Circuit board surface structure and fabrication method thereof

Abstract

A circuit board surface structure and a fabrication method thereof are proposed. The circuit board surface structure includes: a circuit board having a plurality of electrically connecting pads formed on at least one surface thereof; a first and a second insulating protective layers formed on the surface of the circuit board in sequence; first and a second openings respectively formed in the first and second insulating protective layers to expose the electrically connecting pads on the surface of the circuit board, wherein the first and second openings have narrow top and wide bottom and the diameter of the first openings is bigger than that of the second openings; and conductive elements formed in the first and second openings on surfaces of the electrically connecting pads. The present structure facilitates to strengthen the bonding between the conductive elements and the corresponding electrically connecting pads.

1 . A fabrication method of a circuit board surface structure, comprising:
 providing a circuit board having at least one surface formed with a plurality of electrically connecting pads;   forming on the surface of the circuit board a first insulating protective layer and a second insulating protective layer in sequence;   forming first openings and second openings penetrating the first and second insulating protective layers respectively so as to expose the electrically connecting pads on the surface of the circuit board, wherein each of the first and second openings is tapered upward, and the first openings have a greater diameter than the second openings; and   forming conductive elements on surfaces of the electrically connecting pads in the first and second openings.   
     
     
         2 . The method of  claim 1 , wherein the first and second insulating protective layers have different composition ratios. 
     
     
         3 . The method of  claim 2 , wherein the composition ratio of photo-polymerization material in the first insulating protective layer is smaller than the composition ratio of photo-polymerization material in the second insulating protective layer. 
     
     
         4 . The method of  claim 2 , wherein photo-polymerization material in the first and second insulating protective layers is an acrylate-based material. 
     
     
         5 . The method of  claim 2 , wherein the first insulating protective layer features one of presence and absence of a solder resisting effect, and the second insulating protective layer features presence of a solder resisting effect. 
     
     
         6 . The method of  claim 1 , wherein a method for fabricating the conductive elements comprises:
 forming a conductive layer on a surface of the second insulating protective layer and in the first and second openings;   forming a resist layer on the conductive layer and forming third openings in the resist layer to expose the conductive layer on the electrically connecting pads; and   forming conductive elements on the electrically connecting pads in the first, second, and third openings by electroplating.   
     
     
         7 . The method of  claim 6 , further comprising removing the resist layer and the conductive layer covered by the resist layer. 
     
     
         8 . The method of  claim 6 , wherein each of the conductive elements is one of solder and a metal bump. 
     
     
         9 . The method of  claim 8 , wherein the solder is made of one selected from the group consisting of Pb, Sn, Ag, Cu, Au, Bi, Sb, Zn, Ni, Zr, Mg, In, Te, and Ga. 
     
     
         10 . The method of  claim 8 , wherein the metal bump is made of Cu. 
     
     
         11 . The method of  claim 6 , wherein the resist layer is one of a dry film photoresist and a liquid photoresist. 
     
     
         12 . The method of  claim 6 , wherein the resist layer is formed on a surface of the conductive layer by a method selected from the group consisting of printing, spin coating, and attaching, and patterned by exposure and development. 
     
     
         13 . The method of  claim 1 , wherein the conductive elements are formed by stencil printing.