JP2021022686A - Substrate and electronic apparatus - Google Patents

Abstract

To suppress thermal expansion in a heat radiating member installed on a substrate body together with a heat generating element.SOLUTION: A substrate includes a substrate body, a heat generating element, and a heat sink. The heat sink includes a base plate portion, and first to fourth fins erected on the respective base plate portion. The base plate portion includes four regions including a first region to a fourth region formed by a first axis that passes through the center of the base plate and extends to the left and right in a plan view, and a second axis that intersects the first axis at the center of the base plate and extends in the front-rear direction. The first to fourth fins are arranged in the first to fourth regions, respectively, and each extend radially outward from the center of the base plate portion.SELECTED DRAWING: Figure 1

Description

The present invention relates to substrates and electronic devices.

Conventionally, in order to dissipate heat from an electronic device equipped with a heat-generating electronic device or the like, a heat transfer tool having fins erected on a base plate (see, for example, Patent Document 1) or a heat sink having fins erected on a rectangular substrate. (For example, see Patent Document 2), various heat radiating members have been proposed.

Jikkenhei 2-148093 Jitsuto No. 3156485

By the way, with the recent improvement in the performance of electronic devices, it becomes difficult to dissipate heat from electronic devices and the like, and problems such as damage to electronic devices and increase in transmission loss have become problems. Further, if heat is not properly dissipated from the electronic device or the like, for example, thermal expansion may occur in the heat radiating member itself, which may damage the solder bumps that bond the electronic device or the like to the substrate.

In one aspect, the invention disclosed herein aims to suppress thermal expansion in a heat radiating member installed on a substrate body together with a heat generating element.

In one embodiment, the substrate comprises a substrate body, a heat generating element mounted on the top surface of the board body via solder bumps, and a heat radiating member thermally connected to the top surface of the heat generating element. The heat radiating member includes a base plate portion and first fins, second fins, third fins, and fourth fins erected on the base plate portion, respectively, and the base plate portion is the same in a plan view. Four formed by a first axis that passes through the center of the base plate and extends to the left and right and a second axis that intersects the first axis at the center of the base and extends in the front-rear direction. The first fin has a region, and the first fin is arranged in the first region formed right rear of the central portion of the four regions and from the side close to the central portion toward the right rear direction. The second fin extends and is arranged in a second region formed on the left rear side of the central portion of the four regions, and extends from the side close to the central portion toward the left rear portion. The third fin is arranged in the third region formed in the front left of the central portion of the four regions and extends from the side close to the central portion toward the front left, and the fourth fin is formed. Of the four regions, the fourth region is formed in the front right with respect to the center, and extends from the side close to the center toward the front right.

In another aspect, the electronic device is an electronic device in which a substrate is arranged in a housing, and the substrate includes a substrate main body, a heat generating element mounted on the upper surface of the substrate main body via solder bumps, and the like. It has a heat radiating member thermally connected to the upper surface of the heat generating element, and the heat radiating member has a base plate portion and first fins, second fins, and third fins erected on the base plate portion, respectively. The base plate portion includes fins and a fourth fin, and the base plate portion has a first axis extending left and right through the center portion of the base plate portion in a plan view and the first axis line at the center portion of the base plate portion. It has four regions formed by a second axis extending in the front-rear direction while intersecting with the first fin, and the first fin is formed on the right rear side of the central portion of the four regions. The second fin is arranged in the region and extends from the side close to the central portion toward the rear right, and the second fin is arranged in the second region formed behind the central portion of the four regions. At the same time, the third fin extends from the side close to the central portion toward the left rear direction, and the third fin is arranged in the third region formed in front of the central portion of the four regions. The fourth fin extends from the side close to the central portion toward the left front direction, and the fourth fin is arranged in the fourth region formed to the right front of the central portion among the four regions and is located in the central portion. It extends from the near side toward the front right.

According to the invention disclosed in the present specification, it is possible to suppress thermal expansion in the heat radiating member installed on the substrate main body together with the heat generating element.

FIG. 1 is a perspective view showing a substrate included in the electronic device of the embodiment. FIG. 2A is a plan view of the substrate of the embodiment, and FIG. 2B is a sectional view taken along line AA in FIG. 2A. FIG. 3 is an explanatory view showing the extending direction of the fins included in the heat sink of the embodiment. FIG. 4 is an explanatory diagram schematically showing a state of thermal expansion in the fins and the base plate portion of the heat sink of the embodiment. FIG. 5 is an explanatory view showing how the heat sink of the embodiment and the heat sink of the comparative example are compared with each other. FIG. 6 is a table showing the simulation results of the elongation amount of the heat sink of the embodiment and the heat sink of the comparative example and the stress acting on the bump. FIG. 7 is a plan view showing a substrate of a modified example.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, in the drawings, the dimensions, ratios, etc. of each part may not be shown so as to completely match the actual ones. In addition, depending on the drawing, for convenience of explanation, components that actually exist may be omitted, or the dimensions may be exaggerated than they actually are.

(Embodiment)
First, the electronic device 100 of the embodiment and the substrate 1 installed in the housing 101 included in the electronic device 100 will be described with reference to FIGS. 1, 2 (A) and 2 (B). In the following description, for convenience of explanation, the front, rear, left, and right sides of the substrate 1 are set as shown in FIG. 2 (A).

The electronic device 100 of the present embodiment is a communication device, but is not limited thereto. The substrate 1 is equipped with a printed circuit board (FR4 substrate) 2 as a substrate main body and a FOWLP (Fanout wafer level package) 4 as a heat generating element on the printed circuit board 2 via a solder bump 3. FOWLP4 is an example of a heat generating element. Instead of FOWLP4, other heat generating elements such as a semiconductor chip and a flip chip BGA (Ball Grid Array) may be mounted. FOWLP4 is a square with a side length of 20 mm. In the present embodiment, the material of the solder bump 3 is Su-3.0Ag-0.5Cu (SAC305), but the material is not limited to this, and conventionally known materials can be appropriately adopted. .. The diameter of the solder bumps 3 is set to 300 μm, and the bump pitch, that is, the distance between the adjacent solder bumps 3 is set to 600 μm.

The underfill 5 is filled around the solder bump 3. The underfill 5 can be formed of a conventionally known material, but in the present embodiment, a material in which silica is mixed as a filler with an epoxy resin is used. In addition, other resins may be used instead of the epoxy resin, and as the filler, alumina or the like may be used instead of silica or together with silica.

The substrate 1 includes a heat sink 7 as a heat radiating member thermally connected to the upper surface 4a of the FOWLP4. The heat sink 7 includes a base plate portion 8 that functions as a heat spreader, and first fins 11a to 11g, second fins 12a to 12g, third fins 13a to 13g, and fourth fins 14a that are erected on the base plate portion 8. It has ~ 14g.

The base plate portion 8 of the heat sink 7 of the present embodiment is square, and side plate portions 9 are continuously provided on each side thereof. Further, at the lower end of each side plate portion 9, a ground contact portion 10 extending in a brim shape toward the outside is provided. The heat sink 7 is fixed to the surface of the printed circuit board 2 via the grounding portion 10.

Although the heat sink 7 of the present embodiment is made of aluminum, a material capable of exhibiting the thermal conductivity and heat dissipation of the heat generated by the heat generating material such as FOWLP4 can be appropriately selected. For example, metal materials such as copper, copper-molybdenum alloy, stainless steel, silver, and brass can be suitably adopted as the material of the heat sink 7. The difference in the coefficient of thermal expansion between the printed circuit board 2 and the heat sink 7 is within ± 70% in order to suppress the occurrence of problems caused by the thermal stress generated in each part of the substrate 1 and improve the reliability of the substrate 1. It is desirable to do.

The heat sink 7 includes a base plate portion 8, first fins 11a to 11g, second fins 12a to 12g, third fins 13a to 13g, fourth fins 14a to 14g, and a side plate portion 9 and a grounding portion 10. There is. These are integrally formed of the same material. More specifically, the base plate portion 8 and the first fins 11a to 11g, the second fins 12a to 12g, the third fins 13a to 13g, and the fourth fins 14a to 14g do not go through a joint such as welding. It is molded. Further, the base plate portion 8, the side plate portion 9, and the ground contact portion 10 are also formed without using a joint portion such as welding. The heat sink 7 is installed so that the center of the base plate portion 8 and the center of the FOWLP4 coincide with each other.

The base plate portion 8 functions as a heat spreader and is thermally connected to the upper surface 4a of the FOWLP4, but a TIM (Thermal Interface Material) 6 is interposed between the base plate portion 8 and the upper surface 4a of the FOWLP4. There is. In the present embodiment, an indium sheet is used as the TIM6, but any material that can conduct heat from the upper surface 4a of the FOWLP4 to the base plate portion 8 can be used as the material of the TIM6. For example, AuSn (gold tin) paste, silver paste, copper paste, graphite sheet, carbon nanotube sheet, thermal paste and the like can be suitably used as the material of TIM6.

Here, the dimensions of each part of the substrate 1 of the embodiment will be described. In the present embodiment, the printed circuit board 2 is also square, and the length L1 of one side thereof is 100 mm. Further, the base plate portion 8 of the heat sink 7 is also square, and the length L2 of one side thereof is 50 mm. The length L3, which is the distance between the edges of the opposing ground contact portions 10, is 80 mm. The width W1 of the first fins 11a to 11g, the second fins 12a to 12g, the third fins 13a to 13g, and the fourth fins 14a to 14g is 3.5 mm. The height H1 from the surface of the printed circuit board 2 to the surface of the base plate portion 8 of the heat sink 7 is 3.5 mm, and the first fins 11a to 11g, the second fins 12a to 12g, the third fins 13a to 13g, and the fourth fins 13a to 13g. The height H2 of the fins 14a to 14g is 4.0 mm. The thickness t1 of the printed circuit board 2 is 0.5 mm, and the thickness t2 of the FOWLP4 is 1 mm. For convenience of drawing, the dimensions and ratios of each part are not accurately expressed in the drawings.

Next, with reference to FIGS. 2A and 3, the extending directions of the first fins 11a to 11g, the second fins 12a to 12g, the third fins 13a to 13g, and the fourth fins 14a to 14g will be described. ..

With reference to FIGS. 2A and 3, a first axis AX1 and a second axis AX2 are set on the base plate portion 8 of the heat sink 7. The first axis AX1 passes through the central portion CP of the base plate portion 8 in a plan view and extends in the left-right direction. The second axis AX2 intersects the first axis AX1 at the central CP and extends in the front-rear direction. The central portion CP is a region including the central point of the base plate portion 8, and does not necessarily have to completely coincide with the central point. That is, the first axis AX1 and the second axis AX2 may intersect within the central portion CP as a region, and may not necessarily intersect at the central point of the base plate portion 8.

The base plate portion 8 is divided into four regions from the first region to the fourth region by the first axis line AX1 and the second axis line AX2. The first region is formed on the right rear side of the central CP. The second region is formed on the left rear side of the central CP. The third region is formed in the front left with respect to the central CP. The fourth region is formed on the right front side with respect to the central CP.

The first fins 11a to 11g are arranged in the first region. By providing the plurality of first fins 11a to 11g, the surface area can be increased and the heat dissipation efficiency can be improved. Referring to FIG. 3, the first fin axis C11, which is an axis extending in the longitudinal direction of the first fins 11a to 11g, indicates the extending direction of the first fins 11a to 11g. The first fin axis C11 is set for each of the first fins 11a to 11g, and these are set in parallel. That is, the first fins 11a to 11g are provided in parallel. The angle formed by the first axis AX1 and the first fin axis C11 is θ1. The angle θ1 is a counterclockwise angle as shown by arrow 21 from the first axis AX1.

Second fins 12a to 12g are arranged in the second region. By providing the plurality of second fins 12a to 12g, the surface area can be increased and the heat dissipation efficiency can be improved. Referring to FIG. 3, the second fin axis C12, which is an axis extending in the longitudinal direction of the second fins 12a to 12g, indicates the extending direction of the second fins 12a to 12g. The second fin axis C12 is set for each of the second fins 12a to 12g, and these are set in parallel. That is, the second fins 12a to 12g are provided in parallel. The angle formed by the first axis AX1 and the second fin axis C12 is θ2. The angle θ2 is a clockwise angle as shown by arrow 22 from the first axis AX1.

Third fins 13a to 13g are arranged in the third region. By providing the plurality of third fins 13a to 13g, the surface area can be increased and the heat dissipation efficiency can be improved. Referring to FIG. 3, the third fin axis C13, which is an axis extending in the longitudinal direction of the third fins 13a to 13g, indicates the extending direction of the third fins 13a to 13g. The third fin axis C13 is set for each of the third fins 13a to 13g, and these are set in parallel. That is, the third fins 13a to 13g are provided in parallel. The angle formed by the first axis AX1 and the third fin axis C13 is θ3. The angle θ3 is a counterclockwise angle as shown by arrow 23 from the first axis AX1.

Fourth fins 14a to 14g are arranged in the fourth region. By providing the plurality of fourth fins 14a to 14g, the surface area can be increased and the heat dissipation efficiency can be improved. Referring to FIG. 3, the fourth fin axis C14, which is an axis extending in the longitudinal direction of the fourth fins 14a to 14g, indicates the extending direction of the fourth fins 14a to 14g. The fourth fin axis C14 is set for each of the fourth fins 14a to 14g, and these are set in parallel. That is, the fourth fins 14a to 14g are provided in parallel. The angle formed by the first axis AX1 and the fourth fin axis C14 is θ4. The angle θ4 is a clockwise angle as shown by arrow 24 from the first axis AX1.

In this way, by providing the first fins 11a to 11g, the second fins 12a to 12g, the third fins 13a to 13g, and the fourth fins 14a to 14g radially on the base plate portion 8, the heat sink 7 is thermally expanded. It can be suppressed.

Here, with reference to FIG. 4, the state of thermal expansion in the base plate portion 8 and the thermal expansion in the first fins 11a to 11g, the second fins 12a to 12g, the third fins 13a to 13g, and the fourth fins 14a to 14g. The state of is schematically shown. Since the base plate portion 8 is arranged so that the heat-generating FOWLP4 and its centers coincide with each other and are thermally connected to the FOWLP4, the base plate portion 8 is radially outward from the central portion CP as shown by arrows 31 to 34. Attempts to thermally expand towards.

Further, the first fins 11a to 11g, the second fins 12a to 12g, the third fins 13a to 13g, and the fourth fins 14a to 14g also try to thermally expand along their respective longitudinal directions. That is, the first fins 11a to 11g try to extend toward the central CP as shown by the solid line 25a, and extend outward as shown by the dotted line 25b. To do. The second fins 12a to 12g tend to extend toward the central CP as shown by the solid line 26a, and tend to extend outward as shown by the dotted line 26b. The third fins 13a to 13g tend to extend toward the central CP as shown by the solid line 27a, and tend to extend outward as shown by the dotted line 27b. The fourth fins 14a to 14g tend to extend toward the central CP as shown by the solid line 28a, and tend to extend outward as shown by the dotted line 28b.

In this way, the base plate portion 8 that tends to extend radially outward and the first fins 11a to 11g, the second fins 12a to 12g, the third fins 13a to 13g, and the fourth fins 14a to 14g are It is integrally molded. Therefore, the phenomenon that the base plate portion 8 tends to extend outward and the first fins 11a to 11g, the second fins 12a to 12g, the third fins 13a to 13g, and the fourth fins 14a to 14g are the central CPs. The phenomenon of trying to grow toward is canceled out. As a result, it is considered that the amount of elongation of the heat sink 7 as a whole can be suppressed. Since FIG. 4 is a schematic view, the directions indicated by the arrows are not drawn so as to completely match. This is because FIG. 4 shows the direction in which the base plate portion 8 tends to extend and the first fins 11a to 11g, the second fins 12a to 12g, the third fins 13a to 13g, and the fourth fins 14a to 14g. This is because it conceptually shows how the directions cancel each other out.

Here, with reference to FIGS. 5 and 6, the amount of expansion due to thermal expansion of the base plate portion 8 included in the heat sink 7 of the embodiment is compared with the amount of expansion due to thermal expansion of the base plate portion 58 included in the heat sink of the comparative example. I will explain. The base plate portion 58 of the comparative example is provided with fins 61, all of which extend in one direction. The heat sink of the comparative example has the same dimensions as the heat sink 7 of the embodiment except for the extending direction of the fins.

With reference to FIG. 5, a simulation was performed in which one side of the square base plate portion 8 and the base plate portion 58 was fixed, and the displacement amount of the corner portions P1 and P50 located on the opposite sides of the side was the elongation amount. .. In the comparative example, the fin 61 was set to extend in the direction of 90 ° with respect to the fixed side. The simulation compares the amount of elongation when the temperatures of the base plate portions 8 and 58 reach 100 ° C.

As a result, as shown in FIG. 6, the movement amount of the measurement point P10, that is, the elongation amount of the base plate portion 58 is 246 μm, whereas the movement amount of P1, that is, the elongation amount of the base plate portion 8 is 198 μm. there were. Further, when the maximum stress generated in the solder bump 3 at this time was calculated by simulation, it was 146 MPa in the comparative example, whereas it was 117 MPa in the embodiment.

As described above, according to the embodiment, the thermal expansion of the heat sink 7 which is a heat radiating member can be suppressed, and as a result, the stress generated in the solder bump 3 can also be reduced.

Further, for the heat sink 7 of the embodiment, a temperature cycle test was carried out in which a cycle of −50 ° C. for 5 minutes, 25 ° C. for 15 minutes, and 125 ° C. for 5 minutes was set as one cycle, and this was performed for 100 cycles. As a result, when the heat sink 7 of the embodiment was used, no joint defect was observed in the joint portion formed by the solder bump 3, but in the comparative example, the occurrence of the joint defect was confirmed. In this respect as well, the heat sink 7 of the embodiment is advantageous.

As described above, according to the substrate 1 of the embodiment, the thermal expansion of the heat sink 7 can be suppressed by arranging the fins extending radially with respect to the base plate portion 8. In the present embodiment, the angles θ1, θ2, θ3, and θ4 are set to 60 °, respectively, in order to make it easier to obtain such an effect. In order to preferably obtain such an effect, it is desirable that the angles θ1, θ2, θ3 and θ4 are set in the range of 20 ° to 70 °.

In the present embodiment, the first fins 11a to 11g, the second fins 12a to 12g, the third fins 13a to 13g, and the fourth fins 14a to 14g are connected to each other in adjacent regions. Specifically, of the first fins 11a to 11g arranged in the first region, the first fins 11a to 11e are the fourth fins 14a to 11e arranged in the fourth region on the first axis AX1. It is connected with 14e. The first fins 11f and 11g are connected to the second fins 12f and 12g arranged in the second region on the second axis AX2. The second fins 12a to 12e arranged in the second region are connected to the third fins 13a to 13e arranged in the third region on the first axis AX1. The third fins 13f and 13g arranged in the third region are connected to the fourth fins 14f and 14g arranged in the fourth region on the second axis AX2.

As a result, each fin forms a V shape. The fins do not necessarily have to be connected in series and do not have to form a V-shape, but the rigidity of the fins can be increased by forming the V-shape.

As described above, the embodiment includes fins extending outward radially from the central CP in each of the first to fourth regions, and the fins in each region are provided in parallel. Although the heat sink 7 of the embodiment is square, the shape of the base plate portion 78 may be rectangular as in the substrate 71 of the modified example shown in FIG. That is, the size and shape of the heat sink can be appropriately changed according to the number and arrangement of the heat generating elements. When a rectangle as shown in FIG. 7 is adopted, the number of fins arranged in parallel in each region may be increased.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and variations are made within the scope of the gist of the present invention described in the claims. It can be changed.

1 Board 2 Printed circuit board 3 Solder bump 4 FOWLP (heat generating element)
5 underfill 6 TIM
7 Heat sink 8 Base plate 9 Side plate 11a to 11g 1st fin 12a to 12g 2nd fin 13a to 13g 3rd fin 14a to 14g 4th fin AX1 1st axis AX2 2nd axis CP center

Claims (4)

With the board body
A heat generating element mounted on the upper surface of the substrate body via solder bumps,
It has a heat radiating member thermally connected to the upper surface of the heat generating element.
The heat radiating member includes a base plate portion and first fins, second fins, third fins, and fourth fins erected on the base plate portion, respectively.
In a plan view, the base plate portion intersects the first axis that passes through the center of the base plate and extends left and right and the first axis at the center of the base plate and extends in the front-rear direction. It has four regions formed by two axes and
The first fin is arranged in the first region formed right rear of the central portion of the four regions and extends from the side close to the central portion toward the right rear direction.
The second fin is arranged in the second region formed on the left rear side of the central portion of the four regions, and extends from the side close to the central portion toward the left rear portion.
The third fin is arranged in the third region formed on the left front side of the central portion of the four regions, and extends from the side close to the central portion toward the left front direction.
The fourth fin is a substrate that is arranged in a fourth region formed in front of the center of the four regions and extends from a side close to the center toward the front right. The first aspect of claim 1, wherein the extending directions of the fourth fin from the first fin are directions in which the angle formed with the first axis is 20 ° to 70 ° in the first region to the fourth region, respectively. Board. The substrate according to claim 1 or 2, wherein a plurality of the first to fourth fins are provided in each of the first to fourth regions. An electronic device in which a substrate is placed inside a housing.
The substrate is
With the board body
A heat generating element mounted on the upper surface of the substrate body via solder bumps,
It has a heat radiating member thermally connected to the upper surface of the heat generating element.
The heat radiating member includes a base plate portion and first fins, second fins, third fins, and fourth fins erected on the base plate portion, respectively.
In a plan view, the base plate portion intersects the first axis that passes through the center of the base plate and extends left and right and the first axis at the center of the base plate and extends in the front-rear direction. It has four regions formed by two axes and
The first fin is arranged in the first region formed right rear of the central portion of the four regions and extends from the side close to the central portion toward the right rear direction.
The second fin is arranged in the second region formed on the left rear side of the central portion of the four regions, and extends from the side close to the central portion toward the left rear portion.
The third fin is arranged in the third region formed on the left front side of the central portion of the four regions, and extends from the side close to the central portion toward the left front direction.
The fourth fin is an electronic device that is arranged in a fourth region formed in front of the center of the four regions and extends from a side close to the center toward the front right.

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