Patent Publication Number: US-2006011469-A1

Title: Coating system for coating a mold

Description:
FIELD OF THE INVENTION  
      The present invention generally relates to coating systems for coating molds, and more particularly to a system that can be used for coating, for example, a core insert of a mold.  
     GENERAL BACKGROUND  
      Currently, digital camera modules are included as a feature in a wide variety of portable electronic devices. Most portable electronic devices are becoming progressively more miniaturized over time, and digital camera modules are correspondingly becoming smaller and smaller. Nevertheless, in spite of the small size of a contemporary digital camera module, consumers still demand excellent imaging. Image quality of a digital camera is mainly dependent upon the optical elements of the digital camera module.  
      Aspheric lenses are very important elements in the digital camera module. Mandy contemporary aspheric lenses are manufactured by way of glass molding. The glass molding process is generally performed under a high temperature and high pressure. Therefore, molds used in the molding process should have excellent chemical stability in order not to react with the glass material. In addition, the molds should also have enough rigidity and excellent mechanical strength in order not to be scratched. Furthermore, the molds should be impact-resistant at high temperatures and high pressures. Moreover, the molds should have excellent machinability, in order for them to be machined precisely and easily to form desired contours of the molded aspheric lenses. Finally, the molds must have a long working lifetime so that the cost of manufacturing aspheric lenses may be reduced.  
      A typical contemporary mold comprises a substrate and a protective film. The substrate is made of stainless steel, carborundum (SiC), or tungsten carbide (WC). The protective film is made of diamond-like carbon film (DLC), noble metals, or alloys of noble metals. The noble metals can be platinum (Pt), iridium (Ir), or ruthenium (Ru). The alloys of noble metals can be iridium-ruthenium (Ir—Ru), platinum-iridium (Pt—Ir), or iridium-rhenium (Ir—Re). The diamond-like carbon film is coated by a conventional sputtering system, and has a short working lifetime. The noble metals or alloys of noble metals have good chemical stability, rigidity and heat-resistance. Nevertheless, protective films made of noble metals or made of alloys of noble metals have poor adhesion with the substrate. Thus the mold coated by the conventional system generally has a short working lifetime, which escalates the cost of producing aspheric lenses.  
      What is needed is a coating system which is capable of forming a good durable protective film on a mold.  
     SUMMARY  
      A system for coating a core insert comprises a vacuum chamber for providing a coating space, a pump system for evacuating the vacuum chamber, a DC power supplier, a DC magnetron, and a gas-in system for providing the vacuum chamber a sputtering gas. The DC power supplier has a negative end and a positive end. The DC magnetron is installed on one side of the vacuum chamber, and connects to the negative end of the DC power supplier.  
      Another system for coating a core insert comprises a vacuum chamber for providing a coating space, a pump system for evacuating the vacuum chamber, an RF power supplier, an RF (radio frequency) magnetron, and a gas-in system for providing the vacuum chamber a sputtering gas. The RF power supplier has two complementary power supply outputs. The RF magnetron is installed on one side of the vacuum chamber, and the RF magnetron connects to one of the two power supply outputs.  
      Other objects, advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional view of a female mold in accordance with a preferred embodiment of the present invention;  
       FIG. 2  is a schematic view of a coating system in accordance with a first preferred embodiment of the present invention; and  
       FIG. 3  is a schematic view of a coating system in accordance with a second preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PERFERRED EMBODIMENTS  
      Referring to  FIG. 1 , in a preferred embodiment of the present invention, a female mold comprises a substrate  11  and a protective film  111 . The protective film  111  is formed on a surface of the substrate  11 . The substrate  111  is made of tungsten carbide (WC) material. The protective film  111  is made of a material selected from the group consisting of tungsten carbide (WC), carbon, a combination of carbon and tungsten carbide (C—WC), boron nitride carbide (BNC), cubic boron nitride (cBN), silicon nitride (Si 3 N 4 ), carborundum (SiC), and zirconia-yttria (ZrO 2 —Y 2 O 3 ). In other exemplary embodiments, the protective film  111  may be formed on a surface of a male mold or a core insert, depending on the particular application.  
      Referring to  FIG. 2 , in a first preferred embodiment of the present invention, a coating system for coating a female mold comprises a vacuum chamber  19  for providing a coating space, a pump system  10  for evacuating the vacuum chamber  19 , a DC power supplier  18 , a DC magnetron  14 , and a gas supply system  16  for supplying a sputtering gas into the vacuum chamber  19 . The DC power supplier  18  comprises a negative end  181  and a positive end  182 . The DC magnetron  14  is disposed in an upper position in the vacuum chamber  19 , and electrically connects to the negative end  181  of the DC power supplier  18 . Further, the coating system comprises a target  13  assembled on the DC magnetron  14 , a cooling system  15  arranged around the DC magnetron  14  and the target  13 , and a base  12  for holding the substrate  11 . The base  12  is disposed in a lower position in the vacuum chamber  19 , opposite to the target  13 . The base  12  is electrically connected to the positive end  182  of the DC power supplier  18 . The target  13  is formed of a material selected from the group consisting of tungsten carbide (WC), carbon, a combination of carbon and tungsten carbide (C—WC), boron nitride carbide (BNC), and cubic boron nitride (cBN).  
      The pump system  10  includes a mechanical pump  101  and a turbopump  102 . The mechanical pump  101  and the turbopump  102  are separately connected to the vacuum chamber  19  through a first valve  105  and a second valve  103  respectively. The mechanical pump  101  is connected to the turbopump  102  through a third valve  106 . The gas supply system  16  comprises three mass flow controllers  166  and four gas valves  161 . A gas, such as argon, a nitride gas, hydrogen, methane, or ethane, flows into the vacuum chamber  19  through a respective one of the mass flow controllers  166  and gas valves  161 .  
      A method of coating a female mold by means of using the above-described coating system includes the steps of: 
          (1) disposing the substrate  11  on the base  13 , and closing the vacuum chamber  19 ;     (2) opening the first valve  105 , in order to preliminarily evacuate the vacuum chamber  19  with the mechanical pump  101 ;     (3) closing the first valve  105 , and opening the second valve  103  and the third valve  106 , in order to evacuate the vacuum chamber  19  until a pressure therein is lower than 2×10 −6  torr by using the turbopump  102  and the mechanical pump  101 ;     (4) introducing a certain amount (e.g. at a flow rate of between 20-200 SCCM) of sputtering gas into the vacuum chamber  19  through the gas supply system  16 ;     (5) powering on the DC power supplier  18 , in order to apply a bias voltage to the base  12  and the substrate  11 , the bias voltage being in the range from −20 volts to −200 volts, and preferably being in the range from 40 volts to −150 volts;     (6) allowing the sputtering gas to be ionized into an ionized state, with a plasma being formed between the target  13  and the substrate  11 , the ionized gas being accelerated by the DC magnetron  14  toward the target  13  to physically bombard the target  13  and dislodge atoms from the target  13 , the atoms thereby escaping from the target  13  and depositing on the surface of the substrate  11 , thus forming a protective film  111  (see  FIG. 1 ) on the substrate  11 ;     (7) powering off the DC power supplier  18  and opening the vacuum chamber  19 , thereby obtaining a female mold having a protective film  111  formed thereon.        

      In step (5), the cooling system  15  can be employed to cool the target.  
      Referring to  FIG. 3 , in a second preferred embodiment of the present invention, a coating system for coating a female mold includes a vacuum chamber  29  for providing a coating space, a pump system  20  for evacuating the vacuum chamber  29 , an radio frequency (RF) power supplier  28 , an RF magnetron  24 , and a gas supply system  26  for supplying a sputtering gas into the vacuum chamber  29 . The RF magnetron  24  is disposed in an upper position in the vacuum chamber  29 . Further, the coating system comprises a target  23  assembled on the RF magnetron  24 , a cooling system  25  disposed around the RF magnetron  24  and the target  23 , and a base  22  for holding the substrate  11 . The base  22  is disposed in a lower position in the vacuum chamber  29 , opposite from the target  23 . The RF magnetron  24  and the base  22  are separately electrically connected to opposite electrodes of the RF power supplier  28 . An operational frequency of the RF power supplier  28  is approximately 13.56 MHz. The target  23  is formed of a material selected from the group consisting of tungsten carbide (WC), carbon, a combination of carbon and tungsten carbide (C—WC), boron nitride carbide (BNC), cubic boron nitride (cBN), silicon nitride (Si 3 N 4 ), carborundum (SiC), and zirconia-yttria (ZrO 2 —Y 2 O 3 ). A metal backing plate  27  is sandwiched between the target  23  and the RF magnetron  24 , for transferring current to the target  23  if the target  23  is formed of an insulating material. The material of the backing plate  27  can be copper, or an alloy of copper and molybdenum.  
      The pump system  20  includes a mechanical pump  201  and a turbopump  202 . The mechanical pump  201  and the turbopump  202  are separately connected to the vacuum chamber  29  through a first valve  205  and a second valve  203 . The mechanical pump  201  is connected to the turbo pump  202  through a third valve  206 . The gas supply system  26  includes three mass flow controllers  266  and four gas valves  261 . A gas, such as argon, a nitride gas, hydrogen, methane, or ethane, flows into the vacuum chamber  29  through a respective one of the mass flow controllers  266  and gas valves  261 .  
      A method of coating a female mold by means of using the above-described coating system includes the steps of: 
          (1) disposing the substrate  11  on the base  22 , and closing the vacuum chamber  29 ;     (2) opening the first valve  205 , in order to preliminarily evacuate the vacuum chamber  29  with the mechanical pump  201 ;     (3) closing the first valve  205 , and opening the second valve  203  and the third valve  201 , in order to evacuate the vacuum chamber  29  until a pressure therein is lower than 2×10 −6  torr by using the turbopump  202  and the mechanical pump  201 ;     (4) introducing a certain amount (e.g. at a flow rate of between 20-200 SCCM) of sputtering gas into the vacuum chamber  29  through the gas supply system  26 ;     (5) powering on the RF power supplier  28 , in order to supply electric power to the target  23  and the substrate  11 , wherein a proportion of the electric power that is transferred to the target  23  is around 70%-98%, and a proportion of the electric power that is transferred to the substrate  11  is around 2%-30%;     (6) allowing the sputtering gas to be ionized into an ionized state, with a plasma being formed between the target  23  and the substrate  11 , the ionized gas being accelerated by the RF magnetron  24  toward the target  23  to physically bombard the target  23  and dislodge atoms from the target  23 , the atoms thereby escaping from the target  23  and depositing on the surface of the substrate  11 , thus forming a protective film  111  (see  FIG. 1 ) on the substrate  11 ;     (7) powering off the RF power supplier  28  and opening the vacuum chamber  29 , thereby obtaining a female mold having a protective film  111  formed thereon.        

      In step (5), the cooling system  25  can be started for cooling the target.  
      It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.