JP2001244699A - Method for observing electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem where confirming real-time connecting/fixing condition with an optical microscope is impossible or very difficult while it is impossible to selectively leave out a Cu foil to form a wiring and then observe the surface of an IC ship through the wiring. SOLUTION: An FPC is placed on a work table. A wiring is formed of the Cu foil on its surface. A wiring electrode is provided at the tip of the wiring with the IC chip connected and fixed. A bump arranged at the IC chip is connected to the wiring electrode. At connection, an ACF is placed between them. The IC chip, while holding and heating, is aligned with the wiring electrode of the FPC by a heater block for heating and press-fitting. A camera is installed under the workable. The infrared ray generated from the heater block is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring electrode formed on the surface of a circuit board (hereinafter referred to as "FPC") printed on an opaque flexible thin plate, and an anisotropic conductive tape (hereinafter referred to as "ACF").
) Connected to each other through an IC.

[0002]

2. Description of the Related Art On a transparent substrate such as a glass plate, an IC
A method using an ACF is known as a means for mounting a chip or the like. Many IC chips used at this time have bump electrodes called bumps. However, there is a case where the transparent substrate is used as the protruding wiring electrode and the IC chip side is a flat electrode.

[0003] With respect to the mounting using the ACF, if both the electrode on the IC chip side and the electrode on the glass plate side form one or both of the protruding electrodes, the connection and fixing by the ACF, that is, the mounting can be performed. . In this technique, it is not possible to observe from a working direction like the conventional wire bonding method without taking a certain measure. In particular,
That is noticeable if it was an opaque electrode.

In the case where an IC chip having a protruding electrode is a transparent substrate, and after a condition is connected and fixed to the transparent electrode, a test is performed to determine whether the IC chip is correctly connected and fixed to the transparent substrate without displacement. The observation method will be described.

In this case, a common sense arrangement is to observe the electrodes of the IC chip through the transparent substrate and the transparent electrodes with the transparent substrate facing upward and the IC chip facing downward. Since the electrode surface of the IC chip can be easily observed with Al, Au, solder or the like, it is simple and convenient if the ACF is made of a transparent resin.

[0006] However, ACF foams during thermocompression bonding, although the cause is not clear. The bubbles obstruct the optical path of the microscope (actually, the bubbles appear shiny and too bright compared to their surroundings), making observation difficult.

[0007] To solve this problem, Japanese Patent Laid-Open No. 9-1 is disclosed.
96617 proposes the method shown in FIG. Chip 2
The first oblique direction light source B and the second oblique direction light source C irradiate light to the glass substrate 21 to which the camera 2 is bonded.
At 7, two light and dark images are obtained. In these two bright and dark images, the bubbles in the ACF partially shine brightly, but the locations of the brightly shining portions are different. Therefore, when the logical sum image of the two bright and dark images is combined, the bubbles are eliminated and only the positioning bumps are observed bright.

[0008] This known example is premised on A) using a transparent glass substrate and B) having a transparent electrode on the substrate side, as specified in the publication. Therefore, the image can be observed from the glass substrate side, and a bright and dark image is obtained by irradiating coaxial light from two directions, and this is ORed to remove the inconvenience of bubbles.

According to the present invention, A) the IC chip can be connected using an ACF having an opaque metal electrode on the substrate side, which can be observed even if the substrate is colored, opaque, or of course transparent. A method for observing a fixed FPC is proposed.

[0010]

Recently, a method has been developed in which an electric component is mounted using a flexible insulating substrate called an FPC and incorporated into an electric device. This FPC is transparent,
It is made of translucent and opaque insulating material.
u is arranged and selectively left so as to have an arbitrary circuit configuration to form a circuit board, and electric components are connected and fixed to this board for use.

As described in the prior art, irrespective of the material of an opaque or translucent substrate, it is impossible or extremely difficult to confirm the state of connection and fixation in real time with a simple optical microscope. is there. Furthermore, it is impossible to observe the surface of, for example, an IC chip through the wiring after forming the wiring while leaving the Cu foil selectively.

As described above, a method is proposed for solving the problem when the optical microscope is made of a material that cannot be transmitted by the optical microscope, and similarly, the problem when observing the overlapped object when the observation is performed by the reflection. Things.

[0013]

SUMMARY OF THE INVENTION The present invention provides a method for recognizing a position of an electrode of an IC connected to a wiring formed on a surface of an opaque flexible printed circuit board via an anisotropic conductive tape. An electrode observation method is characterized by observing a positional shift between a wiring and an electrode of an IC using an infrared camera that senses an image of infrared rays irradiated from below the table.

Further, there is provided a method for observing an electrode, wherein the work table is made of quartz.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. In the present invention, the FPC 2 is placed on the work table 1. The FPC is polyimide, and a Cu foil is provided on the surface thereof, and the wiring 3 is formed by leaving the Cu foil to provide a predetermined function. The wiring electrode 4 is provided at the tip of the wiring, and the IC chip 5 is connected and fixed. Protrusion electrodes (hereinafter, referred to as bumps) 6 are arranged on the IC chip, and the bumps 6 and the wiring electrodes 4 are finally connected.
For connection, the ACF 7 is interposed between the two.
That is, the bump 6 and the wiring electrode 4 are connected and fixed via the ACF 7.

On the FPC 2 arranged on the work table 1, A
The CF 7 is temporarily adhered and fixed, and is positioned on the wiring electrode 4 of the FPC 2 by the heater block 8 while holding and heating the IC chip 5, and heating and pressure bonding are performed. The work table 1 is formed of quartz and its size depends on the size of the FPC 2. In the present embodiment, quartz having a length, width, and thickness of 25 mm, 100 mm, and 20 mm was used.

A camera 9 is provided below the work table. The camera used was an infrared-sensitive CCD camera. Of course, in the present invention, the object is achieved if the camera block 9 and the camera 9 are optically connected in a straight line, instead of having to install a camera under the work table. Therefore, the object of the present invention is not lost even if the optical path is rotated by the optical fiber glass and the optical block is arranged on the worktable like the heater block. According to the invention, no external light source is required. The present invention uses infrared rays generated from the heater block 8. That is, in the present invention, the infrared ray emitted from the heater block 8 is transmitted to the IC chip 5 provided with the bump 6
The light passes through the CF 7, the FCP 2 provided with the wiring 3, and the work table 1 and is captured by the camera 9.

In connection fixing using ACF, about 250 ° C. is used. The material shape of the work table 1 is important. In the present invention, quartz was selected so as to withstand the operation at 250 ° C. Since the attenuation when passing through the quartz was large, the detection temperature was set to 100 ° C. or higher. Even under such conditions, an accuracy of 0.1 ° C. was confirmed in the embodiment of the present invention.

The observation method according to the present invention will be described with reference to FIG. FIG. 2A) shows an FPC to which a normal connection has been made, and FIG. 2B) shows a case where a positional shift has occurred. Images appear on the camera as if you were looking into the workbench from below.
In the figure, the FPC that transmits infrared rays almost completely is omitted. The heater block as a radiation source is shown without any difference in brightness and is omitted because it is not recognized as a pattern. Further, the absorption by the work table is omitted because the entire image is colored.

As a result, as shown in the figure, what can be recognized as a pattern is the wiring 3 and the wiring electrodes 4 arranged on the FPC, and the IC chip 5 having the bumps 6. The difference between the infrared rays, that is, the temperature difference, is sufficient at least between the IC chip 5 and the wiring 3 and can be discriminated and can be confirmed by the visual angle. However, since the temperature difference between the wiring electrode 4 and the bump 6 is logically very small during the connection operation, it is difficult to distinguish between the two.

Although the two appear to be superimposed, if the alignment fails, the pattern becomes different from the normal pattern, as shown in FIG.

According to the observation method of the present invention, the IC chip
It is possible to observe the situation where the CF is actually connected by crimping to the FPC. It will be described sequentially. First, the bumps of the IC chip come into contact with the temporarily bonded ACF held by the heater block. Then, a resin called a binder constituting the ACF starts to melt. At the same time, it foams and is discharged from under the IC chip together with excess ACF. After a certain period of time, if the heater block is separated from the IC chip, specifically, if it enters the process of turning off the current to the heater,
The flow of air bubbles stops and resin curing starts. It takes about 10 seconds. This time is long enough for the observation method according to the invention.

According to the present invention, it is possible to record the progress from the generation of bubbles to the disappearance from below the IC chip during observation. The change can be observed as a change in temperature. That is, the flow can be seen well because the surface of the IC chip is viewed. Accordingly, it is possible to determine the presence of bubbles after curing of the ACF by setting a limit on the presence of bubbles, and to determine whether the process is performed within the permitted temperature range.

[0024]

The observation according to the present invention is effective for the monitoring work at the time of production of a circuit board to be incorporated into an electric device using the FPC, and for confirming the quality after connection and fixing. Moreover,
As long as a CCD camera and a worktable made of an appropriate material are prepared, equipment for observation can be prepared and no large cost is required.

According to the present invention, since it becomes possible to observe every time the ACF binder is melted and hardened, it is possible to reduce the quality trouble relating to the foam which was conventionally overlooked. If bubbles are present between the IC chip and the FPC, the bumps and the wiring electrodes are stressed by being subjected to a temperature cycle after being incorporated into an electric device, resulting in disconnection or poor contact. That is, this kind of quality and reliability problems could be reduced.

According to the present invention, temperature sensing using infrared rays can be sufficiently determined at about 0.1 ° C. Therefore, since the difference between the temperature of the foam and the temperature of the copper foil or the like can be identified, it is possible to change the color and observe, thereby improving the accuracy of the inspection.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram for explaining the present invention.

FIG. 2 is a video example for explaining the present invention. A) shows a normal FPC, and B) shows an FPC in which a position shift has occurred.

FIG. 3 is an overall conceptual diagram showing a conventional example.

Claims (2)

[Claims] 1. An I-wire connected to a wiring formed on the surface of an opaque flexible printed circuit board via an anisotropic conductive tape.
A method for observing the position of an electrode of C, comprising: observing a positional shift between a wiring and an electrode of an IC by an infrared camera which senses an image of the infrared light emitted from below the worktable and an image thereof when recognizing the position of the electrode of C. 2. The method for observing an electrode according to claim 1, wherein the worktable is made of quartz.