JPH0655297U - Module heat dissipation structure - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a heat dissipation structure for a module that can efficiently dissipate heat generated in each module and is inexpensive to manufacture. A heat transfer that has a printed circuit board (21) on which a heat generating electronic circuit is mounted and a heat receiving surface (251) that is in thermal contact with a heat generating portion of the printed circuit board and that conducts heat to a heat radiation fin (252). Module (20) with plate (25)
, The distance between this heat-generating electronic component and the heat-receiving surface (δ)
Is a value at which only the viscous bottom layer is formed by air.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an apparatus in which a system is composed of a large number of modules such as a sequencer, and more particularly to an improvement for efficiently dissipating heat inside the modules.

[0002]

[Prior art]

 There are various types of module devices, such as a power supply module, a CPU module, an I / O module, and a communication module, as disclosed in, for example, Japanese Patent Laid-Open No. 2-87596 proposed by the present applicant, and these have a bus. It is attached to the base plate to configure the system. In such a device, if the electronic circuit inside the module is densified, the power consumption per module increases, and if it is not cooled efficiently, the temperature rise will be significant and the operation of electronic parts will be hindered. I had a chance.

[0003]

[Problems to be solved by the device]

 Therefore, as disclosed in JP-A-64-61997, a heat sink is mounted on each module and electronic components that generate heat. However, when the amount of heat generation increases, the heat sink becomes larger and becomes an obstacle to the miniaturization of the module. Another problem was that among the heat-generating electronic components, those with holes for screwing were limited to power transistors and the like.

Further, Japanese Utility Model Application Laid-Open No. 4-47295 discloses a technique of radiating heat by thermally coupling each printed circuit board and a base plate having a bus. However, in the case of a module, it is difficult to thermally bond the print substrate and the base plate because the printed circuit board is housed inside the housing made of synthetic resin. In addition, there is a problem that it is difficult to use general-purpose products for the connector that is in charge of electrical connection. Furthermore, although a water-cooled type is known as a method for removing heat from heat-generating electronic components, there is a problem that it cannot be used in low-priced products such as sequencers where high cost is preferred.

The present invention solves such a problem, and an object of the present invention is to provide a heat dissipation structure for a module which can efficiently dissipate heat generated in each module and which is inexpensive to manufacture.

[0006]

[Means for Solving the Problems]

 The present invention which achieves such an object has a printed circuit board (21) on which an electronic circuit for generating heat is mounted, a heat receiving surface (251) which is in thermal contact with a heat generating portion of the printed circuit board, and a heat dissipation fin (252). In the module (20) having a heat transfer plate (25) that conducts heat to), the distance (δ) between the heat generating electronic component and the heat receiving surface is set to a value at which only the viscous bottom layer is formed by air. It has a feature.

[0007]

[Action]

 In the present invention, the distance (δ) between the heat-generating electronic component and the heat receiving surface is set to a value at which only the viscous bottom layer is formed by air, so that no turbulent flow occurs. Therefore, heat transfer can be performed with efficiency close to that of heat transfer in the contact state without contact, and the fins can perform efficient cooling.

[0008]

【Example】

 The present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of the structure of a module showing an embodiment of the present invention. In the figure, the module 20 accommodates a print substrate inside a housing 27. Chip components 261, SOP 262, QFP 263, etc. are mounted on both sides of the printed circuit board 21 as electronic components that generate heat. The chip parts include resistors and transistors, and the SOP (Small outline package) has lead terminals formed on two opposite sides of a quadrilateral. For example, the number of leads is 16. A QFP (Quad flat package) has lead terminals formed on all four sides of a quadrilateral. For example, the number of leads is 120, which is equivalent to a so-called one-chip microcomputer or gate array. In the use of a sequencer, for example, it is an input / output circuit for contact signals. The input / output connector 23 is provided on the front side of the printed circuit board 21, and is equipped with a connector (not shown) that bundles signal lines connected to external devices. The terminals 231 are conductors that connect each terminal of the input / output connector 23 and a circuit provided on the printed board 21. The display unit 24 is provided on the front side of the print substrate 21, and has a display element such as an LED for displaying the signal state of each terminal handled by the input / output connector 23.

The heat transfer plate 25 transfers the heat generated by the heat-generating electronic component to the heat radiation fins 252, and is made of a material having a high thermal conductivity such as aluminum. The heat receiving portion 251 is located on the back side of the printed circuit board 21 and is located at a slight distance δ from the heat-generating electronic component. The heat radiation fins 252 are provided on the opposite side of the heat receiving portion 251, and are responsible for heat radiation inside the module to reduce the thermal load on the base plate 10. The screw 28 mechanically fastens the printed circuit board 21 and the heat transfer plate 25. Preferably, if the surface of the heat transfer plate 25 is subjected to a surface treatment so that the surface becomes close to black, the emissivity approaches 1.00, and heat transfer by radiation can be used together.

Regarding the interval δ, the chip component 261 and the heat receiving portion 251 have an interval δ ₁ , and the SOP 262 and the heat receiving portion 251 have an interval δ ₂ . Since the QFP 263 is mounted on the front side of the printed board, the heat receiving portion 251 and the printed board 21 come into contact with each other, and the heat of the QFP is sent to the heat receiving portion 251 via the printed board 21. This interval δ corresponds to the thickness of the viscous bottom layer known in heat transfer engineering. According to heat transfer engineering, the Reynolds number Re is defined by the following equation with respect to the distance δ from the flat plate. Re = Uτδ / ν (1) where Uτ = (τ ₀ / ρ) ^1/2 , where τ ₀ is the wall friction stress, ρ is the density, and ν is the kinematic viscosity coefficient. In the case of a smooth surface, the viscous bottom layer corresponds to the following region. 0 <Re <4 (2) Therefore, the thickness δ of the viscous bottom layer should be in the following range. δ <4ν / Uτ (3) Actually, this value δ fluctuates depending on the smoothness of the flat plate, but according to experiments, the point of change from the viscous bottom layer to the transition layer is around δ = 0.3 mm.

Next, the heat transfer mechanism will be described. Considering the heat transfer between the fluid and the fixed wall, due to viscous friction between the fluid and the wall, the velocity distribution in the thin layer (boundary layer) near the wall is different from that in the fluid inside away from the wall. The slope is steep. Moreover, even if the part of the boundary layer that is far from the wall surface is turbulent, at the part of the boundary that is particularly close to the wall surface (viscous bottom layer), there is almost laminar flow along the fluid wall surface. Therefore, the heat from the wall surface is first transferred by heat conduction in the viscous bottom layer where the fluid does not have vortices, and from there is transferred to the outside of the boundary layer by vortices or convection. Therefore, the temperature distribution in the boundary layer is steep and the temperature gradient is steep. In the boundary layer, the closer the distance δ between the heat-generating electronic component and the heat dissipation plate is, the more the heat conductive material is, and the better heat dissipation can be performed.

Since the distance δ may be set to a value that does not cause turbulence in design, the assembly dimension error between the heat transfer plate 25 and the printed circuit board 21 should be made strict on the side where the distance increases, and contact should be made. Although it is preferable to set a tolerable value on the side where heat is applied, it is desirable to prevent an excessive response from acting between the heat transfer plate 25 and the heat generating electronic component.

Next, a case will be described in which the heat radiation inside the module is large, and the heat radiation fin 252 alone is insufficient as a heat sink. FIG. 2 is a cross-sectional view of a module that is in contact with the base plate, and FIG. 3 is a perspective view illustrating the assembled state of the base plate 10 and the module. In the figure, a base plate 10 is for mounting a large number of modules 20 and is fixed to another wall such as an instrumentation board. As a main material, a material having a high thermal conductivity such as aluminum and relatively easy to process is used. It is used. The upper locking portion 11 is a convex portion provided on the upper end of the base plate 10, and is formed here in the entire width direction of the base plate 10. The lower locking portion 12 is a convex portion provided on the lower end of the base plate 10, and here, the module mounting location of the base plate 10 is substantially determined. A connector 13 is connected to each module, and is attached to a printed circuit board called a backboard 14 here at intervals corresponding to the width of the module. The backboard 14 is provided with a bus that connects the respective poles of the connector 13. The module contact surface 15 is formed between the backboard 14 and the lower locking portion 12, and the bulk material of the base plate 10 is flattened to facilitate heat transfer. The wall abutting surface 16 is provided on the opposite side of the module abutting surface 15, and has a shape that requires less thermal resistance with the mounting wall facing when mounted on an instrumentation board or the like. .

The module 20 is shown in FIG. 3 with the housing 27 removed. The base connector 22 is provided on the back side of the printed board 21, and is connected to the connector 13 on the base plate 10 side. The heat transfer plate 25 transfers the heat generated by the heat generating electronic components to the heat radiation fins 252 and the base plate 10, and is made of a material having a high thermal conductivity such as aluminum. The base contact surface 253 is exposed on the back surface of the module housing 27 and is in thermal contact with the module contact surface 15. The housing 27 covers the printed circuit board 21 and is provided with locking means (not shown) such as screws and latches for attaching to the upper locking portion 11 and the lower locking portion 12 of the base plate 10.

The operation of the device configured as described above will be described below. In the module 20, the heat generated in the electronic component is conducted by the heat transfer plate 25 and is transmitted to the base plate 10, is radiated to the mounting wall, and is cooled by the air flow generated inside the module 20 by the heat radiation fin 252.

[0016]

[Effect of device]

 As described above, according to the present invention, the space between the heat-generating electronic component and the heat transfer plate is separated by the distance δ corresponding to the viscous bottom layer. Therefore, the components can be mounted on both sides of the printed circuit board 21 while maintaining good heat dissipation efficiency. Since it can be mounted and the printed circuit board can be miniaturized, the cost can be reduced and the practical effect is great. Also, when surface mount components are used for electronic components, the heights of the components are uniform, so the heat transfer plate 25 need only be a simple flat plate, which facilitates manufacturing and has a great effect. .

[Brief description of drawings]

FIG. 1 is a structural cross-sectional view of a module showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a module that is in contact with a base plate.

FIG. 3 is a perspective view illustrating an assembled state of the base plate 10 and the module.

[Explanation of symbols]

 20 Module 21 Printed Circuit Board 25 Heat Transfer Plate 251 Heat Receiving Section 252 Radiating Fin 26 Heat-generating Electronic Component (Chip Component, SOP, QFP)

Claims (1)

[Scope of utility model registration request] 1. A printed circuit board (21) on which a heat generating electronic circuit is mounted, and a heat receiving surface (251) that is in thermal contact with a heat generating portion of the printed circuit board, and conducts heat to a heat radiation fin (252). Module (2 with heat transfer plate (25)
In 0), the heat radiation structure of the module is characterized in that the distance (δ) between the heat-generating electronic component and the heat receiving surface is set to a value at which only the viscous bottom layer is formed by air.