Patent Publication Number: US-2018035551-A1

Title: Printed circuit board and semiconductor memory device including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2016-0097027, filed on Jul. 29, 2016, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     The inventive concepts relate to printed circuit boards (PCBs) and/or semiconductor memory devices including the PCB. 
     A hard disk drive (HDD) has been widely used as a memory device for storing high capacity information. Recently, the HDD is being gradually replaced with a semiconductor memory device (e.g., solid state drive (SSD)) using a non-volatile memory element. 
     The semiconductor memory device includes, for example, a printed circuit board (PCB) and a connector coupled to one side of the PCB and transmitting data to an external device. The PCB and the connector have various standards and different shapes or dimensions according to types. Accordingly, a case is separately manufactured according to standards of the PCB and/or the connector configurations. 
     SUMMARY 
     The inventive concepts provide printed circuit boards (PCBs) with enhanced rigidity and/or semiconductor memory devices including the PCB. 
     The inventive concepts also provide semiconductor memory devices that use the same connector even though a PCB has different thicknesses. 
     According to an aspect of the inventive concepts, a printed circuit board (PCB) includes a body, at least one leaf spring coupled to the body, and a solder layer between the body and the at least one leaf spring, the solder layer coupling the at least one leaf spring with the body. 
     According to another aspect of the inventive concepts, a semiconductor memory device includes a case, a PCB installed in the case, at least one leaf spring coupled onto a lower surface of the PCB, and a solder layer interposed between the PCB and the at least one leaf spring, the solder layer coupling the PCB with the at least one leaf spring. 
     According to still another aspect of the inventive concepts, a semiconductor memory device includes a case including an upper case, a lower case, and support structures extending from the lower case to the upper case, a PCB installed in the case and supported by the support structures, a leaf spring mounted on a lower surface of the PCB and seated on support surfaces of the support structures, and a solder layer interposed between the PCB and the leaf spring, and the solder layer coupling the PCB with the leaf spring. 
     According to yet another aspect of the inventive concepts, a semiconductor memory device includes a case including a supporting structure, the supporting structure extending from one surface of the case, a PCB in the case, the PCB including a top surface and a bottom surface, the top surface of the PCB having a semiconductor device thereon, the bottom surface of the PCB facing and supported by the support structure, a leaf spring between the bottom surface of the PCB and the support structure, the leaf spring has a first portion vertically overlapping the support structure and a second portion vertically not overlapping the support structure, and a solder layer between the PCB and the second portion of the leaf spring, the solder layer coupling the PCB with the leaf spring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments of the inventive concepts will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic perspective view of a semiconductor memory device according to an example embodiment; 
         FIGS. 2A and 2B  are plan views of an upper surface and a lower surface of a printed circuit board (PCB) of  FIG. 1 , respectively; 
         FIG. 3  is a perspective view of a leaf spring of  FIG. 2B ; 
         FIG. 4  is a cross-sectional view of the semiconductor memory device taken along a line IV-IV′ of  FIG. 1 ; 
         FIG. 5  is a cross-sectional view of the semiconductor memory device taken along a line V-V′ of  FIG. 1 ; 
         FIG. 6  is a plan view of a leaf spring according to an example embodiment; 
         FIG. 7  is a cross-sectional view of the semiconductor memory device taken along a line IV-IV′ of  FIG. 1 ; 
         FIG. 8  is a cross-sectional view of the semiconductor memory device taken along a line V-V′ of  FIG. 1 ; 
         FIG. 9  is a plan view of a leaf spring according to an example embodiment; 
         FIG. 10A  is a plan view of a leaf spring according to an example embodiment; 
         FIG. 10B  is a cross-sectional view of a support plate of the leaf spring of  FIG. 10A ; 
         FIG. 11  is a plan view of a leaf spring according to an example embodiment; 
         FIG. 12  is a plan view of a lower surface of a PCB according to an example embodiment; 
         FIG. 13  is a perspective view of a leaf spring of  FIG. 12 ; 
         FIG. 14  is a cross-sectional view of the PCB taken along a line XIV-XIV′ of  FIG. 12 ; 
         FIG. 15  is a schematic perspective view of a semiconductor memory device according to an example embodiment; 
         FIG. 16  is a cross-sectional view of the semiconductor memory device taken along a line XVI-XVI′ of  FIG. 15 ; 
         FIG. 17  is a cross-sectional view of the semiconductor memory device taken along a line XVI-XVI′ of  FIG. 15  according to s an example embodiment; 
         FIG. 18  is a cross-sectional view of the semiconductor memory device taken along a line XVI-XVI′ of  FIG. 15  according to an example embodiment; 
         FIG. 19  is a plan view of a PCB according to an example embodiment; and 
         FIG. 20  is a cross-sectional view of a part of a semiconductor memory device according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     It will be understood that when an element or layer is referred to as being “on,” “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. 
       FIG. 1  is a schematic perspective view of a semiconductor memory device  100  according to an example embodiment.  FIGS. 2A and 2B  are plan views of an upper surface and a lower surface of a printed circuit board (PCB)  110  of  FIG. 1 , respectively. 
     Referring to  FIGS. 1 through 2B , the semiconductor memory device  100  may include a case  120 , the PCB  110  installed in the case  120 , leaf springs  130  mounted on a surface of the PCB  110 , and a connector  160  coupled to one side of the PCB  110 . 
     The PCB  110  may include at least one semiconductor device  115  mounted on one surface thereof or may include connector terminals  117  arranged along one edge thereof. The PCB  110  may be a rigid PCB or a flexible PCB. In more detail, the PCB may include a body  111  forming an exterior thereof. The body  111  may include a base substrate (not shown), wirings (not shown), an upper protection layer (not shown), and a lower protection layer (not shown). The wirings included in the body  111  may connect the semiconductor device  115  and/or other active and passive elements. 
     The semiconductor device  115  may be mounted on the PCB  110  by using, for example, a surface mounting method and/or an insertion mounting method. In more detail, the semiconductor device  115  may be mounted on the PCB  110  by using a ball grid array (BGA) method, a pin grid array (PGA) method, a tape carrier package (TCP) method, a chip-on-board (COB) method, a quad flat package (QFP) method, a quad flat non-leaded (QFN) method, etc. However, a method of mounting the semiconductor device  115  on the PCB  110  is not limited thereto. 
     The semiconductor device  115  may be a logic package that performs a logic calculation or may be a memory package. The logic package may be, for example, a memory controller. The memory package may be, for example, a non-volatile memory. The non-volatile memory may be a flash memory, a phase-change RAM (PRAM), a resistive random-access memory (RRAM), a ferroelectric RAM (FeRAM), a magnetic RAM (MRAM), etc. but is not limited thereto. The flash memory may be, for example, a NAND flash memory. The memory package may be, for example, a volatile memory. The volatile memory may be, for example, a dynamic random-access memory (DRAM), a static RAM (SRAM), a synchronous DRAM (SDRAM), or a high bandwidth memory (HBM) DRAM, etc. However, the semiconductor device  115  is not limited thereto and may include various types of semiconductor devices manufactured based on a semiconductor substrate. 
     The connector terminals  117  may be plated with a conductor, for example, copper and/or gold. The connector terminals  117  may be arranged at an equivalent interval or at different intervals. The connector terminals  117  may have the same side or different sizes. 
     The connector terminals  117  may be electrically connected to the semiconductor device  115  through the wirings formed in the body  111  of the PCB  110 . The connector terminals  117  may include power terminals and/or signal terminals and may include terminals that enable communication with an external device. 
     The connector  160  may be coupled to one side of the PCB  110  and may be electrically connected to the PCB  110 . The connector  160  may be arranged in one edge of the PCB  110  in which the connection terminals  117  are arranged. The connector  160  may include a plurality of connector pins that are electrically connected to the connection terminals  117  of the PCB  110  through internal wirings (not shown) of the connector  160 . 
     The case  120  may accommodate the PCB  110  therein. For example, the case  120  may include an upper case  120   b  and a lower case  120   a  and may have the PCB  110  installed between the upper case  120   b  and the lower case  120   a . The case  120  may include an opening  128  that exposes the connector  160  coupled to the PCB  110  to the outside. Thus, the connector pins of the connector  160  may be exposed to the outside through the opening  128 . 
     The case  120  may include support structures  121  provided to support the PCB  110 . The PCB  110  may be placed on the support structures  121 . The support structures  121  may extend from one surface of the lower case  120   a  to the upper case  120   b . The support structures  121  may be arranged to correspond to pin holes  113  of the PCB  110 . 
     For example, the support structures  121  may include first support structures  123  each having an upper portion  123   a  of  FIG. 4  inserted into some of the pin holes  113  of the PCB  110  and second support structures  125  each having a cavity or recess  125   a  of  FIG. 5  into which a fastening device  127  (e.g., a screw) that passes through the pin holes  113  of the PCB  110  may be inserted. The first support structures  123  and the second support structures  125  will be described in more detail below. 
     The lower case  120   a  may have a protrusion portion  129  protruding from side walls thereof toward inside to easily install the PCB  110 . The protrusion portion  129  may have a shape corresponding to a concave portion  118  formed on one side of the PCB  110 . The PCB  110  may be arranged in the case  120  such that the protrusion portion  129  is fitted into the concave portion  118  of the PCB  110 . That is, before the PCB  110  is fixed to the case  120  through the fastening device  127  (e.g., a screw) the protrusion portion  129  and the concave portion  118  may enable the PCB  110  to be easily arranged in a set location. 
     The case  120  may include a metallic material or a thermosetting or thermoplastic plastic material. Alternatively, the case  120  may include a composite material of metal and plastic. The metallic material may be, for example, aluminum (Al), copper (Cu), titanium (Ti), or an alloy containing one of these, or stainless steel but is not limited thereto. The plastic material may be, for example, polystyrene, polypropylene, acrylonitrile-butadiene-styrene (ABS), polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polymethyl (meth) acrylate, polyester, polyvinyl chloride, polyphenylene ether, polyacetal-based resin such as poly oxymethylene, copolymer thereof, or a mixture thereof but is not limited thereto. 
     The leaf spring  130  may be coupled to the PCB  110 . As shown in  FIG. 2B , a plurality of leaf springs  130  may be placed on a lower surface of the PCB  110 . The leaf spring  130  may be fastened to the PCB  110  by using a surface mounting method. For example, a solder layer  140  of  FIG. 4  that will be described below may be interposed between the leaf spring  130  and the PCB  110 . 
     The leaf spring  130  may include a metallic material (e.g., iron, or aluminum) or may include a plastic material (e.g., a polyimide film). In some example embodiments, the leaf spring  130  may include a composite material of metal and plastic. 
     The semiconductor memory device  100  may be, for example, a solid state disk (SSD), a computer, a Ultra Mobile Personal Computer (UMPC), a workstation, a net-book, a Personal Digital Assistants (PDA), a portable computer, a web tablet, a tablet computer, a wireless phone, a mobile phone, a smart phone, an e-book, a portable multimedia player (PMP), a portable game device, a navigation device, a black box, a digital camera, Digital Multimedia Broadcasting (DMB) player, a 3-dimensional television, a smart television, a digital audio recorder, a digital audio player, a digital picture recorder, a digital picture player, a digital video recorder, a digital video player, a storage constituting a data center, a device transmitting and receiving information in a wireless environment, one of various electronic devices constituting a computer network, one of various electronic devices constituting a telematics network, an RFID device, or one of various components constituting a computing system. 
       FIG. 3  is a perspective view of the leaf spring  130  of  FIG. 2B . 
     Referring to  FIG. 3 , the leaf spring  130  may include a support plate  131 , at least one pad  133 , and at least one hinge  135 . 
     The support plate  131  may include a through hole  137  that vertically penetrates therethrough. The leaf spring  130  may be fastened to the PCB  110  of  FIG. 2B  such that the through hole  137  is connected to the pin hole  113  of  FIG. 2B  of the PCB  110 . 
     The pad  133  may be placed in a peripheral direction of the support plate  131 , and may provide one surface on which a solder layer  140  of  FIG. 4  is arranged. 
     The hinge  135  may connect the support plate  131  with the pad  133  placed in the peripheral direction of the support plate  131 . One end of the hinge  135  may be connected to an edge of the support plate  131  and another end thereof may be connected to the pad  133 . The hinge  135  may extend along at least a part of the edge of the support plate  131 . 
     The hinge  135  may be bent in a first direction when force is applied toward the pad  133 . In such case, the hinge  135  may apply a desired (or alternatively, predetermined) resilience in a second direction opposite to the first direction. The leaf spring  130  may be a flexible leaf spring including the hinge  135  that is bendable. 
     As shown in  FIG. 3 , the support plate  131  may have a circular shape when viewed from above but the shape of the support plate  131  is not limited thereto. In some example embodiments, the support plate  131  may have a polygonal shape (e.g., a triangular shape, a rectangular shape, or an oval shape). 
     As shown in  FIG. 3 , the through hole  137  may have a circular shape when viewed from above but the shape of the through hole  137  is not limited thereto. In some example embodiments, the through hole  137  may have a polygonal shape (e.g., a triangular shape, a rectangular shape, or an oval shape). 
       FIG. 4  is a cross-sectional view of a semiconductor memory device taken along a line IV-IV′ of  FIG. 1 .  FIG. 5  is a cross-sectional view of a semiconductor memory device taken along a line V-V′ of  FIG. 1 . 
     Referring to  FIG. 4 , the leaf spring  130  and the PCB  110  may be coupled to each other through the solder layer  140  interposed between the leaf spring  130  and the PCB  110 . For example, the solder layer  140  may be arranged on the pad  133  of the leaf spring  130 . 
     The solder layer  140  may be formed through a reflow process. That is, the solder layer  140  may be formed through a process of placing a solder between the pad  133  of the leaf spring  130  and the PCB  110  and sequentially melting and curing the solder. 
     The leaf spring  130  may be seated on the first support structure  123  that extends from a surface of the lower case  120   a . The first support structure  123  may provide a support surface  123   b  on which the leaf spring  130  is seated and may have the upper portion  123   a  that may be inserted into the through hole  137  of  FIG. 3  of the leaf spring  130  and the pin hole  113  of the PCB  110 . 
     The support surface  123   b  of the first support structure  123  may be a plane on which the support plate  131  of the leaf spring  130  may be seated and may have a ring shape. The upper portion  123   a  of the first support structure  123  may have a shape protruding from the support surface  123   b  and may be inserted into the through hole  137  of the leaf spring  130  and the pin hole  113  of the PCB  110  to mitigate or prevent the PCB  110  and the leaf spring  130  from shaking in a horizontal direction. 
     Before the PCB  110  is seated on the first support structure  123 , because the hinge  135  is not bent, the support plate  131  and the pad  133  may be placed at the same level. In other words, while the PCB  110  is spaced apart from the first support structure  123  such that a distance between the support plate  131  and a lower surface of the PCB  110  is the same as a height  140   h  of the solder layer  140 . 
     If the support plate  131  of the leaf spring  130  is seated on the first support structure  123 , a load of the PCB  110  may be applied to the leaf spring  130 . Thus, the hinge  135  may be bent in a vertical direction, and a lower surface of the support plate  131  may contact the support surface  123   b  of the first support structure  123  and an upper surface of the support plate  131  may contact the lower surface of the PCB  110 . In other words, the PCB  110  may be spaced from the support surface  123   b  of the first support structure  123  by a distance corresponding to a thickness  131   t  of the support plate  131 . Thus, the thickness  131   t  of the support plate  131  may be the same as or similar to a thickness of the hinge  135  and a thickness of the pad  133 . In some example embodiments, unlike this, the thickness  131   t  of the support plate  131  may be different from the thickness of the hinge  135  or the thickness of the pad  133 . 
     In some example embodiments, in order for semiconductor memory devices including the PCB  110  having different thicknesses to share the case  120  of  FIG. 1  and the connector  160  of  FIG. 1 , the leaf spring  130  may be fastened to the PCB  110 . To share the same connector  160  between different semiconductor memory devices, a distance from a bottom surface of the lower case  120   a  to an upper surface of the PCB  110  needs to be the same. For convenience of description, the distance from the bottom surface of the lower case  120   a  to the upper surface of the PCB  110  is referred to as a first height H 1  below. 
     For example, in order for a first semiconductor memory device including a first PCB having a first thickness and a second semiconductor memory device including a second PCB having a second thickness to share the same case and connector, the leaf spring  130  may be fastened to the second PCB such that a distance from the bottom surface of the lower case to an upper surface of the second PCB may have the first height H 1  that is the same as that of the first PCB. 
     The first height H 1  may be substantially the same as a sum of a thickness  120   at  of the lower case  120   a , a distance  123   t  between the support surface  123   b  of the first support structure  123  and a surface of the lower case  120   a , a thickness  131   t  of the support plate  131 , and a thickness  110   t  of the PCB  110 . 
     If the support plate  131  of the leaf spring  130  is seated on the first support structure  123 , the hinge  135  may be bent in a vertical direction due to the load of the PCB  110 . Accordingly, the pad  133  may be placed at a lower level than that of the support plate  131 , and the upper surface of the support plate  131  may contact the lower surface of the PCB  110  and the lower surface thereof may contact the support surface  123   b  of the first support structure  123 . A material of the leaf spring  130 , the number of the leaf springs  130 , and/or the height  140   h  of the solder layer  140  may be appropriately adjusted such that the hinge  135  may be bent due to the load of the PCB  110 . 
     Referring to  FIG. 5 , the leaf spring  130  may be seated on the second support structure  125  that extends from the surface of the lower case  120   a . The second support structure  125  may provide a support surface  125   b  on which the leaf spring  130  is seated and may have the cavity  125   a  into which the fastening device  127  (e.g., a screw) may be inserted. The support surface  125   b  of the second support structure  125  may be a plane on which the support plate  131  of the leaf spring  130  may be seated and may have a ring shape. The through hole  137  of  FIG. 3  of the leaf spring  130  and the pin hole  113  of the PCB  110  may be coupled together by the fastening device  127 , which passes through the through hole  137  and the pin hole  113  and is received in the cavity  125   a.    
     The upper case  120   b  and the lower case  120   a  may be fastened to each other through the fastening device  127 . The fastening device  127  may sequentially penetrate into the upper case  120   b , the pin hole  113  of the PCB  110 , and the through hole  137  of the leaf spring  130 , and then may be accommodated in the cavity  125   a  of the second support structure  125 . Although not shown, a screw thread may be formed in the fastening device  127 , and a screw thread corresponding to the screw thread of the fastening device  127  may be formed in an inner surface of the second support structure  125  provided by the cavity  125   a . A part of the upper case  120   b  adjacent to an area at which the fastening device  127  is fastened may be curved in order to contact an upper surface of the PCB  110 . 
     If the leaf spring  130  is seated on the support surface  125   b  of the second support structure  125 , the hinge  135  may be bent in a vertical direction due to a load of the PCB  110 . Accordingly, the pad  133  may be placed at a lower level than that of the support plate  131 , and an upper surface of the support plate  131  may contact a lower surface of the PCB  110  and a lower surface of the support plate  131  may contact the support surface  125   b  of the second support structure  125 . The first height H 1  may be the same as or substantially similar to a sum of the thickness  120   at  of the lower case  120   a , a distance  125   t  between the support surface  125   b  of the second support structure  125  and a top surface of the lower case  120   a , the thickness  131   t  of the support plate  131 , and the thickness  110   t  of the PCB  110 . 
     In the example embodiments, the leaf spring  130  may be fastened to the PCB  110  by using a surface mounting method that uses the solder layer  140  such that adhesion may be maintained even though the solder layer  140  is exposed to a high temperature. Thus, the leaf spring  130  may be prevented from being separated from the PCB  110  although a high temperature is applied to a semiconductor memory device during a process of manufacturing or using the semiconductor memory device. 
       FIG. 6  is a plan view of a leaf spring  130   a  according to an example embodiment. 
     Referring to  FIG. 6 , the leaf spring  130   a  may include a support plate  131   a  and a pad  133   a . The leaf spring  130   a  may include one support plate  131   a  and at least two pads  133   a.    
     The support plate  131   a  may have the through hole  137  that vertically penetrates therethrough. The through hole  137  of the support plate  131   a  may be coupled or connected to the pin hole  113  of the PCB  110  of  FIG. 2B . The pad  133   a  may be connected to the support plate  131   a  in a peripheral direction of the support plate  131   a . The solder layer  140  may be arranged on one surface of the pad  133   a.    
     Unlike the leaf spring  130  of  FIG. 3 , the leaf spring  130   a  may be configured such that the pad  133   a  and the support plate  131   a  may be placed at the same level even when force is applied to the pad  133   a . For example, the leaf spring  130   a  may be a rigid leaf spring. 
       FIG. 7  is a cross-sectional view of a semiconductor memory device taken along a line IV-IV′ of  FIG. 1 .  FIG. 8  is a cross-sectional view of a semiconductor memory device taken along a line V-V′ of  FIG. 1 .  FIGS. 7 and 8  are cross-sectional views of the semiconductor memory device in which the leaf spring  130   a  described with reference to  FIG. 6  is fastened to the PCB  110 . The semiconductor memory device shown in  FIGS. 7 and 8  may have the same or substantially similar structure as that of the semiconductor memory device shown in  FIGS. 4 and 5  except for the leaf spring  130   a . The same reference numerals between  FIGS. 7 and 8  and  FIGS. 4 and 5  denote the same components, and thus detailed descriptions thereof are omitted or briefly provided. 
     Referring to  FIG. 7 , the leaf spring  130   a  and the PCB  110  may be coupled to each other through the solder layer  140  interposed between the leaf spring  130   a  and the PCB  110 . For example, the solder layer  140  may be arranged on the pad  133   a  of the leaf spring  130   a.    
     The leaf spring  130   a  may be seated on the first support structure  123  that extends from a surface of the lower case  120   a . The first support structure  123  may include the support surface  123   b  on which the support plate  131   a  of the leaf spring  130   a  is seated and the upper portion  123   a  that may be inserted into the through hole  137  of  FIG. 6  of the leaf spring  130   a  and the pin hole  113  of the PCB  110 . 
     Although the leaf spring  130   a  is seated on the first support structure  123 , the support plate  131   a  and the pad  133   a  may be placed at the same level. That is, the PCB  110  may be spaced from the support surface  123   b  of the first support structure  123  by a distance corresponding to a sum of a thickness  130   t  of the leaf spring  130   a  and the height  140   h  of the solder layer  140 . Accordingly, the first height H 1  that is a distance from a bottom surface of the lower case  120   a  to an upper surface of the PCB  110  may be the same as or substantially similar to a sum of the thickness  120   at  of the lower case  120   a , the distance  123   t  between the support surface  123   b  of the first support structure  123  and a top surface of the lower case  120   a , the thickness  130   t  of the leaf spring  130   a , the height  140   h  of the solder layer  140 , and the thickness  110   t  of the PCB  110 . 
     Referring to  FIG. 8 , the leaf spring  130   a  may be seated on the second support structure  125  that extends from a surface of the lower case  120   a . For example, the second support structure  125  may have the support surface  125   b , on which the support plate  131   a  and the pad  133   a  are seated. The fastening device  127  (e.g., a screw) may pass through the through hole  137  of the leaf spring  130   a  of  FIG. 6  and the pin hole  113  of the PCB  110 . Thus, the fastening device  127  may be accommodated in the cavity  125   a  such that the through hole  137  and the pin hole  113  are communicatively coupled to each other. 
     If the leaf spring  130   a  is seated on the support surface  125   b  of the second support structure  125 , the PCB  110  may be spaced apart from the support surface  125   b  of the second support structure  125  by a distance corresponding to a sum of the thickness  130   t  of the leaf spring  130   a  and the height  140   h  of the solder layer  140 . Accordingly, the first height H 1  may be substantially the same as a sum of the thickness  120   at  of the lower case  120   a , the distance  125   t  between the support surface  125   b  of the second support structure  125  and the top surface of the lower case  120   a , the thickness  130   t  of the leaf spring  130   a , the height  140   h  of the solder layer  140 , and the thickness  110   t  of the PCB  110 . 
     In the example embodiments, the leaf spring  130   a  may be fastened to the PCB  110  having a relatively small thickness, and the thickness  130   t  of the leaf spring  130   a , and the height  140   h  of the solder layer  140  may be adjusted, thereby manufacturing a semiconductor memory device including the same connector  160  and the same case  120  although a thickness of the PCB  110  is different. 
       FIG. 9  is a plan view of a leaf spring  130   b  according to an example embodiment. The leaf spring  130   b  of  FIG. 9  may have the same or substantially similar structure as that of the leaf spring  130  of  FIG. 3  except that the leaf spring  130   b  further includes a first metal layer  150 . The same reference numerals between  FIGS. 9 and 3  denote the same components, and thus detailed descriptions thereof are omitted or briefly provided. 
     Referring to  FIG. 9 , the leaf spring  130   b  may include the support plate  131 , the pad  133 , the hinge  135 , and the first metal layer  150  included in the pad  133 . The first metal layer  150  may be arranged on one surface facing the PCB  110  of  FIG. 4  of the pad  133 . 
     The first metal layer  150  may be plated with a conductor on the pad  133 , for example, copper. The first metal layer  150  may be connected to the solder layer  140 , which is arranged on the pad  133 . 
     In order to bond the leaf spring  130   b  onto a lower surface of the PCB  110 , during a reflow process after placing a solder between the leaf spring  130   b  and the PCB  110 , the first metal layer  150  may be melted at a high temperature and may be stably bonded onto the solder layer  140 . For example, when the leaf spring  130   b  includes a plastic material, the first metal layer  150  may enable the solder layer  140  and the leaf spring  130   b  stably bonded onto each other. 
       FIG. 10A  is a plan view of a leaf spring  130   c  according to an example embodiment.  FIG. 10B  is a cross-sectional view of the support plate  131  of the leaf spring  130   c  of  FIG. 10A . The leaf spring  130   c  of  FIGS. 10A and 10B  may have the same or substantially similar structure as that of the leaf spring  130   b  of  FIG. 9  except that the leaf spring  130   c  further includes a second metal layer  151 . The same reference numerals between  FIGS. 10A and 10B  and  FIG. 9  denote the same components, and thus detailed descriptions thereof are omitted or briefly provided. 
     Referring to  FIGS. 10A and 10B , the leaf spring  130   c  may include the support plate  131 , the pad  133 , the hinge  135 , the first metal layer  150  included in the pad  133 , and the second metal layer  151  included in the support plate  131 . 
     The second metal layer  151  may vertically penetrate through the support plate  131  of the leaf spring  130   c . The second metal layer  151  may be used as an electrical connection path that penetrates into the leaf spring  130   c  when the leaf spring  130   c  includes a non-conductive material. 
     For example, as shown in  FIG. 4 , the leaf spring  130   c  may be arranged such that an upper surface of the support plate  131  may contact a lower surface of the PCB  110  and a lower surface of the support plate  131  may contact the support surface  123   b  of the first support structure  123 . Thus, the second metal layer  151  may vertically penetrate through the support plate  131  and may electrically connect the PCB  110  to the first support structure  123 . 
     The second metal layer  151  may electrically connect the PCB  110  to the first support structure  123 , thereby providing a path through which electronic waves incident into semiconductor devices included in the PCB  110  are discharged to a case. 
       FIG. 11  is a plan view of a leaf spring  130   d  according to an example embodiment. The leaf spring  130   d  of  FIG. 11  may have the same or substantially similar structure as that of the leaf spring  130   c  of  FIG. 10A  except that the leaf spring  130   d  further includes a third metal layer  153 . The same reference numerals between  FIGS. 11 and 10A  denote the same components, and thus detailed descriptions thereof are omitted or briefly provided. 
     Referring to  FIG. 11 , the leaf spring  130   d  may include the support plate  131 , the pad  133 , the hinge  135 , the first metal layer  150  included in the pad  133 , the second metal layer  151  included in the support plate  131 , and the third metal layer  153  extending along the hinge  135 . 
     The third metal layer  153  may be arranged over the hinge  135 , a part of the support plate  131 , and a part of the pad  133  and may connect the first metal layer  150  to the second metal layer  151 . 
     The third metal layer  153  may vertically penetrate through the hinge  135 , a part of the support plate  131 , and a part of the pad  133 . However, example embodiments are not limited thereto. 
       FIG. 12  is a plan view of a lower surface of a PCB  110   a  according to an example embodiment.  FIG. 13  is a perspective view of a leaf spring  130   e  of  FIG. 12 .  FIG. 14  is a cross-sectional view of the PCB  110   a  taken along a line XIV-XIV′ of  FIG. 12 . 
     The PCB  110   a  of  FIG. 12  may have the same or substantially same structure as that of the PCB  110  of  FIGS. 1 through 2B  except that the PCB  110   a  includes a groove (e.g., semicircular pin hole)  119  instead of a pin hole having a circular shape. The leaf spring  130   e  of  FIG. 13  may have the same or substantially similar structure as that of the leaf spring  130  of  FIG. 3  except that the leaf spring  130   e  includes a groove (e.g., semicircular through hole)  137   a  other than a through hole having a circular shape and except for a structure of the leaf spring  130   e . The same reference numerals between  FIGS. 12 through 14  and  FIGS. 1  through  3  denote the same components, and thus detailed descriptions thereof are omitted or briefly provided. 
     Referring to  FIGS. 12 and 13 , the PCB  110   a  may include the grooves  119  arranged in edges thereof. The grooves  119  may have a shape that vertically penetrates through the PCB  110   a  when viewed from above. For example, the grooves  119  may be provided in two for each of both opposite edges of the PCB  110   a . However, the arrangement and number of the grooves  119  according to example embodiments are not limited thereto. 
     The leaf spring  130   e  may include a support plate  131   b , at least one pad  133 , and at least one hinge  135   b . The support plate  131   b  may include the groove  137   a . The support plate  131   b  may have a partially cut disc shape. When viewed from above, the groove  137   a  of the support plate  131   b  may vertically penetrate through the support plate  131   b . The groove  137   a  of the support plate  131   b  may have a shape corresponding to the groove  119  of the PCB  110   a.    
     The groove  119  of the PCB  110   a  and the groove  137   a  of the support plate  131   b  may accommodate a part of the upper portion  123   a  of the first support structure  123  of  FIG. 4 . In some example embodiments, the groove  119  of the PCB  110   a  and the groove  137   a  of the support plate  131   b  may be connected to the cavity  125   a  of the second support structure  125  of  FIG. 5 . A fastening device may pass through the groove  119  of the PCB  110   a  and the groove  137   a  of the support plate  131   b  and may be inserted into the cavity  125   a  of the second support structure  125  of  FIG. 5 . When the leaf spring  130   e  is seated on the first support structure  123  of  FIG. 4  and/or the second support structure  125  of  FIG. 5 , the hinge  135  may be bent in a vertical direction. Thus, a distance between the support surface  123   b  of the first support structure  123  of  FIG. 4  and a lower surface of the PCB  110   a  may be substantially the same as a thickness of the support plate  131   b.    
     Referring to  FIG. 14 , the solder layer  140  may be interposed between the PCB  110   a  and the pad  133  of the leaf spring  130   e  to allow the leaf spring  130   e  to be fastened to the PCB  110   a .  FIG. 14  illustrates that two pads  133  are provided to one leaf spring  130   e . However, example embodiments are not limited thereto. 
     If a load of the PCB  110   a  is applied to the leaf spring  130   e , the hinge  135  of the leaf spring  130   e  may be bent in a vertical direction, and thus an upper surface of the support plate  131   b  may contact a lower surface of the PCB  110   a , and although not shown, a lower surface thereof may contact the support surface  123   b  of the first support structure  123  of  FIG. 4  or the support surface  125   b  of the second support structure  125  of  FIG. 5 . 
       FIG. 15  is a schematic perspective view of a semiconductor memory device  200  according to an example embodiment.  FIG. 16  is a cross-sectional view of the semiconductor memory device  200  taken along a line XVI-XVI′ of  FIG. 15 . 
     Referring to  FIG. 15 , the semiconductor memory device  200  may include a case  220 , a PCB  210  and a connector  260  that are installed in the case  220 , and at least one leaf spring  230  fastened to the PCB  110 . The PCB  210  may include a body  211  forming an exterior thereof, a semiconductor device  215 , and connection terminals  217 . 
     The PCB  210  may include the connection terminals  217  arranged along one edge thereof. A leading portion of the PCB  210  in which the connection terminals  217  are arranged may be inserted into the connector  260  such that the connection terminals  217  are connected to internal wirings (not shown) of the connector  260 . In this regard, the connector  260  may have a socket portion  261  that is configured to accommodate the leading portion of the PCB  210 . The leading portion of the PCB  210  may be supported by the connector  260  when accommodated in the socket portion  261 . 
     The PCB  210  may include a first groove  219  for adhering the PCB  210  to the case  220 . The first groove  219  may be arranged in a rear portion opposite to the leading portion. The PCB  210  may be seated on a PCB support structure  221  such that the first groove  219  is placed on the PCB support structure  221 , which extends from a surface of the case  220 . A PCB fastening device  227  may pass through the first groove  219 , may be inserted into the PCB support structure  221 , and may press an upper surface of the PCB  210 , thereby adhering the PCB  210  to the case  220 . 
     The PCB  210  may include the at least one semiconductor device  215  mounted on one surface thereof and the connection terminals  217  arranged along one edge thereof. The semiconductor device  215  and the connection terminals  217  are described in detail with reference to  FIGS. 1 through 2B , and thus redundant descriptions thereof are omitted. 
     The leaf spring  230  may be mounted on a surface of the PCB  210  and may be arranged in an edge of the PCB  210 . 
     As shown in  FIG. 15 , the leaf spring  230  may be arranged in each of both opposite edges of the PCB  210 . However, example embodiments are not limited thereto. The two or more leaf springs  230  may be arranged in each edge of the PCB  210 . 
     As shown in  FIG. 15 , the leaf spring  230  may be arranged at a center portion of one edge of the leaf spring  230 . However, methods of placing the leaf spring  230  according to example embodiments are not limited thereto. For example, a location of the leaf spring  230  may be arranged adjacent to a corner portion of the PCB  210 . The leaf spring  230  may be arranged in one edge of the PCB  210  in which a second groove  235  is arranged. 
     A part of the leaf spring  230  may protrude in a peripheral direction of the PCB  210 . The part of the leaf spring  230  protruding in the peripheral direction of the PCB  210  may be adhered to the case  220 . For example, the leaf spring  230  protruding in the peripheral direction of the PCB  210  may be seated on a leaf spring support structure (interchangeably, support structure)  223  extending from a surface of the case  220 . The second groove  235  may be formed in one side of the leaf spring  230 . The leaf spring fastening device  229  may pass through the second groove  235  and may be accommodated in a cavity of the leaf spring support structure  223 . The leaf spring fastening device  229  may press at least a part of the leaf spring  230  such that the leaf spring  230  is adhered to the leaf spring support structure  223 . 
     Referring to  FIG. 16 , a solder layer  240  may be interposed between the leaf spring  230  and the PCB  210  and may couple the leaf spring  230  and the PCB  210 . The solder layer  240  may be formed by placing a solder between the leaf spring  230  and the PCB  210  and then a reflow process of sequentially melting and curing the solder. 
     The leaf spring  230  may be connected to a first plate  231  providing one surface on which the solder layer  240  is arranged and a second plate  233  connected to the first plate  231 , protruding in a peripheral direction of the PCB  210 , and adhered to the leaf spring support structure  223 . 
     In some example embodiments, the leaf spring  230  may enhance rigidity of the PCB  210 , thereby reducing damage of the PCB  210  due to an external shock. 
     Because the leaf spring  230  is fastened to the PCB  210 , rigidity of the PCB  210  may be enhanced, and thus an intrinsic frequency of the PCB  210  may increase. An arrangement, number, shape, and material of the leaf spring  230  may be appropriately adjusted, and thus the intrinsic frequency of the PCB  210  may be adjusted to avoid a resonance frequency. For example, a main resonance frequency that causes resonance of a portable electronic device (e.g., a laptop computer) may be less than 500 Hz. Thus, an intrinsic resonance frequency of the PCB  210  may be configured to exceed 500 Hz by fastening the leaf spring  230  to the PCB  210 , thereby mitigating or preventing the semiconductor memory device  200  from being damaged due to resonance. 
       FIG. 17  is a cross-sectional view of the semiconductor memory device taken along a line XVI-XVI′ of  FIG. 15  according to an example embodiment. 
     The semiconductor memory device shown in  FIG. 17  may have the same or substantially similar structure as that of the semiconductor memory device shown in  FIG. 16  except that the leaf spring  230   a  further includes a first metal layer  250 . The same reference numerals between  FIGS. 17 and 16  denote the same components, and thus detailed descriptions thereof are omitted or briefly provided. 
     Referring to  FIG. 17 , the leaf spring  230   a  may include the first plate  231  and the second plate  233  and the first metal layer  250  provided on the first plate  231 . The first metal layer  250  may be plated with a conductor on the first plate  231 . The first metal layer  250  may be connected to the solder layer  240  arranged on the first plate  231 . For example, when the leaf spring  230   a  includes a plastic material, the first metal layer  250  may allow the solder layer  240  to be stably bonded to the leaf spring  230   a.    
       FIG. 18  is a cross-sectional view of the semiconductor memory device taken along a line XVI-XVI′ of  FIG. 15  according to an example embodiment. 
     The semiconductor memory device shown in  FIG. 18  may have the same or substantially similar structure as that of the semiconductor memory device shown in  FIG. 17  except that the leaf spring  230   b  further includes a second metal layer  251 . The same reference numerals between  FIGS. 18 and 17  denote the same components, and thus detailed descriptions thereof are omitted or briefly provided. 
     Referring to  FIG. 18 , the leaf spring  230   b  may include the first plate  231  and the second plate  233 , the first metal layer  250  provided on the first plate  231 , and the second metal layer  251  connecting the first metal layer  250  and the leaf spring support structure  223 . 
     When the leaf spring  230   b  includes a non-conductive material, the second metal layer  251  may be used as an electrical connection path that electrically connects the PCB  210  and the leaf spring support structure  223 . For example, the PCB  210  and the leaf spring support structure  223  may be electrically connected to each other through the solder layer  240 , the first metal layer  250 , and the second metal layer  251 . 
     The first metal layer  250  and the second metal layer  251  may electrically connect the PCB  210  to the leaf spring support structure  223 , thereby providing a path through which electronic waves incident into semiconductor devices included in the PCB  210  are discharged to the case  220  of  FIG. 15 . 
       FIG. 19  is a plan view of a PCB  210  according to an example embodiment. The PCB  210  of  FIG. 19  may have the same or substantially similar structure as that of the PCB  210  of  FIGS. 15 and 16  except for a shape of a leaf spring  230   c . The same reference numerals between  FIG. 19  and  FIGS. 15 and 16  denote the same components, and thus detailed descriptions thereof are omitted or briefly provided. 
     Referring to  FIG. 19 , the leaf spring  230   c  may have a curved shape. For example, the leaf spring  230   c  may include a first plate  231  and a second plate  233   a . The second plate  233   a  may extend in an inclined direction from a direction in which the first plate  231  extends. For example, the first plate  231  and the second plate  233   a  may be perpendicular to each other. 
     The leaf spring  230   c  having the curved shape may be prevented from being separated from the PCB  210  during a reflow process. For example, during the reflow process, the leaf spring  230   c  may be placed on a surface of the PCB  210  with a solder between the leaf spring  230   c  and the PCB  210 . A part of the leaf spring  230   c  may protrude in a peripheral direction of the PCB  210 . If a weight center of the leaf spring  230   c  is not placed inside the PCB  210 , the leaf spring  230   c  may be separated from the PCB  210 . Thus, the leaf spring  230   c  may be curved by placing the weight center of the leaf spring  230   c  inside the PCB  210 , thereby mitigating or preventing the leaf spring  230   c  from moving or being separated from the PCB  210  during the reflow process. 
       FIG. 20  is a cross-sectional view of a part of a semiconductor memory device according to an example embodiment. 
     The semiconductor memory device of  FIG. 20  may have the same or substantially similar structure as that of the semiconductor memory device  200  of  FIGS. 15 and 16  except that a leaf spring  230   d  further includes a dummy mass  234 . The same reference numerals between  FIG. 20  and  FIGS. 15 and 16  denote the same components, and thus detailed descriptions thereof are omitted or briefly provided. For convenience of description, contrary to a lower surface of the PCB  210  facing down in  FIGS. 15 and 16 , the lower surface of the PCB  210  is illustrated to face up in  FIG. 20 . 
     Referring to  FIG. 20 , the leaf spring  230   d  may further include the dummy mass  234  provided to place a weight center M of the leaf spring  230   d  on the PCB  210 . The dummy mass  234  may be arranged opposite to the solder layer  240  with respect to the first plate  231 . The dummy mass  234  may be arranged in a region where at least a part of the dummy mass  234  overlaps with the PCB  210  in a vertical direction. 
     The leaf spring  230   d  may contact a solder arranged on the PCB  210  in order to perform a reflow process. The weight center M of the leaf spring  230   d  including the dummy mass  234  may be placed on the PCB  210 , thereby mitigating or preventing the leaf spring  230   d  from being separated from the PCB  210  during the reflow process. 
     The dummy mass  234  may have a desired (or alternatively, predetermined) amount of mass suitable for adjusting the weight center M of the leaf spring  230   d  to a set location and may have various materials and/or shapes. The dummy mass  234  may be fixed to a part of the leaf spring  230   d  by using various methods. For example, the dummy mass  234  may be attached to the first plate  231  by using an adhesive or by using a fixer (e.g., a hook structure) provided on the first plate  231 . 
     While the inventive concepts have been particularly shown and described with reference to some example embodiments thereof, it will be understood that various changes in form and details may be made therein without departing from the spirit and scope of the following claims.