Abstract:
The present invention discloses a printed circuit board. The printed circuit board is made by the method of providing a substrate; forming a first circuit on the substrate; depositing a thin film on the substrate; building an electronic component on the substrate by the thin film and allowing the electronic component to electrically connect the first circuit; forming a blanket dielectric layer enclosing the electronic component; and removing the substrate.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the right of priority based on Taiwan Patent Application No. 97114790 entitled “Printed circuit board with embedded electronic components and methods for the same” filed on Apr. 23, 2008, which is incorporated herein by reference and assigned to the assignee herein. 
     FIELD OF THE INVENTION 
     This invention relates to a printed circuit board, and more particularly relates to a printed circuit board with embedded electronic components and methods for the same. 
     BACKGROUND OF THE INVENTION 
     A printed circuit board is a device on which a circuit pattern is constructed for providing connection between various electronic components.  FIG. 1  is a cross-sectional view illustrating a conventional printed circuit board  10  with electronic components, such as integrated circuit  20  and passive component  30 , connected thereto. As shown, the conventional printed circuit board  10  and the integrated circuit  20  are connected to each other through a surface mount technology. Typically, the integrated circuit  20  is a packaged electronic component having leads  21 , being connected to lines  11  of the printed circuit board  10  via the leads  21  using a bonding technology. 
     The customers have been continuously seeking more and more compact electronic products, but the conventional printed circuit board  10  is behind the trend. That is, the conventional printed circuit board  10  suffers from obstacle in shrinking device size. For example, the printed circuit board  10  must provide sufficient area for the electronic components mounted thereon, thus, adversely affecting the shrinkage of device size. In addition, the integrated circuit  20  mounted on the printed circuit board  10  has usually been packaged, such that it is much larger than the bare chip and also adversely affecting the shrinkage of device size. 
     Accordingly, an improved structure and method capable of solving the above-mentioned problems are desirable. 
     SUMMARY OF THE INVENTION 
     The invention provides a printed circuit board with embedded electronic components. A circuit is formed on a temporary substrate using a printed circuit board fabrication process, and then electronic components, such as diodes, transistors, and other optical semiconductors, are directly built on the temporary substrate to electrically connect to the circuit. Thereafter, the circuit and the electronic components are simultaneously enclosed employing suitable materials prior to removal of the temporary substrate. 
     The invention at least has the following features capable of facilitating shrinkage in dimension for a final electronic product. The features includes that the electronic components are embedded in an insulation layer; the electronic components are directly built on the substrate, and the circuit and the electronic components are then enclosed simultaneously after completion of the electronic components; the temporary substrate is removed after that the circuit and the electronic components are printed on the enclosing insulation layer. The features result in reduction of the thickness for a final electronic product. 
     One aspect of the present invention is to provide a method of forming a printed circuit board. The method comprises the steps of: providing a substrate; forming a first circuit on the substrate; depositing a thin film on the substrate; building an electronic component on the substrate by the thin film and allowing the electronic component to electrically connect the first circuit; forming a blanket dielectric layer enclosing the electronic component; removing a portion of the dielectric layer to expose an upper surface of the electronic component; forming a second circuit on the dielectric layer, the second circuit being electrically connected to the electronic component; forming an insulating layer covering the second circuit and the dielectric layer; and removing the substrate. 
     Another aspect of the present invention is to provide a method of forming a printed circuit board. The method comprises the steps of: providing a substrate; forming a first circuit on the substrate; building an electronic component electrically connected to the first circuit on the substrate; forming a blanket dielectric layer enclosing the electronic component; removing a portion of the dielectric layer to expose an upper surface of the electronic component; forming a second circuit on the dielectric layer, the second circuit being electrically connected to the electronic component; forming an insulating layer covering the second circuit and the dielectric layer; and removing the substrate. 
     The objects and the features of the present invention may best be understood by reference to the detailed description with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating a conventional printed circuit board with electronic components connected thereto. 
         FIG. 2A  to  FIG. 2I  are cross-sectional views illustrating a printed circuit board with embedded electronic components in accordance with a first embodiment of the present invention. 
         FIG. 3A  to  FIG. 3D  are cross-sectional views illustrating a printed circuit board with embedded electronic components in accordance with a second embodiment of the present invention. 
         FIG. 4A  to  FIG. 4C  are cross-sectional views illustrating a printed circuit board with embedded electronic components in accordance with a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2A  to  FIG. 2I  are cross-sectional views illustrating a printed circuit board with embedded electronic components in accordance with a first embodiment of the present invention. Referring to  FIG. 2A , a substrate  200  is provided for forming a first circuit  201  thereon. The substrate  200 , preferably a conductive metal substrate, can be any suitable substrate, such as copper clad laminates or a thin stainless steel alloy plate. The first circuit  201  can be formed using a conventional printed circuit board fabrication process. For example, a dry film is formed over the substrate  200 , and then patterned to expose a portion of the surface of the substrate  200 . Thereafter, with the dry film serving as a mask, a material including Cu or Ni is electroplated on the exposed surface of the substrate  200 . Subsequently, removal of the dry film leads to formation of the first circuit  201 . 
     As shown in  FIG. 2B , a thin film  202  is deposited on the substrate  200 . For example, the thin film  202  having an end  202   a  connected to the first circuit  201  can be directly formed on the surface of the substrate  200 . The thin film  202  serves a base for forming light emitting diodes (LEDs) thereon subsequently. In one embodiment, an LED epitaxial layer grows employing the thin film  202  made of GsAs, InP, GaP, sapphire, or SiC. The thin film  202  may be formed with patterned profile. Formation of the thin film  202  can utilize appropriate film deposition and masking techniques, such as conventional sputtering, chemical vapor deposition or screening printing. 
     Referring to  FIG. 2C , with the thin film  202  serving as a base, a light emitting structural layer  203  is formed on the substrate  200  using conventional epitaxy and semiconductor deposition techniques. The light emitting structural layer  203  includes several epitaxial layers, such as a first electronic semiconductor layer  204 , a light emitting layer  205  and a second electronic semiconductor layer  206 . For example, the first electronic semiconductor layer  204  can be a n-type epitaxial layer with the formula of (Al x Ga l-x ) 0.5 In 0.5 P, and the light emitting layer  205  can be an undoped epitaxial layer with the formula of (Al x Ga l-x ) 0.5 In 0.5 P, and the second electronic semiconductor layer  206  can be a p-type epitaxial layer with the formula of (Al x Ga l-x ) 0.5 In 0.5 P. An electrical connection between the first electronic semiconductor layer  204  and the first circuit  201  is made through an appropriate relative thickness control for the thin film  202 , the first electronic semiconductor layer  204  and the first circuit  201 . Notably, both of the light emitting layer  205  and the second electronic semiconductor layer  206  should be isolated from the first circuit  201 , or the light emitting structural layer  203  may not work. In other embodiments, the light emitting structural layer  203  also includes other functional layers, such as an ohmic contact layer, a barrier layer and a reflective layer. 
     As shown in  FIG. 2D , a dielectric layer  210  is blanketly formed, enclosing the light emitting structural layer  203  and the first circuit  201 . The dielectric layer  210  can be spin on glass, silicon resin, epoxy, polyimide, or prefluorocyclobutane. Formation of the dielectric layer  210  can be conducted using a conventional precise coating process. It is noted that the light emitting structural layer  203  has not been packaged prior to formation of the dielectric layer  210 . 
     Referring to  FIG. 2E , an appropriate chemical mechanical polishing technique is then employed to remove a portion of the dielectric layer  210 , such that an upper surface  203   a  of the light emitting structural layer  203  is exposed. As shown in  FIG. 2F , a second circuit  220  is formed on the dielectric layer  210 , and electrically connected to the light emitting structural layer  203  through appropriate adjustment. For example, a patterned dry film is formed on the dielectric layer  210  and the upper surface  203   a  of the light emitting structural layer  203 . Thereafter, a sputtering technique is performed to implant seeds of a conductive material with the patterned dry film serving as a mask. Subsequently, a second circuit  220  is formed on the dielectric layer  210  by conducting an electroplating process with the use of the seeds, and electrically connected to the upper surface  203   a  of the light emitting structural layer  203 . In other embodiments, a conductive material, such as copper paste or silver paste, is printed on the dielectric layer  210  to form the second circuit  220  by a screening printing process. 
     Then, referring to  FIG. 2G , an insulating layer  230  is blanketly formed, and connected to the second circuit  220 , the light emitting structural layer  203  and the dielectric layer  210 . The insulating layer  230  can be polyester or polyimide, and it can further contain an appropriate reinforced material. The insulating layer  230  can be formed using a coating process. Alternatively, the insulating layer  230  can be a laminate of the above materials, which is then attached to the second circuit  220  and the light emitting structural layer  203 . By way of appropriate adjustments, the insulating layer  230  can be thick and strong enough to serve as a support layer for the above elements, so that the substrate  200  can be removed using a conventional etching process. Accordingly, the structure shown in  FIG. 2H  is obtained. 
       FIG. 2I  shows an optional step following that of  FIG. 2H . As shown, the thin film  202 , which may absorb light, can be removed using an etching process. In doing so, luminescence of the light emitting diode can be enhanced. Alternatively, as shown, the insulating layer  230  can be properly polished depending on needs, for exposing the second circuit  220 . 
     As described above, the invention provides a method integrating the printed circuit board fabrication process and the semiconductor fabrication process or another electronic component fabrication process instead of directly adhering the whole resultant electronic component, such as a packaged electronic component, to the substrate. That is, in accordance with the present invention, the printed circuit board fabrication process is firstly used to form a peripheral circuit on the substrate, and the semiconductor fabrication process or another electronic component fabrication process is then employed to directly form a principal structure of the electronic component on the substrate. Thereafter, another peripheral circuit electrically connected to the electronic component is formed using the printed circuit board fabrication process again. In the first embodiment of the invention, the electronic component refers to light emitting diode. Alternatively, the method disclosed in first embodiment can be applied in various diodes, such as a PN junction diode, a photodiode or a laser diode. 
       FIG. 3A  to  FIG. 3D  illustrate a second embodiment of the present invention. The second embodiment differs from the first embodiment in that the embedded electronic component is a transistor. As shown in  FIG. 3A , a substrate  300  is provided, and a first circuit  301  is formed thereon. Referring to  FIG. 3B , a thin film  302  is deposited on the substrate  300 . For example, the thin film  302  is directly formed on the surface of the substrate  300 , and possesses an end  302   a  connected to the first circuit  301 . The thin film  302  can be made of Si, GaAs, InP, GaP, sapphire, and SiC. The thin film  302  can be formed using conventional techniques, such as sputtering, chemical vapor deposition or screening printing. 
     As shown in  FIG. 3C , with the thin film  302  serving as a base, a transistor structure  303  is formed thereon utilizing conventional semiconductor techniques and suitable semiconductor materials. The transistor structure  303  includes a source electrode  304 , a drain electrode  305 , a gate insulating layer  306 , and a gate electrode  307 . The source electrode  304  and the drain electrode  305  are respectively connected to the first circuit  301 . The subsequent steps of  FIG. 3C  are similar to those of the first embodiment. As shown in  FIG. 3D , a dielectric layer  310  is blanketly formed, enclosing the transistor structure  303  and the first circuit  301 . It is noted that the transistor structure  303  has not been packaged prior to formation of the dielectric layer  310 . Thereafter, an appropriate chemical mechanical polishing technique is then employed to remove a portion of the dielectric layer  310 , for exposing an upper surface  303   a  of the transistor structure  303 . Subsequently, a second circuit  320  is formed on the dielectric layer  310 , and electrically connected to the transistor structure  303  through appropriate adjustment. An insulating layer  330  is then blanketly formed, and connected to the second circuit  320 , the transistor structure  303  and the dielectric layer  310 . After appropriate adjustments, the insulating layer  330  is thick and strong enough to serve as a support layer for the above elements. Finally, the substrate  300  is removed. 
     Although only the MOS transistor is disclosed as an example of the electronic components in the second embodiment, other transistors, such as bipolar transistor or CMOS transistor can alternatively serve as the electronic component in other embodiments. 
       FIG. 4A  to  FIG. 4C  illustrate a third embodiment of the present invention. The third embodiment differs from the first and second embodiments in that formation method of the electronic components excludes the step of forming the thin film  202  or  302  that serves as a base. In other words, processes that are not high temperature processes, such as vacuum evaporation, spin coating or printing including screening printing, inkjet printing or contact printing can also be employed for fabricating the embedded electronic components of the invention. In the third embodiment, an electroluminescent structure serves as the electronic component. In detail, as shown in  FIG. 4A , a substrate  400  is provided, and a first circuit  401  is formed thereon. Referring to  FIG. 4B , an electroluminescent structure  403  is formed through evaporation, coating or printing accompanying suitable masking techniques. The electroluminescent structure  403  includes an electron injection layer  404 , an electron transport layer  405 , an electroluminescent layer  406 , a hole transport layer  407 , and a hole injection layer  408 . The electron injection layer  404  can be made of alkali metal doped organic materials. The electron transport layer  405  can be made of oxadiazole, triazoles or phenanthroline. The electroluminescent layer  406  can be made of polymers containing various fluorescent pigments. The hole transport layer  407  can be made of allylamine compounds. The hole injection layer  408  can be made of organic materials to which Lewis acid is added. The subsequent steps of  FIG. 4B  are similar to those of the first and second embodiments. As shown in  FIG. 4C , a dielectric layer  410  is blanketly formed, enclosing the electroluminescent structure  403  and the first circuit  401 . It is noted that the electroluminescent structure  403  has not been packaged prior to formation of the dielectric layer  410 . Thereafter, an appropriate chemical mechanical polishing technique is then employed to remove a portion of the dielectric layer  410 , exposing an upper surface  403   a  of the electroluminescent structure  403 . Subsequently, a second circuit  420  is formed on the dielectric layer  410 , and electrically connected to the electroluminescent structure  403  through appropriate adjustment. An insulating layer  430  is then blanketly formed, and connected to the second circuit  420 , the electroluminescent structure  403  and the dielectric layer  410 . After appropriate adjustments, the insulating layer  430  is thick and strong enough to serve as a support layer for the above elements. Finally, the substrate  400  is removed. 
     Although the embodiments of the invention disclose the light emitting diode, transistor and electroluminescent structure as examples of the electronic components, other electronic components suitable for the above-described methods, such as optical components, can also be used in other embodiments. 
     Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from what is intended to be limited solely by the appended claims.