Abstract:
A method of manufacturing a coreless package substrate together with a conductive structure of the substrate is disclosed. The method can produce a coreless package substrate which comprises: at least a built-up structure having a first solder mask and a second solder mask, wherein a plurality of openings are formed in the first and second solder mask to expose the conductive pads of the built-up structure; and a plurality of solder bumps as well as solder layers formed on the conductive pads. Therefore, the invention can produce the coreless package substrate with high density of circuit layout, less manufacturing steps, and small size.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method of manufacturing a core-less package substrate, and more particularly, to a method of manufacturing a coreless substrate that is applicable to non-through hole structures, together with a conductive structure of the substrate, so as to increase integration, and simplify manufacture process. 
   2. Description of Prior Arts 
   With rigorous development of the electronic industry, the directions of the research in electronic products are turning to high integration and miniaturization to meet the needs for multi-function, high speed, and high frequency. Accordingly, the circuit board for connecting a plurality of active and passive components to circuits is evolving from single layer to multi-layers in order to expand spaces of circuit layout to thereby meet the requirements of high wiring density for integrated circuits. 
   The conventional processes of electronic devices begin first by providing chip carriers suitable to semiconductor chips, such as substrates or lead frames, then the chip carriers are forwarded to semiconductor packaging industry to proceed with the processes of chip disposing, molding, and ball mounting, etc.; finally, electronic devices having requested functions are produced. 
   A conventional semiconductor packaging structure is made such that a semiconductor chip is mounted on the top surface of the substrate, and then wire bonding or flip-chip packaging are performed, followed by placing solder balls on the back of the substrate to suffice electrical connections for a printed circuit board. Though high-number leads are achieved in this way, usage on higher frequency and operations at higher speed are restricted due to limited performance of the package structure attributed to lacks of both shorter paths of leads and higher wiring density. 
   In the method of manufacturing a package substrate, the whole steps of a conventional technique start from providing a core substrate, then drilling, plating, hole-plugging, circuit-forming to thereby accomplish an inner layer structure, and further carrying out a build-up process to obtain a multi-layer carrier substrate.  FIGS. 1A to 1E  are schematic illustrations of a t prior art. Referring to  FIG. 1A  about a core substrate  11 , a core layer  111  of predetermined thickness has circuit layers  112  formed on the surface thereof. Meanwhile, a plurality of plating through holes  113  are formed in the core layer  111 , such that the circuit layers  112  are electrically connected. Subsequently, as shown in  FIG. 1B , the core substrate  11  is treated by a build-up process. First, a dielectric layer  12  is formed on the surface of the core substrate  11  with a plurality of openings  13  corresponding to the circuit layers  112 . Then, as shown in  FIG. 1C , a seed layer  14  as a conductor is formed on the surface of the dielectric layer  12  by electroless plating or sputtering, and a patterned resistive layer  15  is formed on the seed layer  14 , having a plurality of open areas  150  therein to thereby expose the parts of the seed layer  14 . Subsequently as shown in  FIG. 1D , a patterned circuit layer  16  and a plurality of conductive vias  13   a  are formed in the open areas  150  of the resistive layer  15  by electroplating through the seed layer  14 , such that patterned circuit layer  16  is electrically connected to circuit layer  112  through the conductive vias  13   a ; then the resistive layer  15  is removed and etching is carried out, thereby removing the seed layer  14  covered underneath the resistive layer  15 , such that the first built-up structure  10   a  is formed. Finally, as shown in  FIG. 1E , likewise, a second built-up structure  10   b  is formed on the first built-up structure  10   a  by the same process, and built-up layers are formed repetitively to thereby obtain a multi-layer substrate. 
   However, in the process described above, a core substrate is formed by forming circuits on a core layer, followed by a build-up process on the core substrate, thereby forming a multi-layer substrate that complies with the required electrical design. As a result, the thickness of the final multi-layer substrate cannot be reduced, which is unfavorable to the developmental trend of a miniaturized semiconductor package structure. If the thickness of the core substrate is reduced to as thin as 60 μm or less, the manufacture of the multi-layer substrate will be seriously compromised, and the yield from the manufacture of substrates will decrease significantly. 
   In addition, there are extra steps in the manufacture of the core substrate, such as the hole-plugging and the scrubbing, which increase the manufacture cost. More importantly, it is necessary to form a plurality of plating through holes in the core substrate; the diameter of a typical through hole formed by drilling is approximately 100 μm or more, while the diameter of the conductive via (laser blind hole) is approximately 50 μm. In comparison, the process of plating through holes makes it more difficult to form a structure with finer circuits. 
   Moreover, in the process of the multi-layer substrate described above, it is necessary to fabricate a core substrate prior to forming dielectric layers and circuit layers, which consequently complicates the manufacture steps, prolongs the process, and increases the manufacture cost. 
   As a result, the industry urgently needs a solution to avoid the drawbacks of the previous technique, such as the increased thickness of a substrate, low wiring density, low yield, complicated manufacture steps, a lengthy process, and a high manufacture cost. 
   SUMMARY OF THE INVENTION 
   In light of the shortcomings of the prior arts described above, the primary objective of the present invention is to provide a method of manufacturing a package substrate and to provide a conductive structure of the substrate, so as to raise the wiring density and reduce the thickness of substrate, and thereby meet the developmental trend toward miniaturization. 
   Another objective of the present invention is to simplify manufacture steps, raise yield, shorten manufacture time, and reduce manufacture cost. 
   To achieve the above and other objectives, the present invention discloses a method of manufacturing a package substrate, which includes: 
   (A) providing a carrier board, and forming a first resistive layer on the top surface of the carrier board, wherein a plurality of first openings are formed in the first resistive layer to expose parts of the substrate; 
   (B) forming in turn an etching-stop layer and a first metal layer in each of the first openings, and then removing the first resistive layer; 
   (C) forming a dielectric layer on the surface of the carrier board and on the first metal layers, wherein a plurality of second openings are formed in the dielectric layer to expose parts of the top surfaces of the first metal layers, and then forming a second metal layer in each of the second openings; 
   (D) forming a second resistive layer on the dielectric layer and on the second metal layers, wherein a plurality of third openings are formed in the second resistive layer at the positions corresponding to the second metal layers, and then forming a third metal layer in each of the third openings, followed by removing the second resistive layer; 
   (E) forming a built-up structure on the dielectric layer and on the third metal layers, which includes at least a dielectric layer, at least a fourth metal layer of patterned circuit, a plurality of conductive vias, as well as a plurality of conductive pads; 
   (F) removing the carrier board and the etching-stop layer to thereby expose the bottom surfaces of the first metal layers; and 
   (G) forming a first solder mask on the built-up structure, wherein a plurality of fourth openings are formed in the first solder mask to expose parts of the built-up structure as electrical connecting pads, and forming a second solder mask on the dielectric layer and on the bottom surfaces of the first metal layers, wherein a plurality of fifth openings are formed in the second solder mask to expose parts of the bottom surfaces of the first metal layers. 
   Thereby, the coreless package substrate prepared by the present invention has higher circuit layout density, fewer manufacturing steps, reduced general thickness of the products, and a small size. 
   The method of manufacturing the coreless package substrate can further comprise a step (H) after step (G), forming a plurality of solder bumps in the fourth openings of the first solder mask and forming a plurality of solder layers in the fifth openings of the second solder mask. 
   In addition, the method of the present invention can further comprise a step (I) after forming solder bumps and solder layer in step (H): attaching at least a metal supporting frame on the surface of the first solder mask, so as to increase general rigidity of the coreless package substrate. 
   Besides, the method of the present invention can further comprise a step (G 1 ) before forming the solder bumps in the fourth openings and forming the solder layers in the fifth openings: forming a filling metal layer as a post in at least one of the fourth openings in the first solder mask and the fifth openings in the second solder mask, to thereby reduce the quantity of solder material needed for the solder layers as well as the solder bumps. 
   The build-up process to form a built-up structure in step (E) is well known in the art, wherein a multi-layer built-up structure can be obtained by repeating the build-up process; thus the details are not described further here. 
   In addition, this invention also disclose a conductive structure of a coreless package substrate, comprising: a dielectric layer having a plurality of first openings and second openings therein, outward to the opposing sides of the dielectric layer, wherein the second openings correspond to and are smaller than the first openings each; a first metal layer formed in each of the first openings as a conductive pad, wherein the thickness of the first metal layer is smaller than the depth of the first opening, therewith the first metal layer contacting the second opening; and a second metal layer formed in each of the second openings as a conductive via, filling up the second opening and contacting the first metal layer in the first opening. 
   Besides, the above structure comprises a solder mask formed on the dielectric layer and the first metal layer, having a plurality of openings formed therein, wherein the openings of the solder mask correspond to and are smaller than the first openings each. 
   Furthermore, the above structure comprises a solder layer formed in each of the openings of the solder mask. 
   Moreover, the above structure can comprise a metal layer formed in each of the openings of the solder mask as a post before forming the solder layer, to thereby reduce the quantity of solder material needed for the solder layer. 
   Other objects, advantages, and features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A to 1E  are cross-sections of the process to make a conventional core package substrate; 
       FIGS. 2A to 2Q  are cross-sections of a coreless package substrate of a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 2A to 2Q  are schematic cross-section illustrations of a coreless package substrate of a preferred embodiment of the present invention. First, as shown in  FIG. 2A , a metal carrier board  201  is provided. Then, as shown in  FIG. 2B , a first resistive layer  202  is formed on the carrier board  201 . As shown in  FIG. 2C , a plurality of first openings  202   a  are formed in the first resistive layer to expose parts of the carrier board  201  underneath. Subsequently, as shown in  FIGS. 2D and 2E , an etching-stop layer  204  and a first metal layer  205  are in turn formed in the first openings  202   a . In this example, the first resistive layer  202  is a dry-film photoresistive layer. 
   Referring to  FIG. 2F , the first resistive layer  202  is removed. As shown in  FIG. 2G , a dielectric layer  206  made of ABF (Ajinomoto Build-up Film) is formed on the surfaces of the carrier board  201  and the first metal layer  205 , wherein a plurality of openings  206   a  is formed by laser ablation in the dielectric layer  206  to expose parts of the first metal layer  205  underneath. Subsequently, as shown in  FIG. 2H , a second metal layer  207  is formed in the second openings  206   a . As illustrated in  FIG. 21 , a second resistive layer  208  is formed on the surfaces of the dielectric layer  206  and the second metal layer  207 , wherein a plurality of third openings  208   a  are formed in the second resistive layer  208  by photolithography, so as to expose the second metal layer  207  underneath. As shown in  FIG. 2J , a third metal layer  209  is formed on the third openings  208   a . Then, as shown in  FIG. 2K , the second resistive layer  208  is removed by photolithography. 
   Subsequently, as shown in  FIG. 2L , a built-up structure  30  is formed on the dielectric layer  206  and the third metal layer  209 , which includes a dielectric layer  300 , a fourth metal layer  301  of patterned circuit, and a plurality of conductive vias  302 . Because the process of forming the built-up structure  30  is well known in the art, the details are not described further here. 
   Further referring to  FIG. 2M , another two built-up structures  30 ′ are formed on the built-up structure  30 , which includes a plurality of conductive pads  303 . As shown in  FIG. 2N , the carrier board  201  and the etching-stop layers  204  are removed by etching. Then, as shown in  FIG. 2O , a first solder mask  304  for insulating protection is coated on surface of the built-up structure  30 ′, and a plurality of fourth openings  304  are formed on the first solder mask  304  by photolithography, so as to expose the conductive pads  303  of the built-up structure  30 ′. A second solder mask  210  for insulating protection is formed on the surface of the dielectric layer  206 , and a plurality of fifth openings  210   a  are formed in the second solder mask  210  by photolithography, so as to expose parts of the surfaces of the first metal layers  205 . 
   Referring to  FIG. 2P , a filling metal layer  305  and  211  can be formed in each of the fourth openings  304   a  of the first solder mask  304 , and the filling metal layer  305  and  211  can also be formed in each of the fifth openings  210   a  of the second solder mask  210 . In this embodiment, the solder bumps  306  and the solder layers  212  are formed on the surfaces of the filling metal layers  305  and  211  in each of the fourth openings  304   a , as well as in each of the fifth openings  210   a , wherein the filling metal layers  305  and  211  serves as a post to thereby reduce the quantity of solder material needed for the solder layers  212  as well as the solder bumps  306 . Finally, as shown in  FIG. 2Q , a metal supporting frame  307  is attached on the surface of the first solder mask  304 , thereby increasing the general rigidity of the coreless package substrate. 
   In the embodiment above, the method of forming the first openings  202   a  in the first resistive layer  202  in  FIG. 2C  as well as that of forming the third openings  208   a  in the second resistive layer  208  in  FIG. 2I , both the fourth openings  304   a  in the first solder mask  304  and the fifth openings  210   a  in the second solder mask  210  in  FIG. 2O  is photolithography, while the method of forming the second openings  206   a  in the dielectric layer  206  in  FIG. 2G  is laser ablation. 
   In the embodiment above, the method of forming the etching-stop layers  204  in  FIG. 2D , as well as that of forming the first metal layers  205  in  FIG. 2E , the second metal layers  207  in  FIG. 2H , the third metal layers  209  in  FIG. 2J , and the fourth metal layers  301  together with the conductive vias  302  in  FIG. 2L  can be either electroplating or electroless plating. 
   In the embodiment above, the etching-stop layer  204  as well as the solder bump  306  and the solder layer  212  can be selected from one of gold, silver, tin, nickel, chromium, titanium, lead, copper, aluminum, and an alloy of a combination of the above metals, while the first metal layer  205 , as well as the second metal layer  207 , the third metal layer  209 , the fourth metal layer  301  together with the conductive vias  302 , and the filling metal layers  305  and  211  can be selected from one of copper, aluminum, tin, nickel, chromium, and an alloy of a combination of the above metals. 
   The present invention also disclose a conductive structure of the substrate, as shown in  FIG. 2Q , comprising: a dielectric layer  206  having a plurality of first openings  202   a  and second openings  206   a  therein, outward to the opposing sides of the dielectric layer  206 , wherein the second openings  206   a  correspond to and are smaller than the first openings  202   a  each; a first metal layer  205  formed in each of the first openings  202   a  as a conductive pad, wherein the thickness of the first metal layer  205  is smaller than the depth of the first opening  202   a , therewith the first metal layer  205  contacting the second opening  206   a ; and a second metal layer  207  formed in each of the second openings  206   a  as a conductive via, filling up the second opening  206   a  and contacting the first metal layer  205  in the first opening  202   a.    
   Besides, the above structure comprises a solder mask  210  formed on the dielectric layer  206  and the first metal layer  205 , having a plurality of openings  210   a  formed therein, wherein the openings  210   a  of the solder mask  210  correspond to and are smaller than the first openings  202   a  each. 
   Furthermore, the above structure comprises a solder layer  212  formed in each of the openings  210   a  of the solder mask  210 . 
   Moreover, the above structure can comprise a metal layer  211  formed in each of the openings  210   a  of the solder mask  210  as a post before forming the solder layer  212 , to thereby reduce the quantity of solder material needed for the solder layer  212 . 
   Thus, the coreless package substrate of the example can increase circuit layout density, simplify process of manufacture, and reduce general thickness of the products, so as to achieve small sizes. 
   Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.