JP6036431B2 - Semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor device.

  In a semiconductor device in which a semiconductor element is cooled by a cooling jacket or a radiating fin (hereinafter referred to as a radiating fin) through which cooling water flows, a heat transfer structure member (for example, a substrate on which the semiconductor element is mounted) and a radiating fin If there is a gap between them, the cooling efficiency is greatly reduced. Therefore, grease mixed with filler particles having good thermal conductivity is interposed in such a gap. Thereby, the heat conduction between the heat transfer structure member and the radiation fins is improved, and the semiconductor element is efficiently cooled.

  The heat conduction between the members connected by the grease depends not only on the thermal conductivity of the filler particles but also on the directionality and connectivity. It has been proposed to improve the directionality and connectivity of filled particles by a fluid heat conduction compound in which a liquid (eg, silicon oil) and magnetic particles are mixed.

  Specifically, for example, a fluid heat conduction compound is interposed in the gap between the substrate on which the semiconductor element is mounted and the heat radiating fin, and a magnetic layer is provided on the substrate or the heat radiating fin, and the fluidity is generated by the magnetic field generated by the magnetic layer. Orient the magnetic particles contained in the heat conduction compound. The magnetic layer provided on the substrate or the heat radiating fin generates a magnetic field parallel to the heat transfer direction. For this reason, the magnetic particles are in a continuous state in the heat transfer direction.

  The thermal conductivity of the magnetic particles is 2 to 4 orders of magnitude higher than the thermal conductivity of the liquid (eg, silicon oil) contained in the fluid heat conduction compound. For this reason, the heat generated by the semiconductor element is released through the magnetic particles in a continuous state. That is, a heat transfer path is formed by the magnetic particles in a continuous state.

JP-A-5-248788

  The fluid heat conduction compound described above is in contact with the magnetic layer. The thermal conductivity of the magnetic layer (for example, ferrite) is much smaller than the thermal conductivity of a substrate (for example, an AlN plate or SiC plate) on which a semiconductor element is mounted and a heat radiation fin or the like (for example, an Al fin). For this reason, even if a fluid heat conduction compound is interposed between a heat radiation fin or the like and a heat transfer structure member (for example, a substrate on which a semiconductor element is mounted), the heat radiation characteristics of the semiconductor device are not sufficiently improved.

  In order to solve the above problem, according to one aspect of the present apparatus, a semiconductor substrate, a package for housing the semiconductor substrate, a heat conductive layer disposed on one surface of the package, and the heat conductive layer A cooler disposed on a surface opposite to the package, and the heat conducting layer is formed of a magnetic fluid layer and a plurality of magnets disposed on one surface of the magnetic fluid layer. And a magnetic field generation layer having a yoke sandwiching each of the plurality of magnets.

  According to the disclosed apparatus, the heat dissipation characteristics of the semiconductor device having the cooler are improved.

FIG. 1 is a cross-sectional view of the semiconductor device of the first embodiment. FIG. 2 is a plan view of the magnetic field generation layer. FIG. 3 is an enlarged sectional view of the vicinity of the magnetic fluid layer. FIG. 4 is an enlarged cross-sectional view of the vicinity of the magnetic fluid layer. FIG. 5 is a cross-sectional view of a semiconductor device having a magnet instead of a magnetic field generating layer having a magnet and a yoke. FIG. 6 is a diagram showing the relationship between the normalized magnetic flux density and the normalized distance in the semiconductor device of the first embodiment. FIG. 7 is a plan view illustrating a modification of the magnetic field generation layer. FIG. 8 is a cross-sectional view illustrating another modification of the magnetic field generation layer. FIG. 9 is an enlarged cross-sectional view of the vicinity of the magnetic field generation layer according to the second embodiment. FIG. 10 is an enlarged cross-sectional view of the vicinity of the magnetic field generation layer according to the second embodiment. FIG. 11 is a diagram showing the relationship between the normalized magnetic flux density and the normalized distance in the semiconductor device of the second embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof. Note that, even if the drawings are different, corresponding parts are denoted by the same reference numerals, and description thereof is omitted.

(Embodiment 1)
(1) Structure FIG. 1 is a cross-sectional view of the semiconductor device 2 of the first embodiment.

  As shown in FIG. 1, the semiconductor device 2 includes a semiconductor substrate (for example, Si substrate) 4 and a package 6 that houses the semiconductor substrate 4. The semiconductor device 2 further has a heat conductive layer 8 disposed on one surface of the package 6. The semiconductor device 2 further includes a cooler 12 disposed on the surface of the heat conductive layer 8 opposite to the package 6.

  The heat conductive layer 8 has a layer (hereinafter referred to as a magnetic fluid layer) 9 formed of a magnetic fluid. The heat conduction layer 8 further includes a magnetic field generation layer 10 disposed on one surface of the magnetic fluid layer 9.

  In the example shown in FIG. 1, the magnetic field generation layer 10 is disposed on the surface of the magnetic fluid layer 9 on the cooler 12 side. However, the magnetic field generation layer 10 may be disposed on the surface of the magnetic fluid layer 9 on the package 6 side. In the first and second embodiments, as shown in FIG. 1, the case where the magnetic field generation layer 10 is disposed on the surface of the magnetic fluid layer 9 on the cooler 12 side will be mainly described. However, the magnetic field generation layer 10 may be disposed on the surface of the magnetic fluid layer 9 on the package 6 side.

―Package―
The package 6 accommodates the semiconductor substrate 4 having an integrated circuit formed on the surface.

  Specifically, the package 6 includes, for example, a package substrate 14 and a heat spreader 16. The planar shape of the package 6 is, for example, a square having a side of about 50 mm.

  The package substrate 14 is, for example, a pad-shaped first end portion (not shown) disposed on the front surface, a pad-shaped second end portion (not illustrated) disposed on the back surface, and the inside of the substrate. A plurality of wirings including an intermediate part (not shown) are provided. The package substrate 14 is, for example, a buildup substrate.

  An integrated circuit of the semiconductor substrate 4 is connected to the first end of the package substrate 14 by, for example, solder bumps 18. The second end of the package substrate 14 is connected to a wiring substrate (for example, a printed circuit board) by solder bumps 20.

  The heat spreader 16 has, for example, a flat plate-like top portion and side portions provided along the outer periphery of the top portion.

  A side portion of the heat spreader 16 is fixed to the surface of the package substrate 14 by, for example, an adhesive (not shown). The top of the heat spreader 16 is connected to the back surface of the semiconductor substrate 4 by, for example, solder 17 (for example, In-Ag alloy). Thereby, the semiconductor substrate 4 is thermally connected to the heat spreader 16. The thickness of the top of the heat spreader 16 is, for example, about 1 mm to 5 mm.

  The heat spreader 16 is made of a material having high thermal conductivity. For example, the heat spreader 16 is made of copper, copper alloy, aluminum, aluminum alloy, iron, iron alloy, nickel, nickel alloy, or a composite material thereof. As a material for the heat spreader 16, copper having a high thermal conductivity is particularly preferable.

  The package 6 may have a magnetic shield layer 22 disposed between the semiconductor substrate 4 and the heat conductive layer 8.

  Specifically, for example, the package 6 may have a magnetic shield layer 22 in the top of the heat spreader 16. The magnetic shield layer 22 is formed of a ferromagnetic material (preferably a soft magnetic material) such as iron, nickel, cobalt, permalloy, a silicon steel plate, an iron alloy, or a nickel alloy. As the material of the magnetic shield layer 22, iron having a high thermal conductivity and a high saturation magnetic flux density is particularly preferable.

  The number of magnetic shield layers 22 may be one or more. The thickness of the magnetic shield layer 22 is, for example, about 10 μm to 1 mm.

  The heat spreader 16 can be formed by, for example, processing (for example, cutting and / or cutting) a clad material (dissimilar metal composite material) in which copper and iron are laminated. The clad material is manufactured by, for example, roll pressure welding (rolling). The clad material can also be formed by diffusion bonding in which a metal plate is heated while being pressurized in a vacuum.

―Magnetic fluid layer―
The magnetic fluid layer 9 is a magnetic fluid layer. This magnetic fluid is a fluid having particles (hereinafter referred to as magnetic particles) formed of a ferromagnetic material and a liquid in which the magnetic particles are dispersed (hereinafter referred to as a base liquid). The thickness of the magnetic fluid layer 9 is, for example, about 1 to 100 μm.

  Magnetic particles can be iron, nickel, cobalt, iron alloys (eg, Fe-Co alloys, Fe-Ni alloys, Fe-Cr alloys, Fe-Mn alloys), or nickel alloys (eg, Mn-Ni alloys, Ni-Cu) An alloy) or the like (preferably a soft magnetic material).

  The magnetic particles may be particles having a core covered with a ferromagnetic material. The core is preferably formed of a material having high thermal conductivity such as alumina, aluminum nitride, boron nitride, magnesium oxide, silica, copper, silver, or diamond.

  The magnetic particles can take various shapes such as a spherical shape, a needle shape, and a flake shape. The diameter of the magnetic particles is, for example, about 10 nm to 50 μm (preferably 10 to 1000 nm). The surface of the magnetic particle may be covered with a surfactant.

  The base liquid is, for example, hydrocarbon oil or fluorine oil.

  The blending ratio (concentration) of magnetic particles in the magnetic fluid layer 9 is, for example, 20 vol% to 70 vol%. When the blending ratio is 20 vol% or less, it is difficult to form a heat transfer path in which magnetic particles are connected. As a result, the thermal conductivity of the magnetic fluid layer 9 is deteriorated.

  On the other hand, when the blending ratio is 70 vol% or more, the fluidity of the magnetic fluid layer 9 is deteriorated. As a result, the magnetic fluid layer 9 cannot follow the deformation (that is, thermal deformation) of the package 6 and the cooler 12 due to heat generation of the integrated circuit. Then, an air gap is formed between the package 6 and the cooler 12, and the package 6 is hardly cooled.

―Magnetic field generation layer―
FIG. 2 is a plan view of the magnetic field generation layer 10. The magnetic field generation layer 10 shown in FIG. 1 is a cross-sectional view taken along line II in FIG.

  As shown in FIG. 2, the magnetic field generation layer 10 includes a plurality of magnets 24 and a yoke 26 that sandwiches each of the plurality of magnets 24. Specifically, each magnet 24 is sandwiched between separate yokes 26.

  The magnet 24 and the yoke 26 extend in the first direction and are arranged at a constant interval in a second direction orthogonal to the first direction.

  The length of the magnet 24 and the yoke 26 in the first direction is, for example, about 40 mm. The length (width) of the magnet 24 and the yoke 26 in the second direction is, for example, about 1 mm. The thickness of the magnet 24 and the yoke 26 is, for example, about 1 mm. Therefore, one side of the magnetic field generation layer 10 is about 40 mm, for example. The other side of the magnetic field generation layer 10 has a width of about 41 mm, for example. The thickness of the magnetic field generation layer 10 is, for example, about 1 mm.

  Each magnet 24 is arranged so that the same poles face each other across the yoke 26. Specifically, for example, in FIG. 2, a magnet having an N pole on the right side and an S pole on the left side and a magnet having an S pole on the right side and an N pole on the left side are alternately arranged.

  The magnet 24 is, for example, a neodymium magnet, a samarium cobalt magnet, an alnico magnet, or a ferrite magnet. The yoke 26 is, for example, iron, silicon steel (Fe—Si alloy), sendust (Fe—Si—Al alloy), permalloy (Fe—Ni alloy), permendur (Fe—Co alloy), soft ferrite. (Mn—Zn ferrite, Ni—Zn ferrite) or a ferromagnetic material (preferably a soft magnetic material) such as nickel.

  The magnetic field generation layer 10 is formed, for example, by joining a magnet 24 and a yoke 26 to the surface of the cooler 12 on the package 6 side with solder. Alternatively, the magnet 24 and the yoke 26 may be bonded to the cooler 12 with an adhesive having high thermal conductivity such as silver paste.

-Cooler-
For example, as shown in FIG. 1, the cooler 12 is a water-cooled cooler having a flowing water passage 28 through which cooling water flows. The cooler 12 may be an air-cooled cooler such as a heat radiating fin.

(2) Operation FIG. 3 is an enlarged cross-sectional view of the vicinity of the magnetic fluid layer 9. In FIG. 3, the lines of magnetic force 30 of the magnet 24 are shown. The symbol “N” is shown at the position of the N pole of the magnet 24. The symbol “S” is shown at the position of the S pole (the same applies to FIGS. 4 and 7 to 10).

  As shown in FIG. 3, the magnetic field lines 30 coming out of the N pole of the magnet 24 (for example, the center magnet in FIG. 3) mostly exit the magnetic field generation layer 10 through the surface of the yoke 26. The magnetic field lines 30 then pass through the package 6 and the like, and from the surface of another yoke 26 (for example, the left yoke of the magnet 24) facing the yoke 26 (for example, the right yoke of the magnet 24) across the magnet 24, the magnetic field generating layer. Enter 10. Thereafter, the magnetic field lines 30 enter the south pole of the magnet 24.

  When the magnetic fluid layer 9 is sufficiently thin, on the magnetic fluid layer 9 side of the magnetic field generation layer 10, most of the magnetic force lines 30 exiting the surface of the yoke 26 pass through the magnetic fluid layer 9 and the package 6. Then, the magnetic field lines 30 pass through the magnetic fluid layer 9 again, and on the surface of another yoke 26 (for example, the left yoke of the magnet 24) facing the yoke 26 (for example, the right yoke of the magnet 24) across the magnet 24. enter. That is, when the magnetic fluid layer 9 is sufficiently thin, the magnetic force lines 30 on the magnetic fluid layer 9 side mostly pass through the yoke 26, the magnetic fluid layer 9, and the package 6.

  FIG. 4 is also an enlarged cross-sectional view of the vicinity of the magnetic fluid layer 9. FIG. 4 shows magnetic particles 32.

  When the magnetic particles 32 are exposed to a magnetic field, they are arranged along magnetic field lines (not shown) as shown in FIG. Therefore, when the magnetic fluid layer 9 is sufficiently thin, the magnetic particles 32 are mostly arranged along the magnetic force lines 34 (see FIG. 3) passing through the yoke 26, the magnetic fluid layer 9, and the package 6.

  The thermal conductivity of the magnetic particles 32 is 2 to 4 digits higher than the thermal conductivity of the base liquid 36. Therefore, heat generated by the integrated circuit in the package 6 is released to the cooler 12 through the array 44 (continuous) of the magnetic particles 32 and the yoke 26. That is, the series of magnetic particles 32 and the yoke 26 form a heat transfer path (path through which heat is transmitted) that thermally connects the package 6 and the cooler 12.

  FIG. 5 is a cross-sectional view of a semiconductor device 40 having a magnet 38 instead of the magnetic field generating layer 10 having the magnet 24 and the yoke 26. The semiconductor device 40 of FIG. 5 includes a heat conductive layer 8a having a magnet 38 and a magnetic fluid layer 9a. The composition and size of the magnetic fluid layer 9a are the same as those of the magnetic fluid layer 9 of the semiconductor device 2 of FIG.

  The surface of the magnet 38 on the package 6 side is one magnetic pole (for example, N pole). The surface of the magnet 38 on the cooler 12 side is the other magnetic pole (for example, the S pole).

  The semiconductor device 40 has the same structure as that of the semiconductor device 2 (see FIG. 1) of the first embodiment except that the semiconductor device 40 has a magnet 38 instead of the magnetic field generation layer 10. FIG. 5 shows magnetic force lines 42 generated by the magnet 38.

  As shown in FIG. 5, magnetic force lines 42 passing through the magnetic fluid layer 9 a and the package 6 are also generated in the semiconductor device 40. Therefore, the semiconductor device 40 of FIG. 5 also has a heat transfer path that connects the magnetic particles and passes through the magnet 38 to thermally connect the package 6 and the cooler 12.

  However, the thermal conductivity of the magnet material (eg, magnetite) is much smaller than the thermal conductivity of the material of the cooler 12 or the heat spreader 16 (eg, copper). For this reason, even if a heat transfer path connecting the package 6 and the cooler 12 is formed by the series of magnetic particles and the magnet 38, the heat dissipation characteristics of the semiconductor device 40 are not sufficiently improved.

  On the other hand, in the semiconductor device 2 of the first embodiment, as shown in FIG. 4, the series 44 of magnetic particles 32 is mostly connected to the yoke 26. The thermal conductivity of the material of the yoke 26 (for example, iron) is about an order of magnitude greater than the thermal conductivity of the magnet material (for example, magnetite). Therefore, according to the semiconductor device 2 of the first embodiment, a heat conduction path with a low thermal resistance (that is, a heat conduction path with good heat conduction) is formed, and the heat dissipation characteristics are remarkably improved.

-Thermal resistance of magnetic field generation layer-
Now, it is assumed that the thermal conductivity of the magnets 24 and 38 (for example, ferrite magnets) is 10 W / m · K, and the thermal conductivity of the yoke 26 (for example, a yoke formed of iron) is 80 W / m · K.

  The length of one side of the magnet 38 of the semiconductor device 40 of FIG. 5 is 40 mm, and the length of the other side is 41 mm. Further, the thickness of the magnet 38 is set to 1 mm. This size is substantially the same as the size of the magnetic field generation layer 10 of the semiconductor device 2 (see FIG. 1) of the first embodiment. The thermal resistance of the magnet 38 calculated from the thermal conductivity and size is 0.0610 K / W.

  On the other hand, the calculated value of the thermal resistance of the magnetic field generation layer 10 of the semiconductor device 2 of the first embodiment is 0.0135 K / W. Therefore, the thermal resistance of the magnetic field generating layer 10 of the first embodiment is approximately 77% lower than the thermal resistance of the magnet 38 in FIG.

  As described with reference to FIG. 3, the magnetic field lines 30 mostly pass through the surface of the yoke 26 on the magnetic fluid layer 9 side. Therefore, the series 44 (see FIG. 4) of the magnetic particles 32 is mostly connected to the yoke 26 having a higher thermal conductivity than the magnet 24. Therefore, the magnetic field generating layer 10 conducts heat better than expected from the calculated value of thermal resistance (decrease of about 77%).

  Therefore, the magnetic field generation layer 10 (see FIG. 1) of the first embodiment conducts heat much better than the magnet 38 of the semiconductor device 40 of FIG.

-Thermal resistance of magnetic fluid layer-
When the attractive force by the magnets 24 and 38 is increased, the force with which the magnetic particles 32 are pressed against each other within the series 44 of magnetic particles is increased. Then, the deformation of the magnetic particles 32 increases, and the contact area between the magnetic particles 32 increases. Then, the thermal conductivity of the series of magnetic particles 44 (see FIG. 4) increases.

  The attractive force by the magnet is proportional to the magnetic field gradient. Therefore, the greater the magnetic field gradient, the greater the thermal conductivity of the series of magnetic particles 44.

  By the way, an integrated circuit malfunctions when exposed to a strong magnetic field. The maximum value of magnetic flux density (hereinafter referred to as the maximum allowable magnetic flux density) at which malfunction of the integrated circuit does not become a problem is about 10 mT.

  Therefore, it is preferable that the magnetic field lines generated by the magnetic field generation layer 10 of the first embodiment have a magnetic flux density in the integrated circuit that is equal to or lower than the maximum allowable magnetic flux density. Similarly, the magnetic field lines generated by the magnet 38 in FIG. 5 are preferably such that the magnetic flux density in the integrated circuit is less than or equal to the maximum allowable magnetic flux density.

Like the magnet 38 in FIG. 5, the magnetic flux density of a magnet without a yoke gradually decreases as the distance from the magnet increases. Therefore, in the semiconductor device 40 of FIG. 5, the difference ΔB ₃₈ between the magnetic flux density at the position of the integrated circuit (the surface position of the semiconductor substrate 4) and the surface magnetic flux density of the magnet ₃₈ is small.

Now, assuming that the magnetic flux density in the integrated circuit is the maximum allowable magnetic flux density (for example, 10 mT), the difference ΔB ₃₈ between the magnetic flux density at the position of the integrated circuit (for example, a position 2 mm from the magnet 38) and the surface magnetic flux density of the magnet _38. Is at most about 1.02 times the maximum allowable magnetic flux density.

FIG. 6 is a diagram showing the relationship between the normalized magnetic flux density and the normalized distance in the semiconductor device 2 of the first embodiment. The vertical axis represents the normalized magnetic flux density (= B / B ₀ ) obtained by normalizing the magnetic flux density B with the surface magnetic flux density B ₀ of the yoke 26. The magnetic flux density B is a magnetic flux density on a straight line passing through the center of the yoke 26 and perpendicular to the yoke 26. The horizontal axis represents a normalized distance (= L / L ₀ ) obtained by normalizing the distance L from the yoke 26 (that is, the distance from the magnetic field generation layer 10) by the interval (pitch) L ₀ between the magnets 24.

  As shown in FIG. 6, the normalized magnetic flux density rapidly decreases in a region 46 where the normalized distance is 1 or less (hereinafter referred to as a strong magnetic field region).

As will be described later, in order to suppress the malfunction of the integrated circuit, the distance between the magnetic field generation layer 10 and the integrated circuit is preferably wider than the distance L ₀ between the magnets 24. That is, the integrated circuit of the first embodiment is preferably arranged in a region 47 (hereinafter referred to as a weak magnetic field region) having a normalized distance larger than 1. In this case, the surface magnetic flux density of the magnetic field generation layer 10 (the magnetic flux density at the normalized distance = 0) is much larger than the magnetic flux density in the integrated circuit (the magnetic flux density in the weak magnetic field region 47), as is apparent from FIG.

Therefore, in the semiconductor device 2 of the first embodiment, when the magnetic flux density in the integrated circuit formed on the semiconductor substrate 4 is the maximum allowable magnetic flux density (for example, 10 mT), the magnetic flux density in the integrated circuit and the surface magnetic flux density of the yoke 26 The difference ΔB ₁₀ is much larger than the maximum allowable magnetic flux density. For example, when the distance L ₀ between the magnets 24 is 1 mm and the distance between the magnetic field generating layer 10 and the integrated circuit is 2 mm, the magnetic flux density difference ΔB ₁₀ is about 26 times the maximum allowable magnetic flux density.

Thus, the magnetic flux density difference ΔB ₁₀ in the semiconductor device 2 of the first embodiment is much larger than the magnetic flux density difference ΔB ₃₈ in the semiconductor device 40 of FIG.

Dividing the magnetic flux density difference by the distance gives the average value of the magnetic gradient. When the distance between the integrated circuit and the magnetic field generating layer 10 of the first embodiment and D _1, the average value of the magnetic gradient between the integrated circuit and the magnetic field generating layer 10 is .DELTA.B _{10 /} D _1. In the first embodiment, as shown in FIG. 6, since the magnetic flux density rapidly decreases in the vicinity of the magnetic field generation layer 10, a magnetic gradient greater than this average value (= ΔB ₁₀ / D ₁ ) acts on the magnetic particles. .

Magnet 38 of FIG. 5 and the spacing of the integrated circuit and D _2, the mean value of the magnetic gradient between the magnet 38 the integrated circuit is .DELTA.B _{38 /} D _2. In the semiconductor device 40 of FIG. 5, since the magnetic flux density is gently reduced, a magnetic gradient equivalent to this average value (= ΔB ₃₈ / D ₂ ) acts on the magnetic particles.

As described above, the magnetic flux density difference ΔB ₁₀ in the semiconductor device of the first embodiment is much larger than the magnetic flux density difference ΔB ₃₈ in the semiconductor device 40 of FIG. Therefore, when D ₁ and D ₂ are equal, the magnetic gradient acting on the magnetic particles of the first embodiment is much larger than the magnetic gradient acting on the magnetic particles of the semiconductor device 40 of FIG.

  As described above, the thermal conductivity of the magnetic particle series 44 (see FIG. 4) increases as the magnetic field gradient increases. Therefore, the thermal conductivity of the series of magnetic particles 44 in the first embodiment is larger than the thermal conductivity of the series of magnetic particles in the semiconductor device 40 of FIG.

  For this reason, the thermal conductivity of the magnetic fluid layer 9 of Embodiment 1 is larger than the magnetic fluid layer 9a of the semiconductor device 40 of FIG.

Now, the distance between the magnet 38 of the semiconductor device 40 of FIG. 5 and the integrated circuit is 2 mm. The magnetic flux density in the integrated circuit is 10 mT. In this case, the surface magnetic flux density of the magnet 38 is 10.2 mT, for example. The magnetic gradient in the magnetic fluid layer 9a is, for example, 0.1 T / m. If the magnetic particles are iron particles having a diameter of 20 μm, the contact area between the magnetic particles is about 70 nm ² . Note that the magnetic shield layer 22 is not provided. For calculation of the contact area, the elastic modulus of iron was used (hereinafter the same).

  Similarly, the distance between the magnetic field generation layer 10 and the integrated circuit in the semiconductor device 2 of the first embodiment is 2 mm. The interval between the magnets 24 is 1 mm. The magnetic flux density in the integrated circuit is 10 mT. It is assumed that the magnetic shield layer 22 is not provided.

In this case, the surface magnetic flux density of the magnetic field generation layer 10 is 260 mT. The magnetic gradient in the magnetic fluid layer 9 at this time is 125 T / m. When the magnetic particles are iron particles having a particle diameter of 20 μm, the contact area between the magnetic particles is about 70000 nm ² .

  Here, the long sides of the magnetic fluid layers 9, 9a are set to 41 mm. The short side is 40 mm. The thickness is 0.1 mm. The base liquid has a thermal conductivity of 0.15 W / m · K. The thermal conductivity of the magnetic particles is 80 W / m · K. Assume that the blending ratio (concentration) of magnetic particles is 50 vol%, and all magnetic particles form a series of magnetic particles.

  Then, the thermal resistance of the magnetic fluid layer 9a in FIG. 5 calculated based on the contact area between the magnetic particles is 0.0374 K / W. Similarly, the thermal resistance of the magnetic fluid layer 9 of the first embodiment, which is calculated based on the contact area between the magnetic particles, is 0.0361 K / W.

  Therefore, the thermal resistance of the magnetic fluid layer 9 in Embodiment 1 is about 3.5% smaller than the thermal resistance of the magnetic fluid layer 9a in FIG. Thus, according to the semiconductor device 2 of the first embodiment, the thermal resistance of the magnetic fluid layer 9 is smaller than that of the magnetic fluid layer 9a of the semiconductor device 40 of FIG.

  When the magnetic gradient is increased and the attractive force of the magnetic particles is increased, the magnetic particles are easily oriented. Therefore, the number of magnetic particle series 44 also increases. Therefore, the thermal resistance of the magnetic fluid layer 9 of Embodiment 1 is actually smaller than the thermal resistance of the magnetic fluid layer 9a of FIG.

  As described above, the magnetic field generation layer 10 (see FIG. 1) of the first embodiment conducts heat better than the magnet 38 of the semiconductor device 40 of FIG. Furthermore, the magnetic fluid layer 9 (see FIG. 1) of the first embodiment conducts heat better than the magnetic fluid layer 9a of the semiconductor device 40 of FIG.

  Therefore, heat conduction layer 8 (see FIG. 1) of the first embodiment conducts heat better than heat conduction layer 8a (see FIG. 5) of semiconductor device 40 in which the magnetic field generation layer does not have a yoke. As a result, the heat dissipation characteristics of the semiconductor device 2 of the first embodiment are greatly improved.

  Note that the calculated value of the thermal resistance of the heat conductive layer 8 of the first embodiment is about 50% smaller than the calculated value of the heat resistance of the heat conductive layer 8a of FIG. The thermal resistance of the heat conductive layers 8 and 8a is calculated based on the calculated value of the thermal resistance of the magnetic field generation layer 10 and the like described above.

―Distance between magnetic field generation layer and integrated circuit―
As shown in FIG. 6, the magnetic flux density of the first embodiment decreases with a substantially constant magnetic gradient in the strong magnetic field region 46. On the other hand, in the weak magnetic field region 47, the magnetic gradient decreases rapidly.

  As is clear from the above description, the stronger the attractive force acting on the magnetic particles 32 is, the better. Since the attractive force is proportional to the magnetic gradient, the larger the magnetic gradient, the better. Therefore, the magnetic particles 32 are preferably disposed in the strong magnetic field region 46 having a large magnetic gradient. Therefore, the magnetic fluid layer 9 having the magnetic particles 32 is preferably thinner than the strong magnetic field region 46. More preferably, the thickness of the magnetic fluid layer 9 is not more than half of the thickness of the strong magnetic field region 46.

The boundary between the strong magnetic field region 46 and the weak magnetic field region 47 is a point where the normalized distance (= L / L ₀ ) is 1, that is, the point where the distance L from the magnetic field generation layer 10 is equal to the interval L _{0 of the} magnet 24.

Accordingly, the interval L ₀ between the magnets 24 is preferably wider than the thickness of the magnetic fluid layer 9.
More preferably, the gap L ₀ between the magnets 24 is wider than twice the thickness of the magnetic fluid layer 9.

  As is apparent from FIG. 6, the magnetic flux density in the strong magnetic field region 46 is large. Therefore, the integrated circuit on the semiconductor substrate 4 is preferably arranged outside the strong magnetic field region 46 so as not to cause a malfunction.

Therefore, the distance between the integrated circuit of the semiconductor substrate 4 and the magnetic field generation layer 10 is preferably larger than the thickness (= L ₀ ) of the strong magnetic field region 46. More preferably, the distance between the integrated circuit of the semiconductor substrate 4 and the magnetic field generation layer 10 is wider than twice the thickness (= L ₀ ) of the strong magnetic field region 46.

Therefore, the distance L ₀ between the magnets 24 is preferably narrower than the distance between the integrated circuit of the semiconductor substrate 4 and the magnetic field generation layer 10. More preferably, the interval L ₀ between the magnets 24 is narrower than half the distance between the integrated circuit of the magnetic field generating layer 10 and the semiconductor substrate 4.

  In the semiconductor device 2 of the first embodiment, the magnetic flux density (average value) in the integrated circuit formed on the semiconductor substrate 4 is about 1 to 10 mT. The surface magnetic flux density (average value) of the yoke 26 is about 100 mT to 1000 mT.

(3) Manufacturing Method The semiconductor device 2 is formed of a package 6, a magnetic fluid, and a cooler 12 having a magnetic field generation layer 10 bonded to the surface on the package 6 side.

  First, the magnetic fluid is adsorbed to the magnetic field generation layer 10 joined to the cooler 12. In this state, the cooler 12 is placed on the heat spreader 16 of the package 6. Then, the magnetic shield layer 22 and the magnetic field generation layer 10 in the package 6 attract each other, and the cooler 12 is attracted to the package 6.

  When the package 6 does not have the magnetic shield layer 22, the cooler 12 may be pressed against the pudding board on which the package 6 is mounted with, for example, bolts and nuts sandwiching the package 6.

  Incidentally, fine irregularities exist on the surface of the package 6. Similarly, fine irregularities exist on the surface of the magnetic field generation layer 10. For this reason, a gap is generated between the package 6 and the magnetic field generation layer 10. The magnetic fluid enters the gap and becomes the magnetic fluid layer 9.

  The magnetic fluid layer 9 is attracted to the magnetic field generation layer 10. Therefore, the magnetic fluid does not flow out between the package 6 and the magnetic field generation layer 10.

  When the cooler 12 is pulled up, it is easily detached from the package 6. Therefore, when the integrated circuit of the semiconductor substrate 4 fails, only the package 6 that houses the integrated circuit can be replaced.

  When the integrated circuit generates heat, the package 6 and the cooler 12 expand. At this time, the gap between the package 6 and the magnetic field generation layer 10 changes. Since the magnetic fluid layer 9 is a fluid, this change can be easily followed.

  In a semiconductor device in which grease is interposed between the package and the cooler, the heat radiation characteristics may be deteriorated due to aging of the grease. However, even if the semiconductor device 2 of the first embodiment is used for a long period of time, its heat dissipation characteristics hardly change.

(4) Modified Example FIG. 7 is a plan view illustrating a modified example 10 a of the magnetic field generation layer 10.

  In the magnetic field generation layer 10 shown in FIG. 2, strip-shaped magnets 24 are periodically arranged in the short side direction of the magnets 24. However, the magnetic field generation layer is not limited to the magnetic field generation layer 10 of FIG. For example, as shown in FIG. 7, tile-shaped magnets 24a may be arranged in a grid pattern.

  The magnet 24a is sandwiched between the yokes 26a similarly to the magnet 24 of FIG.

  FIG. 8 is a cross-sectional view for explaining another modification 10b of the magnetic field generation layer 10. FIG. 8 also shows the magnetic fluid layer 9.

  In the magnetic field generation layer 10 shown in FIG. 3, each magnet 24 is sandwiched between separate yokes 26. However, as shown in FIG. 8, the yoke 26 b includes a connecting portion 48 disposed on the opposite side to the magnetic fluid layer 9 of the plurality of magnets 24, and a protruding portion 50 that protrudes from the connecting portion 48 and sandwiches each magnet 24. You may have. In addition, the broken line of FIG. 8 has shown the boundary of the connection part 48 and the convex part 50. FIG.

  However, when the same poles of the magnets 24 are opposed to each other as shown in FIGS. 3 and 8, it is preferable that the magnets 24 are sandwiched between separate yokes 26 as shown in FIG. According to this arrangement, the magnetic lines of force concentrate on the surface of the yoke 26, so that a series of magnetic particles 44 can be easily connected to the surface of the yoke 26.

In the example shown in FIG. 1, the package 6 has a magnetic shield layer 22 between the semiconductor substrate 4 and the heat conductive layer 8. However, the package 6 may not have the magnetic shield layer 22. If the distance between the integrated circuit on the semiconductor substrate 4 and the magnetic field generating layer 10 is larger than the distance L ₀ between the magnets 24, the magnetic flux density in the integrated circuit on the semiconductor substrate 4 is sufficiently smaller than the surface magnetic flux density of the yoke 26.

  Even if the magnetic shield layer 22 is not provided, if the distance between the integrated circuit of the semiconductor substrate 4 and the magnetic field generating layer 10 is equal to the distance (pitch) of the magnet 24, the magnetic flux density in the integrated circuit is 0.187 of the magnetic flux density on the yoke surface. Double. If the distance between the integrated circuit and the magnetic field generating layer 10 is twice the distance (pitch) between the magnets 24, the magnetic flux density in the integrated circuit is 0.038 times that of the yoke surface.

(Embodiment 2)
Description of portions common to the first embodiment is omitted.

  The semiconductor device of the second embodiment has substantially the same structure as the semiconductor device 2 of the first embodiment except for the structure of the magnetic field generation layer. FIG. 9 is an enlarged cross-sectional view of the vicinity of the magnetic field generation layer 110 of the second embodiment.

  The magnetic field generation layer 110 has a plurality of magnets 124 arranged so that the same pole faces the package 6 side. The magnetic field generation layer 110 further has a yoke 126. The yoke 126 has a connecting portion 48 disposed on the opposite side of the magnetic fluid layer 109 of the plurality of magnets 124, and a convex portion 50 that protrudes from the connecting portion 48 and sandwiches each magnet 124. The broken line in FIG. 9 indicates the boundary between the connecting portion 48 and the convex portion 50.

  Each of the plurality of magnets 124 extends in the first direction and is arranged at a constant interval in a second direction orthogonal to the first direction, like the magnet 24 of the first embodiment shown in FIG.

  The length of one side of the magnet 124 is, for example, about 40 mm. The length (width) of the other side of the magnet 124 is, for example, about 1 mm. The length of one side of the yoke 126 is, for example, about 40 mm. The length (width) of the other side of the yoke 126 is, for example, about 41 mm. The thickness of the yoke 126 is, for example, about 1.5 mm.

  FIG. 10 is an enlarged cross-sectional view of the vicinity of the magnetic field generation layer 110 of the second embodiment. FIG. 10 also shows magnetic field lines 134.

  As shown in FIG. 10, the magnetic field lines 134 coming out from one pole of the magnet 124 mostly enter the magnetic field generation layer 110 through the surface of the yoke 126. Therefore, the magnetic field lines 134 are concentrated on the surface of the yoke 126.

  If the magnetic fluid layer 109 is sufficiently thin, the magnetic field lines 134 exiting one pole of the magnet 124 mostly enter the package 6 through the magnetic fluid layer 109. Thereafter, the magnetic force lines 134 pass through the package 6 and the magnetic fluid layer 109 and enter the magnetic field generation layer 110 from the surface of the yoke 126.

FIG. 11 is a diagram showing the relationship between the normalized magnetic flux density and the normalized distance in the semiconductor device of the second embodiment. The vertical axis represents the normalized magnetic flux density (= B / B ₀ ) obtained by normalizing the magnetic flux density B with the surface magnetic flux density B ₀ of the yoke 126. The magnetic flux density B is a magnetic flux density on a straight line that passes through the center of the convex portion 50 (see FIG. 9) and is perpendicular to the convex portion 50. The horizontal axis is a normalized distance (= L / L ₀ ) obtained by normalizing the distance L from the convex portion 50 (that is, the distance from the magnetic field generation layer 110) by the interval (pitch) L ₀ between the magnets 124.

  As shown in FIG. 11, the magnetic flux density of the second embodiment decreases with a substantially constant magnetic gradient in the strong magnetic field region 146 having a normalized distance of 0.6 or less. The magnetic gradient decreases rapidly in the weak magnetic field region 147 where the normalized distance is greater than 0.6. The boundary between the strong magnetic field region 146 and the weak magnetic field region 147 is a point where the normalized distance is 0.6.

  As described in the first embodiment, the larger the magnetic gradient acting on the magnetic particles, the better. Therefore, the magnetic fluid layer 109 containing magnetic particles is preferably thinner than the strong magnetic field region 146 having a large magnetic gradient. More preferably, the thickness of the magnetic fluid layer 109 is less than half the thickness of the strong magnetic field region 146.

Therefore, the interval (pitch) L ₀ between the magnets 124 is preferably larger than the value obtained by dividing the thickness of the magnetic fluid layer 109 by 0.6. More preferably, the gap L ₀ between the magnets 24 is larger than the value obtained by dividing the thickness of the magnetic fluid layer 9 by 0.3.

  As shown in FIG. 11, the magnetic flux density in the strong magnetic field region 146 is high. Therefore, the integrated circuit on the semiconductor substrate 4 is preferably arranged outside the strong magnetic field region 146 so as not to cause a malfunction.

Thus, the integrated circuit and the distance of the magnetic field generating layer 110 of the semiconductor substrate 4 is wider than the thickness of the high magnetic field region 146 (0.6 times the distance _{L 0} of the magnet 124) are preferred. More preferably, the distance of the integrated circuit and the magnetic field generating layer 110 of the semiconductor substrate 4 is wider than twice the thickness of the high magnetic field region 146 (0.6 times the distance _{L 0} of the magnet 124).

Therefore, the interval L ₀ between the magnets 24 is preferably narrower than the value obtained by dividing the distance between the integrated circuit of the magnetic field generating layer 110 and the semiconductor substrate 4 by 0.6. More preferably, the distance L ₀ between the magnets 24 is narrower than the value obtained by dividing the distance between the integrated circuit of the magnetic field generating layer 10 and the semiconductor substrate 4 by 1.2.

  By the way, as apparent from comparison between FIG. 6 and FIG. 11, the normalized magnetic flux density of the second embodiment is smaller than the normalized magnetic flux density of the first embodiment at the same normalized distance. Specifically, for example, when the normalized distance is 1, the normalized magnetic flux density in the second embodiment is 0.056. On the other hand, the normalized magnetic flux density in the first embodiment is 0.187. When the normalized distance is 2, the normalized magnetic flux density in the second embodiment is 0.003. On the other hand, the normalized magnetic flux density in the first embodiment is 0.038.

  Therefore, according to the second embodiment, the influence of the magnetic field on the integrated circuit of the semiconductor substrate 4 is suppressed as compared with the first embodiment.

  As described above, the magnet 124 is a belt-like magnet extending in one direction. However, the magnet 124 may be a tile-shaped magnet as in the modification of the first embodiment (see FIG. 7).

  Regarding the above first and second embodiments, the following additional notes are disclosed.

  If the reduction in the thermal resistance of the heat conducting layer is estimated by the same method as in the first embodiment, the reduction in the second embodiment is about 38%, for example.

  Regarding the above first and second embodiments, the following additional notes are disclosed.

(Appendix 1)
A semiconductor substrate;
A package for housing the semiconductor substrate;
A thermally conductive layer disposed on one side of the package;
A cooler disposed on a surface of the heat conducting layer opposite to the package;
The heat conducting layer includes a magnetic fluid layer formed of a magnetic fluid, and a magnetic field generation layer including a plurality of magnets disposed on one surface of the magnetic fluid layer and a yoke sandwiching each of the plurality of magnets. Semiconductor device.

(Appendix 2)
In the semiconductor device according to attachment 1,
The magnetic fluid has magnetic particles formed of a ferromagnetic material,
At least a portion of the magnetic particles are arranged along magnetic field lines passing through the yoke, the magnetic fluid layer, and the package;
The semiconductor device according to claim 1, wherein a thermal conductivity of the yoke is larger than a thermal conductivity of each of the magnets.

(Appendix 3)
In the semiconductor device according to attachment 1 or 2,
Each of the magnets is sandwiched between separate yokes, and is disposed so that the same poles face each other across the yoke.

(Appendix 4)
In the semiconductor device according to attachment 3,
Each of the magnets extends in a first direction and is arranged at a constant interval in a second direction orthogonal to the one direction,
The semiconductor device is characterized in that the interval is wider than the thickness of the magnetic fluid layer and narrower than the distance between the integrated circuit formed on the semiconductor substrate and the magnetic field generating layer.

(Appendix 5)
In the semiconductor device according to attachment 1 or 2,
The yoke has a connecting portion disposed on the opposite side of the magnetic fluid layer of the plurality of magnets, and a convex portion protruding from the connecting portion and sandwiching each of the plurality of magnets,
The plurality of magnets are arranged so that the same pole is directed to the package side.

(Appendix 6)
In the semiconductor device according to attachment 5,
Each of the plurality of magnets extends in a first direction and is arranged at a constant interval in a second direction orthogonal to the one direction.
The interval is wider than the value obtained by dividing the thickness of the magnetic fluid layer by 0.6 and narrower than the value obtained by dividing the distance between the integrated circuit formed on the semiconductor substrate and the magnetic field generating layer by 0.6. A semiconductor device characterized by the above.

(Appendix 7)
The semiconductor device according to any one of appendices 1 to 6,
The package includes a semiconductor shield and a magnetic shield layer disposed between the semiconductor substrate and the heat conductive layer.

2 ... Semiconductor device 4 ... Semiconductor substrate 6 ... Package 8 ... Heat conduction layer 9 ... Magnetic fluid layer 10 ... Magnetic field generation layer 12 ... Cooler 22 ... Magnetic shield Layer 24 ... Magnet 26 ... Yoke 34 ... Line of magnetic force 48 ... Connection part 50 ... Convex part 109 ... Magnetic fluid layer 110 ... Magnetic field generation layer 124 ... Magnet 126 ... ·yoke

Claims (5)

A semiconductor substrate;
A package for housing the semiconductor substrate;
A thermally conductive layer disposed on one side of the package;
A cooler disposed on a surface of the heat conducting layer opposite to the package;
The heat conducting layer includes a magnetic fluid layer formed of a magnetic fluid, and a magnetic field generation layer including a plurality of magnets disposed on one surface of the magnetic fluid layer and a yoke sandwiching each of the plurality of magnets. Semiconductor device. The semiconductor device according to claim 1,
The magnetic fluid has magnetic particles formed of a ferromagnetic material,
At least a portion of the magnetic particles are arranged along magnetic field lines passing through the yoke, the magnetic fluid layer, and the package;
The semiconductor device according to claim 1, wherein a thermal conductivity of the yoke is larger than a thermal conductivity of each of the magnets. The semiconductor device according to claim 1 or 2,
Each of the magnets is sandwiched between separate yokes, and is disposed so that the same poles face each other across the yoke. The semiconductor device according to claim 3.
Each of the magnets extends in a first direction and is arranged at a constant interval in a second direction orthogonal to the one direction,
The semiconductor device is characterized in that the interval is wider than the thickness of the magnetic fluid layer and narrower than the distance between the integrated circuit formed on the semiconductor substrate and the magnetic field generating layer. The semiconductor device according to claim 1 or 2,
The yoke has a connecting portion disposed on the opposite side of the magnetic fluid layer of the plurality of magnets, and a convex portion protruding from the connecting portion and sandwiching each of the plurality of magnets,
The plurality of magnets are arranged so that the same pole is directed to the package side.

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