Patent Publication Number: US-2022217839-A1

Title: Method for manufacturing circuit board with high light reflectivity

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional application of patent application Ser. No. 17/036574 filed on Sep. 29, 2020, which is based on and claims priority to China Patent Application No. 202011009995.X filed on Sep. 23, 2020 and China Patent Application No. 202010592598.3 field on Jun. 24, 2020, the contents of which are incorporated by reference herein. 
    
    
     FIELD 
     The subject matter herein generally relates to circuit boards, in particular to a circuit board with a high light reflectivity and a method for manufacturing the same. 
     BACKGROUND 
     In the production of a mini-LED backlight, a LED lamp can be surface-mounted on a circuit board. The higher the light reflectivity of the circuit board, the higher the light emitting efficiency of the LED lamp. To improve the light emitting efficiency of the LED lamp, a solder mask with a high light reflectivity can be placed to cover surfaces of the circuit board. However, a base board layer in an area for mounting the LED lamp has a low light reflectivity which is inconsistent with the light reflectivity of the outer solder mask, which affects the light emitting efficiency and the light emitting uniformity of the mini-LED backlight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present disclosure will now be described, by way of embodiments, with reference to the attached figures. 
         FIG. 1  is a cross-sectional view of an inner wiring base board in accordance with an embodiment. 
         FIG. 2  is a cross-sectional view showing a first wiring base board and a second wiring base board provided on two sides of the inner wiring base board of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a laminated structure formed by pressing the first base, the second wiring base board, and the inner wiring base board of  FIG. 2  together. 
         FIG. 4  is a cross-sectional view showing a conductive hole formed on the laminated structure of  FIG. 3 . 
         FIG. 5  is a cross-sectional view showing outer conductor layers formed on the structure shown in  FIG. 4 . 
         FIG. 6  is a cross-sectional view showing connecting pads formed on the structure shown in  FIG. 5 . 
         FIG. 7  is a cross-sectional view showing a solder mask formed on the structure shown in  FIG. 6 . 
         FIG. 8  is a cross-sectional view of a circuit board in accordance with another embodiment. 
         FIG. 9  is a top view of the first conductor layer of the circuit board of  FIG. 8 . 
         FIG. 10  is a schematic view of the first connecting pad and the circuit pattern of the circuit board of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale, and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure. 
     The term “comprising,” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series, and the like. 
       FIGS. 1 to 7  illustrate a method for manufacturing a circuit board in accordance with an embodiment. The circuit board has a high light reflectivity. The method includes the following steps S 1  to S 4 . 
     In step S 1 , referring to  FIG. 1 , an inner wiring base board  10  is provided. 
     The inner wiring base board  10  includes an insulation layer  11  and two inner conductor layers  13  on opposite surfaces of the insulation layer  11 . One inner conductor layer  13  defines a first opening  131  and the insulation layer  11  is exposed in the first opening  131 . 
     A material of the insulation layer  11  may be, but is not limited to, prepreg (PP) including glass fiber and epoxy resin, polyimide, polyethylene terephthalate, or polyethylene naphthalate. In the embodiment, the material of the insulation layer  11  is the prepreg including glass fiber and epoxy resin. 
     A material of the inner conductor layer  13  may be, but is not limited to, metal, such as copper, silver, or an alloy thereof. In the embodiment, the material of the inner conductor layer  13  is copper. 
     Specifically, step S 1  provides a double-sided copper clad laminate including the insulation layer  11  and two copper layer on opposite surfaces of the insulation layer  11 . The double-sided copper clad laminate is machine-drilled to form a through hole, the through hole is plated or conductive material is infilled in the through hole. An image transfer process and an etching process are also performed. 
     In step S 2 , referring to  FIGS. 2 and 3 , a base board  30  with a high light reflectivity is fixed in the first opening  131 , and a first wiring base board  50  and a second wiring base board  60  are pressed onto opposite surfaces of the inner wiring base board  10 , thereby obtaining a laminated structure  70 . The base board  30  is embedded in the laminated structure  70 . 
     The first wiring base board  50  faces the base board  30 . The first wiring base board  50  includes a first insulation layer  51  and a first metal layer  53  stacked on the first insulation layer  51 . The first insulation layer  51  defines a second opening  511  corresponding in position to the first opening  131 . The first insulation layer  51  covers one inner conductor layer  13 , and at least a portion of the base board  30  is exposed in the second opening  511 . The first metal layer  53  covers the first insulation layer  51  and the base board  30 . 
     The second wiring base board  60  includes a second insulation layer  61  and a second metal layer  63 . The second insulation layer  61  covers the other inner conductor layer  13  and is connected to the insulation layer  11 . 
     A material of the first insulation layer  51  and a material of the second insulation layer  61  may both be, but not limited to, prepreg (PP) including glass fiber and epoxy resin, polyimide, polyethylene terephthalate, or polyethylene naphthalate. In the embodiment, the material of the first insulation layer  51  is the prepreg including glass fiber  512  and epoxy resin  513 . A material of the first metal layer  53  and a material of the second metal layer  53  may both be, but not limited to, copper, silver, or an alloy thereof. In the embodiment, materials of the first metal layer  53  and the second metal layer  63  are copper. 
     The base board  30  is substantially the shape of an inverted T. The base board  30  includes a plate portion  31  and a protrusion portion  33  protruding from a side of the plate portion  31 . The plate portion  31  is received in the first opening  131 . A size of the plate portion  31  is matched with a size of the first opening  131 , so that an edge of the plate portion  31  is in contact with a sidewall of the first opening  131 . In the embodiment, a thickness of the plate portion  31  is the same as a depth of the first opening  131 , so that a surface of the plate portion  31  away from the insulation layer  11  is flush with a surface of the inner conductor layer  13  away from the insulation layer  11 , the inner conductor layer  13  having the first opening  131 . 
     The size of the protrusion portion  33  is matched with the size of the second opening  511 , so that the protrusion portion  33  can be pressed through the second opening  511 . The protrusion portion  33  includes a mounting surface  331  away from the plate portion  31 . An edge of the protrusion portion  33  is a predetermined distance from an edge of the plate portion  31  to form a dam structure  32 , the dam structure  32  prevents the molten epoxy resin from flowing to the mounting surface  331  when the first insulation layer  51  is pressed. After being pressed, the first insulation layer  51  covers one inner conductor layer  13 , the glass fiber  512  is not in contact with the base board  30 , and the epoxy resin  513  infills the dam structure  32 . The surface of the first insulation layer  51  away from the inner wiring base board  13  is flush with the mounting surface  331  of the protrusion portion  33 . 
     A material of the base board  30  may be, but not limited to, ceramic. In some embodiments, a reflectivity of the base board  30  is about 92% to 97%. 
     In step S 3 , referring to  FIGS. 4 to 6 , a first conductor layer  81  and a second conductor layer  83  are formed on opposite surfaces of the laminated structure  70 . The first conductor layer  81  includes a plurality of circuit patterns  813  and a plurality of connecting pads  815 . The circuit patterns  813  are located on the insulation layer  51 . The connecting pads  815  are on the mounting surface  331  and are electrically connected to the circuit patterns  813 . The second conductor layer  83  is located on the second insulation layer  61 . The connecting pads  815  are electrically connected to other electronic elements, such as a light emitting element. 
     Specifically, step S 3  includes steps S 31  to S 33 . 
     In step S 31 , a plurality of through holes are formed on the laminated structure  70 , the laminated structure  70  is plated to form a first plating layer  82 , a second plating layer  84 , and a plurality of conductive holes  74 . Each of the conductive holes  74  connects the first plating layer  82 , the second plating layer  84 , and the two inner conductor layers  13 . The first plating layer  82  covers a surface of the first metal layer  53  away from the second metal layer  63 . The second plating layer  84  covers a surface of the second metal layer  63  away from the first metal layer  53 . The conductive holes  74  are formed by plating the through holes. 
     Each through hole forming a conductive hole  74  penetrates opposite surfaces of the laminated structure  70 . The through holes may be formed by laser cutting, mechanizing drilling, or the like. The number of through holes may be set according to needs. In the embodiments, there are two through holes located adjacent to opposite sides of the base board  30 . 
     The material used for electroplating may be, but not limited to, copper, silver, or alloys thereof. In the embodiment, the material used for electroplating is copper. 
     In step S 32 , the first plating layer  82  and the first metal layer  53  are etched to form a plurality of circuit patterns  813 , and the second plating layer  84  and the second metal layer  63  are etched to form the second conductor layer  83 . Each of the circuit patterns  813  includes the first plating layer  82  and the first metal layer  53 . The mounting surface  331  is exposed outside the circuit patterns  813 . 
     In step S 33 , a plurality of connecting pads  815  are formed on the mounting surface  331 . The connecting pads  815  may be formed by a modified semi-additive process well known in the art. In the embodiment, the material of the connecting pads  815  is copper. 
     In step S 4 , referring to  FIG. 7 , solder masks  90  are formed on outer surfaces of the first conductor layer  81  and the second conductor layer  83 . The mounting surface  331  is exposed outside the solder masks  90 . The connecting pads  815  on the mounting surface  331  are electrically connected to a light emitting element  200 . 
     The solder masks  90  covers all of the exposed surfaces of the circuit patterns  813 , the first insulation layer  51 , the second conductor layer  83 , and the second insulation layer  61 , and infills the conductive holes  74 . The solder masks  90  may be formed by a photolithography process with materials having a high light reflectivity. In some embodiments, the solder masks  90  have a light reflectivity of about 92% to 95%. 
       FIG. 7  illustrates an embodiment of a circuit board  100  with a high light reflectivity. The circuit board  100  includes an inner wiring base board  10 , a base board  30  with a high light reflectivity, a first insulation layer  51 , a first conductor layer  81 , a second insulation layer  61 , and a second conductor layer  83 . The inner wiring base board  10  defines a first opening  131 , and the base board  30  is fixed in the first opening  131 . The first insulation layer  51  is stacked on a surface of the inner wiring base board  10  and defines a second opening  511  corresponding in position to the first opening  131 . At least a portion of the base board  30  is exposed in the second opening  511 . The first conductor layer  81  is located on a surface of the first insulation layer  51  away from the inner wiring base board  10  and includes a plurality of connecting pads  815  arranged on the base board  30 . The second insulation layer  61  is stacked on the other surface of the inner wiring base board  10 , and the second conductor layer  83  is located on the surface of the second insulation layer  61  away from the inner wiring base board  10 . 
     The inner wiring base board  10  includes an insulation layer  11  and two inner conductor layers  13  on opposite surfaces of the insulation layer  11 . One inner conductor layer  13  defines a first opening  131 , the insulation layer  11  is exposed in the first opening  131 . 
     A material of the insulation layer  11  may be, but not limited to, prepreg (PP) including glass fiber and epoxy resin, polyimide, polyethylene terephthalate, or polyethylene naphthalate. In the embodiment, the material of the insulation layer  11  is the prepreg including glass fiber and epoxy resin. 
     A material of the first insulation layer  51  and a material of the second insulation  layer  61  may both be, but not limited to, prepreg (PP) including glass fiber and epoxy resin, polyimide, polyethylene terephthalate, or polyethylene naphthalate. In the embodiment, the material of the first insulation layer  51  is the prepreg including glass fiber  512  and epoxy resin  513 . Materials of the inner conductor layers  13 , the first conductor layer  81 , and the second conductor layer  83  may be copper, silver, or alloy thereof. In the embodiment, the materials of the inner conductor layers  13  and the first conductor layer  81  are all copper. 
     The base board  30  is substantially an inverted T in shape. The base board  30  includes a plate portion  31  and a protrusion portion  33  protruding from a side of the plate portion  31 . The plate portion  31  is received in the first opening  131 . A size of the plate portion  31  is matched with a size of the first opening  131 , so that an edge of the plate portion  31  is in contact with a sidewall of the first opening  131 . In the embodiment, a thickness of the plate portion  31  is the same as a depth of the first opening  131 , so that a surface of the plate portion  31  away from the insulation layer  11  is flush with a surface of the inner conductor layer  13  away from the insulation layer  11 , the inner conductor layer having the first opening  131 . 
     The size of the protrusion portion  33  is matched with the size of the second opening  511 , so that the protrusion portion  33  can be pressed through the second opening  511 . The protrusion portion  33  includes a mounting surface  331  away from the plate portion  31 . An edge of the protrusion portion  33  is a predetermined distance from an edge  of the plate portion  31  to form a dam structure  32 , the dam structure  32  prevents the molten epoxy resin from flowing to the mounting surface  331  when the first insulation layer  51  is pressed. The glass fiber  512  is not in contact with the base board  30 , and the epoxy resin  513  infills the dam structure  32 . The surface of the first insulation layer  51  away from the inner wiring base board  13  is flush with the mounting surface  331  of the protrusion portion  33 . 
     A material of the base board  30  may be, but is not limited to, ceramic. In some embodiments, a light reflectivity of the base board  30  is about 92% to 97%. 
     The first conductor layer  81  further includes a plurality of circuit patterns  813 , the circuit patterns  813  are located on the first insulation layer  51 . Each of the circuit patterns  813  includes the first plating layer  82  and the first metal layer  53 . The mounting surface  331  is exposed outside the circuit patterns  813 . 
     The connecting pads  815  are located on the mounting surface  331  and are electrically connected to the circuit patterns  813 . 
     In some embodiments, the circuit board  100  further includes a plurality of conductive holes  74 . Each of the conductive holes  74  electrically connects the first conductor layer  81 , the second conductor layer  83 , and the two inner conductor layers  13 . 
     In some embodiments, the circuit board  100  further includes solder masks  90 . The solder masks  90  are arranged on outer surfaces of the first conductor layer  81  and the  second conductor layer  83 . The mounting surface  331  is exposed outside the solder masks  90 . The connecting pads  815  on the mounting surface  331  is electrically connected to a light emitting element  200 . The solder masks  90  cover all of the exposed surfaces of the circuit patterns  813 , the first insulation layer  51 , the second conductor layer  83 , and the second insulation layer  61 , and infills the conductive holes  74 . The solder masks  90  may be formed by a photolithography process with materials with a high reflectivity. In some embodiments, the solder masks  90  have a light reflectivity of about 92% to 95%. 
       FIGS. 8 to 10  illustrate a modified embodiment of the circuit board (circuit board  100 ′). Each of the connecting pads  815 ′ of the first conductor layer  81 ′ includes the first metal layer  53 ′ and the first plating layer  82 ′, and materials of the first metal layer  53 ′ and the first plating layer  82 ′ are copper. A material of each of the circuit patterns  813 ′ of the first conductor layer  81 ′ includes silver, and a light reflectivity of the circuit patterns  813 ′ is not less than 95%. The light emitting element  200 ′ is electrically connected to a solder pad  109  through the connecting pads  815 ′ and the circuit patterns  813 ′. Each of the connecting pads  815 ′ may be trapezoidal in shape, and each of the connecting pads  815 ′ may be partially overlapped with a circuit pattern  813 ′. In other embodiment, the circuit patterns  813 ′ may be formed on other materials with a high light reflectivity. When forming the first conductor layer  81 ′, first, the first plating layer  82 ′ and the first metal layer  53 ′ are etched to form the connecting pads  815 ′, and then a plurality of circuit patterns  813 ′ are formed. The circuit patterns  813 ′ may be formed by curing a silver  paste. 
     In the circuit board  100 , the connecting pads  815  for mounting the light emitting element  200  are arranged on the base board  30  which has a high light reflectivity, which improves the light reflectivity of that area, so that the light emitting efficiency of the light emitting element  200  is improved. In addition, the light reflectivity of the base board  30  is approximately the same as the light reflectivity of the solder masks  90 , which improves the uniformity of light emission of the light emitting element  200 . Furthermore, the circuit patterns  813 ′ are made of a material including silver, so that the circuit patterns  813 ′ have a high light reflectivity. 
     It is to be understood, even though information and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the present embodiments, the disclosure is illustrative only; changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present embodiments to the full extent indicated by the plain meaning of the terms in which the appended claims are expressed.