Patent Publication Number: US-2023160764-A1

Title: Pressure sensing circuit board and method for manufacturing the same

Description:
FIELD 
     The disclosure relates to pressure sensing, and more particularly, to a pressure sensing circuit board and a method for manufacturing the pressure sensing circuit board. 
     BACKGROUND 
     With the development of intelligent life, intelligent devices are applied in various fields, such as communication, medical treatment, automobile, and industrial control. Such intelligent devices are usually equipped with pressure sensors. 
     The existing pressure sensors include capacitive pressure sensor, resistance pressure sensor, and piezoelectric ceramic pressure sensor. The capacitive pressure sensor requires high machining accuracy. The resistance pressure sensor has poor linearity and durability. The piezoelectric ceramic pressure sensors require high temperature sintering during fabrication, the fabrication process is difficult, and can only be used to test an instantaneous pressure. Upper and lower surfaces of such pressure sensor need to be supported. 
     SUMMARY 
     To overcome the above shortcomings, a pressure sensing circuit board is needed. 
     In addition, a method for manufacturing the pressure sensing circuit board is needed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-sectional view of a copper-cladding substrate including a dielectric layer and a copper layer according to an embodiment of the present disclosure. 
         FIG.  2    is a cross-sectional view wherein the copper layer of  FIG.  1    is partially etched to form a second copper area and a first copper area. 
         FIG.  3    is a cross-sectional view wherein a copper layer in the second copper area of  FIG.  2    is partially removed to form a copper-free area, and wirings are made on the copper layer to form a wiring layer to form a wiring layer. 
         FIG.  4    is a top view of a portion of the wiring layer having mesh-shaped wirings according to an embodiment of the present disclosure. 
         FIG.  5    is a top view of a portion of the wiring layer having corrugated wirings according to another embodiment of the present disclosure. 
         FIG.  6    is a top view of a portion of the wiring layer having horseshoe-shaped wirings according to yet another embodiment of the present disclosure. 
         FIG.  7    is a cross-sectional view wherein an insulating layer covers the wiring layer in the first copper area of  FIG.  3   . 
         FIG.  8    is a cross-sectional view wherein a strain layer is formed on the dielectric layer in the copper-free zone of  FIG.  7   . 
         FIG.  9    is a cross-sectional view wherein a protective layer is formed on the wiring layer in the second copper area and the strain layer of  FIG.  8   , to form a pressure sensing circuit board. 
         FIG.  10    is a cross-sectional view of a Wheatstone bridge formed by the strain layer according to an embodiment of the present disclosure. 
     
    
    
     Symbol description of main components: 
     pressure sensing circuit board  100 , copper-cladding substrate  10 , dielectric layer  12 , copper layer  14 , wiring layer  145 , insulating layer  20 , strain layer  30 , protective layer  40 , first copper area I, second copper area II, copper-free zone III, resistance R 1 , R 2 , R 3 , or Rx. 
     Many aspects of the disclosure may be better understood with reference to the drawings. 
     DETAILED DESCRIPTION 
     Implementations of the disclosure will now be described, by way of embodiments only, with reference to the drawings. It should be noted that non-conflicting details and features in the embodiments of the present disclosure may be combined with each other. Many specific details are described in the following description to facilitate full understanding of the disclosure. The described embodiments are only portions of but not all of the implementation of the disclosure. Based on the embodiments of the disclosure, other embodiments obtained by ordinary skill in the art without creative work belong to the scope of the disclosure. 
     Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The technical terms used herein are only for the purpose of describing specific embodiments, not to be considered as limiting the scope of the embodiments. The term “and/or” used herein includes all or any combination of one or more related listed items. 
     In the embodiment of the disclosure, in order to facilitate rather than limit the disclosure, the term “connect” used in the specification and the claims, whether direct or indirect, is not limited to physical or mechanical connection. The terms “up”, “down”, “above”, “below”, “left”, “right”, etc. are only used to represent relative position relationships. When the absolute position of the described object changes, the relative position relationship changes accordingly. 
     Referring to  FIGS.  1  to  10   , an embodiment of the present disclosure provides a manufacturing method of a pressing sensing circuit board  100 , which includes the following steps. 
     Step S 1 , referring to  FIG.  1   , a copper-cladding substrate  10  is provided, which includes a dielectric layer  12  and a copper layer  14  formed on the dielectric layer  12 . 
     The dielectric layer  12  can be rigid or flexible. The dielectric layer  12  may include, but are not limited to, polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalene-2,6-dicarboxylate (PEN), liquid crystal polymer (LCP), and modified polyimide (MPI). 
     The copper layer  14  may be on a surface or two opposite surfaces of the dielectric layer  12 . In an embodiment, the copper layer  14  is on a surface of the dielectric layer  12 . 
     In some embodiments, an embedded wiring layer (not shown), which is electrically connected to the copper layer  14 , may be formed in the dielectric layer  12 , so that the pressing sensing circuit board  100  has multilayer wiring layers. 
     Step S 2 , referring to  FIG.  2   , the copper layer  14  is partially etched to form a second copper area II and a first copper area I. 
     After the copper layer  14  is partially etched, a thickness of the copper layer  14  in an area is reduced and a thickness of the copper layer  14  in another area remains unchanged. The area where the thickness of the copper layer  14  is reduced is the second copper area II, and the area where the thickness of the copper layer  14  remains unchanged is the first copper area I. 
     Step S 3 , referring to  FIGS.  3  to  6   , the copper layer  14  in the second copper area II is partially removed to form a copper-free area III, so that the dielectric layer  12  is partially exposed. The copper layer  14  is etched into a wiring layer  145 . The wiring layer  145  include a mesh-shaped wiring portion  1450 , and a gridding treatment is performed on the remaining copper layer  14  in the second copper area II to form the mesh-shaped wiring portion  1450 . 
     The copper layer  14  is absent on the dielectric layer  12  in the copper-free zone III. 
     The copper-free area III and the first copper area I are spaced from each other by the second copper area II. The first copper area I, the second copper area II, and the copper-free area III form stepped surfaces. That is, along a stacking direction of the copper layer  14  and the dielectric layer  12 , the thickness of the copper layer  14  in the first copper area I is greater than that of the copper layer  14  in the second copper area II. 
     The gridding treatment is performed on the remaining copper layer  14  in the second copper area II, and the copper layer  14  in the second copper area II is partially etched or removed again to form a mesh shape. In an embodiment, the copper layer  14  in the second copper area II is partially removed to expose the dielectric layer  12 . 
     The wirings of the mesh-shaped wiring portion  1450  formed by the gridding treatment can be connected to or disconnected from each other. The mesh-shaped wiring portion  1450  may include, but not limited to, mesh-shaped wirings crosslinked with each other (see  FIG.  4   ), corrugated wirings not crosslinked with each other (see  FIG.  5   ), and horseshoe-shaped wirings (see  FIG.  6   ). The mesh-shaped wiring portion  1450  is easily deformed under an external force, which improves the strain capacity of the wiring layer  145 . 
     Step S 4 , referring to  FIG.  7   , an insulating layer  20  covers the wiring layer  145  in the first copper area I. 
     The insulating layer  20  can avoid oxidation of the wiring layer  145 . 
     Step S 5 , referring to  FIG.  8   , a strain layer  30  is formed on the dielectric layer  12  of the copper-free zone III. 
     The strain layer  30  is made of a material that changes the resistance when being deformed under the external force, including but not limited to a metal or a carbon containing conductive resin. 
     During the process of forming the strain layer  30 , a thickness of the strain layer  30  is greater than that of the copper layer  14  in the second copper area II. Due to the fluidity of the strain layer  30 , the strain layer  30  also covers a portion of the wiring layer  145  adjacent to the copper-free zone III. Since the strain layer  30  covers at least a portion of the wiring layer  145  in the second copper area II, the strain layer  30  and the wiring layer  145  forms an overlapping structure, which increases a contact area between the strain layer  30  and the wiring layer  145 , and also increase connection reliability and avoid poor contact. 
     In some embodiments, before forming the strain layer  30 , a step of forming a treatment layer on the wiring layer  145  is also included, and the treatment layer avoids oxidation of the wiring layer  145 . 
     Step S 6 , referring to  FIG.  9   , a protective layer  40  is formed on the wiring layer  145  in the second copper area II, and the protective layer  40  also covers the strain layer  30 . Then, the pressing sensing circuit board  100  is obtained. 
     The protective layer  40  is made of an insulating ink layer, and the ink layer has good ductility. The protective layer  40  will not crack under the external force. 
     In some embodiments, the step of forming the insulating layer  20  may be after the step of forming the strain layer  30  and/or the protective layer  40 . 
     Referring to  FIG.  10   , the pressing sensing circuit board  100  further includes three resistors R 1 , R 2 , and R 3  with fixed resistance values. The resistor R 1  is connected in series with the resistor R 2 . The resistor R 3  is connected in series with the resistor Rx composed of the strain layer  30 . Then, the resistor R 1  and the resistor R 2  connected in series are further connected in parallel with the resistor R 3  and the resistor Rx connected in series, thus forming a Wheatstone bridge. The characteristics of the bridge are used when building the entire circuit loop, so that the pressing sensing circuit board  100  can work more sensitive and effective. 
     Specifically, when the resistance Rx composed of the strain layer  30  changes, a voltage between two points B and D in the figure also changes. The change of resistance Rx can be calculated by the change of voltage, and the external force applied on the strain layer  30  can also be calculated accordingly. 
     Referring to  FIG.  9   , a pressure sensing circuit board  100  is also provided according to an embodiment of the present disclosure, which includes a dielectric layer  12 , a wiring layer  145 , a strain layer  30 , and a protective layer  40 . The wiring layer  145  is formed on a surface of the dielectric layer  12 . The strain layer  30  is formed on the surface of the dielectric layer  12  having the wiring layer  145 . The protective layer  40  is formed on the wiring layer  145  and the strain layer  30 . 
     The pressing sensing circuit board  100  includes a first copper area I, a second copper area II, and a copper-free area III connected in that order. The wiring layer  145  is located in the first copper area I and the second copper area II. Along a stacking direction of the wiring layer  145  and the dielectric layer  12 , a thickness of the wiring layer  145  in the first copper area I is greater than that of the wiring layer  145  in the second copper area II. A portion of the wiring layer  145  located in the second copper area II is mesh-shaped. The strain layer  30  is located in the copper-free zone III and connected to the wiring layer  145 . The protective layer  40  is located on the wiring layer  145  in the second copper area II and covers the strain layer  30 . 
     When the protective layer  40  is subjected to an external force, the external force is transmitted to the strain layer  30 . The strain layer  30  generates strain under the external force, and the resistance of the strain layer  30  changes, thereby changing the resistance of the pressure sensing circuit board  100  in the circuit loop. When the resistance changes, the voltage monitored in the electrical circuit will change, and the value of the external force applied on the strain layer  30  can be calculated according to the change of voltage. 
     The dielectric layer  12  may be rigid or flexible. The dielectric layer  12  may include, but are not limited to, polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalene-2,6-dicarboxylate (PEN), liquid crystal polymer (LCP), and modified polyimide (MPI). In some embodiments, the dielectric layer  12  is flexible, so that the pressure sensing circuit board  100  is flexible and can be bent at a suitable position to meet different needs. 
     The wirings of the mesh-shaped wiring portion  1450  can be connected to or disconnected from each other. The mesh-shaped wiring portion  1450  includes but not limited to at least one of mesh-shaped wirings crosslinked with each other, corrugated wirings not cross-linked with each other, and horseshoe-shaped wirings. The mesh-shaped wiring portion  1450  is easily deformed under the external force, which can improve the strain capacity of the wiring layer  145 . 
     In some embodiments, along the stacking direction of the wiring layer  145  and the dielectric layer  12 , the thickness of the strain layer  30  is greater than that of the wiring layer  145  in the second copper area II, so that at least a portion of the strain layer  30  covers a portion of the wiring layer  145  in the second copper area II. That is, the strain layer  30  and the wiring layer  145  forms an overlapping structure, which increases the contact area between the strain layer  30  and the wiring layer  145  and also improves the connection reliability and avoid poor contact. 
     In some embodiments, the strain layer  30  is further located in the second copper area II and covers a portion of the wiring layer  145  in the second copper area II. The second copper area II and the strain layer  30  form an overlapping structure with the wiring layer  145 . 
     The protective layer  40  is formed on the wiring layer  145  and the strain layer  30 . On the one hand, the protective layer  40  can protect the wiring layer  145  and avoid oxidation of the wiring layer  145 . On the other hand, the protective layer  40  also has ductility to prevent cracks in the protective layer  40  when the protective layer  40  is subjected to the external force. 
     In some embodiments, the pressing sensing circuit board  100  further includes an insulating layer  20 , which covers the wiring layer  145  in the first copper area Ito protect the wiring layer  145 . 
     Referring to  FIG.  10   , the pressing sensing circuit board  100  further includes three resistors R 1 , R 2 , and R 3  with fixed resistance values. The resistor R 1  is connected in series with the resistor R 2 . The resistor R 3  is connected in series with the resistor Rx composed of the strain layer  30 . Then, the resistor R 1  and the resistor R 2  connected in series are further connected in parallel with the resistor R 3  and the resistor Rx connected in series, thus forming a Wheatstone bridge. The characteristics of the bridge are used when building the entire circuit loop, so that the pressing sensing circuit board  100  can work more sensitive and effective. 
     The pressure sensing circuit board  100  in the present disclosure includes the dielectric layer  12  and the wiring layer  145  and the strain layer  30  formed on the dielectric layer  12 . When the strain layer  30  is subjected to the external force, the resistance of the strain layer  30  changes, thereby changing the resistance of the pressure sensing circuit board  100  in the circuit loop. The voltage monitored in the circuit loop then changes. The value of the external force applied on the strain layer  30  can be calculated according to the change of voltage. The resistance of strain layer  30  changes linearly under the external force, and the resistance recovers only when the external force is removed. The external force at any time can be tested, and the linearity is good. The durability of the pressure sensing circuit board  100  is improved by setting the protective layer  40  on the strain layer  30 . In the second copper area II of the pressing sensing circuit board  100 , the mesh-shaped wiring portion  1450  improves the strain capacity of the wiring layer  145 , thereby improving the sensitivity of the pressing sensing circuit board  100 . The dielectric layer  12  is arranged on a single surface of the wiring layer  145 , the strain layer  30 , and the protective layer  40 , which simplifies the structure of the pressure sensing circuit board  100 . The pressure sensing circuit board  100  also has a simple manufacturing method. 
     Although the embodiments of the present disclosure have been shown and described, those having ordinary skill in the art can understand that changes may be made within the principles of the present disclosure, up to and including the full extent established by the broad general meaning of the terms used in the claims. It will, therefore, be appreciated that the embodiments described above may be modified within the scope of the claims.