Abstract:
A repair pre-soldering structure on a circuit board and a method thereof are proposed. A leave out on a circuit board without any pre-soldering is repaired by a micro-depositing process by applying micro droplets on the circuit board, or a short circuit formed by a pre-soldering with higher height is repaired by a micro-corrosion process. Therefore, the present invention improves fine rate of fabrication and avoids increasing fabricating time due to rework the circuit board, fabrication costs, and so on.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a repaired pre-solder structure of a circuit board and a method thereof, and more particularly, to a method for repairing defective pre-solders formed on a circuit board by using micro-droplets. 
       BACKGROUND OF THE INVENTION 
       [0002]    With the rapid growth of portable electronic products, such as communication, network and computer products, integrated circuit package techniques follow the trend toward miniaturization and high integration. Accordingly, various integrated circuit package techniques of high integration, such as ball grid array (BGA), flip chip, chip size package (CSP) and multi chip module (MCM), are brought to the market. An integrated circuit package density is equal to a number of pins per unit area. For an integrated circuit package of high integration, shortening a layout corresponds to increasing the speed of signal transmission. Therefore, the application of conductive bumps is becoming the main stream package of high density. 
         [0003]    The flip chip technique, for example, includes forming a plurality of electrode pads on an active surface of a semiconductor chip, and forming on a circuit board a plurality of electrical connection pads corresponding to the electrode pads. Therefore, the electrode pads are electrically connected to the electrical connection pads via pre-solders or other conductive adhesive materials formed between the semiconductor chip and the circuit board. The pre-solders, and the conductive adhesive materials as well, provide input/output and mechanical connection between the semiconductor chip and the circuit board. 
         [0004]    However, in a pre-solder fabricating cost, some of the electrical connection pads are not covered with the pre-solders due to operating conditions, mechanical equipments or other manufacturing factors. In other words, part of the electrical connection pads formed on the circuit board are not covered with any pre-solders, thereby affecting electrical connection functionalities between the semiconductor chip and the circuit board in following package processes. As the size of components of the semiconductor chip is becoming smaller and smaller, and the circuit integration is required to be higher and higher, even such a tiny flaw will make nonrecoverable impacts on the quality of integrated circuits. 
         [0005]    If the flaw that some of the electrical connection pads are not covered with the pre-solder is found before a reflow-soldering process is performed, the defective pre-solders can not be repaired. In result, a manufacturing yield is greatly reduced, or the whole circuit board has to be reworked to repair the defective pre-solders, and a manufacturing cycle time is increased and a fabricating cost is increased. On the other hand, if the flaw is found after the reflow-soldering process is preformed, the circuit board is useless and is discarded as junk. 
         [0006]    Therefore, how to provide a method for repairing the electrical connection pads, to solve the drawbacks of too low the manufacturing yield and too high the fabricating cost, is becoming one of the most urgent errands in the art. 
       SUMMARY OF THE INVENTION 
       [0007]    In views of the above-mentioned problems of the prior art, it is a primary objective of the present invention to provide repaired pre-solder structure for a circuit board and a method for fabricating thereof, for increasing the manufacturing yield. 
         [0008]    It is another objective of the present invention to provide a circuit board and a method for fabricating thereof, for overcoming the drawbacks of too long the manufacturing cycle time and too high the fabricating cost due to the reworks on the circuit board. 
         [0009]    To achieve the above-mentioned and other objectives, a repaired pre-solder structure of a circuit board and a method thereof are provided according to the present invention. The method includes providing a circuit board comprising a plurality of electrical connection pads, an insulating protection layer being formed on the circuit board, the insulating protection layer having a plurality of opening for exposure of the electrical connection pads, forming a resist layer on the insulating protection layer, a plurality of openings being formed on the resist layer for exposure of the electrical connection pads, so as to form a plurality of pre-solders on the insulating protection layer and the electrical connection pads in the openings of the resist layer, wherein at least one of the pre-solders has a defect; and using a micro-droplet process to micro-deposit the pre-solder having the defect and the electrical connection pads, so as to repair the pre-solder on the pre-solder having the defect and the electrical connection pads. 
         [0010]    The method further includes removing the resist layer. The pre-solder is a pre-solder tin bump. A reflow-soldering process is further performed under a temperature condition high enough to melt the pre-solder, for formation of semiconductor chips and external electronic devices. 
         [0011]    The present invention further provides a method for repairing pre-solders of a circuit board. The method includes providing a circuit board comprising a plurality of electrical connection pads, an insulating protection layer being formed on the circuit board, the insulating protection layer having a plurality of openings for exposure of the electrical connection pads, forming a resist layer on the insulating protection layer, a plurality of openings being formed on the resist layer for exposure of the electrical connection pads, so as to form a plurality of pre-solders on the insulating protection layer and electrical connection pads in the openings of the resist layer, wherein at least one of the pre-solders has a defect; and using a micro-droplet process to micro-etch the pre-solder having the defect, so as to repair the pre-solder having the defect. 
         [0012]    The present invention further provides a repaired pre-solder structure of a circuit board. The structure includes a circuit board comprising a plurality of electrical connection pads; an insulating protection layer formed on the circuit board; a plurality of openings formed in the insulating protection layer for exposure of the electrical connection pads; a plurality of pre-solders formed on the electrical connection pads, the pre-solders comprising at least one defective pre-solders having an insufficient height; and a repaired pre-solder deposited on a top surface of the defective pre-solder formed by a micro-droplet process. 
         [0013]    The method for repairing pre-solders of a circuit board performs the micro deposition solder tin material on the electrical connection pads which are not covered with any pre-solders by using micro-droplets, so as to form repaired pre-solders and increase the manufacturing yield. The present invention performs a micro etching process on the pre-solders having a short circuit formed if the pre-solders are too high, to solve the drawbacks that the cost and manufacturing cycle time is increased resulting from the reworks on the circuit board. 
     
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]    The invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein: 
           [0015]      FIGS. 1A-1C  are flow schematic diagrams of repaired pre-solder structure of a circuit board and a method thereof according to the present invention; and 
           [0016]      FIGS. 2A-2B  are cross sectional views of a second embodiment of a repaired pre-solder structure of a circuit board and a method thereof according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0017]    The following illustrative embodiments are provided to illustrate the disclosure of the present invention, these and other advantages and effects can be apparently understood by those in the art after reading the disclosure of this specification. The present invention can also be performed or applied by other different embodiments. The details of the specification may be on the basis of different points and applications, and numerous modifications and variations can be devised without departing from the spirit of the present invention. 
         [0018]    A repaired pre-solder structure of a circuit board and a method for fabricating the repaired pre-solder structure of the present invention are applied to a fabricating process that pre-solders are already formed. In order to simplify the drawings and specification, a circuit board having a pre-solder fabricating process finished but a resist layer is not removed yet is described as an example in the following paragraphs. 
         [0019]      FIGS. 1A-1C  are flow schematic diagrams of repaired pre-solder structure for a circuit board and a method thereof of a first embodiment according to the present invention. 
         [0020]    As shown in  FIG. 1A , a circuit board  1  having a forepart fabricating cost finished is provided. The circuit board  1  comprises a plurality of electrical connection pads (or land)  10 ,  11  and  11 ′. An insulating protection layer  12  is formed on the circuit board  1 . A plurality of openings  120  are formed in the insulating protection layer  12  for exposure of the electrical connection pads  10 ,  11  and  11 ′. A resist layer  13  is formed on the insulating protection layer  12 . The resist layer  13  is not a material necessary to be covered on the insulating protection layer  12 . A plurality of openings  130  are formed in the resist layer  13  and corresponding in position to the electrical connection pads  10 ,  11  and  11 ′ on the circuit board  1 . A plurality of pre-solders  14  are formed on the electrical connection pads  10  in the openings  130 . The electrical connection pads  11  and  11 ′ are covered without any pre-solders and covered with a defective pre-solder  140  shorter than a normal pre-solder respectively due to fabricating factors. The pre-solders  14  and  140  are tin bumps. 
         [0021]    As shown in  FIGS. 1B and 1C , a micro-droplet  2  is used to perform a chemical reaction of micro-deposition on the electrical connection pad  11 , which is not covered with any pre-solders, to form a pre-solder  14 a on the electrical connection pad  11 , and form on the defective pre-solder  140  a repaired pre-solder  14   a ′, so as to repair the pre-solders  14   a  and  14   a ′ formed on the electrical connection pads  11  and  11 ′. The pre-solders  14   a  and  14   a ′ are one selected from the group consisting of lead, tin, silver, copper, gold, bismuth, antimony, zinc, nickel, zirconium, magnesium, indium, tellurium and gallium. 
         [0022]    Please refer to  FIG. 1C . The resist layer  13  is removed by a chemical divesting process. 
         [0023]    Since the pre-solders  14   a  and  14   a ′ can be tin bumps, a reflow-soldering process can be performed on the tin bumps, under a temperature condition high enough to melt the pre-solders for attaching semiconductor chips or external electronic devices. 
         [0024]    According to the above repaired method, the present invention further provides a repaired structure, which comprises a circuit board  1  having a plurality of electrical connection pads  10 ,  11  and  11 ′. An insulating protection layer  12  is formed on the circuit board  1 . A plurality of openings  120  are formed on the insulating protection layer  12  for exposure of the electrical connection pads  10 ,  11  and  11 ′. A plurality of pre-solders  14  are formed on the electrical connection pad  10 . The pre-solders  14  comprise at least a defective pre-solder  140  shorter than a normal pre-solder, a repaired pre-solder  14   a  formed on a top surface of the defective pre-solder  140  by a micro-droplet process, and an interface  15  formed between the defective pre-solder  140  and the repaired pre-solder  14   a′.    
         [0025]      FIGS. 2A-2B  are cross sectional views of a second embodiment of a repaired pre-solder structure of a circuit board and a method thereof according to the present invention. Different from the first embodiment, the second embodiment provides a circuit board having drawbacks that the pre-solders have too large the size and a short circuit exists among the pre-solders. 
         [0026]    As shown in  FIG. 2A , a circuit board  1  as shown in FIG,  1 A is provided. The electrical connection pads  10  and  11  are covered with a normal pre-solder  14  and at least too high a defective pre-solder  141  respectively, or a drawback of a bridge portion  142  is formed between two pre-solders  14 . In other words, the two pre-solders are shorted. 
         [0027]    Please refer to  FIG. 2B . A chemical reaction of micro-droplet  2  is applied to the pre-solder  141  formed on the circuit board  1  to perform a micro etching process and remove the pre-solder  141 . Therefore, a top portion of too high the detective pre-solder  141  is removed and the pre-solder  141  becomes normal. Further, the bridge portion  141  is removed. In result, two originally connected pre-solders  14  are separated and independent. Therefore, the pre-solder  141  is repaired to have a normal size and be the normal pre-solder  14 . The resist layer  13  can then be further removed (not shown). 
         [0028]    Compared with the prior art, the repaired pre-solder structure and a method thereof perform the micro deposition solder tin material on the electrical connection pads which are not covered with any pre-solders by using micro-droplets, so as to form repaired pre-solders and increase the manufacturing yield. The present invention performs a micro etching process on the pre-solders having a short circuit formed if the pre-solders are too high, to solve the drawbacks that the cost and manufacturing cycle time is increased resulting from the reworks on the circuit board. 
         [0029]    The foregoing descriptions of the detailed embodiments are only illustrated to disclose the features and functions of the present invention and not restrictive of the scope of the present invention. It should be understood to those in the art that all modifications and variations according to the spirit and principle in the disclosure of the present invention should fall within the scope of the appended claims.