JP2003243799A - Method of manufacturing flexible board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a pattern which has a potential disconnection by a stress so as to provide a flexible board that is high and stable in quality. <P>SOLUTION: A voltage is applied between electrodes after patterning, whereby a defective part such as a thinned part of a pattern is broken. Thereafter, an open-short test is carried out for the flexible board. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a film substrate having a fine pattern circuit (generally, a pattern having a pitch of 100 μm or less) and a portable device,
The present invention relates to a display device used in an electronic notebook.

[0002]

2. Description of the Related Art In a liquid crystal display device, COF (Chi) in which a driver IC is mounted and chip parts such as capacitors and resistors and electronic parts such as package ICs are mixedly mounted on a film substrate.
There is known a mode in which p.On.FPC) is mounted on a liquid crystal panel. Conventionally, a film substrate used for such a liquid crystal display device has a film-shaped adhesive attached to a polyimide film, and a Cu foil produced by a manufacturing method such as rolling or electrolysis.
Cu is patterned to form a pattern, and a resist coat and electrolytic plating or electroless plating for surface protection have been performed. The film substrate having such a three-layer structure is not suitable for a fine pattern having a pitch of 100 μm or less in terms of dimensional stability, because the adhesive is deformed by heat and humidity.

Therefore, a film substrate (two-layer film substrate) from which this adhesive is removed has been developed and used. There are two manufacturing methods for such a two-layer film substrate having no adhesive layer.

One is a casting method in which a Cu foil is coated with a polyamic acid varnish and then the solvent is removed, and then the polyimide film is cured. There is a vapor deposition method in which a metal thin film is formed to improve adhesion, a Cu thin film is formed by sputtering or vapor deposition, and then Cu is laminated by electrolytic plating.

The difference between the film substrates of these manufacturing methods is that Cu
Is the thickness of. The thickness of Cu used in the casting method is generally 35 μm or 18 μm, and recently 1
2 μm is mass produced. In the vapor deposition method, the thickness of Cu is
Mass production is possible from 1 μm to 18 μm.

In order to form a fine pattern, the casting method includes a method of half-etching an electrolytic Cu foil and then patterning it. However, since the surface roughness of the Cu foil is relatively large, it is not easy to obtain a stable yield. .
When the pattern has a pitch of 100 μm or less, the film substrate of the vapor deposition method, which can uniformly reduce the thickness of Cu, was more suitable.

The bump pitch of the external connection electrodes of the IC is I
Process development of C is progressing and miniaturization is progressing. Therefore, the bump pitch of the external connection electrodes of the IC has started to be mass-produced at a pitch of 40 μm and a pitch of 30 μm has been developed.

On the other hand, in the display device, a COF (Chip On Fpc) in which an IC is connected to a film substrate is connected to a display panel to manufacture the display device. Since the COF can mount a high-density package such as a drive IC, chip parts such as a capacitor and a resistor, and a power supply IC and an operational amplifier, the display device can be miniaturized and thinned. This display device is widely used in mobile devices, and in particular, the demand for mobile information terminals represented by mobile phones and PDAs is growing significantly in recent years.

[0009]

In order to use a driving IC having a pitch of 30 μm, the width of the pattern of the film substrate to be connected is 10 to 15 μm. The patterning is performed by forming a photoresist on an original fabric having copper formed on the entire surface of the polyimide film, performing exposure and development, and then performing etching, but the original fabric surface, the inside and the surface of the resist, and the exposure mask Foreign matter, stains, stains, etc. on the surface and defects in the original copper cause etching defects. It is desired that the accuracy of the formed pattern width is higher, but practically, a pattern width that can withstand stress such as bending of the flexible substrate is required. As an inspection method for pattern formation, a continuity inspection method by probing (1), an inspection method by which it is compared with CAD master data by vision recognition (), a signal is applied to one end of the pattern by a prober or the like, and the other end is applied. There are a non-contact inspection method (3) in which a signal is detected by the principle of an air condenser, an external appearance inspection by a person using a microscope (4), and the like. However, in (1) probing inspection method, 30μ
It is difficult to connect the probe at the m pitch. Depending on the type of probe, even if an accurate flexible board with bumps is used, even an inspection machine that has an alignment function for aligning the probe and the flexible board will take several seconds, making the inspection cost very expensive. ,And,
It is not possible to detect where the wire is about to break. (2) In the visual inspection machine using vision, the camera magnification must be high in order to accurately judge the state of the pattern, so it takes time, and foreign matter on the pattern and the surface of the substrate are required. False detection occurs depending on the state. Moreover, in (4), since the work is performed by a person, the outflow of defects cannot be zero. Therefore, at present, the non-contact inspection method (3) is the most suitable method. Usually, the inspection is performed with the flexible substrate in a flat state.

However, a flexible substrate having a fine pitch has a disconnection failure mode caused by stress such as thinning and bending of the pattern, which locally occurs in a pattern of thinness of 3 μm or less in conduction. To do. In the non-contact inspection probing inspection, in order to detect this defect, the prober that contacts one end and the sensor that detects it are maintained on the flexible substrate while maintaining the inspection conditions.
It is very difficult to deform the flexible substrate and apply stress to it for inspection under the same conditions on the mechanism of the inspection machine and even if the product pattern or outer size is changed each time.

That is, the present invention is to reliably detect a disconnection defect caused by stress such as pattern thinning and bending, and obtain a flexible board of stable quality.

[0012]

In order to solve the above-mentioned problems, after the pattern is formed, a voltage is applied to both ends of the pattern in order to destroy the pattern in a portion which is about to be broken, such as chipping of the pattern. did. After that, a step of performing a pattern inspection was provided. By electrically destroying the pattern of usually 3 μm or less before the inspection, the disconnection defect caused by bending or the like is eliminated, and the non-contact inspection method can surely perform the inspection.

In the process of destroying the pattern,
Since connecting each electrode is very inefficient, it was possible to easily obtain by applying a voltage to a plurality of electrodes at once by using a conductive rubber or the like.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) A flow chart showing the steps of this embodiment is shown in FIG.

First, a resist is formed on an original fabric having copper formed on the surface of polyimide by sputtering and plating. Next, a mask having a pattern formed of Cr on the glass surface is also exposed. Development is performed with an alkaline solution, and the copper is etched by immersing in an etching solution which is an acidic solution. Dip in an alkaline solution and remove the resist used for etching. Next, a first tin plating is formed on the entire surface of the formed pattern to form a solder resist. The solder resist may be a printing resist or a photo solder resist. Next, second tin plating is performed on the exposed electrode portion. After tin plating, heat treatment is performed to prevent whiskers. Next, the thin portion generated due to the patterning defect is destroyed by applying a voltage. The condition of destruction is 30V-0.5 seconds. The condition may be a constant voltage or a constant current. Since the resistance increases in the thin portion, Joule heat is generated in the thin portion by applying a voltage and passing a current, and the pattern is broken. The step of applying a voltage may be performed at any time after etching, but it is more reliable to perform it on the side closer to shipping. By applying this voltage, it is possible to completely disconnect the thin pattern portion that is disconnected by stress. Next, pattern inspection is performed by the non-contact inspection method. Inspection can be performed for disconnection and short circuit. Next, a reinforcing plate is attached, the outer shape is punched out, and a visual inspection is performed to complete the flexible substrate.

The condition of voltage application may be determined by the thickness of the copper foil and the condition of quality assurance, and is not limited to the above condition. The open / short inspection of patterns is not limited to the non-contact inspection method. It is not necessary to apply the voltage to all electrodes, and the voltage may be applied especially to the fine pattern portion. (Embodiment 2) If there are a plurality of patterns and they are arranged continuously and the electrodes are in a bundle, the ends of the electrodes and one end thereof are contacted with a conductive rubber to apply a voltage. Conductive rubber is made by mixing carbon flakes with elastomer resin. You may make it according to the shape of the product.

[0017]

As described above, according to the present invention, by the voltage application process of the present invention, it is possible to prevent outflow of pattern disconnection caused by stress, and obtain a stable quality of a flexible substrate having a fine pattern.

[Brief description of drawings]

FIG. 1 is a flowchart showing the steps of Example 1 of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Nobukazu Koizumi             2-18-1 Muraoka Higashi, Fujisawa City, Kanagawa Prefecture             Maruwa Manufacturing Co., Ltd. F-term (reference) 2H090 HC12 JB03 JD13 LA01 LA04

Claims (2)

[Claims] 1. A step of forming a metal pattern on an insulating film, and a constant voltage is applied to both ends of the pattern or a constant voltage in order to destroy a portion which is about to be disconnected due to a chip or the like of the pattern. A method of manufacturing a flexible substrate, comprising: a pattern destruction step of passing an electric current; and a step of subsequently performing a pattern inspection. 2. The method of manufacturing a flexible substrate according to claim 1, wherein a voltage is applied to a plurality of electrodes at a time in the pattern destruction step.