Abstract:
The present invention relates to a substrate structure having a solder mask and a process for making the same. The process comprises: (a) providing a substrate having a top surface, the top surface having a die pad and a plurality of solder pads; (b) forming a first solder mask on the top surface, the first solder mask having a plurality of openings, each opening corresponding to each solder pad so as to expose at least part of the solder pad; and (c) forming a second solder mask on the first solder mask. Whereby, the substrate structure of the invention can be used for packaging a thicker die so as to prevent the die crack and the overflow of molding compound will be avoided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a substrate structure and a process for making the same, particularly to a packaging structure having a solder mask and a process for making the same. 
         [0003]    2. Description of the Related Art 
         [0004]    Referring to  FIG. 1 , it shows a conventional substrate structure. The structure  1  of the invention comprises a substrate  10 , a solder mask  11 , a die  12 , a plurality of wires  13  and molding compound  14 . The substrate  10  has a top surface  101 . The top surface  101  has a die pad  102  and a plurality of solder pads  103 . The solder mask  11  is formed on the top surface  101 . The solder mask  11  has a plurality of openings  111 . The openings  111  are formed by using exposure and development. Each opening  111  is corresponding to each solder pad  103  to expose part of the solder pad  103 . 
         [0005]    The die  12  is attached on the solder mask  11  correspondingly on the die pad  102 . The wires  13  are used to electrically connect the die  12  and the solder pads  103 . The molding compound  14  is used to encapsulate the wires  13 , the die  12  and the solder pads  103  to form the package  1 . 
         [0006]    For the above-mentioned package  1 , the solder mask  11  for disposing the die  12  has the same height as that of the solder mask  11  for exposing the solder pads  103 . Therefore, a thinner die should be used to be packaged, and it is easy to cause the die  12  crack. Furthermore, the solder mask  11  cannot avoid the overflow of molding compound so that the solder pads  103  will be polluted. 
         [0007]    Consequently, there is an existing need for providing a substrate structure having a solder mask and a process for making the same to solve the above-mentioned problems. 
       SUMMARY OF THE INVENTION 
       [0008]    One objective of the present invention is to provide a method for making a substrate structure having a solder mask. The process of the invention comprises the steps of: (a) providing a substrate having a top surface, the top surface having a die pad and a plurality of solder pads; (b) forming a first solder mask on the top surface, the first solder mask having a plurality of openings, each opening corresponding to each solder pad so as to expose at least part of the solder pad; and (c) forming a second solder mask on the first solder mask. 
         [0009]    Another objective of the present invention is to provide a substrate structure having a solder mask. The structure of the invention comprises a substrate and a solder mask. The substrate has a top surface having a die pad and a plurality of solder pads. The solder mask is formed on the top surface. The solder mask has a plurality of openings. Each opening is corresponding to each solder pad so as to expose part of the solder pad. The solder mask has a first portion and a second portion. The first portion is correspondingly on the die pad, and the second portion is around the edge of the top surface of the substrate. The first portion is lower than the second portion. 
         [0010]    The solder mask of the above-mentioned structure of the invention is a single structure. By utilizing the higher second portion of the solder mask, a thicker die can be used to be packaged so as to prevent the die crack. Furthermore, the second portion is stair-shaped, and a ring-shaped groove also can be formed on the second portion, so that the overflow of molding compound will be avoided, and the solder pads will not be polluted. 
         [0011]    Still, another objective of the present invention is to provide a substrate structure having a solder mask. The structure of the invention comprises a substrate, a first solder mask and a second solder mask. The substrate has a top surface having a die pad and a plurality of solder pads. The first solder mask is formed on the top surface. The first solder mask has a plurality of openings. Each opening is corresponding to each solder pad so as to expose part of the solder pad. The second solder mask is formed on part of the first solder mask. 
         [0012]    The solder mask of the above-mentioned structure of the invention is a delaminated structure. Since the second solder mask is formed on part of the first solder mask to form a higher solder mask, a thicker die can be used to be packaged so as to prevent the die crack. Furthermore, the first solder mask and the second solder mask form a stair-shaped structure, and a ring-shaped groove may be formed on the second solder mask. Therefore, the overflow of molding compound will be avoided, and the solder pads will not be polluted. 
     
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Referring to  FIGS. 2A to 2D , they show the processes for making a substrate structure having a solder mask according to the present invention. Referring to  FIG. 2A , firstly, a substrate  20  is provided. The substrate  20  has a top surface  201 , and the top surface  201  has a die pad  202  and a plurality of solder pads  203 . Referring to  FIG. 2B , a first solder mask  21  is formed on the top surface  201 . The first solder mask  21  has a plurality of openings  211 . Each opening  211  is corresponding to each solder pad  203  so as to expose the solder pad  203 . In the embodiment, the openings  211  are formed by using exposure and development. 
         [0014]    Referring to  FIG. 2C , a second solder mask  22  is formed on the first solder mask  21  and the solder pads  203 . Referring to  FIG. 2D , part of the second solder mask  22  is then removed by using exposure and development so as to expose part of the solder pads  203  and the first solder mask  21 . The exposed part of the first solder mask  21  is corresponding to the die pad  202 . A top mold (not shown) presses the second solder mask  22  so as to form a higher space for disposing the die when molding. For another application, part of the first solder mask  21  and part of the second solder mask  22  form a stair-shaped structure, as shown in  FIG. 2E . For another application, a groove  221  may be formed on the second solder mask  22  by using exposure and development, as shown in  FIG. 2F . When molding, the groove  221  can be used as a buffering flow channel so that the overflow of molding compound will be avoided. 
         [0015]    Referring to  FIGS. 2G to 2H , the first solder mask  21  and the second solder mask  22  are heated and melt together to form a third solder mask  23 . It should be noticed that the first solder mask  21  and the second solder mask  22  may be a delaminated structure after heating, as shown in  FIG. 2E  and  FIG. 2F , and that actually depends on the baking sequence and heating conditions. 
         [0016]    Referring to  FIG. 3 , it shows a packaging structure having a solder mask according to a first embodiment of the present invention. The packaging structure  3  of the invention comprises a substrate  30 , a solder mask  31 , a die  32 , a plurality of wires  33  and molding compound  34 . The substrate  30  has a top surface  301 . The top surface  301  has a die pad  302  and a plurality of solder pads  303 . The solder mask  31  is formed on the top surface  301 . The solder mask  31  has a plurality of openings  311 . Each opening  311  is corresponding to each solder pad  303  so as to expose part of the solder pad  303 . The openings  311  are formed by using exposure and development. The solder mask  31  has a first portion  312  and a second portion  313 . The first portion  312  is correspondingly on the die pad  302 , and the second portion  313  is around the edge of the top surface  301  of the substrate  30 . The first portion  312  is lower than the second portion  313 , and the second portion  313  is formed as a stair-shaped structure. 
         [0017]    The die  32  is attached on the first portion  312  of the solder mask  31  correspondingly on the die pad  302 . The wires  33  are used to electrically connect the die  32  and the solder pads  303 . The molding compound  34  is used to encapsulate the wires  33 , the die  32  and the solder pads  303  to form the packaging structure  3 . 
         [0018]    Referring to  FIG. 4 , it shows a packaging structure having a solder mask according to a second embodiment of the present invention. The packaging structure  4  of the invention comprises a substrate  40 , a solder mask  41 , a die  42 , a plurality of wires  43  and molding compound  44 . The difference between the packaging structure  4  according to the second embodiment and the packaging structure  3  according to the first embodiment is that a groove  412  may be formed on the solder mask  41  by using exposure and development in the second embodiment. 
         [0019]    Referring to  FIG. 5 , it shows a packaging structure having a solder mask according to a third embodiment of the present invention. The packaging structure  5  of the invention comprises a substrate  50 , a first solder mask  51 , a second solder mask  52 , a die  53 , a plurality of wires  54  and molding compound  55 . The difference between the packaging structure  5  according to the second embodiment and the packaging structure  3  according to the first embodiment is that the first solder mask  51  and the second solder mask  52  are a delaminated structure but not a single structure. 
         [0020]    The first solder mask  51  has a first portion  511  and a second portion  512 . The first portion  511  is correspondingly on the die pad  502 , and the second portion  512  is around the edge of the top surface of the substrate  50 . The second solder mask  52  is disposed on part of the first solder mask  51  (for example, on the second portion  512 ). The second solder mask  52  and the second portion  512  of the first solder mask  51  have a width difference to form as a stair-shaped structure. 
         [0021]    Referring to  FIG. 6 , it shows a packaging structure having a solder mask according to a fourth embodiment of the present invention. The packaging structure  6  of the invention comprises a substrate  60 , a first solder mask  61 , a second solder mask  62 , a die  63 , a plurality of wires  64  and molding compound  65 . The difference between the packaging structure  6  according to the fourth embodiment and the packaging structure  4  according to the second embodiment is that the first solder mask  61  and the second solder mask  62  are a delaminated structure but not a single structure. 
         [0022]    The first solder mask  61  has a first portion  611  and a second portion  612 . The first portion  611  is correspondingly on the die pad  602 , and the second portion  612  is around the edge of the top surface of the substrate  60 . The second solder mask  62  is disposed on part of the first solder mask  61  (for example, on the second portion  612 ) and further has a ring-shaped groove  621 . 
         [0023]    By utilizing the process for making a packaging structure of the present invention, the packaging structure of a single structure or of a delaminated structure can be formed. For the package of a single structure (as shown in  FIG. 3  and  FIG. 4 ), the first portion of the first solder mask is lower than the second portion. By utilizing the second portion, a thicker die can be used to be packaged so as to prevent the die crack. Furthermore, the second portion may form as a stair-shaped structure, and a ring-shaped groove may be formed on the second portion. Therefore, the overflow of molding compound will be avoided, and the solder pads will not be polluted. 
         [0024]    In addition, for the package of a delaminated structure (as shown in  FIG. 5  and  FIG. 6 ), the first portion of the first solder mask is correspondingly on the die pad, the second portion is around the edge of the top surface of the substrate, and the second solder mask is disposed on the second portion of the first solder mask. Since the first solder mask and the second solder mask form a higher solder, a thicker die can be used to be packaged so as to prevent the die crack. Furthermore, the second portion of the first solder mask and the second solder mask form as a stair-shaped structure, and a ring-shaped groove may be formed on the second solder mask. Therefore, the overflow of molding compound will be avoided, and the solder pads will not be polluted. 
         [0025]    While the embodiments of the present invention have been illustrated and described, various modifications and improvements can be made by those skilled in the art. The embodiments of the present invention are therefore described in an illustrative but not restrictive sense. It is intended that the present invention may not be limited to the particular forms as illustrated, and that all modifications that maintain the spirit and scope of the present invention are within the scope as defined in the appended claims.