Method of Manufacturing Thermal Module

Description

FIELD OF THE INVENTION

The present invention relates to a method of manufacturing thermal module, and more particularly to a thermal module manufacturing method that ensures good connection between different heat radiating elements and is environment-friendly.

BACKGROUND OF THE INVENTION

According to the currently available techniques, to form a thermal module by associating heat pipes with a plurality of radiating fins, the joints between the heat pipes and the radiating fins must be welded to ensure firm and stable connection thereof. However, when the heat pipes and the radiating fins are made of two different metals, such as copper heat pipes and aluminum radiating fins, the aluminum radiating fins could not be connected to the copper heat pipe via general welding. Some special types of welding, such as argon arc welding, may be used to weld two pieces of aluminum materials together, but could not weld an aluminum material to other different metal materials, such as copper material. Therefore, when it is desired to weld an aluminum fin to a copper heat pipe, the aluminum fin must be plated first to allow subsequent welding to be successfully completed.

Conventional plating may be generally divided into two types, namely, electric plating and non-electric plating.

The electric plating is an electrochemical process and also an oxidation-reduction process. When it is desired to have a nickel coating formed on a workpiece via electric plating, the workpiece is immersed in a nickel salt solution to serve as a negative electrode, and a nickel plate is used as a positive electrode. When the two electrodes are connected to a direct current (DC) power supply, a nickel coating is deposited on the workpiece.

In the process of forming the nickel coating on the workpiece via electric plating, hydrochloric acid (HCl), industrial nickel sulfate (NiSO₄.6H₂O), nickel chloride crystal (NiCl₂.6H₂O), and boric acid (H₃BO₃) are required.

The non-electric plating is also referred to as chemical nickel plating or autocatalytic plating. In the non-electric plating, no external electric current is supplied. Instead, a reducing agent is used, so that a nickel layer is deposited on an activated surface of the workpiece via autocatalytic reduction. Since nickel has the autocatalytic capability, when the nickel layer starts depositing on the activated workpiece surface, the process will automatically continue until the chemical reduction reaction is ended.

In the process of forming the nickel coating on the workpiece via non-electric plating, industrial nickel sulfate (NiSO₄.6H₂O), boric acid (H₃BO₃), sodium citrate, sodium hypophosphite (NaH₂PO₂.H₂O), and sodium acetate (Ch₃COONa) are required.

To form a deposited coating on the aluminum fins in the conventional thermal module manufacturing method, the following steps are included:

• • 1. Prepare an aluminum material (step 11).
  •  In the first step, an aluminum material, such as an aluminum alloy 5052 or 1050, for forming the radiating fins is provided.
  • 2. Clean the exterior of the aluminum material (step 12).
  •  In the second step, the prepared aluminum material is positioned in a supersonic cleaner, and an amount of acetone (CO(CH₃)₂) is added into the supersonic cleaner to immerse the aluminum material in the acetone. The aluminum material immersed in the acetone is then subjected to supersonic vibration, so as to remove impurities from the surfaces of the aluminum material.
  • 3. Remove any oxidized film from the surfaces of the aluminum material via acid cleaning, and conduct surface activation process on the aluminum material (step 13).
  •  In the third step, the aluminum material is immersed in an acid solution to remove any oxidized film from the surfaces of the aluminum material. Then, the aluminum material is removed from the acid solution and cleansed before being immersed in an activating agent to activate the surfaces of the aluminum material.
  • 4. Form a deposited layer on the aluminum material in a plating bath (step 14).
  •  In the fourth step, the aluminum material is positioned and immersed in a plating bath while the pH value of the plating bath is under control. When a chemical reaction starts in the plating bath, the plating is started.
  • 5. Remove the aluminum material from the plating bath and wash clean and dry the aluminum material (step 15).
  •  In the fifth step, the aluminum material is removed from the plating bath and cleaned using deionized water, and then dried.
  • 6. Weld the aluminum fins to copper heat pipes (step 16).
  •  In the sixth step, the aluminum fins obtained from the fifth step is welded to copper heat pipes.

Either the electric plating or the non-electric plating for forming a plated coating on the workpiece would use a large quantity of acid chemical compositions in the process of plating. The used plating bath is an acid liquid containing heavy metals, which is highly toxic and not suitable for recycling, and is therefore not environment-friendly. When the workpiece to be plated is of a non-conductive substance or a substance with poor electric conductivity, only the non-electric plating can be used to plate the workpiece. However, the non-electric plating has low work efficiency and lacks strict working environmental requirements. Therefore, the plating is easily subject to contamination to produce impurities in the working process, resulting in non-uniform deposited coating and accordingly, unstable welding joints between heat radiating elements and thermal chocking. Further, in the conventional plating methods, the workpiece must be completely immersed in the plating bath. Therefore, it is difficult to form the deposited coating at localized areas on the workpiece while a lot of time and high manufacturing cost are required.

In summary, the conventional thermal module manufacturing method has the following disadvantages: (1) The chemical compositions used are highly toxic and not environment-friendly; (2) Complicated steps are involved to lower the production efficiency; (3) The quality of the deposited coating is not easily controllable; (4) A large quantity of toxic waste liquid is produced to cause environmental pollution; (5) It is uneasy to achieve localized deposited coating; (6) Low working environment requirements tend to result in non-uniform deposited coating containing impurities and oxidations, which in turn causes non-reliable welding joints to adversely affect the connection and heat conductivity between different heat radiating elements; (7) Low production efficiency; and (8) High manufacturing cost.

It is therefore tried by the inventor to develop an improved method of manufacturing thermal module to overcome the disadvantages in the conventional techniques and effectively upgrade the quality of a produced thermal module.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a method of manufacturing thermal module, in which aluminum fins are plated at localized areas thereof in a vacuum environment using physical vapor deposition (PVD), so as to form a nickel coating on predetermined areas on the aluminum fins for welding to a different type of metal element.

Another object of the present invention is to provide a method of manufacturing thermal module, in which aluminum radiating fins are plated without producing toxic waste liquid to hazard the environment.

A further object of the present invention is to provide a method of manufacturing thermal module, in which a dense deposited layer may be obtained to enhance the connection between different heat radiating elements and avoid thermal checking at the joints thereof.

To achieve the above and other objects, the method of manufacturing thermal module according to the present invention uses the physical vapor deposition process to form a localized deposited coating on predetermined areas on aluminum fins for forming the thermal module. To do so, a high voltage is applied across an inert gas to ionize the same. Positive ions are quickly attracted by an electric field near a negative electrode to bombard a target material, such as nickel, at the negative electrode, so that nickel molecules or nickel adatoms are released from the negative electrode and deposited on the aluminum fins as a substrate at a positive electrode. Then, a welding flux, such as Sn—Bi or Sn—Ag—Cu, is applied over areas on heat pipes for forming the thermal module, so that the heat pipes are welded at the areas with welding flux to the areas of the radiating fins with the localized deposited coating to complete the thermal module. Since the localized deposited coating is conducted on the aluminum fins in a vacuum environment, a highly pure nickel coating without impurities and oxidations may be formed without the need of additional chemical compositions, and no chemical pollutant will be produced. The welded joints of the radiating fins and the heat pipes are firm without clearance to avoid thermal chocking and ensure good heat radiating effect.

In brief, the present invention provides the following advantages: (1) Low manufacturing cost; (2) No toxic chemical compositions are involved; (3) Environment friendly; (4) Controllable plating quality; (5) Dense deposited layer; (6) No thermal chocking; (7) High production efficiency; (8) Controllable working area to enable localized deposited coating; and (9) No toxic waste liquid is produced.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein

FIG. 1 is a flowchart showing the steps included in the conventional method of manufacturing a thermal module;

FIG. 2 is a flowchart showing the steps included in the method of manufacturing thermal module according to a preferred embodiment of the present invention;

FIG. 3 is a conceptual view showing a radiating fin material is partially plated via physical vapor deposition according to the method of the present invention;

FIG. 4 shows the forming of a thermal module by joining a plurality of partially plated radiating fins and a plurality of heat pipes according to the method of the present invention;

FIG. 5 is a fragmentary sectional view of FIG. 4; and

FIG. 5A is an enlarged view of the circled area of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the method of manufacturing thermal module according to a preferred embodiment of the present invention, the physical vapor deposition (PVD) process is adopted to form a nickel coating on localized areas on aluminum fins for forming a thermal module. Preferably, the nickel coating is formed using plasma sputtering deposition. The present invention will now be described based on the plasma sputtering deposition process.

In the PVD process, different ways, such as vacuuming, sputtering, ionizing, ion beam, etc., may be used to vaporize pure metal, so that the vapor of the pure metal reacts with gases of hydrocarbon, nitrogen, etc. By “plasma”, it means a partially ionized gas. When a voltage is applied across two corresponding metal electrodes and the molecular concentration of the gas between the two electrodes is within a specific range, secondary electrons emitted from the electrode surfaces due to ion bombardment will obtain sufficient energy in the electric field provided by the electrodes, and will impact on the molecules of the gas between the electrodes to result in different reactions, such as dissociation, ionization, excitation, etc., to produce ions, atoms, radicals, and more electrons, so as to maintain an equilibrium concentration between the particles within the plasma.

FIG. 2 is a flowchart showing the steps included in the method of manufacturing thermal module according to the preferred embodiment of the present invention. As shown, the steps of the method of the present invention include:

• • 1. Provide a material for making radiating fins (step 21).
  •  In the first step of the present invention, a material for making radiating fins 431 is prepared. In the present invention, the material may be an aluminum alloy 5052 or 1050, or other thermal-conductive materials, such as copper.
  • 2. Form a deposited coating on localized areas on the radiating fin material using the physical vapor deposition (PVD) process (step 22).
  •  In the second step, when the sputtering deposition is adopted, metal is heated in a vacuum and vaporized into gas. In the present invention, the sputtering deposition is conducted in a high vacuum below 10−5 Torrs. Please refer to FIG. 3, in which ions and atoms are enlarged in size only for the purpose of clarity in illustration. As shown, a nickel plate is used as a sputtering target at the negative electrode 41, and the radiating fin 431 to be vacuum ion deposited is used as a substrate at the positive electrode 43. A high voltage is applied across an argon atmosphere in a vacuum environment about 10−2 Torrs to produce plasma 42. Part of the argon ions 421 in the plasma 42 separate from the plasma 42 and move toward the sputtering target (i.e. nickel) at the negative electrode 41. The gaseous argon near the negative electrode 41 is ionized to form positive argon ions (Ar+) 422, which bombard the surface of the sputtering target at the negative electrode 41. The sputtering target at the negative electrode 41 bombarded by the positive argon ions 422 will release nickel molecules or nickel adatoms 411, which move into the plasma 42 and are finally transferred to the positive electrode 43 having the material for the radiating fins 431 positioned thereon, and are adsorbed to predetermined areas on the radiating fins 431 to be vacuum ion deposited, so that a thin nickel film 4311 is deposited on the radiating fins 431.
  • 3. Connect the radiating fins to heat pipes, apply a welding flux over areas on the heat pipes to be welded to the radiating fins, and heat the welding flux to a melting point thereof to weld the heat pipes to the radiating fins (step 23).
  •  Please refer to FIGS. 4, 5, and 5A. In the third step, heat pipes 52, which may be made of a copper material, an aluminum material, or other thermally conductive materials, are provided. A welding flux 51, such as Sn—Bi or Sn—Ag—Bi, is applied over areas on the heat pipes 52 to be welded to the radiating fins 431. A suitable fixture is used to tightly clamp the radiating fins 431 and the heat pipes 52 in place before the radiating fins 431 and the heat pipes 52 are heated (not shown). As a result, the heated welding flux 51 located between the nickel coating 4311 on the aluminum radiating fins 431 and the heat pipes 52 firmly bond the radiating fins 431 and the heat pipes 52 together.

By using the physical vapor deposition, the forming of a deposited coating on the radiating fins 431 according to the method of the present invention solves the problem of welding heat radiating elements made of different metal materials, and the deposited coating may be formed only at predetermined localized areas. Further, since the physical vapor deposition adopted by the present invention is a vacuum ion deposition technique, which is not subject to impurities and can therefore produce a highly pure, dense, and uniform deposited layer, which in turn ensures good connection of the heat radiating fins to the heat pipes without the risk of forming any clearance and thermal chocking between them. Moreover, the method of the present invention is cost-effective and environment-friendly because the vacuum ion deposition does not produce toxic waste liquid.

The present invention has been described with a preferred embodiment thereof and it is understood that many changes and modifications in the described embodiment can be carried out without departing from the scope and the spirit of the invention that is intended to be limited only by the appended claims.