Apparatus and method for observation of voltage in many positions on surface of panel under test

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to the electro-optical detection of voltage, and more specifically to the electro-optical detection of voltage as a function of the positions of multiple voltage sources on the surface.

【0002】

[Conventional technology]

To diagnose the completeness of the structure, test voltage generating surfaces such as printed circuit boards, integrated circuit wafers (with or without packaging), and liquid crystal display panels, and obtain voltage information from the voltage generating surface. The demand for being able to retrieve is increasing. The electronic test apparatus of the present invention has a technique capable of testing a circuit board or panel (panel under test or PUT) having a circuit point density of more than about 100 per about 6.45 square Cm (1 square inch).

【0003】

Certain applications, such as testing liquid crystal display panels, are best performed with non-contact detection techniques such as electro-optical techniques. However, these panels are very fragile because they have conductive pixels such as transparent indium tin oxide (ITD) and the thin film transistors adhere directly to the glass surface. An additional insulation layer is also attached on top of the attached structure of those panels, making it impossible to place the voltage probe in a selected position on the panel. Therefore, it is not practical to perform a contact test on such a panel.

【0004】

However, current and planned manufacturing methods and strategies test each pixel for its ability to change voltage states and to measure voltage under various conditions for voltage. Request to do. Current state of the art cannot test such structures.

【0005】

It is known to use an electro-optical device that tests selected circuit points of a voltage generator in series. For example, U.S. Pat. Nos. 4,875,006 and 4,862,075 use a single light beam to access individual sensor circuit points in series with a unique sensor / laser device that controls the light beam. Is disclosed. Thereby, the Pockels cell modulator employs the electro-optical Pockels effect to detect the local electric field generated by the voltage on the surface. These conventional devices require the beam to be controlled by scanning techniques such as an acoustic-photopolarizer or an xy platform. Therefore, conventional equipment is limited to single beam, serial data retrieval.

【0006】

[Summary of Invention]

In accordance with the present invention, the surface is being tested by illuminating its surface with an input beam of light energy via an electro-optical modulation means such as an NCAP modulator, or other device based on a liquid dispersed polymer. Two-dimensional images of the voltage distribution across the surface are taken out at a number of voltage test points on the panel. Observed through an area light sensor (such as a camera) for use to directly generate spatially dependent 2D power modulated images that directly represent the spatially corresponding voltage on the surface of the panel under test A light modulator is placed to allow longitudinal probing geometry so that the voltage on the surface of the panel under test causes the power modulation within the resulting light energy.

【0007】

The device can operate in transmission mode or reflection mode. In transmissive mode, the image is detected through the transparent panel under test. In the reflection mode, the power of light is observed by two transmission reflections via an electro-optical light modulator. A camera or other image forming sensor can be used as a device for detecting a spatial image.

【0008】

Devices operating according to the methods of the invention are present in a light energy source such as a laser and in an NCAP (Nematic Curve Alignment Phase) or PDLC (Polymer Dispersed Liquid Crystal) film when placed in close proximity to the panel under test. It includes an electro-optical sensor (optical modulator) that exhibits an electro-optical effect such as a light scattering effect, and a means for spatially observing a spatially modulated light beam.

【0009】

The present invention tests a high density integrated circuit without invading the integrated circuit before connecting it to the electrical interface and testing the panel before connecting the liquid crystal display (LCD) panel to the electrical interface. Especially used for.

【0010】

[Example]

Figures 1 and 2 show two examples of a voltage imaging device 10 or 10'for observing voltage at multiple positions on the surface 14 of the panel (PUT) 16 or 18 under test. FIG. 3 shows a part of the device 10 in detail (A) and a corresponding voltage space distribution graph (B) of each part. RUT16 is a panel that is transparent to the light energy of the wavelength of interest, and PUT18 is a panel that is opaque to that light energy. PUT16 can be a silicon chip or the like, and PUT18 can be a liquid crystal display (LCD) panel. In either case, the PUT 16 or 18 can be connected to a power source (not shown) in any way to generate a voltage at a selected location on the surface 14 of the PUT 16 or 18.

【0011】

First, a light energy source 20 is provided to measure the voltage. The light energy source can be composed of a xenon lamp, a sodium lamp, a quartz halogen lamp, a pulse laser, a continuous laser, or the like. The light energy from the light energy source is divided into a light energy source beam 22, which is processed into a light input beam 24. The light input beam is magnified by the beam expander 28 into a parallel light beam. A device composed of a lens, a reflector or an optical fiber can be provided for this purpose. The parallel input beams preferably have a constant power density cross section, or at least a known power density cross section.

【0012】

The input beam is directed to an electro-optical modulator means 30 or 31 having a particular type, a particular structure and preferably a particular atomic axis orientation or a particular molecular axis orientation. Suitable modulators for this modulator means 30 include those made of NCAP or PCLD film. The electro-optical modulator 30 utilizes the light scattering property of small droplets of liquid crystal encapsulated in a polymer matrix.

【0013】

With this encapsulation structure, the liquid crystal molecules can be aligned in a curved state, and this alignment state can be optically switched by a control electric field as desired. Therefore, this device is switched from a state in which the light scattering characteristic is very high to a state in which the light transmission characteristic is very high. As will be described later, the electro-optical modulator means 30 has a first surface 32 and a second surface 34 facing the first surface in order to have a measurement structure in the longitudinal direction. The first surface 32 has a transparent conductive coating 36 such as indium tin oxide (ITD). The conductive coating is electrically coupled to a voltage common portion 38 such as ground.

【0014】

The second surface 34 of the modulator means 30 (FIG. 1) is transparent to allow the input beam to pass through the PUT 16. The second surface 34 of the modulator means 31 (FIG. 2) is provided with a highly reflective non-conductive coating 33. This coating 33 reflects the input beam 24. The second surface 34 is provided in close proximity to the area 40 of the surface 14 of the PUT 16 or 18. The input beam 24, which enters the interior of the electro-optical modulator means 30 through the first surface 32 and is irradiated so as to enter the second surface at a position in the immediate vicinity of the area 40 of the surface 14 of the PUT 16 or 18. The electro-optical modulator means 30 is directed so as to intersect at least a portion of the.

【0015】

The voltage at position 12 at or near the surface 14 interacts with the modulator means 30 to change the optical power transmission of the input beam 24 aligned at position 12. This can be observed as a spatially dependent change in the parallel alignment of the output beam 42 with respect to the input beam 24. Those changes are proportional to the voltage at position 12 on the surface 14.

【0016】

B in FIG. 3 shows the interaction between PUT 18 and a type of modulator means 31 having a reflective coating 33 on the second surface 34. The reflective coating 33 can be a dielectric coating or a stack of dielectrics, with voids between the second surface 34 and the surface 14, and gaps filled with solid or liquid layers. Assume. During operation, the electric field (E-electric field) at each position 12 penetrates into the electro-optical modulator means 31 and aligns with the light beam (exactly directly proportional to the voltage at position 12 and parallel to every position 12). (Preferably) to change the scattering and absorption characteristics.

【0017】

Voltage V₁Causes a positive change in power modulation. Voltage V₂ Causes a negative change in power modulation. Voltage V₃ Causes a positive extreme change in power modulation. Power modulation is a function of position and is directly proportional to the voltage difference between the surface 14 and the grounded conductive coating 36 on the first surface of the electro-optical modulator means 31. Therefore, the beam exiting the modulator 31 (in the example described herein, the beam has passed through the modulator twice) contains spatially modulated optical power. This optical power carries information about the voltage at each position 12 relative to the reference of the coating 36.

【0018】

The spacing between the second surface 34 and the surface 14 is controlled and is preferably as narrow as practically possible without causing side effects such as short circuits, heat conduction, or mechanical strain due to stress. The choice of spacing is made to maximize the signal-to-noise ratio. The noise is particularly important due to the noise caused by the crosstalk from the electric field generated by the voltage at the nearby point. A particularly applicable operating rule for LCD panels, such as the area where the voltage source is defined as the pixel area (112 shown in A in FIG. 3), positions the second surface 34 of the electro-optical modulator means. Place it relative to surface 14 with a spacing of 12 and no more than 30% of the pixel area diameter. The spacing can be controlled by mechanical positioning means such as a movable platform device (not shown).

【0019】

In order to retrieve that information, means are provided to detect changes in modulation in the image across the output beam 42 and analyze the voltage. With reference to FIGS. 1 and 2, the detection means can be configured by means such as a sensing camera 48 that receives light through the focusing lens 46, for example. The means 46 captures spatially dependent power modulation and, when viewed by a camera, produces an observable map in two dimensions with features corresponding to the magnitude of the voltage. Further, in order to increase the signal-to-noise ratio, it is possible to use video processing by handling the video captured by the camera 48 in a digitized format. (Digital video handling is a known technology.

【0020】

As shown in FIG. 1, in the one-pass device, the image formation is linear. In the hyperactivity passage device as shown in FIG. 2, the sensitivity can be improved by transmitting the beam twice through the modulator. The beam divider 50 separates the output beam 42 from the colinear input beam 24. Further, the input beam and the output beam can be separated by directing the reflection surface 33 of the phase modulator 31 so that the reflection surface 33 is not perpendicular to the light beam. Then, the output beam 42 is separated by the reflection, so that the beam separator is unnecessary.

【0021】

The present invention has been described above with respect to specific examples. Other examples will be apparent to those skilled in the art. For example, a multi-quantum well electron absorption modulator can be used.

[Simple explanation of drawings]

[Figure 1]

It is a block diagram of the 1st Example of this invention.

[Figure 2]

It is a block diagram of the 2nd Example of this invention.

[Fig. 3]

A is a side cross-sectional view of the electro-optic crystal close to the panel under test, and B is an example of a graph of the voltage spatial distribution associated with A.

[Explanation of symbols]

28 beam magnifier 30,31 Electro-optical light modulator means 32 First aspect of light modulator means 34 Second aspect of light modulator means 48 Sensing camera