Abstract:
The present invention relates to an apparatus for spraying an etchant and a method for manufacturing a printed circuit board. In one exemplary embodiment the apparatus includes a manifold, a plurality of feed pipes in fluid communication with the manifold, each of the feed pipes having a plurality of spray nozzles mounted thereon, the feed pipes cooperatively constitute a spray region, and a pressure-boosting device configured for increasing a spray pressure of the spray nozzles which are located at a central area of the spray region. The apparatus can overcome “the puddle effect” on an upper surface of the printed circuit board.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to an apparatus for spraying an etchant and a method for using such an apparatus to etch a printed circuit board. 
         [0003]    2. Discussion of Related Art 
         [0004]    Recently, as the electronic appliances are becoming smaller in size and diversified in function, printed circuit boards (PCBs) widely used in such electronic appliances are required to have higher circuit density and reliability. 
         [0005]    Usually, a chemical etching process is used for etching a conductive pattern on a copper clad laminate (CCL) as described below. First, a photoresist layer is applied on the CCL by screen printing method. Second, the CCL is driven to pass through an etching bath by a feed roller, thereby an etchant is sprayed simultaneously and evenly onto both an upper surface and a bottom surface of the CCL by a number of spray nozzles. As a result, the copper layer uncovered by the photoresist layer is etched and a conductive pattern is formed on the copper layer. 
         [0006]    This chemical etching process is both cheap and can involve a high level of automation. However, chemical etching also suffers from a problem known as “the puddle effect”. Specifically, “the puddle effect” is due to different refresh rates of etchant between a peripheral area and a central area of the CCL being sprayed, i.e., the refresh rate of etchant in peripheral area is higher than that in central area due to the formation of a puddle of etchant in a central area of the CCL during spraying process. Thus, “the puddle effect” causes different etching speeds between peripheral areas and central areas of an upper surface of the CCL. As a result, the peripheral areas are etched more deeply than the central areas. 
         [0007]    Therefore, there is a desire to develop a new apparatus and method for etching a printed circuit board that can overcome the “the puddle effect”. 
       SUMMARY 
       [0008]    This and other features and advantages of the present invention as well as the preferred embodiments thereof and a metal nanowire array and techniques for fabricating metal nanowire array in accordance with the invention will become apparent from the following detailed description and the descriptions of the drawings. 
         [0009]    In one embodiment, an apparatus for spraying an etchant includes a manifold, a plurality of feed pipes in fluid communication with the manifold, each of the feed pipes having a number of spray nozzles mounted thereon, the feed pipes cooperatively constitute a spray region, and a pressure-boosting device configured for increasing a spray pressure of the spray nozzles which are located in a central area of the spray region. 
         [0010]    In another embodiment, a method for etching a printed circuit board includes the steps of: providing an apparatus as described above; spraying an etchant onto the printed circuit board from the spray nozzles, wherein a spray pressure of the spray nozzles is regulated in a manner such that the spray pressure of the spray nozzles spatially corresponding to a central area of the printed circuit board is greater than that of the spray nozzles spatially corresponding to a peripheral area of the printed circuit board. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Many aspects of the present invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present invention. 
           [0012]      FIG. 1  is a schematic view of an apparatus for spraying an etchant in accordance with the first embodiment; 
           [0013]      FIG. 2  is a schematic view of an apparatus for spraying an etchant in accordance with the second embodiment; 
           [0014]      FIG. 3  is a schematic view of an apparatus for spraying an etchant in accordance with the third embodiment; and 
           [0015]      FIG. 4  is a schematic view of an apparatus for spraying an etchant in accordance with the fourth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    Referring to  FIG. 1 , an apparatus  100  for spraying etchant in accordance with a first embodiment includes pumps  11   a,    11   b,  valves  12   a,    12   b,  manifolds  15   a,    15   b,  a number of feed pipes  13  and a pressure-boosting device  16 . The pump  11   a  and the valve  12   a  are mounted on the manifold  15   a.  The pump  11   b  and the valve  15   b  are mounted on the manifold  15   b.  The valves  12   a,    12   b  are used for regulating a flow of etchant in the manifolds  15   a,    15   b  respectively. The feed pipes  13  are arranged parallel to each other and spaced an equal interval from each other. Two ends of each of the feed pipes  13  are in fluid communication with the manifolds  15   a,    15   b  respectively. Each of the feed pipes  13  is provided with a number of spray nozzles  14  for spraying. In the preferred embodiment, the pressure-boosting device  16  includes a pressure-boosting pipe  162  and a pump  164  mounted on the pressure-boosting pipe  162 . The pressure-boosting pipe  162  is in fluid communication with each of the feed pipes  13  at a central point  132  of each of the feed pipes  13 . The pump  164  is provided to supply additional etchant at high pressure into each of the feed pipes  13  through the pressure-boosting pipe  162 , thereby improving a spray pressure of the nozzles mounted adjacent to the central point  132  on each of the feed pipes  13 . 
         [0017]    As shown in  FIG. 1 , the apparatus  100  is used for etching a printed circuit board  18 . An etchant is sprayed onto an upper surface of the printed circuit board  18 . Generally, the etchant can include a cuprous chloride solution, but other etchants such as ferric trichloride solution can also be used. Because the spray pressure in the section near to the central point  132  of each of the feed pipes  13  is higher than that in the section remote from the central point  132 , the spray speed of the etchant in the section is improved, thus improving a replenishment rate of the etchant in the central area of the printed circuit board  18 , in other words, the etching speed of the central area of the printed circuit board and the peripheral area of the printed circuit board  18  should be roughly identical. 
         [0018]    Specifically, pressure at the central point  132  (hereinafter simply referred to as “central pressure”) is should be 5% to 20% higher than pressure at the two ends of each of the feed pipes  13  (hereinafter simply referred to as “end pressure”). For example, if the central pressure is 2 kilograms of force per square millimeter (kgf/cm 2 ), the end pressure can be in the approximate range from 1.6 kgf/cm 2  to 1.9 kgf/cm 2 . The central pressure can be controlled using the pump  164  and the end pressure can be controlled using the pump  11   a,    11   b.    
         [0019]    Preferably, an oxidant gas such as oxygen or air can be pumped into the pressure-boosting pipe  162 . The oxidant gas can also improve etching speed in the central area of the printed circuit board. First, the oxidant gas improves etchant reactivity. Second, bubbles formed by the oxidant gas forms a number of overfalls (i.e., temporarily shielded surface areas) in the puddle on the central area thereby improving replenishment rate of the etchant in the central area. 
         [0020]    Referring to  FIG. 2 , an apparatus  200  for spraying an etchant in accordance with the second embodiment includes a pump  21 , a valve  22  and feed pipes  23   a,    23   b,    23   c,    23   d,    23   e,    23   f,    23   g,    23   h.  The pump  21  supplies etchant to each of the feed pipes through a manifold  27 . The feed pipes  23   a,    23   b,    23   c,    23   d,    23   e,    23   f,    23   g,    23   h  are disposed at equal intervals. A mass flow controller (MFC)  25  is mounted on each of the feed pipes  23   a,    23   b,    23   c,    23   d,    23   e,    23   f,    23   g,    23   h.  A pressure-boosting pump  26  is mounted on each of the feed pipes  23   d,    23   e.  The pressure-boosting pump  26  is configured for improving a spray pressure in the feed pipes  23   d,    23   e.    
         [0021]    When a printed circuit board  28  is etched with the apparatus  200 , the printed circuit board  28  conveyed by a feed roller (not shown) at a direction that is parallel to the feed pipes or at a certain angle with the feed pipes. Because the spray pressure in the feed pipes  23   d,    23   e  is higher than that in the feed pipes  23   a,    23   b,    23   c,    23   f,    23   g,    23   h,  specifically, the spray pressure in the feed pipes  23   d,    23   e  can be proportionally higher than the spraying pressure in the feed pipes  23   a,    23   b,    23   c,    23   f,    23   g,    23   h  by an amount in the range from 5% to 20%, thus improving replenishment rate of the etchant in the central area of the printed circuit board  28 , in other words, the etching speed of the central area of the printed circuit board and the peripheral area of the printed circuit board  28  become roughly equal. 
         [0022]    Additionally, spray pressure in each of the feed pipes  23   a,    23   b,    23   c,    23   f,    23   g,    23   h  can be controlled by a corresponding MFC in such a manner that spray pressure in each of the feed pipes  23   e,    23   f,    23   g,    23   h  is 5%-20% less than spray pressure in each of the feed pipes  23   d,    23   c,    23   b.    
         [0023]    Referring to  FIG. 3 , an apparatus  300  in accordance with the third embodiment is similar to that of the first embodiment except that the pressure-boosting device includes a number of heating apparatuses  36 . Each of the heating apparatuses  36  surrounds a corresponding feed pipe  33  at central section of the feed pipe  33 . In the preferred embodiment, the heating apparatuses  36  are resistance coils. The heating apparatuses  36  heating the etchant in the feed pipe  33 , the etchant expand thus increasing pressure, and as a result replenishment rate of the etchant in the central area of the printed circuit board  38  is also improved. Furthermore, the etching reaction is also accelerated by increasing temperature of the etchant, in other words, the etching speed of the central area of the printed circuit board and the peripheral area of the printed circuit board  38  become roughly equal. 
         [0024]    Referring to  FIG. 4 , an apparatus  400  in accordance with the fourth embodiment is similar to that of the first embodiment except that the pressure-boosting pump is replaced with a heating apparatus  46 . The heating apparatus  46  and its effect is similar to that of the third embodiment. 
         [0025]    Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the invention. Variations may be made to the embodiments without departing from the spirit of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.