Patent Application
20170016131
(a) Field of the Invention
The present invention relates to a growth method of dendritic crystal structure that provides directional heat transfer, and more particularly to a method that uses a current concentration effect to achieve the growth of dendritic crystals that provide directional heat transfer. Moreover, the dendritic crystals that are formed differ from whiskers grown by extrusion using the internal stress of ductile metal.
(b) Description of the Prior Art
Due to the current development trend for light weight and greater slimness in electronic devices, thus, how to enable heat transfer components, under the condition of smaller dimensions, achieve more rapid effective cooling of the heat produced by electronic devices is a persistent technical problem waiting to be resolved by relevant manufacturers.
The majority of current common heat transfer components use copper or an aluminum substrate that have a good heat conduction effect, and a plurality of heat dissipating fins are disposed on the copper or the aluminum substrate. Moreover, heat dissipating fins are used to transmit outward the heat produced by electronic devices and cool down the devices. However, the heat dissipation areas provided by the heat dissipating fins and the copper or aluminum substrate themselves are limited, thus it is difficult to further improve the heat dissipation efficiency of the electronic devices.
Other manufacturers have developed a method whereby they use whisker structures originally regarded as defects during the process of electroplating to serve as heat transfer components, which are primarily used in heat pipe elements. Related inventions of the prior art include Europe patent No. EP0999590 titled “Heat sink for electric and/or electronic devices,” U.S. Pat. No. 3,842,474 titled “Heat transfer between solids and fluids utilizing polycrystalline metal whiskers,” and Taiwan patent No. 201326718 titled “Heat dissipating structure for heat dissipating device.”
However, the aforementioned whiskers grow via release of residual internal stress in the plating, and the speed of growth using such a mechanism is not only considerably slow but also requires a comparatively longer preparation time. Furthermore, the majority of whiskers assume rod shapes with comparatively thin diameters, and are of single crystal type, which are unable to provide a greater interfacial area. Hence, the heat dissipation areas that such a method are able to provide is similarly limited, and the heat dissipation effect is inferior.
Furthermore, another defect commonly seen in current electroplating is dendritic crystals, and the reason why dendritic crystals are produced is because during the process of electroplating, metal ions concentrate on protruding areas due to the electric current, and such an effect influences deposit concentration on the protruding areas of the substrate, on which grow dendritic crystals. Because such dendritic crystals seriously affect the smoothness and aesthetics of the plated elements, thus, they have always been regarded as defects that must be avoided.
For example, in 2008, Mr. Tsai Yi-da wrote a master's thesis titled “Effect of a complexing agent in electrotinning-bismuth lead-free solder material composition control, adhesivity, and dendritic structure growth” for his master's degree at National Chung Cheng University, and in the abstract he mentions: “ . . . previous studies have pointed out that problems exist in Sn—Bi plating obtained using electroplating methods including inferior adhesivity and dendritic structure growth. Hence, in order to effectively control the production of dendritic structures, it is necessary to add a complexing agent or add an interfacial agent to control such . . . .” Accordingly, current dendritic crystals in the field of electroplating are still regarded as defects, and have no special function.
Accordingly, in order to improve the shortcomings of the limited heat dissipation areas of heat dissipation elements of the prior art, the author of the present invention devoted himself to research to provide a growth method of dendritic crystal structure that provides directional heat transfer, and which comprises the following steps:
A. Providing a substrate, whereby the substrate is provided with a plurality of crystal defects separated at intervals;
B. Depositing a plurality of metal ions on the substrate using a deposition method, whereby the aforementioned metal ions deposited on the crystal defects enable the growth of dendritic crystals, and an interspace is formed between each of the dendritic crystals.
Furthermore, in step A, a coated whisker layer is plated on the substrate, and the material of the coated whisker layer is any one or a combination of the following: tin, cadmium, zinc, antimony, or indium. The plurality of whiskers formed on the substrate serve as the aforementioned crystal defects.
Moreover, in step A, processing is carried out on the substrate to form the aforementioned crystal defects on the substrate.
Wherein the processing is a cutting process.
Furthermore, in step B, the substrate serves as an electrode for electroplating, wherein the electroplating current density for is 1 A/dm2˜5 A/dm2, and the electroplating time is 60 min˜180 min.
Furthermore, the length of the aforementioned dendritic crystals is 0.1 mm˜15 mm.
Furthermore, the length of the aforementioned dendritic crystals is 1 mm˜5 mm.
Furthermore, the interspace between each of the aforementioned dendritic crystals is at least 0.1 mm˜0.5 mm.
Furthermore, in step A, a cover member with poor electrical conductivity is disposed at a predetermined position on the substrate, and the cover member prevents the growth of dendritic crystals at the predetermined position.
Furthermore, the density of the aforementioned dendritic crystals on the substrate is 3/cm2˜15/cm2.
Furthermore, the substrate is a conductive metal, and in step B, the substrate first undergoes a pre-processing for cleaning. The pre-processing comprises a degreasing procedure used to remove grease and a sensitization procedure, in which the sensitization procedure comprises soaking the substrate in an acidic solution, which increases the adhesion effect of the aforementioned metal ions when carrying out electroplating.
The procedure further comprises a step C, wherein the substrate and the dendritic crystals are coated with an anti-oxidation layer.
Furthermore, the substrate serves as an electrode for electroplating, and in step B, the temperature condition for deposition is 30° C.˜60° C., the deposition time is 2 hours, and the current density is 28 A/dm2˜8 A/dm2. Moreover, the pH value of the copper plating solution used to soak the aforementioned substrate is 0˜2.5.
Furthermore, in step B, the substrate serves as an electrode for electroplating, and the temperature condition for electroplating is 30° C.˜60° C., the electroplating time is 2 hours, and the current density is 2.8 A/dm2˜8 A/dm2. Moreover, the pH value of the copper plating solution used to soak the aforementioned substrate is 1.45, and the specific gravity is 1.190.
The effectiveness of the present invention lies in:
1. In traditional electroplating technology, dendritic crystals have always been regarded as defects, however, the present invention overcomes the prejudice of this technology and uses the dendritic crystals for application in heat transfer components to provide directional heat transfer. Moreover, the present invention uses the dendritic crystals to provide more heat dissipation areas to further improve heat dissipation efficiency.
2. The present invention uses whiskers or processing to provide crystal defects required for the growth of dendritic crystals, thereby enabling superior growth effectiveness of the dendritic crystals. Moreover, the present invention enables control of the position of dendritic crystal growth on the substrate, and thus has superior practical value.
3. The present invention uses whiskers to serve as crystal defects to enable the dendritic crystals to compactly and firmly join to the substrate, thereby further increasing the heat dissipation efficiency of the dendritic crystals.
4. Regarding the plurality of dendritic crystals of the present invention, an interspace is provided between each of the dendritic crystals to serve as heat exchange interspaces to prevent a thermal deposition phenomena from occurring ensure the heat dissipation effect of the dendritic crystals.
5. Regarding the plurality of dendritic crystals of the present invention, when the length of each dendritic crystal is 1 mm˜5 mm, and the interspace between each of the dendritic crystals is at least 0.1 mm˜5 mm, then the heat dissipation effect is optimum.
To enable a further understanding of said objectives and the technological methods of the invention herein, a brief description of the drawings is provided below followed by a detailed description of the preferred embodiments.
The above and other detailed contents, features and effects with respect to the growth method of dendritic crystal structure that provides directional heat transfer of the present invention will be clearly presented in the following preferred embodiments and accompanying drawings.
Referring first to
However, it is hereby specially stated that the substrate (1) is not limited to conductive materials but can also be made from non-conductive materials such as plastic or ceramic. For example, when the substrate (1) is made from plastic or ceramic, then the substrate (1) must first undergo chemical etching and surface activation procedures, which are procedures described in the prior art, and thus not further detailed herein.
It is preferred that a cover member having poor electrical conductivity is first disposed at a predetermined position on the substrate (1), thereby preventing growth of dendritic crystals (13) at the predetermined position. For example, a stainless steel piece is disposed on the periphery of the substrate (1).
B. Depositing a plurality of metal ions on the substrate (1) using deposition method to form a metal layer (12). Because of a current concentration effect, thus, the aforementioned metal ions enable the dendritic crystals (13) to grow on the aforementioned crystal defects (11). However, it is hereby specially stated that the aforementioned metal layer (12) does not have to completely cover the substrate (1), and the current concentration effect principle can be used to independently grow the dendritic crystals (13). Furthermore, the deposition method includes practical methods such as electroplating, physical vapor disposition (PVD), chemical vapor disposition (CVD), and the like. In the present embodiment, the substrate (1) is used to serve as an electrode for electroplating, and an electroplating method is used to serve as an example.
Each of the dendritic crystals (13) comprises a main branch (131) and at least one side branch (132) connected to the main branch (131). It is preferred that the length of the dendritic crystals (13) is 0.1 mm˜15 mm, and the optimal preference is that the length of the dendritic crystals (13) is 1 mm˜5 mm. Moreover, there is an interspace (D) between each of the dendritic crystals (13), and the optimal length of the interspace (D) is 0.1 mm˜5 mm, wherein the specific value of the diagonal length of the height and cross-section of the dendritic crystal (13) is greater than 2 so as to provide adequate space to serve as a heat exchange interspace and prevent a thermal deposition phenomena from occurring. In more detail, current density for the electroplating is 1 A/dm2˜5 A/dm2, and electroplating time is 60 min˜180 min. Referring to
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However, it is important to note that the present invention is not limited by such. Referring to
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A. Providing the aforementioned dendritic crystal structure that provides directional heat transfer.
B. Then, causing the substrate (1) of the aforementioned dendritic crystal structure that provides directional heat transfer to come into contact with a heat source, and transferring the heat produced by the heat source from the substrate (1) in the direction of the main branch (131) and the side branches (132) of the aforementioned dendritic crystal (13).
The following first provides a description of the circumstances of tests carried out using the dendritic crystal structure that provides directional heat transfer of the present invention in actual use.
Referring to
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Referring to Table 1, which discloses thermal resistance values and heat transfer factors of various test pieces compared to those of the dendritic crystal structure of the present invention. The thermal resistance values of an aluminum plate and a micro-perforated plates were 12.35 and 12.10° C./W respectively, and the thermal resistance values of 3 mm and 10 mm dendritic crystals grown on a micro-perforated plate according to the present invention were 9.90 and 9.58° C./W, respectively. The copper plated micro-perforated plates were plated for a period of 30 min and 180 min, respectively, and the respective thermal resistance values were 11.50 and 10.55° C./W. By comparing the differences in thermal resistance values, it can be seen that the thermal resistance values of dendritic crystals grown on a micro-perforated plates according to the present invention are relatively lower. Wherein the preferred optimum is 10 mm.
A thermal imager was further used to film and view the temperature distribution and further analyze the heat dissipation situation and effective radial areas of dendritic copper crystals.
Referring first to
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As additional remarks, the laboratory apparatus used in the present invention include a thermal imager camera and a scanning electron microscope (SEM). Regarding specifications of the thermal imager camera: an infrared detector and an optical imaging lens are used to absorb the infrared radiation energy distribution of a test piece, whereupon an image forms on a photosensitive element of the infrared detector, from which is obtained an infrared thermograph. This thermograph and thermal field distribution of the test piece mutually correspond. Laboratory experiments carried out for the present invention used two thermal imagers for analysis, which separately analyzed macroscopic views and microscopic views to understand heat transfer situations and convection phenomena.
In conclusion, the aforementioned description of the embodiments provide a complete understanding of the operation, use, and effectiveness of the present invention.
It is of course to be understood that the embodiments described herein are merely illustrative of the principles of the invention and that a wide variety of modifications thereto may be effected by persons skilled in the art without departing from the spirit and scope of the invention as set forth in the following claims.
