JPH0480604A - Scanning tunneling microscope and through-hole plating inspection device including same - Google Patents

Abstract

PURPOSE:To enable an inner surface of a fine hole to be observed by designing a traveling mechanism which can change a position of a probe in cylindrical coordinate and by forming the probe in a shape for scanning an inner surface of the fine hole. CONSTITUTION:A probe 1 can move in axial direction by a height-direction traveling mechanism 4, in traveling-diameter direction by a piezoelectric element 2, and in circumferential direction by a rotary mechanism 3. While the probe 1 is being inserted into a fine through-hole 13, the tip part is placed so that it crosses an inner surface which is subjected to copper plating 11 of the hole 13. A bias voltage is applied between the probe 1 and the copper plating 11 by a bias voltage application device 6 and tunnel current flows when distance between the probe 1 and the copper plating 11 is reduced, thus enabling distance between the probe 1 and a surface of the copper plating 11 to be controlled with high accuracy. Then, by recording the traveling amount in traveling- diameter direction continuously while moving the tip part of the probe 1 so that it traces an inner surface of the hole 13, a shape of the inner surface of the hole 13 can be measured highly accurately.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a scanning tunneling microscope and a through-hole inspection device including the same, and particularly to a scanning tunneling microscope in which a probe can move in a cylindrical coordinate system. This is a through-hole plating inspection device that uses a microscope and this scanning tunneling microscope to non-destructively detect the state of copper plating on the inner surface of through-holes provided on a printed circuit board before printed patterns are created. The present invention relates to a through-hole plating inspection device suitable for inspecting through-holes of about 0.2 mm or less, which are so minute that inspection by visual observation or optical equipment is impossible.

[Conventional technology]

Conventional techniques for through-hole plating inspection include a destructive inspection in which a sample board is sampled during the manufacturing process, the sample board is cut, and the sample board is observed under a microscope. In addition, there are non-destructive tests, which include continuity tests to confirm the presence or absence of electrical continuity, and visual tests using a stereoscopic microscope or the like. Furthermore, non-destructive inspection 1
Inspection using X-rays is also performed, and a known example of such a device is reported, for example, in Electronic Materials Vol. 26, No. 10 (1987), pages 169 to 173.

[Problem to be solved by the invention]

Among the conventional non-destructive tests mentioned above, the electrical continuity test is only effective in the case of significant defects where there is no electrical continuity between the front and back surfaces of the board, and this alone is sufficient. It is not possible to carry out thorough inspections. Furthermore, with this inspection method, it is impossible to inspect a board immediately after the through holes are opened and the entire surface is plated with copper. Visual inspection using a microscope is also difficult due to the recent trend in substrates toward the use of minute patterns and minute through-holes for high-density mounting for a given substrate thickness. It is impossible to inspect the inside. On the other hand, destructive inspection is effective when carried out to investigate the cause after a defective part has been identified by other means. It is difficult to detect during the manufacturing process, even through a random inspection. As described above, with the conventional technology, it has not been possible to non-destructively test the copper plating on the inner surface of a minute through-hole before creating a printed pattern.

Furthermore, although the known inspection method using X-rays described above is an effective method, the inner wall of the through hole is observed from an oblique direction through a multilayer pattern, and the multilayer pattern overlaps, making it difficult to detect defects. Detection is not easy and requires judgment by an expert.

Furthermore, since the defects are so small, they may be overlooked, resulting in an unreliable inspection.

An attempt was made to solve the problems of the present invention described above by using a scanning tunneling microscope. In order to solve this problem, a new method of moving the probe, which does not exist in conventional scanning tunneling microscopes, and a device configuration that realizes this method of movement were adopted. Therefore, in this application, such a scanning tunneling microscope is also disclosed.

A first object of the present invention is to provide a scanning tunneling microscope that can move a probe on a cylindrical coordinate system and that can easily move the probe within a hole with a minute diameter. It is in.

A second object of the present invention is to inspect a copper-plated multilayer board with through holes before creating a printed pattern,
To provide a through-hole plating inspection device capable of non-destructively inspecting the plating condition inside the through-holes of a copper-plated multilayer board at an early stage of the manufacturing process.

[Means to solve the problem]

A first scanning tunneling microscope according to the present invention has a probe, and when the tip of the probe is brought close to a part to be measured, the surface of the object to be measured is observed using tunneling current flowing through the probe. In a scanning tunneling microscope, the probe has a tip oriented in a direction perpendicular to its axis, and a first driving mechanism that moves the probe in the axial direction, and a probe that moves the tip in the direction that the tip is oriented. The probe is configured to include a second drive mechanism that moves the needle, a rotation mechanism that rotates the probe around its axis, and a control means that controls operations of the first and second drive mechanisms and the rotation mechanism, respectively. Ru.

A second scanning tunneling microscope according to the present invention includes the first scanning tunneling microscope.
In the scanning tunneling microscope, the second driving mechanism is attached to the rotating mechanism, the probe is located at the center of a circle created by the rotational movement of the rotating mechanism, and the probe is moved by the second driving mechanism. The characteristic point is that it moves in the radial direction of the circle.

A through-hole plating inspection device according to the present invention is an inspection device for inspecting the state of plating on the inner surface of a through-hole provided in a printed circuit board, and a bias voltage is applied between a probe and the plating on the inner surface of the through-hole. tunnel current detection means for detecting a tunnel current flowing between the probe and the plating on the inner surface of the through hole; and a radial direction movement mechanism for moving the probe in the radial direction of the through hole. , a rotation mechanism that rotates the probe inside the through hole, a depth direction movement mechanism that moves the probe in the depth direction within the through hole, and a horizontal movement that aligns the horizontal position of the probe and the through hole. and a servo control mechanism that controls the radial movement mechanism to keep the tunnel current at a constant value, and data that reconstructs and displays the shape of the inner surface of the through hole based on servo control information obtained from the servo control mechanism. a processing means, a determining means for determining the state of plating on the inner surface of the through hole by comparing data reconstructing the shape of the inner surface of the through hole with data of a normal through hole given in advance, and a determining means for measuring and determining the through hole. The method is characterized by comprising an inspection procedure control means for repeating the same measurement by moving the probe to another pre-stored through hole position after completion of the inspection.

[Effect]

In the scanning tunneling microscope according to the present invention, the shape of the probe is changed so that the tip is provided in a direction perpendicular to the axial direction, thereby making it possible to measure the inner wall of a minute hole. Since the first and second drive mechanisms and rotation mechanisms are provided, the probe can be moved in a cylindrical coordinate system consisting of the radius vector r and the angle θ, thereby making it possible to scan the inner surface of a minute hole.

The through-hole plating inspection device according to the present invention can basically scan the inner surface of a minute through-hole formed in a substrate by using the scanning tunneling microscope according to the present invention. The plating condition can be accurately inspected.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a conceptual configuration diagram of a scanning tunneling microscope according to the present invention and a through-hole plating inspection apparatus constructed using the same, and FIG. 2 is an enlarged view of the vicinity of the through-hole.

In Figure 1, 1 is a conductor (usually tungsten, etc.)
2 is a piezoelectric element for radial movement that positions the probe 1 in the radial direction; 3 is a rotation mechanism that rotates the probe 1 and the piezoelectric element 2 for radial movement. . Probe 1
is attached to the tip of the piezoelectric element 2, and the piezoelectric element 2 is arranged so that its driving direction faces in the radial direction of the rotation mechanism 3, and the base of the piezoelectric element 2 is provided at the peripheral edge of the lower surface of the rotation mechanism 3. Therefore, the probe 1 is located around the center of the rotating mechanism 3.

Further, as is clear from FIG. 2, the probe 1 has an elongated shape, and its tip 1a is oriented in a direction perpendicular to its axial direction. 4 is a height (or depth) positioning device for moving the probe in the height direction; 5 is a piezoelectric element drive device for driving the piezoelectric element 2 for radial movement; and 6 is a bias for the probe 1. This is a bias voltage application device for applying voltage. The height direction of the probe 1 is the depth direction within the through hole. The bias voltage is a fairly low voltage (for example, about 1 V), and when the distance between the tip of the probe 1 and the surface of the object becomes less than a predetermined distance, the probe 1
A weak tunnel current flows due to the bias voltage.

The tunnel current detection device 7 detects a weak tunnel current generated in the probe 1, amplifies it, and sends it to the servo control device 8. The servo control device 8 controls the piezoelectric element drive device 5 based on this tunnel current value. Control information at that time is sent to the computer 9 and recorded as data.

The rotation mechanism 3 and the height direction positioning device 4 are connected to a computer 9.
controlled by 10 is the printed circuit board of the test object, 11
12 is a defect occurring in the copper plating 11, 13 is a minute through hole,
The defect 12 is present on the inner surface of the fine through hole 13. 14 is a horizontal positioning device, on which the printed circuit board 10 is installed.

In the above, the probe 1 is movable in its heel direction by the height direction moving mechanism 4, movable in the radial direction by the piezoelectric element 2, and movable in the circumferential direction by the rotation mechanism 3. Therefore, the probe 1 is moved in the cylindrical coordinate system by the above-mentioned moving mechanism 4, piezoelectric element 2, and rotation mechanism 3.

When the probe 1 is inserted into the through hole 13, the tip 1a of the probe 1 is disposed perpendicularly facing the inner surface of the through hole 13. Since the inner surface of the through hole 13 is coated with copper plating 11, the tip portion 1a faces the surface of the copper plating 11. A bias voltage (usually about 1 volt to several volts) is applied between the probe 1 and the copper plating 11 by a bias voltage applying device 6, and the distance between the probe 1 and the copper plating 11 is set to 10. When brought close to about 1 angstrom, a tunnel current flows. This current value is very small, on the order of several nanoamperes, but it is very sensitive to the distance between the probe 1 and the copper plating 11, and if the distance changes by 10 angstroms, the current value increases by about one digit. Change. Therefore, it is possible to control the distance between the probe 1 and the surface of the copper plating 11 with high accuracy. By using a piezoelectric element to control this distance, the above accuracy can be achieved.

The tunnel current is separated from noise by a tunnel current detection device 7, and then amplified and sent to a servo control device 8. Servo control is performed to keep the current value at a constant value given by a voltage of about 1 volt, and the piezoelectric element 2 for radial movement is connected to the tip of the probe 1 via the piezoelectric element drive device 5. The distance from the surface of the plating 11 is maintained at a constant distance.

In this state, the tip of the probe 1 is not moved by the rotating mechanism 3 so as to trace the inner surface of the through hole 13, and the amount of movement in the radial direction is continuously recorded, and this is recorded by the height direction positioning device 4.
By repeating this from the upper opening to the lower opening of the through hole 13, the shape of the inner surface of the through hole 13 can be measured with high precision. The above procedure for measuring the inner surface shape of the through hole is programmed into the computer 9. In addition, the computer 9 reconstructs the inner surface shape of the through hole 13 from the obtained data and displays it on a display device (not shown), and compares it with a predetermined normal through hole plating state to identify areas where the plating state is insufficient. Determine whether or not there is a defect. Furthermore, after the judgment is completed,
Pull out the probe 1 from the through hole 13 and move the probe 1 to another through hole position stored in the computer 9 in advance.
, and repeat the same measurement and judgment.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a scanning tunneling microscope is provided with a moving mechanism that can change the position of the probe in a cylindrical coordinate system, and also allows the probe to scan the inner surface of a minute hole. Since it is formed into a shape, it is possible to observe the inner surface of the minute hole. Further, according to the present invention, since the scanning tunneling microscope is used, it is possible to non-destructively, accurately and easily inspect the state of copper plating on the inner surface of a through hole provided on a printed circuit board before creating a printed pattern. I can do it. The present invention is particularly effective for nondestructive testing of multilayer boards. In addition, according to the present invention, it has high resolution performance, improves inspection accuracy, and can obtain images at the atomic level, so it can be used as a tool for researching and improving the manufacturing process of through-hole plating. is also helpful.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a scanning tunneling microscope according to the present invention and a through-hole plating inspection device including the same;
FIG. 2 is an enlarged sectional view of the main part in FIG. 1. [Explanation of symbols] 1... 1, a I +l・e 2, 轡・・φ 3... 4... 5... 6... -... 7. ...... 8... 10... 11φ-ψ・ 13... ・Probe, probe tip, piezoelectric element for radial movement, rotation mechanism, height (depth) Directional movement mechanism, piezoelectric element drive device, bias voltage application device, tunnel current detection device, servo control device, printed circuit board, copper plating, through hole, horizontal positioning device

Claims (3)

[Claims] (1) A scanning tunneling microscope that has a probe and is configured to observe the surface of the object to be measured using tunnel current flowing through the probe when the tip of the probe approaches the object to be measured. In the above, the probe has a tip facing in a direction perpendicular to its axial direction, and further includes a first drive mechanism for moving the probe in the axial direction, and a first driving mechanism for moving the probe in the direction in which the tip is oriented. A second drive mechanism that moves the probe, a rotation mechanism that rotates the probe about its axis, and a control means that controls operations of the first and second drive mechanisms and the rotation mechanism, respectively. Scanning tunneling microscope. (2) In the scanning tunneling microscope according to claim 1,
The second driving mechanism is attached to the rotating mechanism, the probe is located near the center of a circle created by the rotational movement of the rotating mechanism, and movement by the second driving mechanism causes the probe to move toward the center of the circle. A scanning tunneling microscope that moves in the radial direction of a circle. (3) In an inspection device for inspecting the state of plating on the inner surface of a through hole provided on a printed circuit board, the probe includes a bias voltage applying means for applying a bias voltage between the probe and the plating on the inner surface of the through hole. , a tunnel current detection means for detecting a tunnel current flowing between the probe and the plating on the inner surface of the through hole; a radial direction moving mechanism for moving the probe in the radial direction of the through hole; a rotation mechanism that rotates the needle inside the through hole; a depth direction moving mechanism that moves the probe in a depth direction within the through hole; and a horizontal position of the probe and the through hole. a horizontal movement mechanism;
a servo control mechanism that controls the radial movement mechanism to keep the tunnel current at a constant value; and data that reconstructs and displays the shape of the inner surface of the through hole based on servo control information obtained from the servo control mechanism. a processing means; a determining means for determining the state of plating on the inner surface of the through hole by comparing data reconstructing the shape of the inner surface of the through hole with data of a normal through hole given in advance; A through-hole plating inspection apparatus characterized by having an inspection procedure control means for moving the probe to a pre-stored position of another through-hole after completion of measurement and determination, and repeating the same measurement.