JP2006343264A - Characteristic impedance inspection device of circuit wiring board, and inspection method of characteristic impedance of circuit wiring board using device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection method and an inspection device of the characteristic impedance of a measuring line capable of determining which is generated, a contact failure between a line to be measured on a wiring circuit board and a measuring probe or an impedance failure of the line to be measured, in an inspection method for inspecting the characteristic impedance of the line to be measured on the circuit wiring board by TDR method. <P>SOLUTION: This characteristic impedance inspection device of the circuit wiring board has a characteristic impedance waveform measuring means 10 capable of measuring a characteristic impedance waveform of the line to be measured on the circuit wiring board; a normal value registering means 20 for registering beforehand a characteristic impedance value and a time until divergence occurs by the characteristic impedance waveform of the line to be measured; and a comparison/determination means 30 for calculating the characteristic impedance value and the time until the divergence occurs from the characteristic impedance waveform of the line to be measured at the inspection time, and performing comparison operation processing with normal data of the line to be measured registered beforehand, to thereby perform quality determination. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inspection apparatus and an inspection method for guaranteeing characteristic impedance of a circuit wiring board such as a semiconductor package including a high-speed signal line on which a semiconductor element is mounted.

  At present, the speed of semiconductor devices is remarkable. For example, Intel Pentium (registered trademark) 4 exceeds 3 GHz, and Rambus memory RDRAM has 800 MHz. High-speed signal characteristics have also been required for circuit wiring boards including substrate boards used for these components.

That is, since the wavelength becomes shorter as the frequency becomes higher, even a short line length such as a semiconductor package cannot be ignored. For example, since the wavelength is 10 cm at 3 GHz, including the connection length with the peripheral components in which the device is used, the length can be longer than the wavelength, so that the signal reflection cannot be ignored.
Therefore, characteristic impedance matching that has not been particularly problematic in the past has been required.

As a method for measuring the characteristic impedance of a wiring board, a TDR (Time Domain Reflectometry) method is generally used in which a step pulse with a fast rise time (usually about 25 ps to 45 ps) is applied and the characteristic impedance is obtained from the level of the reflected wave. Used.
Therefore, a high-frequency probe suitable for measuring a TDR (Time Domain Reflectometry) characteristic of a conductor pattern on an inspection target substrate such as a high-frequency circuit board has been proposed (for example, see Patent Document 1).

  In an inspection device that measures and inspects the characteristic impedance of a circuit wiring board, the sampling oscilloscope that can be measured by the TDR method is in contact with the line to be measured via the high-frequency measurement cable and the high-frequency measurement probe that matches the shape of the line to be measured. And measure the results, and check the results.

Therefore, the inspection apparatus is an apparatus that automatically moves the probes one after the other according to pre-programmed inspection conditions for each object to be inspected to contact the line to be measured.
Japanese Patent Laid-Open No. 2003-4768

  Even if the probe is in contact with the line to be measured as an automatic inspection machine, there are cases where the line to be measured is broken halfway including vias, and there is no measurement waveform because the probe itself is not correctly in contact. There is a problem that cannot be distinguished.

  Explaining with reference to the drawing, the measurement waveform that is open at the probe end as shown in FIG. 3 and the measurement waveform that appears due to disconnection or poor contact even if the probe is in contact with the line to be measured This means that it cannot be distinguished from the waveform.

As an inspection device, there are several reasons why contact failure occurs when it is brought into contact with the line to be measured, but one is that the area of contact with the probe is small. This is because the copper pad of the wiring board cannot have a large opening portion of a solder resist (hereinafter referred to as SR) (as a product, there is a case where it is desired to reduce the area of this portion as much as possible, while on the other hand, the manufacturing process) (There is a situation that the top cannot be plated unless SR is attached).

Another major reason is displacement due to the mechanical accuracy of the inspection apparatus.
The allowable accuracy of repeated positioning determined from the opening area of the SR is ± 20 μm at the maximum, but the repeated position accuracy of the probe shaft of the inspection apparatus is absolutely difficult (including sudden phenomena) to be within this range. There is.

  In addition, since there is a thickness of SR (about 20 μm), there may be a situation that even if only the probe tip is in the SR opening, it is not in contact with the copper pad.

In addition, the inspected wiring circuit board side also has variations due to the relationship between patterning accuracy (including shrinkage of the base material) and SR relative position accuracy.
That is, even if the mechanical accuracy is high, contact failure due to variations on the inspected wiring circuit board side can occur.

  In addition, the elements caused by the inspected wiring circuit board side also include poor contact due to insufficient pressing of the measurement probe due to height variations due to warpage, distortion, etc. in the thickness direction of the inspected wiring circuit board. Yes.

  In any case, since it is not possible to determine whether or not the defect is truly caused by the product only from the measured waveform data, there has been a problem that a characteristic impedance abnormality due to a contact failure causes a product failure.

  The present invention has been devised in view of the above problems. In the inspection method for inspecting the characteristic impedance of the line to be measured of the circuit wiring board by the TDR method, the contact between the line to be measured on the wiring circuit board and the measurement probe is poor. An object of the present invention is to provide an inspection method and an inspection apparatus for characteristic impedance of a measurement line that can determine whether the impedance of the measurement line is defective.

  In order to achieve the above object in the present invention, first, in the inspection apparatus for inspecting the characteristic impedance of the circuit wiring board by the TDR method, the characteristic impedance waveform measuring means 10 and the characteristic impedance of the line to be measured are provided. A normal value registration means 20 for registering in advance the characteristic impedance value and the time until divergence from the waveform, and calculating the characteristic impedance value and the time until divergence from the characteristic impedance waveform of the line under test at the time of inspection, The circuit wiring board characteristic impedance inspection apparatus includes comparison / determination means 30 that performs comparison calculation processing with the registered data of the measured line and performs pass / fail determination.

  According to claim 2, in the inspection method for inspecting the characteristic impedance of the line to be measured of the circuit wiring board by the TDR method, in order to determine the contact failure of the measurement probe to the line to be measured of the circuit wiring board, From the characteristic impedance waveform of the measured line when the measurement probe is correctly in contact with the measured line, the process of registering the characteristic impedance value and the time until divergence, and the characteristic impedance measured waveform at the time of inspection, the characteristic impedance Calculates the value and the time to diverge, compares it with the pre-registered data of the measured line, and compares it with the characteristic impedance waveform of the measured line or the open waveform due to poor contact of the measuring probe The circuit wiring board is characterized by having a step of determining and eliminating pseudo defects due to poor contact of the measurement probe. It is obtained by the inspection method of impedance.

By inspecting the characteristic impedance of the printed circuit board using the characteristic impedance inspection apparatus of the present invention, detection conditions can be set in a relatively simple manner for each line to be measured on the printed circuit board, thereby preventing erroneous detection. Is possible.
In addition, since a pseudo defect due to a contact failure of the measurement probe can be identified as a defect, even if the characteristic impedance is inspected by an automatic inspection machine, it is possible to avoid a defect that causes a characteristic impedance abnormality due to a contact failure of the measurement probe as a product failure. it can.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is a schematic configuration schematic diagram showing an embodiment of a characteristic impedance inspection apparatus for a circuit wiring board according to the present invention.

The characteristic impedance inspection device 100 for a circuit wiring board includes a characteristic impedance waveform measuring unit 10 that can measure a characteristic impedance waveform of a line to be measured on the circuit wiring board, and a time until the characteristic impedance value diverges from the characteristic impedance waveform of the line to be measured. And the normal value registration means 20 for pre-registering, and the characteristic impedance value and the time until divergence are calculated from the characteristic impedance waveform of the measured line at the time of inspection, and the normal data of the measured line registered in advance And a comparison / determination means 30 for performing a comparison calculation process and determining pass / fail.
For example, a TDR oscilloscope or the like is used as the characteristic impedance waveform measurement unit 10, and a computer device is used as the normal value registration unit 20 and the comparison / determination unit 30, for example.

  Hereinafter, a method for inspecting the characteristic impedance of the line to be measured of the circuit wiring board using the characteristic impedance testing apparatus 100 for the circuit wiring board will be described.

The characteristic impedance waveform measuring means 10 has a built-in digital sampling oscilloscope that can be measured by a TDR (Time Domain Reflectometry) method.
When measuring the characteristic impedance of the line to be measured on the circuit wiring board by the TDR method, a dedicated probe is used in consideration of the high frequency characteristics. Measure with a high-frequency probe consisting of GND-SIGNAL-GND with a fine pitch (usually several 100 μm).
When this measurement probe is brought into contact with the pad portion of the line to be measured, the tip portion is slid in order to improve the adhesion. That is, the contact position moves by utilizing the fact that the probe plate itself bends when pushed in the vertical direction (z-axis).

In addition, an opening of a solder resist (hereinafter referred to as SR) is formed in the pad portion of the line to be measured, and the measurement probe is brought into contact with the opening.
At this time, the SR has a minimum SR width, and the distance between the SIGNAL adjacent to the GND is determined, so that the opening dimension of the SIGNAL portion is about 100 μm due to restrictions. This is about twice the plate width of the measurement probe. Therefore, the tolerance in the width direction between the pad of the line to be measured and the probe tip is only about ± 25 μm, and this can be said to be the limit of the tolerance of mechanical accuracy allowed for the apparatus.
In addition to such a dimensional relationship, the contact state of the measurement probe depends on the variation due to the deflection of the circuit wiring board, the thickness of the SR itself (about 20 μm), and the opening position accuracy of the pad portion of the circuit wiring board and the line to be measured. It will change, and the contact failure of a measurement probe will occur.

First, a measurement probe consisting of a dedicated high-frequency probe is brought into contact with the pad portion of the line to be measured on the circuit wiring board, and the characteristic impedance of each line to be measured on the circuit wiring board is measured by the characteristic impedance waveform measuring means 10 consisting of a digital sampling oscilloscope. Then, the characteristic impedance value Z _n and the time t _n until the divergence are registered in the normal value registration means 20 from the obtained characteristic impedance waveform of each measured line.
An example of the characteristic impedance waveform of the measured line at that time is shown in FIG. 2, and an example of the measurement waveform when the measurement probe is open is shown in FIG.
Here, in the characteristic impedance waveform 41, Z ₁ is the characteristic impedance value when the measurement probe is open, t ₁ is the time when the characteristic impedance Z ₁ diverges, Z _n is the characteristic impedance value of the line to be measured, t _n denotes a time until the characteristic impedance Z _n diverges.

Next, automatic inspection of the characteristic impedance of the transmission line to be measured of the circuit wiring board is started, the characteristic impedance waveforms of the measured line has been tested and measured, until the characteristic impedance value Z _n and the divergence of the measurement line The time t _n is displayed on the comparison / determination means 30 and is compared with the data of the measured line registered in advance, depending on whether the characteristic impedance waveform of the measured line is good or bad, and the measurement probe contact failure Determine if open waveform.
Here, comparing and the determining means 30, to determine the acceptability of the characteristic impedance of the transmission line to be measured of the circuit wiring board in the automatic inspection, the characteristic impedance of the transmission line to be measured of the circuit wiring board value Z _n and the divergent By appropriately setting the threshold value of the time t _n until the measurement, it is possible to accurately determine whether the characteristic impedance value of the measured line is good or bad or whether the characteristic impedance value is bad due to poor contact of the measurement probe.
Specifically, since the characteristic impedance value Z _n cannot be manufactured at a constant value (design value Z ₀ ± 10% tolerance, etc.), it is checked whether it is within a certain range (Z _{n1 to} Z _n2 )
When the measured value> Z _n2, the pseudo open is determined, and when the measured value <Z _n1 , the pseudo short is determined.

  The circuit wiring board determined to have a contact failure of the measurement probe is subjected to the characteristic impedance inspection again by adjusting the measurement probe position again.

It is a schematic block diagram which shows one Example of the characteristic impedance test | inspection apparatus of the circuit wiring board of this invention. It is explanatory drawing which shows an example of the characteristic impedance waveform of each to-be-measured track | line of a circuit wiring board. It is explanatory drawing which shows an example of a characteristic impedance waveform when a measurement probe is open.

Explanation of symbols

10: Characteristic impedance waveform measuring means 20: Normal value registering means 30 for registering in advance the characteristic impedance value and time until divergence 30 ... Comparison / determination means 41, 42 ... Characteristic impedance waveform 100 ... Circuit wiring board Characteristic impedance testing equipment

Claims (2)

  In the inspection apparatus for inspecting the characteristic impedance of the circuit wiring board by the TDR method, the characteristic impedance waveform measuring means (10) and the normal value for registering in advance the characteristic impedance value and the time until divergence from the characteristic impedance waveform of the line to be measured From the registration means (20) and the characteristic impedance waveform of the measured line at the time of inspection, the characteristic impedance value and the time until divergence are calculated, and the data of the measured line registered in advance are compared and processed. A circuit impedance characteristic inspection apparatus for a circuit wiring board, comprising: a comparison / determination means (30) for performing quality determination.   In the inspection method for inspecting the characteristic impedance of the line to be measured on the circuit wiring board by the TDR method, in order to determine the contact failure of the measurement probe to the line to be measured on the circuit wiring board, the measurement probe is correctly connected to the line to be measured in advance. The process of registering the characteristic impedance value and the time until divergence from the characteristic impedance waveform of the line to be measured when in contact, and the characteristic impedance value and the time until divergence from the characteristic impedance measurement waveform at the time of inspection And calculating and comparing with the data of the measured line registered in advance and comparing the characteristic impedance waveform of the measured line with the open waveform due to poor contact of the measurement probe, Method for inspecting characteristic impedance of circuit wiring board, characterized by eliminating false defects due to poor contact of probe

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