Patent Publication Number: US-9907178-B2

Title: Printed circuit board having electronic component embedded

Description:
FIELD OF THE INVENTION 
     The present invention relates to a printed circuit board. More particularly, the present invention relates to a printed circuit board which has an electronic component embedded. 
     BACKGROUND OF THE INVENTION 
     It is a trend to make electronic products small in size and compact in thickness. There are many issues, such as heat dissipation, which need to be settled during the design process. One of these issues is how to consolidate necessary components into an integrated circuit (IC) or a printed circuit board (PCB). An electronic component can be embedded in a printed circuit board during the printed circuit board manufacturing processes. The technique started from buried resistor technology Ohmega Technologies, Inc. Although it was only passive components can be used in the beginning, it becomes well accepted to the industrial now days that active components can be applied by various modifications and invention. 
     Among all integrated circuits, there are several kinds which have specified functions and need to work interactively with external environment. Exemplary examples are charge-coupled devices (CCD) and complementary metal-oxide-semiconductors (CMOS). A fingerprint reader sensor and a mouse sensor are typical products for the CCD and CMOS, respectively. The fingerprint reader sensor needs to detect change of capacitance and the mouse sensor needs to receive light change over a surface. Even those integrated circuits are embedded into a PCB, it is required a proper arrangement and configuration for the integrated circuits to expose to the external environment. Meanwhile, a good design for the integrated circuits to work is important, as well. 
     Reviewing the prior arts, there are several inventions that have focused on some of the requirements mentioned above. First, the U.S. Pat. No. 8,083,954 discloses a method for fabricating a component-embedded printed circuit board. The method includes: providing a carrier plate having a plating metal layer plated thereon, disposing an electronic component on the plating metal layer of the carrier plate, laminating a metal layer onto the plating metal layer having the electronic component disposed thereon and the carrier plate by a dielectric film, removing the carrier plate and exposing the plating metal layer, and patterning at least one of the metal layer and the plating metal layer to be a circuit layer. &#39;954 focuses on how to reduce the overall thickness of a printed circuit board. It can not apply to active components for embedding processes. 
     Next, the U.S. Pat. No. 8,302,299 discloses a method of manufacturing a multilayer printed circuit board of a built-in electronic device. It provides a substrate having a copper clad laminate and a first dielectric layer. The first dielectric layer is laminated onto the copper clad laminate and has a cavity for accommodating the electronic device. A second dielectric layer is laminated onto the substrate and electronic device to produce a base circuit board with an embedded electronic device. A build-up circuit layer is formed on the base circuit board. The first and second dielectric layers are made of a plastic material. Obviously, the embedded electronic device can not be the CCD or CMOS because there is no window for a portion to expose to the external environment. 
     Last, the US Patent Application No. 20130092420 depicts an invention which relates to a method of manufacturing an embedded printed circuit board. An embedded multilayer printed circuit board includes first, second and third circuit substrates, and a flexible circuit substrate. The first circuit substrate includes a first base layer and a first electrically conductive layer. The second circuit substrate includes a second base layer and a second circuit layer. The second circuit substrate also defines a receiving hole. The third circuit substrate includes a third circuit layer, a third base layer, a fourth circuit layer, and an electronic element mounted on the third circuit layer. The third circuit layer and the fourth circuit layer are formed on the opposite sides of the third base layer. The electronic element is received in the receiving hole. The flexible circuit substrate includes a flexible base layer and a flexible circuit layer. The first circuit layer is electrically connected to the fourth circuit layer by the flexible circuit layer. The invention indicates a simple and low-cost method to manufacture embedded printed circuit boards. However, it is still fail to expose the embedded electronic element. As well, no solution for protective an expose embedded active component is mentioned. 
     Therefore, a method for manufacturing printed circuit board which has an electronic component embedded, allowing the electronic component exposed to external environment, providing necessary designs for the electronic component to work and minimizing the overall thickness of the printed circuit board assembly is still desired. 
     SUMMARY OF THE INVENTION 
     This paragraph extracts and compiles some features of the present invention; other features will be disclosed in the follow-up paragraphs. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims. 
     In accordance with an aspect of the present invention, a printed circuit board having an electronic component embedded, comprises: a first electrically conductive layer; a first core layer having a portion removed to expose at least a portion of the electronic component and a portion of a second core layer; the second electrically conductive layer; a second core layer having an area which is hollow so as to locate the electronic component therein; a third electrically conductive layer; a third core layer; and a fourth electrically conductive layer. A bound pad is formed on a portion of a top surface of the electronic component. A number of via holes from the bound pad to the first electrically conductive layer are formed and electrically connected therebetween. Each of the electrically conductive layers forms a desired circuit. At least one side of an exposed top surface of the electronic component is higher than or equal to a side of a top surface of the exposed second core layer neighboring to each other. 
     Preferably, the electronic component is an integrated circuit (IC), a module or a light emitting diode (LED). 
     Preferably, the integrated circuit is a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS). 
     Preferably, the module is a fingerprint reader module. 
     Preferably, the bound pad is a layer of copper, aluminum, gold or alloy thereof, having thickness of 4 μm or thicker. 
     Preferably, the bound pad is at least 200 μm×200 μm. 
     Preferably, the via hole is a laser via hole or a plated through hole. 
     Preferably, a wire bonding is applied in the laser via hole to electrically connect two sides thereof. 
     Preferably, an adhesive is applied between adjacent electrically conductive layer and core layer for lamination. 
     Preferable, the bound pad is used to electrically link the electronic component to the first electrically conductive layer and provide protection to the electronic component when the via holes are forming. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cross-sectional view of a multilayer printed circuit board in a first embodiment according to the present invention. 
         FIG. 2  illustrates another cross-sectional view of the multilayer printed circuit board after a removing process in the first embodiment. 
         FIG. 3  is an illustrative top view of the multilayer printed circuit board in the first embodiment. 
         FIG. 4  is a flowchart of a method of manufacturing a printed circuit board which has an electronic component embedded according to the present invention. 
         FIG. 5  illustrates a cross-sectional view of a multilayer printed circuit board in a second embodiment according to the present invention. 
         FIG. 6  illustrates a cross-sectional view of a multilayer printed circuit board in a third embodiment according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described more specifically with reference to the following embodiments. 
     First Embodiment 
     Please refer to  FIG. 1  to  FIG. 4 . A first embodiment of the present invention is disclosed.  FIG. 1  illustrates a cross-sectional view of a multilayer printed circuit board in the first embodiment according to the present invention.  FIG. 2  illustrates another cross-sectional view of the multilayer printed circuit board after a removing process in the first embodiment.  FIG. 3  is an illustrative top view of the multilayer printed circuit board in the first embodiment.  FIG. 4  is a flowchart of a method of manufacturing a printed circuit board which has an electronic component embedded according to the present invention. 
     According to the present invention, a method of manufacturing a printed circuit board which has an electronic component embedded starts from providing a multilayer printed circuit board  100  (S 01 ). The multilayer printed circuit board  100  is a 4-layer printed circuit board and has at least four electrically conductive layers and three core layers. In the present embodiment, there are a first electrically conductive layer  101 , a first core layer  111 , a second electrically conductive layer  102 , a second core layer  112 , a third electrically conductive layer  103 , a third core layer  113  and a fourth electrically conductive layer  104 . In order to have a better description of the embodiment and make it easy to understand the drawings, the first electrically conductive layer  101  uses two blocks to represent the cross section of a real circuit layout of copper. So are the second electrically conductive layer  102 , the third electrically conductive layer  103  and the fourth electrically conductive layer  104 . Each of the electrically conductive layers forms a desired circuit. It should be noticed that sketches of  FIG. 1  and  FIG. 2  are not to scale. Dimensions in vertical direction are exaggerated just for a clear view. 
     An embedded portion  1121  of the second core layer  112  is hollow and an electronic component is located there. In this embodiment, the electronic component is a fingerprint reader module  121 . The fingerprint reader module  121  has a bound pad  1211  at a top surface of the fingerprint sensor  121 . Preferably, it is along one edge of that surface. The only bound pad  1211  is shown because the cross section only has one bound pad. The number of the bound pad  1211  is not limited to one. There can be many bound pads based on the requirement of design. The fingerprint reader module  121  has a p-type substrate  122  at its bottom. It is fixed and electrically linked to the third electrically conductive layer  103  by a conductive adhesive  1221 . 
     According to the present invention, the electronic component can be other device. For example, an integrated circuit (IC), another module or a light emitting diode (LED) is commonly used. Most applied components are a charge-coupled device (CCD) and a complementary metal-oxide-semiconductor (CMOS). This is because a portion of those components needs to be exposed to the external environment to perform normal functions. For instance, the fingerprint reader module  121  is a kind of charge-coupled device. It needs to identify a specified fingerprint by detect change of capacitances when a finger is in contact with its sensor surface (not shown). Therefore, the sensor must face out from the multilayer printed circuit board  100  rather than be blocked by some part of the multilayer printed circuit board  100 . 
     The bound pad  1211  is coated with a layer of copper. In practice, the coated material is not limited to copper. It can be aluminum, gold or alloy of the metals. It has thickness of 4 μm or thicker. Sizewise, the bound pad  1211  is around 200 μm×200 μm. According to the present invention, 200 μm×200 μm is the smallest area which can be embedded in the multilayer printed circuit board  100 . 
     Next, according to the present invention, form a number of via holes for electrical conduction (S 02 ). That is, the via holes are formed from the bound pad  1211  to the first electrically conductive layer  101 . A first plated through hole  131  is used in  FIG. 1  and  FIG. 2  for illustration. When the multilayer printed circuit board  100  was formed and the fingerprint reader module  121  is embedded, many other via holes were already ready. For example, a second plated through hole  132  and a buried via hole  133  were formed. However, these via holes are made only for electrical conduction between two electrically conductive layers. The first plated through hole  131  made by S 02  is only for electrical conduction between one electrically conductive layer (or circuit) with the fingerprint reader module  121 , for providing power to the fingerprint reader module  121  and data transmission. Of course, the first plated through hole  131  is not limited to link to the first electrically conductive layer  101  on the top side. The bound pad  1211  is used to electrically link the fingerprint sensor  121  to the first electrically conductive layer  101  and provide protection to the fingerprint sensor  121  when the first plated through hole  131  was forming. 
     Then, electrically connect two sides of each via hole (S 03 ). This is for the fingerprint reader module  121  to get power, link to other circuit in other electrically conductive layer and transmit data. 
     Finally, remove a portion of the first core layer  111  to expose at least a portion of the fingerprint reader module  121  and a portion of the second core layer  112  (S 04 ). Comparing  FIG. 1  and  FIG. 2 , a portion of the first core layer  111  between dash lines are removed. In this embodiment, there is no first electrically conductive layer  101  extending to the top surface of the removed portion of the first core layer  111  because no designer will waste material. Therefore, the present invention doesn&#39;t emphasize on this. It should be emphasized that it is not necessary to expose all the top surface of the fingerprint reader module  121 . It is workable to reveal only the “reader portion” and conceal other portion under the protection of the first core layer  111  as show in  FIG. 1  and  FIG. 2 . The size of exposed area to the external environment also varies with the printed circuit board design. Please refer to  FIG. 3 . It is a top view of the multilayer printed circuit board  100 . It is easily to identify that only a portion of the fingerprint reader module  121  and a portion of the second core layer  112  are exposed. It is noticed that the circuit on  FIG. 3  is also illustrative. It is not necessarily identical to the design shown on the cross-sectional view in  FIG. 1  and  FIG. 2 . 
     A key point of the present invention is that at least one side of an exposed top surface of the fingerprint reader module  121  is higher than or equal to a side of a top surface of the exposed second core layer  112  neighboring to each other. Please see  FIG. 2  again. The solid double-arrowed line is the height of the revealed top surface of the fingerprint reader module  121  to the third core layer  113 . The dash double-arrowed line is the height of the revealed top surface of the second core layer  112  to the third core layer  113 , including an adhesive layer  141 . The difference in between shows one side of the exposed top surface of the fingerprint reader module  121  is higher than the neighboring side of the top surface of the exposed second core layer  112 . 
     For the fingerprint reader module  121 , it has an advantage that the when a user&#39;s finger is in contact with the top of the “reader portion”, the exposed second core layer  112  won&#39;t cause a blind corner to partially block the finger to be detected. 
     Meanwhile, the step of removing is realized by a die-cutting process. It means that there is not adhesive below the removed portion of the first core layer  111 . The removed portion of the first core layer  111  can easily be removed with glue after die-cutting. According to the spirit of the present invention, the adhesive layer  141  is applied between adjacent electrically conductive layer and core layer for lamination, but not necessary for all of them, as long as a laminating process is required. 
     According to the arrangement mentioned above, the thickness of the printed circuit board assembly with fingerprint reader module  121  embedded can be thinner than the one with fingerprint reader module  121  mounted on. Thus, it meets the trend to make electronic products small in size and compact in thickness. 
     Second Embodiment 
     Please refer to  FIG. 5 .  FIG. 5  illustrates a cross-sectional view of a multilayer printed circuit board in the second embodiment according to the present invention. 
     A multilayer printed circuit board  200  is a 4-layer printed circuit board and has a first electrically conductive layer  201 , a first core layer  211 , a second electrically conductive layer  202 , a second core layer  212 , a third electrically conductive layer  203 , a third core layer  213 , a fourth electrically conductive layer  204 , a second plated through hole  232 , a buried via hole  233 , an conductive adhesive  2221 , and an adhesive layer  241 . Functions and relative locations of the items mentioned above correspond to the first electrically conductive layer  101 , the first core layer  111 , the second electrically conductive layer  102 , the second core layer  112 , the third electrically conductive layer  103 , the third core layer  113 , the fourth electrically conductive layer  104 , the second plated through hole  132 , the buried via hole  133 , the conductive adhesive  1221 , and the adhesive layer  141  in the first embodiment, respectively. It is not necessary to illustrate them to same time. 
     The difference between the first embodiment and the second embodiment is that a light emitting diode  221  with a p-type substrate  222  below is used as the embedded electronic component to be exposed. The light emitting diode  221  has a bound pad  2211  at a top surface of the light emitting diode  221 . The number of the bound pad  2211  is also not limited to one. There can be many bound pads based on the requirement of design. The light emitting diode  221  has a p-type substrate  222  at its bottom. It is fixed and electrically linked to the third electrically conductive layer  203  by a conductive adhesive  2221 . 
     As many people may know that the light emitting diode  221  emits light in a specified direction, for example, in this embodiment, it is upward. Please refer to  FIG. 5 . The solid double-arrowed line is the height of the revealed top surface of the light emitting diode  221  to the third core layer  213 . The dash double-arrowed line is the height of the revealed top surface of the second core layer  212  to the third core layer  213 , including the adhesive layer  241 . There is no difference between those two lines. It meant one side of the exposed top surface of the light emitting diode  221  is flush with the neighboring side of the top surface of the exposed second core layer  212 . Light beams of the light emitting diode  221  can transmit out without being stopped and the light emitting diode  221  can get protection by the second core layer  212  around. 
     The other difference is that a via hole  231  is a laser via hole. Not like the first plated through hole  131  in the first embodiment, the via hole  231  has no conductive material coated inside. Therefore, a wire bonding  2311  is applied in the laser via hole  231  to electrically connect two sides. 
     Third Embodiment 
     Please refer to  FIG. 6 .  FIG. 6  illustrates a cross-sectional view of a multilayer printed circuit board in a third embodiment according to the present invention. 
     A multilayer printed circuit board  300  is a 4-layer printed circuit board and has a first electrically conductive layer  301 , a first core layer  311 , a second electrically conductive layer  302 , a second core layer  312 , a third electrically conductive layer  303 , a third core layer  313 , a fourth electrically conductive layer  304 , a conductive adhesive  3221 , a first plated through hole  331 , a second plated through hole  332 , a buried via hole  333  and an adhesive layer  341 . Functions and relative locations of the items mentioned above correspond to the first electrically conductive layer  101 , the first core layer  111 , the second electrically conductive layer  102 , the second core layer  112 , the third electrically conductive layer  103 , the third core layer  113 , the fourth electrically conductive layer  104 , the conductive adhesive  1221 , the first plated through hole  131 , the second plated through hole  132 , the buried via hole  133  and the adhesive layer  141  in the first embodiment, respectively. It is not necessary to illustrate them to same time. 
     The difference between the first embodiment and the third embodiment is that a module  321  with a p-type substrate  322  below which has uneven top surface is used as the embedded electronic component to be exposed. According to the spirit of the present invention, any kind of module can be applied as long as there is a requirement to make the printed circuit board as slim as possible. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.