JPH0277980A - Method for inspecting connected part by soldering - Google Patents

Abstract

PURPOSE:To easily discriminate the quality of a connected part by soldering by applying a paint, the physical property of which changes when the soldered part is heated and observing the soldered part after heating. CONSTITUTION:Particles 7 of the paint applied on the surface of a soldered reed 5 do not deform and maintain their original shapes even when hot air of about 80 deg.C is blown on the reed 5 for 1-2 minutes, because the heat capacity of the solder is large. On the other hand, particles 7 of the paint applied on the surface of another reed 6 which is not soldered are melted by the hot air and form a film 8 of the paint and the particles 7 disappear. The part of the film 8 formed as a result of heating becomes flat and strongly reflects inspection light from a light source 10 and strong reflected light enters a detector 11. Since the particles 7 maintain the original shapes at a well soldered part, the light reflectivity of the part is low and the reflected light entering the detector 11 becomes less in quantity. Therefore, when such states are processed with a processor 12, the quality of the connected part by soldering can be discriminated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for inspecting soldering connections, and in particular, a method suitable for inspecting soldering connections of electronic components soldered onto a printed circuit board. Soldering relates to a method of inspecting connections.

[Conventional technology]

Conventionally, the inspection method for this type of soldering connection was, for example,
As described in Japanese Patent Application Laid-open No. 49-41855, soldering involves irradiating a laser beam onto a connection, detecting infrared rays reflected from the connection, and detecting changes in the temperature of the connection. In soldering, the quality of the connection was judged based on the degree of change. This is based on the fact that since the heat capacity of a solder joint with a poor connection is small, the temperature of a normal solder joint with a large heat capacity increases by irradiation with laser light, which is larger than that of a joint part.

[Problem to be solved by the invention]

By the way, the above conventional method of inspecting the soldering connection is as follows:
Since laser light is used, soldering is easily affected by the surface condition of the connection part and differences in light reflectance, making it difficult to determine whether the connection is good or bad. For this reason, complicated processing must be performed to determine whether the connection is good or not, and there is a problem in that accurate determination results cannot be stably obtained.

The present invention has been made to solve the above problems.

SUMMARY OF THE INVENTION An object of the present invention is to provide a soldering connection inspection method that can stably obtain accurate results of determining whether the connection is good or bad.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means to solve the problem]

In order to achieve the above object, one aspect of the present invention is as follows.

Soldering involves applying a paint that causes a physical change to the connection part, applying heat to the applied paint, identifying the physical change in the paint at the connection part, and determining whether the connection part is good or bad in soldering. It is characterized by

[Effect]

According to the above means, in the soldering connection inspection method, a paint that undergoes a physical change due to heat is applied to the soldering connection, and heat is applied to the applied paint. This results in
Soldering identifies differences in physical changes in the paint due to differences in heat capacity of the connection, and soldering determines whether the connection is good or bad.

In other words, soldering involves applying a paint that physically changes due to heat to the connected parts, and when heat is applied to the applied paint, the soldering changes between the unconnected parts and the connected parts. Differences in heat capacity due to differences in the amount of paint applied cause differences in physical changes when heat is applied to the applied paint, and by recognizing this difference, soldering determines whether the connection is good or bad.

In this way, when a paint that causes a physical change due to heat is applied to a soldering connection and heated, the physical change in the paint is large because the heat capacity of the unconnected area is small; Since the connected parts have a large heat capacity, physical changes in the paint are small. For the former and latter soldering, by identifying and comparing the physical changes in the coating at the connection site, it is possible to easily inspect the connection quality of the connection site.

In addition, physical changes in the paint on the joints can be easily detected visually, and when soldering involves a large number of joints, inspection equipment can be used to determine whether the connections are good or bad all at once. You can also do it.

The inspection equipment differs depending on the nature of the paint that undergoes physical changes due to the heat used in this inspection method. In this case, the quality of the soldered connection can be determined by the difference in the light intensity change, and if a paint that changes color when heated is applied, the quality of the soldered connection can be determined by the change in the wavelength of the light. can.

〔Example〕

Hereinafter, one embodiment of the present invention will be specifically described using the drawings.

FIG. 1 is a sectional view of a soldered connection portion of a printed circuit board to be inspected by a soldered connection inspection method according to an embodiment of the present invention. In Fig. 1, 1 is a printed circuit board;
2 is a connection pad, and 3 is solder. 4 is a lead of an electronic component, and the connection pad 2 on the printed circuit board 1 and the solder are the leads that need to be connected. In order to explain the inspection method of the soldered connection part of this embodiment, FIG. It shows. The soldered leads 5 are integrated with the connecting pads 2 and the solder 3, and are in a normally connected state. Further, the leads 6 which are not connected by soldering are separated from the connection pads 2 on which the solder 3 is formed in a convex shape and are not connected to each other.

FIG. 2 is a sectional view of the soldering connection portion of the printed circuit board shown in FIG. 1, showing a state in which the soldering connection portion of the printed circuit board is coated with a paint that causes a physical change due to heat. The paint used here, which undergoes physical changes due to heat, is used, for example, when soldering is used to prevent specular reflection when inspecting the condition of connections, and the main material is ethylene-propylene copolymer. Soldering of the printed circuit board to be inspected using coalescing wax is performed using a diameter 5.
It is applied in the form of particles of around 0 microns.

FIG. 3 is a sectional view of the soldering connection portion of the printed circuit board showing the state after the soldering connection portion of the printed circuit board in the state shown in FIG. 2 has been heated. The heating method after applying the paint is, for example, by blowing hot air at about 80°C for 1 to 2 minutes from above the printed circuit board 1. As a result, the solder is applied to the surface of the connected leads 5. The paint particles 7 do not deform and remain as they are because the heat capacity of the solder is large, but the paint particles 7 that were applied to the surface of the unsoldered leads 6 melt due to the heat. A paint film 8 is formed, and the paint particles 7 disappear. In other words, since the heat capacity of the connected lead 5 is large during soldering, the temperature does not rise to the point where the paint particles 7 melt even after blowing hot air at about 80'C for 1 to 2 minutes, and the paint particles 7 remain as they are. However, since the part of the lead 6 that is not soldered has a small heat capacity, blowing hot air at about 80°C for 1 to 2 minutes will raise the temperature to the point where the paint particles 7 will melt, causing the paint to melt. The particles 7 melt and turn into a paint film 8.

The change in shape of the paint particles 7 resulting from the physical change in the applied paint can be visually determined as a change in the amount of reflected light. Further, in order to further improve the discrimination accuracy, a change in the amount of reflected light may be detected by a detection device.

FIGS. 4a and 4b are diagrams illustrating the principle of detecting changes in light amount using an inspection device.

FIG. 4a is a diagram showing a case where the amount of reflected light from the soldered leads 5 is detected.

In addition, Fig. 4b shows a lead 6 that is not soldered.
FIG. 3 is a diagram showing a case where the amount of reflected light is detected in FIG.

The inspection light generated from the light source 10 is reflected by the paint particles 7, and the reflected light is detected by the detector 11 and discriminated by the processing device 12. At this time, since the paint particles 7 are minute, the inspection light generated from the light source 10 is diffusely reflected by the paint particles 7, the light reaching the detector 11 is weak, and the amount of light detected by the detector 11 is will be very small.

On the other hand, as shown in FIG. 4b, the paint applied to the leads 6, which are not soldered, becomes a paint film 8 as a result of heating, and the light irradiated onto this paint film 8 Due to the flatness of the paint film 8, the inspection light from the light source 10 is directly reflected, and the strong reflected light enters the detector 11. Therefore, the amount of light detected by the detector 11 is large, and the amount of electricity output from the detector 11 is approximately twice as large. These differences in electrical quantities are binarized and processed by the processing device 12, and the quality of the soldering connection is determined. Here, as the light source 10, a known halogen lamp, fluorescent lamp, laser diode, or the like is used. Similarly, the detector 11 may be a known photodiode array, CCD linear sensor, television camera, or the like.

Next, another embodiment will be described. In the above explanation, a paint whose main material is ethylene-propylene copolymer wax is used as a paint that undergoes physical changes due to heat, and particles with a diameter of approximately 50 microns are used so that the amount of reflected light changes due to shape changes due to heat. As an example, we explained the case where the solder of the printed circuit board to be inspected is applied to the entire surface of each component of the connection part, but instead of this, the amount of reflected light and the wavelength of light are directly You may use the paint which changes. As a paint that undergoes physical changes due to heat,
For example, clear line temperature-indicating paint.

There are multi-color temperature-indicating paints, temperature-indicating melt crayons, etc.

Temperature-indicating paint changes color at a predetermined temperature setting, and temperature-indicating melt crayon changes from a dull chalk color to a glossy transparent color at a predetermined temperature setting. When using a paint whose wavelength (color) of light changes due to a physical change due to heat, the physical change in the paint is identified by identifying the difference in color change of reflected light.

In addition, in the inspection method for such solder connections, if the solder to be inspected has many connections, it is necessary to apply paint that changes the amount of reflected light or the wavelength of light due to physical changes caused by heat. In soldering, heat may be applied to the connection portion all at once, and the entire physical change in the paint may be detected at once using a television camera or the like. In this case, many soldered joints can be detected at once, and the soldered joints can be efficiently inspected.

The present invention has been specifically explained above based on examples, but
It goes without saying that the present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit thereof.

〔Effect of the invention〕

As explained above, according to the present invention, the heat capacity of soldering is different between the unconnected area and the soldered area, and the heat capacity is different between the soldered and connected areas. By applying it and inspecting it after heating, you can easily determine whether the soldering connection is good or bad.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a cross-sectional view of a soldered connection portion of a printed circuit board to be inspected using a soldered connection inspection method according to an embodiment of the present invention. Soldering on a printed circuit board shown in Figure 1 is a cross-sectional view of the connecting part, and Figure 3 is a cross-sectional view of the connecting part. The soldering state of the printed circuit board is a cross-sectional view of the connection section showing the state after the connection section has been heated. FIGS. 4a and 4b are diagrams illustrating the principle of detecting changes in light amount using an inspection device. In the figure, 1... printed circuit board, 2... connection pad,
3...Solder, 4...Lead, 5...Soldered is a connected lead, 6...Soldered is an unconnected lead, 7...Paint particles, 8...Paint membrane, 10...
- Light source, 11...detector, 12...processing device. 1st episode 4a side 4b figure

Claims (4)

[Claims] 1. Applying a paint that causes a physical change due to heat to a soldered joint, applying heat to the applied paint, identifying the physical change in the paint at the joint, and determining whether the soldered joint is good or bad. A soldered joint inspection method characterized by: 2. Paints that undergo physical changes due to heat are paints that change the amount of reflected light due to changes in the shape of paint particles due to heat. Physical changes in paint can be identified by identifying differences in changes in the amount of reflected light. A soldered joint inspection method according to claim 1, characterized in that: 3. The paint that undergoes a physical change due to heat is a paint whose wavelength of light changes due to heat, and the physical change in the paint is identified by identifying the difference in color change of reflected light. A soldered joint inspection method according to claim 1. 4. In the method for inspecting soldered joints according to claim 1, heat is applied all at once to the soldered joints coated with paint, and physical changes in the paint are detected all at once. Features a soldered joint inspection method.