WO2006115326A1

WO2006115326A1 - Case bonding method for a flat plate heat spreader by brazing and a heat spreader apparatus thereof

Info

Publication number: WO2006115326A1
Application number: PCT/KR2006/000914
Authority: WO
Inventors: Hyuck-Jin Kwon; Hyun-Tae Kim; Min-Jung Oh; Su-Hyeon Kim; Hwan-Hee Oh; Yong-Duck Lee
Original assignee: Ls Cable Ltd.
Priority date: 2005-04-07
Filing date: 2006-03-14
Publication date: 2006-11-02

Abstract

A method for bonding a case of a flat plate heat spreader is provided. In this method, a first case having an open upper portion and including a first sidewall provided at its edge and defining a first receiving space is prepared. Subsequently, a second case having an open upper portion and including a second sidewall provided its an edge and defining a second receiving space is prepared. Then, the first and second cases are assembled by inserting the open surface of the first case containing a heat spreading medium into the second receiving space, thereby forming a gap between the first and second sidewalls. Finally, the first and second cases are bonded by placing and melting a welding parent metal along the gap. This method prevents contamination of the cases during bonding, and shortens a process time, gives a tender welding surface, regardless of planar surface of the case.

Description

METHOD FOR CASES BONDING OF FLAT PLATE HEAT SPREADER BASED ON BRAZING AND APPARATUS MANUFACTURED USING THE SAME

Technical Field

[1] The present invention relates to a method for manufacturing a flat plate heat spreader, and more particularly to a method for bonding a case of a flat plate heat spreader and a flat plate heat spreader manufactured using the method. Background Art

[2] Recently, size and thickness of an electronic device such as a notebook or PDA get smaller due to the development of high integration technique. In addition, as the demand for high response property and improved functions is increased, power consumption tends to be increased.

[3] Accordingly much heat is generated from electronic parts in the electronic device while the device is operating, so various flat plate heat spreaders are used for emitting such heat to outside.

[4] A flat plate heat spreader is manufactured in a way of inserting a heat spreading medium such as a screen mesh between upper and lower cases to configure a case assembly, bonding the upper and lower cases except for a coolant injection hole, then injecting a coolant into the case, and finally sealing the coolant injection hole. At this time, in order to bond the upper and lower cases, TIG welding, laser welding or soldering is frequently used.

[5] FIG. 1 shows an example of a conventional case bonding process using TIG welding or laser welding.

[6] According to the bonding process shown in FIG. 1, a case assembly 30 is firstly fixed between an upper jig 10 and a lower jig 20. And then, with pressing the jigs 10, 20 by upper and lower press cylinders 40, 50, a pulse current is applied to a TIG welding rod or a laser welding rod 60 to weld a border where an upper case 30a and a lower case 30b are contacted.

[7] However, since the above bonding method is a spot welding using an instant pulse current, a welding surface is not continuous and thus it is not suitable for welding a case with a complicated shape. In addition, due to the generate of a minute leak, it is difficult to completely bond the upper case 30a and the lower case 30b, and a long process time is needed.

[8] FIG. 2 shows an example of another conventional case bonding process using soldering. [9] According to the bonding process shown in FIG. 2, when the upper case 30a and the lower case 30b are assembled, a soldering material 70 is inserted between contact surfaces of the cases. And then, the case assembly 30 is fixed between the upper jig 10 and the lower jig 20 by using the press cylinders 40, 50, and an edge of the case assembly 30 is heated. Then, the soldering material is melt and the upper and lower cases 30a, 30b are bonded.

[10] However, the above bonding method has advantages that it is not dependent on a shape of the case and allows tender welding surface and rapid process time, but impurities such as flux included in the soldering material are penetrated into the case, thereby deteriorating performance of the flat plate heat spreader. Disclosure of Invention Technical Problem

[11] The present invention is designed in consideration of the above problems, and therefore it is an object of the invention to provide a method for bonding a case, which may give various advantages of the soldering method as they are together with preventing contamination of the inside of the case in a case bonding process of a flat plate heat spreader, and also provide a flat plate heat spreader manufactured by the method.

Technical Solution

[12] In order to accomplish the above object, the present invention provides a method for bonding a case of a flat plate heat spreader, which (a) preparing a first case having an open upper portion and including a first sidewall provided at an edge thereof and defining a first receiving space; (b) preparing a second case having an open upper portion and including a second sidewall provided at an edge thereof and defining a second receiving space so that the open surface of the first case is inserted therein; (c) assembling the first and second cases by inserting the open surface of the first case into the second receiving space of the second case with a heat spreading medium being inserted in the first receiving space of the first case so that a gap is formed between the first sidewall and the second sidewall; and (d) bonding the first and second cases by placing a welding parent metal along the gap and then melting the welding parent metal.

[13] Preferably, the method further includes forming an opening in the first sidewall and the second sidewall so that a coolant injection tube is inserted therein; and inserting the coolant injection tube through the opening up to an inside of the first receiving space.

[14] Meanwhile, a flange is formed on the first sidewall of the first case so as to be extended outside, and the gap is formed by the flange when the first case and the second case are assembled. [15] At this time, the flange is closely contacted with a bottom of the second case to keep the first receiving space airtight.

[16] According to the present invention, the step (d) includes: mounting the case assembly between an upper jig and a lower jig; and bonding the case assembly by applying a high frequency power to a coil installed in the jig and thus melting the welding parent metal by means of high frequency induction heating.

[17] Preferably, in the step (d), argon gas or nitrogen gas is supplied to a surface of the case assembly so as to prevent oxidization of the surface of the case assembly during the high frequency induction heating.

[18] Preferably, the method further includes cooling the bonded case assembly by circulating a coolant using a cooling tube installed in the jig.

[19] Preferably, the upper jig and the lower jig have grooves conforming to a shape of the case assembly so as to fix the case assembly.

[20] Preferably, the welding parent metal is a bent or pressed welding wire corresponding to an edge shape of the case assembly provided with the gap, which is free from a flux.

[21] In the present invention, it is preferred that the second case further includes a plurality of ribs extended from the second sidewall, and the ribs are bent toward the welding parent metal placed in the gap so as to fix the welding parent metal.

[22] In the present invention, the step (d) includes: putting the case assembly into a heating furnace; and bonding the case assembly by applying heat to the heating furnace and thus melting the welding parent metal.

[23] Preferably, wherein an inside of the heating furnace is in a vacuum state or filled with at least one selected from the group consisting of hydrogen, nitrogen and ammonia.

[24] In another aspect of the present invention, there is also provided a flat plate heat spreading apparatus, which includes a heat spreading medium; a first case provided with a first sidewall defining a first receiving space that receives the heat spreading medium; a second case provided with a second sidewall defining a second receiving space that receives the first case so that a gap is formed between the first sidewall and the second sidewall; a coolant injected into the receiving space containing the heat spreading medium; and a bonding member fused along the gap between the first sidewall and the second sidewall to bond the first and second cases.

[25] Here, it is preferred that the first case includes a flange extended from the sidewall, and the flange is closely contacted with a bottom of the second case to form the gap between the first sidewall and the second sidewall.

[26] In addition, it is preferable that the second case includes a plurality of ribs extended from the sidewall by a predetermined length, and the plurality of ribs are bent toward the bonding member.

Brief Description of the Drawings

[27] These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings:

[28] FIG. 1 shows an example of a conventional case bonding process using TIG or laser welding;

[29] FIG. 2 shows an example of a conventional case bonding process using soldering;

[30] FIGs. 3 and 4 are sectional views showing first and second cases respectively used in a bonding process according to the present invention;

[31] FIG. 5 is a sectional view showing a case assembly after the first and second cases are assembled;

[32] FIG. 6 is a sectional view showing a case assembly after a welding parent metal is placed on an edge of the case assembly;

[33] FIG. 7 is a partial perspective view showing that a coolant injection tube is inserted into the case assembly and a rib is bent toward the welding parent metal;

[34] FIGs. 8 and 9 show a process of bonding the case by executing a brazing welding process according to the present invention; and

[35] FIG. 10 is a sectional view showing the case after the case bonding process is completed according to the present invention. Best Mode for Carrying Out the Invention

[36] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the invention.

[37] In a method for bonding a case of a flat plate heat spreader, as shown in FIG. 3, a first case A having an open upper portion and including a sidewall S provided to its edge and defining a first receiving space 100 is prepared. At this time, the first case A is a member corresponding to one sidewall of the flat plate heat spreader to be made, and it is provided with a flange 110 having a predetermined width and extended from the sidewall S to outside. In addition, an opening 120 is prepared in the sidewall S so that a coolant injection tube of the flat plate heat spreader is inserted therein. [38] Subsequently, as shown in FIG. 4, a second case B coupled with the first case A to configure the other sidewall of the flat plate heat spreader is prepared. The second case has an open upper portion and includes a sidewall S provided to its edge and defining a second receiving space 130 so that the first case A is received therein. The second receiving space of the second case has a size so as to receive the open surface on which the flange is formed, and a plurality of ribs 135 having a predetermined length are formed on the sidewall S . An opening 140 corresponding to the opening 120 formed in the sidewall S of the first case A is prepared in the sidewall S of the second case B

1 2 so that the coolant injection tube may be inserted therein.

[39] If the first and second cases A, B are prepared, as shown in FIG. 5, a heat spreading medium 150 is inserted into the first receiving space 100, and then the first and second cases A, B are assembled. At this time, the first case A is assembled such that its open surface is inserted into the second receiving space 130 of the second case B. In this assembled state, since the flange 110 is formed on the edge of the first case A, a gap

160 is formed between an outer side of the sidewall S i of the first case and an inner side of the sidewall S of the second case, as shown in the figures.

[40] Preferably, the gap 160 is successively prepared on the circumference of the case assembly A-B. In addition, when assembling the first and second cases A, B, the flange 110 provided to the first case A is closely contacted with the bottom of the second case B (see 170).

[41] The heat spreading medium 150 is composed of a metal screen mesh having good heat transfer property. The screen mesh gives a diffusion channel of an evaporated coolant and a flow channel of a liquefied coolant at the same time. The heat spreading medium 150 is preferably composed of a composite layer of sparse mesh and dense mesh in order to improve the heat transfer efficiency.

[42] If the first and second cases A, B are assembled, as shown in FIG. 6, a welding parent metal 180 is placed along the gap 160. The welding parent metal 180 preferably has a bent or pressed wire shape depending on the shape of the gap 160. As for material of the welding parent metal 180, a brazing welding parent metal not including a welding flux is adopted. Preferably, the welding parent metal is silver solder alloy. At this time, the plurality of ribs 135 formed on the sidewall S of the second case B are bent toward the welding parent metal 180 placed in the gap 160 so as to fix the welding parent metal 180 as shown in FIG. 7. In addition, since the plurality of ribs 135 are bent toward the welding parent metal 180, the first case A is compressed so that the first case A and the second case B are closely contacted.

[43] If the welding parent metal 180 is placed, as shown in the figures, a coolant injection tube 190 is inserted through the openings 120, 140 formed in the sidewalls S and S of the first and second cases A, B. At this time, an end of the tube 190 is

2 extended up to the first receiving space 100 of the first case A.

[44] If the first and second cases A, B are completely assembled, the cases are coupled with each other by means of welding.

[45] Preferably, as shown in FIG. 8, the case assembly A-B is mounted to a lower jig

200 of a brazing welding device. A rectangular groove 210 is prepared in an upper portion of the lower jig 200 so that a lower portion of the case assembly A-B is tightly inserted therein. Thus, the case assembly A-B is inserted along a sidewall of the groove 210 and then closely fixed on the lower jig 200.

[46] Meanwhile, a high frequency generation coil 220 and a cooling tube 230 are included in the lower jig 200. Preferably, the coil 220 and the tube 230 are inserted along an edge of the lower jig 200. In the following process, a high frequency current is applied to the coil 220, and a coolant is circulated in the cooling tube 230.

[47] Subsequently, as shown in FIG. 9, an upper jig 240 of the brazing welding device is moved using a press cylinder 250 to cover the case assembly A-B. Preferably, a rectangular groove is also prepared in a lower surface of the upper jig 240 so that an upper portion of the case assembly A-B is tightly inserted therein. Thus, if the upper jig 240 covers the case assembly A-B, the upper portion of the case assembly A-B is inserted along the sidewall of the groove and then closely fixed to the upper jig 240. After that, a pressure is applied to the press 250 to closely contact the flange 110 of the first case A and the bottom of the second case B (see 170 of FIG. 5) so as to keep airtight of the first receiving space 100 in which the heat spreading medium 150 is inserted.

[48] With the first receiving space 100 being kept airtight as mentioned above, brazing welding is executed. That is to say, a high frequency current is applied to the high frequency generation coil 220 to melt the welding parent metal 180 placed in the cap 160 by means of high frequency induction heating.

[49] Preferably, in order to prevent oxidization of the surface of the case assembly A-B during the high frequency induction heating, argon gas or nitrogen gas is supplied to the surface of the case assembly A-B.

[50] As another embodiment for coupling the assembled first and second cases A, B with each other by welding in the method for bonding a case of a flat plate heat spreader according to the present invention, the case assembly A-B is put into a heating furnace (not shown) and a high is applied to the heating furnace to melt the welding parent metal 180.

[51] At this time, the inside of the heating furnace is preferably in a vacuum state or filled with at least one of hydrogen, nitrogen and ammonia.

[52] Then, as shown in FIG. 10, due to viscous movement of a melt welding parent metal 180' and a capillary phenomenon caused in a contact interface between the first and second cases A, B, the first and second cases A, B are bonded. Using the same principle, the coolant injection tube 190 is also bonded to the openings provided in the sidewalls of the first and second cases A, B. The welding parent metal 180 is substantially melted at the same time along the edge of the case assembly A-B. Accordingly, a linear welding characteristic is obtained. That is to say, it is possible to shorten a welding time and give a tender welding surface.

[53] While the welding work is progressed, the first receiving space 100 in which the heat spreading medium 150 is inserted is kept airtight due to the pressure of the press, thereby capable of preventing the first receiving space 100 from being contaminated by the melt welding parent metal 180'. In addition, since the welding parent metal 180 does not contain a flux, contamination of the first receiving space 100 caused by a flux is not generated.

[54] If the brazing welding is completed, a coolant, for example water, is circulated in the cooling tube 230 installed to the lower jig 200 so that the case assembly A-B is cooled. Accordingly, the bonding process of the first and second cases A, B is completed.

[55] After the bonding process is completed, a vacuum pump is used to decompress the first receiving space 100 into a vacuum state, then a coolant (e.g., a distilled water) is injected through the coolant injection tube, and then the tube 190 is sealed, thereby completing a flat plate heat spreader.

[56]

[57] The inventors of this application has compared performance of a flat plate heat spreader made by applying the present invention with performance of a flat plate heat spreader made by applying a conventional laser welding. At this time, all conditions are identical except for the bonding method of the case.

[58] As a result, it has been revealed that the flat pate heat spreader made by applying the present invention shows more excellent maximum heat carrying capability by about 33% and more excellent heat conduction performance by about 20% than the flat plate heat spreader made by applying the conventional laser welding.

[59] The present invention has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. Industrial Applicability

[60] According to the present invention, it is possible to prevent contamination in the case since a space in which a heat spreading medium is inserted is kept airtight during the case bonding process. In addition, a welding parent metal used for bonding the case does not contain a flux, so contamination caused by flux is never found. Moreover, since the welding parent metal is melt at the same time on the edge by means of high frequency induction heating or heating using a heating furnace, it is possible to give a linear welding characteristic. Thus, a process time is shortened, a tender welding surface is obtained, and a surface shape of the case cannot be any trouble. Furthermore, due to the improvement of heat carrying capability, it is possible to make a cooling module of a high temperature heating product, and also it is possible to make a cooling module with a smaller size by decreasing a size of the flat plate heat spreader.

Claims

[1] A method for bonding a case of a flat plate heat spreader, comprising:

(a) preparing a first case having an open upper portion and including a first sidewall provided at an edge thereof and defining a first receiving space;

(b) preparing a second case having an open upper portion and including a second sidewall provided at an edge thereof and defining a second receiving space so that the open surface of the first case is inserted therein;

(c) assembling the first and second cases by inserting the open surface of the first case into the second receiving space of the second case with a heat spreading medium being inserted in the first receiving space of the first case so that a gap is formed between the first sidewall and the second sidewall; and

(d) bonding the first and second cases by placing a welding parent metal along the gap and then melting the welding parent metal.

[2] The method for bonding a case of a flat plate heat spreader according to claim 1, further comprising: forming an opening in the first sidewall and the second sidewall so that a coolant injection tube is inserted therein; and inserting the coolant injection tube through the opening up to an inside of the first receiving space. [3] The method for bonding a case of a flat plate heat spreader according to claim 2, wherein a flange is formed on the first sidewall of the first case so as to be extended outside, and wherein the gap is formed by the flange when the first case and the second case are assembled. [4] The method for bonding a case of a flat plate heat spreader according to claim 3, wherein the flange is closely contacted with a bottom of the second case to keep the first receiving space airtight. [5] The method for bonding a case of a flat plate heat spreader according to claim 1, wherein the step (d) includes: mounting the case assembly between an upper jig and a lower jig; and bonding the case assembly by applying a high frequency power to a coil installed in the jig and thus melting the welding parent metal by means of high frequency induction heating. [6] The method for bonding a case of a flat plate heat spreader according to claim 5, wherein argon gas or nitrogen gas is supplied to a surface of the case assembly so as to prevent oxidization of the surface of the case assembly during the high frequency induction heating. [7] The method for bonding a case of a flat plate heat spreader according to claim 5, further comprising: cooling the bonded case assembly by circulating a coolant using a cooling tube installed in the jig. [8] The method for bonding a case of a flat plate heat spreader according to claim 5, wherein the upper jig and the lower jig have grooves conforming to a shape of the case assembly so as to fix the case assembly. [9] The method for bonding a case of a flat plate heat spreader according to claim 1, wherein the welding parent metal is a bent or pressed welding wire corresponding to an edge shape of the case assembly provided with the gap. [10] The method for bonding a case of a flat plate heat spreader according to claim 9, wherein the welding parent metal is free from a flux. [11] The method for bonding a case of a flat plate heat spreader according to claim 1, wherein the second case further includes a plurality of ribs extended from the second sidewall, and wherein the ribs are bent toward the welding parent metal placed in the gap so as to fix the welding parent metal. [12] The method for bonding a case of a flat plate heat spreader according to claim 1, wherein the step (d) includes: putting the case assembly into a heating furnace; and bonding the case assembly by applying heat to the heating furnace and thus melting the welding parent metal. [13] The method for bonding a case of a flat plate heat spreader according to claim

12, wherein an inside of the heating furnace is in a vacuum state or filled with at least one selected from the group consisting of hydrogen, nitrogen and ammonia. [14] A flat plate heat spreading apparatus, comprising: a heat spreading medium; a first case provided with a first sidewall defining a first receiving space that receives the heat spreading medium; a second case provided with a second sidewall defining a second receiving space that receives the first case so that a gap is formed between the first sidewall and the second sidewall; a coolant injected into the receiving space containing the heat spreading medium; and a bonding member fused along the gap between the first sidewall and the second sidewall to bond the first and second cases. [15] The flat plate heat spreading apparatus according to claim 14, wherein the first case includes a flange extended from the sidewall, and wherein the flange is closely contacted with a bottom of the second case to form the gap between the first sidewall and the second sidewall. [16] The flat plate heat spreading apparatus according to claim 14, wherein the second case includes a plurality of ribs extended from the sidewall by a predetermined length, and wherein the plurality of ribs are bent toward the bonding member.