JP2010164427A - Apparatus and method of inspecting printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection apparatus of a printed circuit board for accurately determining the quality of the printed circuit board using a TDR. <P>SOLUTION: The inspection apparatus 1 of the printed circuit board includes a pulse generator 41 for generating pulses, a probe 32, an oscilloscope 46 and a determination unit 53. The probe 32 is used for applying a pulse wave to the wiring pattern on the printed circuit board connected to an inspection region. The oscilloscope 46 measures through the probe 32 a reflection wave which is the pulse wave reflected from the printed circuit board. The determination unit 53 determines the quality of the inspection region of the printed circuit board to be inspected by comparing the differentiated waveform of the reflection wave measured for the printed circuit board to be inspected with the differentiated waveform of the reflection wave measured, in advance, for the reference printed circuit board. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an inspection apparatus and an inspection method for electrically inspecting a short circuit or disconnection of an inspection portion of a printed circuit board.

  Solder using TDR (Time Domain Reflectometer) to electronic parts that are difficult to see the solder connection, such as BGA (Ball Grid Array) and SOJ (Small Outline J-leaded) packages. A method for performing a false inspection is known.

  For example, in the technique disclosed in Japanese Patent Laid-Open No. 9-61486 (Patent Document 1), a pulse wave generated by a high-frequency pulse generator is applied from a land of a substrate to a substrate wiring via a high-frequency probe. At this time, the waveform of the reflected wave caused by the difference in the line impedance of the propagation path of the pulse wave, particularly the waveform of the reflected wave due to the difference between the open state and the shorted state of the solder connection portion between the terminal of the integrated circuit device and the substrate Measure the difference with an oscilloscope. Then, the waveform measurement result is analyzed by the waveform analyzer to identify the quality state of the solder connection portion.

JP-A-9-61486

  As described above, in the TDR measurement, a pulse having a high-speed rising waveform is input to a via on a printed circuit board through a probe. Then, the quality of the printed circuit board is determined by comparing the reflected waveform of the input pulse with the previously measured reflected waveform of the printed circuit board for reference.

  However, when the distance from the pulse input point to the BGA package to be inspected is long, or when a low impedance element is interposed between the pulse input point and the BGA package, the waveform of the input pulse is distorted. Therefore, it is impossible to measure with high accuracy.

  In addition, even when the contact between the printed circuit board and the probe is poor, the input pulse is attenuated, making it difficult to measure with high accuracy. In extreme cases, even if the printed circuit board for measurement is a non-defective product, it may be determined to be defective due to poor probe contact.

  A main object of the present invention is to provide a printed circuit board inspection apparatus that uses TDR to accurately determine the quality of an inspection region of a printed circuit board.

  In summary, the present invention is a printed circuit board inspection apparatus that inspects the quality of an inspection site of a printed circuit board, and includes a pulse generator that outputs a pulse wave, a probe, a measuring instrument, and a determination unit. The probe is used to apply a pulse wave to a wiring pattern on a printed circuit board connected to an inspection site. The measuring instrument measures a reflected wave obtained by reflecting the pulse wave from the printed board through the probe. The determination unit compares the differential waveform of the reflected wave measured with respect to the printed circuit board for inspection with the differential waveform of the reflected wave measured in advance with respect to the printed circuit board for reference. The quality of the examination site is determined.

  According to the present invention, it is possible to accurately determine the quality of the inspection portion of the printed circuit board by using the differential waveform of the reflected wave.

It is a block diagram which shows the structure of the printed circuit board inspection apparatus 1 according to embodiment of this invention. It is a figure which shows the schematic structure of the interface part 30 among the printed circuit board test | inspection apparatuses 1 of FIG. FIG. 3 is an enlarged view of a part of an interface unit 30 in FIG. 2. It is a figure for demonstrating the problem of the inspection method of the printed circuit board 20 by the conventional TDR. It is a figure which shows an example of the voltage waveform of each part of FIG. It is a flowchart which shows the test | inspection procedure using the printed circuit board test | inspection apparatus 1 of FIG. It is a flowchart which shows the detailed procedure of step S6 of FIG. It is a figure for demonstrating step S12 of FIG. It is a figure which shows the example of the measurement waveform by the printed circuit board inspection apparatus. It is a figure for demonstrating the principle of the quality determination method by the printed circuit board inspection apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Configuration of printed circuit board inspection apparatus 1)
FIG. 1 is a block diagram showing a configuration of a printed circuit board inspection apparatus 1 according to an embodiment of the present invention. Referring to FIG. 1, printed circuit board inspection apparatus 1 includes a time domain reflectometer (TDR) 40, an interface unit 30, and a computer 50 as a control unit.

  The TDR 40 includes a pulse generator 41 that outputs a steep rising pulse wave, and an oscilloscope 46 as a measuring instrument that measures the waveform of the reflected wave of the pulse wave output from the pulse generator 41. The pulse generator 41 and the oscilloscope 46 are connected to the connector 35 of the interface unit 30 by a high frequency cable 37. The pulse wave output from the pulse generator 41 is applied to the printed circuit board (reference numeral 20 in FIG. 2) via the interface unit 30. The oscilloscope 46 detects a reflected wave generated by reflecting the pulse wave by the printed circuit board 20 via the interface unit 30. The reflected wave detected by the oscilloscope 46 is digitally converted and output to the computer 50.

  FIG. 2 is a diagram showing a schematic configuration of the interface unit 30 in the printed circuit board inspection apparatus 1 of FIG. FIG. 2 also shows a schematic configuration of the printed circuit board 20 to be inspected.

  FIG. 3 is an enlarged view of a part of the interface unit 30 of FIG. 2 and 3, the cross-sectional portion is hatched.

  2 and 3, the printed circuit board 20 is obtained by mounting a large number of electronic components on an insulating substrate 21 on which a wiring pattern is formed (that is, the printed wiring board 20A). The wiring pattern includes a conductive layer 22 embedded in the through hole, lands 23 and 24 connected to the conductive layer 22, and the like.

  The printed circuit board inspection apparatus 1 of the present embodiment inspects the quality of the solder connection state of electronic components mounted on the printed wiring board 20A. FIG. 2 shows an IC (Integrated Circuit) package 10 (also referred to as a BGA package 10) mounted by BGA as one of inspection targets. BGA is a method of mounting with solder balls 11 formed in a lattice pattern on the back surface of the package. In BGA, since the solder connection portion is on the back surface of the package, it is difficult to visually inspect the solder connection state. Therefore, the printed circuit board inspection apparatus 1 is used to inspect the quality of the connection state of the solder balls 11 that are inspection parts by time domain reflectance measurement (TDR method).

  The interface unit 30 includes an insulating substrate 33, a wiring pattern 34 formed on the substrate 33, a plurality of probes 32, and an insulating block 31 in which the plurality of probes 32 are embedded. A plurality of probes 32 are provided to inspect a plurality of inspection parts of the printed circuit board 20 at a time.

  The probe 32 includes a cylindrical portion 32A, first and second contacts 32B and 32C inserted at both ends of the cylindrical portion 32A, and a spring member 32D provided between the contacts 32B and 32C. The first contact 32B is in electrical contact with the land 24 of the printed circuit board 20 to be inspected. In order to obtain a good electrical contact, the end of the contact 32B has a shape protruding in a crown shape. The second contact 32 </ b> C is in electrical contact with the wiring pattern 34 formed on the substrate 33. The contact 32 </ b> C is connected to the connector 35 via the wiring pattern 34.

  The spring member 32D biases the contacts 32B and 32C so as to protrude from both ends of the cylindrical portion 32A. This ensures electrical contact between the probe 32 and the land 24 of the printed circuit board 20 and between the probe 32 and the wiring pattern 34.

  In addition, the board | substrate 33 with which the wiring pattern 34 was formed becomes a structure which can be replaced | exchanged according to the printed circuit board 20 to be examined. It is preferable that the surface of the wiring pattern 34 is gold-plated so as to ensure electrical contact when the printed circuit board 20 for inspection is replaced.

  Referring to FIG. 1 again, the interface unit 30 further includes a plurality of switches 36 such as relays. Each switch 36 corresponds to each probe 32 individually, and is provided in the path of the wiring pattern 34 that connects each probe 32 and the connector 35. The computer 50 sequentially switches the probes 32 connected to the TDR 40 by switching the connection of the switch 36. In this way, the printed circuit board inspection apparatus 1 sequentially inspects the quality of the plurality of solder connection portions 11 of the IC package 10 shown in FIG.

  Next, the configuration of the computer 50 will be described. The computer 50 includes a central processing unit, a memory circuit, an interface circuit for inputting / outputting signals, and the like. Viewed functionally, the computer 50 includes a measurement control unit 54, a differential calculation unit 51, a storage unit 52, and a determination unit 53.

  The measurement control unit 54 controls the timing at which the pulse generator 41 outputs a pulse wave. Further, the measurement control unit 54 selectively connects the solder ball 11 to be inspected and the TDR 40 by switching the switch 36 of the interface unit 30. Thus, the pulse wave output from the pulse generator 41 reaches the solder ball 11 that is the inspection site via the wiring pattern 34 of the interface unit 30, the probe 32, and the wiring pattern of the printed circuit board 20 for inspection shown in FIG. To do. The reflected wave generated according to the connection state of the solder ball 11 returns to the pulse generator 41 along the reverse path and is detected by the oscilloscope 46.

  The differential calculation unit 51 differentiates the waveform data of the reflected wave detected by the oscilloscope 46. Since the waveform of the reflected wave input to the differentiation calculation unit 51 is digital data, the differentiation can be approximated by a difference quotient. The reflected wave waveform data and its differential waveform data are output to the determination unit 53.

  The storage unit 52 stores the waveform of the reflected wave measured using a good reference printed circuit board as a reference waveform. Further, the storage unit 52 stores a differential waveform of the reference waveform.

  The determination unit 53 compares the differential waveform of the reflected wave measured with respect to the printed circuit board for inspection with the differential waveform of the reference waveform measured in advance. Based on the result of the waveform comparison, the determination unit 53 determines whether the probe 32 is in good contact and whether the examination site is good. By comparing the differential waveforms in this way, the inspection site of the printed circuit board 20 can be inspected with higher accuracy than in the past.

(Judgment method of printed circuit board quality)
Next, the printed circuit board inspection apparatus 1 shown in FIG. 1 will be described in detail with reference to a printed circuit board inspection method according to the TDR method.

  FIG. 4 is a diagram for explaining a problem of the conventional method for inspecting the printed circuit board 20 by TDR. Referring to FIG. 4, printed circuit board 20 includes a wiring pattern 25, a ground pattern 27, and a BGA package 10 and a capacitor 26 connected between the wiring pattern 25 and the ground pattern 27. In order to inspect the connection state of the BGA package 10, the pulse wave output from the pulse generator 41 sequentially passes through the wiring pattern 34, the probe 32, and the wiring pattern 25 of the interface unit 30 and reaches the BGA package 10. . Then, the reflected wave obtained by reflecting the pulse wave by the BGA package 10 reaches the TDR 40 by reversing the path of the input pulse wave, and is measured by the oscilloscope 46.

FIG. 5 is a diagram illustrating an example of a voltage waveform at each part in FIG.
FIG. 5A shows an example of the waveform of the pulse wave output from the pulse generator 41. The magnitude of the pulse wave rising at time t1 in FIG. 5A is about 400 mVpp (pp represents peak-to-peak).

  FIG. 5B shows an example of the waveform of the reflected wave measured by the oscilloscope 46. Referring to FIGS. 4 and 5B, the pulse wave actually output from TDR 40 is reflected by a large number of elements mounted on printed circuit board 20. Furthermore, since the reflected wave is related to the impedance and length of the wiring, the reflected wave measured by the oscilloscope 46 becomes a complex waveform 81 as shown in FIG. Therefore, in the conventional TDR, the quality of the printed circuit board is determined by comparing the measurement waveform of the measurement printed circuit board with the reference waveform measured in advance by the reference printed circuit board.

  For example, if the voltage divergence between the measurement waveform and the reference waveform exceeds a threshold value (for example, about 50 mV) even for a moment, the printed circuit board 20 is determined to be abnormal. Further, if the deviation continues for a threshold time or longer (for example, about 200 to 400 p seconds) even with a deviation width lower than the threshold, the printed circuit board 20 is determined to be abnormal.

  When setting the threshold values for these deviation widths, the standard deviation of data is obtained from waveforms measured for a plurality of normal printed circuit boards during mass production, and the threshold value is set based on the standard deviation. desirable. When the variation in the waveform of the reflected wave is actually calculated using a large number of non-defective printed circuit boards, about 1% of the magnitude of the pulse output from the TDR 40 is equal to the standard deviation. For example, in the case of a 400 mVpp pulse, the standard deviation σ is about 4 mV. Therefore, the threshold of the deviation width needs to be set to at least 3σ = 12 mV or more.

  Here, as shown in FIG. 4, when the capacitor 26 is present up to the BGA package 10 to be measured, the high frequency component of the incident pulse wave is reflected by the capacitor 26 as in the case of the short-circuited termination. As a result, the high frequency component of the pulse wave traveling forward from the capacitor 26 is attenuated, so that the waveform of the reflected wave from a position farther than the capacitor 26 with respect to the probe 32 as shown by a broken line waveform 82 in FIG. Becomes smaller. For this reason, it is difficult to determine whether the connection state of the BGA package 10 is good or bad.

  Further, as the wiring pattern 25 to the BGA package 10 to be measured becomes longer, the high-frequency component of the pulse wave attenuates before the pulse wave of the fast rising waveform reaches the BGA package 10 to be measured. The reflected waveform becomes smaller. For this reason, it is difficult to determine whether the connection state of the BGA package 10 is good or bad.

  Further, poor contact between the probe 32 and the wiring pattern 25 is one of the causes that makes it difficult to determine whether the connection state of the BGA package 10 is good or bad.

  FIG. 5C is an example of the waveform of the reflected wave when the probe 32 has a poor contact. FIG. 5C shows a comparison between a reflected wave waveform 83 when the probe 32 is in good contact and a reflected wave waveform 84 when the probe 32 is in poor contact.

  As shown in FIG. 5C, when the probe 32 is in poor contact, the contact resistance between the probe 32 and the printed circuit board 20 increases, and therefore a voltage drop corresponding to the contact resistance appears in the waveform as an offset. For this reason, there is a possibility that the printed circuit board 20 in which the connection state of the BGA package 10 is good is erroneously determined as defective. In addition, when the contact of the probe 32 is poor, the overall tendency such as the unevenness of the waveform does not change as compared with the case where the contact is good.

  Therefore, the printed circuit board inspection apparatus 1 in FIG. 1 determines the quality of the printed circuit board 20 based on the differential waveform of the reflected wave. Thereby, even when the input pulse wave is attenuated due to the presence of a capacitor which has been difficult in the past, it is possible to accurately determine whether the connection state of the BGA package 10 is good or bad. Furthermore, erroneous determination due to poor probe contact can be prevented.

  FIG. 6 is a flowchart showing an inspection procedure using the printed circuit board inspection apparatus 1 of FIG. The inspection procedure of FIG. 6 is started after each probe 32 is brought into contact with a land in the vicinity of each inspection portion of the printed circuit board.

  Referring to FIGS. 1 and 6, in step S1, measurement control unit 54 turns on switch 36 connected to solder ball 11 of BGA package 10 of FIG. It is switched to become. As a result, the solder balls 11 of the BGA package 10 that is the measurement site and the TDR 40 are connected via the probe 32.

  In the next step S2, the measurement control unit 54 applies a pulse wave to the printed circuit board for inspection via the interface unit 30 by the pulse generator 41.

  In the next step S3, the oscilloscope 46 measures the reflected wave of the pulse wave input to the printed circuit board for inspection. The waveform of the reflected wave measured by the oscilloscope 46 is digitally converted and input to the computer 50.

  In the next step S4, the differential calculation unit 51 of the computer 50 performs a moving average of the measured reflected wave data. Data before and after each data is used for calculating the moving average. Note that step S4 is not necessarily a necessary step, but is preferably performed when there is variation in the measured reflected wave waveform data.

  In the next step S5, the differential operation unit 51 calculates a differential waveform of the reflected wave. Here, since the waveform of the reflected wave input to the computer 50 is digital data, the differentiation can be approximated by a difference quotient.

  In the next step S6, the determination unit 53 determines the differential waveform of the reflected wave (also referred to as a measurement waveform) measured with respect to the inspection printed board and the reflected wave (also referred to as a reference waveform) previously measured with the reference printed board. ) And the differential waveform. Based on the comparison result of the differential waveform, the determination unit 53 determines whether the probe 32 is in good contact and whether the examination site is good.

FIG. 7 is a flowchart showing a detailed procedure of step S6 of FIG.
Referring to FIGS. 1 and 7, in step S11, determination unit 53 compares the differential waveform of the reflected wave on the inspection printed board with the differential waveform of the reflected wave on the reference printed board. It is determined whether or not the deviation width of the waveform (that is, the absolute value of the difference between the differential values at each time) exceeds a predetermined threshold TH1. If the differential waveform deviation width exceeds the threshold value TH1 even at one time point (YES in step S11), the process proceeds to step S12. If the differential waveform deviation width is equal to or smaller than the threshold value TH1 at any time point (NO in step S11), step is performed. Proceed to S21. First, the case where the deviation width of the differential waveform exceeds the threshold value TH1 (YES in step S11) will be described.

  FIG. 8 is a diagram for explaining step S12 in FIG. FIG. 8 shows the voltage waveform of the reflected wave.

  1 and 8, the pulse wave output from pulse generator 41 rises at time t1. Here, the propagation time of the pulse wave from the TDR 40 to the probe 32 is Ta, and the propagation time of the pulse wave from the TDR 40 to the BGA package 10 is Tb (where Tb> Ta). Then, the TDR 40 observes the reflection from the probe 32 at time t2 when 2 × Ta has elapsed from time t1, and observes the reflection from the BGA package 10 at time t3 when time has elapsed by 2 × Tb from time t1. To do. Note that the reflections observed at times t2 and t3 are reflections of the rising portion of the input pulse wave.

  Therefore, when the connection state of the solder balls 11 of the BGA package 10 is defective, as shown in FIG. 8, the reference waveform 85 measured for the reference printed board in advance after time t3 and the reflection of the printed board for inspection. There is a deviation from the measured waveform 86 of the wave. On the other hand, in the case of poor contact of the probe 32, a difference occurs between the reference waveform 85 and the measurement waveform 86 after time t2.

  The characteristic of the differential waveform of the reflected wave is slightly different from the characteristic of the reflected wave itself shown in FIG. When the connection state of the BGA package 10 is defective, a difference occurs between the differential waveform of the reference waveform 85 and the differential waveform of the measurement waveform 86 after time t3. This point is not different from the characteristics of the reflected wave itself. On the other hand, when the probe 32 is in poor contact, there is a difference between the differential waveform of the reference waveform 85 and the differential waveform of the measurement waveform 86 only in the vicinity of time t2. Subsequent times, there is almost no divergence between the differential waveform of the reference waveform 85 and the differential waveform of the measured reflected wave waveform 86. The quality determination procedure in FIG. 7 uses the characteristics of the differential waveform.

  Referring to FIGS. 1 and 7 again, in step S12, the determination unit 53 confirms the time at which the deviation width between the differential waveform of the reference waveform and the differential waveform of the measurement waveform exceeds the threshold value TH1. Then, in the next step S13, it is determined whether or not there is a divergence of the differential waveform only near the observation time of the reflection from the probe 32 (corresponding to the time t2 in FIG. 8). The observation time of reflection from the probe 32 means the observation time of reflection at the rising portion of the incident pulse wave.

  If the result of determination in step S13 is that there is a divergence in the differential waveform only near the observation time of reflection from the probe 32 (YES in step S13), the process proceeds to step S17.

  In step S17, the determination unit 53 determines whether or not the difference width of the differential waveform near the observation time of the reflection from the probe 32 exceeds the threshold value TH2 (usually, the threshold value TH2 is set to a value different from the threshold value TH1). Determine. As a result, when the deviation width of the differential waveform exceeds the threshold value TH2 (YES in step S17), the determination unit 53 determines that the probe is in poor contact and ends the process (step S18). Further, when the deviation width of the differential waveform is equal to or smaller than the threshold value TH2 (NO in step S17), the determination unit 53 determines that the connection state of the solder ball 11 of the BGA package 10 that is the inspection site is good and performs the processing. The process ends (step S19).

  On the other hand, if the result of determination in step S13 is that there is a divergence in the differential waveform after the time when reflection from the probe 32 is observed (NO in step S13), the process proceeds to step S14.

  In step S14, the determination unit 53 has a differential waveform exceeding the threshold value TH1 at least at one time point after the observation time (corresponding to the time t3 in FIG. 8) of reflection from the solder ball 11 of the BGA package 10 that is the inspection part. It is determined whether or not there is a divergence. As a result, if there is a difference in the differential waveform after the observation time of reflection from the inspection site (YES in step S14), the determination unit 53 indicates that the solder ball 11 of the BGA package 10 that is the inspection site is defective. And the process is terminated (step S15). Further, when the differential waveform has a divergence before the observation time of the reflection from the inspection site (NO in step S14), the determination unit 53 is not the solder ball 11 of the BGA package 10 that is the inspection site. Is determined to be defective, and the process is terminated (step S16).

  Next, a case will be described where the divergence width of the differential waveform is equal to or less than the threshold value TH1 in step S11 (NO in step S11). In this case, in the next step S21, the determination unit 53 compares the waveform of the reflected wave on the inspection printed circuit board with the reference waveform of the reference printed circuit board. Then, the determination unit 53 determines whether or not the absolute value (that is, the deviation width) of the difference between the reflected wave waveform and the reference waveform exceeds the threshold value TH3.

  As a result of the determination in step S21, when the divergence width of the reflected wave exceeds the threshold value TH3 (YES in step S21), the determination unit 53 determines that the probe is in poor contact and ends the process (step S22). On the other hand, as a result of the determination in step S21, when the divergence width of the reflected wave is equal to or smaller than the threshold TH3 (NO in step S21), the determination unit 53 determines that the examination site is good and ends the process (step S23).

  Here, when the probe 32 is actually in poor contact, the contact resistance between the probe 32 and the wiring pattern 25 of the printed circuit board 20 is several tens of ohms. When the threshold value TH3 is set to about 12 mV in consideration of the standard deviation of the magnitude of the pulse wave output from the TDR 40, the divergence width is sufficiently larger than the threshold value TH3 of 12 mV. it can.

  FIG. 9 is a diagram illustrating an example of a waveform measured by the printed circuit board inspection apparatus 1. The upper graph in FIG. 9 shows the voltage waveform of the reflected wave measured by the oscilloscope 46, and the lower graph shows the differential waveform of the waveform of the reflected wave in the upper stage. Further, solid lines 61 and 71 in FIG. 9 show a case where a non-defective printed board is measured, and broken lines 62 and 72 in FIG. 9 show a case where a non-defective printed board is measured in a state where the probe is in poor contact. Dotted lines 63 and 73 in FIG. 9 indicate a case where a defective printed board is measured.

  First, the graphs of the solid lines 61 and 71 (good products) and the graphs of the dashed lines 63 and 73 (defective products) are compared. In this case, the difference between the waveform 61 of the non-defective product and the waveform 63 of the non-defective product is not so large, but the difference between the differential waveform 71 of the non-defective product and the differential waveform 73 of the non-defective product is shown. The width is large. Moreover, the differential waveform divergence occurs not only in some time zones. Therefore, it is possible to easily determine whether the printed circuit board is good or not by determining that the difference width of the differential waveform exceeds the threshold and the time zone (steps S11 and S13 in FIG. 7).

  Next, the graphs of the solid lines 61 and 71 (good product) and the graphs of the broken lines 62 and 72 (contact failure) are compared. In this case, the difference between the waveform 61 of the non-defective reflected wave and the waveform 62 of the reflected wave when the probe is in poor contact is large. Therefore, in the conventional method using TDR, a non-defective printed circuit board may be erroneously determined as defective.

  On the other hand, the differential waveform 71 of the reflected wave of the non-defective product and the differential waveform 72 of the reflected wave when the probe is in poor contact are separated only in a part of the time zone (observation time of the reflected wave from the probe). However, the divergence in other time zones is small. Therefore, by determining that the time zone in which the deviation width of the differential waveform exceeds the threshold is limited to a part of the time zone (steps S11, S13, and S17 in FIG. 7), it is possible to easily determine the probe contact failure.

Next, the principle of the printed circuit board quality determination method using the differential waveform will be described.
FIG. 10 is a diagram for explaining the principle of the quality determination method by the printed circuit board inspection apparatus 1. Referring to FIG. 10, printed circuit board 20 includes wiring pattern 25, ground pattern 27, BGA package 10 connected between wiring pattern 25 and ground pattern 27, capacitors 26, 26B, and 26C, and an IC package. 28. In order to inspect the connection state of the BGA package 10, the pulse wave output from the pulse generator 41 passes through the wiring pattern 34 of the interface unit 30 and the probe 32 in order, and is applied to the wiring pattern 25. At this time, in addition to the reflected wave 87 from the BGA package 10 to be measured, a reflected wave 88 from the capacitor 26B and a reflected wave 89 from the capacitor 26C and the IC package 28 are generated. Then, a synthesized wave obtained by synthesizing these reflected waves 87, 88, and 89 reaches the TDR 40 by reversing the path of the input pulse wave, and is measured by the oscilloscope 46.

  When the contact of the probe 32 is poor, the magnitude of the pulse wave applied to the printed circuit board is reduced due to the contact resistance of the probe 32, so that the combined wave of the reflected wave from each part of the printed circuit board 20 is as a whole. The size of is reduced. Therefore, the slope of the measured waveform of the TDR 40 changes at the time when the reflected wave from the probe 32 is observed, but the slope of the synthesized wave of the reflected wave from each part of the printed circuit board changes after that time. Absent. For this reason, the differential waveform of the measured waveform of the TDR 40 is deviated from the differential waveform of the reference waveform at the time when the reflected wave from the probe 32 is observed, but no deviation occurs after that time.

  On the other hand, when the connection state of the BGA package 10 is poor, the waveform of the reflected wave 87 from the BGA package 10 changes, so the waveform of the combined wave with the reflected waves 88 and 89 from other parts changes. For this reason, the position of the inflection point of the measurement waveform of the TDR 40 is greatly different from the position of the inflection point of the reference waveform. This difference in the position of the inflection point can be clearly observed as the difference between the maximum and minimum points of the differential waveform of the measured waveform and the maximum and minimum points of the differential waveform of the reference waveform (waveform 71 in FIG. 9). 73).

  Therefore, in the printed circuit board inspection apparatus 1 of the present embodiment, the differential waveform of the waveform measured by the TDR 40 is compared with the differential waveform of the reference waveform. Thereby, it is possible to easily determine whether the printed circuit board is good or not, as distinguished from the case where the probe has poor contact.

  In the case of poor contact of the probe 32, as shown by the waveform 62 in FIG. 9, the offset voltage due to the contact resistance is uniformly set to the reference waveform 61 at a time later than the time when the reflected wave from the probe 32 is observed. Is added. Therefore, the contact resistance added uniformly can be obtained by converting the voltage measured by the TDR 40 into impedance, similarly converting the voltage of the reference waveform into impedance, and taking the difference between the two. Furthermore, if the contact resistance is subtracted from the impedance-converted waveform measured by the TDR 40 with respect to a time later than the time when the reflected wave from the probe 32 is observed, then the impedance is re-converted into a voltage. It is possible to calculate a voltage waveform when there is no contact failure. However, this method has a drawback that the calculation is complicated and it takes a long time for the determination. On the other hand, according to the printed circuit board inspection apparatus 1 of the present embodiment, the case of contact failure can be accurately determined in a short time.

  The embodiment disclosed this time must be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Printed circuit board inspection apparatus, 10 BGA package, 11 Solder ball, 20 Printed circuit board, 20A Printed wiring board, 22 Contact hole conductive layer, 23, 24 Land, 25 Wiring pattern, 26, 26B, 26C Capacitor, 27 Ground pattern, 30 interface unit, 32 probe, 34 wiring pattern, 36 switch, 41 pulse generator, 46 oscilloscope, 50 computer, 51 differential operation unit, 52 storage unit, 53 determination unit, 54 measurement control unit.

Claims (8)

A printed circuit board inspection device for inspecting the quality of an inspection part of a printed circuit board,
A pulse generator that outputs a pulse wave;
A probe for applying the pulse wave to a wiring pattern on the printed circuit board connected to the inspection site;
A measuring instrument for measuring the reflected wave reflected from the printed circuit board through the probe;
By comparing the differential waveform of the reflected wave measured for the printed circuit board for inspection with the differential waveform of the reflected wave measured in advance for the printed circuit board for reference, the inspection site of the printed circuit board for inspection is A printed circuit board inspection apparatus comprising: a determination unit that determines pass / fail.   The determination unit has an absolute value of a difference between a differential waveform of the reflected wave measured with respect to the printed circuit board for inspection and a differential waveform of the reflected wave measured in advance with respect to the printed circuit board for reference. 2. The inspection part of the printed circuit board for inspection is determined to be defective when a predetermined first threshold value is exceeded at least at one time point after the time at which reflection from the inspection part is observed. The printed circuit board inspection apparatus as described.   The determination unit has an absolute value of a difference between a differential waveform of the reflected wave measured with respect to the printed circuit board for inspection and a differential waveform of the reflected wave measured in advance with respect to the printed circuit board for reference. The contact between the probe and the printed circuit board for inspection is determined to be poor when a predetermined second threshold value is exceeded only near the time at which reflection from the probe is observed. The printed circuit board inspection apparatus described in 1.   The determination unit has an absolute value of a difference between a differential waveform of the reflected wave measured with respect to the printed circuit board for inspection and a differential waveform of the reflected wave measured in advance with respect to the printed circuit board for reference. Of the difference between the reflected wave measured for the printed circuit board for inspection and the reflected wave measured for the printed circuit board for reference in advance. The printed circuit board inspection according to claim 1, wherein the contact between the probe and the inspection printed circuit board is determined to be poor when the absolute value exceeds a predetermined fourth threshold value at least at one time point. apparatus. A method for inspecting a printed circuit board for inspecting the quality of an inspection part of a printed circuit board for inspection,
Applying a pulse wave via a probe to a wiring pattern on the printed circuit board for inspection connected to the inspection site;
Measuring the reflected wave reflected from the printed circuit board for inspection through the probe;
The step of determining pass / fail of the inspection site by comparing the differential waveform of the reflected wave measured with respect to the printed circuit board for inspection with the differential waveform of the reflected wave previously measured with respect to the printed circuit board for reference. A method for inspecting a printed circuit board.   The step of determining pass / fail of the inspection site is a difference between a differential waveform of the reflected wave measured with respect to the printed circuit board for inspection and a differential waveform of the reflected wave previously measured with respect to the printed circuit board for reference. Is determined to be defective when the inspection part of the printed circuit board for inspection is defective when the absolute value of the inspection value exceeds a predetermined first threshold at least at one time after the time when reflection from the inspection part is observed. The printed circuit board inspection method according to claim 5, further comprising:   The step of determining pass / fail of the inspection site is a difference between a differential waveform of the reflected wave measured with respect to the printed circuit board for inspection and a differential waveform of the reflected wave previously measured with respect to the printed circuit board for reference. When the absolute value of the probe exceeds a predetermined second threshold value only near the time when reflection from the probe is observed, it is determined that the contact between the probe and the printed circuit board for inspection is poor. The printed circuit board inspection method according to claim 5, comprising a step.   The step of determining pass / fail of the inspection site is a difference between a differential waveform of the reflected wave measured with respect to the printed circuit board for inspection and a differential waveform of the reflected wave previously measured with respect to the printed circuit board for reference. Is within a third threshold value determined at any time, and is measured in advance with respect to the reflected wave measured with respect to the printed circuit board for inspection and the printed circuit board for reference. A step of determining that the contact between the probe and the printed circuit board for inspection is poor when the absolute value of the difference from the reflected wave exceeds a predetermined fourth threshold at at least one time point. Item 6. A printed circuit board inspection method according to Item 5.

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