JPH07249840A - Printed substrate and its deterioration diagnosing method - Google Patents

Abstract

PURPOSE:To quantitatively diagnose the deterioration of the short circuit and the like caused by corrosion and migration on a printed substrate. CONSTITUTION:In the printed substrate 4 on which a plurality of conductors 7, which constitute a part of an electronic circuit 6, are printed and wired on the surface of a base substrate 5, a pair of electrode conductors 8 and 9 are opposingly printed and wired in advance in close vicinity without coming into contact with each other on the independent position against each conductor 7 constituting the electronic circuit 6 on the surface of the base substrate 5 in such a manner that a fixed resistance value and electrostatic capacitance are provided between both electrode conductors 8 and 9. When deterioration is diagnosed, the induction tangent tan delta in the low frequency region of 1Hz to 1kHz between the pair of electrode conductors 8 and 9 is measured, and the time until the short circuit between the conductors 7 is estimated based on the value of the measured induction tangent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board on which electrodes for deterioration diagnosis are printed and printed together with ordinary conductors in advance, and a method for diagnosing deterioration of a printed circuit board for diagnosing deterioration of the printed circuit board using the electrodes for deterioration diagnosis.

[0002]

2. Description of the Related Art Generally, electronic circuits incorporated in various home appliances, electronic devices, industrial devices, etc. are mounted on a printed circuit board. In this printed circuit board, as is well known, a plurality of conductors formed of a metal material such as copper that forms a part of the electronic circuit are printed on the surface of a base substrate formed of glass epoxy resin, phenol resin, or the like. It is wired.

In recent years, the miniaturization and weight reduction of the above-mentioned various devices into which this printed circuit board is incorporated have progressed, and the printed circuit board itself has also become smaller. Higher density is required. To meet this demand, the electrode spacing and the conductor spacing on the printed circuit board are becoming smaller.

Further, conventionally, the flux residue after soldering was cleaned using chlorofluorocarbon, but due to global environmental problems and the like, the use of fluorocarbon is regulated, and the cleaning by chlorofluorocarbon is stopped and no cleaning is performed. The number of substrates is increasing.

On the other hand, from the viewpoint of effective utilization of limited resources, it is required to prolong the life of the above-mentioned various devices themselves, and the printed circuit boards incorporated in these devices tend to be used for a long period of time. Therefore, it is necessary to extend the service life of the printed circuit board and to effectively use the printed circuit board until just before the service life is exhausted.

For this purpose, it is necessary to easily and accurately grasp the remaining usable time (remaining life) of the printed circuit board when inspecting the machine itself. The operating environment has a great influence on the life of the printed circuit board. In other words, there are various usage environments for devices that use printed circuit boards.
In some cases, it may be exposed to extremely severe conditions such as corrosive gas and condensation.

In particular, when the humidity is high even without dew condensation, as shown in FIG. 8, between the conductors 2a and 2b having different polarities printed and wired on the pace substrate 1,
Migration occurs in which the conductor material grows like a tree from the conductor 2a of one pole to the conductor 2b of the other pole. In the migration, finally, the growing portion 3 has the other conductor 2b.
And the conductors 2a and 2b are short-circuited. As a result, there arises a problem that the electronic circuit does not work normally and the device in which the printed circuit board is incorporated malfunctions or stops.

The conductor 2 resulting from this migration
The short-circuit phenomenon between a and 2b tends to occur as the distance between the conductors becomes narrower, and also tends to occur as the electric field in the gap between the conductors 2a and 2b increases. Therefore, as described above, when the electrode spacing and the conductor spacing in the printed circuit board are reduced, a short circuit due to migration is more likely to occur than in the conventional printed circuit board.

Further, since the corrosion and migration are affected by the ionic substance of the printed circuit board, the flux residue after soldering without cleaning as described above may be corroded. There is a concern that the occurrence of migration is further promoted and the deterioration of the printed circuit board is promoted. In particular,
It doesn't matter in the environment such as normal temperature and humidity,
In a high-humidity environment, the ionic substance is ionized by the water to further promote the above-mentioned deterioration.

Conventionally, since it has not been possible to independently inspect the occurrence of a short circuit due to the above-mentioned corrosion or migration, it is possible to periodically inspect whether or not the operation of the entire device incorporating this printed circuit board is normal. If no abnormalities were detected in the examination, it was considered normal.

[0011]

However, in the above-mentioned operation test, since only the inspection as to whether or not the operation is normal is performed, the degree of deterioration cannot be quantitatively grasped. Therefore, an abnormality occurs in the operation of the device when the short circuit occurs, and at that time, the operation check of each electronic circuit is performed to find the short circuit phenomenon.

That is, there arises a problem that a defective printed circuit board cannot be repaired or replaced in advance. Especially in a large-scale plant, unexpected stoppage of equipment may lead to deterioration of quality of products manufactured in this plant and may cause great damage.

As a method of preventing such a situation, it is conceivable to periodically measure the insulation resistance between the conductors (between the electrodes) on the printed circuit board. However, in order to carry out this method, it is necessary to pull out the printed circuit board from the device for measurement, and it is necessary to stop the device. Therefore, there is a problem that this test cannot be frequently performed in a case where the plant is constantly operating, such as a large-scale plant.

Further, in this resistance measuring method, the measured insulation resistance value greatly depends on the distance between the conductors, and there is a problem that the criterion for judging deterioration is not uniquely determined when the electrode distance is different.

Further, in the case of a short-circuit accident due to migration, the conductor 2 is in the process of growing.
The resistance value between a and 2b does not change so much, and the resistance value tends to sharply decrease immediately before the short circuit. Therefore, at the time when it is detected that the resistance value has dropped significantly, it is often after a short circuit occurs, and
There is a concern that short circuits cannot be predicted in advance with sufficient margin.

The present invention has been made in view of such circumstances, and electrode conductors dedicated to deterioration detection are printed and wired from the beginning on the surface of the base substrate in addition to the respective conductors constituting the ordinary electronic circuit. Accordingly, it is an object of the present invention to provide a printed circuit board that can accurately and quantitatively diagnose deterioration caused by corrosion and migration even during operation of a device, and a deterioration diagnosis method for the printed circuit board.

[0017]

In order to solve the above-mentioned problems, the present invention is directed to a printed board in which a plurality of conductors forming a part of an electronic circuit are printed and wired on the surface of a base board.
Printing a pair of electrode conductors on the surface of the base substrate, at positions independent of each other that form an electronic circuit, so as to have a constant resistance value and electrostatic capacitance between them, closely facing each other without touching each other Wiring.

Further, in the invention of claim 2, a plurality of arc-shaped conductors arranged between the arc-shaped conductors forming the other electrode conductor, each electrode conductor forming the above-mentioned pair of electrode conductors, It is composed of a basic conductor that connects each arcuate conductor belonging to its own electrode conductor.

According to the third aspect of the present invention, each of the electrode conductors forming the above-mentioned pair of electrode conductors is a spiral conductor which is formed in a spiral shape so as to face each other.

Further, in the method for diagnosing deterioration of a printed circuit board according to the present invention, a constant resistance value and electrostatic capacitance are provided at positions independent of the conductors forming the electronic circuit on the surface of the base substrate. In addition, a pair of electrode conductors are printed and wired in advance so as to face each other without touching each other,
When diagnosing deterioration, measure the dielectric loss tangent between a pair of electrode conductors in the low frequency range of 0.1Hz or more and 1kHz or less, and based on the measured value of the dielectric loss tangent, lead to short circuit between the conductors. I try to predict the time.

[0021]

According to the printed circuit board and the method of diagnosing its deterioration configured as described above, the deterioration caused by the above-mentioned corrosion or migration is diagnosed at a position independent of each conductor forming the electronic circuit on the surface of the base board. A pair of dedicated electrode conductors for printing are printed and wired.

Therefore, the deterioration can be diagnosed in a state where the device in which the printed circuit board is incorporated is maintained in the operating state.
Further, the pair of electrode conductors are printed and wired so as to have a constant resistance value and a constant capacitance between the respective electrode conductors, and closely face each other without contacting each other.

At the time of performing the deterioration diagnosis, the dielectric loss tangent between the pair of electrode conductors in the low frequency region of 0.1 Hz or more and 1 kHz or less is measured. As described above, the generation and promotion of corrosion or migration between conductors on a printed circuit board largely depends on the amount of ionic substances on the surface of the printed circuit board. This ionic substance absorbs moisture on the surface of the printed board to become a conductive substance. Therefore, when the dielectric loss tangent tan δ between a pair of electrode conductors having a predetermined resistance value and capacitance value is measured, it appears as an increase in the resistance component between the electrode conductors, and the dielectric loss tangent tan δ increases. Therefore, by measuring the dielectric loss tangent tan δ, the amount of ionic substances, that is, the time until a short circuit occurs between the electrode conductors due to corrosion or migration (remaining life)
Can be grasped.

Incidentally, the reason why the frequency of the electric voltage applied between the electrode conductors in the case of measuring the dielectric loss tangent is limited to the low frequency region of 1 kHz or less is as shown in FIG.
This is because when a measured high frequency exceeding kHz is applied, the dielectric loss tangent tan δ does not depend so much on the amount of the conductive substance (water content) in which the ionic substance has changed. Also,
If the measurement frequency is set to an excessively low frequency of less than 0.1 Hz, the measurement accuracy and the measurement efficiency will decrease. Therefore, the measurement frequency range is limited to the low frequency region of 0.1 Hz or more and 1 kHz or less.

Even when the surface of the printed circuit board has a small amount of ionic substances, in a high humidity environment, the amount of water increases, causing corrosion and migration to occur and accelerate. Therefore, the dielectric loss tangent tanδ is measured. Life expectancy prediction is effective.

Further, even in the case of an environment of various gases such as hydrogen sulfide and chlorine that obviously promotes insulation deterioration between conductors, the life prediction by measuring this dielectric loss tangent tan δ is effective. Moreover, by setting the arrangement and shape of the pair of electrode conductors as set forth in claim 2.3, it is possible to measure the dielectric loss tangent tan δ with a small area and with high accuracy.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a schematic configuration of a printed circuit board according to an embodiment. In the printed circuit board 4 of this embodiment, a plurality of highly conductive metal materials such as copper forming a part of the electronic circuit 6 are formed on the surface of the base substrate 5 made of glass epoxy resin, phenol resin or the like. The conductor 7 is printed and wired. Further, a pair of electrode conductors 8 and 9 are printed and wired on the base substrate 5 at corner positions independent of the electronic circuit 6.

Further, the base substrate 5 having a substantially rectangular shape
A convex portion 10 for mounting the printed circuit board 4 on a socket attached to a chassis of an electronic device is formed on one side. A plurality of conductor terminals 11 connected to the plurality of conductors 7 and a pair of measuring terminals 12a and 12b connected to the pair of electrode conductors 8 and 9 are printed and wired on the convex portion 10.

The pair of electrode conductors 8 and 9 are made of the same metal material as the conductors 7 forming the electronic circuit. Then, one electrode conductor 8 forming the pair of electrode conductors 8 and 9
Is composed of a plurality of arc-shaped conductors 8a having a common center, and one base conductor 8b connecting the plurality of concentric arc-shaped conductors 8a to each other. The basic conductor 8b is connected to one measuring terminal 12a formed on the convex portion 10.

Similarly, the other electrode conductor 9 has a plurality of arc-shaped conductors 9a having a center common to that of the one arc-shaped conductor 8a.
And a single basic conductor 9b that connects the plurality of arcuate conductors 9a arranged concentrically to each other. The basic conductor 9b is connected to the other measurement terminal 12b formed on the convex portion 10.

The arcuate conductors 8a and 9a are alternately arranged at regular intervals so as not to contact each other. The arcuate conductors 8a and 9a are arranged at positions opposite to their own base conductors 8b and 9b so as not to contact the counterpart base conductors 9b and 8b.

Dielectric loss tangent t between the pair of electrode conductors 8 and 9
In order to accurately measure anδ, a capacitance of 10 pF or more is required between the two. Therefore, the measuring terminal 12
The distance between the arc-shaped conductors 8a and 9a, the width of the arc-shaped conductors 8a and 9a, and the pair of electrode conductors so that the above-mentioned predetermined capacitance Cs of 10 pF or more can be obtained between a and 12b. The dimensions of each part are determined in consideration of the area required for printed wiring of 8 and 9.

Further, there is a constant insulation resistance value between the pair of electrode conductors 8 and 9. When the printed circuit board 4 is mounted in the socket of the chassis and the equipment is in operation, the same voltage as the voltage applied between the conductors 7 forming the electronic circuit 6 is applied between the measurement terminals 12a and 12b. A voltage is applied. That is, the same energization history is secured.

FIG. 3 shows a pair of electrode conductors 1 printed and wired on a base substrate of a printed circuit board according to another embodiment of the present invention.
It is a wiring diagram which shows 3,14. The other parts are the same as in the previous embodiment shown in FIG.

A pair of electrode conductors 13 in this embodiment,
Each of the electrode conductors 13 and 14 that form 14 is a spiral conductor 14a that forms the electrode conductor 14.13 of the other side.
It is formed by one continuous spiral conductor 13a, 14a forming one spiral in common with 3a. Then, the corresponding signal terminals 12 of the convex portions 10 of the base substrate 5 respectively.
a, 12b.

The distance between the pair of electrode conductors 13 and 14 is 1
The mutual distance and the overall size of the spiral conductors 13a and 14a are determined so that the predetermined electrostatic capacitance Cs of 0 pF or more is obtained.

Next, a method for diagnosing the deterioration of the printed circuit board 4 in a state where the printed circuit board 4 configured as described above is incorporated in each device and is normally operated is shown in FIG.
Will be explained.

While the printed circuit board 4 is in operation, a voltage is applied to the pair of electrode conductors 8 and 9 through the socket 15 in the same manner as between the other conductors 7. When conducting the deterioration test, the pair of electrode conductors 8 and 9 are de-energized and the LCR meter 16 is connected to the measuring terminals 12a and 12b as shown in FIG. LC
An AC power supply 17 capable of varying the frequency f of the output signal from 0,1 Hz to 1 kHz is incorporated in the R meter 16. The AC voltage V output from the AC power supply 17 is the resistance 1
8, the voltage waveform detection circuit 19, and the current waveform detection circuit 20 are applied to the signal terminals 12a and 12b.

The voltage waveform signal detected by the voltage waveform detection circuit 19 and the current waveform signal detected by the current waveform detection circuit 20 are input to the phase difference detection circuit 21. The phase difference detection circuit 21 detects the phase difference Δ between the voltage waveform and the current waveform and sends it to the next dielectric loss tangent calculation unit 22.

The dielectric loss tangent calculation unit 22 subtracts the phase difference Δ from π / 2 (90 °) to obtain the delay angle δ due to the dielectric loss from the regular lead phase π / 2 (90 °) with respect to the dielectric.
Is calculated (δ = π / 2−Δ) to calculate the dielectric loss tangent tan δ. Then, the calculated dielectric loss tangent tan δ is displayed on, for example, a display.

Next, various experimental results demonstrating that the deterioration diagnosis method for measuring the dielectric loss tangent tan δ is effective will be described. 5 is a pair of electrode conductors 8 shown in FIG.
Using three printed circuit boards 4 on which printed wiring 9 is preliminarily printed, four types of samples A, B, and C having different amounts of ionic substances on the surface of the printed circuit boards 4 are prepared, and LCR is prepared.
When the frequency f of the voltage output from the AC power supply 17 of the meter 16 is changed from 0,1 Hz to 1 kHz,
It is an actual measurement figure which shows the relationship between the frequency f and the calculated dielectric loss tangent tandelta.

As can be understood from FIG. 5, when the applied frequency f exceeds 1 kHz, the change of the water content changes with the dielectric loss tangent tan δ.
It becomes difficult to clearly see the deterioration caused by migration. Therefore, the applied frequency f needs to be in the low frequency region of 1 kHz or less.

When the applied frequency f is lowered, the change in the water content clearly appears as the change in the dielectric loss tangent tan δ.
At an excessively low frequency of less than 0.1 Hz, there are problems such as deterioration of measurement accuracy and lengthening of measurement time. Therefore, it was proved that the frequency range from 0,1 Hz to 1 kHz is the optimum range.

In the actual measurement of the dielectric loss tangent tan δ, if one specific frequency f _S is set as the applied frequency from this frequency range, or if the average value of the measured dielectric loss tangent tan δ at a plurality of frequencies is adopted. Good.

FIG. 6 shows a pair of electrode conductors 8 and 9 shown in FIG.
Is used, the relative humidity on the surface of the printed circuit board 3 is set to 60%. 70%. 85%,
90% and 95% of 5 types of samples were prepared, and the number of days (hours) until a short circuit due to migration occurred between the electrode conductors 8 and 9 in a state where a normal voltage was applied in each sample, FIG. 5 is an actual measurement diagram showing the relationship with the dielectric loss tangent tan δ of each sample measured before the start of voltage application.

It can be understood that as the relative humidity increases, the dielectric loss tangent tan δ increases and the time until a short circuit is shortened. FIG. 7 shows a pair of electrode conductors 8 shown in FIG.
Using five printed circuit boards 4 on which printed wiring 9 is used, the amount of ionic substance on the surface of the printed circuit board 4 is 0.001 μm.
g, 0.1 μg, 1 μg, 10 μg, 100 μg of 5 types of samples are prepared, and a short circuit due to migration occurs between the electrode conductors 8 and 9 in a state where a normal voltage is applied in each sample. FIG. 4 is an actual measurement diagram showing the relationship between the number of days of (1) and the dielectric loss tangent tan δ of each sample measured before the start of voltage application.

When the amount of ionic substance increases, the dielectric loss tangent t
It can be understood that anδ becomes large and the time to reach a short circuit becomes short. According to the measured values shown in FIGS. 6 and 7,
It can be understood that the logarithmic value of the measured loss tangent tan δ and the time (days) until the short circuit occur are in a substantially linear relationship.
On the contrary, on the contrary, if the value of the dielectric loss tangent tan δ at that time is obtained, even if the operating environment such as the relative humidity on which the printed wiring board 4 is placed and the amount of ionic substances is unknown. From this, it is possible to estimate the time (number of days) until the remaining short circuit when the same operating environment is considered to continue.

Therefore, by measuring the dielectric loss tangent tan δ, the remaining life, that is, the degree of deterioration can be quantitatively grasped. According to the printed circuit board and the deterioration diagnosing method configured as described above, as shown in FIG. 1, due to corrosion or migration, the surface of the base substrate 5 is independent of each conductor 7 forming the electronic circuit 6 due to corrosion or migration. Dedicated pair of electrode conductors 8, 9 or 13 for diagnosing deterioration due to
14 is printed and wired. Therefore, the deterioration can be diagnosed in a state where the device in which the printed circuit board 4 is incorporated is maintained in the operating state.

Further, the pair of electrode conductors 8, 9 or 13, 1
Since the positions of the four printed circuit boards 4 are fixed, even if the type of the printed circuit board 4 changes and the spacing between the conductors 7 or the width of the conductor 7 changes, the same for all types of printed circuit boards 4. Objective deterioration diagnosis can be carried out under certain conditions.

Furthermore, it is possible to quantitatively calculate the remaining life by the dielectric loss tangent tan δ between the pair of electrode conductors. Therefore, compared to the conventional method of directly measuring the insulation resistance between the conductors 7, the time can be predicted long before the actual occurrence of the short circuit, so that a short circuit accident unexpectedly occurs and the device malfunctions. It is possible to prevent the equipment from stopping.

Further, the pair of electrode conductors of the present invention is mounted on, for example, a printed circuit board 4 and a QFP (Quad Flat Paka).
If the printed wiring is placed on the bottom surface of ge) where moisture is likely to occur, a more effective diagnosis of deterioration can be carried out from the viewpoint of safety.

This dielectric loss tangent is used as a product inspection method after the manufacturing process of printed circuit boards and the mounting process of various electronic parts.
It is possible to adopt a diagnostic method using tan δ measurement. Further, this method can be directly used for the evaluation of the flux residue after the soldering process.

[0053]

As described above, according to the printed circuit board and the deterioration diagnosing method of the present invention, a pair of electrode conductors dedicated to the deterioration detection are provided on the surface of the base substrate in addition to the respective conductors forming the ordinary electronic circuit. Keep printed wiring from the beginning, and at the time of diagnosis, measure the dielectric loss tangent between a pair of electrode conductors,
The remaining lifetime is predicted from the value of this dielectric loss tangent. Therefore, even when the device is in operation, it is possible to accurately and quantitatively diagnose deterioration caused by corrosion and migration.

[Brief description of drawings]

FIG. 1 is an external view of a printed circuit board according to an embodiment of the present invention.

FIG. 2 is a view showing a pair of electrode conductors formed on the printed circuit board of the embodiment.

FIG. 3 is a view showing a pair of electrode conductors formed on a printed circuit board according to another embodiment of the present invention.

FIG. 4 is a block diagram for realizing a method of diagnosing deterioration of a printed circuit board according to an embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between an applied frequency and a dielectric loss tangent obtained by the deterioration diagnosis method.

FIG. 6 is a diagram showing a relationship between a dielectric loss tangent obtained by the deterioration diagnosis method and a time until a short circuit.

FIG. 7 is a diagram showing the relationship between the dielectric loss tangent obtained by the same deterioration diagnosis method and the time until a short circuit.

FIG. 8 is a diagram showing migration that occurs between conductors.

[Explanation of symbols]

4 ... Printed circuit board, 5 ... Base circuit board, 6 ... Electronic circuit, 7
... conductors, 8, 9, 13, 14 ... pair of electrode conductors, 10 ...
Convex part, 11 ... Conductor terminal, 12a, 12b ... Measuring terminal, 1
5 ... Socket, 16 ... LCR meter.

Claims (4)

[Claims] 1. A printed circuit board, wherein a plurality of conductors forming a part of an electronic circuit are printed and wired on the surface of the base substrate, at a position independent of each conductor forming the electronic circuit on the surface of the base substrate, A printed circuit board, in which a pair of electrode conductors are printed and wired so as to have a constant resistance value and a constant electrostatic capacitance between them so as not to contact each other but to closely face each other. 2. Each of the electrode conductors forming the pair of electrode conductors belongs to a plurality of arc-shaped conductors arranged between the arc-shaped conductors forming the other electrode conductor and each of the electrode conductors belonging to its own electrode conductor. The printed circuit board according to claim 1, wherein the printed circuit board is formed of a base conductor that connects arc-shaped conductors. 3. The print according to claim 1, wherein each of the electrode conductors forming the pair of electrode conductors is formed of a spiral conductor formed in a spiral shape so as to face each other. substrate. 4. A method for diagnosing deterioration of a printed circuit board, wherein a plurality of conductors forming a part of an electronic circuit are printed and wired on the surface of the base substrate, the method being independent of each conductor forming the electronic circuit on the surface of the base substrate. At a predetermined position, a pair of electrode conductors are printed and wired in advance so as to have a constant resistance value and a constant electrostatic capacitance between them, without being in contact with each other and closely facing each other. 1Hz or more 1kHz
A method for diagnosing deterioration of a printed circuit board, comprising: measuring a dielectric loss tangent in the following low frequency region and predicting a time until a short circuit occurs between the conductors based on the measured value of the dielectric loss tangent.