JPH05107212A - Inspecting method of external appearance of printed circuit board having parts mounted thereon - Google Patents

Abstract

PURPOSE:To find out simply a faulty place of a printed circuit board having parts mounted thereon, without taking many processes, regarding inspection of the external appearance of the printed circuit board. CONSTITUTION:A heat-sensitive sheet 3 of which the color changes dependently on temperature is put on a printed circuit board 2 having parts 1 mounted thereon, a prescribed wiring pattern 2a of the printed circuit board 2 is electrified subsequently and, by making the color of the heat-sensitive sheet 3 changed, a changed-color pattern 4 is formed. Then, the degree of the change of the color of the changed-color pattern 4 is compared with a standard pattern 5 which is formed on a good printed circuit board and of which the color is made to change, and thereby the quality of the board 2 is determined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a visual inspection of a printed board on which components are mounted. The printed board is covered with a heat-sensitive sheet and electricity is applied to the printed board. This is related to the appearance inspection method that finds out the defective part by knowing the degree.

The trend toward lighter, thinner, shorter, and smaller electronic devices in recent years is largely due to the miniaturization of electronic components such as semiconductor devices. In response to such miniaturization of electronic components, the wiring density of printed boards is reduced. The mounting density of components and components is increasing.

By the way, after the components are mounted on the printed board, the visual inspection is performed before the electrical function inspection. This visual inspection is mainly conducted by humans, either visually or through a microscope. Therefore, a more efficient inspection method is desired.

[0004]

2. Description of the Related Art A manufacturing process for mounting parts on a printed board is divided into a step of mounting the parts on the printed board and a step of soldering the mounted parts.

Regarding the process of mounting the components on the printed board, conventionally, the terminals of the components are inserted into through holes provided on the printed board, and immersion soldering called dip soldering is often performed. ..

However, in recent years, SMT has been adopted in order to reduce the size and height of printed boards in response to lighter, thinner, shorter, and smaller electronic devices.
(Surface mount technology) has progressed, and the components to be mounted are also small and low in height. According to this SMT, the wiring pattern of the printed board is densely made fine, and the terminal spacing of parts is also made narrow.

Therefore, it is impossible to manually mount the components, and generally, the automatic mounting machine is used. The soldering process is also automated, such as reflow soldering, in which the entire printed board is passed through a furnace in a high temperature atmosphere.

However, in any case, a printed board on which such components are mounted is inspected by visual inspection or the like, and in some cases, a visual inspection is necessary for correction by a soldering iron or the like.

This appearance inspection confirms erroneous mounting such as whether or not a component having a predetermined specification is mounted at a predetermined position. Therefore, there is no problem in soldering, that is, disconnection due to missing solder or solder bridging. Check for short circuits.

[0010]

This visual inspection is usually performed by relying on visual inspection, whether the microscope is a magnifying glass or the like. However, in response to the downsizing of equipment, the parts are also downsized, and the printed wiring boards are becoming finer in wiring pattern, and the mounting density is increasing.
Therefore, it is unavoidable that there are individual differences in the accuracy of the inspection or there are oversights, and it takes a lot of man-hours to inspect every corner of such a high-density printed circuit board. was there.

On the other hand, an automatic inspection machine for performing inspection by a machine is also used. However, since such an inspection machine involves image processing, it is expensive and difficult to handle.

[0012] Therefore, an object of the present invention is to provide a visual inspection method for covering a printed board on which components are mounted with a heat-sensitive sheet, energizing the printed board, and making a quality decision from the degree of heat generated at that time. There is.

[0013]

[Means for Solving the Problems] The above-mentioned problem is that the printed board on which the components 1 are mounted is covered with a heat-sensitive sheet that changes color depending on temperature, and then a predetermined wiring pattern of the printed board is applied. The heat sensitive sheet is turned on to form a discolored pattern, and then the discoloration degree of the discolored pattern is compared with a standard pattern discolored by a non-defective printed board to judge pass / fail. It is solved by a visual inspection method of a printed board on which components are mounted.

[0014]

[Function] The appearance inspection of the printed board on which the parts are mounted
As the mounting density of wiring patterns and components increases, it becomes more difficult, but in the present invention, the appearance inspection can be performed easily and accurately over the entire area of the printed board.

That is, the entire surface of the printed board is covered with a heat sensitive sheet, and a predetermined wiring pattern of the printed board is energized to heat the mounted components. Then, this heat is received by the heat-sensitive sheet to form a discoloration pattern.

Comparing the discoloration pattern formed on the heat-sensitive sheet with a standard pattern obtained by a good printed board, the wiring pattern is broken, or the solder joint is incomplete during soldering for mounting components. It is possible to determine a defect such as a short circuit or a short circuit due to cross-linking.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a process chart for explaining an embodiment of the present invention.
FIG. 1A shows a heat-sensitive sheet covered, FIG. 1B shows a color change pattern formed by energizing, and FIG. 1C shows a comparison with a standard pattern. In the figure, 1 is parts, 2 is a printed board, 2a is a wiring pattern, 3 is a heat sensitive sheet, 4 is a color change pattern, 5
Is a standard pattern.

The components 1 are active components such as semiconductor devices, individual passive components such as resistors and capacitors, and the like. Many of these parts are in the form of SMD (surface mount device) in response to recent high-density mounting.

The printed board 2 may be a normal printed board using resin as a base material or a printed board using ceramic as a base material. Depending on the terminal form of the component 1, it may have a through hole or may be an SMD. It may have a connection pad corresponding to. The wiring pattern 2a is formed by a printed wiring and is led out to the outside by a card edge connector or the like at the end of the printed board 2.

The heat-sensitive sheet 3 comprises, for example, a leuco salt of an organic dye used for heat-sensitive paper and a heat-sensitive chemical consisting of an oxidizing agent encapsulated in microcapsules, which is applied to a paper or plastic substrate. It is composed of well-kneaded sheets. This type of heat-sensitive sheet 3 has an irreversible heat-sensitive property, and when the temperature rises, the density of coloring changes from white to high depending on the temperature. Further, for example, in the case of the heat sensitive sheet 3 using cholesteric liquid crystal,
It has a reversible heat-sensitive property, and its hue changes with temperature.

The heat sensitive sheet 3 is put on the printed board 2 on which the components 1 are mounted as shown in FIG. Since the components 1 are mounted on the surface of the printed board 2 to have irregularities, the base material of the heat-sensitive sheet 3 should be elastic to conform to the irregularities of the components 1 as shown in FIG. 1 (B). A rubber-based plastic sheet such as soft silicone is preferable. In addition, vacuum suction in the same way as a vacuum pack and parts 1
It is better to bring the heat-sensitive sheet 3 into close contact with. Then, a predetermined voltage is applied to a predetermined wiring pattern 2a such as a power supply line for a predetermined time to obtain a color change pattern 4 on the heat sensitive sheet 3 as shown in FIG.

On the other hand, a printed sheet having no defects is covered with a heat-sensitive sheet 3 in the same manner as above, and electricity is supplied.
Make a standard pattern 5. Then, the degree of discoloration or coloring of the discoloration pattern 4 is compared with the standard pattern 5 to find the defective portion 6.

Then, there is a problem such as soldering on the printed board 2, for example, abnormal heat is generated at a portion where the connection is incomplete and the electric resistance is high, and the portion becomes a defective portion 6, and a dark discoloration or Develops color. Further, for example, no heat is generated at a portion where the connection is incomplete and the wire is broken, so that the portion also becomes the defective portion 6 and the discoloration or color development that should be caused does not occur.

When the heat-sensitive sheet 3 has an irreversible heat-sensitive property, the heat-sensitive sheet 3 may be transparent or opaque, and is peeled from the printed board 2 for observation after the electricity is supplied. When the heat-sensitive sheet 3 has reversible heat-sensitive characteristics, the heat-sensitive sheet 3 is transparent and the discolored pattern 4 is observed while energizing.

In this way, the defective portion 6 can be obtained without visually observing every corner of the appearance inspection of the printed board 2 which has a high wiring density and a high mounting density of the components 1.
Can be found.

[0026]

The appearance inspection is indispensable for the printed board on which the parts are mounted. However, in the present invention, the heat sensitive sheet is put on the printed board to energize the printed board to generate a predetermined heat at a predetermined place. Then, a discolored pattern is formed, and the defective portion is found by comparing with the standard pattern.

As a result, there is no need to rely on visual inspection, which requires a time-consuming work, and there is no individual difference in the accuracy of inspection. Therefore, the present invention greatly contributes to the improvement of the productivity of the mounting process of the printed board. ..

[Brief description of drawings]

FIG. 1 is a process diagram illustrating an embodiment of the present invention, (A)
Shows a heat-sensitive sheet, (B) shows a color change pattern formed by energizing, and (C) shows a comparison with a standard pattern.

[Explanation of symbols]

 1 Parts 2 Printed board 2a Wiring pattern 3 Thermal sheet 4 Discoloration pattern 5 Standard pattern 6 Faulty part

Claims (2)

[Claims] 1. A printed circuit board (2) on which components (1) are mounted.
Then, cover with a heat-sensitive sheet (3) that changes color depending on temperature, and then, a predetermined wiring pattern (2a) of the printed board (2).
Then, the heat-sensitive sheet (3) is discolored to change the color.
(4) is formed, and then, the degree of color change of the color change pattern (4) is compared with the standard pattern (5) which is changed by a non-defective printed board to judge the quality. Printed board appearance inspection method. 2. A method for inspecting the appearance of a printed board on which components are mounted according to claim 1, wherein the heat sensitive sheet (3) is vacuum-sucked to bring the heat sensitive sheet (3) into close contact with the components (1) and the printed board (2).