JP2013001968A - Thermally conductive sheet and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further improve thermal conductivity, to easily adjust a sheet thickness in assembly, and to contribute to cost reduction.SOLUTION: In a thermally conductive sheet 10, a first metallic material 12 and a second metallic material 16 are compositely molded in a sheet shape. The first metallic material 12 is an indium sheet, and the second metallic material 16 is metallic powder grains having higher thermal conductivity and higher melting point than indium. The metallic powder grains 16 are included in the indium sheet 12. The metallic powder grains 16 are, for instance, copper powder grains 14 with a surface coated with a gold layer 15.

Description

  The present invention relates to a heat conductive sheet and a manufacturing method thereof.

  The heat conductive sheet according to the present invention is applied to a semiconductor device that requires high heat dissipation, such as a CPU (central processing unit) or a GPU (graphic processing unit).

  A semiconductor element (chip) used for a CPU, GPU, or the like is electrically connected and fixed on a wiring board (package). Since such a semiconductor element becomes very hot during its operation, a heat dissipating component (for example, a heat spreader made of metal such as copper (Cu)) for dissipating heat generated during the operation to the atmosphere is disposed on the chip. At that time, a material called TIM (thermal interface material) is sandwiched and thermally bonded between the chip and the heat spreader.

  Such thermal interface material (TIM) is required to have high thermal conductivity, and indium (In) is used as one of them. For example, an indium sheet is sandwiched between a heat spreader and a semiconductor element (chip), and the heat spreader and the chip are once mounted using a resin material (adhesive) that cures at a temperature below the melting point of indium (156.6 ° C). Secure the package to the package. Thereafter, reflow is performed at a temperature equal to or higher than the melting point of indium, and the thickness of the indium melted is controlled while being pressed to join the heat spreader and the chip.

  An example of a technique related to the conventional technique is described in Patent Document 1 below. This reference discloses a heat conductor in which copper fibers are dispersed in an indium sheet.

JP 2004-238646 A

  As described above, in the current technology, indium is used as the thermal interface material (TIM) between the semiconductor element (chip) and the heat spreader, but there are the following problems.

  First, indium has a low thermal conductivity of about 1/5 (copper 398 W / m · K compared to copper 398 W / m · K), so indium can be a bottleneck in the heat dissipation path. That is, copper having high thermal conductivity is often used because heat dissipation is required for the heat spreader, but indium used as the TIM is only in contact with a part of the heat spreader (copper). For this reason, when it sees as the whole thermal radiation path | route, since the thermal resistance in the part near a heat source becomes high compared with another part, the whole thermal conductivity will fall.

  Further, when bonding the heat spreader and the chip (when assembling), an indium sheet is sandwiched between the chip and the heat spreader, and heat is applied to bond them. At this time, since indium liquefies, it is difficult to control the indium (sheet) to a required thickness while applying pressure.

  Furthermore, since indium is a rare earth, there is a fluctuation in cost (relatively expensive), and there is a possibility that it may be affected, for example, when it becomes difficult to stably obtain an international transaction problem.

  In view of the above, an object of the present invention is to provide a thermal conductive sheet and a method for manufacturing the same, which can further improve thermal conductivity.

  Furthermore, it aims at providing the heat conductive sheet which can adjust the sheet | seat thickness at the time of an assembly easily, and can contribute to cost reduction, and its manufacturing method.

  According to the first aspect of the following disclosure, the first metal material and the second metal material are formed into a sheet shape, and the second metal material has higher heat conduction than the first metal material. The heat conductive sheet characterized by having the property is provided.

  According to a second aspect, in the thermal conductive sheet according to the first aspect, the first metal material is an indium sheet, and the second metal material has a higher melting point than indium. There is provided a heat conductive sheet, characterized in that it is a metal particle, and the metal particle is included in the indium sheet.

  According to the third aspect, the first metal material and the second metal material having higher thermal conductivity than the first metal material are prepared, and the heating unit and the pressurizing unit are used. In addition, a method for manufacturing a heat conductive sheet is provided, which includes combining the first metal material and the second metal material and forming the composite into a sheet shape.

  According to a fourth aspect, in the method for manufacturing a heat conductive sheet according to the third aspect, an indium sheet is used as the first metal material, and a melting point higher than that of indium is used as the second metal material. In the state where the indium sheet is melted by a heating roller, the metal particles are mixed in the melted indium sheet, and then the pressure roller is used. There is provided a method for producing a heat conductive sheet, characterized in that an indium sheet mixed with the metal particles is formed to a required thickness.

  According to the heat conductive sheet and the method for manufacturing the same according to the first and third aspects, the second metal material (for example, indium) has a second heat conductivity higher than that of the first metal material. Since a metal material (for example, copper) is compounded, the overall thermal conductivity is increased and the thermal resistance is decreased.

  Moreover, according to the heat conductive sheet and the manufacturing method thereof according to the second and fourth aspects, the melting point of the second metal material (metal particle powder) even at the temperature at which the first metal material (indium) melts. Therefore, the sheet thickness can be easily adjusted with respect to compression during assembly.

  In addition, when copper is used as the second metal material (metal particles), if the amount (volume) used as the thermal interface material (TIM) is the same, the price of copper is lower than that of indium alone Because it is low, it also contributes to cost reduction.

1 shows the configuration of a heat conductive sheet according to the first embodiment, (a) is a diagram showing a cross-sectional structure of the heat conductive sheet, and (b) is a schematic view of the structure when the heat conductive sheet is seen in perspective. FIG. 1 shows a configuration according to a modification of the heat conductive sheet shown in FIG. 1, (a) is a diagram showing a cross-sectional structure of the heat conductive sheet, and (b) is a structure when the heat conductive sheet is seen in perspective. FIG. It is sectional drawing which shows an example at the time of comprising a semiconductor device using the heat conductive sheet shown in FIG. 1 (FIG. 2, FIG. 7). It is a side view which shows roughly the structure of the apparatus for manufacturing the heat conductive sheet which concerns on 1st Embodiment. It is an external view when the structure of the stage used for the manufacturing apparatus of FIG. 4 is seen perspectively. It is a top view which shows typically a mode that the copper particle powder with a plating is aligned using the stage of FIG. 5, and is sent out downstream. It is sectional drawing which shows the structure of the heat conductive sheet which concerns on 2nd Embodiment. It is a side view which shows roughly the structure of the apparatus for manufacturing the heat conductive sheet which concerns on 2nd Embodiment.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

(First embodiment: see FIGS. 1 to 6)
FIG. 1 shows a configuration of a heat conductive sheet according to the first embodiment, (a) is a cross-sectional structure of the heat conductive sheet, and (b) is a perspective view of the heat conductive sheet. The structure is shown schematically.

  The heat conductive sheet 10 according to the present embodiment is formed by mixing a large number of metal particle powders 16 having higher thermal conductivity and higher melting point than indium in an indium (In) sheet 12.

  The metal granule 16 has a spherical shape (FIG. 1 (b)) and has a structure (FIG. 1 (a)) in which a plating layer 15 is deposited on the surface of the copper (Cu) granule 14. Yes. The plating layer 15 includes a gold (Au) plating layer for improving adhesion with indium. Further, a nickel (Ni) plating layer as a barrier metal layer is included between the Au plating layer and the copper (Cu) granular powder 14. That is, the plating layer 15 has a two-layer structure of Ni / Au.

  In the following description, the copper particle powder 14 (metal particle powder 16) to which the plating layer 15 is applied is also referred to as “plated copper particle powder” for convenience.

  In the heat conductive sheet 10 of the present embodiment, a large number of plated copper particles 16 contained in the indium sheet 12 are aligned (that is, uniform) as schematically shown in FIG. It is preferable to be mixed at a high density. If the plated copper particles 16 are included in such an aligned state, when the thermal conductive sheet 10 is used as a thermal interface material (TIM) (see FIG. 3), copper having good thermal conductivity ( Since the amount of heat passing through the portion of Cu) is relatively large, the heat dissipation as the entire TIM is enhanced.

  In addition, by mixing the plated copper particles 16 in the indium sheet 12 in an aligned state, it becomes easier to adjust the sheet thickness during assembly as will be described later. It is advantageous.

  In the present embodiment, the copper particle powder 14 is used as a material of the metal particle 16 mixed in the indium sheet 12, but it is a metal having required attributes (higher thermal conductivity and higher melting point than indium). If there is enough. For example, silver (Ag) granules may be used.

  FIG. 2 shows a configuration of a heat conductive sheet according to a modification of the first embodiment (FIG. 1), (a) is a cross-sectional structure of the heat conductive sheet, and (b) is the heat conductive sheet. Fig. 2 schematically shows a structure when viewed in perspective.

  Compared with the heat conductive sheet 10 (FIG. 1) of the above-described embodiment, the heat conductive sheet 10a of this modification has a rectangular parallelepiped or cubic shape in which the plated copper particle powder 16a included in the indium sheet 12 is formed. (FIG. 2B) is different. The other configurations (the point where the plated layer (Ni / Au) 15a is deposited on the surface of the copper particle powder 14a, the point where the plated copper particle powder 16a is mixed and aligned) are described above. Since it is the same as that of the embodiment, the description thereof is omitted.

  FIG. 3 is a cross-sectional view showing an example in which a semiconductor device is configured using the heat conductive sheet 10 shown in FIG. 1 (heat conductive sheet 10a shown in FIG. 2, heat conductive sheet 60 shown in FIG. 7). Is.

  In the semiconductor device 40 shown in FIG. 3, reference numeral 20 denotes a semiconductor element (chip) to be radiated, and the semiconductor element (chip) 20 is a surface on which a circuit such as an active element is formed (circuit forming surface). ) On the wiring board (package) 22 with the bottom facing down. Although a specific illustration of the connection (joining) portion between the package 22 and the chip 20 is omitted, the configuration of this portion is the same as the configuration when the chip is flip-chip mounted on a general printed wiring board or the like. The same.

  For example, when a resin substrate (plastic package) is used as the package 22, a chip is formed on a pad (a portion defined in a required portion of the wiring layer covered with the solder resist layer) exposed from the solder resist layer of the resin substrate. The 20 electrode terminals are electrically connected via a solder bump or the like (flip chip connection). Furthermore, the gap between the mounted chip 20 and the package 22 is filled with an underfill resin (such as a thermosetting epoxy resin), and is thermally cured and mechanically joined.

  Reference numeral 30 denotes a metal heat spreader for releasing heat generated by the semiconductor element (chip) 20 during operation to the atmosphere. The heat spreader 30 is made of copper (Cu) as a material, and nickel (Ni) plating is applied to the surface thereof. The heat spreader 30 has a structure in which a main portion (portion responsible for heat dissipation) is formed into a plate shape (plate portion 30a), and a side wall portion 30b is integrally formed around the plate portion 30a. ing. The side wall portion 30b is formed in a square ring shape in accordance with the outer shape (square shape) of the chip 20 in plan view. The heat spreader 30 is fixed on the package 22 by a fixing resin (thermosetting resin such as epoxy resin or polyimide resin) 32 through the side wall portion 30b.

  Further, the heat conductive sheet 10 (10a, 60) serving as a thermal interface material (TIM) includes a surface opposite to the circuit forming surface of the semiconductor element (chip) 20 and an inner side of the plate-like portion 30a of the heat spreader 30. It is interposed between each surface (on the side facing the chip 20) while being adhered to each surface. That is, the chip 20 and the heat spreader 30 are thermally coupled via the heat conductive sheet 10 (10a, 60).

  Next, a method for manufacturing the heat conductive sheet 10 (10a) according to the first embodiment will be described with reference to FIGS.

  FIG. 4 is a schematic view of the configuration of the apparatus for manufacturing the heat conductive sheet according to the first embodiment as viewed from the side. FIG. 5 is an external view of the structure of the stage used in this manufacturing apparatus when viewed in perspective, and FIG. 6 shows the state in which the plated copper particles are aligned and sent to the downstream side using this stage. It is a top view showing typically. In the embodiment shown in FIGS. 4 to 6, the case where the heat conductive sheet 10 a shown in FIG. 2 is manufactured is illustrated.

  As shown in FIG. 4, the manufacturing apparatus 50 includes a stage 51, a vibrator 52, a supply roller 53, a heating roller 54, a pressure roller 55, and a winding roller 56.

  The stage 51 is divided into a first stage 51a and a second stage 51b and is integrally formed (see FIG. 5). The vibrator 52 is disposed on the lower side of the first stage 51a of the stage 51 (see FIG. 4), and applies appropriate vibration to the first stage 51a via the vibration part 52S.

  An indium sheet 12 </ b> A is wound around the supply roller 53 in a roll shape. For example, the indium sheet 12A has a thickness of about 100 μm and a width of about 22 mm. The width of the indium sheet 12A corresponds to the vertical or horizontal dimension of the size (vertical × horizontal rectangle) of the semiconductor element 20 (see FIG. 3) in plan view.

  The heating roller 54 is disposed downstream of the supply roller 53 and is provided so as to be in contact with a workpiece (indium sheet 12A, plated copper particle 16a) on the second stage 51b of the stage 51. The heating roller 54 melts the indium sheet 12 </ b> A drawn and moved from the supply roller 53, while the plated copper particle powder 16 a conveyed on the second stage 51 b is melted with the molten indium ( Sheet) for mixing in 12A. For this reason, the temperature of the heating roller 54 is set to a temperature at least exceeding the melting point of indium (156.6 ° C.), for example, a temperature around 170 ° C. This temperature is much lower than the melting point (copper: 1083.4 ° C./nickel: 1450 ° C./gold: 1064.4 ° C.) of the plated copper particle 16a.

  The pressure roller 55 is disposed after the heating roller 54 and can contact the workpiece (the sheet 10A in which the plated copper particle 16a is mixed in the indium (sheet) 12A) on the second stage 51b. Is provided. The pressure roller 55 is for forming the sheet 10A integrated by the heating roller 54 to a required thickness.

  The heat conductive sheet 10 </ b> A thus formed to a required thickness is wound up by the winding roller 56. Thereafter, the heat conductive sheet 10A (FIG. 2) is obtained by cutting the heat conductive sheet 10A into an appropriate length.

  In the method described above, the heat conductive sheet 10a of FIG. 2 is manufactured, but the heat conductive sheet 10 shown in FIG. 1 can be similarly manufactured using the manufacturing apparatus 50 (FIG. 4).

  In the manufacturing apparatus 50 (FIG. 4), the first stage 51a of the stage 51 stores the plated copper particle powder 16a to be mixed in the indium sheet 12A, and aligns it with a uniform density so that the second stage 51b side. It is used as a part for sending out. On the other hand, the second stage 51b is used as a portion for controlling the sheet 10A integrated by the heating roller 54 to a required thickness in cooperation with the pressure roller 55. For this reason, each stage 51a, 51b is formed into a specific shape as shown in FIGS.

  First, the first stage 51a is provided so as to be inclined upward as shown in FIG. 5 with respect to the second stage 51b arranged in the horizontal direction. Furthermore, guides 51G that are bent upward are provided in portions around the stages 51a and 51b (excluding the exit side portion of the second stage 51b).

  By inclining the first stage 51a upward, the plated copper particle powder 16a stored on the first stage 51a is moved to the second stage 51b side by vibration applied from the vibrator 52 (vibrating unit 52S). It becomes easy to do. Further, the presence of the guide 51G of the first stage 51a can prevent the stored plated copper particle powder 16a from spilling from the first stage 51a due to the vibration of the vibrator 52. Further, the presence of the guide 51G of the second stage 51b can prevent the indium 12A liquefied by the heating roller 54 (mixed with the plated copper particle powder 16a) from protruding from the second stage 51b.

  Further, the first stage 51a is shaped such that, when seen in a plan view, the exit portion (tip portion) toward the second stage 51b side has a tapered shape as shown in FIG. By thinning the tip in this way, the plated copper particle powder 16a collected at the tip by the vibration of the vibrator 52 is forcedly aligned (that is, at a uniform density) in the second state. It is sent out to the stage 51b side.

  Thus, when heated and pressurized on the second stage 51b, the plated copper particle powder 16a can be evenly distributed in the indium sheet 12A. Thus, the heat conductive sheet 10 (10a) which does not produce nonuniformity in heat conductivity can be manufactured by mixing the plated copper particle powder 16a with a uniform density in the indium sheet 12A.

  As described above, according to the heat conductive sheet 10 (10a) and the manufacturing method thereof according to the first embodiment, the plated copper particle powder 16 having higher heat conductivity than indium in the indium sheet 12. Since (16a) is mixed, the thermal conductivity can be further enhanced as compared with the case of indium alone. That is, the thermal conductivity of the thermal conductive sheet 10 (10a) as a whole increases and the thermal resistance decreases.

  Further, as illustrated in FIG. 3, when the heat conductive sheet 10 (10a) is applied as a thermal interface material (TIM) (during assembly), the melting point of the plated copper particle 16 (16a) even at a temperature at which indium melts. Therefore, it is possible to easily adjust the sheet thickness with respect to compression.

  Further, if the amount (volume) used as the thermal interface material (TIM) is the same, the price of copper is lower than that of indium alone, which can contribute to cost reduction.

(Second embodiment: see FIGS. 7 and 8)
FIG. 7 shows the configuration of the heat conductive sheet according to the second embodiment in the form of a sectional view.

  The heat conductive sheet 60 of the second embodiment is formed by laminating indium (In) sheets 64 on both surfaces of a copper (Cu) sheet 62 having higher thermal conductivity and higher melting point than indium. ing. That is, the heat conductive sheet 60 has a three-layer structure of In / Cu / In. The thickness of the copper sheet 62 is selected to be greater than the thickness of the indium sheet 64.

  Hereinafter, a method for producing the heat conductive sheet 60 of the second embodiment will be described with reference to FIG. FIG. 8 is a schematic view of the configuration of the apparatus for manufacturing the heat conductive sheet 60 as viewed from the side.

  As shown in FIG. 8, the manufacturing apparatus 70 includes supply rollers 71, 72 and 73, heating rollers 74 and 75, pressure rollers 76 and 77, and a winding roller 78.

  A copper sheet 62A is wound around the supply roller 71 in a roll shape. For example, the copper sheet 62A has a thickness of about 100 μm and a width of about 22 mm. The width of the copper sheet 62A corresponds to the vertical or horizontal dimension of the size (vertical × horizontal rectangle) of the semiconductor element 20 (see FIG. 3) in plan view.

  An indium sheet 64A is wound around the supply rollers 72 and 73 in a roll shape. The indium sheet 64A is selected to have a thickness of about 50 μm and a width of about 22 mm (same as the width of the copper sheet 62A), for example. One supply roller 72 is disposed on the upper side, and the other supply roller 73 is disposed on the lower side.

  The heating rollers 74 and 75 are disposed at the subsequent stage of the corresponding supply rollers 74 and 75, respectively, and are provided so as to be in contact with the object to be processed (copper sheet 62A, indium sheet 64A). The heating rollers 74 and 75 superimpose the indium sheet 64A drawn and moved from the supply rollers 72 and 73 on both surfaces of the copper sheet 62A drawn and moved from the supply roller 71, and thermally bonded. It is for making it happen. For this reason, the temperature of the heating rollers 74 and 75 is set to a temperature of around 170 ° C., as in the case of the first embodiment described above.

  The pressure rollers 76 and 77 are arranged at the subsequent stage of the corresponding heating rollers 74 and 75, respectively, and are provided so as to be in contact with the object to be processed (a thermally bonded three-layer structure (In / Cu / In) sheet 60A). ing. The pressure rollers 76 and 77 are for forming the sheet 60A integrated through the heating rollers 74 and 75 to a required thickness.

  The heat conductive sheet 60 </ b> A thus formed to a required thickness is wound up by the winding roller 78. Thereafter, the heat conductive sheet 60A (FIG. 7) is obtained by cutting the heat conductive sheet 60A into an appropriate length.

  According to the heat conductive sheet 60 and the manufacturing method thereof according to the second embodiment, the copper sheet 62 having higher heat conductivity and higher melting point than indium is interposed in the heat conductive sheet 60. The same effects as in the case of the first embodiment can be achieved.

  Further, in the second embodiment, the processing for aligning the plated copper particle powder 16 (16a) in the indium sheet 12 as required in the first embodiment is unnecessary. As a result, when the heat conductive sheet 60 is used as a thermal interface material (TIM) (FIG. 3), the total amount of heat during heat dissipation passes through the copper sheet 62, as in the first embodiment. Compared with the case of passing through the plated copper powder 16 (16a), the heat dissipation as a whole of the TIM can be further enhanced.

  In addition, compared to the case of the first embodiment (when the plated copper particle powder 16 is mixed in the indium sheet 12 in an aligned state), the solid copper sheet 62 is interposed, It becomes easier to adjust the sheet thickness during assembly.

  In each of the above-described embodiments, as the thermal interface material (TIM), a form in which the plated copper particle powders 16 and 16a are included in the indium sheet 12 (the heat conductive sheet 10 in FIG. 1 and the heat conductive sheet 10a in FIG. 2). ), Or a form in which both surfaces of the copper sheet 62 are sandwiched between indium sheets 64 (the heat conductive sheet 60 in FIG. 7) has been described as an example. However, the form of the TIM is not limited thereto.

  For example, as a modification of the first embodiment (FIGS. 1 and 2), carbon nanotubes may be included in an indium sheet instead of the plated copper particles 16 and 16a. In this case, it is preferable to arrange the carbon nanotubes in the heat conduction direction in the indium sheet. Since carbon nanotubes are excellent in thermal conductivity and have very high bending strength, it is expected that carbon nanotubes can flexibly follow shape changes (warping) that may occur due to heat generation during operation of the semiconductor element. This contributes to maintaining high thermal conductivity.

10, 10a, 10A, 60, 60A ... heat conduction sheet,
12, 12A, 64, 64A ... sheet of indium (In),
14, 14a ... Copper (Cu) powder,
15, 15a ... plating (Ni / Au) layer,
16, 16a ... Copper-coated powder (metal particles) with plating,
20: Semiconductor element (chip),
30 ... heat spreader,
40. Semiconductor device,
50, 70 ... (thermal conductive sheet) manufacturing equipment,
51 ... Stage,
62, 62A. Sheet of copper (Cu).

Claims (8)

The first metal material and the second metal material are composite-molded into a sheet shape,
The heat conductive sheet, wherein the second metal material has higher heat conductivity than the first metal material.   The first metal material is an indium sheet, the second metal material is a metal particle having a melting point higher than that of indium, and the metal particle is included in the indium sheet. The heat conductive sheet according to claim 1, wherein   The heat conductive sheet according to claim 2, wherein the metal particles are copper or silver particles having a gold layer deposited on the surface thereof.   The first metal material is an indium sheet, the second metal material is a copper sheet, and the indium sheets are laminated on both sides of the copper sheet. The heat conductive sheet according to claim 1. Providing a first metal material and a second metal material having higher thermal conductivity than the first metal material;
A method for producing a heat conductive sheet, comprising: combining the first metal material and the second metal material into a sheet by using a heating unit and a pressurizing unit. Preparing a sheet of indium as the first metal material, and preparing metal particles having a melting point higher than that of indium as the second metal material,
Next, in a state where the indium sheet is melted by a heating roller, the metal particles are mixed into the melted indium sheet,
6. The method of manufacturing a heat conductive sheet according to claim 5, wherein the sheet of indium mixed with the metal particles is formed to a required thickness by a pressure roller.   The method for producing a heat conductive sheet according to claim 6, wherein the second metal material is a copper or silver particle having a surface plated with gold. An indium sheet is prepared as the first metal material, and a copper sheet is prepared as the second metal material,
Next, the indium sheets are laminated on both sides of the copper sheet by a heating roller,
6. The method for producing a heat conductive sheet according to claim 5, wherein the laminated sheets are formed to a required thickness by a pressure roller.

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