JP2005093760A - Electronic instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic instrument in which a weight load is not applied on a circuit substrate and which is high in reliability under a severe usage in the condition of the vibration or shock of a motorcar or the like, in particular. <P>SOLUTION: The electronic instrument is provided with a structure wherein circuit components provided on the circuit substrate 20 and necessitating heat dissipation are contacted to a heat dissipating plate 23 attached to the circuit substrate 20 with pressure optimum for the heat dissipation. The heat dissipating plate 23 is formed with fixing holes 23a, 23b to fix the circuit components to a case 15 by screwing through the fixing holes 23a, 23b, and the circumference of the circuit substrate 20 is freely maintained in the case 15. The heavy-weight heat dissipating plate 23 is fixed to the case 15 by screwing. By this constitution, the circuit substrate 20 can freely be retained without fixing the same to the case 15 whereby stress is not applied on the soldering part of the circuit components even in a using state that the load of vibration or shock is applied, thereby permitting the improvement of reliability. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electronic device using a circuit board having a heat sink.

  FIG. 6 is an example of a sectional view showing a conventional electronic device using this type of circuit board. In FIG. 6, a circuit component 2 constituting a necessary circuit unit is mounted on a circuit board 1. In general, the circuit board 1 is used with its end fixed to the mounting portion 5 of the case 4 using screws 3 or the like.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
Japanese Utility Model Publication No. 63-97286

  When a circuit component attached to a circuit board requires heat dissipation, a heat sink is attached to the circuit board or the circuit component for this heat dissipation, and heat is generally released by pressing the circuit component against the heat sink.

  However, in the conventional circuit board mounting structure as shown above, since the end of the circuit board is fixed to the mounting part of the case, in the case of a circuit board having a large and heavy heat sink, vibration and shock Under operating conditions where a large load is applied, stress due to vibration concentrates on the mounting part of the heat sink and the soldering part of the circuit components that are in pressure contact with it, causing damage to the soldering part or the circuit board itself Had the problem of doing.

  The present invention solves such problems, and provides a highly reliable electronic device that is not subjected to a heavy load on a circuit board and that is particularly used under severe vibration and impact conditions such as an automobile. It is intended.

  In order to solve the above-mentioned problem, the invention according to claim 1 of the present invention presses a circuit component that requires heat dissipation provided on a circuit board to a heat sink attached to the circuit board at a pressure suitable for heat dissipation, Provide a fixing hole in the heat sink, and fix it by screwing it to the case through this fixing hole, so that the periphery of the circuit board is kept free in the case. By fixing the heavy heat sink to the case by screwing, it becomes possible to keep the circuit board free without fixing it to the case. There is an effect that the reliability can be improved without applying stress to the soldering portion of the component.

  In the invention according to claim 2 of the present invention, a fixing boss is provided in the case so as to correspond to a fixing hole formed in the heat radiating plate. According to the position and height of the heat radiating plate to be fixed. Since the fixing boss is provided, the circuit board can be fixed to the case stably and reliably.

  In the invention according to claim 3 of the present invention, a concave hole that can be fitted to the outer periphery of the fixing boss provided in the case is provided on the case surface side of the fixing hole of the heat sink. When fixed to the case, the position can be regulated.

  In the invention according to claim 4 of the present invention, the pressure contact of the circuit component to the heat radiating plate is configured to use the elasticity of the leaf spring attached to the heat radiating plate. By maintaining, the stress on the soldered portion of the circuit component due to thermal expansion and contraction and vibration is relieved, and the heat radiation can be surely performed.

  The invention according to claim 5 of the present invention is such that the leaf spring is processed in a U shape, one has a surface that contacts the back surface of the heat sink and the other presses the circuit component to the heat sink. The intermediate portion is fixed to the heat radiating plate with screws, and this has the effect of stabilizing the pressure contact force of the circuit components and enabling a stable heat radiating effect.

  In the electronic device of the present invention, a circuit component that requires heat dissipation is pressed against the heat sink at a pressure suitable for heat dissipation, and a fixing hole is provided in the heat sink, and the case is screwed to the case through the fixing hole. In this case, the circuit board is configured so that the circuit board is kept free in the case, enabling reliable heat dissipation and soldering of circuit components even in usage conditions that are subject to vibration or shock. The attachment portion is not stressed and the reliability can be greatly improved.

  Embodiments of the present invention will be described below with reference to the drawings.

  As an example of an embodiment of the present invention, an electronic device for a charge / discharge circuit will be described with reference to FIGS. In these drawings, illustrations are omitted except for parts related to the present invention. Although not shown in the figure, a circuit pattern of an electronic device for charge / discharge circuit is formed on the circuit board 20. In the embodiment of the present invention, two FETs 21a and 21b are illustrated as charging circuit components, and a diode 22a and a resistor 22b are illustrated as discharging circuit components. These circuit components are circuit components that generate heat when a large current flows during charge and discharge. The FETs 21a, 21b, the diode 22a, and the resistor 22b are each fixed to the circuit board 20 by soldering the lead wires, and the heat radiating portion formed on the back surface thereof is in pressure contact with the heat radiating plate 23 with an appropriate pressure. ing.

  The heat sink 23 is formed with two holes 23a and 23b for fixing to the case 15, and the case 15 is formed with fixing bosses 24a and 24b at positions corresponding thereto, and screws 24c and 24d. Screwed.

  Concave circles 23d and 23e are formed in the surface 23c on the side of the radiator plate 23 to be incorporated into the case 15 and are concentric with the holes 23a and 23b, and fit into the fixing bosses 24a and 24b of the case 15. The position is regulated by the holes 23d and 23e and the fixing bosses 24a and 24b.

  In this fixed state, the circuit board 20 is stored upright with respect to the case 15, and the outer peripheral surfaces 20 a, 20 b, 20 c, and 20 d are kept free in the case 15.

  As described above, in the embodiment of the present invention, since the heat radiating plate 23 is fixed to the case 15, the circuit board 20 can be kept free without being fixed to the case 15. Even in the case where a load is applied, no stress is applied to the soldered portion of the circuit component mounted on the circuit board 20, and an improvement in reliability can be expected.

  Next, a stable heat dissipation method for the heat sink 23 of the FETs 21a and 21b and the diodes 22a and the resistors 22b, which are circuit components for charging and discharging, will be described with reference to FIGS.

  In FIG. 4, a leaf spring 25 made of an elastic member such as stainless steel has a substantially U shape, and a fixing hole 25 a to the heat radiating plate 23 is formed at the center thereof. Both ends are bent, and one is an elastic piece 25b extending like an arm, and the rounded portion 25c is formed so as to stably press-contact the fixed positions of the body portions of the FETs 21a and 21b, the diode 22a, and the resistor 22b. Is provided. The other is a guide portion 25d which is in an appropriate length and comes into contact with the surface 23c on the side of the heat radiating plate 23 incorporated into the case 15.

  Further, although not shown, heat radiation promoting grease made of silicon or the like is applied to the surface where the FETs 21a and 21b, the diode 22a, the resistor 22b and the heat radiating plate 23 are pressed, and the pressure contact force by the plate spring 25 is the surface pressure. Is set between 0.1N and 4.5N.

  The leaf spring 26 shown in FIG. 5 is manufactured by connecting the structure of the leaf spring 25 shown above. When there are a plurality of circuit components that need to be dissipated (four in this embodiment), it is possible to press-contact at the same time by using a connection-type leaf spring 26 having elastic pieces 26a corresponding to the number of circuit components. .

  By adopting the pressure contact structure by the leaf spring 26 in this way, the FET 21a, 21b, the diode 22a, and the resistor 22b, which are the circuit components for charging and discharging, are fixed at the soldering portion to the circuit board 20, Since the heat sink 23 is only pressed by an appropriate pressure, the stress generated in the soldering portion can be alleviated even if there is a difference in the thermal expansion / contraction of each member due to a temperature change or the like. Further, the variation in the pressure contact force can be reduced by making the leaf spring 25 substantially U-shaped and restricting the position of the leaf spring 25 with the heat radiating plate 23 by the guide surface 25d. Furthermore, the pressure contact force itself can be reduced by using the heat radiation promoting grease. In addition, a plurality of circuit components can be simultaneously pressed by the leaf spring 26, so that the number of work steps can be reduced and the pressing force can be made uniform.

  The pressure contact force was set to 0.1N to 4.5N. This is due to vibrations of the lead wires of the circuit components and the soldered portions of the circuit board 20 that are pressed against the minimum load capable of reliably releasing heat to the heat sink 23, allowable stress of the soldered portions due to temperature changes, and the like. By managing within this range, it is possible to prevent damage to the soldered part due to reliable heat dissipation, vibration, temperature change, etc., leading to improved reliability.

  The electronic device according to the present invention is the one in which the heat sink is fixed by screwing to the case, and the circuit board is in a free state in the case. It provides a holding structure that can be significantly improved, and is suitable for use in applications where vibration resistance and thermal shock resistance are required.

The disassembled perspective view which shows the electronic device in embodiment of this invention 1 is a partially cutaway perspective view of a state in which a circuit board according to an embodiment of the present invention is held in a case The disassembled perspective view of the circuit board and case in embodiment of this invention The disassembled perspective view which shows the attachment state of the leaf | plate spring attached to the heat sink in embodiment of this invention The disassembled perspective view which shows another attachment state of the leaf | plate spring attached to the heat sink in embodiment of this invention Sectional view showing conventional electronic equipment

Explanation of symbols

15 Case 20 Circuit board 21a, 21b FET
22a Diode 22b Resistor 23 Heat sink 23a, 23b Hole 23d, 23e Recessed hole 24a, 24b Fixing boss 24c, 24d Screw 25 Leaf spring 25b Elastic piece 25c Round processing portion 26 Leaf spring

Claims (5)

A circuit component that requires heat dissipation provided on the circuit board is pressed against a heat sink attached to the circuit board with a pressure suitable for heat dissipation, and a fixing hole is provided in the heat sink, and the fixing hole is inserted through the fixing hole. An electronic device configured to be fixed to the case by screwing, and the circuit board is kept free in the case. The electronic device according to claim 1, wherein a fixing boss is provided in the case so as to correspond to a fixing hole formed in the heat radiating plate. The electronic device according to claim 2, wherein a recessed hole that can be fitted to an outer periphery of a fixing boss provided in the case is provided on a case surface side of a fixing hole of the heat radiating plate. The electronic device according to claim 1, wherein the pressure contact of the circuit component to the heat sink uses a elasticity of a leaf spring attached to the heat sink. The leaf spring is processed into a U-shape, one has a surface that contacts the back surface of the heat sink, and the other is formed so that the circuit component is pressed against the heat sink. The electronic device according to claim 4, wherein the electronic device is configured to be fixed.

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