JP5391530B2 - Method for manufacturing thermally conductive resin sheet and method for manufacturing power module - Google Patents

Description

  The present invention relates to a heat conductive resin sheet for forming a heat conductive resin layer used for transferring heat from a heat generating element to a heat radiating member, and in particular, transfers heat from a heat generating element such as a power semiconductor element to the heat radiating member. And a heat conductive resin sheet for forming a heat conductive resin layer that also functions as an insulating layer. Moreover, it is related with the power module using the said heat conductive resin sheet.

  The heat conductive resin layer that transfers heat from the heat generating part of the electric / electronic device to the heat radiating member has high heat conductivity, insulation, and adhesive properties. A resin composition is used.

  For example, in a power module, a thermosetting resin sheet or coating film containing an inorganic filler is used as a heat conductive resin layer provided between the back surface of a lead frame on which a power semiconductor element is mounted and a metal plate serving as a heat dissipation part. (For example, refer to Patent Document 1).

  As a heat conductive resin layer interposed between a heat-generating electronic component such as a CPU and a heat radiating fin, there is a thermosetting resin sheet filled with highly heat conductive inorganic powder (for example, see Patent Document 2).

  Also, when preparing a compound sheet filled with inorganic powder, it is disclosed that inorganic powders having different particle sizes are blended as a method for increasing the filling rate of inorganic powder in order to obtain high thermal conductivity. (For example, Patent Document 3 and Patent Document 4).

  Patent Document 3 is to increase the contact area of inorganic fillers having different particle diameters and improve thermal conductivity. Patent Document 4 is to convert spherical alumina having three different particle diameters into biphenyl type epoxy resin. In addition, the moldability and solder crack resistance are improved.

JP 2001-196495 A (page 3, FIG. 1) JP 2002-167560 A (page 3, FIG. 1) JP-A-6-310824 Japanese Patent Laid-Open No. 7-278415 (page 7, FIG. 1)

  However, when the filling rate of the inorganic filler with respect to the resin is increased in order to improve the thermal conductivity, there is a problem that voids are formed and the electrical insulation and mechanical strength of the thermally conductive resin sheet are lowered. Further, when the resin is filled with two or more inorganic fillers having different particle diameters, it is difficult to determine a blending ratio for ensuring high thermal conductivity.

  The present invention has been made to solve the above-described problems. Two or more inorganic fillers having different particle sizes are filled at a high filling rate to ensure high thermal conductivity, and a resin is used. It is intended to obtain a heat conductive resin sheet in which workability is ensured by blending and voids are suppressed and good electrical insulation is ensured, and a power module using the same.

The manufacturing method of the heat conductive resin sheet which concerns on this invention makes the one with a larger average particle diameter the 1st filler among the several electrically insulating inorganic fillers divided according to the magnitude | size of a particle size, and is small. Preparing one as a second filler,
The critical volume fraction of the first filler is CFVC ₁ ;
The critical volume fraction of the second filler is CFVC2,
The ratio of the volume of the first filler to the sum of the volume of the first filler and the volume of the second filler is α,
When (i) 0 <(volume of the first filler) / (total volume of the inorganic filler) ≦ α / (α + α / CFVC ₁ × CFVC ₂ ) (1−α) / CFVC, ₂ × (1-CFVC ₂ ) / {1+ (1-α) / CFVC ₂ × (1-CFVC ₂ )}
(Ii) When α / (α + α / CFVC ₁ × CFVC ₂ ) <(volume of first filler) / (total volume of inorganic filler) <1, (α / CFVC ₁ −1) / (α / CFVC ₁ ) the step of determining,
Kneading the resin, the first filler, and the second filler based on the volume blending ratio to produce a compound;
And a step of applying a load and compressing the applied product obtained by applying the compound to a substrate.

The method for manufacturing a power module according to the present invention includes a lead frame on which a power semiconductor element is mounted , through a cured body of a thermally conductive resin sheet manufactured by the method according to any one of claims 1 to 4. A step of bonding the heat dissipating member ;

  According to this invention, two or more inorganic fillers having different particle sizes are filled at a high filling rate to ensure high thermal conductivity, and the resin is blended to ensure processability and suppress voids. Thus, it is possible to obtain a heat conductive resin sheet in which good electrical insulation is ensured.

  Moreover, the power module excellent in heat dissipation and electrical insulation can be obtained by using the heat conductive resin sheet of this invention.

Embodiment 1 FIG.
In the field of paint technology, Temple C.I. Patton (Paint Flow and Pigment Dispersion, p. 126-p. 138, 1979, John, Wiley & Sons, Inc.) increases the pigment volume concentration (PVC: Pigment Volume Concentration) with respect to the binder. When the pigment concentration is low, the filling ratio becomes low, reaching the closest packing at a certain blending ratio, and when the pigment is further increased, it indicates that voids are generated. From the Critical Pigment Volume Concentration (CPVC) and PVC The porosity φ _AIR is being calculated.

Here, the heat conductive resin sheet 4 is examined. When the volume concentration (FVC: Filler Volume Concentration) of the filler 1 is increased with respect to the resin 3, the void 5 is less likely to be generated when the concentration of the filler 1 is low (FIG. 1 (a)). )), A close-packed state is reached at a predetermined filler blending ratio (FIG. 1 (b)), and it is considered that when the filler 1 is further increased, voids 5 are generated between the fillers (FIG. 1 (c)). Here, when the compounding ratio in the close-packed state shown in FIG. 1B is a critical filler volume concentration (CFVC), the porosity φ _AIR at a compounding ratio of FVC equal to or higher than CFVC is expressed as follows. , 1-CFVC / FVC.

  Furthermore, in the close-packed state of the filler 1 in FIG. 1B, the second filler 2 having a smaller particle diameter than the first filler 1 is densely packed in the gap between the fillers 1 (hereinafter referred to as the first filler). If the heat transfer path of the first filler 1 and the heat transfer path of the second filler 2 are formed by burying them in, a higher thermal conductivity can be expected (FIG. 2). Here, by filling the gap between the first filler 1 and the second filler 2 with the resin 3 in a state where no void 5 is generated, the insulation, workability, and adhesion can be improved.

  If the heat transfer path can be secured by filling the periphery of the first filler 1 or the gap with the second filler 2, the volume fraction of the first filler does not necessarily have to be large. For example, as shown in FIG. Thus, the volume fraction of the second filler 2 may be increased.

A cured body of the thermally conductive resin sheet 4 containing a kind of filler in FIG. 1 was produced by the following procedure, and the critical filler volume fraction was determined.
First, several molded bodies were prepared in which only the first filler 1 was mixed with the resin 3 and the volume concentration FVC ₁ of the first filler ₁ was arbitrarily increased. The measured density ρ _m1 obtained from the actually measured weight and volume of these molded bodies, and the ideal density ρ ₁ (ρ ₁ = (weight of the first filler + weight of the resin) / (volume of the first filler + resin) The void ratio φ _A1 (φ _A1 = 1−ρ _m1 / ρ ₁ ) was calculated from the volume of the gas, and the filling rate and the volume concentration of the first filler 1 were plotted as shown in FIG. The critical volume fraction CFVC ₁ of the first filler 1 with a rate of zero was determined.

Similarly, several molded bodies were prepared by blending only the second filler 2 with the resin 3 and arbitrarily increasing the volume concentration C FVC ₂ of the second filler 2, and the measured weights of these molded bodies and From the measured density ρ _m2 obtained from the volume and the ideal density ρ ₂ (ρ ₂ = (weight of first filler + weight of resin) / (volume of first filler + volume of resin), porosity φ _A2 (φ _A2 = 1−ρ _m2 / ρ ₂ ), and the critical volume of the second filler 2 where the porosity is zero by plotting the filling rate and the volume concentration of the second filler 2 as shown in FIG. The rate CFVC ₂ was determined.

Furthermore, from the critical volume fractions CFVC ₁ and CFVC _{2 of} the first filler 1 and the second filler 2, respectively, the heat conductive resin sheet 4 containing the resin 3 shown in FIG. 2 or 3 and two kinds of fillers is blended. The close-packed state was examined as follows.
(I) Low volume ratio (region I) in which the volume fraction of the first filler 1 is relatively smaller than that of the second filler 2
In the region I, the filler total volume fraction φ _c12 , that is, the closest packing ratio at which no void 5 is generated when two kinds of fillers having different particle diameters are filled in the resin 3 can be obtained by the following equation.

φ _c12 = (V ₁ + V ₂ ) / (V ₁ + V ₂ + V ₃ ) (3)

(Where V ₁ is the volume of the first filler 1, V ₂ is the volume of the second filler 2, and V ₃ is the volume of the resin 3).

Further, in the formula (3), the total volume of the first filler 1 and the second filler 2, that is, the total volume of the filler (V ₁ + V ₂ ) is 1, and the ratio of the first filler volume V _{1 to} the total volume of the filler If α is α, the following equation holds.

_{V 3 = V 2 / CFVC 2} × (1-CFVC 2)
= (1-α) / CFVC ₂ × (1-CFVC ₂ ) (4)

Therefore, as shown in the relationship diagram of the volume fraction of the first filler, the second filler, and the resin and the first filler volume / total filler volume in FIG. 5, the void 5 is suppressed below the allowable porosity. The volume fractions of the first filler, the second filler, and the resin that are in the closest packing state of the filler are as follows.

Volume fraction of first filler 1:
α / {1+ (1-α) / CFVC ₂ × (1-CFVC ₂ )} (5)
Volume fraction of second filler 2:
(1-α) / {1+ (1-α) / CFVC ₂ × (1-CFVC ₂ )} (6)
Volume fraction of resin 3:
(1-α) / CFVC ₂ × (1-CFVC ₂ )
/ {1+ (1-α) / CFVC ₂ × (1-CFVC ₂ )} −φ _AC (7)
Here, φ _AC is an allowable porosity, but in a state where there are very few voids, φ _AC ≈0. Therefore,
(Resin volume fraction) = (1-α) / CFVC ₂ × (1-CFVC ₂ )
/ {1+ (1-α) / CFVC ₂ × (1-CFVC ₂ )} (8)

That is, if the volume mixing ratio of the first filler 1, the second filler 2, and the resin is determined based on the above formulas (5), (6), and (8), the void 5 is suppressed to an allowable porosity or less. It becomes the closest packing state of the filler. In reality, considering the securing of CFVC _{2 as} the sum of the volume fractions of the first filler 1 and the second filler 2 in order to ensure the thermal conductivity, the volume mixing of the resin from the viewpoint of suppressing the void 5 Need to increase the ratio,

(I) When 0 <(Volume of first filler) / (Total volume of inorganic filler) ≦ α / (α + α / CFVC ₁ × CFVC ₂ )

(1-α) / CFVC ₂ × (1-CFVC ₂ ) / {1+ (1-α) / CFVC ₂ × (1-CFVC ₂ )} ≦ (resin volume fraction) ≦ 1-CFVC ₂ (9)

As a result, the volume ratio of the resin may be determined.
At this time, the filler total volume fraction φ _c12 is obtained by the following equation.

_{φ c12 = 1 / {1+ (} 1-α) / CFVC 2 × (1-CFVC 2)} (10)

(Ii) On the other hand, the volume of the filler is similarly set to V in the high blending ratio region (region II) where the blending ratio of the first filler 1 having a large particle size is relatively large compared to the second filler 2 having a small particle size. _{When 1} + V ₂ = 1 and the ratio of the first filler volume V _{1 having} a large particle size to the total volume of the filler is α, the volume V _{3 of the} resin 3 and the filling that provides the closest packed state of the filler The material total volume fraction φ _c12 can be obtained by the following equation.

V ₃ = α / CFVC ₁ −1 (11)

_{V 2 / CFVC 2 × (1} -CFVC 2)
= (1-α) / CFVC ₂ × (1-CFVC ₂ ) (12)

From this, the volume fraction of each component for obtaining the close-packed state of the filler in which the void 5 is suppressed to an allowable porosity or less is as follows:
Volume fraction of first filler 1: CFVC ₁ (13)

Volume fraction of second filler 2:
(1-α) / (α / CFVC ₁ ) (14)

Volume fraction of resin 3:
(α / CFVC ₁ −1) / (α / CFVC ₁ ) −φ _AC (15)

It becomes. Here, φ _AC is an allowable porosity, but in a state where there are very few voids, φ _AC ≈0. Therefore,
(Volume fraction of resin) = (α / CFVC ₁ −1) / (α / CFVC ₁ ) (16)

That is, if the volume mixing ratio of the first filler 1, the second filler 2, and the resin is determined based on the above formulas (13), (14), and (16), the void 5 can be suppressed to an allowable porosity or less. It becomes the closest packing state of the filler. In reality, considering the securing of CFVC _{1 as} the sum of the volume fractions of the first filler 1 and the second filler 2 in order to secure the thermal conductivity, the volumetric composition of the resin from the viewpoint of suppressing the void 5 Need to increase the ratio,

(Ii) When α / (α + α / CFVC ₁ × CFVC ₂ ) <(volume of first filler) / (total volume of inorganic filler) <1

(α / CFVC ₁ −1) / (α / CFVC ₁ ) ≦ (resin volume fraction)
≦ 1-CFVC ₁ (17)

As a result, the volume ratio of the resin may be determined.
At this time, the filler total volume fraction φ _c12 is obtained by the following equation.

φ _c12 = 1 / (α / CFVC ₁ ) (18)

Further, as shown in FIG. 5, the filler total volume fraction φ _c12 becomes the maximum at the boundary between the region I and the region II, and even if the volume fraction of the first filler 1 is increased, the CFVC ₁ becomes the limit. I understand. In other words, suppressed to less than the allowable void porosity, in order to increase the filler overall volume fraction phi _c12, the total volume of the first filler volume / filler becomes less _{α / (1 × CFVC 2 α} + α / CFVC) region Thus, it is preferable to determine the blending ratio between the first filler 1 and the second filler 2. That means
From 0 <V ₁ / (V ₁ + V ₂ ) ≦ α / (α + α / CFVC ₁ × CFVC ₂ ),

0 <α ≦ α / (α + α / CFVC ₁ × CFVC ₂ ) (19)

As described above, the critical volume fraction CFVC ₁ of the first filler ₁ and the critical volume fraction CFVC ₂ of the second filler 2 are obtained experimentally, for example, and the volume of the first filler, the second filler, and the resin is determined. By deriving the relationship between the fraction and the first filler volume / filler total volume, the optimum blending ratio in which the void 5 is less than or equal to the allowable porosity and the filler is in the closest packing state is obtained.

That is, the second filler 2 having an ideally small particle diameter is disposed in the gap between the first filler 1 having a large particle diameter, and a state close to a saturated state without voids 5 filling the gap with the resin 3 can be realized. As a result, it is possible to ensure heat conductivity by close-packing of the filler and to be filled with the resin 3 with few voids 5, thereby ensuring workability, adhesion, and insulation. For this reason, a highly reliable heat conductive sheet can be obtained. Here, the filling rate of the filler is given by the filler total volume fraction _φc12 .

  In the present embodiment, the average values of the particle sizes of the first filler 1 and the second filler 2 are used from the respective particle size distributions. When two or more kinds of fillers are used, the numerical values can be similarly obtained by roughly classifying them into two kinds and using the average particle diameter.

Embodiment 2. FIG.
In Embodiment 2 according to the present invention, the first filler 1 is substantially spherical aluminum nitride particles having a particle diameter of about 30 μm, and the second filler 2 is a flat shape having a major axis L of about 5 to 15 μm shown in FIG. The critical filling rate was obtained by replacing the filler 6 with the second filler 2 in the first embodiment. The major axis L of the flat filler 6 in the present embodiment is the longest length in the flat portion of the flat filler 6 as shown in FIG. In this embodiment, an improvement of the filling factor of about 35% is obtained with respect to the critical volume fraction CFVC _{1 in} which the number of voids 5 is small and only the first filler 1 is used as the filler, and the thermal conductivity is It improved about twice.

  By interposing the flat filler 6 between the spherical first fillers 1, the adjacent spherical first fillers 1 distributed in the thickness direction of the heat conductive resin sheet 4 are flattened fillers 6. This is because heat is more easily transmitted in the thickness direction of the heat conductive resin sheet 4 because the heat transfer paths are formed.

  In the present embodiment, the flat filler 6 has a flat plate shape as shown in FIG. 6, but the shape of the outer edge is not limited, and the effect of improving the thermal conductivity when it is particularly rectangular. I found out that As a material, electrically insulating aluminum oxide (alumina), boron nitride, silicon carbide, or the like may be used. Two or more of these may be used.

  In the first embodiment and the second embodiment, the first filler 1 is preferably substantially spherical, but may be a pulverized polygonal shape. As a material, electrically insulating aluminum oxide (alumina), silicon oxide (silica), silicon nitride, aluminum nitride, silicon carbide, boron nitride, or the like may be used. Two or more of these may be used.

  Moreover, in the said Embodiment 1 and Embodiment 2, although the example using 2 types of fillers was shown, either the 1st filler 1 and the 2nd filler 2, or both of several different diameters were shown. It is good also as a filler. That is, the volume fraction of each material that achieves the closest packing when a plurality of fillers are applied is not limited to two, and the filling rate can be significantly improved, so that the thermal conductivity can be improved. Further, since the space between the fillers is filled with the resin 3 without generating the void 5, the insulation, workability, and adhesion can be improved.

  Further, as the resin 3, a composition such as an epoxy resin, an unsaturated polyester resin, a phenol resin, a melamine resin, a silicone resin, or a polyimide resin can be used. The epoxy resin is an insulating property of the heat conductive resin sheet 4. From the viewpoint of adhesiveness, it is particularly preferable.

As the main component of the epoxy resin composition, for example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, orthocresol novolac type epoxy resin, phenol novolac type epoxy resin, alicyclic aliphatic epoxy resin, glycidyl aminophenol type epoxy resin Is mentioned. Two or more of these epoxy resins may be used in combination.
Examples of the curing agent for the epoxy resin composition include alicyclic acid anhydrides such as methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and hymic anhydride, aliphatic acid anhydrides such as dodecenyl succinic anhydride, and anhydride. Aromatic anhydrides such as phthalic acid and trimellitic anhydride, organic dihydrazides such as dicyandiamide and adipic acid dihydrazide, tris (dimethylaminomethyl) phenol, dimethylbenzylamine, 1,8-diazabicyclo (5,4,0) undecene And derivatives thereof, imidazoles such as 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole and the like. Two or more of these curing agents may be used in combination.

The heat conductive resin sheet 4 may contain a coupling agent as necessary. Examples of coupling agents used include γ-glycidoxypropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, and γ-mercaptopropyl. Examples include trimethoxysilane. Two or more of the above coupling agents may be used in combination.
When the above-described coupling agent is contained in the heat conductive resin sheet 4, the adhesive strength with the base material or the heat sink member 24 on which the power semiconductor element 23 of the electronic device serving as the heat generating portion is mounted is further preferable. .

  In addition, when a thermosetting epoxy resin composition is used for the resin 3 serving as a matrix of the heat conductive resin sheet 4, when an epoxy resin having a number average molecular weight of 3000 or more is used as a part of the main agent, the heat conductive resin sheet 4 is improved, and the adhesiveness to the heat generating part and the heat radiating part of the electric / electronic device is increased, which is preferable. The compounding ratio of the epoxy resin having a number average molecular weight of 3000 or more is 10 to 40 parts by weight with respect to 100 parts by weight of the liquid epoxy resin as the main agent. When the blending ratio is less than 10 parts by weight, the above-described improvement in adhesion is not recognized. When this mixing ratio is larger than 40 parts by weight, the heat resistance of the thermally conductive resin sheet cured body is lowered.

Embodiment 3 FIG.
A substantially spherical aluminum nitride having a particle size of about 30 μm is used as the first filler 1, and a flat filler 6 is used as the second filler 2, and the volume V1 of the first filler 1 is set to a total volume V ₁ + V ₂ of the filler. On the other hand, the heat conductive resin sheet 4 was prepared by changing the resin volume V ₃ while fixing to 30%, and the filling rate φ and the heat conductivity λ of the filler of the heat conductive resin sheet 4 were measured.
FIG. 7 shows φ / CFVC ₁ (CFVC ₁ : critical filler volume fraction of first filler 1) and V ₂ / (V ₂ + V ₃ ) (V ₂ : volume of filler 2, V ₃ : resin 3. FIG. 8 shows the relationship between λ / λ _CFVC1 (λ _CFVC1 : thermal conductivity when only the first filler is critically filled) and V ₂ / (V ₂ + V ₃ ). It is a plot.

As shown in FIG. 7, by filling only the first filler 1 and the second filler 2 as compared with the case where only the first filler 1 is critically filled (φ = CFVC ₁ , φ / CFVC ₁ = 1). It can be seen that the filling rate φ can be improved. Further, when the V ₂ / (V ₂ + V ₃ ) value is 0.66 or more, the saturated state is reached, and the filling rate is improved by about 27%.
Further, as shown in FIG. 8, the thermal conductivity is V ₂ / (V ₂ ) as compared to the thermal conductivity λ _CFVC1 (λ / λ _CFVC1 = 1) when only the first filler 1 is critically filled. The + V ₃ ) value was about 0.66, which was improved about 60%. Here, a preferable range in which the thermal conductivity can be improved is 0.6 ≦ V ₂ / (V ₂ + V _3), which can achieve a thermal conductivity improvement of about 40% when only the first filler 1 is critically filled. ) ≦ 0.72, and a more preferable range is 0.62 ≦ V ₂ / (V ₂ + V ₃ ) ≦ 0.7, which can achieve a thermal conductivity improvement of about 50%, and the most preferable range is about It can be seen that 0.65 ≦ V ₂ / (V ₂ + V ₃ ) ≦ 0.675 that can improve the thermal conductivity by 60%. Thus, it was found that the thermal conductivity can be improved to about 12 W / m · K or more.

Further, FIG. 9 shows the relationship between the specific gravity ratio ρ / ρo (ρo: ideal density without voids in each compounding ratio) and V ₂ / (V ₂ + V ₃ ), and FIG. 10 shows the BDV (Break Down Voltage) ratio BDV / BDVo: shows the relationship of (BDVo average BDV value when the void is not) and _V and _{2 / (V 2 + V 3} ). Note that the average BDV value when there is no void is the average BDV value when the specific gravity ratio ρ / ρo is approximately 1, that is, V ₂ / (V ₂ + V ₃ ) ≦ 0.66 from FIG. Moreover, ρ was obtained from the weight and volume obtained by actually measuring the molded body. 1−ρ / ρo corresponds to the porosity. The BDV measurement was performed with a Mitsubishi Electric Cable discharge detector device.

From FIG. 9, in the heat conductive resin sheet 4 having a small V ₂ / (V ₂ + V ₃ ) value, that is, a large resin ratio, the specific gravity ratio ρ / ρo is almost 1, and the porosity is almost zero. However, it can be seen that when the resin volume V ₃ decreases, the void 5 is generated and the ρ / ρo value decreases. From the same relationship, it can be seen from FIG.

Further, from FIG. 10, the V ₂ / (V ₂ + V ₃ ) value that can secure the BDV value is 0.675 or less, and in FIG. 9 ρ / ρ o when the V ₂ / (V ₂ + V ₃ ) value is 0.675. Since the value is 0.98, it can be seen that the allowable porosity is 2% or less. More preferably, the V ₂ / (V ₂ + V ₃ ) value is 0.665 or less, and the allowable porosity is 1% or less.

In the present embodiment, the volume V ₁ of the first filler 1 shows a fixed examples and 30% filler total volume V _{1 +} V _2, similarly established in another mixing ratio One.

Embodiment 4 FIG.
Among the heat conductive resin sheets 4 described in the above first to third embodiments, a method for manufacturing the heat conductive resin sheet 4 in which the volume fraction of the filler was particularly increased was examined.

  First, a thermosetting resin composition containing a predetermined amount of a main component of a thermosetting resin and an amount of a curing agent necessary to cure the main component, and the thermosetting resin composition and, for example, the same weight of solvent. Are mixed to obtain a solution of the thermosetting resin composition.

  Next, a mixed filler obtained by mixing the first filler 1 and the second filler 2 in advance is added to the solution of the thermosetting resin composition and premixed. This preliminary mixture is kneaded with, for example, three rolls or a kneader to form a compound.

  Next, the obtained compound is applied to a substrate such as a polyethylene terephthalate (PET) film or metal foil that has been subjected to a release treatment by a doctor blade method.

  Next, this coated material is dried, the solvent in the coated material is volatilized, formed into a sheet, and further heated to form a B stage.

  Next, the thermal conductive resin sheet 4 was compressed by applying a linear pressure load of about 100 kgf / cm using a roll press.

  In the case of a thermosetting resin composition having a low viscosity, addition of a solvent can be omitted. A catalyst may be added as appropriate to accelerate curing, and a coupling agent may be added as appropriate to improve adhesive strength.

Embodiment 5 FIG.
FIG. 11 is a schematic cross-sectional view of a power module according to Embodiment 5 of the present invention.
As shown in FIG. 11, in the power module 20 of the present embodiment, a power semiconductor element 23 is placed on the first surface of a lead frame 22 that serves as both a wiring member and a heat radiating member. A heat sink member 24 is provided on the second surface opposite to the surface on which the power semiconductor element 23 is placed via the cured body 21 of the heat conductive resin sheet 4 according to the first to fourth embodiments. ing. The power semiconductor element 23 is connected to the control semiconductor element 25 also placed on the lead frame 22 by a metal wire 26. The power module constituent members such as the cured body 21 of the heat conductive resin sheet, the lead frame 22, the heat sink member 24, the power semiconductor element 23, the control semiconductor element 25, and the metal wire 26 are sealed with a mold resin 27. .

  The power module 20 of the present embodiment is manufactured as follows. First, the power semiconductor element 23 and the control semiconductor element 25 are joined to predetermined portions of the lead frame 22 by soldering or the like. Next, the heat sink member 24 is laminated on the second surface opposite to the surface on which the power semiconductor element 23 of the lead frame 22 is placed via the B-stage-like thermally conductive resin sheet 4 and heated. The heat conductive resin sheet 4 is cured by applying pressure, and the heat sink member 24 is bonded. Next, a metal wire 26 is bonded to the power semiconductor element 23 and the control semiconductor element 25 by a wire bond method, and wiring is performed. Finally, the power module 20 is completed by sealing with a mold resin 27 by, for example, a transfer molding method.

  In the power module 20 of the present embodiment, the cured body 21 of the heat conductive resin sheet 4 according to the above first to third embodiments is placed on the lead frame 22 on which the power semiconductor element 23 that is a heat generating part of the power module is placed. The heat sink member 24 is bonded via the gap. The cured body 21 of the thermally conductive resin sheet has electrical insulation and excellent thermal conductivity that has not been conventionally available, and can transmit heat generated in the power semiconductor element 23 to the heat sink member 24 with high efficiency and dissipate heat. Therefore, the power module can be reduced in size and capacity.

  In the present embodiment, the example in which the thermally conductive resin sheet 4 is interposed between the lead frame 22 and the heat sink member 24 has been described. However, the thermally conductive resin sheet 4 according to the present invention is electrically insulating and has high heat. Since it has conductivity, a configuration in which the heat sink member 24 is omitted can be realized.

  Further, in the present embodiment, an example in which the heat sink member 24 is molded with a mold resin has been shown. However, for example, as shown in FIG. 12, a power semiconductor element 43, a circuit board 42, and a heat sink member 44 are provided in a case 45, The heat spreader 47 outside the case 45 may be the cured body 41 of the heat conductive resin sheet 4 according to the first to fourth embodiments. The inside of the case 45 is protected by a casting resin 46, for example. In the power module 40 shown in FIG. 12, at least one of the circuit board 42 and the heat sink member 44 functions as a heat dissipation member.

  In the heat conductive resin sheet 4 according to the present invention, the resin 3 serving as a matrix can be in a B-stage state. Good metal heat sink members 24 and 44 and heat spreader 47 can be bonded and electrically insulated. Furthermore, since the cured product 21 of the heat conductive resin sheet 4 has improved the volume fraction of the filler, it has high heat conductivity and the voids 5 are extremely suppressed, so that the electrical characteristics can be remarkably improved.

It is sectional drawing which showed typically the heat conductive resin sheet which concerns on Embodiment 1 of this invention. It is sectional drawing which showed typically the heat conductive resin sheet which concerns on Embodiment 1 of this invention. It is sectional drawing which showed typically the heat conductive resin sheet which concerns on Embodiment 1 of this invention. It is the schematic diagram which showed the relationship between the filling rate which concerns on Embodiment 1 of this invention, and the volume concentration of a filler. FIG. 4 is a relationship diagram of the volume fraction of the first filler, the second filler, and the resin according to Embodiment 1 of the present invention and the total volume of the first filler / total volume of the filler. It is the perspective view which showed typically the 2nd filler which concerns on Embodiment 2 of this invention. Is a graph showing the relationship between the form 3 to such a φ / CFVC ₁ and _{V 2 / (V 2 + V} 3) of the present invention. FIG. 6 is a relationship diagram between λ / λ _CFVC1 and V ₂ / (V ₂ + V ₃ ) according to Embodiment 3 of the present invention. FIG. 10 is a relationship diagram between ρ / ρo and V ₂ / (V ₂ + V ₃ ) according to Embodiment 3 of the present invention. It is a graph showing the relationship between BVD / BDVo and _{V 2 / (V 2 + V} 3) according to the third embodiment of the present invention. It is sectional drawing which showed typically the power module which concerns on Embodiment 5 of this invention. It is sectional drawing which showed typically the power module which concerns on Embodiment 5 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st filler, 2nd 2 filler, 3 resin, 4 thermally conductive resin sheet, 5 void, 6 flat filler, 20, 40 power module, 21, 41 Cured body of thermally conductive resin sheet, 22 Lead frame, 23, 43 Power semiconductor element, 24, 44 Heat sink member, 45 Case, 46 Cast resin, 47 Heat spreader

Claims (5)

Of the plurality of electrically insulating inorganic fillers separated from the size of the particle size, the step of preparing the larger average particle size as the first filler and the smaller one as the second filler;
The critical volume fraction of the first filler is CFVC ₁ ;
The critical volume fraction of the second filler is CFVC ₂ .
The ratio of the volume of the first filler to the sum of the volume of the first filler and the volume of the second filler is α,
When (i) 0 <(volume of the first filler) / (total volume of the inorganic filler) ≦ α / (α + α / CFVC ₁ × CFVC ₂ ) (1−α) / CFVC, ₂ × (1-CFVC ₂ ) / {1+ (1-α) / CFVC ₂ × (1-CFVC ₂ )}
(Ii) When α / (α + α / CFVC ₁ × CFVC ₂ ) <(volume of first filler) / (total volume of inorganic filler) <1, (α / CFVC ₁ −1) / (α / CFVC ₁ ) the step of determining,
Kneading the resin, the first filler, and the second filler based on the volume blending ratio to produce a compound;
A method for producing a thermally conductive resin sheet, comprising: drying an applied material obtained by applying the compound to a base material, and then applying a load to compress the applied material. A step of calculating a porosity φ _A1 from an actually measured density ρ _m1 and an ideal density ρ ₁ produced by measuring a plurality of molded bodies 1 in which only the first filler is blended with a resin;
Plotting the volume concentration of the filler of the molded body 1 and the filling rate (1-void ratio φ _A1 ) of the molded body 1, the critical volume fraction CFVC ₁ of the first filler is obtained by extrapolation. Process,
A step of calculating a porosity φ _A2 from an actually measured density ρ _m2 and an ideal density ρ ₂ which are prepared by actually preparing a plurality of molded bodies 2 in which only the second filler is blended with the resin, and
Plotting the volume concentration of the filler of the molded body 2 and the filling rate of the molded body 2 (1-porosity φ _A2 ), the critical volume fraction CFVC ₂ of the second filler is obtained from extrapolation. The method for producing a thermally conductive resin sheet according to claim 1, further comprising a step. The method for producing a thermally conductive resin sheet according to claim 1 or 2, wherein compression is applied while applying a load until the porosity becomes 2% or less. The method for producing a thermally conductive resin sheet according to claim 1 or 2, wherein the first filler is a spherical filler, and the second filler is a flat filler. A power module comprising a step of adhering a heat radiating member to a lead frame on which a power semiconductor element is mounted via a cured body of a thermally conductive resin sheet manufactured by the method according to any one of claims 1 to 4. Manufacturing method.

Images