JPH03255966A - Withstanding voltage testing method for inspecting product of circuit board for hybrid integrated circuit - Google Patents

Abstract

PURPOSE:To surely discriminate an insulation breakdown strength by measuring a local discharge in an insulated layer with impressing a specified voltage between a circuit conductor and metal base on a circuit board and discriminating the normal/defective state of insulation breakdown strength for the circuit board in accordance with the size of discharged electric charge. CONSTITUTION:The insulated layer 2 is provided on the metal base 1 which is used as a heat sink, and the copper circuit conductor 3 is provided further on this insulated layer. In this circuit board, the insulated layer 2 is constituted of a polymer film 21 such as a polyimide film, etc., and layers 22 of adhesive material such as a epoxy resin, etc. which are arranged on the upper and lower parts of the film. Further by a sealing part 4, the side and edge of conductor 3 are sealed with an insulating material to suppress a corona discharge from the edge part of conductor 3. The test can be performed in the air, since the corona discharge from the edge of conductor 3 is thus effectively suppressed by the sealing part 4.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a test method for determining the quality of voltage resistance of a circuit board for forming a hybrid integrated circuit, that is, a hybrid IC.

(Prior art) As a circuit board for high-density packaging or high-power hybrid ICs, an insulating layer made of an organic insulator such as epoxy resin, polyimide, or glass epoxy is placed on a metal base, such as an aluminum base, which serves as a heat sink. Circuit boards are often used, which have an insulating layer containing an organic insulator such as, for example, and further have a circuit conductor thereon. Routine product inspections to test the voltage resistance, or dielectric breakdown strength, of such circuit boards are exclusively conducted using a test method in which a voltage of 2 to 54 AC is applied for 1 minute between the circuit conductor of the circuit board and the metal base. is adopted, and the quality of the dielectric breakdown strength of the product is determined based on whether or not dielectric breakdown occurs through this test.

On the other hand, for high-voltage electrical equipment such as high-voltage cables, power capacitors, and transformers that require long-term reliability of 30 or 40 years or more, internal discharges in the insulating layer due to lipoids, etc. In other words, partial discharge measurement for measuring partial 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 research and development of high-voltage electrical equipment, certification tests, etc. It is used to diagnose the degree of deterioration of the insulation performance of electrical equipment. In addition, for example, regarding power cables, recently partial discharge measurements are also performed during product inspections for high-voltage cables of 60KV or higher before product shipment. AC voltage breakdown tests and DC impact voltage breakdown tests are separately conducted to check reliability and to determine whether a product's dielectric breakdown strength is good or bad.

(Problem to be Solved by the Invention) A semiconductor such as a transistor is mounted 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 described above, and further provided with a circuit conductor thereon. element,
When manufacturing modules or boards with electronic functions that include resistors, capacitors, etc., so-called mounted products,
Despite using a board that has passed the above-mentioned withstanding voltage test, the insulating layer of the circuit board may be damaged during the withstanding voltage test conducted during the manufacturing process of manufacturing the mounted product or the withstanding voltage test after the manufacturing of the mounted product. dielectric breakdown often occurs. Therefore, even if we increase the voltage applied between the metal base and the circuit conductor and make the test conditions for the withstand voltage test of the circuit board more severe,
The frequency with which dielectric breakdown occurs in the insulating layer of a circuit board during or after the manufacturing process of a mounted product does not change or even worsens.

This fact means that conventional withstand voltage testing methods cannot adequately evaluate the voltage withstand ability, that is, the dielectric breakdown strength, of circuit boards. It is necessary to establish a new testing method that can reliably identify and eliminate circuit boards that cause dielectric breakdown during voltage tests.

The present invention seeks to solve this new problem.

(Means for Solving the Problems) The withstand voltage testing method of the present invention has an insulating layer made of an organic insulator or an insulator containing an organic insulator on a metal base, and further has a circuit conductor on the insulating layer. This is a test method for determining whether the dielectric breakdown strength of a circuit board for a hybrid integrated circuit is good or bad, and the partial discharge in the insulating layer is measured by applying a predetermined voltage between the circuit conductor of the circuit board and the metal base. The present invention is characterized in that it determines whether the dielectric breakdown strength of the circuit board is good or bad based on the magnitude of the discharged charge.

Circuit boards whose discharge charge exceeds a predetermined value have a high possibility of causing dielectric breakdown during the manufacturing of mounted products or during withstand voltage tests after manufacturing. be excluded. In actual inspection, it is not necessarily necessary to measure the maximum value of the amount of discharged charge, but it is simply possible to measure whether or not there is discharge of discharged charge exceeding a prescribed value when a prescribed voltage is applied. It is also possible to determine whether the dielectric breakdown strength is good or bad.

The discharge charge mentioned here refers to the discharge charge that occurs at a frequency of occurrence more than a predetermined frequency when a predetermined voltage is applied, and the predetermined frequency is 10 pps, 20 pps, 100 pps.
pps etc. can be selected as appropriate, but it is usually convenient to select 50 pps or 60 pps depending on the number of commercial cycles.

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

(Function) Despite using a circuit board that has passed a conventional withstand voltage test, the inventor of the present application has developed a precision According to research, dielectric breakdown is caused by voids existing in the insulating layer of the circuit board. Repeated withstand voltage tests by manufacturers of electronic components, or the application of high voltage during product inspection of circuit boards, can cause discharge in the voids in the insulating layer of the circuit board, deteriorating the organic insulating material in the insulating layer, and causing damage to the insulating layer. Coupled with the peculiarity of the circuit board that the thickness is extremely thin, even though the circuit board has passed the withstand voltage test in the product inspection of the circuit board, the withstand voltage test during the manufacturing process of the mounted product or after the manufacturing process is difficult. It is thought that dielectric breakdown occurred during the test. This means that even if the applied voltage is increased and the conditions of the withstand voltage test are made more severe in the conventional withstand voltage test for circuit boards, dielectric breakdown will occur in the circuit board during the withstand voltage test during the manufacturing process of the mounted product or after the withstand voltage test. This agrees well with the above-mentioned result that the frequency does not change much or even increases.

Therefore, this test is a test that can sufficiently evaluate the dielectric breakdown strength of circuit boards and completely eliminate products with insufficient dielectric breakdown strength that would cause dielectric breakdown during the manufacturing process of mounted products or during withstand voltage tests after manufacturing. As in the invention, it is considered essential to conduct a test that observes the state of internal discharge due to voids in the insulating layer of a circuit board and determines whether the circuit board is good or bad based on this.

Partial discharge measurement is a measurement method for observing internal discharge caused by lipoids in an insulating layer, and there are various test methods such as measurement of discharge starting voltage, measurement of discharge extinction voltage, and measurement of corona average current. In this method, when a predetermined voltage is applied between the circuit conductor and the metal paste, the discharge charge due to internal discharge in the insulating layer is measured, and the dielectric breakdown strength of the circuit board is judged based on the magnitude of the discharge charge. More specifically, when a predetermined voltage is applied, the quality of the dielectric breakdown strength of the circuit board is determined by detecting the presence or absence of discharge of a discharge charge exceeding a predetermined value.

The larger the amount of discharged charge, the more it deteriorates the organic insulator and causes the dielectric breakdown of the extremely thin circuit board insulating layer. Therefore, this method is most suitable for the purpose of the present invention, and the simplicity of the test makes it suitable for routine work. Due to its suitability for product inspection.

The experimental example shown below, which shows the correlation between the results of long-term withstand voltage tests of circuit boards and the results of partial discharge measurements, also shows that circuit boards that break down in a short period of time can be identified and eliminated by the above partial discharge measurements. It is clear that it can be done.

As mentioned above, partial discharge measurements are sometimes performed along with AC voltage breakdown tests and DC impact voltage breakdown tests in product inspections of electrical equipment such as high-voltage power cables. Although the insulation layer has a sufficient thickness and has passed the AC voltage breakdown test and DC impact voltage breakdown test, if the insulation breaks down for a short period of time during subsequent use, it may be due to subsequent trauma, chemical corrosion, etc. , which will not occur unless a special reason occurs, and partial discharge measurement in this case is to check the reliability of insulation performance over a long period of 30 or 40 years or more. In contrast, the test method of the present invention is for determining whether the dielectric breakdown strength of a product is good or bad, and in the case of product inspection of high-voltage power cables, it is suitable for AC voltage breakdown tests and DC impact voltage breakdown tests. This is equivalent to partial discharge measurement in high-voltage power cables, etc., and its purpose and characteristics are different.

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

Figures 1 (a) ←) (c) and (e) respectively show cross-sectional views of circuit boards, each of which has an insulating layer 2 on a metal base 1 that serves as a heat sink. Furthermore, a copper circuit conductor 3 is provided thereon. In the circuit boards shown in Fig. 1 (a) and (→), 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. Fig. 1 ←
→ and 2), the insulating layer 2 is an adhesive layer made of epoxy resin or the like, and an inorganic filler is often mixed into this adhesive layer to improve thermal conductivity.

In FIG. 1(e), the insulating layer 2 is composed of a glass epoxy layer. Regarding circuit conductor 3, see Figure 1 (E).
1 shows the conductive foil (before etching) stretched over the insulating layer 2, and FIGS. 1(A) to 1(C) show the circuit conductors formed by etching the conductive foil to form a circuit. ing. 4. A sealing part made of an insulating or semiconductive material that seals the sides and edges of the circuit conductor that has been etched to form a circuit, and the sealing part prevents corona from the edge part of the circuit conductor. This has the effect of inhibiting discharge, and was proposed by the inventors of the present invention in Japanese Patent Application No. 313969/1983.

To give an example of the dimensions of these circuit boards, the thickness of the metal base is usually 2 to 31E1, and the thickness of the circuit conductor is usually 35μ.
m, and the thickness i- of the insulating layer is usually 50 μm in the case of the circuit board shown in FIG. 1 (A) and (B) (the thickness of the polymeric film is usually 25 μm) and )
In the case of the circuit board shown in , it is usually 1100P.

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

In any of the circuit boards shown in FIG.
When applied to a polymer film, etc., voids are likely to be mixed into the adhesive layer. Particularly when the adhesive contains an inorganic filler, or when the thickness of one application of the adhesive is relatively thick, 30 μm (
voids are likely to be mixed in the adhesive layer.

Therefore, circuit boards of the type shown in Figures 1 (c) and 2), in which the insulation JI2 is made of an adhesive containing an inorganic filler, tend to have voids in the insulation layer, and cannot be tested using conventional withstanding voltage tests. Even if the circuit board passes the test, it is most likely that the insulation breakdown of the circuit board will occur during the manufacturing process of the mounted product or during the withstand voltage test after manufacturing.

Therefore, the testing method of the present invention is most effective in product inspection of such circuit boards.

Partial discharge measurement itself is already well known, and partial discharge measurement in the method of the present invention can also be performed using a commercially available known partial discharge measuring device.

Partial discharge (11Il constant) measures minute voltages based on partial discharges that occur when high voltage is applied, so it is easily affected by various noises. Noise countermeasures are required, such as cutting off the intrusion route or removing intruding noise, but the circuit board that is the object of measurement must also be protected against electrical discharges from the edges of circuit conductors during measurement. It is necessary to prevent measurement from being disturbed by noise.For this reason, the charging electrode should be designed with a rounded structure and shape that will prevent corona discharge from occurring.
In addition, it is necessary to devise measures such as immersing the circuit board in insulating oil for measurement and installing guard electrodes.

What is advantageous in this respect is a circuit board in which the sides and edges of the circuit conductor are sealed with an insulating or semiconductive material, such as the circuit board shown in FIG. In this case, corona discharge from the edges of the circuit conductor is effectively suppressed by the sealing part 4, so the test can be performed in air, immersed in insulating oil, and insulated from the circuit board after the test. There is no need to worry about removing oil.

In the test, for example, when several circuit conductors are insulated from each other, such as the circuit conductor shown in Figure 2,
A energized W pole is brought into contact with each conductor, and these are collectively connected to a test circuit. Furthermore, 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, such as 30fa, and connect the energized electrodes of each circuit board under test to the test circuit at once. do.

In the case of the present invention, the voltage applied between the circuit conductor and the metal base is appropriately selected in the range of 1 to 3 KV, and usually 2 KV.
It is KV.

In the present invention, the dielectric breakdown strength of the circuit board is determined based on the magnitude of the discharge charge measured by partial discharge measurement.
The magnitude of the discharge charge used as the criterion for this judgment varies depending on the thickness of the insulating layer, the structure of the insulating layer (the difficulty of deterioration of the insulating layer due to internal discharge, etc.), the operating voltage of the mounted product using the board, etc. -Although it cannot be generalized, it is usually appropriate to select a value of about 10 to 20 PC (picocoulombs). Strictly speaking, it is preferable to determine this by comparing with a long-term energization test.

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

(Experiment example) A 35 μm thick copper foil was bonded onto a 2.0 m thick aluminum base via a 100 μm thick inorganic filler-containing epoxy resin adhesive layer. The copper foil of the L-type board was etched to form a circuit conductor. A sample of the circuit board for a hybrid integrated circuit formed with the above was immersed in insulating oil, a voltage of AC 2 KV was applied between the circuit conductor and the aluminum base, and a partial discharge meter QM-20 manufactured by Mitsubishi Cable Industries, Ltd. was used. A maximum discharge charge of 60 pps was measured using the same method. Based on the measurement results, 5 samples with large maximum discharge charges were selected, and 5 samples with small maximum discharge charges were selected, for a total of 10 samples. AC 2 KV was applied between the circuit conductor and the aluminum base in air for a long period of time. A charging test was conducted. Table 1 shows the maximum discharge charge of each sample, the charging time until dielectric breakdown occurs, and the location of dielectric breakdown.
It was as shown in

Table 1 As is clear from Table 1, the samples with a large amount of discharged charge experienced dielectric breakdown in a short time, and the location of the dielectric breakdown was the insulating layer under the copper foil of the circuit conductor.

On the other hand, in the sample with a small amount of discharged charge, dielectric breakdown occurred under the edge of the circuit conductor. This result shows that those with a large discharge charge have defects in the insulating layer and are destroyed in a short time, while those with a small discharge charge have no defects in the insulating layer and the conductor circuit during long-term HTIt. This shows that the insulating layer deteriorates due to the corona discharge generated at the edge, leading to dielectric breakdown. According to the present invention, if the dielectric breakdown strength of a circuit board for a hybrid integrated circuit is determined based on the magnitude of discharged charge, products that pass a conventional one-minute withstand voltage test but break down in a short period of time can be removed. The results in Table 1 clearly show that the following can be eliminated.

(Effects of the Invention) As explained above, the dielectric breakdown strength of a circuit board can be sufficiently evaluated in the conventional withstand voltage test, but even if the circuit board has passed the withstand voltage test, the There have been many accidents such as dielectric breakdown of the insulating layer of circuit boards during the manufacturing process or during withstand voltage tests after manufacturing.
According to the test method of the present invention, it is possible to reliably identify products that do not have sufficient dielectric breakdown strength and have the possibility of such an accident, and to exclude them from shipped products.

In addition, when determining whether the dielectric breakdown strength of a circuit board product is good or bad using the test method of the present invention and abolishing the conventional withstand voltage test, the test method of the present invention can reduce the applied voltage compared to the conventional withstand voltage test. In many cases, the voltage can be lowered, so in this case, the insulation deterioration of the product due to the application of high voltage for testing will be reduced.

Claims (3)

[Claims] (1) The quality of dielectric breakdown strength of the product regarding circuit boards for hybrid integrated circuits that have an insulating layer made of an organic insulator or an insulator containing an organic insulator on a metal base, and further have a circuit conductor thereon. A test method for determining
A hybrid device characterized by applying a predetermined voltage between the circuit conductor of the circuit board and the metal base, measuring the partial discharge in the insulating layer, and determining whether the dielectric breakdown strength of the circuit board is good or bad based on the magnitude of the discharged charge. A withstand voltage test method for product inspection of circuit boards for integrated circuits. (2) The withstand voltage test method for product inspection of a circuit board for a hybrid integrated circuit according to claim (1), wherein the insulating layer of the circuit board for a hybrid integrated circuit is made of an adhesive containing an inorganic filler. (3) Product inspection of the circuit board for a hybrid integrated circuit according to claim (1) or (2), wherein the side surfaces and edges of the circuit conductor are sealed with an electrically insulating or semiconductive material. withstand voltage test method.