a of the lower mold 51, the upper mold 52 is moved toward the lower mold 51 as shown in FIG. close. Accordingly, the metal plate 54 is sandwiched between the base 52 a of the upper mold 52 and the table 51 a of the lower mold 51, and the press-fit pins 52 d are press-fitted so as to bite into the metal plate 54. By press-fitting the press-fit pin 52d, the metal plate 54 is deformed as shown in FIG. 12, and the deformed portion is formed as a protrusion 54a.

  By using the method for forming the protrusions by the above die press, the protrusions can be easily and accurately formed on the heat spreader in the above-described embodiment.

It is sectional drawing of the semiconductor device with which the heat sink and the circuit board were connected by welding. It is sectional drawing which shows the heat sink and circuit board shown in FIG. FIG. 3 is an enlarged cross-sectional view of a portion surrounded by a dotted circle A in FIG. 2. It is sectional drawing of the heat spreader and circuit board which are used for the semiconductor device by 1st Example of this invention. It is sectional drawing which expands and shows the part enclosed by the dotted-line circle B in FIG. It is a figure which shows the process of arrange | positioning a board | substrate and a heat spreader on a jig | tool. It is a figure which shows the state by which the board | substrate and the heat spreader are arrange | positioned on the jig | tool. It is a figure which shows the process of irradiating a laser and welding the heat spreader and the welding part of a board | substrate. It is sectional drawing of the heat spreader and circuit board which are used for the semiconductor device by 2nd Example of this invention. It is sectional drawing which expands and shows the part enclosed by the dotted line circle C in FIG. It is a figure for demonstrating the process of forming the projection part shown in FIG. It is sectional drawing which expands and shows the vicinity of the projection part formed in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Semiconductor element 12 Board | substrate 13 Heat spreader 14 Sealing resin 15 Solder ball 16 Die attachment material 17 Bonding wire 18 Pattern wiring 19 Core material 20, 21 Resist 22 Welding part 23 Air gap 30, 50 Heat spreader 30a, 50a Concave 40 Set jig 41 Floating Part 42 Spring 43 Welding mask 43a Concave part 43b Welding through hole 50b Protrusion part 51 Lower mold 51a Table 51b Concave part 51c Base 52 Upper mold 52a Base 52b Leg part 52c Shim 52d Press-fit pin 54 Metal plate 54a Protrusion part

Claims (1)

A method for manufacturing a semiconductor device comprising a heat sink welded to a welded portion of a circuit board,
Placing the circuit board on the floating portion of the setting jig, and placing the heat sink on the circuit board;
Press the welding mask from above the heat sink, sandwich the circuit board and the heat sink between the floating part and the welding mask,
A semiconductor device, wherein a laser is irradiated through a through-hole provided in the welding mask to a recess formed in the heat dissipation plate by etching, and the heat dissipation plate is laser welded to the welded portion of the circuit board. Production method.

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