JPH075223A - Insulation property testing method of circuit board - Google Patents

Abstract

PURPOSE:To provide a testing method which enables the judging of the propriety in the insulation property of an insulation layer in a metal base circuit board provided with a circuit conductor through the insulation layer on a metal base. CONSTITUTION:A specific voltage is applied between a circuit conductor 3 of a circuit board 10 and a metal base 1 to measure the frequency of a partial discharge generated in an insulation layer 2. When the frequency of occurrence of the partial discharge in a specified discharged electric charge is large, a rejection is identified and when the frequency of the occurrence is zero or very limited, acceptance is identified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for testing good insulation between a metal base and a circuit conductor in a metal base circuit board.

[0002]

2. Description of the Related Art A metal base circuit board having a circuit conductor provided on a metal base via an insulating layer is widely used as a circuit board for high power hybrid ICs and the like. In the insulation evaluation test of such a circuit board, the judgment was made based on the presence or absence of insulation breakdown when a voltage of AC 2 to 5 KV was applied between the circuit conductor and the metal base for 1 minute.

[0003]

However, dielectric breakdown may occur in the insulating layer of the circuit board in the withstand voltage test performed during or after mounting the components on the circuit board that has passed the above test method. Not a little, there is a problem that the test method cannot sufficiently judge the quality of the insulating layer.

[0004]

SUMMARY OF THE INVENTION A circuit board insulation test method according to the present invention comprises a circuit board having a circuit conductor provided on a metal base with an insulating layer interposed between the circuit conductor and the metal base. Is applied, and the occurrence frequency of partial discharge that occurs in the insulating layer at this time is measured to judge whether the insulation property of the circuit board is good or bad.

[0005]

The present inventors have found that there is a close relationship between the quality of the dielectric breakdown strength of the insulating layer on the metal base and the frequency of partial discharge that occurs when a predetermined voltage is applied to the insulating layer. I found that there is. That is, if the frequency of occurrence of partial discharge of a specific discharge charge is high, it is determined as a defective product, and if the frequency of occurrence of partial discharge is zero or very low, it is determined as pass.

[0006] The quality of insulation of the insulating layer mainly depends on the existence degree of voids in the insulating layer. However, it is almost void-free that the conventional dielectric strength test method can judge the quality. If there is a large number of voids, and the presence degree of voids is intermediate between the two, if the initial test as described above was passed, the component mounting process or after mounting This causes the inconvenience that dielectric breakdown occurs in the withstand voltage test. According to the present invention, it has been found that the so-called "semi-defective product" can be checked in advance, and the present invention has been proposed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a circuit board 10 which is the subject of the test method of the present invention. In the figure, reference numeral 1 denotes a metal base for a heat sink made of an aluminum plate or the like, on which an insulating layer 2 and a circuit conductor 3 are sequentially laminated. The insulating layer 2 is one in which an adhesive layer such as an epoxy resin adhesive is provided on both surfaces of an insulating film such as a polyimide film, or an epoxy resin adhesive is mixed with an inorganic filler for improving thermal conductivity. It consists of things. Reference numeral 4 denotes a sealing portion made of an insulating or semi-conductive material that seals the edge portion of the circuit conductor 3, which is provided to prevent corona discharge from the edge portion of the circuit conductor 3. There is.

FIG. 2 is a simplified circuit diagram showing an example of a partial discharge test method for evaluating the insulation property by the method of the present invention. In the insulation test of the circuit board according to the present invention, as shown in the figure, a high voltage is applied between the metal base 1 and the circuit conductor 3 of the test circuit board 10, and a void or the like exists in the insulating layer 2. The basic idea is to create a partial discharge when there is a discharge. The high voltage application circuit is composed of a power source E, a high voltage transformer Tr, a blocking coil Bc and the like. Further, 6 is a standard charge generator used for the configuration of the measurement system in the partial discharge measurement, and the pulse generator 6
It has 1 and so on.

A partial discharge measuring instrument 5 is connected to the above-mentioned high voltage applying circuit in parallel with the test circuit board 10 via a coupling capacitor Ck. The measuring device 5 is a pulse counter for measuring the number of times per second in the insulating layer 2 a partial discharge having a discharge charge amount of a certain value or more is generated with a constant voltage applied by the high voltage applying circuit. , The level input section that sets the partial discharge generation level that is the reference for quality judgment is compared with the number of measured pulses of the pulse counter and the number of reference pulses, and if the number of measured pulses exceeds the number of reference pulses, then N
A comparison circuit for outputting the G signal is provided.

The voltage applied between the circuit board 3 and the metal base 1 may be appropriately determined depending on the thickness of the insulating layer 2 and the like, but it is suitable to select it in the range of approximately 1 to 5 KV, and particularly 2 to 3 KV. Is.

Further, in the present invention, the quality of insulation of the circuit board is judged by the frequency of occurrence of partial discharge. The size of partial discharge (size of discharge charge amount) and the number of times of occurrence, which are criteria for the judgment, are , The thickness and material of the insulating layer of the circuit board,
It is set appropriately according to the voltage used on the substrate, and is generally 10
It is appropriate to judge that the partial discharge having a discharge charge amount of about 30 pc is about 10 to 40 times or less per second and that the partial discharge is acceptable.

(Test Example) A copper foil having a thickness of 35 μm was formed with a thickness of 1
It is adhered on an aluminum base having a thickness of 2 mm through an epoxy resin adhesive layer mixed with an inorganic filler of 00 μm,
A circuit conductor was formed by etching the copper foil to prepare a test circuit board. This circuit board was subjected to a conventional withstand voltage test of applying 3 KV for 1 minute, and a circuit board that passed this test was used as a test circuit board.

Using the measuring circuit as shown in FIG. 2 to the above circuit board, when an alternating current of 3.0 KV is applied for 1 second, how many partial discharge pulses with a discharge charge amount exceeding 20 pc are generated. The partial pulse occurrence frequency was measured by setting the above-mentioned pulse counter so as to measure, and setting the number of level pulses as a reference for the quality judgment to 20 times.

From these measurement results, five circuit boards each having a frequency of occurrence of partial discharge of 20 times or more per second and five circuit boards having a frequency of 20 times or less per second are selected. A long-term voltage application test was performed in which an AC voltage of 3 KV was applied between the conductor and the aluminum base. The results are shown in Table 1.

[0015]

[Table 1]

From the above results, the circuit boards judged to be acceptable by the insulation test method of the present invention did not cause dielectric breakdown in the long-term voltage application test, while those judged to be unacceptable in a short time. Dielectric breakdown was confirmed, and the reliability of the test method of the present invention was confirmed.

[0017]

As described above, according to the test method of the present invention, dielectric breakdown may occur in the insulating layer of the circuit board in the withstand voltage test performed in the process of mounting the component on the circuit board or after the mounting. The circuit board having insufficient dielectric breakdown strength can be reliably identified, and the manufacturing efficiency of the component mounting circuit board can be significantly improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a circuit board to be tested by a test method of the present invention.

FIG. 2 is a simplified circuit diagram showing an example of a partial discharge test method performed when evaluating insulation by the method of the present invention.

[Explanation of symbols]

 1 metal base 10 circuit board 2 insulating layer 3 circuit conductor 5 partial discharge measuring instrument

Front page continuation (72) Inventor Hidefumi Morita 4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Cable Industries, Ltd. Itami Works (72) Inventor Hideaki Matsuda 4-3 Ikejiri, Itami City, Hyogo Mitsubishi Cable Industries Itami Co., Ltd. Inside the Works (72) Inventor Seiji Okada 4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Cable Industries, Ltd. Itami Works

Claims (1)

[Claims] 1. A partial discharge generated in the insulating layer when a predetermined voltage is applied between the circuit base and the metal base of a circuit board provided with a circuit conductor on a metal base via an insulating layer. A circuit board insulation test method, comprising determining the quality of insulation of the circuit board by measuring the occurrence frequency of the circuit board.