JPH09223854A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a safety function virtually without increases in cost by forming an area not covered with solder resist in proximity to the center of a wiring pattern between lands made of copper foil, applying solder to the surface of the copper foil, and fusing part of it in a short time. SOLUTION: For a printed wiring board for automobile electrical equipment, a wiring pattern 40 that provides connection between lands 39A, 39B for connecting electronic parts is so designed that temperature rise in the non-solder resist area 41 in the center of the wiring pattern 40 will be 20 deg.C or below at the steady current value in normal condition. The width of the wiring pattern 40 is so set that the temperature rise will be 200 deg.C or so, at which solder is melted, at the current value at which the motor is locked, and solder is applied to the non-solder resist area 41 in the center as well. This fuses the wiring pattern in a short time, and enables adjustment of time it takes for the wiring pattern to be fused according to the magnitude of overcurrent. Therefore, it is possible to provide the printed wiring board with a safety function virtually without increases in cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board having a fuse function for use in various electronic devices as a safety measure when an overcurrent is applied.

[0002]

2. Description of the Related Art A conventional technique for providing a printed wiring board with a safety function when an overcurrent is applied will be described with reference to FIGS.

6A and 6B show a printed wiring board 1
3A and 3B are a plan view and a cross-sectional view showing the general configuration of FIG.

In the figure, reference numeral 2 is an insulating substrate as a base material, on which a wiring pattern 3 made of copper foil is adhered by an adhesive 4, and a solder resist layer 5 is formed thereon by printing. Lead wires 8A, 8B of the electronic components 7A, 7B are connected and fixed to the land portions 6A, 6B left uncovered by the resist layer 5 by solders 9A, 9B.

FIG. 7 shows a method implemented as a safety measure during overcurrent conduction between the land portions 6A and 6B of the printed wiring board 1 configured as described above.

FIG. 1A shows a central portion 10A of the wiring pattern between the land portions 6A and 6B which is thinned to increase the internal resistance (conductor resistance) of this portion, and FIG. 1B shows the land portion 6A, 6B. The wiring pattern 10 between 6B has a thin and long shape 11
Further, the internal resistance (conductor resistance) in the meantime is further increased, and in the same figure (c), the fuse 12 is connected in the middle of the wiring pattern 10 between the lands 6A and 6B.

The operation of the safety measures when these overcurrents are applied will be described. In the method shown in FIG. 7A or 7B, when the overcurrent flows between the land portions 6A and 6B, wiring is performed. Joule heat is generated by the internal resistance of the central portion 10A of the pattern 10 or the wiring pattern 11, and this heat melts the copper foil of the wiring pattern,
The wiring pattern 10A or 11 is cut to cut off the current, and also in the method shown in FIG. 7C, the fuse 12 is also blown and the current is cut off. Was prevented from burning.

[0008]

However, in the conventional printed wiring board 1 provided with a safety measure against an overcurrent, the method of narrowing the width of the wiring pattern 10 causes almost no increase in cost due to the safety measure and a large excess. When a current flows, the thinned portion 10A or 11 of the wiring pattern 10 melts in a short time, but when an overcurrent flows to such an extent that the wiring pattern 10 does not melt immediately (for example, when the motor locks, Current, etc.), Joule heat generated by the internal resistance of the copper foil forming the wiring pattern 10 heats the insulating substrate 2 of the printed wiring board 1, and in the worst case, the insulating substrate 2 burns,
There is a problem that a resin material or the like near the printed wiring board 1 may be damaged.

Further, in the method of connecting the fuse 12 in the middle of the wiring pattern 10, since the fuse is blown in a short time, there is no danger of damage due to heat generation as described above, but there is a problem that the cost is considerably increased. there were.

The present invention solves such a conventional problem. In the case where an overcurrent flows to the extent that the copper foil is not immediately melted by a safety measure at the time of overcurrent energization in which the copper foil of the wiring pattern is thinned. However, it is an object of the present invention to provide a printed wiring board that can melt a part of a wiring pattern in a short time, and that has a safety function during overcurrent energization with little increase in cost.

[0011]

In order to solve the above problems, the present invention provides a portion which is not covered with solder resist near the center of the wiring pattern between lands made of copper foil of a printed wiring board. The solder is attached on the copper foil.

As a result, heat is generated in the vicinity of the center of the wiring pattern between lands when an overcurrent is applied, the solder is melted at a low temperature, and the copper foil in the central portion of the wiring pattern is diffused into the melted solder. It is possible to accelerate the fusing of the copper foil in this part by causing a "copper cracking phenomenon".

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention comprises a copper foil adhered on an insulating substrate, and is covered with a solder resist in the vicinity of the center of the wiring pattern connecting between the electronic component connecting lands. This is a printed wiring board with a non-existing part and soldering to this part.When the wiring pattern connecting the electronic component connecting lands generates heat due to overcurrent, it is difficult to dissipate heat By providing a soldered portion near the center of the wiring pattern, the temperature is higher than the temperature (about 1100 ° C) at which the copper foil melts due to the Joule heat generated by the internal resistance of the copper foil of the wiring pattern when overcurrent is applied. Low temperature (about 200 ℃)
The solder melts, and the molten solder and the copper foil of the wiring pattern cause a chemical reaction, causing a "copper cracking phenomenon" in which the copper in the copper foil diffuses and the wiring pattern melts in a short time. Have.

According to a second aspect of the present invention, in the first aspect of the invention, the width of the portion to which solder is applied without being covered with the solder resist is 1 / the width of the wiring pattern.
It is designed to be 2 or more. By attaching solder to a copper foil having a width of 1/2 or more of the wiring pattern width, the copper foil diffuses into the solder melted by the heat generated when an overcurrent is applied. It has an effect that a safety function of promoting melting of the wiring pattern works effectively.

According to a third aspect of the present invention, in the first or second aspect of the invention, the width of the wiring pattern of the portion to which the solder is applied without being covered with the solder resist is the portion covered with the solder resist on both sides thereof. Is smaller than the width of the wiring pattern, and even if the width of the portion of the wiring pattern to which the solder is attached is narrow, the conductor cross-sectional area increases due to the solder, so Joule heat is not concentrated at this portion under normal current. However, when the solder is melted due to the application of overcurrent, the width of the wiring pattern in this part is narrow, so the thinning of the copper foil due to the "copper cracking phenomenon" accelerates, and the wiring pattern melts in a shorter time. By adjusting the width of the part where this wiring pattern is thinned, the magnitude of the current that can flow in this part and when the wiring pattern melts An effect that can be adjusted.

According to a fourth aspect of the present invention, in the first or second aspect of the invention, the wiring pattern of a portion to which solder is attached without being covered with the solder resist is one in a direction in which the width of the portion is reduced. The above slit portion is provided, and has the same effect as the invention according to claim 3.

According to a fifth aspect of the invention, in the invention according to any one of the first to fourth aspects, the position of the wiring pattern in the portion to which the solder is attached without being covered with the solder resist is
The maximum heat generation part is used, and the position where the heat is generated most in the wiring pattern of the printed wiring board, that is, the position where the largest current flows, or the width of the wiring pattern is the smallest and the internal resistance (conductor resistance) is the largest. Large position,
Alternatively, by providing a portion to which solder is attached to a wiring pattern at a position where heat is most generated by a combination of these or the like, it has an effect that it works most effectively as a safety measure during overcurrent conduction.

According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, a temperature rise of a portion to which solder is attached without being covered with a solder resist in a normal use state of a device to be used is 20 ° C. The following is done so that even if the environmental temperature of the equipment using the printed wiring board rises, it does not damage the insulating substrate, which is the base material of the printed wiring board, or the nearby resin material. Have.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. (Embodiment 1) FIGS. 1A and 1B are a plan view and a sectional view, respectively, of a printed wiring board 21 according to a first embodiment of the present invention. A wiring pattern 23 made of copper foil is attached to an insulating substrate 22 serving as a material by an adhesive 24, and a solder resist layer 25 is printed thereon to form a solder resist layer 25.
The lead wires 28A and 28B of the electronic components 27A and 27B are soldered to the land portions 26A and 26B which are not covered with the solder 29.
The structure in which the connection and the fixation are made by A and 29B is the same as that of the conventional example.

A non-solder resist portion 31 not covered with the solder resist layer 25 is provided at the center of the wiring pattern 30 connecting the land portions 26A and 26B.
It is provided with a size of ½ or more of the width of 0, and the solder 32 is also attached here.

The solder 32 is applied to the lead wires 28A and 28B of the electronic components 27A and 27B and the land portion 2 by a soldering device.
When the solder 29A, 29B is attached and fixed between 6A, 26B, it is attached at the same time.

FIG. 2 shows an example of an electric circuit diagram of a printed wiring board used for an electric component of an automobile. In the figure, 33 is a battery, 34 is a motor, 3
5 is a switch, 36 is a relay consisting of a relay coil 36A and a relay contact 36B, and 37 is a circuit portion arranged on a printed wiring board.

When the circuit portion 37 arranged on the printed wiring board is applied to the printed wiring board shown in FIG. 1, the relay coil 36A and the relay contact 36B, which are electronic parts, are equivalent to the electronic parts 27A and 27B shown in FIG. , Lead wires 38A and 38B (28A and 28)
B) is connected and fixed with solder (29A and 29B), and the non-solder resist portion 41 (3) is provided at the center of the wiring pattern 40 (30) connecting between the land portions 39A and 39B (26A and 26B).
1) is provided, and the solder 42 (32) is attached here.

Next, the operation of the safety function of the printed wiring board of this embodiment will be described.

First, in the circuit of FIG. 2, the switch 35
When is closed, a current flows through the relay coil 36A, the relay contact 36B is turned on, the motor 34 is energized, and the motor 34 starts rotating.

At this time, the current flowing in the wiring pattern 40 of the circuit portion 37 arranged on the printed wiring board is 3 to 5 A which is the steady current of the motor 34, and the temperature due to the Joule heat generated in the wiring pattern 40 is thereby caused. Rise 2
The width of the wiring pattern 40 is determined so as to be 0 ° C. or less.

However, when the motor 34 is locked due to an external binding force or a failure, the load current of the motor 34 rises to about 23 to 30 A, and when this overcurrent flows to the wiring pattern 40, the wiring pattern 40 is Joule heat is generated by the internal resistance, and the temperature of the wiring pattern 40 rapidly rises.

When this temperature exceeds about 200 ° C. which is the melting point of the solder 42, the solder 42 in the non-solder resist portion 41 in the center of the wiring pattern 40 is melted, and the wiring pattern 40 is formed in the melted solder 42. The "copper cracking phenomenon" that causes the copper foil to diffuse to form the intermetallic compound 43 [see FIG. 3 (b)] occurs.

Since the intermetallic compound 43 has a high resistance value, it further promotes the "copper scuffing phenomenon", and the copper foil of the non-solder resist portion 41 in the central portion of the wiring pattern 40 is rapidly thinned. At the same time, the heat generated in the wiring pattern 40 causes the insulating substrate 44, which is a base material of the printed wiring board, to undergo thermal contraction to generate internal stress, which results in a change from the normal state shown in FIG. ), The adhesive 45 that has adhered the wiring pattern 40 to the insulating substrate 44 is peeled off, and a crack 46 is cut into the thinned wiring pattern 40 due to the "copper cracking phenomenon" and cut,
The lock current of the motor 34 will be cut off.

Therefore, in the case of the printed wiring board for electric components of the automobile of the present embodiment, when designing the wiring pattern 40 connecting the land parts 39A and 39B for connecting electronic parts,
The temperature rise of the non-solder resist portion 41 in the center of the wiring pattern 40 is 20 ° C. at the normal current value of the motor in the normal state.
Below, the current value when the motor is locked (23 to 30A)
Then, the width of the wiring pattern 40 may be set so that the solder melts at about 200 ° C., and the solder may be attached also to the non-solder resist portion 41 at the center thereof.

Here, the reason why the temperature rise value of the wiring pattern portion due to the steady-state current of the motor in the normal state is set to 20 ° C. or less is that the environmental temperature of the electronic device using the printed wiring board is the electrical equipment for automobiles. If the temperature rise of the wiring pattern part is 20 ° C or less, even if it reaches the maximum temperature of 90 ° C specified as the usage condition, the temperature of this part is 1
This is because the temperature is 10 ° C. or lower, which is lower than the thermal deformation temperature of the insulating substrate portion of the printed wiring board and the resin material near the printed wiring board, and they are not damaged by heat.

In the printed wiring board for electric components of automobiles of the present embodiment, the time until the wiring pattern portion provided with the safety measure is blown off by the overcurrent is compared with the results of a comparative experiment of the present invention and the conventional example. It is shown in 1).

[0033]

[Table 1]

As can be seen from this (Table 1), the safety measure of the present invention is such that the wiring pattern is more likely to be blown out than in the conventional method, and the time until the blowout is shortened to almost half.

(Second Embodiment) FIGS. 4A and 4B are a plan view and a sectional view of a printed wiring board 47 according to a second embodiment of the present invention, respectively. At the connection land portion 49 of the electronic component 48A, 48B
A non-solder resist portion 52 not covered with the solder resist layer 51 at the center of the wiring pattern 50 connecting A and 49B.
The width of the portion to be provided is the solder resist layer 5 on both sides thereof.
The width of the portion covered with 2 is narrower and the solder 53 is attached.

In this case, even if the width of the non-solder resist portion 52 is thin, the conductor 53 has a large cross-sectional area due to the solder 53. Therefore, Joule heat is not concentrated at normal current, and overcurrent can be applied. In the state where the solder 53 is melted, the width of the wiring pattern 50 is thin, so that the pattern copper foil is thinned quickly due to the "copper erosion phenomenon", and it takes a short time to melt and the non-solder resist portion 5 is formed.
By changing the width of 2, it is possible to adjust the time for the wiring pattern to melt.

(Third Embodiment) FIGS. 5A and 5B are a plan view and a sectional view of a printed wiring board 54 according to a third embodiment of the present invention, respectively. At the connection land portion 56 of the electronic components 55A and 55B.
A non-solder resist portion 59 not covered with the solder resist layer 58 at the center of the wiring pattern 57 connecting A and 56B.
Is the slit 6 in the direction of reducing the width of the wiring pattern 57.
Solder 61 is attached as a form in which 0 is provided.

Also in this case, as in the second embodiment, even if the width of the non-solder resist portion 59 is narrowed, the solder 61 increases the cross-sectional area of the conductor, and Joule heat is concentrated at normal current. In the state where the solder 61 is melted by the overcurrent energization, the width of the wiring pattern is narrow, so that the pattern copper foil is thinned quickly due to the "copper cracking phenomenon", and the time until it is fused is shortened. By changing the number and width of the slits 60 of the non-solder resist portion 59, the time for the wiring pattern 57 to melt can be adjusted.

As described above, as a safety measure for the printed wiring board, a portion which is provided near the center of the wiring pattern between the electronic component connecting lands and which is soldered without being covered with the solder resist is the printed wiring. It is needless to say that it is most effective to provide it on the maximum heat generating portion of the substrate.

[0040]

As described above, according to the present invention, in the fuse function as a safety measure against the overcurrent of the printed wiring board, the copper foil of the wiring pattern is made thin so that the copper foil does not melt immediately. The wiring pattern can be melted down in a short time even with respect to overcurrent, and the time taken for the wiring pattern to melt can be adjusted depending on the magnitude of the overcurrent. Furthermore, the printed wiring board has a safety function. It is of high practical value because there is almost no cost increase.

[Brief description of drawings]

FIG. 1A is a plan view of a printed wiring board according to a first embodiment of the present invention, and FIG. 1B is a sectional view of the same.

FIG. 2 is an electric circuit diagram of a printed wiring board used for electric components of the automobile.

FIG. 3A is a cross-sectional view of the printed wiring board in the normal state, and FIG. 3B is a cross-sectional view of the printed wiring board when the overcurrent is applied.

FIG. 4A is a plan view of a printed wiring board according to a second embodiment of the present invention, and FIG.

FIG. 5A is a plan view of a printed wiring board according to a third embodiment of the present invention, and FIG.

FIG. 6A is a plan view of a conventional printed wiring board, and FIG. 6B is a sectional view of the same.

FIG. 7 is a plan view illustrating a conventional safety measure method when overcurrent is applied to a printed wiring board.

[Explanation of symbols]

21, 47, 54 Printed wiring board 22, 44 Insulation board 23, 30, 40, 50, 57 Wiring pattern 24, 45 Adhesive 25, 51, 58 Solder resist layer 26A, 26B, 39A, 39B, 49A, 49B, 5
6A, 56B Land portion 27A, 27B, 48A, 48B, 55A, 55B Electronic component 28A, 28B, 38A, 38B Lead wire 29A, 29B, 32, 42, 53, 61 Solder 31, 41, 52, 59 Non-solder resist portion 33 battery 34 motor 35 switch 36 relay 36A relay coil 36B relay contact 60 slit

Claims (6)

[Claims] 1. A copper foil adhered on an insulating substrate,
A printed wiring board in which a portion not covered with solder resist is provided near the center of the wiring pattern that connects the electronic component connecting lands, and solder is attached to this portion. 2. The width of the portion to which solder is applied without being covered with the solder resist is 1 of the wiring pattern width of that portion.
The printed wiring board according to claim 1, wherein the printed wiring board is not less than / 2. 3. The printed wiring board according to claim 1, wherein the width of the wiring pattern in a portion to be soldered without being covered with the solder resist is smaller than the width of the portions covered with the solder resist on both sides thereof. 4. The printed wiring board according to claim 1, wherein one or more slit portions are provided in a wiring pattern of a portion to be soldered without being covered with the solder resist in a direction in which the width of the portion is narrowed. 5. The printed wiring board according to any one of claims 1 to 4, wherein the position of the wiring pattern in the portion to which the solder is attached without being covered with the solder resist is the maximum heat generating portion. 6. The printed wiring board according to claim 1, wherein a temperature rise of a portion to be soldered without being covered with the solder resist is 20 ° C. or less in a normal use state of the device to be used.