JP2004028975A - Lead soldering fault detection method in digital ic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a simple detection method that does not require any addition of an exclusive sensor or the like, and is not affected by a temperature change in the characteristics of a protection diode, electric characteristics in a printed circuit board, and a lot variation, a temperature change, and a lot variation. <P>SOLUTION: A constant voltage is applied between either a common power supply line 51 or a common GND line 52, and lines for composing a bus line with each by aiming at a line group where the electric characteristics of a digital IC are identical, for example the bus line, for measuring a current value, or, the capacitance value of each line is measured, and the current value or the capacitance value of each line for composing the bus line is compared each, thus detecting the soldering fault in the lead of the digital IC. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an inspection method for a mounted circuit board, and more particularly to an inspection method for detecting a soldering failure of a lead of a mounted IC to a circuit board pattern.
[0002]
[Prior art]
The inspection of the soldering failure of the IC lead of the mounting circuit board is performed by an in-circuit tester or the like. In the in-circuit tester, in order to inspect various mounted components on the mounted circuit board, the probe pins with built-in springs are brought into contact with the pattern on the circuit board, and the component state is inspected by measuring the component constant. I do.
Further, in the case of detecting a soldering failure of an IC lead, a method of measuring a capacitance value between a metal plate placed above the IC and a lead frame of the IC through a pattern of a printed pattern board. (For example, see Patent Document 1).
Further, there is a method in which a current is supplied from a constant voltage source to a protection diode inside the IC to measure the current, and the measured current is compared with the current of a non-defective substrate (for example, see Patent Document 2).
Furthermore, there is a method of measuring the capacitance value of a specific line and comparing it with the capacitance value of a non-defective substrate (for example, see Patent Document 3).
[0003]
[Patent Document 1] JP-A-6-34714 [Patent Document 2] JP-A-7-218580 [Patent Document 3] JP-A 7-218573
[Problems to be solved by the invention]
In the in-circuit tester described in Patent Literature 1, it is necessary to additionally install a dedicated sensor in addition to the probe pins for inspection, so that the cost of the jig is inevitable due to the sensor cost and the jig processing cost.
Further, in the method for detecting foot lifting and bridge soldering by an in-circuit tester of a digital IC described in Patent Document 2, a simple comparison with a good board shows that the ambient temperature at the time of measuring the good board and the ambient temperature at the time of inspection are different. Is normal, and the current flowing through the protection diode fluctuates greatly due to a change in temperature.
Further, in the method of measuring the capacitance value of a specific line described in Patent Document 3 and comparing it with the capacitance value of a non-defective substrate, a simple comparison with a non-defective substrate is performed by comparing the ambient temperature at the time of measuring the non-defective substrate with the ambient Normally, the ambient temperature of the IC is different, and the input capacitance value of the IC and the capacitance value of the printed circuit board pattern not only fluctuate due to the temperature change but also fluctuate depending on the manufacturing lot. Is very difficult.
[0005]
[Means for Solving the Problems]
The present invention has been made in order to solve the above-described problems of the related art, and in a terminal group of an IC having uniform electric characteristics, for example, in a bus line of a digital IC, a current value measuring method is used. By flowing a current through the protection diode inside the IC of each line constituting the line group, comparing the flowing current values with each other, and detecting a line having a significantly different value from the other lines, Next, in the capacitance value measuring method, the capacitance value of each line constituting the line group with respect to the GND pattern or the power supply pattern is detected for each line. By detecting a line with a value that is significantly different from the others, the lead soldering failure of the IC connected to that line is detected. To detect.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method of detecting a soldering defect of an IC lead by comparing currents of group constituent lines and a method of detecting a defect by comparing capacitance values according to the present invention will be described with reference to the drawings.
FIG. 1 is a circuit connection diagram of a bus line constituting a target digital IC, and also serves as an explanatory diagram showing a method of measuring the current of each line.
FIG. 2 is an explanatory diagram showing a defect detection method based on capacitance value comparison.
[0007]
1 and 2, digital ICs 10, 20, and 30 mounted on a circuit board to be inspected are interconnected via bus lines 41 to 48, and a common power supply line 51 and a common GND line 52. Also form a line common to the digital ICs 10, 20, 30.
Taking the bus line 41 constituting the digital IC 10 as an example, the bus line 41 is connected to an intermediate connection point between the two IC built-in protection diodes 11 and 12 connected in series.
Also in the digital ICs 20 and 30, the bus line 41 is connected to an intermediate connection point between the IC built-in protection diodes 21 and 22, and 31 and 32, respectively.
Similar connection relationships exist for the other bus lines 42 to 48.
[0008]
The present invention focuses attention on the connection relationship between line groups in a digital IC circuit having the same electrical characteristics, and detects current in each line to detect defective soldering of IC leads.
FIG. 1 shows an embodiment for detecting soldering failure of an IC lead in three digital ICs, and uses a constant voltage source 62, an ammeter 61, and three probe pins 71, 72, 73 to detect three. FIG. 4 is an explanatory diagram for detecting a soldering failure of an IC lead in the digital ICs 10, 20, and 30 of FIG.
[0009]
In a state where the digital ICs 10, 20, and 30 mounted on the circuit board to be inspected are connected by the bus lines 41 to 48, a bus line is formed with one or each of the common power supply line 51 and the common GND line 52. A constant voltage is applied between each line and a constant voltage source 62 to flow a current through a protection diode inside each of the digital ICs 10, 20, and 30. The current value is measured by an ammeter 61, and the value is measured. Remember.
This current measurement is performed on all the lines 41 to 48 constituting the bus line, and the obtained current values are compared with each other.
The current value to be compared is measured under the same temperature environment by short-time measurement (several ms / line), so that it is not affected by changes in the ambient temperature.
[0010]
FIG. 2 shows an embodiment in which an IC lead soldering defect in three digital ICs is detected by measuring the capacitance value of each line in the same manner as in FIG. 1, and an AC constant voltage source 82 and an AC ammeter 81 FIG. 4 is an explanatory diagram for detecting a soldering failure of IC leads in three digital ICs 10, 20, 30 using a measurement common line switch 91 and three probe pins 71, 72, 73.
[0011]
In a state where the digital ICs 10, 20, and 30 mounted on the circuit board to be inspected are connected by the bus lines 41 to 48, a bus line is formed with one or each of the common power supply line 51 and the common GND line 52. An AC voltage is applied from an AC constant voltage source 82 to each line, the current value is measured by an AC ammeter 81, and the capacitance value is calculated from the measured value and stored.
The capacitance value is a composite value of the stray capacitance value of the printed board pattern and the input capacitance value of each IC connected to the pattern.
This capacitance measurement is performed on all the lines 41 to 48 constituting the bus line, and the obtained capacitance values are compared with each other.
[0012]
In the comparison method, an average value is calculated and compared with a difference from the average value, and when the difference from the average value exceeds a preset threshold value, it is determined to be defective. Since the average value calculation at that time is expected to include a defective value, calculating the average value excluding the minimum value and the maximum value improves the defect detection accuracy.
[0013]
Also, among the bus lines, there are lines whose connection is not uniform, such as lower bits and upper bits of the address bus, and these lines may not have the same electrical characteristics. In such a case, a current value or a capacitance value at a specific temperature is measured in advance by the same method as the above-described current measurement method and capacitance measurement method, and the current value or the capacitance value is obtained from the measured value. The calculated rate of temperature change is calculated for each line and stored as a measured value. The defect is determined by the same average value as described above.
This method of comparing the rate of change in temperature can be applied to general digital connection lines even if the target is not a bus line and the electrical characteristics are not significantly different.
[0014]
【The invention's effect】
As described above, according to the method for detecting lead soldering failure of a digital IC according to the present invention, there is no need to add a dedicated sensor or the like, so that the cost of the jig does not increase, and the temperature of the current of the protection diode does not increase. Since it is not affected by the change, the temperature change of the electrical characteristics of the printed circuit board, and the lot variation, stable defect detection can be performed.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a method for measuring a current of each line.
FIG. 2 is an explanatory diagram showing a method for measuring a capacitance value of each line.
[Explanation of symbols]
10,20,30 Digital IC
11, 12, 21, 22, 31, 32 Protection diodes 41 to 48 with built-in IC Bus line 51 Common power supply line 52 Common GND line 61 Ammeter 62 Constant voltage source 71 to 73 Probe pin 81 AC ammeter 82 AC constant voltage source 91 Measurement common line switch

Claims (4)

In a defect detection method for detecting a soldering defect of a digital IC mounted on a circuit board,
A constant voltage is applied between each of the constituent lines of the line group having the same electrical characteristics such as bus lines constituting a plurality of digital ICs and the common power supply line or the common GND line, or both. A digital IC characterized in that an average value is obtained from a current value for each line or a value calculated from the current value, and a soldering defect is detected by comparing the measured value for each line with the average value. Lead soldering failure detection method. If the connections of individual lines are not uniform and the electrical characteristics are not uniform, use the current value at a specific temperature and the temperature change rate obtained from the measured current value as the measurement value for each line. A method for detecting defective soldering of a digital IC by comparing an average value calculated from the measured value with a measured value. In a method for detecting a soldering failure of a digital IC mounted on a circuit board,
The capacitance value between each of the constituent lines of the line group having the same electrical characteristics such as bus lines constituting a plurality of digital ICs and the common power supply line or the common GND line is measured, and the static value of each line is measured. A method for detecting lead soldering failure of a digital IC, wherein an average value is obtained from a capacitance value, and a soldering failure is detected by comparing the measured value for each line with the average value. When the connection of individual lines is not uniform and the electrical characteristics are not uniform, the temperature change rate obtained from the capacitance value of a specific substrate at a specific temperature and the measured capacitance value is used. A method for detecting defective soldering of a lead in a digital IC, wherein the measured value is measured for each line, and the average value calculated from the measured value is compared with the measured value to detect a defective soldering.

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