Patent Publication Number: US-2021176568-A1

Title: Guard ring in cavity pcb

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the priority benefit of U.S. Provisional patent Application No. 62/946,368, filed Dec. 10, 2019 and incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates generally to the field of microphone assemblies and substrates for such assemblies. 
     Microphone assemblies are utilized in a variety of applications, such as, mobile phones, and recording devices, to record acoustic signals. Microphone assemblies can include a can soldered to a substrate to protect components and improve functions of the microphone assemblies. Solder contacting the components can cause malfunctioning and/or failure of the microphone assembly during operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. These drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope. Various embodiments are described in more detail below in connection with the appended drawings. 
         FIG. 1  is a partial-section view of a microphone assembly. 
         FIG. 2  is a partial-section view of the microphone assembly of  FIG. 1 . 
         FIG. 3A  is a perspective view of an array of microphone assemblies. 
         FIG. 4A  is a partial-section view of the array of microphone assemblies of  FIG. 3A . 
         FIG. 3B  is a perspective view of an array of microphone assemblies. 
         FIG. 4B  is a partial-section view of the array of microphone assemblies of  FIG. 3B . 
         FIG. 3C  is a perspective view of an array of microphone assemblies. 
         FIG. 4C  is a partial-section view of the array of microphone assemblies of  FIG. 3C . 
         FIG. 5A  is a graph of electromagnetic compatibility at 0 degrees. 
         FIG. 5B  is a graph of electromagnetic compatibility at 90 degrees. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments disclosed herein are structured to limit flow of solder onto components mounted on the substrate during manufacturing. In particular, the microphone assemblies disclosed herein have a trench on a surface of the substrate which is formed during manufacturing of the microphone assemblies. The trench is shaped to have the can mounted thereon and limit contact of the solder with the components on the substrate. The trench may be formed around a perimeter of the substrate and a portion of the can extends below a surface of the substrate and is mounted to a surface of the trench. 
     During production, a plurality of microphone assemblies may be formed as an array. The trench of each of the microphone assemblies of the array may be manufactured during a single manufacturing step. The trench is at least partially filled with a bonding material, such as solder, to couple the can to the substrate. 
     Among other benefits, the surface of the substrate being raised relative to a surface of the trench restricts the solder from flowing onto the components on the substrate. The overall size of the microphone assembly can also be reduced, as the can extends partially below the surface of the substrate. The can may also form a barrier to reduce signal leaking from the substrate. The details of the general depiction provided above will be more fully explained by reference to  FIGS. 1-5B . 
     Referring generally to the figures a microphone assembly  10  is shown. Microphone assembly  10  is configured to sense acoustic activity (e.g., sound waves, etc.) and generate an electrical signal in response to the acoustic activity. Microphone assembly  10  is configured to be installed within a device (e.g., a mobile phone, a camera, a recorder, etc.). Microphone assembly  10  includes an acoustic transducer  12 . Acoustic transducer  12  is configured to generate an electrical signal responsive to acoustic activity. In some embodiments, acoustic transducer  12  is a microelectromechanical systems (MEMS) transducer. Microphone assembly  10  also includes an integrated circuit  14 . Integrated circuit  14  is configured to receive the electrical signal from acoustic transducer  12  and generate an output signal representative of the acoustic activity. In some embodiments, integrated circuit  14  is an application specific integrated circuit (ASIC). Microphone assembly  10  also includes a substrate, shown as substrate  16 . In some embodiments, substrate  16  is a printed circuit board. In some embodiments, acoustic transducer  12  and integrated circuit  14  are coupled to substrate  16 . Microphone assembly  10  also includes a cover  18 . In some embodiments, acoustic transducer  12  is coupled to cover  18 . In some embodiments, cover  18  is a can, such as a metal can. Cover  18  is structured to define an internal cavity between cover  18  and substrate  16 . Cover  18  includes a foot, shown as foot  48 . Foot  48  protrudes from cover  18  at an angle. 
     Referring to  FIG. 1  a cross-section view of microphone assembly  10  is shown. Microphone assembly  10  includes acoustic transducer  12 , integrated circuit  14 , cover  18 , and substrate  16 . Substrate  16  is formed from at least one layer, which includes a first layer  28 . First layer  28  is configured to form a mounting surface for acoustic transducer  12  and integrated circuit  14 . In some embodiments, first layer  28  is a non-conductive material (e.g., solder mask, solder resist, solder oil, etc.). Substrate  16  also includes conductive layers  30 ,  34 ,  36 , and  40 , and nonconductive layers  32 , and  38 . In other embodiments, different numbers of layers or different layers may be utilized. Substrate  16  includes a second layer  42  opposite first layer  28 . Second layer  42  defines an outer surface of microphone assembly  10 . In some embodiments, second layer  42  is a non-conductive material (e.g., solder mask, solder resist, solder oil, etc.). In some embodiments, substrate  16  defines port  26  formed through the layers of substrate  16 . In other embodiments, cover  18  defines a port (e.g., similar to port  26  and performing the same function), extending through cover  18 . Port  26  is structured to provide a pathway for acoustic signals to pass through substrate  16 , or cover  18  and into contact with acoustic transducer  12 . 
     Substrate  16  also defines a trench  46  around a perimeter of substrate  16 . Trench  46  is formed by conductive layer  30  and nonconductive layers  32  being smaller (e.g., smaller diameter) than conductive layers  34 ,  36 , and  40  and nonconductive layer  38 . In other embodiments, trench  46  is defined by different layers of substrate  16 . Conductive layer  34  defines a surface to which cover  18  couples (e.g., with a bonding material  44 ). 
     Referring to  FIG. 2 , trench  46  is shown with greater detail. Foot  48  of cover  18  is between first layer  28  and conductive layer  34 , when cover  18  is coupled to trench  46 . First layer  28  defines a first surface  29 , to which acoustic transducer  12  and integrated circuit  14  are coupled. Conductive layer  34  defines a second surface  52 , to which at least one of foot  48  and bonding material  44  are coupled. First layer  29  is raised relative to second surface  52 , facilitating first layer  28 , conductive layer  30 , and nonconductive layer  32  being disposed within a perimeter of cover  18 . In some embodiments, foot  48  being between first layer  28  and conductive layer  34  facilitates formation of a barrier, within cover  18 , for limiting acoustic signals from leaving substrate  16 . Side walls of first layer  28 , conductive layer  30 , and nonconductive layer  32 , define side wall  49  of trench  46 . Side wall  49  helps cover  18  couple to substrate  49  by defining another surface to which bonding material  44  can adhere. 
       FIG. 3A  is a partial view of an array  10  of microphone assembly substrates  16 . A spacing layer  50  separates each microphone assembly substrate from each other a distance d3 (e.g., 174±5 μm, etc.). Spacing layer  50  is a portion of nonconductive layer  32 . In some embodiments, spacing layer  50  is formed separately of nonconductive layer  32 . Spacing layer  50  also defines a side wall of trench  46 . 
       FIG. 4A  is a section view of the array  10  of microphone assembly substrates  16 . During manufacturing of substrate  16 , conductive layers  30 ,  34 ,  36 , and  40 , nonconductive layers  32  and  38 , first layer  28 , and second layer  42  are coupled to form substrate  16 . Trench  46  around a perimeter of each substrate  16 . Trench  46  is defined by side wall  49  and spacing layer  50  on sides, and second surface  52  of conductive layer  34  on a bottom. In some embodiments, trench  46  is formed by removal of a portion of substrate  16  (e.g., laser, etc.). In other embodiments, trench  46  is formed during coupling of layers of substrate  16 , without removal of material. Trench  46  is formed to have a lower distance, d1, of 203-207 μm, and an upper distance, d2, of 227-235 μm. In some embodiments, d1 and d2 are equal. 
       FIG. 3B  is the array  10  of microphone assembly substrates  16  during formation of trench  46 . Acoustic transducer  12  and integrated circuit  14  are coupled to each substrate  16 . Trench  46  of each microphone assembly  10  is at least partially filled with bonding material  44 . 
       FIG. 4B  is a section view of the array  10  of microphone assembly substrates  16  during formation of trench  46 . Trench  46  is at least partially filled with bonding material  44 . Bonding material  44  is held within trench  46  by spacing wall  50  and side wall  49 . First surface  29  being raised relative to second surface  52  limits bonding material  44  from leaving trench  46 . 
       FIG. 3C  is an array of microphone assemblies  10  during coupling of cover  18  to substrate  16 . Each substrate  16  accepts a cover  18 , which limits access to acoustic transducer  12  and integrated circuit  14 . 
       FIG. 4C  is a section view of the array of microphone assemblies  10  during coupling of cover  18  to substrate  16 . Trench  46  accepts foot  48  of cover  18  and bonding material  44  couples cover  18  to substrate  16 . Foot  48  is lowered relative to first layer  28  when cover  18  is coupled to substrate  16 . In some embodiments, foot  48  contacts second surface  52 . In other embodiments, foot  48  is raised relative to second surface  52  and bonding material interfaces between second surface  52  and foot  48 . Each individual microphone assembly  10  of the array of microphone assemblies  10  is diced from each other to form microphone assembly  10 . In some embodiments, dicing occurs at a dicing line, shown as dicing line A. In other embodiments, dicing occurs at another dicing line, shown as dicing line B. 
       FIGS. 5A and 5B  are a graph of test results of microphone assembly  10 . Acoustic signals are directed toward a microphone assembly at an angle. The microphone assembly being tested has a response in decibels representing a resistance of the microphone assembly to unintentional acceptance of acoustic signals. A first table, shown as table  100 , represents an Electro Magnetic Compatibility (e.g., EMC, etc.) test at 0 degrees. Lines  114  and  116  each represent a response of an existing microphone assembly to the acoustic signals. Lines  118  and  120  each represent a response of microphone assembly  10  to the acoustic signals. Another table, shown as table  120 , represents an Electro Magnetic Compatibility (e.g., EMC, etc.) test at 90 degrees. Lines  134  and  136  represent a response of an existing microphone assembly to the acoustic signals. Lines  138  and  140  represent a response of microphone assembly  10  to the acoustic signals. Microphone assembly  10 , as shown by lines  118  and  120  in table  100  and lines  138  and  140  in table  120 , has better resistance to external RF signals than prior microphone assemblies. 
     A first aspect of the present disclosure relates to a microphone assembly. The microphone assembly including an acoustic transducer configured to generate an electrical signal responsive to acoustic activity, an integrated circuit electrically coupled to the acoustic transducer and configured to receive the electrical signal from the acoustic transducer and generate an output signal representative of the acoustic activity, a cover, and a substrate. The substrate including a first surface and a second surface to which the cover is coupled, wherein the second surface is disposed at a perimeter of the substrate and the first surface is raised with respect to the second surface wherein the cover is coupled to the substrate to form a housing in which the transducer and integrated circuit are disposed. 
     A second aspect of the present disclosure relates to a microphone assembly substrate. The substrate including a first surface defined by a first layer, and a second surface defined by a second layer. The first surface is raised relative to the second surface. The substrate also including a third surface defined by a third layer, and a conductive trace on the first surface and extending to the third surface, the conductive trace facilitating electrical signal transmission from a component mounted on the first surface to a device external the microphone assembly. 
     The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are illustrative, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable,” to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components. 
     With respect to the use of plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 
     It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). 
     Although the figures and description may illustrate a specific order of method steps, the order of such steps may differ from what is depicted and described, unless specified differently above. Also, two or more steps may be performed concurrently or with partial concurrence, unless specified differently above. Such variation may depend, for example, on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure. Likewise, software implementations of the described methods could be accomplished with standard programming techniques with rule-based logic and other logic to accomplish the various connection steps, processing steps, comparison steps, and decision steps. 
     It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation, no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). 
     Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general, such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” 
     Further, unless otherwise noted, the use of the words “approximate,” “about,” “around,” “substantially,” etc., mean plus or minus ten percent. 
     The foregoing description of illustrative embodiments has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.