JP6149241B2 - Heater for bonding apparatus and cooling method thereof - Google Patents

Description

  The present invention relates to a structure of a bonding apparatus heater and a cooling method thereof.

  As a method of mounting a semiconductor chip on a substrate, solder bumps are formed on the electrodes, a method of mounting electronic components with solder bumps on a substrate by thermocompression bonding, or forming gold bumps on the electrodes of electronic components, A thin solder film is provided on the surface, and gold solder fusion bonding, in which gold and solder of gold bumps are bonded by heat melting, or bonding using a resin adhesive such as thermoplastic resin or anisotropic conductive film (AFC) The method is used. In any of these joining methods, the electronic component is heated to melt the solder or adhesive on the electrode and the electronic component is pressed against the substrate with a crimping tool, and then the solder or adhesive is cooled and fixed. Thus, the electronic component is bonded to the substrate. The electronic component mounting apparatus used for such joining includes a heater for heating the solder to a molten state or heating the adhesive to a softened state, and a cooling means for cooling the solder and the adhesive after joining, rapid heating, Rapid cooling is required.

  In order to shorten the tact time, the problem is how to cool in a short time rather than rapid heating. For this reason, a method has been proposed in which an air flow path is provided in a heat insulating material superimposed on a plate-shaped ceramic heater, and cooling air is caused to flow on the surface of the ceramic heater to cool the heater and the bonding tool attached to the heater ( For example, see Patent Document 1).

  In addition, there is a method in which a space is provided between the pulse heater and the base member overlapped with the pulse heater, and the air blown out from the cooling hole provided in the base member is blown to the heat insulating material side of the pulse heater to rapidly cool the pulse heater. It has been proposed (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 2002-16091 JP-A-10-275833

  By the way, in general, when fluid is flowed between narrow parallel plates, heat transfer from the surface of the parallel plates to the cooling medium is dominated by heat conduction in the direction perpendicular to the flow, and heat accompanied by material movement such as turbulent flow. The movement is very small. For this reason, in order to increase the amount of heat transfer between the surface of the parallel plate and the cooling medium, it is important to shorten the distance between the parallel plates, that is, the distance of heat conduction in the cooling medium. come. In particular, when air having a low thermal conductivity is used as the cooling medium (for example, the thermal conductivity of 0.1 to 0.5 Mpa air is 0.026 W / (m · K) and the water is 0.6 W / ( In order to be very small compared to m · K), it is necessary to further reduce the distance between the parallel plates. For this reason, as in the prior art described in Patent Document 1, the heater is effectively cooled even if air is passed through a rectangular channel having a distance between parallel plates of about 0.5 mm to 2 mm to cool it. There is a problem that can not be. Moreover, when it is going to cool a heater by spraying air on the surface of a heater like the prior art described in patent document 2, since it is necessary to spray a large amount of air on a base member, There was a problem that the bonding atmosphere was disturbed.

  An object of this invention is to cool the heater for bonding apparatuses more effectively.

The heater for the bonding apparatus according to the present invention has a first surface made of ceramics to which a bonding tool is attached, and a second surface to which a heat insulating material is attached on the side opposite to the first surface, and current flows. A flat plate-type bonding apparatus heater that generates heat, the width of the direction along the second surface being in the range of 0.1 mm to 0.02 mm, and the second heater A plurality of capillary slits whose width in the direction along the surface is smaller than the depth in the direction perpendicular to the second surface, and a plurality of capillary slits and a mating surface of the heat insulating material attached to the second surface The bonding device heater that generated heat by forming the capillary cooling flow path is directly cooled by cooling air, and the second surface is provided with a recess in the vicinity of the center, and a heat insulating material attached to the recess and the second surface. The mating surface is the cooling air There is formed a cavity which flows, a number of capillary slits, extend to the side surface of the cavity, characterized by.

The heater for a bonding apparatus according to the present invention has a first surface made of ceramics to which a bonding tool is attached and a second surface to which a heat insulating material is attached on the side opposite to the first surface, and current flows. A heater for a flat-plate bonding apparatus that generates heat by being provided on the second surface, the width in the direction along the second surface being in the range of 0.1 mm to 0.02 mm, and the first A plurality of capillary slits whose width in the direction along the second surface is smaller than the depth in the direction perpendicular to the second surface, and a plurality of capillary slits and a mating surface of the heat insulating material attached to the second surface The bonding device heater that has generated heat by forming a number of capillary cooling channels is directly cooled by cooling air, and the heat insulating material is provided with a second depression near the center of the mating surface, and the second depression and the first depression. The second side is where cooling air flows. The cavities are formed, a number of capillary slit communicates with the cavity, extend between each opposing side surfaces, and wherein.

In the heater for a bonding apparatus of the present invention, the ratio of the depth of the capillary slit to the width of the capillary slit is preferably in the range of 3 to 10.

The method for cooling a heater for a bonding apparatus according to the present invention has a first surface made of ceramics to which a bonding tool is attached, and a second surface to which a heat insulating material is attached on the side opposite to the first surface. It is a flat plate shape that generates heat by flowing, is provided on the second surface, and the width in the direction along the second surface is in the range of 0.1 mm to 0.02 mm and along the second surface. A plurality of capillary slits whose width in the direction is smaller than the depth perpendicular to the second surface, and the number of capillary slits and the mating surface of the heat insulating material attached to the second surface are a number of capillary cooling flows The bonding apparatus heater that has generated heat by directly forming a path is directly cooled by cooling air, and the second surface is provided with a recess in the vicinity of the center, and the recess and the mating surface of the heat insulating material attached to the second surface Cavitation where cooling air flows The number of capillary slits is a cooling method for a heater for a bonding apparatus extending from the cavity to the side surface, and the temperature of the cooling air flowing out from the outlet of the capillary cooling channel is higher than the temperature of the wall surface of the capillary slit. The flow rate of the cooling air flowing into the capillary cooling flow path is adjusted so that the temperature is lower by the threshold value. Further, the method for cooling a heater for a bonding apparatus according to the present invention has a first surface made of ceramics to which a bonding tool is attached, and a second surface to which a heat insulating material is attached on the side opposite to the first surface, A flat plate shape that generates heat when an electric current flows, is provided on the second surface, has a width in the direction along the second surface in the range of 0.1 mm to 0.02 mm, and on the second surface. A plurality of capillary slits whose width in the direction along the second surface is smaller than the depth perpendicular to the second surface, and the number of capillary slits and the mating surface of the heat insulating material attached to the second surface are The bonding device heater that has generated heat by forming a cooling channel is directly cooled by cooling air, and the heat insulating material is provided with a second recess near the center of the mating surface, and the second recess and the second surface. Forms a cavity into which cooling air flows The plurality of capillary slits is a cooling method for the bonding apparatus heater that communicates with the cavity and extends between the opposing side surfaces, and the temperature of the cooling air flowing out from the outlet of the capillary cooling flow path is The flow rate of the cooling air flowing into the capillary cooling channel is adjusted so that the temperature is lower by a predetermined threshold than the temperature of the wall surface.

  The present invention has an effect that the heater for the bonding apparatus can be cooled more effectively.

It is explanatory drawing which shows the structure of the heater for bonding apparatuses in embodiment of this invention. It is the top view and sectional drawing of the heater for bonding apparatuses in embodiment of this invention. It is sectional drawing which shows the detail of the capillary slit of the heater for bonding apparatuses in embodiment of this invention. It is a perspective view which shows the capillary cooling flow path of the heater for bonding apparatuses in embodiment of this invention. It is sectional drawing which shows the detail of the cooling groove of the heater for bonding apparatuses by a prior art. It is a graph which shows the relationship between the capillary slit width of the heater for bonding apparatuses in embodiment of this invention, and thermal resistance. It is a graph which shows the relationship between the length of the capillary cooling flow path of the heater for bonding apparatuses in embodiment of this invention, and air temperature. It is explanatory drawing which shows the structure of the heater for bonding apparatuses in other embodiment of this invention. It is the top view and sectional drawing of the heater for bonding apparatuses in other embodiment of this invention.

  Hereinafter, a bonding apparatus heater according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the heater 30 for a bonding apparatus of the present embodiment includes a flat plate-shaped main body 31, a lower surface 31 b that is a first surface to which the bonding tool 40 is attached, and a second member to which the heat insulating material 20 is attached. And an upper surface 31a which is a surface. A substantially rectangular parallelepiped recess 34 is provided in the vicinity of the center of the upper surface 31 a, and the body 31 is provided with a number of capillary slits 35 extending from the recess 34 to the side surface 33. The recess 34 and the mating surface 21 of the heat insulating material 20 aligned with the upper surface 31a form a cavity 36 into which cooling air flows, and the many slits 35 and the mating surface 21 of the heat insulating material 20 attached to the upper surface 31a A number of capillary cooling channels 37 extending from the cavity 36 to the side surface 33 are formed.

  A stainless steel base member 10 is attached to the upper portion of the heat insulating material 20, and this base member 10 is attached to a bonding head of a bonding apparatus (not shown) and is driven by a vertical driving device built in the bonding head. The base member 10, the heat insulating material 20, the bonding device heater 30, and the bonding tool 40 are integrally moved in the vertical direction.

  The bonding apparatus heater 30 is formed, for example, by embedding a heating resistor composed of platinum or tungsten in a ceramic such as aluminum nitride. The heat insulating material 20 prevents the heat of the bonding apparatus heater 30 from being transmitted to the base member 10 and is made of ceramics such as Adseram (registered trademark).

  The structures of the bonding apparatus heater 30 and the heat insulating material 20 will be described in detail with reference to FIG. 2A is a plan view showing the upper surface 31a of the bonding apparatus heater 30, FIG. 2B is a cross-sectional view taken along the line AA in FIG. 2A, and FIG. It is sectional drawing of BB shown to Fig.2 (a).

As shown in FIG. 2 (a), two depressions 34 are provided in the center of the upper surface 31 a of the bonding apparatus heater 30 in the vertical direction. A number of capillary slits 35 extend into the main body 31. In the heater 30 for the bonding apparatus of this embodiment, 63 capillary slits 35 extend from the vertical walls of the recesses 34 to the vertical side surfaces 33 of the main body 31. Accordingly, a total of 63 × 2 × 2 = 252 capillary slits 35 are formed on the upper surface 31a shown in FIG. The length of KakukeHoso slit 35 is _{L 1.} The capillary slit 35 may be formed by cutting with a dicing device, for example.

As shown in FIG. 3, the width W ₁ of each capillary slit 35 is 0.05 mm, the thickness D ₁ of the wall 38 between the capillary slits 35 is 0.1 mm, and the depth H ₁ of the capillary slit 35 is 0.3 mm. It is. Thus, capillary slits 35 is smaller than the depth _{H 1} is the width _{W 1,} in the present embodiment, the ratio of the depth _{H 1} to the width _{W 1} (depth _{H 1} / width _W 1) = (0. 3 / 0.05) = 6.0. Further, the depth of the recess 34 is 0.3 mm, which is the same as that of the capillary slit 35.

  As shown in FIGS. 2B and 2C, the heat insulating material 20 is overlaid on the upper surface 31 a of the main body 31. The mating surface 21 of the heat insulating material 20 is a flat surface, and is in close contact with the surface around the recess 34 and the capillary slit 35 provided on the upper surface 31a. For this reason, as shown in FIG. 2B, when the mating surface 21 of the heat insulating material 20 is overlapped with the upper surface 31 a of the main body 31, the upper release surface of the substantially rectangular parallelepiped recess 34 and the upper release of the capillary slit 35 are released. The surfaces are closed, and the recesses 34 and the mating surface 21 form cavities 36 that are substantially rectangular parallelepiped. Similarly, as shown in FIG. 2C, the large number of capillary slits 35 and the mating surface 21 form a large number of capillary cooling channels 37 elongated in the vertical direction. Further, as shown in FIG. 2B, the heat insulating material 20 is provided with two cooling air holes 25 communicating with the cavities 36, respectively. Then, the cooling air supplied to each cooling air hole 25 flows into the cavity 36 from the cooling air hole 25 as shown by a downward arrow in FIG. 37, and flows out from the side surfaces 33 to the outside as indicated by the up and down arrows shown in FIG. 2A to cool the bonding apparatus heater 30.

As shown in FIG. 4, the capillary cooling flow path 37 of the bonding apparatus heater 30 of the present embodiment is a flow path having a rectangular cross section with a width W ₁ , a depth H ₁ , and a length L ₁ . The flow enters from the inlet 371 communicating with the cavity 36 and flows out from the outlet 372 on the side surface 33. While the width W ₁ of the capillary cooling channel 37 is very narrow as 0.05 mm, the depth H ₁ is 0.3 mm, which is six times as wide as the width W _1. The flow of air flowing through 37 is a flow between narrow parallel plates, and heat exchange between the main body 31 of the bonding device heater 30 and the air is performed on both side surfaces of the capillary slits 35 constituting both side surfaces 37a of the capillary cooling channel 37. 35a is dominant and the bottom surface 35b of the capillary slit 35 constituting the bottom surface 37b of the capillary cooling channel 37 hardly contributes to heat exchange. Since the number of the capillary cooling channels 37 is 252 in the heater 30 for the bonding apparatus of the present embodiment, the effective heat exchange area is as follows.

Effective heat exchange area = area of both side surfaces 35a of the capillary slit 35 = H ₁ × L ₁ × 2 × number of capillary cooling channels 37
= H ₁ × L ₁ × 504
It becomes.

In addition, the total channel cross-sectional area of the capillary cooling channel 37 is
Total channel cross-sectional area = W ₁ × H ₁ × number of capillary cooling channels 37 = W ₁ × H ₁ × 504
It becomes.

On the other hand, as shown in FIG. 5, a case is considered in which a cooling air flow path 26 having the same cross-sectional area as that of the capillary cooling flow path 37 of the present embodiment is formed on the mating surface 21 of the heat insulating material 20. . In the example shown in FIG. 5, the cooling air channel 26 is formed as a channel without a partition in the horizontal direction in the figure. In this case, the total length of the width W _{1 of the} two capillary cooling channels 37 and the thickness D ₁ of the wall 38, that is, the width W ₂ for two pitches of the capillary cooling channels 37 is (0.05 + 0.1). × 2 = 0.3 mm, which is the same as the depth H ₁ of the capillary cooling channel 37, so that the height H ₂ of the cooling air channel 26 is set to 0. 2 times the width W ₁ of the capillary cooling channel 37. If it is set to 1 mm, both channel cross-sectional areas will become the same. Then, the effective heat exchange area of the cooling air flow path 26 having a width W ₂ shown in FIG. 5 is only the bottom 26b facing the upper surface 31a of the cooling air flow path 26, do not contribute to the side surface 26a is mostly heat exchanger, effective While the heat exchange area is W ₂ × L ₁ , the effective heat exchange area of the capillary cooling channel 37 in the width W ₂ portion is H ₁ × L ₁ × 2 (both sides) × 2 (2 channels) ) Here, since W ₂ = H ₁ , the effective heat exchange area of the capillary cooling flow path 37 in the width W ₂ portion is four times the effective heat exchange area of the cooling air flow path 26 of width W _2. It will be.

  In addition, the heat transfer from each surface 35a of the capillary slit 35 constituting the capillary cooling flow path 37 to the cooling air is dominated by the heat conduction in the direction perpendicular to the flow. The accompanying heat transfer is very small. For this reason, as shown in FIG. 6, the thermal resistance during heat transfer increases as the width W of the capillary slit 35 increases.

  Accordingly, the capillary cooling flow path 37 of the bonding apparatus heater 30 of this embodiment described with reference to FIGS. 1 to 4 is four times as large as the cooling air flow path 26 of the prior art described with reference to FIG. Since it has an effective heat exchange area and has a lower thermal resistance than the cooling air flow path 26, a larger heat exchange can be performed and the bonding apparatus heater 30 can be cooled more effectively.

As shown in FIG. 7, the temperature inside the capillary cooling channel 37 of the heater 30 for the bonding apparatus of the present embodiment varies depending on the position of the capillary cooling channel 37 in the flow direction and the flow rate of air. FIG. 7A is a graph showing changes in the air temperature with respect to the longitudinal distance at the center in the width direction of the capillary cooling channel 37. FIG. 7B shows the air temperature in the capillary cooling channel 37 on the wall surface (capillary). is a diagram showing the temperature T ₂ a position of the wall surface) of the slit 35. If the air flow rate is small, the line a of FIG. 7 (a), as shown in line p in FIG. 7 (b), the temperature of the air flowing in the temperature T ₁ of the inlet 371 of the capillary cooling channel 37 rapidly Rises to the temperature T2 of the wall surface of the capillary cooling channel 37 (wall surface of the capillary slit 35) in the first half of the channel, and flows out from the outlet 372 as it is. In this case, since the air temperature in the second half of the channel they've reached a temperature T ₂ of the wall, will no longer be able to take the heat from the body 31, the cooling capacity is not be sufficiently exhibited.

Conversely, when the flow rate is large, the line c in FIG. 7 (a), as shown in line r in FIG. 7 (b), the air flowing into the inlet 371 at a temperature T _1, the temperature wall surface temperature T It flows out from the outlet 372 to the outside ₂ of about half of the temperature. In this case, since the temperature difference between the air and the wall surface (wall surface of the capillary slit 35) is large over the entire length of the capillary cooling channel 37, the cooling capacity increases, but the cooling capacity does not increase in place of the cooling air flow rate. .

Therefore, the bonding device for a heater 30 of the present embodiment, a capillary temperature of the air flowing out of the outlet 372 of the cooling channel 37 is slightly wider than the temperature T ₂ of the wall surface (wall surface of the capillary slit 35), or a predetermined threshold value ΔT Adjust the air flow rate so that the temperature is as low as possible. This flow rate is determined in advance by a test or the like, and the pressure of the air supplied to the cooling air hole 25 is adjusted so as to be the flow rate, or the flow rate adjusting valve or regulator provided on the inlet side of the cooling air hole 25 is used. Or may be adjusted. Thus, by adjusting the cooling air flow rate, the bonding device heater 30 can be effectively cooled with a small cooling air flow rate.

  Another embodiment of the present invention will be described with reference to FIGS. Parts similar to those of the embodiment described above with reference to FIGS. 1 to 7 are denoted by the same reference numerals and description thereof is omitted. As shown in FIG. 8, in this embodiment, a depression 134 that is a second depression is provided in the vicinity of the center of the mating surface 21 of the heat insulating material 20, and is provided in the main body 31 as shown in FIG. 9A. The capillary slit 35 extends from one side surface 33 to the other side surface 33 facing it. The cooling air hole 25 is connected to the recess 134. The number, width, and depth of the capillary slits 35 are the same as those of the embodiment described above with reference to FIGS.

As shown in FIG. 8 and FIG. 9B, when the mating surface 21 of the heat insulating material 20 is aligned with the upper surface 31 a of the main body 31, the depression 134 provided on the mating surface 21 of the heat insulating material 20 becomes the upper surface 31 a of the main body 31. A cavity 136 into which the air from the cooling air hole 25 enters is formed in close contact with the surface where the capillary slit 35 is not provided. As shown in FIG. 9C, the capillary slit 35 and the mating surface 21 of the heat insulating material 20 constitute a capillary cooling channel 37. As shown in FIG. 9 (a), the length of the capillary cooling passage 37 is L _1. Further, as shown in FIG. 9B, the lower surface of the cavity 136 communicates with the open ends on the upper side of the many capillary slits 35. Then, after the air that has entered the cavity 136 from the cooling air hole 25 flows into the lower capillary slit 35 from the cavity 136, as shown in FIG. Then, the bonding device heater 30 is cooled.

  In the present embodiment, in addition to the same effects as those of the embodiment described above with reference to FIGS. 1 to 7, the processing of the ceramic main body 31 is simple, and the structure can be made simpler. Play.

In the above described embodiment, the width _{W 1} of the capillary slit 35 is described as 0.05 mm, the width _{W 1} of the capillary slit 35 may be selected freely as long as the range of 0.5mm~0.01mm . A range of 0.1 mm to 0.02 mm is more preferable, and a range of 0.05 mm to 0.02 mm is more preferable. Further, the depth H ₁ of the capillary slit 35 is 0.3 mm, and the ratio of the width W ₁ of the capillary slit 35 to the depth H ₁ of the capillary slit 35 is 1: 6. ₁ may be deeper than the width _{W 1} of the capillary slits 35, for example, may be selected freely within a range of 1.0Mm～0.1Mm. The width _{W 1} and depth ratio of an _{H 1} capillary slits 35 of capillary slit 35 is 1: 6 to limited without, 1: 3 to 1: can be freely selected as long as the range of 10.

  10 base member, 20 heat insulating material, 21 mating surface, 25 cooling air hole, 26 cooling air flow path, 30 heater for bonding device, 31 main body, 31a upper surface, 31b lower surface, 33 side surface, 34, 134 recess, 35 capillary slit, 35a, 37a side surface, 35b, 37b bottom surface, 36, 136 cavity, 37 capillary cooling channel, 38 walls, 40 bonding tool, 371 inlet, 372 outlet.

Claims (5)

For a flat-plate bonding device made of ceramics and having a first surface on which a bonding tool is attached and a second surface to which a heat insulating material is attached on the opposite side of the first surface, and generates heat when an electric current flows A heater,
Provided in the second surface, the width in the direction along the second surface is in the range of 0.1 mm to 0.02 mm, and the width in the direction along the second surface is the second A plurality of capillary slits smaller than the depth in the vertical direction on the surface of
A large number of the capillary slits and the mating surface of the heat insulating material attached to the second surface form a large number of capillary cooling channels and directly cool the heater for the bonding apparatus that has generated heat with cooling air,
The second surface is provided with a depression near the center,
The mating surface of the heat insulating material attached to the recess and the second surface forms a cavity into which the cooling air flows,
A large number of the capillary slits extend from the cavity to the side surface. For a flat-plate bonding device made of ceramics and having a first surface on which a bonding tool is attached and a second surface to which a heat insulating material is attached on the opposite side of the first surface, and generates heat when an electric current flows A heater,
Provided in the second surface, the width in the direction along the second surface is in the range of 0.1 mm to 0.02 mm, and the width in the direction along the second surface is the second A plurality of capillary slits smaller than the depth in the vertical direction on the surface of
A large number of the capillary slits and the mating surface of the heat insulating material attached to the second surface form a large number of capillary cooling channels and directly cool the heater for the bonding apparatus that has generated heat with cooling air,
The heat insulating material is provided with a second depression near the center of the mating surface,
The second recess and the second surface form a cavity into which the cooling air flows,
A large number of the capillary slits communicate with the cavity and extend between the opposing side surfaces. The heater for a bonding apparatus according to claim 1 or 2,
The ratio of the depth of the capillary slit to the width of the capillary slit is in the range of 3 to 10,
A heater for a bonding apparatus. It has a first surface made of a ceramic and to which a bonding tool is attached, and a second surface to which a heat insulating material is attached on the side opposite to the first surface. Provided in the second surface, the width in the direction along the second surface is in the range of 0.1 mm to 0.02 mm, and the width in the direction along the second surface is the second surface. A plurality of capillary slits smaller than the depth in the vertical direction, and the plurality of capillary slits and the mating surface of the heat insulating material attached to the second surface form a plurality of capillary cooling channels. The heated heater for the bonding apparatus is directly cooled by cooling air, and the second surface is provided with a recess in the vicinity of the center, and the recess and the mating surface of the heat insulating material attached to the second surface are: Cavity into which the cooling air flows Forming a I, a large number of the capillary slits, a cooling method of a bonding device for a heater extending sides from the cavity,
The flow rate of the cooling air flowing into the capillary cooling channel is adjusted so that the temperature of the cooling air flowing out from the outlet of the capillary cooling channel is lower than the temperature of the wall surface of the capillary slit by a predetermined threshold value. To do,
A cooling method characterized by the above. It has a first surface made of a ceramic and to which a bonding tool is attached, and a second surface to which a heat insulating material is attached on the side opposite to the first surface. Provided in the second surface, the width in the direction along the second surface is in the range of 0.1 mm to 0.02 mm, and the width in the direction along the second surface is the second surface. A plurality of capillary slits smaller than the depth in the vertical direction, and the plurality of capillary slits and the mating surface of the heat insulating material attached to the second surface form a plurality of capillary cooling channels. The heated heater for the bonding apparatus is directly cooled by cooling air, and the heat insulating material is provided with a second recess in the vicinity of the center of the mating surface, and the second recess and the second surface are Forming a cavity into which cooling air flows Number of the capillary slit, the communication with the cavity, a cooling method of a bonding device for a heater extending between each opposing side surfaces,
The flow rate of the cooling air flowing into the capillary cooling channel is adjusted so that the temperature of the cooling air flowing out from the outlet of the capillary cooling channel is lower than the temperature of the wall surface of the capillary slit by a predetermined threshold value. To do,
A cooling method characterized by the above.

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