Abstract:
An apparatus for metal plating on a substrate with through-holes includes a chamber that the substrate is disposed inside the chamber to be divided into two sections. A pressure generator and a pressure controller are connected to this and correspond to two sides of the substrate respectively. The pressure generator is used for pumping a electrolyte flowed parallel to the surface of the substrate into the chamber. The pressure controller is used for channeling the electrolyte off the chamber and controlling the pressure differences between the two sides of the substrate. So that the electrolyte flowed parallel to the surface of the substrate is pumped by the pressure generator and it passes several through-holes to control the thickness of metal plating on the.substrate and inner walls of the through-holes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 094147334 filed in Taiwan, R.O.C. on Dec. 29, 2005, the entire contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of Invention  
         [0003]     The present invention relates to an apparatus for forming a metal film, in particular an apparatus for forming a metal film with a uniform thickness on the surface of a substrate and on the inner wall of a through-hole in the substrate.  
         [0004]     2. Related Art  
         [0005]     With the development of electronic devices, printed circuit boards (PCBs) have been gradually developed for high density packaging, such that the line width of a metal circuit formed on a surface has become smaller, and the aperture of a through-hole in the surface for a pin of an electronic element to pass through has been gradually reduced. Therefore, the thickness of the metal films formed on printed circuit boards must be highly uniform; and defects of the metal films must be minimized, so as to improve the ductility and tensile strength, and prevent printed circuit boards from being cracked and broken due to thinner circuits and insufficient strength.  
         [0006]     Japanese Patent JP56-58999 provides an apparatus for washing a substrate on which a metal film is to be formed, while the substrate is conveyed between two tanks, such that the time consumed for washing the substrate is reduced. In US Patent U.S. Pat. No. 5,077,099, a periodic vibration source is provided for vibrating the substrate. The electrolyte is driven by vibration on the surface of a substrate and is circulated. The method controls the thickness of a metal film uniformly. In US Patent U.S. Pat. No. 5,077,099, only the thickness of the metal film on the surface of the substrate can be improved. But for the metal film on the inner wall of the through-holes in the substrate, the electrolyte cannot flow within the through-holes and even cannot wet the through-holes effectively. Moreover, as the dimension of through-hole reduces, the aspect ratio, the proportion between the axial length and the radial width increases. So that forming metal film within the through-holes become more difficult. Also the metal films formed on the inner walls of the through-holes are extremely poor, and affect the yield of printed circuit boards. Therefore, how to design a desirable metal film technology directed to through-holes with small apertures and high aspect ratios has become an important issue.  
       SUMMARY OF THE INVENTION  
       [0007]     In view of aforementioned problem, the object of the present invention is to provide an apparatus for forming a metal film to solve the problem that prior to when the metal film is formed on the substrate, the thickness of the metal films on the surface of a substrate and on inner walls of through-holes is non-uniform.  
         [0008]     In order to achieve the aforementioned object, an apparatus for forming a metal film is provided to form the metal film on the substrate with at least one through-hole, and comprises a sealed chamber, a pressure generator, and a pressure controller. The substrate is disposed within the sealed chamber to divide the sealed chamber into a first section and a second section. The pressure generator and the pressure controller are connected to the sealed chamber and correspond to the first and second sections, respectively. The pressure generator is used to pump a electrolyte and enable it to flow in parallel with the surface of the substrate, and the pressure controller is used to derive the electrolyte and control the pressure difference between the two sides of the substrate. Thereby, the electrolyte is pumped by the pressure generator to flow into the sealed chamber, so as to flow in parallel with the surface of the substrate and to flow through the through-holes. Therefore, through the adjustment of the pressure controller, the thickness of the metal films formed respectively on the surface of the substrate and on the inner walls of the through-holes is controlled.  
         [0009]     According to another embodiment of the present invention, the apparatus for forming a metal film further comprises an electrolyte stabilizing device for stirring the electrolyte flowing into the sealed chamber, so as to enable solute and solvent in the electrolyte to be fully mixed, such that the ingredients are more uniform.  
         [0010]     According to another embodiment of the present invention, the apparatus for forming a metal film further comprises a temperature controller for controlling the temperature of the electrolyte flowing into the sealed chamber, so as to control the conditions for forming the metal film.  
         [0011]     According to another embodiment of the present invention, the apparatus for forming a metal film further comprises a laminar flow stabilizing device for eliminating the boundary layer of the fluid flowing into the sealed chamber, such that the flow rate of the electrolyte on the surface of the substrate will become more uniform.  
         [0012]     According to another embodiment of the present invention, the apparatus for forming a metal film further comprises a flow rate controlling element disposed in the sealed chamber. Through adjusting the space between the flow rate controlling element and the surface of the substrate, the flow rate of the fluid flowing on the surface of the substrate can be adjusted.  
         [0013]     According to another embodiment of the present invention, the apparatus for forming a metal film further comprises an electric field controller with two electrodes. Two electrodes are immersed in the electrolyte in the sealed chamber and located on the two sides of the substrate, so as to generate an electric filed. Thus, the substrate is located in the electric field to strengthen the metal film forming effect.  
         [0014]     Further scope of applicability of the present invention. will become apparent from the detailed description given hereinafter. 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.  
         [0015]     Both the foregoing general description about the present invention and the following detailed description about the embodiments are intended to demonstrate and explain the principles of the present invention, and to provide further explanation of the present invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The present invention will become more fully understood from the detailed description given herein below for illustration only, and which thus is not limitative of the present invention, and wherein:  
         [0017]      FIG. 1  shows an apparatus for forming metal film according to the present invention;  
         [0018]      FIG. 2  is an exploded view of the apparatus for forming metal film according to a first embodiment of the present invention;  
         [0019]      FIG. 3  is a schematic cross-sectional view depicted in  FIG. 2 ;  
         [0020]      FIG. 4  is a system block diagram depicted in  FIG. 2 ;  
         [0021]      FIG. 5  is a system block diagram of the apparatus for forming metal film according to a second embodiment of the present invention;  
         [0022]      FIGS. 6 and 7  are system block diagrams of other implementation aspects according to the second embodiment of the present invention;  
         [0023]      FIG. 8  is a system block diagram of the apparatus for forming metal film according to a third embodiment of the present invention; and  
         [0024]      FIG. 9  is a system block diagram of the apparatus for forming metal film according to a fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     In order to make the objects, structures, features, and functions of the present invention more comprehensible, preferred embodiments accompanied with figures are described in detail below.  
         [0026]     Please refer to  FIG. 1  of an apparatus for forming a metal film according to the present invention. The apparatus for forming metal film comprises a frame  1 , a delivery system  2 , and a plurality of electrolyte tanks A, B, C, D, E, F, G, H, and I. The delivery system  2  is disposed above the frame  1  to move a substrate to be processed among each of the electrolyte tanks A, B, C, D, E, F, G, H, and I. Each of the electrolyte tanks A, B, C,.D, E, F, G, H, and I is used to conduct a surface treatment process and a metal film forming process, respectively. The surface treatment process is used to form a substrate film on the surface of the substrate, and after that, a catalyst is coated on the surface of the substrate in a specific pattern. Next, the metal film forming process is conducted to deposit the metal on the region coated with the catalyst, so as to form the metal film with a predetermined pattern. The apparatus for forming a metal film of the present invention can be applied in each of the electrolyte tanks to enable the plate solutions with different ingredients or the deionized water to flow on the surface of the substrate uniformly, so as to control the grown thickness of the metal film.  
         [0027]      FIGS. 2, 3 , and  4  show the apparatus for forming a metal film according to the first embodiment of the present invention. The apparatus for forming a metal film can be applied to any of the aforementioned electrolyte tanks. Each of the electrolyte tanks includes a sealed chamber  10 , and the substrate  20  to be processed is disposed within the sealed chamber  10  and divides the sealed chamber  10  into a first section and a second section. Additionally, each substrate  20  is provided with a plurality of through-holes  21 , such that the fluid may flow through the substrate  20  and circulate between two sides of the substrate  20 .  
         [0028]     A fluid feeding element  11  and a fluid deriving element  12  are further disposed within the sealed chamber  10 . The fluid feeding element  11  is shaped as a frame. Also, a circulating pipe  111  is disposed within the fluid feeding element  11  and connected to a pressure generating apparatus  31  via a connecting tube, such that the electrolyte or the deionized water is fed into the circulating pipe  111  and flows into the sealed chamber  10  via the apertures  112  formed at the inner edge of the fluid feeding element  11 . The fluid deriving element  12  is substantially the same as the fluid feeding element  11 , shaped as a frame. Also, a circulating pipe  121  is disposed within the fluid deriving element  12 , and a plurality of apertures  122  is formed in the inner edge and used for absorbing the electrolyte in the sealed chamber  10 , and then deriving the electrolyte out of the sealed chamber  10  via a pressure controller  32  connected to the fluid deriving element  12 . The fluid feeding element  11  and the fluid deriving element  12  are disposed in parallel with the two sides of the substrate  20 , such that the pressure generator  31  and the pressure controller  32  are correspondingly connected to the first and second sections of the sealed chamber  10 , respectively.  
         [0029]     The fluid feeding element  11  and the fluid deriving element  12  are disposed at the two sides of the substrate  20  in parallel with each other, such that the direction of the apertures  112  and  122  in the inner edge is parallel to the surface of the substrate  20 . Therefore, both the fluid fed into the sealed chamber  10  through the fluid feeding element land the fluid ,such as the electrolyte or the deionized water, drawn out by the fluid deriving element  12  flow in the direction parallel to the surface of the substrate  20  and flow through the through-holes  21  in the direction perpendicular to the substrate  20 . The pressure generator  31  can be a fluid pump, and the pressure controller  32  can be a valve. The pressure difference between the two sides of the substrate  20  is controlled through adjusting the pressure generator  31  together with the pressure controller  32 , so as to adjust the flow rate. Thus, the flow rate  41  of the fluid flowing in parallel with the surface of the substrate  20  is the same as that of the flow rate  42  of the fluid flowing through the through-holes  21 . As such, the conditions for forming the metal film on the surface of the substrate  20  are similar to those for forming it on the inner walls of the through-holes  21 , such that the growing rate of the metal film on the surface of the substrate  20  is the same as that of the metal film on the inner walls of the through-holes  21 . Therefore, the thickness of the metal film is uniform and the electrical conductivity or the stress is relatively uniform, and no significant difference occurs. A predetermined pattern is formed on the surface of the substrate  20  via the catalyst. When the substrate  20  is immersed in the electrolyte, an ion or a proton exchange occurs between the ingredients of the electrolyte and the catalyst, such that the metal is precipitated and plated on the substrate to form a pattern.  
         [0030]     Referring to  FIG. 5 , it shows the apparatus for forming a metal film according to the second embodiment of the present invention. As shown in  FIG. 5 , an electrolyte stabilizing device  51  is further disposed between the pressure generator  31  and the sealed chamber  10 . The electrolyte stabilizing device  51  is used to stir the electrolyte, such that the solute and the solvent in the electrolyte are mixed more uniformly to further stabilize the quality of the electrolyte. For the embodiment, the electrolyte stabilizing device  51  is a stirring device, which stirs the electrolyte before it flows into the sealed chamber  10 , so as to further stabilize the feature of the electrolyte.  
         [0031]     Referring to  FIGS. 6 and 7 , the electrolyte stabilizing device can be a gas source  52 , which feeds the gas into the electrolyte and stirs the electrolyte by tiny bubbles. The gas is fed into the electrolyte before it flows into the sealed chamber  10  and stabilizes the electrolyte in advance, as shown in  FIG. 6 . The gas source  52  also can be connected to the fluid feeding element  31 , and then the gas is directly fed into the sealed chamber  10  to stir and stabilize the electrolyte in the sealed chamber  10 , as shown in  FIG. 7 .  
         [0032]     Please refer to  FIG. 8  of a system block diagram of the apparatus for forming a metal film according to the third embodiment of the present invention. In order to control the condition of the electrolyte effectively, a temperature controller  53  and a laminar flow stabilizing device  54  are disposed between the pressure generator  31  and the pressure controller  32  in this embodiment, and the status of the fluid boundary layer of the electrolyte is changed before being fed into the sealed chamber  10  by the pressure generating apparatus  31 , such that the flow rate of the electrolyte flowing in parallel with the surface of the substrate- 20  is uniform and stable.  
         [0033]     The temperature controller  53  includes a heater, used to control the temperature of the electrolyte. Thus, an optimal reaction temperature is achieved before the electrolyte flows into the sealed chamber  10 , so as to enhance the rate for forming the metal film. The laminar flow stabilizing device  54  is consisted of a porous medium. Since the thickness of the boundary layer of the fluid is gradually increased due to the flowing of the electrolyte within the pipe, the flow rate of the electrolyte is not uniform when the electrolyte reaches the substrate  20 . If the electrolyte flows through the laminar flow stabilizing device  54  before flowing into the sealed chamber  10 , the laminar flow phenomenon is destroyed, and the boundary layer grows once again. Thus; when the electrolyte flows into the sealed chamber  10 , the flow rate becomes more uniform, such that the growth rate and the thickness of the metal film will be relatively uniform.  
         [0034]     Additionally, a flow rate controlling element  55  is further provided in this embodiment, which is a plate body moving relative to the substrate  20  to adjust the space W between the flow rate controlling element  55  and the substrate  20 , the flow rate of the electrolyte flowing on the surface of the substrate  20  can be changed. Thus, the flow rate of the electrolyte can be further adjusted.  
         [0035]     Please refer to  FIG. 9  of a schematic view of the apparatus for forming a metal film according to the fourth embodiment of the present invention. In order to further control the metal film forming process and strengthen the metal film forming rate, an electric field controller  56  is disposed to generate an alternating current or a direct current. The electric field controller  56  has two electrodes  561  disposed within the sealed chamber  10 , immersed in the electrolyte, and located on the two sides of the substrate  20  respectively. Through applying a direct current or an alternating current, the substrate  20  is disposed within an electric field to strengthen the metal film forming rate.  
         [0036]     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.