JPH11223652A - Solder connection detecting method for digital ic using field detecting probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solder connection detection of a fine pin for a digital IC in a non-contacting manner. SOLUTION: In this detecting method for a digital IC 4 soldered and mounted on board pads 2a, 2b of a printed circuit board 1, a gland 12 of a signal source 10 is connected a board gland 3 of the printed circuit board 1 and an AC signal from the signal source 10 is applied to the board pad 2b, to which a pin 5b is solder-connected, with a pin probe 13 to measure the voltage of the pin 5b in a non-contacting manner with a field detecting probe 8 arranged near the shoulder 6 of the pin 5b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting solder connection of a board on which a semiconductor integrated circuit (IC) or the like is mounted, and more particularly to a method for inspecting solder connection of a digital IC using an electric field detection probe.

[0002]

2. Description of the Related Art Conventionally, as a method for inspecting solder connection of a digital IC, for example, Japanese Patent Application Laid-Open No. 7-218580 discloses an inspection method using an in-circuit tester using two stylus probes.

FIG. 5 is a diagram showing an outline of an inspection method using this in-circuit tester, and is a diagram showing a connection relationship between two digital ICs mounted and soldered on a mounting board. In this inspection method, all the power pins 52 and 55 and all the ground pins 54 and 57 are connected by independent patterns 58 and 60, respectively, and at least one input pin 56 and one output pin 53 are connected by independent patterns 59. An independent pattern 59 for connecting the input / output pins 56 and 53 and an independent pattern 58 for connecting all the power pins 52 and 55 or all the ground pins 54 and 57 to the plurality of connected digital ICs 50 and 51 with an input protection circuit. Between the independent pattern 60,
The current is measured by applying a constant voltage of AC or DC, and the presence or absence of the foot lifting of the pin and the bridge solder is determined based on the current value.

FIG. 6 is a diagram showing an example of a circuit in a case where the floating of a digital IC on such a mounting board is inspected by using an XY type in-circuit tester. In the figure, 7
0 is an AC or DC constant voltage power supply, 71 is an ammeter, 72
(72a, 72b) is the ground of the measurement circuit. At the time of inspection, first, two sets of X provided for the in-circuit tester
The Y-unit is controlled, and one probe contacts an independent pattern 59 connecting the input / output pins 56 and 53, and the other probe contacts an independent pattern 58 connecting the power pins 52 and 55.

Next, when a constant voltage is applied from a constant voltage power supply 70, the constant voltage is applied to the protection diodes 63 and 64 and the resistor 6
5 and protection diodes 61 and 62 connected in parallel to both ends thereof. Therefore, when the ammeter 71 is connected in series to the constant voltage application circuit, a current (combined current) flowing to the outside through the internal circuits can be measured.

Therefore, each of the pins 52, 53, 55, 56 for each of the independent patterns 58, 59 with which both probes come into contact.
Is compared with the current when all of the pins 52, 53, 55 and 56 are soldered properly and one or more of the pins 52, 53, 55 and 56 are in a floating state. Then, in the latter case, the current value decreases by 20 to 30%, so that the presence or absence of foot lifting can be determined based on the current value.

On the other hand, in the case of a solder bridge in which adjacent input pins or output pins are connected by solder, the current value increases by 20 to 30% as compared with a normal case, so that a solder bridge can be detected by a similar inspection method. .

[0008] As a general inspection method using an in-circuit tester other than the above, two probe probes are used.
There is also a method in which the resistance between the pin and the substrate pad is measured by using the four-terminal method by abutting the C pin and the substrate pad, and the lifting of the foot is inspected from the resistance value.

[0009]

However, in the above-described method based on current measurement, the combined current flowing through a plurality of pins connected in parallel is measured and the connections of all the pins are collectively inspected. It is difficult to specify the pins, and if the number of parallel connections increases, the current value per pin with respect to the combined current becomes relatively small.

Further, in the method based on the resistance value measurement that can be inspected for each pin, it is difficult to stably contact the probe with a fine pin, and if the impact force or pressing force at the time of contact is large, the pin may be damaged. There is a problem of missing a foot float.

As a method for solving the problem of the conventional inspection method using an in-circuit tester, an inspection method using an EO (electro-optical) sensor has been proposed by the present inventors in Japanese Patent Application Laid-Open Nos. 9-72947 and 9-72947. 22245
No. 4 publication.

According to Japanese Patent Application Laid-Open No. 9-72947, among pins (lead terminals) of a semiconductor package (IC) mounted on a circuit board, a pin shoulder on a resin mold side, which is separated from a solder connection portion, is provided. An EO sensor is brought into proximity, a test probe is brought into contact with a pad portion on the circuit board to which the pin is connected by soldering, a voltage is applied by a signal source, and the EO sensor detects the electric field strength at the pin shoulder. From the magnitude of the electric field strength, the solder connection state between the pins and the pads on the circuit board is inspected.

Japanese Patent Application Laid-Open No. 9-222454 discloses a semiconductor package (IC) mounted on a circuit board by applying a voltage from a signal source by bringing an inspection probe into contact with a pad portion on a circuit board connected by soldering. ) Of the pins (lead terminals), the total of the electric field strengths of the pin shoulders is detected by an EO sensor arranged in proximity to the pin shoulders on the resin mold side, which is distant from the solder connection portion, and Inspection of the solder connection state with the pad and short circuit between the IC pins are performed.

These EO sensors (electric field detection probes)
In the solder connection inspection method using the method, there is a problem in detection accuracy.

The present invention relates to the in-circuit tester and E
An object of the present invention is to provide a method for non-contact inspection of a solder connection state of a fine pin (lead terminal) which solves a problem of an inspection method using an O sensor.

[0016]

According to the present invention, a digital IC having a plurality of pins (lead terminals) on a pad on a printed circuit board and having the pins connected by soldering uses an electric field detection probe for detecting the solder connection state of the pins. In the method of inspecting, the ground of the printed circuit board, or in a state where the ground and all power supplies are connected to the ground of the signal source, the pins are solder-connected to the pads of the printed circuit board using a stylus probe. A signal from a signal source is applied, and the electric field intensity near the shoulder of the pin of the digital IC is detected using an electric field detection probe. Based on the detected intensity, the solder connection of the pin is opened and the adjacent pins are short-circuited. Is determined.

The signal of the signal source in the present invention may be a pulse signal or a waveform signal offset to the plus side, and the signal source may be provided with a current limiter.

In the present invention, the determination of whether the pins are open or short is made by previously determining the average value of the detected electric field intensities of the respective soldered pins of a standard sample, which is a non-defective soldered board of the same plurality of digital ICs. Calculating, determining a non-defective range for each pin using the average value as a reference value, determining that the pin that is larger than the upper limit of the non-defective range is short, and that the pin that is smaller than the lower limit of the non-defective range is open. Features.

In the present invention, in the open determination processing, when the adjacent pin is a ground pin or a power supply pin and the current of the signal source has reached a set limit, the pin is determined to be short-circuited. Features.

In the present invention, the stylus probe is attached to the board pad of the printed circuit board to which the pin is soldered in a state where the ground of the printed circuit board or the ground and all power supplies are connected to the ground of the signal source as described above. By applying the signal from the signal source, it is possible to prevent the signal from being supplied to the pin to be inspected through another path, and to improve the solder connection inspection accuracy.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining a method for inspecting solder connection of a digital IC using an electric field detection probe according to the first embodiment of the present invention. Digital IC
Reference numeral 4 denotes solder pins of the pins 5a and 5b on board pads 2a and 2b (usually formed by patterning copper foil by thickening copper plating). An electric field detection probe 8 is arranged close to a pin shoulder 6 of the pin 5b with respect to the pin 5b to be inspected, and an AC signal 11 from a signal source 10 is applied to the corresponding substrate pad 2b by using a stylus probe 13. 2b. The ground 12 of the signal source 10 is connected to the substrate ground 3 of the printed circuit board 1.
This is a ground pin (not shown) of all ICs connected to the board ground 3 of the printed circuit board 1 in order to prevent a signal from being supplied to the pin to be inspected by another path.
Is short-circuited to the ground 12 of the signal source 10.

When the solder connection between the board pad 2b and the pin 5b is good, the voltage supplied to the board pad 2b is applied to the pin 5b through the solder connection portion 7, and the voltage near the pin shoulder 6 is An electric field proportional to the voltage is induced. On the other hand, when the solder connection between the substrate pad 2b and the pin 5b is open, the voltage applied to the pin 5b decreases, and the electric field strength near the pin shoulder 6 also decreases. Accordingly, by determining the magnitude of the electric field detection strength of the electric field detection probe 8 by the signal processing unit 9, the solder connection state between the board pad 2b and the pin 5b can be inspected.

Here, the electric field detection probe will be specifically described. FIG. 2 is a diagram for specifically explaining the electric field detection probe shown in FIG. As shown in FIG. 2, the electric field detection probe 8 transmits the emitted light from the laser 14 to the electro-optic crystal 19 placed on the metal body 20 at the tip of the electric field detection probe 8, the collimating lens 15, the isolator 16, the polarization beam splitter 17, The light condensed through the first condenser lens 18 and reflected by the electro-optic crystal 19 is
First condenser lens 18, polarizing beam splitter 17, 1
The light receiving element 24 receives the light through the ４ wavelength plate 21, the Wollaston prism 22, and the second condenser lens 23. According to such a configuration, the emitted light from the laser 14 is collimated by the collimator lens 24 and transmitted through the isolator 16. At this time, the return light is removed by the isolator 16.

Further, the parallel laser beam 25 passes through the polarization beam splitter 17, but here, the S-polarized component is totally reflected and the P-polarized component is almost transmitted. The linearly-polarized laser light 25 composed of the P-polarized light component transmitted through the polarization beam splitter 17 is focused on the electro-optic crystal 19 by the first focusing lens 18. The electro-optic crystal 19 is placed at the focal position of the first condenser lens 18, has a metal reflection film on the back surface, and changes birefringence in an electric field.

Therefore, the probe 8 facing the pin shoulder 6
When the metal body 20 at the tip is in an electric field, the reflected laser light reflected by the reflection film undergoes a polarization change while reciprocating in the electro-optic crystal 19 to become elliptically polarized light. Then, the reflected laser light of the elliptically polarized light passes through the first condenser lens 18 again,
A part of the light is reflected by the polarization beam splitter 17 in a direction different from the direction of incidence on the electro-optic crystal 19, and is converted into linearly polarized light by a 波長 wavelength plate 21 placed on the reflected optical axis. The linearly polarized light beam is applied to the Wollaston prism 2
2, the laser light is split into two P-polarized light components and an S-polarized light component, and the split two
Is received by the light receiving element 24. This light receiving element 24
Converts the difference between the received light intensities of the two polarized light components into an electric signal.

FIG. 3 schematically shows an electric field distribution when the electric field detection and detection probe shown in FIG. 2 is placed in an electric field. An ITO transparent electrode 40 is provided on the upper surface of the electro-optic crystal 19, and the transparent electrode 40 is connected to the ground 12 of the signal source. When a signal is applied to the pin 5b to be inspected, an electric field is generated using the pin 5b as a voltage potential source, and the adjacent metal surface 20 and the adjacent pins 5c,
A potential is applied to 5d. As a result, electric fields 41a and 41b proportional to the potential difference between the metal body 20 and the transparent electrode 40 are generated in the electro-optic crystal 19, and the electro-optic crystal 19 undergoes a change in birefringence. Here, if the pin 5b to be inspected is short-circuited with the adjacent pin 5c by soldering, a voltage potential source having the same magnitude is generated at the adjacent pin 5c, and the voltage generated at the metal body 20 becomes relatively large. Conversely, when the pin 5b to be inspected is open solder, the substrate pad serves as a voltage potential source, and a potential is applied to the pin 5d and the metal body 20, respectively.
Causes a smaller potential.

As described above, if the tip of the probe 8 is placed in an electric field, an electric signal proportional to the electric field strength is obtained, and the electric field detection probe 8 determines whether a signal voltage is applied to the pin. Can be detected without contact.

Next, a method of applying a voltage signal will be described. FIG. 4 is a diagram showing a configuration of an equivalent circuit of the digital IC. I / O pins 38a of digital ICs 26 and 27,
38b, 39a and 39b are protection diodes 30 provided between the ground pins 34 and 35 and the power pins 36 and 37, respectively.
a, 30b, 30c, 30d, 31a, 31b, 31
It is connected to the connection point of c and 31d. The cathodes of these diodes are connected in series toward the power supply pins 36 and 37, and the ground pin side diodes 30b,
The anodes of 30d, 31b and 31d share a common resistor 32,
It is configured to be connected to ground pins 34 and 35 via 33. The ground pins 34 and 35 of the digital ICs 26 and 27 and the power pins 36 and 37 are connected to each other by wiring on a printed circuit board, and the corresponding input / output pins 38
b and 39a are also connected by the wiring of the printed circuit board. Reference numerals 28 and 29 in FIG. 4 indicate internal circuits. In addition to these, in the actual mounting board, various pins such as input / output pins use resistors,
In many cases, it is connected to a power supply or ground via circuit elements such as capacitors, coils, and diodes. Therefore, when a signal is applied to a certain pin, a signal may be supplied to another IC or another pin through the wiring of the printed circuit board.

Further, in an IC and a printed circuit board, a capacitance between wirings exists, and a parasitic capacitance with a ground line or a power supply line having an inner layer pattern having a large area becomes large. Therefore, a signal may be supplied to the ground or the power supply line from the signal-supplied wiring by capacitive coupling. In the present invention, in order to supply power to the substrate pad and determine whether the pin is open or short from the voltage level of the pin, there is no need to supply power to any pin other than the pin to be inspected, and also to prevent a signal from being supplied to the pin to be inspected through another path. And the signal source ground,
It is technically significant to perform the inspection by connecting to both the ground line (substrate ground) of the printed circuit board and the substrate power supply line, and shorting the ground pins of all the ICs to the ground of the signal source.

In FIG. 4, the ground 12 of the signal source 10
Are connected to a ground line (substrate ground) of the printed circuit board and a substrate power supply line. The AC signal 11 of the signal source 10 is supplied to the input / output pin 38a. With such a configuration, first, the ground pins 34 and 35 and the power supply pins 36,
No signal is supplied to the other digital IC 27 through 37, and conversely, no signal is supplied from the other IC 27.

Next, consider the application of signals within the same IC. When the signal voltage is a positive voltage, the input / output pin 38a
Current flows between the power supply pin 36 and the protection diode 30
A voltage is applied to a. No current flows to the ground pin 34 side, and the anode voltage of the ground pin 34 side diode 30b is maintained at the ground potential. Therefore, the power supply side cathode and the ground side anode of the two diodes 30c and 30d connected to the other input / output pins 38b in the same digital IC 26 remain at the ground potential of the signal source. , 30d are connected to the other input / output pin 38b at the ground potential. On the other hand, when the signal voltage has a negative potential, a current flows between the output pin 38a and the ground pin 34, and a voltage is applied to the diode 30b and the resistor 32 on the ground pin 34 side. As a result, a certain voltage is generated on the anode side of the diode, which is determined by the voltage dividing ratio with the resistor. As a result, the potential of the other input / output pin 38b connected to the connection point of the two diodes 30c and 30d is not fixed to the ground potential, and a negative potential is generated under the influence of the anode voltage of the ground side diode 30d. It is possible. For this reason, it is desirable that the signal applied for connection inspection be a signal offset to the plus side. Empirically,
When a normal sine wave signal having no offset is applied, a voltage of about 50% of the signal source voltage may be generated depending on a pin.

In this embodiment, the case where both the ground line (substrate ground) of the printed circuit board and the power supply line are connected to the ground of the signal source has been described. However, the additional capacitance between the ground line and the power supply line is limited. When the applied signal is large and the frequency of the applied signal is high, the ground line and the power supply line can be regarded as almost short-circuited, and the same effect can be obtained by connecting only the ground line to the ground of the signal source.

Next, a second embodiment of the present invention will be described. In the inspection method according to the first embodiment, the inspection is performed with the ground of the signal source connected to the ground line and the power line of the printed circuit board. In some cases, an overcurrent may flow between these pins, destroying the internal circuit of the IC. In this embodiment, in order to avoid such a problem, a current limiter is provided in the signal source so that an overcurrent does not flow to the IC. In this case, almost no voltage is applied to the pin, and the output of the electric field detection probe is smaller than the normal solder open.

Next, a method of determining open / short according to the present invention will be described. The inspection method of the present invention measures the electric field near the shoulder of a pin (lead terminal) of a digital IC, and determines the quality of the solder connection of the pin of the digital IC from the detected intensity. Since it differs depending on the specific wiring structure and parasitic capacitance, it is necessary to set a good quality standard for each product. In the present invention, a plurality of non-defective substrates are measured, an average value is determined for each pin, and a non-defective range is set based on the average value. From the results of experiments and simulations, it has been found that the detected electric field output is reduced to about half when open, and about 1.3 times when short-circuited. Practically, a range of about 0.7 to 1.2 times the average value is set as a good product range, and a value less than 0.7 times is determined to be open, and a value exceeding 1.2 times is determined to be short.

Further, when the ground pin or the power supply pin is short-circuited, almost no voltage is applied to the substrate pad, and the output is further smaller than that of the normal open. Therefore, this case can be determined by the following two methods. The first method is a method of setting an open determination range and determining a range smaller than the lower limit as a short circuit with a ground pin or a power supply pin. The second method is a method of monitoring the current of a signal source other than measuring the electric field strength, and judging a short circuit with a ground pin and a power supply pin from an abnormal current.

Either of the above two methods can be used to discriminate between a normally open state and a short circuit with a ground pin or a power supply pin.

[0037]

As described above, in the present invention,
With the ground on the printed circuit board, or the ground and all power supplies connected to the ground of the signal source, supply a signal to the board pad to which the IC terminal is soldered and measure the voltage of the pin in a non-contact manner using an electric field detection probe Digital I
The effect that the inspection of the solder connection open and the short circuit of the C input / output pin can be surely performed without damaging the pin is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a method for inspecting solder connection of a digital IC using an electric field detection probe according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the electric field detection probe shown in FIG.

FIG. 3 is a view for explaining a measuring method of the electric field detection and detection probe shown in FIG. 2;

FIG. 4 is a diagram showing an equivalent circuit of a digital IC.

FIG. 5 is a diagram for explaining a conventional example.

FIG. 6 is a diagram illustrating an example of a conventional measurement circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Printed board 2a, 2b Board pad 3 Board ground 26, 27, 50, 51 Digital IC 5a, 5b, 5c, 5d Pin 6 Pin shoulder 7 Solder connection part 8 Electric field detection probe 9 Signal processing part 10 Signal source 11 Signal 13 Probe 14 Laser 15 Collimating lens 16 Isolator 17 Polarizing beam splitter 18 First focusing lens 19 Electro-optic crystal 20 Metal body 21 Quarter-wave plate 22 Wollaston prism 23 Second focusing lens 24 Light receiving element 25 Laser light 28, 29 Internal circuit 30a-30d Protection diode 31a-31d Protection diode 61-64 Protection diode 33,65 Resistance 34,35 Ground pin 36,37 Power supply pin 38a, 38b, 39a, 39b, 53,56 Input / output pin 40 ITO transparent electrode 41a 41b electric field 52, 55 All supply pins 54 and 57 all the ground pins 58, 59 and 60 independently pattern 70 constant-voltage power supply 71 ammeter 72a, 72b Grand

[Procedure amendment]

[Submission date] January 5, 1999

[Procedure amendment 1]

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[Procedure amendment 2]

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[0016]

According to the present invention, a digital IC having a plurality of pins (lead terminals) on a pad on a printed circuit board and having the pins connected by soldering uses an electric field detection probe for detecting the solder connection state of the pins. In the method of inspecting, the ground of the printed circuit board, or in a state where the ground and all power supplies are connected to the ground of the signal source, the pins are solder-connected to the pads of the printed circuit board using a stylus probe. Offset to the positive side as the signal of the signal source
Applying a pulse signal or a waveform signal, and detecting the electric field intensity near the shoulder of the pin of the digital IC using an electric field detection probe, and opening the solder connection of the pin and the adjacent pin based on the detected intensity. It is characterized in that a short circuit between them is determined.

[Procedure amendment 3]

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[Correction target item name] 0021

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[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining a method for inspecting solder connection of a digital IC using an electric field detection probe according to the first embodiment of the present invention. Digital IC
Reference numeral 4 denotes solder pins of the pins 5a and 5b on board pads 2a and 2b (usually formed by patterning copper foil by thickening copper plating). An electric field detection probe 8 is arranged close to a pin shoulder 6 of the pin 5b with respect to the pin 5b to be inspected, and an AC signal 11 from a signal source 10 is applied to the corresponding substrate pad 2b by using a stylus probe 13. 2b. Ground 12 of the signal source 10 is connected to the substrate ground 3 of the printed circuit board 1. This is to short-circuit the ground pins (not shown) of all the ICs connected to the board ground 3 of the printed circuit board 1 to the ground 12 of the signal source 10 in order to prevent signals from being supplied to the pins to be inspected by another path. To do that.

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[0033] In the inspection method of the first embodiment above SL,
Inspection is performed with the ground of the signal source connected to the ground line and power supply line of the printed circuit board.If there is a solder short between the input / output pin, the ground pin, and the power supply pin, an overcurrent will occur between those pins. There is a possibility that the internal circuit of the IC may be destroyed. In order to avoid or hunt problem,
The current limiter is provided on the signal source, the overcurrent can be prevented from flowing to the IC. In this case, almost no voltage is applied to the pin, and the output of the electric field detection probe is smaller than the normal solder open.

[Procedure amendment 6]

[Document name to be amended] Drawing

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Claims (6)

[Claims] 1. A digital I / O device having a plurality of pins (lead terminals) on pads on a printed circuit board and soldering the pins.
In the method of inspecting the solder connection state of the pin C by using an electric field detection probe, the pin is connected by soldering with the ground of the printed circuit board or the ground and all power supplies connected to the ground of the signal source. The signal of the signal source is applied to the pad of the printed circuit board using a stylus probe, and the electric field intensity near the shoulder of the pin of the digital IC is detected using an electric field detection probe. A method for inspecting solder connection of a digital IC using an electric field detection probe, wherein open solder connection of pins and short circuit between adjacent pins are determined. 2. The method according to claim 1, wherein the signal of the signal source is a pulse signal or a waveform signal offset to the plus side. . 3. The method according to claim 1, wherein the signal source has a current limiter. 4. The determination of the open state of the solder connection of the pins and the short-circuiting of the adjacent pins is performed in advance by performing a solder connection on a standard sample, which is a good solder connection board of a plurality of digital ICs identical to the digital ICs. The average value of the detected electric field strength of each pin is calculated in advance, a non-defective range is determined for each pin using the average value as a reference value, and the pin that is larger than the upper limit of the non-defective range is short-circuited, and the lower limit of the non-defective range is determined. 4. The method according to claim 1, wherein said small pin is determined to be open. 5. The non-defective range is set to 0.7 to 1.2 times the average value of the detected electric field strength of each pin of the standard sample connected by soldering, and the pin which is less than 0.7 times the average value is determined. 5. The method for inspecting solder connection of a digital IC using an electric field detection probe according to claim 4, wherein the pin which is open and which exceeds 1.2 times the average value is determined as a short circuit. 6. In the open determination, when the adjacent pin is a ground pin or a power supply pin and the current of the signal source has reached a set limit, the pin is determined to be short-circuited. Item 5. A method for inspecting solder connection of a digital IC using the electric field detection probe according to Item 4.