JP2024062137A - Thermal Conductive Materials - Google Patents

Abstract

[Problem] To provide a thermally conductive member for use in a vapor chamber, which has little warping or distortion of the container during manufacturing and has good heat dissipation efficiency. [Solution] The thermally conductive member includes a container in which the outer edges of opposing first and second sheets are joined by heat and pressure bonding via a sealant layer to form a sealed internal space, a working fluid sealed in the internal space, and a wick, which is a layer provided on the inner surface of the first sheet or the second sheet or both and which moves the working fluid by capillary action, and the sealant layer includes a sealant having a polyolefin skeleton or a sealant having an epoxy skeleton. [Selected Figure] Figure 1

Description

The present invention relates to a thermally conductive member.

In recent years, electronic devices have become more powerful, smaller, and thinner, and the amount of heat generated by elements such as CPUs has increased. This has led to the development of thermally conductive materials with high heat transport capacity to effectively cool these elements. In particular, flat vapor chambers that apply the principles of heat pipes have attracted attention due to their excellent heat dissipation properties and space efficiency.

The operating principle of a typical vapor chamber will be explained with reference to Figure 4, which is a cross-sectional view of a vapor chamber. The vapor chamber body is a sealed container formed by joining metal materials with good thermal conductivity, such as plates or foils of copper or aluminum. Inside the vapor chamber, there is a closed space with reduced pressure, in which a liquid for transferring heat, such as water, is sealed as the working fluid. In addition, a porous structure called a wick that can transport the working fluid by capillary force is provided along the inner surface of the container. Spacers may also be provided to ensure internal space.

One side of the vapor chamber is a heat absorption section, which is attached in close proximity to or in contact with an external heat source such as a CPU or MPU. The heat generated from the heat source is absorbed by the heat absorption section, and the working fluid (e.g., water) is vaporized from the wick on the heat absorption section side by the heat and moves to the heat dissipation section on the opposite side. The vaporized water vapor passes through the wick on the heat dissipation section side and is cooled when it comes into contact with the copper container, and re-condenses to become water. The latent heat transferred to the copper container at this time is diffused from the large area of the heat dissipation section to the outside of the container, cooling the container. The re-condensed water moves to the heat absorption section side within the wick due to capillary action and gravity, and once again absorbs heat generated from the heat source and vaporizes. By repeating this cycle, the heat generated from the heat source can be diffused from the large area of the heat dissipation section, allowing the heat source to be cooled efficiently.

In conventional vapor chambers, as shown in Figure 5, the container is generally constructed by joining two metal sheets, a first sheet and a second sheet, at their outer edges, and the outer edges of the first sheet and second sheet are generally joined and sealed at high temperatures for a long period of time using methods such as laser welding, diffusion bonding, hot pressing, and solder bonding. One issue with this is that the container can warp due to the release of thermal distortion and residual stress caused by joining at high temperatures for a long period of time, as shown in Figure 6. As a countermeasure to this, it has been proposed to form supports to support the container (Patent Document 1), but this results in a complex shape and makes manufacturing cumbersome.

In addition, the container is made of metal, which has good thermal conductivity, and the metal parts are joined together at the outer edge, so as shown in Figure 7, there is a problem that the heat from the heat source is conducted to the heat dissipation part through the outer edge, and less heat is added to the evaporation from the wick in the heat absorption part. There is also the problem that the heat is easily conducted to the heat dissipation part, which reduces the efficiency of heat dissipation.

Patent No. 6923091

Therefore, an object of the present invention is to provide a thermally conductive member that can be used in a vapor chamber, that causes little warping or distortion of the container during manufacturing, and that dissipates heat efficiently.

In order to solve the above problems, the present invention provides
a container in which outer edge portions of a first sheet and a second sheet facing each other are joined by heat and pressure via a sealant layer to form a sealed internal space;
A hydraulic fluid sealed in the internal space; and
a wick, which is a layer provided on the inner surface side of the first sheet, the second sheet, or both of them, and which moves the working fluid by capillary action;
A heat conductive member having
The sealant layer is a heat conductive member characterized in that it contains a sealant having a polyolefin skeleton or a sealant having an epoxy skeleton.

In the above-mentioned heat conductive member,
The first sheet and the second sheet may be metal, and the sealant layer may be a sealant having a polyolefin skeleton, and may be at least one layer having polar groups in the layer in contact with the first sheet and the second sheet.

The sealant layer has polar groups on the surface that comes into contact with the metal, improving metal adhesion.

In the above-mentioned heat conductive member,
The sealant layer is a sealant having a polyolefin skeleton, and the melting point of the layer in contact with the first sheet and the second sheet may be 90°C or higher and 170°C or lower.

This allows sealing to be done at low temperatures in a short time.

In the above-mentioned heat conductive member,
The sealant layer may have a three-layer structure of acid-modified polyolefin/polyolefin/acid-modified polyolefin, and the melting point of the layers may be polyolefin>acid-modified polyolefin.

In the above-mentioned heat conductive member,
The polyolefin may have a melt flow rate of 3 g/10 min or less.

In the above-mentioned heat conductive member,
The sealant layer may have a thickness of 20 μm or more and 300 μm or less.

This allows the thermal conductive material to be made thinner.

In the above-mentioned heat conductive member,
The sealant having an epoxy backbone may be hardened by curing.

The thermal conduction member of the present invention is free from the risk of warping or distortion during manufacturing, and can efficiently transport heat generated by a CPU, application processor (AP), etc. to a heat dissipation section for cooling, thereby providing a thermal conduction member that can suppress the occurrence of abnormal operation.

1 is a schematic cross-sectional view of one embodiment of a heat conductive member of the present invention. FIG. 4 is an explanatory diagram of an embodiment of sealing the outer edge of the heat conductive member of the present invention. 1 is an explanatory diagram of a situation in which a heat source is cooled by the heat conductive member of the present invention. 1 is an explanatory diagram of a state in which heat is dissipated from a heat source by the heat conductive member of the present invention; FIG. 1 is a schematic cross-sectional view of an example of a conventional heat conductive member. 1 is an explanatory diagram of a conventional method for sealing the outer edge of a heat conductive member. 1 is an explanatory diagram of a situation in which a heat source is cooled by a conventional heat conductive member.

The following describes in detail the embodiments of the present invention with reference to the drawings. Note that the present invention is not limited to the embodiments described below. In addition, the embodiments described below have technically preferable limitations for implementing the invention, but these limitations are not essential requirements for the present invention.

Figure 1 is a schematic cross-sectional view of one embodiment of the thermally conductive member of the present invention. The thermally conductive member 1 has a container 2 in which a first sheet 3 and a second sheet 4 are joined at their outer edges to form a sealed internal space. The first sheet 3 and the second sheet 4 are joined at the joint 12 of the outer edges by thermocompression bonding via a sealant layer 5 made of a sealant resin. One side of the container 2 (the side facing the second sheet 4 in Figure 1) is a heat absorbing part 10 that comes into contact with an external heat source and absorbs heat, and the opposite side (the side facing the first sheet 3 in Figure 1) is a heat dissipating part 9 that diffuses the absorbed heat to the outside of the container 2.

The first sheet 3 and the second sheet 4 are made of a material with good thermal conductivity and good workability, typically a metal foil or a thin metal plate. Of these, copper, aluminum, and the like, which have excellent thermal conductivity, are preferred. Note that the terms first sheet and second sheet are used here simply for the purpose of distinction, and there is no other particular difference between them. However, for convenience in processing, one sheet (second sheet 4 in FIG. 1) is made flat, and the other (first sheet 3 in FIG. 1) has a concave portion formed by drawing or the like to form an internal space.

The internal space is filled with working fluid 7, which acts as a medium for transferring heat from the heat absorption section 10 to the heat dissipation section 9. A wick 6 made of a material with a porous or capillary structure is provided along the inner surface of the first sheet 3 and the second sheet 4. The wick 6 is a layer that transfers the working fluid 7 by capillary action, and when the working fluid 7 is in a liquid state, most of it is impregnated in the wick 6. The internal space is kept slightly reduced in pressure relative to atmospheric pressure to facilitate the evaporation of the working fluid 7, and a spacer 8 is provided to keep the container 2 from collapsing.

The working fluid 7 on the heat absorption section 10 side is vaporized by the heat from the heat source, and as a gas it moves inside the container 2 to the heat dissipation section 9 side, where it releases heat and returns to liquid. The working fluid 7 that has returned to liquid returns to the heat absorption section 10 side again due to capillary action caused by the wick 6, absorbs heat from the heat source, and vaporizes again. By repeating this cycle, the heat of the heat source is diffused to the outside, and the heat source is cooled. Therefore, the working fluid 7 changes from gas to liquid and vice versa within a certain temperature range, and a liquid that is not reactive with the metal container 2 is used; for example, pure water is preferably used.

The wick 6 allows the gaseous working liquid 7 to pass through and uses capillary action to move the liquid working liquid 7. A material with good wettability with the working liquid 7 is used, and specific examples include a porous sintered body, a mesh metal, a bundle of ultrafine wires, and a nonwoven fabric. The shape of the wick 6 is not particularly limited as long as it can move the working liquid 7, and it can be a sheet, etc., and its thickness and structure may be constant or may vary partially. The wick 6 may be formed on the entire inner surface of the container 2, or may be formed partially.

A sealant having a polyolefin skeleton or an epoxy skeleton is used as the sealant layer 5. Specific examples include a polyolefin (PO) film and an epoxy film.

Conventional methods for directly joining metals together require heating to several hundred degrees Celsius at the highest and several tens of minutes at the longest, and the large amount of heat applied to the container causes warping and distortion. With the thermally conductive member of the present invention, a sealant layer 5 is provided between the outer edges of the first and second sheets, and this warping and distortion can be prevented by sealing at a relatively low temperature with a heat seal that lasts for several seconds.

By using polyolefin film or epoxy film, as shown in Figure 2, heat sealing at the joint 12 is completed by heating for several to several tens of seconds, so high temperature and long time joining is not necessary as in the past. Heat sealing at low temperature and for a short time can reduce distortion due to residual stress and prevent warping. In addition, the manufacturing takt time can be significantly shortened. In addition, these films have low thermal conductivity, and a gap of the thickness of the sealant layer 5 is formed between the first sheet 3 and the second sheet 4. As shown in Figure 3, this makes it possible to reduce the amount of heat transferred from the outer edge to the heat dissipation part 9 side with respect to the heat generated by the heat source 11, and the amount of heat added to the vaporization of the working fluid 7 in the wick 6 increases, improving the efficiency of heat dissipation.

In addition, due to the structure, the working fluid 7 in the container 2 is vaporized by the heat source, so if the sealant layer 5 does not have barrier properties, the vaporized working fluid 7 will gradually escape to the outside and will no longer perform its function, so barrier properties are important. In contrast, polyolefin skeletons or epoxy skeletons have high barrier properties and can be used stably.

The sealant layer 5 is not limited to a single layer, and may be multiple-layered. It is also preferable that the layer of the sealant layer 5 that contacts the first sheet 3 and the second sheet 4 has a polar group. The first sheet 3 and the second sheet 4 are made of copper or aluminum due to their thermal conductivity, but these surfaces are not treated as much as possible because they may hinder thermal conduction. For this reason, a normal sealant may have low adhesion to metals, so by using a sealant with a polar group such as an acid-modified group, adhesion is improved and the sealant will not burst when the internal pressure increases. Even in this case, the sealant layer 5 may be a single layer or multiple layers.

The melting point of the layer of the sealant layer 5 that contacts the first sheet 3 and the second sheet 4 is preferably 90°C or higher and 170°C or lower. The temperature and time of heat sealing can be controlled by the melting point of the sealant used, and a melting point of 170°C or lower is preferable for low-temperature, short-time sealing. On the other hand, since it is a thermally conductive material, heat resistance is required. However, since the heat resistance of semiconductors in electronic devices such as mobile phones is 80°C, by setting the melting point to 90°C or higher, the sealant layer 5 does not melt within the heat resistance temperature range of the electronic device, and it is possible to seal at a relatively low temperature and in a short time while maintaining strength.

It is also preferable that the sealant layer 5 is a three-layer structure consisting of acid-modified polyolefin (PO)/polyolefin (PO)/acid-modified polyolefin, with the melting point being polyolefin > acid-modified polyolefin. By configuring a PO resin with a higher melting point than the acid-modified PO in the middle layer of the three-layer structure, thickness fluctuation due to heat sealing can be reduced. When joining by heat sealing, the sealant resin flows due to heat, and the thickness is likely to vary. However, by providing a PO layer with a melting point higher than the acid-modified PO as described above, the PO does not melt or melts less easily, the resin does not flow easily, and the thickness can be maintained. By maintaining the thickness of the sealant layer 5 in this way, the heat conduction between the first sheet 3 and the second sheet 4 at the joint 12 can be stably reduced.

When the sealant layer 5 has the above three-layer structure, it is preferable that the polyolefin in the intermediate layer has a melt flow rate (MFR) of 3 g/10 min or less. By reducing the MFR of the PO in the intermediate layer, the resin is less likely to flow even when melted by heat sealing, so that thickness variation can be reduced.

The thickness of the sealant layer 5 is preferably 20 μm or more and 300 μm or less. If the thickness is too thick, it becomes difficult to make it thin, and if it is too thin, the strength will be weakened.

When the sealant layer 5 is an epoxy sealant, it is preferable that the epoxy sealant is cured. The curing effect can impart heat resistance and adhesion.

The present invention will now be described more specifically with reference to examples.
Using the following materials, samples were prepared under the conditions shown in Table 1, with a single or three-layer sealant layer, and with different melting points, thicknesses, etc., to give samples of Examples 1 to 17. Additionally, samples were prepared as Comparative Example 1, which had no sealant layer, and Comparative Example 2, which had an amorphous PET (A-PET) sealant layer.
First sheet: 90 mm x 100 mm electrolytic copper foil (thickness 20 μm) with a molded pocket
Cold forming was performed using a 70 mm x 80 mm molding machine to form a recess with a depth of 300 μm.
Second sheet: 90 mm x 100 mm electrolytic copper foil (thickness 20 μm)
Working medium: Pure water Wick: Copper mesh Support: Copper support Sealant layer: See Table 1 Except for Comparative Example 1, a sealant film cut to a width of 10 mm was placed on the outer edge of the first sheet, and three sides were heat sealed with a heat sealer at 190°C x 0.65 MPa x 2 s. 3 g of pure water was poured into the remaining unsealed part, and heat sealing was performed under the same conditions as above while reducing the pressure to -90 kPa with a vacuum sealer. Comparative Example 1 was bonded under general metal bonding conditions. Each material was evaluated as follows.

◇After sealing all warped sides, place the sample on the smooth surface with the second sheet facing down, and measure the height of the four corners from the smooth surface with a ruler. The total value of all these heights is calculated as the warpage value.
Less than 10mm: 〇 10mm or more: ×
⇒ A score of 〇 or above is considered a pass.

◇Barrier properties: The prepared sample was stored in a humidity-free environment at 60°C for 1 week, and the amount of working fluid lost was measured from the change in weight of the sample. The seal width was 3 mm.
Reduction amount is less than 0.1%: 〇 Reduction amount is 0.1 to 0.2%: △
Reduction of 0.2% or more: ×
⇒ A score of 〇 or above is considered a pass.

◇Heat conduction An 80℃ heating element was attached to the second sheet side of the prepared sample, and the temperature of the first sheet, 10 mm away from the heating element, was measured after 10 seconds.
Below 40℃: ◎
40℃ to less than 50℃: 〇 50℃ or more: ×
⇒ A score of 〇 or above is considered a pass.

◇The thicker the remaining sealant layer, the lower the thermal conductivity of the outer edge. Therefore, measure the thickness of the outer edge with a contact type film thickness gauge, and then measure the thickness of the sealant layer.
50μm or more: ◎
30μm to less than 50μm: 〇～◎
10μm to less than 30μm: 〇 5μm to less than 10μm: △
Less than 5 μm: ×
⇒ △ or above is considered a pass.

Adhesion to sheets: Using a tensile tester, the first and second sheets were gripped with a chuck and pulled at a speed of 50 mm/min to measure the peel strength.
3N/15mm or more: 〇 Less than 3N/15mm: ×
⇒ A score of 〇 or above is considered a pass.

◇Heat resistance
Since the sheet is heated by the heat source, it is necessary for the sheet to adhere to the sheet even in a high-temperature environment. After leaving the sheet in an 80°C environment for 5 minutes, the first sheet and the second sheet are gripped by a chucking machine and pulled at a speed of 50 mm/min to measure the peel strength.
1N/15mm or more: 〇 Less than 1N/15mm: ×
⇒ A score of 〇 or above is considered a pass.

The evaluation results are shown in Table 1. The thermally conductive member of the present invention achieved good results in all areas including warping, barrier properties, thermal conduction, seal residue, adhesion, and heat resistance. On the other hand, in the comparative examples, the one without the sealant layer failed in warping, thermal conduction, and seal residue, and the one with the A-PET sealant layer had insufficient barrier properties.

Reference Signs List 1: Heat conductive member 2: Container 3: First sheet 4: Second sheet 5: Sealant layer 6: Wick 7: Working fluid 8: Spacer 9: Heat dissipation section 10: Heat absorption section 11: Heat source 12: Joint section

Claims (7)

a container in which outer edge portions of a first sheet and a second sheet facing each other are joined by heat and pressure via a sealant layer to form a sealed internal space;
A hydraulic fluid sealed in the internal space; and
a wick, which is a layer provided on the inner surface side of the first sheet, the second sheet, or both of them, and which moves the working fluid by capillary action;
A heat conductive member having
The heat conductive member, wherein the sealant layer contains a sealant having a polyolefin skeleton or a sealant having an epoxy skeleton. The thermal conductive member according to claim 1, characterized in that the first sheet and the second sheet are metal, the sealant layer is a sealant having a polyolefin skeleton, there is at least one layer, and the layer in contact with the first sheet and the second sheet has a polar group. The heat conductive member according to claim 1, characterized in that the sealant layer is a sealant having a polyolefin skeleton, and the melting point of the layer in contact with the first sheet and the second sheet is 90°C or higher and 170°C or lower. The heat conductive member according to claim 1, characterized in that the sealant layer has a three-layer structure consisting of acid-modified polyolefin/polyolefin/acid-modified polyolefin, and the melting point of the layer is polyolefin > acid-modified polyolefin. The heat transfer member according to claim 4, characterized in that the melt flow rate of the polyolefin is 3 g/10 min or less. The heat conductive member according to claim 1, characterized in that the thickness of the sealant layer is 20 μm or more and 300 μm or less. The heat conductive member according to claim 1, characterized in that the sealant layer having an epoxy skeleton is hardened by curing.

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