JP7257785B2 - Printed wiring board and its conduction inspection method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a printed wiring board and a continuity testing method thereof.

As the number of vehicles such as HVs and EVs increases, the number of used printed wiring slopes per vehicle tends to increase. Due to the limited space available for printed wiring boards to be installed in automobiles, printed wiring boards and important safety parts for automobiles are becoming smaller and denser. Under such circumstances, through-plated through-holes are also required to be reduced in finished hole diameter from 0.25 mm to 0.20 mm. Hereinafter, "through-plated through holes" and "non-through-plated through holes" will be collectively referred to as "via holes".

When the hole diameter (finished hole diameter φ) of the via hole is reduced from 0.25 mm to 0.20 mm, the plating thickness is reduced from 20 to 25 μm on one side to 15 to 20 μm. Also, the conduction resistance value per hole is as low as 10 mΩ or less. As the thickness of the plating becomes thinner, it is more likely that the wiring pattern will become partially disconnected, resulting in a defective product.

Conventionally, a two-terminal method has been used as a continuity test by an electric checker. In the two-terminal method, first, (i) an inspection net consisting of a wiring pattern network is selected, (ii) a plurality of inspection points are set in the inspection net, and (iii) the plurality of inspection points are set two by two. In combination, the net resistance value between each inspection point is measured, and finally, (iv) the net resistance value between each inspection point is compared with a preset failure determination threshold value between each inspection point, and printed wiring It is to make pass/fail judgment of the board.

However, in the conventional method, in (iii) above, a certain inspection point is used as a reference inspection point, and a net located between the reference inspection point and each of the other inspection points (for example, a Measure the net resistance value of the nets such as b, ac, ad, and ae, which are called "overlapping nets" in this specification, because they are partially overlapping nets. Therefore, there is a possibility that a long overlapping net whose net resistance value exceeds 1000 mΩ is included, and failure modes such as partial disconnection cannot be detected in some cases.
Therefore, instead of the above-mentioned "duplicate net", the present applicant has previously proposed that from a plurality of inspection points in the inspection net, without determining the reference inspection point, so that the resistance value of the net becomes the minimum resistance value. , two inspection points with no other inspection points between them are selected and combined (that is, combined so that each net length is the shortest), and a net located between the two points (in this specification, this is called " It is reported that by measuring the net resistance value of a branch net" by the four-terminal method, it is possible to improve the ability to inspect a slight increase in resistance value such as a partial disconnection (Patent Document 1).

JP-A-2015-105908

In the four-terminal method "branch net" test, the net resistance value of each branch net was set to 200 mΩ or less. However, the lower limit of the net resistance value of the branch net is several tens of mΩ or more because the net includes a plurality of via holes and wiring circuits. It has become clear that it is difficult to inspect for continuity defects in via holes with a hole diameter of 0.20 mm or less.

On the other hand, when the present inventor investigated the relationship between the thickness of the printed wiring board and the stress applied to the small-diameter via hole, it was found that the thicker the board, the greater the stress applied to the central portion of the via hole. That is, as shown in FIG. 3, four-layer printed wiring board 200 having via holes 24 with a hole diameter of 0.2 mm or less and a plating thickness of 20 μm has two thicknesses of 1.6 mm and 1.2 mm. According to simulation measurements, in the case of a printed wiring board with a thickness of 1.6 mm, a stress of 236 MPa is applied to the central portion 28 of the via hole 24, and in the case of a printed wiring board with a thickness of 1.2 mm, It was found that a stress of 229 MPa was applied to the central portion 28 of the via hole 24 .
Usually, when a printed wiring board is used as an in-vehicle product, a thermal shock test is performed to evaluate the reliability of the printed wiring board. Although the conditions of the test vary, for example, 1000 to 3000 cycles are performed with a high temperature of 125° C. for 30 minutes and a low temperature of −65° C. for 30 minutes. On the high temperature side, the via hole portion of the printed wiring board expands as a whole, and on the low temperature side, it contracts. If the temperature cycle is repeated in units of thousands of cycles, the load on the via hole becomes greater, and a large stress is applied to the central portion of the via hole. Therefore, for example, if a relatively large pinhole 22 exists in the inner wall of the via hole 24 as shown in FIG. By the way, one of the causes of defects in via holes in printed wiring boards is that when copper plating is deposited in the through holes, air is trapped and the copper plating does not deposit well in the through holes.
In this way, although the thermal shock test is used to verify the reliability of printed wiring boards, there is no such thermal shock test in the normal manufacturing process of printed wiring boards. It was the actual situation that a new method capable of detecting was required.

SUMMARY OF THE INVENTION The present invention has been made in view of the conventional problems and the actual situation as described above. The task is to provide

As a result of repeated research to solve the above problems, the present inventors have found that a probe pin for conducting a continuity test by bringing a probe pin for four-terminal continuity test into contact with a small via hole having a hole diameter of 0.2 mm or less. It was found that a very good result can be obtained by providing a contact inspection section, contacting the inspection section with a probe pin for four-terminal conduction inspection, and measuring the conduction resistance value of each via hole, thereby obtaining the present invention. completed. Hereinafter, measurement of the conduction resistance value of each via hole having a hole diameter of 0.2 mm or less will be referred to as "individual net".

That is, the present invention is a method for inspecting continuity of a printed wiring board, in which at least through or non-through hole diameters of 0.2 mm or less are detected from an electrically connected wiring pattern network including through or non-through plated through holes. selecting a non-penetrating plated through-hole ; providing a probe pin contact inspection portion for four-terminal continuity test in the selected through -hole or non-penetrating plated through-hole; and providing a four-terminal continuity test in the probe pin contact inspection portion contacting a probe pin for measuring the conduction resistance value of the selected through or non-through plated through hole ; the conduction resistance value of the through or non-through plated through hole and preset through or non-through plating and a pass/fail judgment of the printed wiring board by comparing with the defect identification threshold value of the through hole , and is used in combination with the conduction test by the following two-terminal method and/or the conduction test by the following four-terminal method. The above problem is solved by a printed wiring board conduction inspection method characterized by:
Continuity inspection by the two-terminal method: (i) selecting an inspection net consisting of a wiring pattern network, (ii) setting a plurality of inspection points in the inspection net, (iii) using a certain inspection point as a reference inspection point, The net resistance value of the net located between the reference inspection point and each other inspection point is measured by the two-terminal method, and finally, (iv) the net resistance value between each inspection point and each preset inspection An inspection in which a pass/fail judgment is made for a printed wiring board by comparing a point-to-point failure judgment threshold value.
Continuity test by the 4-terminal method: (i) After selecting an inspection net consisting of a wiring pattern network, (ii) setting a plurality of inspection points in the inspection net, (v) without determining the reference inspection point, From a plurality of inspection points in the inspection net, two inspection points with no other inspection points intervening between them are selected and combined so that the resistance value of is the minimum resistance value, and the net located between the two points The net resistance value of is measured by the four-terminal method, and finally, (vi) the net resistance value between each inspection point is compared with the preset failure judgment threshold value between each inspection point, and the pass/fail of the printed wiring board is determined. A test that makes a judgment.

According to the printed wiring board of the present invention and the continuity inspection method thereof, by measuring the continuity resistance value of each via hole having a hole diameter of 0.2 mm or less, it was difficult to detect by the conventional continuity inspection method. It is possible to accurately detect a conduction defect such as a half disconnection of the via hole. Further, if the continuity test method of the present invention is used in combination with the conventional "branch net" test and/or "duplicate net" test, finer differences in resistance values can be detected, resulting in higher connection reliability. becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic cross-sectional explanatory drawing which shows embodiment of this invention printed wiring board. 1 is a schematic flow chart for explaining the continuity testing method of the present invention; FIG. 4 is a schematic cross-sectional view for explaining stress applied to a via hole; FIG. 4 is a schematic cross-sectional view for explaining pinholes generated in via holes;

An embodiment of the printed wiring board of the present invention will be described below with reference to FIG.

In FIG. 1, reference numeral 100 denotes a four-layer printed wiring board comprising a core substrate 10, inner layer circuits 11 formed on the front and rear surfaces of the core substrate 10, and insulating resin layers laminated on the front and back surfaces of the core substrate 10, respectively. A layer 12, an outer layer circuit 13 formed on the outer layer side of each of the insulating resin layers 12, and an inner layer circuit 11 and an outer layer circuit 13 penetrating through the core substrate 10 and formed on the core substrate 10. It is composed of a via hole 14 connecting in the vertical direction and a solder resist 17 for protecting the outer layer circuit 13 .

In such a four-layer printed wiring board 100, the via holes 14 are plated with copper and have a thickness (copper plating thickness) of 15 to 20 μm. The conduction resistance value is 10 mΩ or less. Moreover, the board thickness of the four-layer printed wiring board 100 is 1.0 to 1.6 mm.
On the surface of the insulating resin layer 12, a via hole pad 16 with a diameter of 0.5 mm or less drawn out from the via hole land 15 of the via hole 14 is formed. It is used as a probe pin contact inspection part for inspection. The via hole pad 16 may be as small as φ0.23 mm.
In this embodiment, the shape of the via hole pad 16 is circular, but the shape itself can be arbitrarily selected such as an elliptical shape in accordance with the shape of the probe pin. A shape close to a circle is desirable for arranging via hole pads.
Further, when it is difficult to form the via hole pad 16 due to the miniaturization and high density of the printed wiring board, a probe for contacting the via hole land 15 formed in the via hole 14 with a probe pin for 4-terminal continuity test may be used. It may be used as a pin contact inspection section.

In FIG. 1, a four-layer printed wiring board is illustrated, but at least a printed wiring board having a via hole with a hole diameter of 0.2 mm or less and a board thickness of 1.0 to 1.6 mm can be used as a core Needless to say, any specification of a double-sided board having inner layer circuits 11 on the front and back sides of the board 10, a 6-layer board, an 8-layer board, or a build-up board can be implemented.

Next, taking the printed wiring board 100 shown in FIG. 1 as an example, a method for testing continuity of the printed wiring board will be described with reference to FIG.
First, in printed wiring board 100, via holes 14 having a hole diameter of 0.2 mm or less are selected from a network of electrically connected wiring patterns including via holes.
Next, the selected via hole 14 is provided with a probe pin contact test portion for contacting a probe pin for four-terminal continuity test to conduct a continuity test. The probe pin contact inspection portion may be a via hole land 15 formed in the via hole 14 or a via hole pad 16 drawn out from the via hole land 15 .
Next, a probe pin for a four-terminal continuity test is brought into contact with the probe pin contact inspection portion, and the continuity resistance value of the via hole 14 is measured.
Finally, the conductive resistance value of the via hole 14 is compared with a predetermined via hole defect identification threshold to determine whether the printed wiring board 100 is acceptable.

In this way, by measuring the conduction resistance value of each via hole with a hole diameter of 0.2 mm or less among the via holes, that is, by performing an "individual net" inspection, it is possible to determine whether the via hole is normal or defective. Since it is possible to detect a minute difference in the resistance value between and, it is possible to accurately detect a conduction failure such as a half disconnection of such a small-diameter via hole.
For example, when conducting a conduction test on a 6-layer printed wiring board using the "individual net" test of the present invention, the 4-terminal method "branch net" test, and the "duplicate net" test, 59% of the total was " 33% of the total had a "branch net" conduction resistance threshold of 200 mΩ or less, and 8% of the total had a "overlapping net" conduction resistance threshold of 300 mΩ or more.
Therefore, if the "individual net" inspection of the present invention and the conventional "branch net" inspection and/or "duplicate net" inspection are used together, finer differences in resistance values can be detected. Gain reliability.

10: Core substrate 11: Inner layer circuit 12: Insulating resin layer 13: Outer layer circuit 14, 24: Via hole 15: Via hole land 16: Via hole pad 17: Solder resist 22: Pin hole 28: Via hole central part 100, 200: 4 layer printing wiring board

Claims (3)

A continuity testing method for a printed wiring board, wherein at least through or non-through plated through-holes having a hole diameter of 0.2 mm or less are selected from an electrically connected wiring pattern network including through or non-through plated through-holes. providing a probe pin contact inspection portion for 4-terminal continuity test in the selected through -hole or non-through-plated through hole ; bringing a probe pin for 4-terminal continuity test into contact with the probe pin contact inspection portion a step of measuring the conduction resistance value of the selected through or non- through plated through hole; and a step of making a pass/fail judgment of the printed wiring board , and is used in combination with the continuity test by the following two-terminal method and / or the continuity test by the following four-terminal method Printed wiring characterized by being Board continuity test method.
Continuity inspection by the two-terminal method: (i) selecting an inspection net consisting of a wiring pattern network, (ii) setting a plurality of inspection points in the inspection net, (iii) using a certain inspection point as a reference inspection point, The net resistance value of the net located between the reference inspection point and each other inspection point is measured by the two-terminal method, and finally, (iv) the net resistance value between each inspection point and each preset inspection An inspection in which a pass/fail judgment is made for a printed wiring board by comparing a point-to-point failure judgment threshold value.
Continuity test by the 4-terminal method: (i) After selecting an inspection net consisting of a wiring pattern network, (ii) setting a plurality of inspection points in the inspection net, (v) without determining the reference inspection point, From a plurality of inspection points in the inspection net, two inspection points with no other inspection points intervening between them are selected and combined so that the resistance value of is the minimum resistance value, and the net located between the two points The net resistance value of is measured by the four-terminal method, and finally, (vi) the net resistance value between each inspection point is compared with the preset failure judgment threshold value between each inspection point, and the pass/fail of the printed wiring board is determined. A test that makes a judgment. 2. The printed wiring according to claim 1 , wherein the probe pin contact inspection part for the four-terminal continuity test is a through-hole or non-through-plated through-hole land formed in the selected through-hole or non-through-hole plated through- hole. Board continuity test method. 3. The printed wiring board according to claim 2 , wherein the probe pin contact inspection portion for testing four-terminal continuity is a through-hole or non-penetration plated through-hole pad drawn out from the through-hole or non-penetration plated through-hole land. Continuity test method.

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