JP2011134138A - Semiconductor memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an SSD apparatus which suppresses influence of heat generated from a controller on a recording medium. <P>SOLUTION: The SSD apparatus has a print circuit board 3 in which a NAND 5 and a controller 6 are mounted on a lower face through a plurality of bumps, respectively, a chassis that is configured with a top cover 1 and a bottom housing 9 each having conductive property and that holds the print circuit board 3, and a heat dissipating sheet 10 that exists between the bottom housing 9, and the controller 6 and the NAND 5, and that thermally connects the controller 6 and the NAND 5, and the bottom housing 9. In the heat dissipating sheet 10, coupling capacitance of a capacitor formed by parallel plates configured by an area facing the print circuit board 3 of the bottom housing 9 and the print circuit board 3 is smaller than coupling capacitance in a state where an object having relative permittivity of 5.8 is directly arranged between the parallel plates. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a semiconductor memory device.

  As an auxiliary storage device mounted on a computer, an auxiliary storage device using an HDD (Hard Disk Drive) (hereinafter referred to as an HDD device) has been used (see Patent Document 1).

  In recent years, auxiliary storage devices (so-called solid state disks, hereinafter referred to as SSD devices) using nonvolatile semiconductor memory chips such as NAND flash memories as recording media have been mounted on computers instead of HDD devices. Yes. An SSD device includes a plurality of NAND flash memories (hereinafter referred to as NAND) and a controller IC that controls the NAND flash memory mounted on a printed circuit board via ball-shaped electrodes (bumps). Is housed in a casing of the same size and shape as an HDD device whose outer dimensions and shape are defined in the standard (for example, a casing of the same size and shape as a 2.5-inch HDD device) and stored in a computer. Implemented. There are several types of standards related to the housing of the HDD device depending on the size of the magnetic disk, but the housing is generally a metal box shape, including 2.5 inch HDD devices.

  During the actual operation of the SSD device (when reading / writing actual data), the controller generates heat by repeatedly performing the switching operation at a high speed. A part of the heat generated from the controller is transmitted to the printed circuit board through bumps in contact with the controller, and further transferred to the NAND through wiring patterns on the printed circuit board and bumps in contact with the NAND. Since the operation principle of NAND tends to become unstable due to an increase in leakage current in a high temperature environment, the operation guarantee temperature is set lower than that of other types of ICs. For example, the guaranteed operation temperature of other types of IC is about 100 ° C., while the guaranteed operation temperature of NAND is about 85 ° C.

  Therefore, in the SSD device, it is necessary to suppress the transfer of heat from the controller to the NAND by cooling the controller. In the case of an HDD device using a magnetic disk as a recording medium, the controller and the magnetic disk are arranged apart from each other, and the heat generated from the controller does not affect the mechanical part of the magnetic disk. It can be said that the problem is unique to the device.

  As a structure for cooling the controller in the SSD device, it is conceivable to dispose a heat dissipation sheet between the controller and the bottom housing. Even if a heat radiating sheet is interposed between the controller and the bottom housing, not all of the heat generated from the controller is transmitted to the bottom housing, but a part is transmitted to the bottom housing via the heat radiating sheet. As a result, the amount of heat transferred to the NAND is reduced, so that the temperature of the NAND does not exceed the guaranteed operating temperature.

  By the way, with the improvement of the performance of the SSD device and the computer equipped with the SSD device, the amount of heat generated during actual operation of the controller tends to increase. For example, the data transfer rate of an SSD device was 100 Mbyte / sec for reading and 40 Mbyte / sec for writing in the old generation SSD device, but now it is improved to 240 Mbyte / sec for reading and 200 MB / sec for writing. . For this reason, even if a heat radiating sheet is disposed only between the controller and the bottom housing, it is difficult to sufficiently dissipate the heat generated from the controller. However, an SSD device that has taken measures against this problem has not been realized.

JP 2007-30837 A

  An object of the present invention is to provide an SSD device that suppresses the influence of heat generated from a controller on a recording medium.

  According to one aspect of the present invention, a printed circuit in which a plurality of nonvolatile semiconductor memory chips and a controller that controls reading and writing of data to and from the nonvolatile semiconductor memory chip are mounted on one surface via a plurality of bumps, respectively. Interposed between the controller and each non-volatile semiconductor memory chip, a board formed of a conductive material and housing the printed circuit board, a surface facing one side of the printed circuit board of the housing, and the controller and each nonvolatile semiconductor memory chip A heat dissipation sheet that thermally connects the controller and each nonvolatile semiconductor memory chip and the housing, and the heat dissipation sheet is a capacitor formed by a region of the housing facing the printed circuit board and the printed circuit board. There is provided a semiconductor memory device characterized in that the coupling capacitance is smaller than the coupling capacitance in a state where an object having a relative dielectric constant of 5.8 is disposed between the parallel plates.

  According to the present invention, there is an effect that unnecessary radiation can be reduced while suppressing the influence of heat generated from the controller on the recording medium.

FIG. 1 is a diagram illustrating a configuration of an SSD device and a configuration of a lower surface of a printed circuit board according to a first embodiment. FIG. 2 is a diagram showing a configuration of a template provided with through holes at locations corresponding to the controller and NAND. FIG. 3 is a diagram illustrating a configuration of an SSD device that covers a controller and a NAND with a single solid heat dissipation sheet and a configuration of a lower surface of a printed circuit board. FIG. 4 is a view showing a model of a parallel plate capacitor including a printed circuit board and a bottom housing. FIG. 5 is a diagram showing EMI characteristics of an SSD device using individual heat dissipation sheets. FIG. 6 is a diagram showing EMI characteristics of an SSD device using a solid heat dissipation sheet. FIG. 7 is a diagram illustrating an example in which one heat radiating sheet is arranged for each of a plurality of cooling targets. FIG. 8 is a diagram illustrating the configuration of the SSD device and the configuration of the bottom surface of the printed circuit board according to the second embodiment. FIG. 9 is a perspective view of a heat dissipation sheet according to the third embodiment. FIG. 10 is a diagram showing a configuration of an SSD device using a printed circuit board on which both sides are mounted with NAND and a configuration on the lower surface of the printed circuit board on which both sides are mounted with NAND.

  Hereinafter, an SSD device as a semiconductor memory device according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments.

(First embodiment)
FIG. 1A is an exploded perspective view showing the configuration of the SSD device according to the first embodiment of the present invention. FIG. 1B is a perspective view showing the configuration of the lower surface of the printed circuit board 3. The SSD device according to the present embodiment includes a printed circuit board 3 on which eight NANDs 5 and a controller 6 are mounted on the lower surface side, and is printed on a casing composed of a top cover 1 and a bottom housing 9. The circuit board 3 is accommodated. The top cover 1 and the bottom housing 9 are made of a metal material such as aluminum or iron.

  The top cover 1 and the bottom housing 9 are connected by a cover fixing screw 2 to form a substantially hexahedron-shaped housing having one side opened. The printed circuit board 3 is screwed to the bottom housing 9 with a fixing screw 8 in a state where a heat dissipation sheet 10 is interposed between the controller 6 and the NAND 5 and the bottom housing 9. A connector 4 formed at one end of the printed circuit board 3 is exposed to the outside of the housing at the opening surface of the housing, and is connected to a computer as a mounted device via the connector 4.

  Each of the heat dissipating sheets 10 is formed so as to have flexibility by a material including a silicone resin and a ceramic filler, and both are pressed by the controller 6 and the NAND 5 and the bottom housing 9 mounted on the printed circuit board 3. It is in close contact with. As a result, the controller 6 or NAND 5 and the bottom housing 9 are thermally connected. In addition, although the heat radiating sheet 10 is not disposed between the SDRAM 7 and the bottom housing 9, the SDRAM 7 has high heat resistance, and no trouble occurs even when heat from the controller 6 is transmitted. The heat dissipating sheet 10 has a sufficient heat dissipating effect to prevent the temperature of the controller 6 and NAND 5 from rising to a design value (for example, 85 ° C.) or higher.

  Here, the assembly procedure of the SSD device according to the present embodiment will be described. As shown in FIG. 2, the heat radiating sheet 10 includes a template 20 having a through hole 20a at a position corresponding to the controller 6 and the NAND 5 at a predetermined position in the bottom housing 9, and the bottom housing through the through hole 20a. 9 is attached to the inner surface. After pasting the heat radiating sheet 10, the template 20 is removed from the bottom housing 9, the printed circuit board 3 is loaded thereon, and fixed with screws 8. (In this figure, the procedure using a template is shown, but a heat dissipation sheet may be attached directly to the corresponding IC package without using the template. The device which does not give a damage is needed.) By installing the heat radiating sheet 10 between the controller 6 and the NAND 5 and the bottom housing 9 through such a procedure, the installation workability of the heat radiating sheet 10 is improved. . Further, since the assembly is performed such that the printed circuit board 3 is placed on the heat radiating sheet 10, the heat radiating sheet 10 is not dropped from the top surface (the surface facing the bottom housing 9) of the controller 6 or the NAND 5 during the assembling work. . Thereafter, the top cover 1 is put on the bottom cover 9 and the cover fixing screw 2 is fastened to complete the assembly of the SSD device.

  Next, the reason why the heat dissipation sheet 10 is separated into pieces in the present embodiment will be described.

  As a heat countermeasure for the NAND, it is conceivable to thermally connect the NAND and the bottom housing via a heat dissipation sheet. As this structure, as shown in FIG. 3, there is a structure in which a minimum rectangular heat radiation sheet 11 covering a plurality of NANDs 5 and the controller 6 is interposed between the controller 6 and the NANDs 5 and the bottom housing 9. FIG. 3A is an exploded perspective view of the SSD device configured to cover the controller 6 and the NAND 5 with a single solid heat radiation sheet 11, and FIG. 3B illustrates the configuration of the lower surface of the printed circuit board 3. It is a perspective view shown. Except that the heat dissipating sheet 11 has a minimum rectangular shape that covers the controller 6 and the NAND 5, it is the same as the SSD device shown in FIG. Hereinafter, the SSD apparatus shown in FIG. 3 will be described in comparison with the SSD apparatus according to the first embodiment shown in FIG.

  Since the printed circuit board 3 of the SSD device is disposed substantially parallel to the bottom housing 9, it can be considered that a parallel plate capacitor is formed by the printed circuit board 3 and the bottom housing 9. FIG. 4 shows a model of a parallel plate capacitor including the printed circuit board 3 and the bottom housing 9. The printed circuit board 3 and the bottom housing 9 are parallel flat plates, and a coupling capacity (capacitance) is generated. Since the heat radiation sheets 10 and 11 are disposed between the parallel plates, the coupling capacitance varies depending on the area of the region where the heat radiation sheets 10 and 11 are present and the relative dielectric constant of the heat radiation sheets 10 and 11.

  The printed circuit board 3 operates as an SSD when supplied with power from a computer connected via the connector 4. High-frequency noise is generated from the NAND 5 and the controller 6 by the internal operation clock and read / write data. This noise also propagates to the bottom housing 9 due to capacitive coupling between the printed circuit board 3 and the bottom housing 9.

  The bottom housing resonates with respect to electromagnetic waves having a frequency (n = 1, 2) times the frequency (n = 1, 2, 4, 8,...) Of a frequency whose vertical and horizontal and diagonal directions are one wavelength, and efficiency. It functions as a good antenna. For example, if the bottom housing 9 has a long side of 0.1 m, a short side of 0.069.85 m, and a diagonal of 0.122 m, in the long side direction, 3 GHz, 1.5 GHz, 0.75 GHz, 0.375 GHz · The electromagnetic wave with the frequency of ・ ・ resonates. In the short side direction, electromagnetic waves having frequencies of 4.295 GHz, 2.147 GHz, 1.074 GHz, 0.537 GHz, etc. resonate. Furthermore, in the diagonal direction, electromagnetic waves of 2.459 GHz, 1.230 GHz, 0.615 GHz, 0.307 GHz,. Electromagnetic waves having these frequencies are radiated into the air using the bottom housing 9 as an antenna.

  In the above example, the measurement range is included in the EMI (Electromagnetic Interference) standards of each country and region specified by CE, VCCI (Voluntary Control Council for Interference by Information Technology Equipment), FCC (Federal Communications Commission), etc. A resonance frequency exists over almost the entire region from 300 MHz to 1 GHz. However, due to the difference in dimensions of the bottom housing 9 in the vertical and horizontal and diagonal directions, the resonance frequency is 0.537 GHz at the 1/8 wavelength in the short side direction, and the resonance frequency is 0 at the 1/4 wavelength in the diagonal direction. The frequency difference between the resonance frequencies is small at .615 GHz, which is 0.750 GHz, which is the resonance frequency at a quarter wavelength in the long side direction. When the operation speed of the SSD device is increased, noise corresponding to this band is likely to be generated, and resonance with the bottom housing 9 is likely to occur. Therefore, unnecessary radiation due to the bottom housing 9 functioning as an antenna becomes more prominent as the operating speed of the SSD device increases.

  As described above, disposing the heat radiating sheets 10 and 11 for the purpose of cooling the controller 6 and the NAND 5 has a specific dielectric constant (between the printed circuit board 3 and the bottom housing 9) between the parallel plates of the parallel plate capacitor (between the printed circuit board 3 and the bottom housing 9). It is nothing other than inserting an object having a relative dielectric constant of the material of the heat radiation sheets 10 and 11. Therefore, by disposing the heat dissipation sheets 10 and 11, the coupling capacity of the parallel plate capacitor is increased as compared with the state in which the printed circuit board 3 and the bottom housing 9 are just facing each other, and the bottom housing 9 functions as an antenna. It becomes easy to do. In addition, when the solid heat dissipating sheet 11 is installed, the coupling capacity of the capacitor is greatly increased as compared with the case where the individual heat dissipating sheet 10 is disposed. Therefore, unnecessary radiation due to the bottom housing 9 functioning as an antenna is reduced. This is disadvantageous.

  The relative dielectric constant of the material of the existing heat dissipation sheet is about 5.8. However, when this heat dissipation sheet is placed on a solid surface, the EMI characteristics of the SSD device can be adapted to the EMI standard, and the computer that is the mounted device. Depending on the shielding performance, there is a possibility that it does not conform to the standard. If the operation speed of the SSD device is further increased, the possibility of not conforming to the EMI standard is further increased. In addition, when a more stringent specification with a margin (margin) is required for the EMI standard, there is a possibility that the required specification cannot be satisfied even at the current operation speed. Come.

  In the present embodiment, taking the above points into consideration, an increase in the coupling capacity of the parallel plate capacitor is suppressed by using the individual heat radiation sheet 10. The heat radiating sheet 10 is divided into pieces, and the total area occupied by the heat radiating sheet 10 is smaller than the area of the solid heat radiating sheet 11. For this reason, the coupling capacity of the capacitor is reduced, the impedance from the noise source to the antenna side is increased, the transmission level is reduced, and unnecessary radiation due to the bottom housing 9 functioning as an antenna is reduced.

  Hereinafter, the difference between the case of using the individual heat dissipation sheet 10 and the case of using the solid heat dissipation sheet 11 will be described in more detail with specific numerical values, but the present invention is limited to the exemplified numerical values. Is not to be done.

  The individual heat dissipation sheets 10 are each 0.01 m in length and width and 0.003 m in thickness. The printed circuit board 3 is 0.063 m long and 0.0865 m wide. The bottom housing 9 has a long side of 0.1 m, a short side of 0.069.85 m, and a diagonal of 0.122 m.

  The distance between the printed circuit board 3 and the bottom housing 9 is 0.0044 m, and the mounting height of the controller 6 and the NAND 5 is 0.0014 m. That is, the distance between the controller 6 and the NAND 5 and the bottom housing 9 is 0.003 m.

  The solid heat-dissipating sheet 11 has a length of 0.05 m, a width of 0.07 m, and a thickness of 0.003 m.

Each piece of the heat radiation sheet 10 has an area of 0.0001 m ² , and the solid heat radiation sheet 11 has an area of 0.0035 mm ² . Since a total of nine pieces of the heat radiation sheet 10 are used corresponding to each of the controller 6 and the NAND ₅ , the area ratio between the total area S _{1 of the} individual heat radiation sheets 10 and the area S ₂ of the solid heat radiation sheet 11 is as follows. Is S ₁ : S ₂ = 0.0009: 0.0035≈1: 3.9.

The coupling capacitance C of the parallel plate capacitor is represented by the following formula (1).
C = ε ₀ × ε × S ₃ ÷ d (1)
In equation (1), ε ₀ : dielectric constant in vacuum (F / m), ε: relative dielectric constant of an object existing between parallel plates, S ₃ : area of parallel plates (m ² ), d: parallel plates The distance (m).

In the SSD device according to the present embodiment, the area of the printed circuit board 3 smaller than the bottom housing 9 is an area as a parallel plate, and S ₃ = 0.063 × 0.0865 = 0.0054495 m ² . When the heat radiation sheets 10 and 11 exist in a part between the parallel plates, the coupling capacity of the capacitor is the sum of the coupling capacity in the region where the heat radiation sheets 10 and 11 are present and the coupling capacity in the region where the heat radiation sheets 10 and 11 are not present.

  Here, the relative dielectric constant of air is approximated by 1. For the sake of simplification of explanation, it is assumed that the relative permittivity of the electronic components such as the controller 6 and the NAND 5 is 1.

When the heat radiating sheets 10 and 11 are not used, since only air exists between the parallel plates, the coupling capacity is 8.85419 × 10 ⁻¹² × 1 × 0.0054495 ÷ 0 from the above formula (1). 0044 = 1.10 × 10 ⁻¹² F = 11.0 pF.

When the individual heat dissipation sheet 10 is used, the area of the region where the heat dissipation sheet 10 exists is 0.0009 m ² , and the area of the region where the heat dissipation sheet 10 does not exist is 0.0045495 m ² . The coupling capacity in the region where the heat radiating sheet 10 is not present is 8.85419 × 10 ⁻¹² × 1 × 0.0045495 ÷ 0.0044 = 9.16 × 10 ⁻¹² F = 9.16 pF from the above formula (1). .

On the other hand, the coupling capacity in the region where the heat radiating sheet 10 exists is a combined capacity in series of the coupling capacity of the part of the heat radiating sheet and the coupling capacity of the part of the electronic component. The combined capacitance C _{C in} series of the two capacitors C _A and C _B is expressed by the following formula (2).
1 / C _C = (1 / C _A ) + (1 / C _B ) (2)

From the above formula (1), the coupling capacity of the heat dissipation sheet 10 is 8.85419 × 10 ⁻¹² × 5.8 × 0.0009 ÷ 0.003 = 5.9 × 10 ⁻¹² = 5.69 pF. . Further, the coupling capacity of the electronic component portion is 8.85419 × 10 ⁻¹² × 1 × 0.0009 ÷ 0.0014 = 1.5 × 10 ⁻¹¹ F = 15.4 pF from the above formula (1). . For this reason, the coupling capacity of the entire region where the heat dissipation sheet 10 exists is 4.16 pF from the above formula (2). Therefore, the coupling capacitance of the entire capacitor is 9.16 pF + 4.16 pF = 13.32 pF.

When the solid heat dissipation sheet 11 is used, the area of the region where the heat dissipation sheet 11 exists is 0.0035 m ² , and the area of the region where the heat dissipation sheet 11 does not exist is 0.0019495 m ² . According to the same calculation as when the individual heat radiation sheet 10 is used, the coupling capacity in the area where the solid heat radiation sheet 11 does not exist is 3.92 pF, and the coupling capacity in the area where the solid heat radiation sheet 11 exists is 16.2 pF. . Therefore, the coupling capacitance of the entire capacitor is 20.1 pF.

  As a result, the coupling capacity can be reduced by about 44% by using the individual heat radiation sheet 10 as compared with the case of using the solid heat radiation sheet 11.

  FIG. 5 shows the EMI characteristics of the SSD device using the individual heat dissipation sheet 10. FIG. 6 shows EMI characteristics of an SSD device using a solid heat dissipation sheet 11. Here, the measurement result by the test method specified in VCCI is shown, and the SSD unit is connected to the computer with an extension cable and the SSD unit is out of the computer (in the state where it is originally incorporated in the computer as the mounted device). Measure the intensity of electromagnetic waves (unwanted radiation) entering an antenna installed 10m away. A condition that complies with the VCCI standard is that 30 dB or less in the 30 to 230 MHz band and 37 dB or less in the 230 to 1000 MHz band. In the SSD apparatus using the solid heat radiation sheet 11, the intensity of unnecessary radiation near 700 MHz exceeds the standard value, whereas in the SSD apparatus using the individual heat radiation sheet 10, unnecessary radiation near 700 MHz. The strength is improved by about 16 dB and is below the standard value.

  Thus, by using the individualized heat dissipation sheet 10, the coupling capacity of the capacitor is reduced, and unnecessary radiation due to the bottom housing 9 functioning as an antenna is reduced. In order to realize a coupling capacity equivalent to that of the individual heat dissipation sheet 10 with the solid heat dissipation sheet 11, it is necessary to form the heat dissipation sheet 11 with a material having a relative dielectric constant of 1.586. Forming the heat radiation sheet 11 is difficult to realize at present. That is, by using the separated heat dissipation sheet 10, the coupling capacity can be reduced to a level that is difficult to achieve when the solid heat dissipation sheet 11 is used, and unnecessary radiation can be reduced.

Moreover, the weight of the SSD device can be reduced by dividing the heat dissipation sheet 10 into individual pieces. When the specific gravity of the heat dissipation sheets 10 and 11 is 2.7, in the above example, the difference in area is 0.0026 m ² and the thickness of the sheet is 0.003 m, so the difference in weight is approximately 21 g. That is, by using the individual heat radiating sheet 10, it is possible to reduce the weight by about 21 g as compared with the case where the solid heat radiating sheet 11 is used.

  Here, the configuration in which the heat dissipation sheet 10 is individually disposed in each of the controller 6 and the NAND 5 is described as an example. However, as illustrated in FIG. 7, one heat dissipation sheet may be disposed for each of a plurality of cooling objects. good. In FIG. 7, each of the heat radiation sheets 10a, 10b, and 10c covers three objects to be cooled (one controller 6 and eight NANDs 5). By setting it as such a structure, the man-hour of the operation | work which sticks a heat radiating sheet can be reduced, and it becomes possible to improve assembly workability | operativity. As the number of objects to be cooled covered with one heat radiating sheet increases, the assembly workability increases. However, since the heat radiating sheet is arranged also in the area where the object to be cooled does not exist, the coupling capacity of the capacitor increases, and the bottom housing 9 serves as an antenna. Unwanted radiation due to functioning increases. In this way, the assembly workability when placing the heat dissipation sheet and the EMI characteristics of the SSD device are in a trade-off relationship, so the number of cooling objects covered with one heat dissipation sheet is selected according to the required specifications. Good.

(Second Embodiment)
FIG. 8A is an exploded perspective view showing the configuration of the SSD device according to the second embodiment of the present invention. FIG. 8B is a perspective view showing the configuration of the lower surface of the printed circuit board 3. The SSD device according to the second embodiment is the same as the configuration shown in FIG. 3, and the heat dissipation sheet 12 covers the controller 6 and the eight NANDs 5 with one sheet. However, in this embodiment, the relative permittivity of the heat dissipation sheet 12 is 3.8, which is lower than that of the heat dissipation sheet 10 of the first embodiment.

  As is clear from the above equation (1), the coupling capacity of the parallel plate capacitor is proportional to the relative dielectric constant of the object existing between the parallel plates. The dimensions of the heat dissipation sheet 12 are the same as the dimensions of the heat dissipation sheet 11 exemplified in the first embodiment, and other conditions such as the area of the printed circuit board 3 and the distance between the bottom housing 9 and the printed circuit board 3 are also included. Assuming that they are the same, the coupling capacity of the parallel plate capacitors is 3.92 pF in the area where the heat dissipation sheet 12 is not present and the coupling capacity in the area where the heat dissipation sheet 12 is present according to the above formulas (1) and (2) The capacitance is 14.1 pF. Therefore, the coupling capacity of the entire capacitor is 18.0 pF. Therefore, by applying a heat dissipation sheet formed of a material with a low relative dielectric constant, the coupling capacity of the capacitor between the printed circuit board and the bottom housing can be reduced, and unnecessary radiation due to the bottom housing functioning as an antenna can be reduced. .

(Third embodiment)
As in the second embodiment, the SSD device according to the third embodiment of the present invention covers the controller and the eight NANDs with a single heat dissipation sheet. FIG. 9 shows a perspective view of the heat dissipation sheet 13 according to the present embodiment. The heat radiation sheet 13 has a structure in which each piece 13a corresponding to the object to be cooled and a plate-like portion 13b having these on the surface are integrally formed. By reducing the thickness of the plate-like portion 13b, the amount of increase in coupling capacity due to the presence of the plate-like portion 13b between the printed circuit board 3 and the bottom housing 9 is suppressed as compared with the case where the plate-like portion 13b is disposed in a solid state. be able to. Therefore, in this embodiment, the coupling capacity of the capacitor can be made smaller than in the case of the solid shape, and the pasting operation of the heat radiation sheet 13 is only required once. For this reason, both EMI characteristics and assembly workability can be achieved.

  In each of the above embodiments, the controller 6 and the NAND 5 are mounted on the lower surface of the printed circuit board 3, and the heat radiation sheets 10, 12, and 13 are arranged between the printed circuit board 3 and the bottom housing 9. Although described as an example, the controller 6 and the NAND 5 are mounted on the upper surface of the printed circuit board 3, and the same effect as described above can be obtained even when the heat dissipation sheet is disposed between the printed circuit board 3 and the top cover 1. Needless to say.

  Further, in each of the above-described embodiments, the configuration in which the NAND 5 is mounted only on the lower surface of the printed circuit board 3 has been described as an example. However, as shown in FIGS. A configuration using the mounted printed circuit board 3 is also possible. FIG. 10A is an exploded perspective view showing a configuration of an SSD device using the printed circuit board 3 on which NANDs 5 are mounted on both sides. FIG. 10B is a perspective view showing the configuration of the lower surface of the printed circuit board 3 on which the NANDs 5 are mounted on both sides. When the printed circuit board 3 having the NANDs 5 mounted on both sides is used, the same piece as the heat radiation sheet 10 of the first embodiment is also provided between each NAND 5 on the upper surface side of the printed circuit board 3 and the top cover 1. By disposing the heat dissipation sheet 15, the coupling capacity of the parallel plate capacitor by the printed circuit board 3 and the top cover 1 can be reduced, and unnecessary radiation due to the top cover 1 functioning as an antenna can be reduced. It goes without saying that the same effect can be obtained even if the heat dissipating sheet 15 is the same as in the second and third embodiments. As described above, the present invention can be variously modified.

  DESCRIPTION OF SYMBOLS 1 Top cover, 3 Printed circuit board, 5 NAND, 6 Controller, 9 Bottom housing 10, 10a, 10b, 10c, 11, 12, 13 Radiation sheet.

Claims (6)

A plurality of nonvolatile semiconductor memory chips and a controller that controls reading and writing of data to and from the nonvolatile semiconductor memory chip, a printed circuit board mounted on one surface via a plurality of bumps,
A housing made of a conductive material and containing the printed circuit board;
The controller and each non-volatile semiconductor memory chip and the case are interposed between a surface of the case facing the one surface of the printed circuit board and the controller and each non-volatile semiconductor memory chip. A heat dissipating sheet for thermal connection;
With
The heat dissipation sheet is characterized in that a coupling capacity of a capacitor formed by the housing and the printed circuit board is smaller than a coupling capacity in a state where an object having a relative dielectric constant of 5.8 is disposed between the capacitors. A semiconductor memory device.   2. The semiconductor memory device according to claim 1, wherein the heat radiating sheet is divided into a plurality of pieces, and the pieces of the heat radiating sheet divided into a plurality of pieces are arranged at intervals.   3. The semiconductor memory device according to claim 2, wherein each piece of the plurality of heat-dissipating sheets is disposed corresponding to each of the controller and the nonvolatile semiconductor memory chip.   4. The semiconductor memory device according to claim 2, wherein the heat dissipating sheet includes each of the plurality of pieces divided into a plurality of pieces and a plate-like portion provided on the surface with each of the pieces divided into the plurality of pieces. 5.   5. The semiconductor memory device according to claim 1, wherein the heat dissipation sheet is formed of a material having a relative dielectric constant smaller than 5.8. A plurality of nonvolatile semiconductor memory chips are also mounted on the other surface of the printed circuit board,
The other surface of the printed circuit board is interposed between the nonvolatile semiconductor memory chip mounted on the other surface of the printed circuit board and the inner surface of the housing facing the other surface of the printed circuit board. 6. The semiconductor memory device according to claim 1, further comprising a heat dissipating member that thermally connects the nonvolatile semiconductor memory chip mounted on the housing and the housing.

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