JP2015114164A - Inspection method of printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-precision inspection method of a printed wiring board.SOLUTION: An inspection method of a printed wiring board has: a measurement step for measuring impedance of a conductor part of the printed wiring board; a conversion step for converting the impedance into admittance; and a determination step for determining the printed wiring board as a non-defective unit when the admittance is within a prescribed range, and determining the printed wiring board as a defective unit when the admittance is out of the prescribed range.

Description

  The present invention relates to a printed wiring board inspection method for performing pass / fail judgment of a printed wiring board using a measurement result of an electrical resistance measuring instrument.

  Conventionally, in order to determine the quality of a printed wiring board, the electrical resistance of the conductor part constituting the wiring is measured, and from the measured value of the electrical resistance, it is determined whether there is a defect such as a defect in the conductor part and the presence of via abnormality doing. As a method for measuring such electrical resistance, a two-terminal method has been conventionally known. However, there is a problem that an error occurs in a measured value due to a voltage drop caused by a contact resistance and a residual resistance of a lead wire. However, in the measurement of electrical resistance of several ohms to several megohms, the measurement error by the two-terminal method has little influence on the quality judgment of the printed wiring board, and the two-terminal method can sufficiently perform the quality of the printed wiring board. It was done.

  In recent years, with the miniaturization of electronic devices, miniaturization of printed wiring boards has been demanded, and the electrical resistance of conductor portions constituting wiring has often become several ohms or less. In addition, the wiring becomes more complex depending on the use of the electronic device, and it is required to accurately determine whether or not there is a defect or the like in the conductor portion. For this reason, when measuring the electrical resistance of miniaturized and complicated wiring, the measurement error by the two-terminal method has a great influence on the quality judgment of the printed wiring board, and the quality judgment of the printed wiring board should be performed accurately. I could not.

  In order to solve such a problem, a method of measuring electrical resistance by a four-terminal method that does not cause a measurement error due to contact resistance or residual resistance of a lead wire, and determining a quality of a printed wiring board from the measurement result is implemented. It became so. For example, Patent Document 1 discloses a circuit board inspection method using a four-terminal method.

JP 2013-24724

  Here, as a specific method for judging the quality of the printed wiring board from the electrical resistance value of the conductor, a predetermined reference range is set for the cross-sectional area of the conductor, which is a parameter for judging the presence or absence of defects in the conductor. The reference range of electrical resistance is calculated in correspondence with the reference range of the cross-sectional area of the conductor. The presence or absence of a conductor defect or the like is determined depending on whether or not the measurement value belongs within the calculated reference range of electrical resistance.

  However, since the inverse relationship is established between the electrical resistance of the conductor and the width of the conductor, the smaller the value of the conductor cross-sectional area, the smaller the change in electrical resistance. The larger the numerical value, the smaller the change in the electrical resistance. Therefore, the evaluation based on the measured value of the electrical resistance is not uniform with respect to the cross-sectional area of the conductor to be inspected, and the possibility of erroneous determination is increased.

  This invention is made | formed in view of such a subject, The place made into the objective is to provide the inspection method of a printed wiring board provided with a higher precision.

  In order to achieve the above object, a printed wiring board inspection method of the present invention includes a measuring step of measuring an impedance of a conductor portion of a printed wiring board, a converting step of converting the impedance into admittance, and the admittance being within a predetermined range. And determining the printed wiring board as a non-defective product, and determining the printed wiring board as a defective product when the admittance is out of a predetermined range.

  Moreover, in the measurement step of the inspection method described above, the impedance of the conductor portion may be measured using a four-terminal method. By using the four-terminal method, errors such as contact resistance can be suppressed, and a more accurate inspection can be realized.

  Furthermore, in the measuring step of any of the inspection methods described above, a DC resistance may be measured using a DC signal source as the impedance. When measuring DC resistance, the equipment in the measurement process can be simplified, and conversion in the conversion process can be easily performed, thereby reducing the cost of inspecting the printed wiring board. become.

  In the printed wiring board inspection method according to the present invention, the quality of the printed wiring board is determined using the admittance obtained by converting the impedance without determining the quality of the printed wiring board using the impedance of the conductor portion of the printed wiring board. Therefore, the accuracy in the printed wiring board inspection method can be improved. That is, according to the present invention, it is possible to provide a printed wiring board inspection method with higher accuracy.

It is a flowchart for demonstrating the test | inspection flow of the test | inspection method of the printed wiring board which concerns on an Example. It is a schematic explanatory drawing for demonstrating the measurement process of the inspection method of the printed wiring board which concerns on an Example. It is a graph which shows the relationship between the cross-sectional area of the conductor of a printed wiring board, and an electrical resistance characteristic. It is a graph which shows the relationship between the cross-sectional area of the conductor of a printed wiring board, and an admittance characteristic.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited to the content demonstrated below, In the range which does not change the summary, it can change arbitrarily and can implement. In addition, various numerical values used in the embodiment may be an example and can be variously changed as necessary.

<Example>
Hereinafter, a printed wiring board inspection method according to an embodiment of the present invention will be described with reference to FIGS. Here, FIG. 1 is a flowchart for explaining the inspection flow of the printed wiring board inspection method according to the present embodiment. FIG. 2 is a schematic explanatory diagram for explaining the measurement process of the printed wiring board inspection method according to the present embodiment. Further, FIG. 3 is a graph showing the relationship between the cross-sectional area of the conductor portion of the printed wiring board and the electric resistance characteristics. And FIG. 4 is a graph which shows the relationship between the cross-sectional area of the conductor part of a printed wiring board, and an admittance characteristic.

  As shown in FIG. 1, the printed wiring board inspection method according to the embodiment of the present invention includes a measuring step (step S1) for measuring the DC resistance of the conductor of the printed wiring board, and the DC resistance as a measured value as admittance. A conversion step (step S2) for conversion and a determination step (step S3) for determining pass / fail of the printed wiring board using the converted admittance are included. Each process may be performed in one inspection apparatus (that is, one inspection line), but an apparatus according to each process may be provided independently and may be performed using three apparatuses. Below, each process is demonstrated in detail.

  First, in the measurement process of step S1, as shown in FIG. 2, the direct current resistance between the terminal 12 and the terminal 13 of the predetermined wiring 11 which is a conductor portion of the printed wiring board 10 is measured by the electric resistance measuring device 20. It is measured by the 4-terminal method used. In this embodiment, as the electrical resistance measuring instrument 20, a probe head 21, probe pins 22, 23, 24, 25 for inspecting a plurality of wirings formed on one printed wiring board 10 at the same time, and a direct current signal A common substrate inspection apparatus with a source (not shown) was used. In FIG. 2, for convenience of explanation, only one wiring 11 is shown on the printed wiring board 10, and only four probe pins 22, 23, 24, 25 protrude from the probe head 21. In practice, however, a plurality of wirings are formed on the printed wiring board 10, and a large number of probe pins protrude from the probe head 21.

  As a specific measuring method, four probe pins 22 to 25 protruding from the probe head 21 of the electric resistance measuring instrument 20 are brought into contact with the terminal 12 and the terminal 13, and a DC signal source provided in the electric resistance measuring instrument 20. DC resistance is measured using a DC signal supplied from More specifically, a direct current is supplied through the probe pins 22 and 25, and the voltage drop in the wiring is measured by the probe pins 24 and 23. That is, a probe pin for supplying a direct current and a probe pin for measuring a voltage drop are brought into contact with each of the terminals 12 and 13, and a direct current flows between the terminals.

  In the present embodiment, the substrate inspection apparatus including the probe head 21 and a plurality of probe pins is used as the electric resistance measuring instrument 20, but a general tester that measures DC resistance by the two-terminal method is used. Also good. Moreover, as the electrical resistance measuring device 20, an impedance measuring device capable of measuring impedance may be used. In such a case, the impedance may be measured, but only the resistance that is the real part of the impedance may be measured. That is, the direct current resistance may be measured using an impedance measuring instrument.

  In FIG. 2, the wiring 11 is formed on the surface of the printed wiring board 10, but may be formed inside the printed wiring board 10. Moreover, although the terminal 12 and the terminal 13 are formed in the same plane of the printed wiring board 10, the terminal 12 and the terminal 13 may be formed in different planes. In such a case, an electric resistance measuring device having a structure in which a measurement pin can be brought into contact with two terminals formed on different planes is used.

  Next, in the conversion process of step S2, the DC resistance measured in step 1 is converted into admittance. Specifically, the value of the DC resistance measured in step S1 is recorded in the memory of the electrical resistance measuring instrument 20 or other device. Then, a processing apparatus in which a processing program capable of converting DC resistance into admittance is installed to convert the DC resistance recorded in the memory into admittance. Here, converting DC resistance into admittance means calculating the reciprocal of DC resistance.

  Even when impedance is measured in the measurement process of step S1, impedance is converted into admittance by calculating the reciprocal of the impedance.

  Hereinafter, the reason for converting the DC resistance into admittance will be described in detail with reference to FIGS.

  First, a general electric resistance R is defined by the following mathematical formula (1).

In Equation (1), ρ is the resistivity (Ω · m), L is the wiring length (m), and S is the cross-sectional area of the conductor portion (conductor cross-sectional area (m ² )). Here, in the electrical inspection of the printed wiring board 10, due to the structure of the printed wiring board 10, the wiring length is constant for each product and each net. Therefore, the formula (1) can be rewritten as the following formula (2).

In Equation (2), A is a constant indicating resistivity (ρ) × wiring length (L). As shown in Equation (2), the electrical resistance R is in an inversely proportional relationship with the cross-sectional area S of the conductor portion of the printed wiring board 10, and this relationship can be represented by the graph of FIG. In FIG. 3, the horizontal axis is the conductor cross-sectional area (× 10 ⁻¹² m ² ), and the vertical axis is the electrical resistance (Ω). Further, in the printed wiring board 10 according to FIG. 3, the conductor thickness is 18 μm, the conductor length is 0.05 m, and the resistivity is 16.78 × 10 ⁻⁹ Ω.

As shown in FIG. 3, when the conductor cross-sectional area is changed from 50 × 10 ⁻¹² m ² to 100 × 10 ⁻¹² m ² (change width is 50 × 10 ⁻¹² m ² ), the electric resistance is changed from 16.8Ω to 8 It changes to 4Ω (change width is 8.4Ω). On the other hand, when the conductor cross-sectional area changes from 1200 × 10 ⁻¹² m ² to 1250 × 10 ⁻¹² m ² (change width is 50 × 10 ⁻¹² m ² ), the electric resistance changes from 0.7Ω to 0.67Ω. (Change width is 0.03Ω). As described above, when the conductor cross-sectional area is relatively small and when the conductor cross-sectional area is large, the change width of the electric resistance differs even if the change width of the conductor cross-sectional area is the same. Therefore, if an attempt is made to evaluate the conductor cross-sectional area using the electric resistance R, a constant evaluation cannot always be performed on the value of the conductor cross-sectional area, and the inspection accuracy of the printed wiring board 10 cannot be improved.

  Therefore, when evaluating the conductor cross-sectional area of the printed wiring board 10, attention is paid to the admittance Y, which is a parameter different from the electrical resistance. Here, the admittance Y (S) can be defined by the following mathematical formula (3).

In Formula (3), R is electrical resistance (Ω), ρ is resistivity (Ω · m), L is wiring length (m), and S is a cross-sectional area of the conductor portion (conductor cross-sectional area (m ^2). )). Here, in the electrical inspection of the printed wiring board 10, due to the structure of the printed wiring board 10, the wiring length is constant for each product and each net. Therefore, Equation (3) can be rewritten as Equation (4) below.

Y = B × S (4)

In Equation (4), B is a constant indicating 1 / (resistivity (ρ) × wiring length (L)). As shown in Equation (4), the admittance Y is proportional to the cross-sectional area S of the conductor portion of the printed wiring board 10, and this relationship can be represented by the graph of FIG. In FIG. 4, the horizontal axis represents the conductor cross-sectional area (× 10 ⁻¹² m ² ), and the vertical axis represents the admittance (S). Also in FIG. 4, the conductor thickness is 18 μm, the conductor length is 0.05 m, and the resistivity is 16.78 × 10 ⁻⁹ Ω.

As shown in FIG. 4, when the conductor cross-sectional area changes from 50 × 10 ⁻¹² m ² to 100 × 10 ⁻¹² m ² (change width is 50 × 10 ⁻¹² m ² ), the admittance decreases from 0.06 S to 0.00. It changes to 12S (change width is 0.06S). On the other hand, when the conductor cross-sectional area changes from 1200 × 10 ⁻¹² m ² to 1250 × 10 ⁻¹² m ² (change width is 50 × 10 ⁻¹² m ² ), the admittance changes from 1.43 S to 1.49 S ( The change width is 0.06S). Thus, even if the conductor cross-sectional area values are different, if the change width of the conductor cross-sectional area is the same, the change width of the admittance is also the same. Therefore, by evaluating the conductor cross-sectional area using the admittance Y, the conductor cross-sectional area value can always be evaluated to be constant, and the presence or absence of a defect in the conductor portion of the printed wiring board 10 can be determined. Can do. That is, by evaluating the conductor sectional area using the admittance Y, the inspection accuracy of the printed wiring board 10 can be improved.

  Next, in the determination step of step S3, the pass / fail determination of the printed wiring board 10 is performed using the admittance obtained in step 2. Specifically, for each type of printed wiring board 10, a range of admittance Y that is determined to be non-defective is defined in advance, and it is determined whether or not the admittance obtained in step S2 is within the predetermined range. . That is, when the admittance obtained in step S2 is within the predetermined range, it is determined as a non-defective product, and when it is outside the predetermined range, it is determined as a defective product. In addition, the range of the admittance Y defined for each type of the printed wiring board 10 is preliminarily defined in consideration of the value of the standard conductor cross-sectional area and the change in the conductor cross-sectional area corresponding to the loss of the conductor portion. become.

  As described above, the inspection flow of the printed wiring board 10 is completed through the steps S1 to S3 described above.

<Effect of Example>
The printed wiring board inspection method according to the present embodiment includes a measurement process for measuring impedance between terminals of the printed wiring board 10, a conversion process for converting impedance to admittance, and printed wiring when the admittance is within a predetermined range. Determining that the board 10 is a non-defective product and determining the printed wiring board 10 as a defective product when the admittance is outside a predetermined range. Here, in this embodiment, the quality of the printed wiring board 10 is determined using the admittance obtained by converting the impedance without determining the quality of the printed wiring board 10 using the impedance between the terminals of the printed wiring board 10. Therefore, the quality of the printed wiring board can be more accurately determined without depending on the size of the cross-sectional area of the conductor that is the wiring 11 of the printed wiring board 10. That is, according to the printed wiring board inspection method of the present embodiment, it is possible to achieve a more accurate pass / fail judgment.

  Further, in the measurement process of the printed wiring board inspection method according to the present embodiment, the impedance between terminals is measured using a four-terminal method. By using such a four-terminal method, it is possible to suppress errors such as contact resistance and realize a more accurate inspection.

  Furthermore, in the measurement process of the printed wiring board inspection method according to the present embodiment, the DC resistance is measured using a DC signal source as the impedance. If the DC resistance is measured in this way, the equipment in the measurement process can be simplified, and the conversion in the conversion process can be easily performed, thereby reducing the cost associated with the inspection of the printed wiring board. It becomes possible to do.

DESCRIPTION OF SYMBOLS 10 Printed wiring board 11 Wiring 12, 13 Terminal 20 Electrical resistance measuring device 21 Probe head 22, 23, 24, 25 Probe pin

Claims (3)

A measurement process for measuring the impedance of the conductor part of the printed wiring board;
A conversion step of converting the impedance into admittance;
A determination step of determining the printed wiring board as a non-defective product when the admittance is within a predetermined range, and determining the printed wiring board as a defective product when the admittance is outside the predetermined range. Inspection method.   The printed wiring board inspection method according to claim 1, wherein in the measuring step, the impedance of the conductor portion is measured using a four-terminal method.   The printed wiring board inspection method according to claim 1, wherein in the measuring step, a DC resistance is measured using a DC signal source as the impedance.

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