JPH07212066A - Fixing method of power transistor - Google Patents

Abstract

PURPOSE:To ensure an enough creepage distance of insulation for a power transistor so as to meet safety standards when the power transistor is fixed to a board. CONSTITUTION:Holes 26 and 28 are bored in a board 10 on both sides of a spot where a power transistor 18 is fixed to form a bridge 30. Then, the power transistor 18 is sandwiched in between the board 10 and a heat sink 12, and the board 10 and the heat sink 12 are fixed together with screws 20a to 20c and nuts 22a to 22c located at both the end of the bridge 30. At this point, an insulating sheet 14 may be sandwiched in between the heat sink 12 and the power transistor 18. By these processes, the bridge 30 presses the transistor 18 against the heat sink 12 by pressure. By this setup, a creepage distance of insulation from the screws 20a to 20c and the heat sink 12 can be ensured enough for the power transistor 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for fixing a power transistor, and more particularly, to a method for fixing a power transistor which handles a high voltage and fixes a power transistor which generates a large amount of heat, thereby reducing the risk of creeping discharge. Regarding

[0002]

2. Description of the Related Art When mounting a high power device such as a power transistor on a circuit board, it is necessary to satisfy various conditions in order to ensure safety. One of the conditions is to prevent discharge between electrodes having a large potential difference.

A creeping discharge which is a kind of discharge will be described with reference to FIG. In this figure, the plate electrode 2 is provided on one main surface of the insulating layer 3, and the small electrode 1 is applied to the other main surface. At this time, when an AC voltage is applied to both electrodes, a creeping discharge is generated from the contact portion of the small electrode 1 on the surface of the insulating layer 3. This is because the charge due to the discharge current accumulates on the surface of the insulating layer 3 and contributes to the next half-wave discharge of the AC voltage.

FIG. 4 is a sectional view showing a conventional fixing method of the power transistor 18 to the substrate 10. power·
The transistor 18 usually has a hole in its main body, and is fixed to the circuit board 10 and the heat sink 12 by screwing a screw 20 into this hole. Power transistor 1
An electrode (collector electrode) 16 (indicated by diagonal lines) 8 is provided on the main body surface. This is mainly to dissipate the large heat generated in the power transistor. The insulating sheet 14 having good thermal conductivity is used for the electrode 16 and the heat sink 12.
The heat generated in the power transistor 18 is efficiently transferred to the heat sink 12 at the same time as the heat insulation.

[0005]

The screw 20 and the heat sink 12 are normally grounded, and there is a potential difference between the screw 20 and the heat sink 12 and the electrode 16. When this potential difference is smaller than the specified value,
There is no problem even with the fixing method shown in FIG. However, when the potential difference exceeds a predetermined value, there is a risk that the above-mentioned creeping discharge may occur, and as required by various safety standards (UL standard, etc.), the creeping surface between the screw 20, etc. and the electrode 16 may be increased. The distance (the distance between the screw 20 and the heat sink 12 with respect to the electrode 16 along the surface on which the electrode 16 is provided) needs to be sufficiently large.

Therefore, an object of the present invention is to provide a method of fixing a power transistor which can secure a sufficient creeping distance and is highly safe. Another object of the present invention is to
An object of the present invention is to provide a method of fixing a power transistor, which has a simple assembling process.

[0007]

According to the method of fixing a power transistor of the present invention, a bridge is formed by forming holes on both sides of a fixed position of a power transistor on a substrate. Next, the power transistor is sandwiched between the substrate and the heat sink, and the substrate and the heat sink are fixed to each other at both ends of the bridge portion. At this time, an insulating means (insulating sheet) may be sandwiched between the heat sink and the power transistor. As a result, the bridge portion presses the power transistor toward the heat sink, so that the heat generated in the power transistor can be efficiently transmitted to the heat sink. Further, it is not necessary to pass a screw through the hole of the power transistor body to fix it, and a sufficient creepage distance can be secured.

[0008]

1 is an exploded perspective view of a preferred embodiment of the present invention. 2 is an assembled sectional view of FIG. In addition,
Those corresponding to those in FIG. 4 are designated by the same reference numerals. Also,
Although the figure shows the case of two power transistors, the present invention can be applied to one power transistor. Of course, it can be easily expanded to have two or more power transistors.

According to the invention, the power transistor 18
Are sandwiched between the substrate 10 and the heat sink 12. The screw 20 does not pass through the hole of the power transistor 18, but fixes the substrate 10 and the heat sink 12 to indirectly fix the power transistor 18 to the substrate 10 and the heat sink 12. 1 of the body of the power transistor 18
The electrode 16 on the surface faces the heat sink 12 side (upward in the drawing). In this case, power transistor 1
An insulating sheet 14 having good thermal conductivity is provided between the heat sink 12 and the heat sink 12. The electrode 2 is grounded on the surface of the substrate 10.
4 is provided and the screw 20 contacts the electrode 24 and is grounded. Similarly, the heat sink 12 is also grounded via the screw 20. If the area of the insulating sheet 14 is widened, the creepage distance from the electrode 16 to the heat sink 12 along the surface of the insulating sheet 14 can be lengthened accordingly. Instead of the insulating sheet 14, an insulating layer having good thermal conductivity may be provided on the power transistor 18. Further, if the heat sink 12 is made of an insulating material, an insulating sheet is not necessary.

A bridge portion 30 for arranging the power transistor 18 is formed between the screws 20a and 20b on the substrate 10. In order to form the bridge portion 30, holes 26 that are long in the axial direction and pass through the screws 20a and 20b on both sides of the bridge portion 30.
And 28 are provided. Referring to FIG. 2, the length h of the recess of the heat sink 12 is slightly lower than the total thickness of the power transistor 18 and the insulating sheet 14. Therefore, when the heat sink 12 is fixed to the substrate 10 with the screws 20 and 22, the bridge portion 30 is pushed by the power transistor 18 and bent. Therefore, the bridge part 3
The stress indicated by the white arrow acts on the power transistor 18 due to 0. Due to this stress, the power transistor 18 is pressed against the insulating sheet 14. That is, the bridge part 3
0 is pressing the power transistor 18 toward the heat sink 12. Therefore, the heat from the electrode 16 is efficiently transferred to the heat sink 12.

As is apparent from FIGS. 1 and 2, the power
By disposing the transistor 18 in the bridge portion 30, particularly in the central portion thereof, the screws 20a at both ends of the bridge portion 30 are provided.
The creepage distance between the electrodes 20 and 20b and the electrode 16 can be significantly increased, and the safety standard can be satisfied.

In recent years, the size of equipment has been reduced by directly soldering electronic components to the surface of a substrate by surface mounting (SMD). In this case, if stress is applied to the substrate, there is a risk that the parts will come off. According to the present invention, the bridge portion 30 provided on the substrate 10 is stressed, but this stress is terminated by the screws 20 and 22 (fixing means) at both ends (fixing portions) of the bridge portion 30, and No stress is applied to the part. Therefore, it can be used without problems even when manufacturing a circuit board by surface mounting.

According to the invention, the assembly is also relatively easy and simple. After soldering the power transistor, the screw 20 is inserted into the substrate 10. The screw 20 is fixed to the substrate 10 with solder or the like. Next, the insulating sheet 14 and the heat sink 12 may be fastened with the screws 22. In these steps, it is only necessary to work toward one surface of the substrate, and it is not necessary to work while supporting three or more parts at a time, and therefore work with both hands is easy.

[0014]

According to the method of fixing the power transistor of the present invention, it is not necessary to fix the power transistor by inserting the screw into the hole of the main body of the power transistor, and a sufficient creeping distance can be obtained. Further, since the bridge portion presses the power transistor toward the heat sink, the heat generated in the power transistor can be efficiently transmitted to the heat sink. Moreover, the stress applied to the bridge ends at both ends (fixed parts) of the bridge, and the stress does not reach other parts of the substrate. Therefore, it can be used without problems even when manufacturing a substrate by surface mounting.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a preferred embodiment of the present invention.

FIG. 2 is an assembled sectional view of FIG.

FIG. 3 is a diagram illustrating creeping discharge.

FIG. 4 is a sectional view of an example of a conventional fixing method of a power transistor.

[Explanation of symbols]

 10 circuit board 12 heat sink 14 insulating sheet 16 electrode 18 power transistor 20 screw 22 screw 24 electrode 26 hole 28 hole 30 bridge part

Claims (3)

[Claims] 1. A bridge portion is formed by forming holes on both sides of a fixed position of a power transistor on a substrate, the power transistor is sandwiched between the substrate and a heat sink, and the substrate is formed at both ends of the bridge portion. A method of fixing a power transistor, wherein the heat sinks are fixed to each other. 2. A bridge portion is formed by forming holes on both sides of a fixed position of a power transistor on a substrate, and insulating means is sandwiched between the heat sink and the power transistor, so that the power source is connected between the substrate and the heat sink. A method of fixing a power transistor, comprising sandwiching a transistor and fixing the substrate and the heat sink to each other at both ends of the bridge. 3. The power according to claim 1, wherein the substrate and the heat sink are fixed to each other at both ends of the bridge portion, and the power transistor is pressed against the heat sink at the bridge portion.・ How to fix the transistor.