JPH0581864B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a circuit board inspection method for inspecting the quality of a circuit board on which electronic components, etc. are mounted, and is particularly suitable for circuit boards on which low impedance components are mounted. It is related to the inspection method.

[Conventional example]

2. Description of the Related Art A circuit board testing device called an in-circuit tester has come to be used to test circuit boards on which electronic components and the like are mounted.

Figure 7 shows the patent application filed in 1982, which was previously proposed by the applicant.
The invention of No. 316875 is disclosed, and to briefly explain its outline, for example, a signal source 1 that emits an AC signal for measurement is held in a jig (not shown) and contacts circuit patterns 2a to 2d of a circuit board 2 to be inspected. Nodes (contact pins) N ₁ to N ₄ , the above signal source 1
Relays S ₁ to S ₄ and AC ammeter 5 connected to the side
A scanner 3 consisting of relays S ₁ ′ to S ₄ ′ connected to the side, a controller 4 that controls these relays on and off, and a current detected by the AC ammeter 5 detect the impedance of the components mounted on the circuit board 2. It is equipped with an impedance measuring section 6 for measuring.

When inspecting a board using this device, for example, first, a circuit board that has been confirmed to be a good product is measured, the data is collected, and a tolerance is set. After that, the production board is measured and compared with the data of the non-defective board to determine whether it is good or bad.

That is, the controller 4 controls one of the relays S ₁ ′ to S ₄ ′, for example in the illustrated example.
S ₃ ′ is turned on and connected to AC ammeter 5, and other relays S ₁ ′, S ₂ ′, and S ₄ ′ are turned off, and relay S ₃
is off, relays S ₁ , S ₂ , and S ₄ are on and signal source 1 is turned off.
Connect to.

When a measurement signal is emitted from the signal source 1, the other contact pins N ₁ , N ₂ , N ₄ except for one contact pin N ₃
A signal is applied to the contact pin N3, and a current flows from each contact pin to the contact pin _N3 via the jumper wire JP, the resistor R, and the capacitor C, and is detected by the ammeter 5. Thereby, the minimum impedance N _N3 of the circuit pattern that the contact pin N ₃ is in contact with is measured by the impedance measuring section 6 . By sequentially switching the relays of scanner 3, the impedance Z _N1 , is calculated from each current flowing into the contact pins N ₁ , N ₂ , ...
After measuring Z _N2 ,... and setting the tolerance for each, we begin measuring the production board.

[Problem to be solved by the invention]

According to the above inspection method, a measurement signal is applied to all the other patterns except for one pattern, and the impedance is measured by the current flowing into the excluded one pattern, which is the so-called measurement between one pin and all other pins. Since the pass/fail judgment is performed, if an element having a certain level of impedance is mounted, solder bridges or the like can be detected at any position on the board. Another advantage is that the switching control of the scanner need only be executed the same number of times as the number of contact pins, and therefore the number of test steps will not be more than that.

However, if a low impedance element that is close to a short circuit at the measurement frequency is installed, such as a jumper wire, a large capacitor, or a small inductance coil, the value obtained by measuring between one pin and all other pins will be different. It may be difficult to detect whether it refers to a component or a solder bridge. Such problems may also occur during harness tests and board through-hole tests.

For example, if the impedance of the jumper wire JP is Z _JP ≒0, and the capacitor C has a large capacity, then Z _C = 1/ωC ≒0, so the impedance measured through each contact pin is Z _N1 ≒0... Contact pins N ₁ and N ₂ are short-circuited Z _N2 ≒ 0... Contact pins N ₂ and N ₁ are short-circuited Z _N3 ≒ 0... Contact pins N ₃ and N ₄ are short-circuited Z _N4 ≒ 0...Contact pins _N4 and _N3 are short-circuited. Therefore, as shown in FIG. 8, missing parts or bridges may not be detected. In such cases, detection is possible if the user considers the jumper wire to be part of the pattern and reduces the number of contact pins, or specifies a pin for measuring resistance and adds pin-to-pin measurement.
Setting such a test program each time is extremely troublesome and may be undesirable for some users.

This invention was made in view of the above circumstances,
The purpose is to automatically generate a test step between specified pins and perform the measurement instead of testing between one pin and all other pins when the measured impedance is less than a predetermined value, thereby increasing the overall test steps. It is an object of the present invention to provide a highly accurate circuit board inspection method that can detect the presence or absence of bridges and the like without any problems.

[Means to solve the problem]

FIG. 1 shows an embodiment of an in-circuit tester to which the present invention is applied, and FIG. 2 shows the internal functions of a controller that measures impedance to determine pass/fail. Referring to both figures, the measuring section 10 includes, for example, an amplifier 11, an A/D converter 12, and a controller 13, and the controller 13 controls signal generation to the signal source 1, switches the scanner 3, controls the gain of the amplifier 11, and The data from the A/D converter 12 is read, the impedance is measured, and the impedance is compared with the data of a non-defective board to determine the quality of the production board.

In order to solve the above problems, this device is equipped with the following means (a) to (d).

B. Comparison value setting means 17 for setting, for example, a comparative minimum impedance value (K) in order to detect whether or not the pattern to be measured on the production board is in a state close to a short circuit.

(b) If the pattern impedance of the production board measured in the test step between 1 pin and all other pins is less than or equal to the above K, the test step between 1 pin and all other pins of the relevant pattern is deleted. Measurement deletion means 18.

(c) Pin-to-pin measurement generation means 19 that automatically generates a specified pin-to-pin test step in place of the deleted step.

D. A unit operation control means 2 which switches the scanner 3 in response to the specified pin-to-pin test step generated above, adds a measurement signal to the pattern, and inputs the response current into the amplifier 11.
0.

[Effect]

By providing the above means, a pin-to-pin measurement step is automatically generated especially when the measured value is a low impedance (below K), and the measured data is finally compared with the judgment value collected from the good board. Therefore, for example, if the measurement data is outside the tolerance range of the judgment value, it will be determined that there is a short circuit (solder bridge), and if the measurement data is within the tolerance range of the judgment value, it will be determined as normal, allowing accurate board inspection.

〔Example〕

Hereinafter, while referring to the flowchart shown in FIG. 3 and the scanner control code shown in FIG. 4,
Automatic generation of an impedance test between one pin and all other pins and an impedance test between specified pins will be explained.

P ₁ : Set the range for low impedance detection after initial setting. For example, if the predetermined comparison value is 5Ω in consideration of wiring impedance, etc., when an impedance of 5Ω is detected, the A/D converter 1
The range of the amplifier 11 is fixed so that the digital conversion value of 2 becomes K, and the following steps begin.

P ₂ : Input the number n of nodes (contact pins) on the jig. In impedance measurement between one pin and all other pins, the number of nodes is the number of steps.

P ₃ , P ₄ : An example in which the scanner code of the inspection control memory (not shown) has 4 steps is shown in FIG. 4A. Files for all steps are created and scanner control code is generated. In the test between one pin and all other pins, one of the signal source sides (S ₁ to S ₄ ) is off, the others are on, and the measurement side (S ₁ ' to S 4 ) is off.
S ₄ ′) can be controlled by the reversal signal and easily generated automatically.

P ₅ : Inspection is performed from the upper step. Fourth
In Figure A, for example, n=4, so the relay is set by the scanner control code in step 4.

P ₆ , P ₇ : Execute measurement and judge whether the A/D conversion value is equal to or less than K, which is equivalent to 5Ω.

[If larger than 5Ω] Subtract one of n in P ₈ and proceed to P ₉ . here,
S represents the number of pin-to-pin designation tests set as described later. If the step is not completed as a result of subtracting n in P ₉ , set the step deletion number S to "0" in P ₁₀ .
and repeat this operation. If the test has been completed, the process moves to the actual measurement data collection routine for each test step (not shown).

[When judged as 5Ω or less] P ₁₁ : Replace with M=n. Since M is used as a scanner number, for example, it is treated as a variable different from the number of steps n.

_P12 : Check if scanner number M-1 has already been processed using this routine and exists at the number stored in _P19 . If it exists, proceed to page ₁₆ .

P ₁₃ : Turn on only scanner M-1 on the signal source side,
Leave the measurement side as is. In other words, it is as follows.

S ₁ S ₂ S ₃ S ₄ S ₁ ′ S ₂ ′ S ₃ ′ S ₄ ′ 0 0 1 0 0 0 0 1 If this is illustrated, it will be in the scanner state as shown in Figure 5, for example, and the next P ₁₄ In this case, only the impedance of capacitor C is measured.

P ₁₅ : Determine whether the A/D conversion value is below K, that is, below 5Ω.

[If it is larger than 5Ω] P ₁₆ , P ₁₇ : Determine whether the scanner has been executed up to the first step, and if it has not finished, return to P ₁₂ ; if it has finished, return to P ₈ .

[If it is 5Ω or less] P ₁₈ : Check whether the test step has already been generated as a specified pin-to-pin measurement step, and M-1 in all steps other than the specified pin-to-pin measurement step.
Enter the control code ``0'' so that the scanner of the number does not turn on. ...Figure 4, P ₁₉ : In order to be able to determine in P ₁₂ above that this scanner has already been reduced, write its number in the memory.

P ₂₀ : Delete measurement step M-1.
...Figure 4C P ₂₁ : Sort step numbers. ...Fig. 4P ₂₂ : Sorting always leaves the highest step as an empty step. Enter the control code for the relay used in this judgment routine here. Also, write a pin-to-pin mark indicating that this step is provided as a pin-to-pin measurement. ...Figure 4 E P ₂₃ : Increment the number of sorting and return to P ₁₇ .

By operating as described above, the test steps as shown in FIG. 4, for example, are finally generated for the circuit board to be measured 2 shown in FIG.
However, the resistance value of R was 5Ω or more.

In this inspection step, Step 4: Measurement between pins between jumper wires JP Step 3: Measurement between pins of capacitor C Step 2: Measurement between pins of R, C series circuit Step 1: Measurement between pins of C, R series circuit This is a pin-to-pin measurement. In the above example, the number of nodes is 4, so the measurement contents of step 2 and step 1 are the same, but in reality, since there are many nodes, such cases are rare.

An example of performing this inspection step is shown in FIG. 6, but even if, for example, node N ₁ or N ₂ or node N ₃ or N ₄ bridges with another pattern, missing parts or bridges will not occur. etc. can be detected.

〔effect〕

As described above in detail, the present invention measures the pattern impedance of a circuit board by a preset test between one pin and all other pins, and if the value is less than, for example, a predetermined comparison value K, It is designed to automatically generate a test step between measurement pins and perform measurements.

Therefore, according to this inspection method, it is possible to easily detect low impedance parts such as solder bridges and missing parts, which are difficult to detect with tests between one pin and all other pins, and the user has to specially create software. Inspection capacity can be improved without any problems. In addition, high-speed inspection can be performed without increasing the number of test steps, and when applied to through-hole tests, harness tests, etc., automatic short and short tests can be performed.
Open test steps can be created.

[Brief explanation of the drawing]

Figures 1 to 6 relate to embodiments of the present invention, with Figure 1 being a block diagram showing an example of the configuration of a circuit board inspection device, Figure 2 being a functional block diagram of the controller, and Figure 3 showing designated pins. FIG. 4 is a scanner control code diagram, FIG. 5 is an explanatory diagram of scanner operation, FIG. 6 is an explanatory diagram of detection operation, FIG. 7 is a block diagram of the conventional device, and FIG. The figure is an explanatory diagram of the detection operation. In the figure, 1 is a signal source, 2 is a circuit board to be inspected, and 2a
or 2d is the circuit pattern, 3 is the scanner, 10
14 is a measuring section, 14 is an impedance measuring means, 15 is
16 is a comparison means, 16 is a judgment means, 17 is a judgment lower limit value setting means, 18 is a measurement deletion means between one pin and all pins, 19 is a measurement generation means between pins, and N ₁ to N ₄ are contact pins.

Claims (1)

[Scope of Claims] 1. A plurality of pins that contact predetermined pattern positions on a circuit board to be inspected can be switched and connected to a signal source side and a measurement section side respectively using a scanner, and a measurement AC signal is transmitted from the signal source to the board. In a circuit board inspection method, the impedance of the board is measured by inputting a response signal obtained by applying a signal to a measuring section, and the measured value is compared with data collected in advance from a non-defective circuit board to determine the quality of the board. , one pin is connected to the measurement section side and all other pins are connected to the signal source side, and this is sequentially switched for each test step, and the impedance of the above board at each step is determined by measuring between one pin and all other pins. If a measured value equal to or lower than the predetermined comparison value is obtained in the middle of the above test steps, specified pin-to-pin measurement steps are automatically generated and measured in place of the following test steps. A method for inspecting a circuit board, characterized in that the measured values are compared with the predetermined comparison values.