JPH0614092B2 - Withstanding voltage test method for product inspection of circuit boards for hybrid integrated circuits - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a test method for determining whether or not a withstand voltage of a product is good for a hybrid integrated circuit, that is, a circuit board for forming a hybrid IC.

(Prior Art) As a circuit board for high-density mounting or high-power hybrid IC, etc., an insulating layer made of an organic insulating material such as epoxy resin or polyimide on a metal base such as an aluminum base to be a heat sink, or glass epoxy, etc. There is often used a circuit board having an insulating layer containing the organic insulating material, and further having a circuit conductor provided thereon. In the routine product inspection for testing the withstand voltage property of the circuit board, that is, the dielectric breakdown strength, a test method for applying a voltage of 2 to 5 KV AC for 1 minute between the circuit conductor of the circuit board and the metal base is exclusively used. Adopted, this test determines whether the dielectric breakdown strength of the product is good or not depending on whether dielectric breakdown occurs.

On the other hand, for high-voltage cables, power capacitors, transformers and other high-voltage electrical equipment that requires long-term reliability of 30 or 40 years or more, internal discharge of the insulation layer due to voids in the insulation layer, that is, partial Partial discharge measurement, which measures the discharge, is known. This partial discharge measurement is effective for evaluating the long-term reliability of the insulation performance of electrical equipment, and is useful for evaluating the long-term reliability of insulation performance in high-voltage electrical equipment research and development and certification tests, and during long-term use. It is used to diagnose the degree of deterioration of the insulation performance of electrical equipment. In addition, regarding power cables, for example, recently, for high-voltage cables of 60 KV or more, partial discharge measurement is also carried out during product inspection before product shipment. In this case, partial discharge measurement is also effective for long-term insulation performance. This is to check the reliability, and as a test for determining the quality of the dielectric breakdown strength of the product, an AC voltage breakdown test and a DC shock voltage breakdown test are separately performed.

(Problems to be Solved by the Invention) A semiconductor such as a transistor is provided on a circuit board having an insulating layer made of an organic insulating material or an insulating layer containing an organic insulating material on the metal base, and a circuit conductor provided on the insulating layer. element,
When manufacturing a module or board that has electronic functions by mounting resistors, capacitors, etc., so-called mounted products,
Insulation layer of the circuit board in the withstand voltage test that is performed during the manufacturing process of manufacturing the mounted product or the withstand voltage test after manufacturing the mounted product, even though the board that has passed the above-mentioned withstand voltage test is used. It often happens that dielectric breakdown occurs. Therefore, even if the voltage applied between the metal base and the circuit conductor is increased to set the test condition of the withstand voltage test of the circuit board to "Shibiya", the withstand voltage test of the circuit board is performed during or after the manufacturing process of the mounted product. The frequency of dielectric breakdown in the insulating layer remains unchanged or worsens.

This fact means that the conventional dielectric strength test method cannot fully evaluate the dielectric strength of the circuit board, that is, the dielectric breakdown strength. It is necessary to establish a new test method that can reliably identify and eliminate circuit boards that cause dielectric breakdown in voltage tests.

The present invention seeks to solve this new problem.

(Means for Solving the Problems) The withstand voltage test method of the present invention has an insulating layer made of an organic insulating material or an insulating material containing an organic insulating material on a metal base, and further has a circuit conductor formed thereon. A test method for determining whether the dielectric breakdown strength of a product has a circuit board for a hybrid integrated circuit, and measuring a partial discharge in the insulating layer by applying a predetermined voltage between the circuit conductor of the circuit board and the metal base. However, the quality of the dielectric breakdown strength of the circuit board is determined based on the magnitude of the discharged electric charge.

A circuit board whose discharge charge exceeds the specified value has a high possibility of causing a dielectric breakdown during the withstand voltage test during or after the manufacturing of the mounted product. Will be eliminated. In the actual inspection, it is not always necessary to measure the maximum value of the discharge charge amount, and simply, when the predetermined voltage is applied, the dielectric breakdown depending on whether or not the discharge charge exceeds the predetermined value is discharged. It is also possible to determine the quality of the strength.

The discharge charge referred to here is a discharge charge generated at a frequency of occurrence of a predetermined frequency or more when a predetermined voltage is applied, and the predetermined frequency can be appropriately selected from 10 pps, 20 pps, 100 pps, etc. Normally, it is convenient to select 50 pps or 60 pps according to the number of commercial cycles.

The circuit conductor referred to in the present invention includes both the conductor circuit formed by etching the conductor foil on the insulating layer and the conductor foil before etching.

(Function) The inventor of the present invention has made a precise determination regarding a circuit board that has undergone insulation breakdown during a withstand voltage test during or after the manufacturing process of a mounted product, despite using a conventional circuit board that has passed the withstand voltage test. The dielectric breakdown is caused by the voids existing in the insulating layer of the circuit board. Repeated withstand voltage test by the manufacturer of the mounted product or application of high voltage during product inspection of the circuit board causes discharge in voids in the insulating layer of the circuit board, degrading the organic insulator of the insulating layer, and In combination with the peculiarity of the circuit board that the thickness of the circuit board is extremely thin, it is a circuit board that has passed the withstand voltage test in product inspection of the circuit board, but withstand voltage test during or after the manufacturing process of the mounted product. It is probable that there was a dielectric breakdown in. This means that dielectric breakdown occurs in the circuit board during the withstand voltage test during or after the manufacturing process of the mounted product, even if the applied voltage is increased in the conventional withstand voltage test for the circuit board and the conditions of the withstand voltage test are severe. It is in good agreement with the above result that the frequency does not change much or increases on the contrary. Therefore, the dielectric breakdown strength of the circuit board can be fully evaluated,
As a test that can completely eliminate a product having insufficient dielectric breakdown strength such as dielectric breakdown during a withstand voltage test during or after the manufacturing process of a mounted product, as in the present invention, a void in an insulating layer of a circuit board is used. It is considered necessary to conduct a test for observing the state of internal discharge due to the above and determining pass / fail based on this.

Partial discharge measurement is a measurement method for observing internal discharge due to voids in the insulating layer, and there are various test methods such as discharge start voltage measurement, discharge extinction voltage measurement, and corona average current measurement. In the present invention, the discharge charge due to the internal discharge in the insulating layer when a predetermined voltage is applied between the circuit conductor and the metal base is measured, and the quality of the dielectric breakdown strength of the circuit board is determined by the magnitude thereof. More simply, when a predetermined voltage is applied, it is determined whether or not the dielectric breakdown strength of the circuit board is good by detecting the presence or absence of discharge of a discharge charge that exceeds a predetermined value. This is because the organic insulator is deteriorated as the amount of discharged electric charge is large and the extremely thin circuit board insulating layer is dielectrically broken down. Therefore, it is most purposeful for the problem of the present invention, and the convenience of the test is a routine work. Because it is suitable for product inspection.

Also by the experimental example described below showing the correlation between the result of the long-term withstand voltage test of the circuit board and the result of the partial discharge measurement, it is possible to identify and eliminate the circuit board that causes dielectric breakdown in a short time by the above partial discharge measurement. It is clear that you can.

As described above, in product inspection of electric equipment such as high-voltage power cables, partial discharge measurement may be performed together with AC voltage breakdown test and DC shock voltage breakdown test. A product that has an insulating layer of sufficient thickness and that has passed the AC voltage breakdown test and DC shock voltage breakdown test, but that will cause dielectric breakdown in a short period of time during subsequent use, such as subsequent external damage, chemical corrosion, etc. It does not occur unless there is a special reason, and the partial discharge measurement in this case is to check the reliability of long-term insulation performance of 30 years or 40 years or more. On the other hand, the test method of the present invention is for determining whether the dielectric breakdown strength of the product is good or bad, and in the case of the product inspection of the high-voltage power cable, the AC voltage breakdown test and the DC shock voltage breakdown test are performed. It is equivalent, and its purpose and character are different from the partial discharge measurement in a cable for high-voltage power.

(Example) First, a specific example of a circuit board which is a target of the test method of the present invention will be described.

1 (a), (b), (c), (d), and (e) are cross-sectional views of the circuit board, respectively, in which the insulating layer 2 is provided on the metal base 1 serving as a heat sink. And further has a copper circuit conductor 3 thereon. In the circuit boards shown in FIGS. 1A and 1B, the insulating layer 2 is composed of a polymer film 21 such as a polyimide film and an adhesive layer 22 such as an epoxy resin above and below the polymer film 21. In FIGS. 1C and 1D, the insulating layer 2 is an adhesive layer such as an epoxy resin, and an inorganic filler is often mixed in this adhesive layer in order to improve thermal conductivity. In FIG. 1 (e), the insulating layer 2 is composed of a glass epoxy layer. Regarding the circuit conductor 3, a conductor foil (before etching) stretched on the insulating layer 2 is shown in FIG. 1 (e), and a conductor foil is shown in FIGS. 1 (a) to 1 (c). Circuit conductors are shown etched to form circuits. Reference numeral 4 denotes a sealing portion made of an insulative or semiconductive material that seals the side surface and the edge of the circuit conductor that is etched to form a circuit, and the sealing portion is a corona from the edge portion of the circuit conductor. Has the effect of suppressing discharge,
This is proposed by the inventors of the present application in Japanese Patent Application No. 61-313969.

To give an example of the dimensions of these circuit boards, the thickness of the metal base is usually 2 to 3 mm, the thickness of the circuit conductor is usually 35 μm, and the thickness of the insulating layer is shown in FIGS. 1 (a) and (b). In the case of the circuit board shown in FIG. 1, it is usually 50 μm (the thickness of the polymer film is usually 25 μm), and in the case of the circuit board shown in FIGS.

FIG. 2 shows a top view of an example of a conductor circuit formed by etching a copper foil. In the figure, the circuit conductors 3 are hatched for the sake of clarity.

In any of the circuit boards shown in FIGS. 1 (a) to 1 (d), the adhesive layer 2 is used.
When the adhesive layer 2 or the insulating layer 2 is applied to a metal base, a copper foil, a polymer film or the like, voids are easily mixed in the adhesive layer. In particular, when the adhesive contains an inorganic filler, or when the thickness of one application of the adhesive is relatively thick and exceeds 30 μm (the thickness after drying), voids are likely to be mixed in the adhesive layer.

Therefore, the circuit board of the type shown in FIGS. 1 (c) and 1 (d), in which the insulating layer 2 is made of an adhesive material containing an inorganic filler, is apt to mix voids in the insulating layer, and is Even though the circuit board has passed the test, the phenomenon that dielectric breakdown occurs in the insulating layer of the circuit board is most likely to occur during the withstand voltage test during or after the manufacturing process of the mounted product. Therefore, in the product inspection of such a circuit board, the test method of the original surface is most effective.

The partial discharge measurement itself is already well known, and the partial discharge measurement in the method of the present invention can be carried out using a known commercially available partial discharge measuring instrument.

Since the partial discharge measurement measures a minute voltage based on the partial discharge generated when a high voltage is applied, it is easily affected by various noises. Therefore, in the configuration of the test circuit, noise countermeasures such as cutting off the source of noise or the intrusion route or removing the intruding noise are taken, but the circuit board to be measured is also measured from the edge of the circuit conductor at the time of measurement. It is necessary to prevent the measurement from being disturbed by noise such as corona discharge. For this reason, it is necessary to take measures and measures such as providing a round electrode with a structure and a shape that are unlikely to cause corona discharge, and immersing the circuit board in insulating oil for measurement, and providing a guard electrode.

In this respect, what is advantageous is a circuit board in which the side surface and the edge of the circuit conductor are sealed with an insulating or semi-conductive material like the circuit board shown in FIGS. 1 (b) and 1 (d). In this case, the corona discharge from the edge of the circuit conductor is effectively suppressed by the sealing portion 4, so that the test can be performed in the air, the immersion in the insulating oil, and the insulating oil from the circuit board after the test. There is no trouble of removing.

In the test, when several circuit conductors exist such that they are insulated from each other, such as the circuit conductor shown in FIG. 2,
The charging electrode is brought into contact with each conductor, and these are collectively connected to the test circuit. Further, since the test method of the present invention is applied to product inspection, it is desirable to test a large number of products at the same time, for example, 30 products. Connecting.

In the case of the present invention, it is appropriate to select the voltage applied between the circuit conductor and the metal base in the range of 1 to 3 KV, usually 2 KV.
Is.

In the present invention, the quality of the dielectric breakdown strength of the circuit board is determined by the magnitude of the discharge charge measured by the partial discharge measurement,
The magnitude of the discharge charge used as a criterion for the determination depends on the thickness of the insulating layer, the configuration of the insulating layer (such as difficulty of deterioration of the insulating layer due to internal discharge), the operating voltage of the mounted product using the board, and the like. Although it cannot be generally stated, it is usually appropriate to select about 10 to 20 PC (pico coulomb). Strictly speaking, it is preferable to determine it by comparison with a long-term voltage application test.

Next, an experimental example comparing the partial discharge measurement tested by the test method of the present invention and the long-term withstand voltage will be described.

(Experimental example) A circuit conductor is formed by etching a copper foil of a substrate in which a 35 μm-thick copper foil is bonded onto an aluminum base having a thickness of 2.0 mm through an epoxy resin adhesive layer mixed with an inorganic filler having a thickness of 100 μm. A sample of the hybrid integrated circuit circuit board was immersed in insulating oil to apply a voltage of AC2KV between the circuit conductor and the aluminum base, and a partial discharge measuring instrument QM-20 manufactured by Mitsubishi Cable Industries, Ltd. was used. The maximum discharge charge of 60 pps was measured. From this measurement result, 5 samples with large maximum discharge charge and 5 samples with small maximum discharge charge were selected, and a total of 10 samples were charged with AC2KV between the circuit conductor and aluminum base in air for a long time. Conducted a voltage test. Table 1 shows the voltage application time until the maximum discharge charge dielectric breakdown and the dielectric breakdown location of each sample.

As is clear from Table 1, the sample having a large amount of discharged electric charge was subjected to dielectric breakdown in a short time, and the location of the dielectric breakdown was the insulating layer below the copper foil of the circuit conductor. On the other hand, the sample with a small discharge charge has a dielectric breakdown under the edge portion of the circuit conductor. This result shows that the one with a large discharge charge has a defect in the insulating layer and therefore it is destroyed in a short time, and the one with a small discharge charge has no defect in the insulating layer and shows a conductor during long-term charging. It shows that the insulating layer deteriorates due to the corona discharge generated at the circuit edge, leading to dielectric breakdown. According to the present invention, if the breakdown strength of the circuit board for a hybrid integrated circuit is determined by the magnitude of the discharge charge, the product will be able to breakdown in a short time after passing the conventional 1 minute withstand voltage test. It is well shown in the results in Table 1 that the can be eliminated.

(Effects of the Invention) As described above, even if the circuit board has passed the withstand voltage test because the conventional dielectric strength test cannot sufficiently evaluate the dielectric breakdown strength of the circuit board, There were not a few accidents such as dielectric breakdown of the insulating layer of the circuit board during the withstand voltage test during or after the manufacturing process.
According to the test method of the present invention, a product having a possibility of such an accident and having insufficient dielectric breakdown strength can be reliably identified and excluded from shipped products.

Further, when the quality of the dielectric breakdown strength of the circuit board product is determined by the test method of the present invention and the conventional withstand voltage test is abolished, the test method of the present invention uses the applied voltage in comparison with the conventional withstand voltage test. In many cases, the insulation deterioration of the product due to the application of high voltage for the test is also reduced in this case.

[Brief description of drawings]

1 (a) to 1 (e) are sectional views of a circuit board which is a target of the test method of the present invention, and FIG. 2 is a top view of another example of the circuit board to be tested. 1 ... metal base, 2 ... insulating layer, 3 ... circuit conductor

Claims (3)

[Claims] 1. A circuit board for a hybrid integrated circuit having an insulating layer made of an organic insulating material or an insulating material containing an organic insulating material on a metal base, and further having a circuit conductor thereon. Is a test method to determine whether the circuit board is good or bad, and a certain voltage is applied between the circuit conductor of the circuit board and the metal base to measure partial discharge in the insulating layer. A withstand voltage test method for product inspection of a circuit board for a hybrid integrated circuit, characterized in that the quality of the product is determined. 2. The insulating layer of the circuit board for a hybrid integrated circuit is made of an adhesive material containing an inorganic filler.
(1) Withstanding voltage test method for product inspection of a circuit board for a hybrid integrated circuit as described above. 3. The circuit board for a hybrid integrated circuit according to claim 1, wherein the side surface and the edge of the circuit conductor are sealed with an electrically insulating or semiconductive material. Withstand voltage test method for product inspection.