JP2002134853A - Printed board and method of discriminating stress history thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reliably discriminate whether a specified stress or more has been exerted on a board in the past. SOLUTION: A specified stress or more exerted on a board 2 causes a part of a conductive line 3 to be broken or deformed. A measuring instrument is connected to a measuring terminal 4 to measure the resistance of the conductive line with a current flowing on this line, thereby recognizing that the specified stress or more has been exerted on the board 2 in the past. In this case the once broken or deformed conductive line 3 never recovers its original state and, even if, e.g. no stress is exerted on the board 2 at present, the history that the specified stress or more has been exerted on the board 2 is never deleted.

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 and a method for determining a stress history thereof.

[0002]

2. Description of the Related Art In recent years, electronic components mounted on printed circuit boards have been reduced in size and thickness, and may be easily destroyed by slight distortion generated on the printed circuit boards (particularly, multilayer ceramic capacitors). Is easily destroyed). In order to prevent such destruction of the electronic mounting component, it is necessary to use a substrate which has not been subjected to a predetermined stress or more and has no distortion. Therefore, conventionally, the strain of the substrate has been measured using a strain gauge as shown in FIG.

[0003] That is, in FIG.
A strain gauge 103 having a resistor 104 inside is uniformly attached to the mounting component mounting surface of one substrate 102 with an adhesive. Then, the resistance value of the resistor 104 is measured by the measurement terminal 105.
The amount of distortion on the surface of the substrate 102 is measured based on the measurement from the above, and the substrate 102 having the amount of distortion exceeding a predetermined value is excluded as a rejected product.

[0004]

However, in order to reliably prevent the destruction of mounted components that are becoming smaller and thinner, not only the current amount of distortion is not more than a predetermined value but also a certain amount of distortion in the past. Strict quality standards that substrates that have not been subjected to the above stresses should be used
2 must be applied.

However, the data of the amount of strain obtained when the strain gauge 103 shown in FIG. 8 is used is at the present time, and it is not possible to know the stress history indicating how much stress has been applied in the past. That is, even if a certain level of stress is applied to the substrate 102 at present, and a large distortion can be recognized by the detection signal from the measuring terminal 105, the stress applied to the substrate 102 Is removed, the amount of distortion shows the original small value.
2 will be treated as a passing product. Therefore, in the quality inspection of the conventional substrate 102 using the strain gauge 103, what should originally be rejected products is used as acceptable products, and there is a possibility that the mounted components may be destroyed.

Further, since the printed board 101 in which the strain gauge 103 is once adhered to the substrate 102 with an adhesive is no longer usable as a product, it is impossible to carry out a 100% inspection. Therefore, the conventional method for measuring the distortion of the substrate cannot be said to have sufficient reliability also in this respect.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a printed circuit board capable of reliably determining whether or not a certain level of stress has been applied to a substrate in the past, and a printed circuit board having the same. It is intended to provide a history determination method.

[0008]

As a means for solving the above-mentioned problems, the invention according to the first aspect is characterized in that when a certain level of stress is applied to a substrate, the resistance value changes and the state of the change is changed. The stress detection member formed of a conductive material is provided on the surface around the mounting part mounting location so that the above is maintained.

According to a second aspect of the present invention, in the first aspect of the invention, the stress detecting member is formed by a conductive path having a shape such that distortion or disconnection occurs when the predetermined stress or more is applied. It is a formed stress detection pattern.

According to a third aspect of the present invention, in the second aspect of the present invention, the conductive path is formed of the conductive material having a small diameter and has corners formed at predetermined intervals. It is characterized by.

According to a fourth aspect of the present invention, in the second aspect of the invention, the conductive path has a dense portion in which a plurality of short straight portions extending in parallel are densely arranged. Features.

According to a fifth aspect of the present invention, in the second aspect of the present invention, the conductive path connects a plurality of landless through holes formed in the substrate.

According to a sixth aspect of the present invention, in the first aspect of the invention, the stress detecting member has a plurality of conductive members having a shape such that distortion or disconnection occurs when the predetermined stress or more is applied. And a conductive path connecting between the plurality of conductive chip members.

According to a seventh aspect of the present invention, in the first aspect of the present invention, the stress detection member connects a plurality of conductive chip members and the plurality of conductive chip members via a conductive ball member. When the stress of a certain level or more is applied, between the conductive chip member and the conductive ball member that were in a connected state, or the conductive ball member The relative position between the conductive path and the conductive path varies.

According to the present invention, the surface around the mounting part mounting portion is provided with a conductive material so that the resistance value changes and the changed state is maintained when a predetermined stress or more is applied to the substrate. By providing a stress detection member formed of a conductive material in advance and measuring the resistance value of the stress detection member at the end of a predetermined manufacturing process, the stress equal to or more than the predetermined level is applied to the printed board to be inspected. It is determined whether or not there is an added history.

[0016]

FIG. 1 is a configuration diagram of a printed board 1 according to a first embodiment of the present invention. In this figure,
A stress detection pattern as a stress detection member is formed by a conductive path 3 on the surface of the substrate 2 (for example, made of glass epoxy resin) around the mounting part mounting portion of the printed board 1. Has two measurement terminals 4 attached thereto. The stress detection pattern is formed in such a shape that the conductive path 3 is disconnected or deformed when a certain level of stress is applied to the substrate 2. The conductive path 3 is formed of a small-diameter conductive material (for example, copper), and has corners 3a at predetermined intervals. The reason for forming the corners 3a is to make it easy for disconnection or deformation at this portion.

According to the configuration shown in FIG. 1, it is possible to easily determine whether or not the substrate 2 of the printed board 1 has a history in which a certain level of stress has been applied in the past. In other words, when a certain level of stress is applied to the substrate 2, disconnection or deformation occurs in a part of the conductive path 3 (normally, most occurs near the corner 3 a).
The worker connects a measuring device to the measuring terminal 4, applies a current to the conductive path 3, and measures the resistance of the conductive path 3, so that the substrate 2 has been subjected to a certain level of stress in the past. You can know. In this case, since the conductive path 3 once broken or deformed is not restored to its original state, even if no stress is applied to the substrate 2 at the present time, a certain level or more is thereby obtained. The history of having ever been stressed is never erased.

The stress history obtained based on the presence / absence of the disconnection of the conductive path 3 is only the presence / absence of a certain level of stress applied in the past, and does not include information on when the stress was applied in the past. I can't get it. However, in the manufacturing process of the printed board, it is sufficient that such a substrate 2 can be simply removed, and there is no need to specify up to the time when stress is applied. Therefore, it is sufficient to provide only information on whether or not a certain level of stress has been applied in the past as described above.

The constant value of the stress when the conductive path 3 is disconnected or deformed can be adjusted by appropriately selecting the diameter of the conductive material forming the conductive path 3. In other words, as the diameter of the conductive material is reduced, disconnection or deformation is more likely to occur. Conversely, as the diameter of the conductive material is increased, disconnection or deformation is less likely to occur. Although the conductive path 3 shown in FIG. 1 is a pattern formed along the end face of the substrate 2, it is not always necessary to form the pattern along the end face as described above. When the arrangement position is known in advance, a pattern may be formed along the periphery of the arrangement position.

FIG. 2 is a configuration diagram of a printed board 1A according to a second embodiment of the present invention. The conductive path 3A of the printed board 1A in this figure is formed of a small-diameter conductive material such as copper as in the first embodiment, but unlike the case of the first embodiment, it is parallel. It has a dense portion 3A1 in which a plurality of extending short straight portions are densely arranged.
Since such a dense portion 3A1 is provided, the conductive path 3A has a longer wire length than the conductive path 3 in the first embodiment, and the amount of change in resistance value when a stress is applied to the substrate 2 is reduced. Can be bigger. Therefore, it is possible to further improve the accuracy of determining whether or not a certain level of stress has been applied in the past. Note that other configurations are the same as those of the first embodiment shown in FIG. 1, and thus redundant description will be omitted.

FIG. 3 is a configuration diagram of a printed board 1B according to a third embodiment of the present invention. The printed board 1B in this figure has a large number of landless through holes 3B
1 are formed, and the landless through-holes 3B1 are connected by the conductive path 3B. 4A and 4B are explanatory views of a landless through-hole. FIG. 4A is a partially enlarged plan view of FIG. 3, FIG. 4B is a cross-sectional view of FIG. 3A, and FIG. FIG. 3D is a cross-sectional view of FIG.
It is. In addition, (c) and (d) show the state in which the land portion is formed for reference, and are not necessarily the configurations according to the present embodiment.

FIGS. 4 (a) and 4 (b) and FIGS. 4 (c) and 4 (d)
As is clear from the comparison with the above, a conductive path 3 is formed between the landless through holes 3B1 where no land portions are formed.
In the configuration connected by B, disconnection or deformation near the edge is more likely to occur. Therefore, according to the third embodiment, similarly to the first and second embodiments, it is possible to obtain history information as to whether or not a certain level of stress has been applied in the past. In addition,
In the present embodiment, “landless through-hole” includes not only a land portion not formed at all but also a land portion formed slightly. Therefore, by changing the diameter of the land, it is possible to adjust a constant value of the stress when the conductive path 3B is disconnected or deformed.

FIG. 5 is a configuration diagram of a printed board 1C according to a fourth embodiment of the present invention. The printed board 1C in this figure has a configuration in which a plurality of conductive chip members 5 are arranged on a substrate 2, and a conductive path 3C is connected between the plurality of conductive chip members 5. The conductive chip member 5 and the conductive path 3C constitute a stress detecting member.

FIG. 6 shows the conductive chip member 5 shown in FIG.
It is explanatory drawing about the shape of (a), a top view,
(B) is a front view. As shown in these figures, the conductive chip member 5 has a thin plate portion 5a, and thick solder connection portions 5b, 5b are formed at both ends of the thin plate portion 5a. A plating portion 5b1 is formed on a part of the solder connection portion 5b for performing good soldering. The plated portion 5b1 and the conductive path 3C are connected to the solder 6
Are connected by soldering.

In such a configuration, when a certain level of stress is applied to the substrate 2, cracks and deformation occur in the thin plate portion 5 a of the conductive chip member 5, so that the resistance value measured at the measurement terminal 4 changes. I do. It is possible to determine whether or not a certain level of stress has been applied to the substrate 2 in the past due to the change in the resistance value. When such a conductive chip member 5 is used,
When the stress applied to the substrate 2 exceeds a certain level, the change in the resistance value becomes extremely remarkable, so that it is possible to reliably determine whether or not the past stress has occurred.
The adjustment of the constant value of the stress when the crack or deformation occurs in the thin plate portion 5a can be performed by changing the thickness of the thin plate portion 5a or appropriately selecting the material of the thin plate portion 5a. .

FIG. 7 is a configuration diagram of a main part of a printed board according to a fifth embodiment of the present invention. In this embodiment, a conductive chip member 7 and a conductive ball member 8 are used instead of the conductive chip member 5 in the fourth embodiment. That is, a plurality of conductive ball members 8 are arranged below the substantially block-shaped conductive chip member 7, and the conductive chip member 7 and the conductive path 3D are connected via the conductive ball members 8. ing. FIG.
As shown in (b), the bottom surface of the conductive chip member 7 and the upper portion of the conductive ball member 8 are in point contact with each other, and a small amount of solder 6 is piled up near this contact point and both are soldered. ing. Similarly, the lower part of the conductive ball member 8 and the upper surface of the conductive path 3D are in point contact with each other, and a small amount of solder 6 is piled near this contact point and both are soldered. The conductive ball member 8 is a so-called GB.
This is the same as the ball member used for A (gate ball array).

In such a configuration, when a certain level of stress is applied to the substrate 2, a force is applied to the soldered portion in the vicinity of the above-mentioned point contact state. The relative position between the bottom surface and the upper part of the conductive ball member 8 or the lower part of the conductive ball member 8 and the upper surface of the conductive path 3D is shifted. As a result, the resistance value measured at the measurement terminal 4 changes. In the case of the fifth embodiment, similarly to the case of the fourth embodiment, when the stress applied to the substrate 2 exceeds a certain level, the change in the resistance value becomes extremely noticeable. Can be reliably determined. The adjustment of the constant value of the stress when the relative position between the conductive ball member 8 and the conductive chip member 7 and the conductive path 3D is shifted is performed by appropriately adjusting the amount of the solder 6. Is possible.

The determination of the stress history for the printed boards 1 to 1D according to the first to fifth embodiments is performed, for example, as follows. First, the worker measures the resistance value between the measuring terminals 4 and 4 using a measuring device before the mounting component is mounted on the mounting component mounting surface of the substrate 2. Then, after the mounting component is mounted on the mounting component mounting surface, the resistance value between the measuring terminals 4 and 4 is measured again by the measuring device, and the difference between the second measurement value and the first measurement value is a predetermined value. With respect to the above, it is considered that a stress of a certain level or more has been applied to the substrate 2 in the past, and this is excluded as a rejected product.

As a result, the substrate 2 to which the mounted components are attached has only been subjected to a certain level of stress in the past, and strict quality standards can be applied. Moreover, since it is assumed that the stress detection members such as the conductive paths in the printed board of each embodiment are shipped as a product with the components added as they are, it is possible to apply this strict quality standard to all the products. . Therefore, the reliability of the determination of the stress history according to the present invention is much improved compared to the conventional determination of the stress history. In the above example,
Although the number of times of measurement of the resistance value is two, in an actual production line, there are a plurality of steps between the time when the stress detection member of the present invention is provided on the printed board and the time when the mounted component is mounted. In some cases, three or more measurements may be performed in consideration of various conditions and necessity.

[0030]

As described above, according to the present invention, a printed board and a stress history thereof capable of reliably determining whether or not a certain level of stress has been applied to a substrate in the past. A determination method can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a printed board 1 according to a first embodiment of the present invention.

FIG. 2 is a printed circuit board 1A according to a second embodiment of the present invention.
FIG.

FIG. 3 is a printed circuit board 1B according to a third embodiment of the present invention.
FIG.

4A and 4B are explanatory views of a landless through hole, wherein FIG. 4A is a partially enlarged plan view of FIG. 3 and FIG.
3A is a cross-sectional view, FIG. 3C is a plan view when a land portion is formed in FIG. 3A, and FIG. 3D is a cross-sectional view of FIG.

FIG. 5 is a printed circuit board 1C according to a fourth embodiment of the present invention.
FIG.

FIGS. 6A and 6B are explanatory views of the shape of the conductive chip member 5 in FIG. 5, wherein FIG. 6A is a plan view and FIG. 6B is a front view.

FIG. 7 is a main part configuration diagram of a printed board according to a fifth embodiment of the present invention.

FIG. 8 is an explanatory view of a conventional technique.

[Explanation of symbols]

 1, 1A-1C Printed board 2 Substrate 3, 3A-3D Conductive path 3a Corner 3A1 dense part 3B1 Landless through hole 4 Terminal for measurement 5 Conductive chip member 5a Thin plate part 5b Solder connection part 5b1 Plating part 6 Solder 7 Conductivity Chip member 7a Solder connection part 8 Conductive ball member

Claims (8)

[Claims] 1. A conductive material is formed on a surface around a mounting part mounting portion so that a resistance value changes and a changed state is maintained when a predetermined stress or more is applied to a substrate. A printed board characterized by comprising a stress detecting member. 2. The stress detecting member is a stress detecting pattern formed by a conductive path having a shape such that distortion or disconnection occurs when the predetermined stress or more is applied. The printed board according to claim 1, wherein 3. The printed board according to claim 2, wherein the conductive path is formed of the conductive material having a small diameter and has a corner formed at predetermined intervals. 4. The printed circuit board according to claim 2, wherein said conductive path has a dense portion in which a plurality of short straight portions extending in parallel are densely arranged. 5. The printed board according to claim 2, wherein said conductive path connects between a plurality of landless through holes formed in said substrate. 6. The stress detection member comprises: a plurality of conductive chip members having a shape such that distortion or disconnection occurs when the predetermined stress or more is applied; and a space between the plurality of conductive chip members. The printed board according to claim 1, further comprising: a conductive path to be connected. 7. The stress detecting member, comprising: a plurality of conductive chip members; and a conductive path connecting the plurality of conductive chip members via a conductive ball member. When stress is applied, the relative position between the conductive chip member and the conductive ball member, or the relative position between the conductive ball member and the conductive path, which has been in a connected state, fluctuates. The printed board according to claim 1, wherein: 8. A conductive material is formed on a surface around a mounting part mounting portion so that a resistance value is changed and a changed state is maintained when a predetermined stress or more is applied to a substrate. A stress detection member is provided in advance, and by measuring the resistance value of the stress detection member at the end of a predetermined manufacturing process, whether there is a history of applying a stress equal to or more than the predetermined level to the printed board to be inspected A method for determining the stress history of a printed board, comprising determining whether or not the stress history has occurred.