JPH11186673A - Printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the safety and reliability of a printed board having Ag through-holes and provide a high-density small-size board by previously detecting the reduction of a resistance value of the board due to the migration. SOLUTION: Ag through-holes 1 and through-holes 2 are disposed with spacings equal to 70% of the min. pitch of other through-holes so that the electric field intensity between the through-holes 1, 2 is higher than that between any other through-holes. When the Ag migration reduces the resistance between the through-holes 1, 2 to specified value or less, a power fuse 3 is blown to stop the operation of a printed board.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a through hole in a printed circuit board, and more particularly to a silver through hole using silver and patterning.

[0002]

2. Description of the Related Art Conventionally, a printed circuit board using a silver through hole of this type is more expensive in terms of cost than a printed circuit board having the same area using a copper through hole. Have been.

[0003] In this case, when a positive potential is applied to the silver through-hole, silver in the silver paste when forming the silver through-hole is separated from the through-hole or the conductor pattern having a negative potential at a short distance. In, the migration due to the precipitation of silver is likely to occur, and as a result, the silver through-hole having a positive potential and the through-hole having a negative potential at a short distance or the conductor pattern may cause a reduction in insulation resistance. I have.

Heretofore, as a measure for preventing the migration, a method of mainly increasing a distance between through holes and a method of selecting a substrate material have been adopted, thereby increasing the life of the printed circuit board.

[0005]

In a printed circuit board using the above-mentioned silver through-hole, when a positive potential is applied to the silver through-hole, a gap between the silver through-hole and a conductive pattern having a negative potential at a short distance. In the above, silver in the silver paste when the silver through-hole is formed is precipitated from the silver through-hole, and migration is easily caused.

In general, the migration speed increases as the electric field intensity increases and the environmental temperature and humidity increase. Among them, it is known that the influence of humidity is particularly large. That is, the traveling speed is remarkably high in a high humidity environment. Therefore, even if the printed circuit board has no abnormality in a normal humidity environment, migration occurs when power is continuously supplied in a high humidity environment, so that a decrease in insulation resistance cannot be ignored.

[0007] However, it is difficult to completely prevent the occurrence of migration under all environments, and furthermore, the increase in the through-hole pitch as a preventive measure described in the section of the prior art has led to the development of high-density patterns. There is a drawback in that it is an obstacle to the production, hinders cost reduction, and makes miniaturization difficult.

An object of the present invention is to detect the decrease in resistance value due to migration, shut off the input power to the board, and maintain the function and safety of the printed board to ensure the safety and reliability of the board. Another object of the present invention is to reduce the size of a printed circuit board by enabling high-density wiring.

[0009]

A printed circuit board according to the present invention is a printed circuit board having a silver through-hole in which a through-hole is formed of silver, wherein at least one specific board having a positive electric field when a current is applied to the board. And a first through hole or a conductor pattern provided in close proximity to the specific silver through hole, and the electric field strength of the specific silver through hole with respect to the first through hole or the conductive pattern. Has a specific silver through-hole formed so as to have a larger electric field strength than any other silver through-hole and other through-holes or conductor patterns.

Further, there is provided a device for interrupting the current supply to the printed circuit board when the resistance value between the specific silver through-hole and the first through-hole or the conductor pattern becomes equal to or less than a predetermined value. .

The second printed circuit board of the present invention has means for measuring an electric resistance value between a specific silver through hole and the first through hole or the conductor pattern, and the electric resistance value is determined by the measuring means. Is provided with a device that cuts off the power supply to the printed circuit board when it is detected that the value has fallen below the value.

The specific silver through-hole is marked with a silk pattern for distinguishing it from other through-holes, and the specific silver through-hole does not participate in the normal operation of the printed circuit board.

As described above, on the printed circuit board according to the present invention, a specific silver through-hole provided with a condition in which migration is more likely to occur as compared with other through-holes, and the first through-hole close to the specific silver through-hole Alternatively, a pair of conductor patterns is provided, and when migration occurs between them and the insulation resistance value falls below a predetermined value, the power supply to the printed circuit board is cut off and the function of the printed circuit board is normal. Is to be kept. As a result, the reliability and safety of the printed circuit board are ensured, and high-density wiring is enabled, so that the size of the printed circuit board can be reduced.

[0014]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic partial plan view of an embodiment of the printed circuit board of the present invention.

The silver through hole 1 is a through hole formed of silver, is connected to a single input power supply of the substrate, has a positive potential with respect to the ground potential when energized,
In addition, it is a specific through hole that is not involved in the normal operation of the printed circuit board. A silk pattern is provided around the hole to distinguish it from other through holes.

The through-hole 2 is provided near the silver through-hole 1, is connected to the negative side of the input power source, and has a ground potential. The distance between the through hole 2 and the silver through hole 1 is smaller than the pitch of any other through holes, and is set to 70% of the minimum pitch.

The power supply fuse 3 is provided on the power supply side with respect to the silver through hole 1, and the silver fuse 1 and the through hole 2 are provided.
Is a power supply fuse that blows when the resistance value between the first and second electrodes decreases and a current of a predetermined value or more flows.

The through-hole formed by silver is liable to cause so-called migration in which silver flows under the influence of an applied electric field and the temperature and humidity of the environment, and therefore undesirable phenomena such as oxidation corrosion occur. . The migration speed increases as the electric field strength increases and as the environmental temperature and humidity increase. Among them, it is known that the influence of humidity is particularly large. That is, the traveling speed is extremely high in a high humidity environment. Therefore, even if the printed circuit board has no abnormality in a normal humidity environment, migration occurs when the power supply is continued in a high humidity environment, and a decrease in insulation resistance due to the migration cannot be ignored.

In the present invention, between the specific silver through-hole 1 and the through-hole 2 which are arranged at a pitch 30% narrower than the pitch of the other through-holes and to which a high power supply voltage is applied, Since the electric field intensity is 30% larger than that of the through hole, the migration between the two through holes progresses faster than any other through hole under the environment of the same temperature and humidity, and the resistance value between the two through holes. Drops. When the resistance value between the two through holes decreases, a leak current occurs between the two through holes, and the value increases as the migration proceeds. If the power supply fuse is set so that the power supply fuse 3 is blown when the current increase exceeds a predetermined value,
Since no power is supplied to the printed circuit board due to fusing, the operation is stopped, and thus the function of the printed circuit board is protected.

Next, a second embodiment of the present invention will be described. FIG. 2 is a schematic partial plan view of the second embodiment of the present invention.

In the first embodiment, the protection operation is performed by directly cutting the power supply fuse by the leakage current flowing from a specific silver through-hole. In the second embodiment, the leakage current is detected. A device for further improving the accuracy was added.

In FIG. 2, silver through holes 1 and 2 are the same as the through holes provided in FIG. That is, the silver through-hole 1 is a through-hole which is connected to an input power supply and maintains a positive potential when energized, and the through-hole 2 is arranged at an interval of 70% of the minimum pitch between the other through-holes with respect to the silver through-hole 1. This is a through hole that is normally at ground potential via a resistor.

The comparator 5 is a comparison circuit connected to the silver through-holes 1 and 2 via a resistor, and detects that the resistance value between the silver through-holes 1 and 2 has decreased. The transistor 4 can short the power supply voltage by the output of the comparator 5.

In the above configuration, the process of decreasing the resistance between the silver through-hole 1 and the through-hole 2 due to migration is the same as that described in the first embodiment. In this embodiment, the operation of the comparator 5 provided to improve the detection accuracy is to compare the reference voltage applied to the silver through-hole 1 with the voltage obtained by dividing the power supply voltage by the resistance between the resistor and the through-hole. I do.
The (+) side of the input of the comparator 5 is at the ground potential in an initial state, that is, in a state where the insulation resistance does not decrease due to migration, and the output of the comparator 5 is at a low level.

The migration proceeds between the silver through-hole 1 and the silver through-hole 2 and the (+)
When the voltage level on the side rises and becomes higher than the reference voltage on the (-) side, the output of the comparator 5 is inverted, and when the output exceeds a predetermined value, the transistor switch 4 connected to the next stage is turned on. . The fuse 3 is blown by the short-circuit current generated by the transistor switch 4 and the operation of the printed circuit board is stopped, so that the function of the printed circuit board is protected.

In the first and second embodiments, the distance between a specific pair of through-holes to which a high voltage is applied is made narrower than the distance between the other through-holes. Although the migration that occurs between a pair of through holes is accelerated, the effect similar to applying a high voltage can be obtained by further reducing the interval between a specific pair of through holes even in a low voltage portion. Of course, it can be obtained. Furthermore, in the above-described embodiment, the migration between the specific silver through hole and the paired through hole has been described. However, the migration between the specific silver through hole and the conductor pattern adjacent thereto is not limited. A condition similar to that described above can be given to provide the same function as described above.

[0027]

As described above, according to the present invention, in a printed circuit board having a silver through-hole, a condition that migration is more likely to occur in a specific through-hole than in other through-holes is provided, and a decrease in the resistance value is detected. The circuit configuration for operating the safety device prevents the malfunction of the printed circuit board with silver through-holes, which is the biggest problem due to the lowering of the insulation resistance between the through-holes due to the migration of silver, and the safety of the device. As well as reliability, and it is not necessary to increase the distance between through-holes or between through-holes and the conductor pattern more than necessary. Therefore, the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic partial plan view of a printed circuit board according to the present invention.

FIG. 2 is a schematic partial plan view of another embodiment of the present invention.

[Explanation of symbols]

 1 silver through hole 2 through hole 3 power fuse 4 transistor switch 5 comparator

Claims (6)

[Claims] 1. A printed circuit board having a silver through hole in which a through hole is formed of silver, wherein at least one specific silver through hole having a positive electric field when the printed circuit board is energized; A first through hole or a conductor pattern provided in close proximity to the hole, wherein the electric field intensity of the specific silver through hole with respect to the first through hole or the conductor pattern is any other positive electric field. A printed circuit board having the specific silver through-hole formed so as to have a larger electric field strength than another silver through-hole or a conductor pattern having the silver through-hole. 2. The method according to claim 2, wherein the specific silver through hole is provided in the first silver through hole.
The printed circuit board according to claim 1, further comprising a device that cuts off current to the printed circuit board when a resistance value between the through hole and the conductor pattern becomes a predetermined value or less. 3. The specific silver through hole and the first silver through hole
2. The printed circuit board according to claim 1, further comprising: means for measuring an electric resistance value between the through hole and the conductor pattern. 4. The method according to claim 1, wherein the specific silver through hole and the first silver through hole are provided.
4. The printing method according to claim 3, further comprising: a device that cuts off current to the printed circuit board when an electric resistance value between the through hole and the conductor pattern is detected to be equal to or less than a predetermined value by the measuring unit. substrate. 5. The printed circuit board according to claim 1, wherein the specific silver through-hole has a silk pattern marking around the through-hole. 6. The printed circuit board according to claim 1, wherein the specific silver through hole does not participate in a normal operation of the printed circuit board.