JP4843071B2 - Inspection apparatus and inspection method for printed wiring board - Google Patents

Description

  The present invention relates to an inspection apparatus and an inspection method for a printed wiring board, and more particularly to an inspection apparatus and an inspection method for a printed wiring board for finding a disconnection failure and a short-circuit failure of a circuit (net) in the printed wiring board.

  In general, the printed wiring board has a plurality of circuits electrically connected using wiring patterns, through holes, etc., and whether or not the circuit of the manufactured printed wiring board is correctly formed as designed, that is, It is necessary to electrically inspect whether the circuit in the printed wiring board is formed as designed without causing disconnection failure or short circuit failure with other circuits.

  As an electrical inspection method for short circuit inspection, a voltage is applied between the circuits to be inspected, the insulation resistance between the circuits is obtained from the voltage at that time and the measured current, and if the insulation resistance is below the reference value, A method for determining that a portion is a short-circuit defective portion is known.

  However, in the case of the above inspection method, the number of short circuit inspection combinations is n (n-1) / 2 in the printed wiring board having n nets, and for example, in the case of a printed wiring board having 1000 nets, 499,500. There is a problem that the short circuit inspection is required and the inspection time is required. For this reason, a method of short-circuiting only adjacent nets that may be short-circuited instead of performing a short-circuit inspection on all combinations between nets is known (for example, Patent Document 1).

  Separately from the above technique, the capacitance between the net on the printed wiring board and the net covering the entire printed wiring board such as the GND net or the power supply net or the reference plane outside the printed wiring board is measured, A method of performing an inspection by comparing with a capacity value of a non-defective product is known (for example, Patent Documents 2 and 3).

  However, in the inspection method for measuring the capacitance described above, since a high voltage cannot be applied between the nets, it is difficult to find a net short-circuited with a high resistance. For this reason, a method of determining a short circuit failure by applying a rectangular pulse to a net and analyzing a voltage transient characteristic is known (for example, Patent Documents 4 to 6).

JP-A-63-206667 JP 52-096358 A Japanese Patent Publication No. 04-017394 Japanese Patent Application Laid-Open No. 06-107996 US Pat. No. 5,438,272 US Pat. No. 6,573,728

  However, the inspection methods described in Patent Documents 4 to 6 have a problem that an expensive measuring instrument such as a transient digital analyzer is required because waveform evaluation is performed for evaluation of the inspection result.

  Accordingly, the present invention provides a printed wiring board inspection apparatus and inspection method that solves the above-described problems and that can detect a disconnection failure of a net or a short-circuit failure with another net at a low cost. With the goal.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  That is, the printed wiring board inspection apparatus according to the present invention has first and second probes for contacting a net of a printed wiring board to be inspected, and the first probe is provided on a reference surface of the printed wiring board. , Contact the second probe with the net of the printed wiring board, apply a rectangular pulse voltage to the net through the second probe, measure the voltage with the first probe, The first voltage measurement and the second voltage measurement are performed on all nets of the printed wiring board, and the values are stored in the storage means. The measured value of the non-defective product, the first measured value and the first measured As a result of the comparison, disconnection failure is detected with the first measurement value, and short-circuit failure is detected with the second measurement value.

  In the printed wiring board inspection method according to the present invention, the first probe is brought into contact with the reference surface of the printed wiring board to be inspected, the second probe is brought into contact with the net of the printed wiring board, and the second probe Applying a rectangular pulse voltage to the net via a probe and measuring as a first measurement value and a second measurement value with the first probe; and performing the measurement for all nets of the printed wiring board The step of storing the value in the storage means, the step of comparing the measured value of the non-defective product measured in advance with the measured value measured, and determining the disconnection failure based on the first measured value as a result of the comparison The determination of a short circuit failure is performed using the second measurement value.

  According to the printed wiring board inspection apparatus and inspection method of the present invention, a disconnection failure of a net and a short-circuit failure with another net can be easily and inexpensively found.

It is a figure which shows the structural example of the printed wiring board test | inspection apparatus by one embodiment of this invention. In one embodiment of the present invention, it is a top view showing an example of a printed wiring board. It is a figure which shows the model of the circuit on a printed wiring board in one embodiment of this invention. It is a figure which shows the model which paid its attention to the disconnection test | inspection of the model of the circuit shown in FIG. FIG. 5 is a circuit diagram showing an equivalent circuit of the model of the circuit shown in FIG. 4. It is a graph which shows the relationship between the measurement voltage and time of the equivalent circuit of the disconnection test | inspection shown in FIG. In the graph shown in FIG. _{6, V = 250V, C 0} = graph showing _{0.01μF, C 11 = 10pF, C} 12 = 30pF, R a = 1kΩ, the measured voltage versus time in the case of t ₀ = 45 nsec It is. FIG. 4 is a circuit diagram showing an equivalent circuit focused on a short circuit inspection of the circuit model shown in FIG. 3. It is a graph which shows the relationship between the measurement voltage and time of the equivalent circuit of the short circuit test | inspection shown in FIG. 9 is a graph showing the relationship between the measurement voltage and time when V = 250 V, C ₀ = 0.01 μF, C ₁ = 15 pF, C ₂ = 15 pF, R ₁₂ = 50 MΩ, and t ₀ = 200 μsec. It is. It is a flowchart which shows the flow of the printed wiring board inspection method by one embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted. Unless otherwise specified, a symbol representing a terminal name also serves as a wiring name and a signal name, and also serves as a voltage value in the case of a power supply.

FIG. 1 shows an overall configuration of a printed wiring board inspection apparatus according to an embodiment of the present invention. The printed wiring board inspection apparatus according to this embodiment includes, for example, two probes 1, a probe support unit 2, a moving mechanism unit 6, a measurement unit 7, a storage unit 8, a control unit 9, and the like.
The moving mechanism unit 6 includes various motors and a motor driver that drives the motors. A probe 1 is attached to the moving mechanism 6 via a probe support 2, and the probe 1 can move in a parallel direction (XY direction) and a vertical direction (Z direction) with respect to the printed wiring board 3. In the present embodiment, a case where there are two probes 1 will be described as an example, but three or more probes may be used.

  The measuring unit 7 is composed of a voltage source, a current source, a measuring instrument, and the like, and is connected to the probe 1. A circuit in the printed wiring board 3 can be obtained by flowing a current or applying a voltage between the probes. It is possible to measure the resistance. In addition, after measuring the potential difference between a net (reference plane) that covers the entire printed wiring board such as the GND net and power supply net in the printed wiring board 3 and the circuit to be inspected, it is converted into a capacitance component. Is possible. When there is no net that covers the entire printed wiring board, it is possible to use the conductive reference surface 5 (see FIG. 3) provided outside the printed wiring board.

  The storage unit 8 is configured by a memory such as a RAM or a hard disk, for example, and temporarily stores a measured value, a calculation result thereof, and the like.

  The control unit 9 includes a CPU, a RAM, a ROM, and the like. The control unit 9 controls driving of the moving mechanism unit 6 and determines whether the resistance value and the capacitance value measured by the measurement unit 7 are defective. I do. The control unit 9 can also be realized by incorporating a program for realizing the above functions and the following operations in a general computer, and the program is read by a computer such as a floppy (registered trademark) disk or a hard disk. It can also be recorded on a possible recording medium. The program can also be read from communication means such as the Internet.

  FIG. 2 is a plan view showing an example of a printed wiring board to be inspected. As shown in FIG. 2, the printed wiring board 3 to be inspected has a large number of nets 4a to 4e formed of a conductive material such as metal.

  Next, an operation example of inspection by the printed wiring board inspection apparatus of the present embodiment will be described. First, the printed wiring board 3 is fixed using a printed wiring board fixing tool (not shown).

Next, the control unit 9 controls the moving mechanism unit 6 to bring one of the probes 1 (first probe) into contact with the reference surface 5 inside or outside the printed wiring board. The other probe 1 (second probe) is brought into contact with the inspection point on the net, and a rectangular pulse voltage V is applied to the inspection target net via the second probe. Then, a signal (voltage V ₀ ) that crosses (passes) the external capacitor C ₀ provided outside the printed wiring board is measured. This is performed for all nets on the printed wiring board. The measurement takes a first measurement value for determining disconnection failure and a second measurement value for determining short circuit failure. The measured value of each net is compared with the non-defective value of each net that has been measured and registered in advance. Here, if the measured voltage V ₀ and the non-defective value are the same value for all nets, it is determined as non-defective, and if there is even one that is not the same value, it is determined as defective. In case of short circuit failure, it may not be possible to determine which net on the printed wiring board and which net is short-circuited, so one probe is brought into contact with the inspection point on the net that may be short-circuited. After the other probe is brought into contact with another net, the resistance value between the probes is measured, and the nets having a resistance value smaller than a preset reference value (threshold value) are short-circuited. Can also be specified.

The disconnection inspection will be described in detail with reference to FIGS. The disconnection inspection is for inspecting an increase in conduction resistance due to complete disconnection, pattern thinning or through-hole chipping. When the model of FIG. 3 is focused on the disconnection inspection and simplified, it becomes as shown in FIGS. FIG. 4A shows a good state, and FIG. 4B shows a case where there is an increase in conduction resistance. Here, R _a indicates _a conduction resistance, and when R _a = 0Ω, it is the same as FIG. When R _a = ∞, complete disconnection is indicated. Further, C ₁ ≈C ₁₁ + C ₂₂ is satisfied. C ₁ , C ₁₁ , and C ₂₂ indicate capacities between the reference plane 5 and the net, respectively.

ｔ＞０でのＶ₀は式（２）で表すことができる。

式（２）において、Ｒ_aが有限であればｔ＝∞ではＶ₀は式（３）になる。

Here, the model of FIG. 4B is represented by an equivalent circuit as shown in FIG. However, since the resistances R ₁₁ and R ₁₂ between the net and the reference plane are infinite, they are ignored. Also, the measurement resistance R ₀ is omitted because it is set to a sufficiently large value. At time t = 0, C ₂₂ is disconnected from the circuit by R _a , so that V ₀ can be expressed by equation (1).

t> V ₀ at 0 can be expressed by Equation (2).

In Expression (2), if R _a is finite, V ₀ becomes Expression (3) at t = ∞.

で立ち上り、Ｒ_aの指数関数で、良品値である

に収束することが解る。その時の関係を図６のグラフに示す。Ｒ_aの値が小さくなるに従って収束時間が短くなるので、矩形パルス印加直後の最適測定時間ｔ₀でＶ₀を測定することにより、断線検査を行うことができる。 From Equation (1) to Equation (3), V ₀ is

It rises at, is an exponential function of _Ra , and is a non-defective value

It can be seen that it converges to. The relationship at that time is shown in the graph of FIG. Since the convergence time becomes shorter as the value of _Ra becomes smaller, the disconnection inspection can be performed by measuring V ₀ at the optimum measurement time t ₀ immediately after the rectangular pulse application.

であるため、Ｖ₀＝１Ｖとなる。時間ｔ₀での測定値８３０ｍＶは、良品時の１Ｖと比較して、１７％減少することになる。よって、時間ｔ₀での測定値と良品時の測定値を比較することで、回路ネットに導通抵抗の増加があるかを判定することができる。一般的に断線検査の場合、検出すべき導通抵抗は低ければ低いほど良く、矩形パルス印加後の比較的微少な時間が最適な測定時間となる。 The detection of the disconnection inspection will be described with an example. In the equivalent circuit of FIG. 5, it is assumed that V = 250V, C ₀ = 0.01 μF, the circuit net is C ₁₁ = 10 pF, C ₁₂ = 30 pF, and R _a = 1 kΩ. Further, the measurement is performed by setting the optimum measurement time t ₀ immediately after the rectangular pulse is applied to 45 nsec (nanoseconds). In this circuit net, when t = 0, V ₀ is V ₀ = 250 mV from equation (1), and at t = ∞, V _{0 is} 1 V from equation (3). Further, at t ₀ = 45 nsec, V ₀ = 830 mV from equation (2). FIG. 7 shows the characteristics when t ≧ 0. As shown in FIG. 7, when the circuit net is a non-defective product, that is, when R _a = 0Ω,

Therefore, V ₀ = 1V. The measured value 830 mV at time t ₀ is reduced by 17% compared to 1 V for the non-defective product. Therefore, by comparing the measured value at time t ₀ and the measured value at a non-defective product, it can be determined whether there is an increase in conduction resistance in the circuit net. In general, in the case of disconnection inspection, the lower the conduction resistance to be detected, the better, and the relatively small time after the application of the rectangular pulse is the optimum measurement time.

Next, the short circuit inspection will be described in detail with reference to FIGS. The short circuit inspection is for inspecting a decrease in insulation resistance between nets due to a complete short circuit and etching residue. When the model of FIG. 3 is focused on the short circuit inspection and converted to an equivalent circuit, it is as shown in FIG. Here, R ₁₂ indicates an insulation resistance, and when R ₁₂ = ∞, a good case is indicated, and when R ₁₂ = 0Ω, a complete short circuit is indicated. Since the capacity between NetA and NetB is very small, it is ignored. The resistances R ₁ and R ₂ between the reference planes NetA and NetB are infinite. Further, the resistance R ₀ for measurement is also omitted because it is set to a sufficiently large value. The equivalent circuit of FIG. 8 has the same configuration as the equivalent circuit of FIG. 5, and it can be seen that the disconnection inspection and the short-circuit inspection can be handled equally.

ｔ＞０でのＶ₀は式（５）で表すことができる。

ｔ＝∞でのＶ₀は式（６）に収束することになる。

In the equivalent circuit of FIG. 8, V ₀ at t = 0 can be expressed by Expression (4).

t> V ₀ at 0 can be expressed by Equation (5).

V ₀ at t = ∞ converges to equation (6).

から立ち上り、

に収束するようになる。その時の関係を図９のグラフに示す。Ｒ₁₂の値が大きいほど収束時間は長くなる。よって、絶縁抵抗の減少を検査するには、矩形パルス印加後の最適測定時間ｔ₁経過後にＶ₀の測定を行えば良いことになる。実際の短絡検査において、ｔ₁は検査にかけられる時間、検査すべき抵抗値、基準プレーンとの静電容量などから計算や実験などで最適時間として設定される。 According to the equations (4) to (6), V ₀ is a non-defective value.

Get up from

To converge. The relationship at that time is shown in the graph of FIG. As the value of R ₁₂ is large convergence time becomes longer. Therefore, in order to inspect the decrease in insulation resistance, V ₀ may be measured after the optimum measurement time t ₁ after application of the rectangular pulse. In an actual short circuit inspection, t ₁ is set as an optimum time by calculation or experiment from the time required for the inspection, the resistance value to be inspected, the capacitance with the reference plane, and the like.

であるため、Ｖ₀＝３７５ｍＶとなる。時間ｔ₁での測定値４６２ｍＶは良品時の３７５ｍＶと比較して、２３％増加することになる。よって、ｔ₁での測定値と良品時の測定値を比較することで、回路ネットに短絡不良を有しているかを判定することができる。一般に短絡検査の場合、検出すべき絶縁抵抗は高ければ高いほど良く、矩形パルス印加後の比較的長い時間が最適な測定時間となる。 An example is given and demonstrated about the detection of a short circuit test | inspection. In the equivalent circuit of FIG. 8, it is assumed that V = 250V, C ₀ = 0.01 μF, the circuit net is C ₁ = 15 pF, C ₂ = 15 pF, and R ₁₂ = 50 MΩ. Further, the measurement is performed by setting the optimum time t ₁ after applying the rectangular pulse to 200 μsec. In this circuit the net, at time t = 0, from equation (4), V ₀ = 375mV, and the at t = ∞, from equation (6), and V ₀ = 750 mV. Further, at t ₁ = 200 μsec, V ₀ = 462 mV. FIG. 10 shows the characteristics when t ≧ 0. If this circuit net is a good product, that is, R ₁₂ = ∞Ω (infinity),

Therefore, V ₀ = 375 mV. The measured value 462 mV at time t ₁ is increased by 23% compared to 375 mV for the non-defective product. Therefore, it is possible to determine whether the circuit net has a short circuit defect by comparing the measured value at t ₁ with the measured value at the time of non-defective product. In general, in the case of short-circuit inspection, the higher the insulation resistance to be detected, the better, and the relatively long time after applying the rectangular pulse is the optimum measurement time.

  As described above, it is only necessary to measure the measurement value 1 for disconnection inspection and the measurement value 2 for short-circuit inspection at an optimum measurement time for one inspection point, and an expensive waveform observer or transient digital analyzer. It is possible to find a disconnection failure of a net or a short-circuit failure with a nearby net without using the. Further, this measurement value can be easily stored in the memory by using a generally used analog-digital conversion IC.

  FIG. 11 shows an operation example of inspection by the printed wiring board inspection apparatus of the present embodiment. As shown in FIG. 11, first, in step 101, the probe is moved to the inspection point.

Next, in step 102, a pulse voltage is applied to the inspection point. After measuring the measured value 1 after elapse of t ₀ shown in FIG. 6, the measured value 1 is stored in the storage unit 8 or the like (step 103), and the measured value 2 after elapse of t ₁ shown in FIG. 9 is measured. The measured value 2 is stored in the storage unit 8 or the like (step 104). Measurement is performed on all nets to be inspected, and steps 101 to 104 are repeated until all inspections are completed.

  Next, in step 106, the measurement value 1 measured in step 103 is compared with the measurement value 1 already stored in the non-defective substrate. If the measurement value 1 in step 103 is small, a disconnection failure is determined in step 107. To detect. In step 108, the measurement value 2 measured in step 104 is compared with the measurement value 2 already stored in the non-defective substrate. If the measurement value 2 in step 108 is large, a short circuit failure is detected in step 109. To detect. Comparison / detection is performed for all nets to be inspected, and steps 106 to 109 are repeated until all inspections are completed.

  It should be noted that after step 105 is omitted and measurement value 1 in step 103 and measurement value 2 in step 104 are measured, defect determination in steps 106 to 109 may be performed subsequently. At this time, if all the inspections in step 110 are not completed, the process returns to step 101.

  Therefore, according to the printed wiring board inspection apparatus and inspection method according to the present embodiment, the disconnection failure of the net and the short-circuit failure with other nets can be achieved without using an expensive waveform observer or transient digital analyzer. Can be easily and inexpensively discovered.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  The present invention can be used for inspection of a printed wiring board.

DESCRIPTION OF SYMBOLS 1 Probe 2 Probe support part 3 Printed wiring board 4a-4e Circuit (net) on a printed wiring board
5 Reference plane 6 Moving mechanism unit 7 Measuring unit 8 Storage unit 9 Control unit

Claims (6)

First and second probes for contacting the net of the printed wiring board to be inspected;
Storage means,
The first probe is brought into contact with a reference surface of the printed wiring board, the second probe is brought into contact with a net of the printed wiring board, and a rectangular pulse voltage is applied to the net through the second probe. ,
The first probe measures the first voltage of the external capacitor C ₀ provided outside the printed wiring board immediately after the rectangular pulse is applied, and after the lapse of the optimum measurement time set to determine the insulation resistance. A second voltage measurement of the external capacitor C ₀ is performed,
The first and second voltage measurements of the external capacitor C ₀ are performed on all nets to be inspected of the printed wiring board, and the values are stored in the storage means.
Immediately after applying the rectangular pulse measured in advance and after the optimal measurement time has elapsed , the first and second measured values of the non-defective product measured by the first and second voltage measurements of the external capacitor C ₀ , Comparing the first and second measured values measured in the first and second voltage measurements of the external capacitor C ₀ ;
A printed wiring board inspection apparatus configured to detect an increase in conduction resistance including a complete disconnection in the same net and a decrease in insulation resistance including a complete short circuit with an adjacent net. . In the detection of the decrease in insulation resistance, compared with the second measured value of the non-defective product measured by the second voltage measurement of the external capacitor C ₀ after the optimal measurement time elapsed in advance ,
Second measurement printed circuit board inspection apparatus according to claim 1, characterized in that it is determined that it has short circuit failure net net increase which second measured at the voltage measurement of the external capacitor C _0. Compared with the first measured value of the non-defective product measured in the first voltage measurement of the external capacitor C ₀ immediately after application of the rectangular pulse measured in advance in detecting the increase in the conduction resistance ,
First measurement printed circuit board inspection apparatus according to claim 1, characterized in that to determine the reduced and it is disconnection net net first measured by the voltage measurement of the external capacitor C _0. A first probe is brought into contact with a reference surface of the printed wiring board, a second probe is brought into contact with a net of the printed wiring board, a rectangular pulse voltage is applied to the net through the second probe,
The first probe measures the first voltage of the external capacitor C ₀ provided outside the printed wiring board immediately after the rectangular pulse is applied, and after the lapse of the optimum measurement time set to determine the insulation resistance. A second voltage measurement of the external capacitor C ₀ is performed,
First and second voltage measurements of the external capacitor C ₀ are performed for all nets to be inspected of the printed wiring board, and the values are stored in the storage means.
Immediately after applying the rectangular pulse measured in advance and after the optimal measurement time has elapsed , the first and second measured values of the non-defective product measured by the first and second voltage measurements of the external capacitor C ₀ , Comparing the first and second measured values measured in the first and second voltage measurements of the external capacitor C ₀ ;
A method for inspecting a printed wiring board, comprising detecting an increase in conduction resistance including a complete disconnection in the same net and a decrease in insulation resistance including a complete short circuit with an adjacent net. In the detection of the decrease in insulation resistance, compared with the second measured value of the non-defective product measured by the second voltage measurement of the external capacitor C ₀ after the optimal measurement time elapsed in advance ,
Second inspection method of the printed wiring board according to claim 4, wherein the measured value and judging a short circuit failure net nets have increased with the second measured at the voltage measurement of the external capacitor C _0. Compared with the first measured value of the non-defective product measured in the first voltage measurement of the external capacitor C ₀ immediately after application of the rectangular pulse measured in advance in detecting the increase in the conduction resistance ,
The printed wiring board inspection method according to claim 4, wherein a net in which the first measurement value measured by the first voltage measurement of the external capacitor C ₀ decreases is determined as a disconnection defective net.

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