Description PACKAGING STRUCTURE OF MEMS MICROPHONE

Technical Field

[1] The present invention relates to a packaging structure of a MEMS microphone, and more particular, to a packaging structure of a MEMS microphone for securing binding force between a printed circuit board (PCB) and a case. Background Art

[2] In general, a microphone is classified, based on a method of converting mechanical vibration into electric signals, into a carbon microphone, a crystal microphone, a moving-coil microphone, a velocity microphone, and a condenser microphone. The carbon microphone uses electrical resistance characteristic of carbon grains. The crystal microphone uses piezo-electricity effect of rochelle salt. The moving-coil microphone vibrates a diaphragm having a coil in the magnetic field to generate induced current. The velocity microphone uses a phenomenon that induced current is created when a metal leaf set within the magnetic field receives a sound wave to vibrate. The condenser microphone uses a variation in capacitance caused by vibration of a film by a sound wave.

[3] The microphone is widely used in communication devices, e.g., mobile phones, moving picture experts group layer 3 (MP3), telephones, etc., a medical device such as a hearing aid, a built-in microphone for minimized multi-function smart sensors, or small-sized precision instruments. It is difficult to microminiaturize the microphone into a size ranging from the minimum size (μm unit) to the maximum size (mm unit) because the microphone is fabricated by a mechanical processing. However, with miniaturization of sound equipments or information communication devices in which the microphone is installed, the microminiaturization of the microphone is greatly required.

[4] Therefore, in order to overcome a limitation of the microminiaturization of the microphone, a micro electro mechanical system (MEMS) microphone that directly forms a capacitive structure on a silicon wafer by using a semiconductor technology is researched and developed. Since the MEMS microphone can be microminiaturized and fabricated through a batch process, thereby improving performance and efficiency.

[5] With the increasing demand of the microminiaturization, integration, and high performance, the MEMS microphone is fabricated by applying a semiconductor fabrication technology using a surface mount technology (SMT) and a micromachining technology.

[6] The SMT is a technique that prints a solder paste such as lead (Pb) onto a printed

circuit board (PCB) to attach a various surface mount devices (SMDs) using a mounter equipment, and then passes through a reflow machine to connect an electrical component having a lead wire to the PCB or other component. The SMT microphone mounts the electric circuit components such as an amplifier and a filter on the PCB by using the SMT, thereby simplifying the fabrication of the microphone or miniaturizing the microphone.

[7] A MEMS technology uses semiconductor processes, particularly a micromachining technology applying an Integrated Circuit (IC) technology. The micromachining technology includes a bulk micromachining, a microstructure processing, surface micromachining, thin film processing, a bonding process of substrates of the same kind or a different kind, and a three-dimensional structure molding process. A micro-based sensor, actuator, and electric mechanical structure can be fabricated using the micromachining technology. Micro machines having a size of less than a millimeter (mm) or precision of less than a micrometer (μm) may be fabricated using the micromachining technology.

[8] A MEMS die can be fabricated using the SMT and MEMS technologies. A transducer, i.e., diaphragm, which is a key component in the MEMS microphone with the microminiaturization and high performance is formed in the MEMS die. The microphone can be microminiatured by fabricating the PCB using the MEMS die and SMT technology, and also various processes can be simplified, thereby improving productivity. That is, in a packaging structure of the MEMS microphone (hereinafter, referred to as a MEMS microphone packaging structure), the MEMS die is mounted on the PCB and then the PCB is bonded to the case to fabricate the MEMS microphone.

[9] Meanwhile, in a typical MEMS microphone packaging process, when a PCB is fixed to a case by the laser welding, a copper layer of the PCB is damaged due to high laser power. As a result, a conductive pattern between components mounted on the PCB is cut off or malfunction of the components occurs due to the high laser power.

[10] The copper layer formed on the PCB and the case are formed of a metal material, but the copper layer is formed on the PCB formed of a resin-based material such as phenolic resin and epoxy resin. Therefore, the tension force between the case and the PCB is reduced to do not support each other when the copper layer is damaged. In addition, the laser power to be applied must be increased in order to secure binding between the PCB and the case. However, the laser power must be always applied below a deformation point of the copper layer of the PCB to do not provide strong binding between the PCB and the case. Therefore, the separation of the PCB from the case occurs, thereby causing malfunction of the microphone during the MEMS microphone packaging process.

Disclosure of Invention

Technical Problem

[11] Accordingly, the present invention is directed to a MEMS microphone packaging structure that substantially obviates one or more problems due to limitations and disadvantages of the related art.

[12] An object of the present invention is to provide a MEMS microphone packaging structure in which a first and second cases are molded by laser welding to prevent a copper layer of a PCB from damage caused during bonding of a typical PCB and case using the laser welding and enhance bonding force between microphone internal components and the cases.

[13] Another object of the present invention is to provide a MEMS microphone packaging structure in which laser power applied between a first and second cases formed of a metal material is greater than that applied between a copper layer of a typical PCB and case, thereby further securing the bonding between the first and second cases and the binding force between the microphone internal components and the case.

[14] A further object of the present invention is to provide a MEMS microphone packaging structure in which a FPCB that can be easily bonded to a metal material, has high flex and heat resistance, and can achieve miniaturization and light weight is used as a PCB, thereby enhancing the performance of the microphone, preventing the separation of the PCB from a case, and reducing the failure rate of the microphone.

[15] A still further object of the present invention is to provide a MEMS microphone packaging structure in which the epoxy sealing process is further performed after the laser welding process of the first and second case, thereby securing the bonding between the first and second cases and cleaning the external appearance due to covering of the laser welding portion. Technical Solution

[16] According to an aspect of the present invention, there is provided a MEMS (micro electro mechanical system) microphone packaging structure, including: a first case including: a printed circuit board (PCB) mounting a MEMS microphone structure thereon; a stopper supporting the PCB disposed thereon; and a support having a predetermined height and extending from one side of the stopper to wrap an external wall of the PCB, and a second case disposed on the stopper and bonded to the first case to seal the PCB from the outside.

[17] In the MEMS microphone packaging structure, a MEMS die including a transducer, i.e., diaphragm, may be separately packaged without being mounted on the PCB. However, it is preferable that a MEMS microphone structure including a basic circuit

device such as an amplifier and a filter and the MEMS die must be mounted on the

PCB using a wire bonding technology or a surface mount technology (SMT) technology, and then the MEMS microphone structure is packaged with the case. [18] In the MEMS microphone packaging structure, there is presented various bonding methods using a stopper or the bonding, the application of the quality of the PCB, and various forms and bonding methods of a first case and a second case. [19] It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

Brief Description of the Drawings [20] FIG. 1 is an exploded perspective view of a MEMS microphone packaging structure according to a first embodiment of the present invention. [21] FIG. 2 is a partial cut-away view of the MEMS microphone packaging structure according to the first embodiment of the present invention. [22] FIG. 3 is a perspective view of the packaged MEMS microphone according to the first embodiment of the present invention. [23] FIG. 4 is a cross-sectional view of a coupled structure of the MEMS microphone in which a support of a first case is curled to fix a printed circuit board (PCB), according to the first embodiment of the present invention. [24] FIG. 5 is a cross-sectional view of the coupled structure of a MEMS microphone in which a first stopper and a support of a first case are fixedly bonded to a PCB, according to the first embodiment of the present invention. [25] FIG. 6 is a perspective view of an example of epoxy-sealing a welding portion after laser welding between the first case and a second case, according to the first embodiment of the present invention. [26] FIG. 7 is an exploded perspective view of a MEMS microphone packaging structure according to a second embodiment of the present invention. [27] FIGs. 8 and 9 are perspective views of the packaged MEMS microphone according to the second embodiment of the present invention. [28] FIGs. 10 and 11 are perspective views of an example of various recesses formed in a first case according to the second embodiment of the present invention. [29] FIG. 12 is a cross-sectional view of the MEMS microphone according to the second embodiment of the present invention. [30] FIGs. 13 and 14 are perspective views of an example of various MEMS microphone packaging structures according to the second embodiment of the present invention. [31 ] DESCRIPTION OF THE SYMBOLS IN MAIN PORTIONS OF THE

DRAWINGS>

[32] 100a, 100b: first case 120a: first stopper

[33] 130a: second stopper 130b: stopper

[34] 150a, 150b: support 170b: first recess

[35] 200a, 200b: PCB 220a, 220b: electrode

[36] 250a, 250b: MEMS die 270b: bending portion

[37] 280b: first surface 290b: second surface

[38] 300a, 300b: second case 330a, 330b: sound hole

[39] 370b: second recess 500a, 500b: MEMS microphone packaging structure 550a: welding portion Best Mode for Carrying Out the Invention

[40] Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[41] FIG. 1 is an exploded perspective view of a micro electro mechanical system

(MEMS) microphone packaging structure 500a according to a first embodiment of the present invention. FIG. 2 is a partial cut-away view of the MEMS microphone packaging structure 500a according to the first embodiment of the present invention. FIG. 3 is a perspective view of the packaged MEMS microphone according to the first embodiment of the present invention.

[42] Referring to FIGs. 1 to 3, the MEMS microphone packaging structure 500a includes a first case 100a, a PCB 200a, and a second case 300a.

[43] The first case 100a includes a first stopper 120a, a second stopper 130a, and a support 150a. The first stopper 120a supports a printed circuit board (PCB) 200a such that the PCB is disposed on the first stopper 100a. The second stopper 130a supports the second case 300a such that the second case 300a is disposed on the first case 100a. The support 150a having a predetermined height extends from one side of the stopper to wrap a lateral wall of the PCB 200a. In other words, the support 150a fixes the PCB 200a disposed on the first stopper 120a such that the PCB 200a is not swung. Hence, the inside diameter of the support 150a must be greater than the outside diameter of the PCB 200a.

[44] The support 150a can bisect the stopper from an inside to an outside thereof. The stopper is divided into the inside plate, i.e., the first stopper 120a and the outside plate, i.e., the second stopper 130a based on the support 150a.

[45] A size of the support 150a of the first case 100a may be adjusted for fixing the PCB

200a such that the PCB 200a is adequately inserted into the first case 100a. Preferably, the first stopper 120a is bonded to the PCB 200a by an adhesive, or an upper portion of the support 150a is curled inside the support 150.

[46] Referring to FIG. 3, the PCB 200a includes an electrode 220a electrically

connecting an external device. The PCB provides a conduction path to a MEMS die 250a, an amplifier, or a filter, and also mounts at least one or more components of the MEMS die 250a, the amplifier, and the filter. Preferably, a MEMS microphone structure is entirely mounted on the PCB 200a using a wire bonding or surface mount technology (SMT) when the MEMS microphone components are mounted on the PCB 250a. The MEMS microphone structure includes the MEMS die 250a in which a diaphragm is formed, the amplifier, and the filter.

[47] As described above, a method of fixing the PCB 200a to the first case 100a is to bond the PCB 200a to the first case 100a using the adhesive and curl the support 150a of the first case 100a inside the support 150a. In case where the PCB is bonded to the first case 100a, the PCB 200a formed of typical epoxy resin or phenolic resin is not easily bonded to the first case 100a formed of a metal material due to the properties of the resin. Therefore, a flexible printed circuit board (FPCB) is used as the PCB 200a. The FPCB has light weight, flex resistance, and high tension. A bonding layer is formed on both sides or one side of an insulation material, i.e., polyimide film and then a copper layer is formed on the insulation material, or only the copper layer is formed on the both sides or one side of the insulation material to fabricate the FPCB. A cover- lay layer may be further formed on the copper layer in order to protect copper patterns after the formation of the copper layer. The FPCB is widely used in portable electronics such as a portable terminal, a camcorder, and a digital camera and display devices such as a liquid crystal display and a plasma display panel.

[48] The second case 300a includes a sound hole 330a through which external sound is transmitted to the MEMS die 250a. The second case 300a protects and shields the PCB 200a on which the MEMS die 250a, the amplifier, and the filter are mounted against external impact and external electrical noise. The second case 300a is disposed on the second stopper 130a of the first case 100a and then bonded to the first case 100a using a laser welding. Therefore, it is preferable that the second case 300a is formed of a material selected from the group consisting of nickel, aluminum, copper and an alloy thereof which are suitable for welding fluxes.

[49] As illustrated in FIG. 2, tension force between the first and second cases 110a and

300a can be further secured by sealing a welding portion 550a after the welding of the first and second cases 110a and 300a.

[50] FIG. 4 is a cross-sectional view illustrating a coupled structure of the MEMS microphone in which the support of the first case 100a is curled to fix the PCB 200a, according to the first embodiment of the present invention. FIG. 5 is a cross-sectional view illustrating the coupled structure of the MEMS microphone in which the first stopper and the support of the first case are fixedly bonded to the PCB, according to the first embodiment of the present invention.

[51] Referring to FIGs. 4 and 5, in a method of fixing the first case 100a to the PCB

200a, the PCB 200a may be fixed by curling the support 150a as illustrated in FIG. 4. On the other hand, the first case 100a may be fixed to the PCB 200a without curling the support 150a of the first case 100a as illustrated in FIG. 5. This is done because the PCB 200a is bonded to a support surface 155a of the first case 100a and at least one stopper surface 125a using an adhesive.

[52] Thereafter, the second case 300a is disposed on the second stopper 130a of the first case 100a to bond them by laser welding or arc welding. In the case of micro- welding, it is preferable that the laser welding is used. When performing a laser welding operation, laser power applied between the first and second cases 100a and 300a is greater than that applied between a copper layer and a case of a typical PCB. Accordingly, the binding between the two cases 100a and 300a is further secured by extending the welding range between the first and second cases 100a and 300a due to the increasing of the laser power. Therefore, it is possible to solve a problem that a connection portion between the typical PCB and case easily comes off.

[53] As illustrated in FIG. 6, a welding portion 550a may be epoxy-sealed after laser welding between the first and second cases 100a and 300a. Therefore, the binding force between the first and second cases 100a and 300a is secured, and a surface of the welding portion 550a is clean-finished during packaging the MEMS microphone.

[54] According to a second embodiment of the present invention, the first and second cases 100a and 300a may have various forms and a different PCB may be used. According to the first embodiment of the present invention, a bottom surface of the first case 100a may be opened or closed. The first and second cases 100a and 300a may include the PCB recesses, and the FPCB may be used instead of the typical PCB.

[55] FIG. 7 is an exploded perspective view of a MEMS microphone packaging structure

500b according to the second embodiment of the present invention. FIGs. 8 and 9 are perspective views of the packaged MEMS microphone according to the second embodiment of the present invention.

[56] Referring to FIGs. 7 to 9, the MEMS microphone packaging structure 500b includes a first case 100b, a second case 300b, and PCB 200b.

[57] The PCB 200b includes a first surface 280b and a second surface 290b. A MEMS die 250b of the PCB 200b, amplifier, and filter are mounted on the first surface 280b. The first surface 280b is disposed inside a support 150b of the first case 100b. The second surface 290b disposed on a rear surface of the first case 100b includes an electrode 220b electrically connecting an external device. A bending portion 270b includes a pattern for providing a conduction path to the first and second surfaces 280b and 290b. The bending portion 270b passes through a first recess 170b of the first case 100b to mechanically and electrically connect the first surface 280b to the second

surface 290b. In the second embodiment of the present invention, a FPCB is used as the PCB 200b. Roles and characteristics of the PCB 200b are identical to those of the embodiments described above except that the FPCB is used as the PCB 200b, their detailed description will be omitted.

[58] The first case 100b includes a stopper 130b, a support 150b, the first recess 170b.

The stopper 130b supports the second case 300b such that the second case 300b is disposed on a top surface of the first case 100b. The support 150b fixes the PCB 200b disposed on the first stopper 120b such that the PCB 200b is the PCB 200b is not swung from side to side. Hence, the inside diameter of the support 150b must be greater than the outside diameter of the PCB 200b.

[59] A size of the support 150b may be adjusted for fixing the first case and the PCB

200b such that the PCB 200b is adequately inserted. Preferably, the stopper 130b is bonded to the PCB 200b by an adhesive, or an upper portion of the support 150b is curled. The support 150b serves as a passage for electrically connecting the PCB 200b to the external device. The support 150b includes at least one first recess 170b formed by removing one side of the support 150b. The first recess 170b formed in the support 150b makes a pair with a second recess 370b formed in the second case 300b, and the first and second recesses are disposed in the same direction in order to easily connect the PCB 200b to the external device. Although the first case 100b is coupled to the second case 300b, the first recess 170b of the first case 100b and the second recess 370b of the second case 300b are put together to define a predetermined hole corresponding to the size of the bending portion 270b. Therefore, the passage capable of connecting the electrode 220b of the PCB 200b to the external device can be secured.

[60] The second case 300b includes a sound hole 330b through which external sound is transmitted to the MEMS die 250b. The second case 300b protects and shields the PCB 200b on which the MEMS die 250b, the amplifier, and the filter are mounted against external impact and external electrical noise. The second case 300b includes the second recess 370b for electrically connecting the PCB 200b to the external device. A position of the second recess 370b formed in the second case 300b must be the same as that of the first recess 170b formed in the first case 100b. The second case 300b is disposed on the stopper 130b of the first case 100b and then coupled to the first case 100b by a laser welding and an epoxy sealing.

[61] The first recess 170b can be formed in the first case 100b according to various embodiments. Referring to FIG. 10, the stopper 140b as well as the support 150b may also include a recess 175b in order to form the first recess 170b. As a result, wear and physical transformation due to curvature of the PCB 200b are prevented during packaging a MEMS microphone. The curvature of the PCB 200b may occur in a coupling process between the case and the PCB 200b. Referring to FIG. 11, in the first

case 100b, the first recess 170b may be formed in any one of four sides of the support 150b. That is, the first recess 170b formed in the first case 100b may be formed on at least one or more sides of the support 150b. A predetermined recess may be formed in the stopper 130b corresponding to the recess formed in the support 150b, and the recess may be formed in anywhere of the four sides. The second recess 370b formed in the second case 300b also must be formed in the same number and direction as the first recess 170b formed in the first case 100b.

[62] FIG. 12 is a cross-sectional view of the MEMS microphone according to the second embodiment of the present invention.

[63] Referring to FIG. 12, in the MEMS microphone, the FPCB is used as the PCB

200b. The PCB 200b having improved flexibility is folded based on the recess such that both side surfaces of the folded PCB faces the first case 100b and is opposite to each other. A curling method or bonding method is used during fixing the PCB 200b to the first case 100b. However, it is preferable that the first surface 280b of the PCB 200b must be coupled to the first case 100b using the curling method or the bonding method, and the second surface 290b of the PCB 200b must be bonded to the first case 100b using the bonding method.

[64] In the MEMS microphone packaging structure according to the embodiments of the present invention, the case including the stopper, the support, and the recess has been described in two forms and the FPCB has been mainly described as a kind of the PCB. However, the present invention is not limited thereto, but can be changed or modified in various forms in the case form, the quality of the material of the PCB, and kind of the PCB.

[65] Also, although the case has been mainly described in a square shape, the present invention is not limited thereto, but can be changed or modified in various forms in an oval cylindrical shape or a polygonal cylindrical shape with respect to the external device used to the MEMS microphone, as illustrated in FIGs 13 and 14. FIGs. 13 and 14 illustrate examples of various MEMS microphone packaging structures according to the second embodiment of the present invention. The MEMS microphone packaging structure according to the first embodiment of the present invention is also fabricated in the oval cylindrical shape or the polygonal cylindrical shape.

[66] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. Industrial Applicability

[67] As described above, in the MEMS microphone packaging structure according to the

embodiments of the present invention, the first and second cases are molded by the laser welding to prevent the copper layer of the PCB from damage caused during bonding of a typical PCB and case using the laser welding. The MEMS microphone structure enhances the bonding force between the microphone internal components and the cases.

[68] In the MEMS microphone packaging structure according to the embodiments of the present invention, the laser power applied between the first and second cases formed of the metal material is greater than that applied between the copper layer of the typical PCB and the case, thereby further securing the binding between the first and second cases. Therefore, the bonding force between the microphone internal components and the case is further secured.

[69] In the MEMS microphone packaging structure according to the embodiments of the present invention, the FPCB that can be easily bonded to the metal material, has high flex and heat resistance, and can achieve miniaturization and light weight is used as the PCB, thereby enhancing the performance of the microphone, preventing the separation of the PCB from the case, and reducing the failure rate of the microphone.

[70] In the MEMS microphone packaging structure according to the embodiments of the present invention, the epoxy sealing process is further performed after the laser welding process of the first and second case, thereby securing the binding between the first and second cases and cleaning the external appearance due to covering of the laser welding portion.