JPH05187838A - Device for monitoring applied state of solder paste - Google Patents

Abstract

PURPOSE:To enable a substrate-inspecting device which inspects a substrate coated with solder paste before mounting electronic parts on the substrate, to especially reduce defective soldering. CONSTITUTION:The irradiating position of slit light emitted from a slit light projector 102 for emitting slit light is decided by means of a galvano mirror 103. The picture of the position is taken with a TV camera 101 and the shape of solder paste applied to the surface of a printed board is measured by means of a picture processing system 113.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a board inspection apparatus after applying a solder paste before mounting electronic parts, and is particularly representative of an unapplied state of a solder paste applied to an electronic board which requires high-density surface mounting. The present invention relates to a solder paste application state inspection device having a detection optical system suitable for defective inspection.

[0002]

2. Description of the Related Art Conventionally, the inspection of the solder paste application state after the application of the solder paste on the surface mounting component mounting board has not been carried out, or even if it has been carried out, it is an inspection based on the visual experience of an operator. A rigorous inspection could not be performed.

[0003]

SUMMARY OF THE INVENTION In the above-mentioned prior art, consideration is given to the work of reducing the soldering failure or improving the printing condition of the solder paste printing machine by inspecting the application condition of the solder paste. However, there is a problem that many soldering defects occur.

An object of the present invention is to inspect a solder paste application state applied to a printed circuit board to reduce soldering defects caused by an abnormal application state, and
Evaluating the condition of the solder paste printing machine is to keep the solder paste printing condition good.

[0005]

The above object is to incorporate a device for inspecting a solder paste application state after printing a solder paste by measuring the shape of the applied paste by irradiating an optical cutting line in a soldering process. Further, it is achieved by evaluating the printing state of the solder paste printing machine from the inspection result of the coating state and notifying the state to the solder paste printing machine or an operator of the printing machine.

[0006]

The inspection of the paste application state by measuring the paste by the optical cutting line makes it possible to remove the board in which the paste application is abnormal from the soldering process, thereby reducing the soldering failure. In addition, notifying the solder paste printing machine or the operator of the printing machine of the printing state of the solder paste facilitates maintaining the printing state of the solder paste in a good state.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system configuration diagram showing an embodiment of an apparatus used for solder paste analysis of the present invention. In the figure 10
1 is a TV camera, 102 is a slit light projector for projecting a light cutting line, 103 is a galvano mirror for reflecting the slit projected from the slit light projector and controlling the irradiation position of the light cutting line on the substrate. , This is 106
It is controlled by the optical section control circuit shown in FIG. 104 is a substrate to be inspected to which solder paste is applied, and 105
It is driven by an XY table that is movable in a plane as shown in FIG.
This XY table is controlled by the XY table control circuit 107. In this device, the solder paste is irradiated with an optical cutting line and captured by the TV camera 101. The captured image is input to the system bus 112 through the image input circuit 108. At this time, the image passed through the image input circuit 108 is an image sampled as, for example, 512 × 512. Reference numeral 109 is a light cutting line extraction circuit for calculating the position of the light cutting line in the image, and the image signal is input to the image input circuit.
Input through 108, and the vertical position of the light cutting line at every horizontal position of each pixel is obtained from the light cutting line image captured at 108. 110, a CPU, 111 a memory, 106, 107, 10
The image processing system 113 is composed of 8,109,110,111 and a system bus that integrates these.

FIG. 2 shows an image of a light cutting line taken by the TV camera 101 by irradiating the solder paste with slit light by this system. In the figure, 201 indicates an irradiated light cutting line, and 202 indicates a solder paste. The light section line passes through the TV camera 101 and the image input circuit 108 and is processed by the light section line extraction circuit 109. By irradiating the solder paste with the optical cutting line in this manner, the shape of the solder paste can be obtained. Hereafter, the solder paste that has been properly applied is called a normal paste, and the solder paste that has not been applied is called a defective paste. It is possible to identify whether the paste is normal or not based on the shape of the solder paste. A portion of the solder paste printing mask corresponding to the printed circuit board is called a pad.

First, several light-cutting lines are irradiated in parallel with the short sides of the pads at appropriate positions of the paste. This will be described with reference to FIG. The figure shows the arrangement of pads of a multi-pin QFP, and as shown in the figure, the pad shape of the surface mount component is an elongated rectangle. Since the change in the height of the paste is gentler in the long side direction than in the short side direction, if the light cutting line is irradiated in parallel to the short side direction, the height of the non-irradiated part is irradiated. There is less error when interpolating from the height of. Also, as is clear from the arrangement of the pads in the figure, the height information of many pastes can be obtained with one cutting line, so when inspecting multiple pastes, the number of times the light cutting line is irradiated is small. Inspection is possible.
For the cutting line irradiation position, an appropriate position is selected so that the shape of the entire paste can be measured. At this time, since there is a possibility that the paste may be applied by sticking out of the pad, more accurate measurement can be performed by irradiating the cutting line to an outer portion of the pad in a certain appropriate range.

Next, the substrate surface is calculated from the two light-cutting lines radiated near the ends of the long side of the pad or outside the pad when viewed in the vertical direction among the light-cutting lines radiated to the paste. To do. This will be described with reference to FIGS. 4, 5 and 6. In the figure, reference numeral 401 denotes a light cutting line irradiated on a substrate which is not installed horizontally, and 402 denotes a solder paste. Since the height of the paste is determined by the height from the substrate, it is necessary to find the substrate position in the height direction at every horizontal position of the image irradiated with the light cutting line from the observed light cutting line. This can be obtained by linearly approximating the light cutting line irradiated on the substrate surface.

However, when it is necessary to apply the paste at a narrow pitch as in the case of a multi-pin QFP, the paste may be applied by sticking out of the pad and the optical cutting line may not be applied to the substrate surface. Hereinafter, a defect in which the paste protrudes from the pad and bonds with the nearby paste is referred to as a blur. This state will be described with reference to FIG. In the figure 501
Is the applied paste, and 502-505 are the light cutting lines irradiated on the paste. 506 is a pad, and 507 and 508 are optical cutting lines used to calculate the substrate surface. Figure 5
3A shows a state in which the paste is applied to the portion shown by the dotted line portion in FIG. 3 and a light cutting line is applied to the paste. The paste shown in 501 is bleeding. At this time, the adjacent pastes are bonded to the central part of the long side of the pad, and the 503 and 504 irradiating the paste do not irradiate the substrate surface. Since the paste is separated near both ends of the long side of the pad, the substrate surface can be obtained in the case of a cutting line 502, 505 irradiated near the both ends of the pad. As described above, it is desirable to use the light cutting line used for calculating the substrate surface, which is irradiated to a portion where paste is not present as much as possible.

From this fact, when there is no light cutting line irradiated to the outside of the pad portion, the light cutting line irradiated to both ends and the cutting line irradiated to the outside, if any, are about to be measured. The substrate surface is guided using two pastes that are not affected by the pastes other than the paste. Figure 5
It shows in (b). FIG. 6 shows a method of linearly approximating the cutting line. In the figure, reference numeral 601 indicates a cutting line irradiated on a substrate which is not installed horizontally. When the vertical axis is taken in the direction shown in FIG. 6, A indicating the horizontal position of the light cutting line,
The minimum value of the vertical position of the light cutting line existing between B is Y ₁ , and the horizontal position where Y ₁ appears is X ₁ . The same processing between C and D is shown as Y ₂ ,
X ₂ . From now on, between A and B, the left substrate surface extraction unit, C,
The area between D is called the right board surface extraction unit. Now, in the left and right substrate surface extraction units, if the light cutting lines at a part or all of them irradiate the substrate surface, the cutting line is Y =
_{((Y 2 -Y 1) /} (X 2 -X 1)) X + (X 2 Y 1 -X
_A linear approximation can be made by ₁ Y ₂ ) / (X ₂ −Y ₁ ).

Here, a method of determining the position of the substrate surface extraction unit will be described. When performing digital processing, it is preferable that a long space be provided between the left and right substrate surface extraction units in order to minimize the quantization error. However, since the substrate surface extraction unit needs to measure the substrate surface, it is necessary to set the substrate surface extraction unit at a place other than the portion where the paste is likely to be applied, that is, the pad portion. However, if the device does not have the positional information of all the pads on the substrate, it is difficult to find the part without the pads. The present invention utilizes the property that the pads are not bonded to each other, no matter how close the pads are to each other. That is, when a certain pad is present, the area near the outside of the pad is not necessarily the pad portion, and therefore the substrate surface can be measured with the optical cutting line as shown in FIG. 5B.

The substrate surface extraction unit is set according to the conditions described so far. This will be described with reference to FIG. In the figure, 701 is a pad. Reference numerals 702 and 703 are left and right substrate surface extraction units. It is possible to obtain height information of multiple pastes by irradiating one cutting line,
The positions of the board surface extraction units are set so that the left and right ends of the pads located at the leftmost and right positions are connected to the right ends B and C of the respective board surface extraction units.
However, there is a possibility that the substrate surface cannot be detected at the left end and the right end of the pad due to bleeding of the paste or the like.
Therefore, the sections indicated by A, B and C, D of the board surface extraction unit are set to have appropriate intervals.

Next, the substrate surface at the cutting line which has not been obtained yet is obtained by interpolation from the two optical cutting lines which have already obtained the substrate surface. In the present invention, the irradiation position of the light cutting line is determined by the deflection angle of the galvanometer mirror. This will be described with reference to FIG. Now, suppose that the optical system is arranged as shown in FIG. In the figure, 801 is a galvanometer mirror, 802 is a substrate surface, 803 is a slit light projector, and 804 is a path through which the slit light projected from the projector reaches the substrate. θ indicates the deflection angle of the mirror. For the substrate surface of the cutting line for which the linear approximation calculation is not performed, the approximate expression Y = a ₁ X + of the two cutting lines for which the linear approximation calculation is performed
b ₁ , Y = a ₂ X + b ₂ and the deflection angles θ ₁ and θ ₂ of the galvano-mirror when the respective cutting lines are irradiated, and the deflection of the galvano-mirror when the cutting lines that seek the substrate surface are irradiated. It is obtained by interpolating from the angle θ. At this time, the substrate surface obtained by interpolation is Y = (| tan (2θ
₁ −π / 2) -tan (2θ−π / 2) | a ₂ + | tan
(2θ ₂ −π / 2) -tan (2θ−π / 2) | a ₁ ) /
| Tan (2θ ₁ −π / 2) −tan (2θ ₂ −π / 2)
| Through the processing up to this point, the height of the target solder paste from the substrate can be accurately obtained.

Next, the defective paste is detected.
In FIG. 9, reference numeral 901 indicates a pad. A shaded area 902 is an area provided for inspecting the paste and is called a paste window. This is provided in order to measure the volume of the paste that has overflowed from the pad and is applied (volume of paste applied on the paste window-volume of paste applied on the pad).
Is the volume of the paste protruding from the pad. The defect of the paste is judged by the capacity of the paste existing on the pad, the capacity of the paste protruding from the pad, the area of the paste existing on the pad which exceeds a certain reference height, and the positional deviation. Now, assume that the ideal paste is a rectangular parallelepiped having an appropriate height and applied only on the pad. This height is called the ideal height here. The quality of the paste capacity is determined by the ratio of the measured capacity of the paste to a rectangular parallelepiped having this ideal height.

The capacity of each paste is represented by the sum of the heights measured at all measurement points, that is, the pixels, which are measured at the light section line in each area.
From this, evaluation is made by the ratio of the product of all the measured pixels at the pad and the protruding portion from the pad to the ideal height and the sum of the measured heights of the respective portions. By using this method, it is possible to perform an evaluation that is not largely influenced by the size of the pad or the number of pixels that cannot be measured due to noise.

A certain reference height is an appropriately set value such that ideal height ≧ reference height. The area equal to or larger than the reference height is a ratio of the number of all the measured pixels in the pad portion to the number of the measured pixels exceeding the set reference height. This is to detect the case where the paste is applied with deviation. Hereinafter, the paste capacity, the protruding capacity, and the area above the reference height are in the above-mentioned ratios. Here, the paste capacity applied on the pad is divided into four, and the protruding capacity is divided into four parts protruding in the vertical and horizontal directions, and VU, VD, VL, and VR, and an area above the reference height is S. A flowchart for obtaining this ratio is shown in FIG.

The upper and lower thresholds Th1 and Th2 are set for the paste capacity V applied on the pad, and when Th1 <V <Th2, it is regarded as normal. The protruding capacities VU, VD, VL, and VR are set to the upper limit threshold value Th3 for each of them, and are regarded as normal when less than Th3. For the area S equal to or higher than the reference height, a lower limit threshold Th4 is provided, and when Th4 <S, it is considered normal. The positional deviation can be detected, for example, in the same manner as in JP-A-01-100409. Here, a flowchart of the entire inspection apparatus is shown in FIG. The paste inspection can be realized as described above.

Next, a method of controlling the soldering process using the solder paste printing state inspection apparatus as described above will be described. First print the solder paste. Next, the solder paste printing state is inspected by the inspection apparatus as described above. If the print condition is good, mount the parts and solder using a reflow oven. However, if the paste printing condition is not good, there is a high possibility that there is a problem with the paste printing condition. For example, if the paste that should be applied on the pad is not applied or the amount of paste is insufficient, it is possible that the mask used when printing the solder paste has clogged. Therefore, it is necessary to wash the mask. By observing the solder paste application state in this way, the state at the time of printing can be improved, and by making this improvement, soldering defects can be greatly reduced. The solder paste printing machine or the operator of the printing machine is notified of the evaluated solder paste printing state, and if the state is not good, an instruction is given to improve the printing state.

[0021]

According to the present invention, it becomes possible to inspect the solder paste application state after solder paste printing, and as a result, the substrate in which the solder paste application state is not good is removed from the soldering process, or the solder paste printing state is obtained. It is possible to maintain good solderability, and there is an effect that soldering defects are significantly improved.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an image of a light cutting line taken in by irradiating a solder paste with slit light.

FIG. 3 is a layout view of pads of a multi-pin QFP.

FIG. 4 is a view of a light cutting line applied to a printed circuit board that is not installed horizontally.

FIG. 5 is a diagram when a light-cutting line is applied to a solder paste in which adjacent ones are bonded to each other.

FIG. 6 is an explanatory diagram of a method of obtaining a height position of a printed circuit board that is not installed horizontally by linear approximation.

FIG. 7 is an explanatory diagram showing which position of an optical cutting line is used for calculation when determining the height position of a printed circuit board that is not installed horizontally.

FIG. 8 is a layout diagram of an optical system.

FIG. 9 is a setting diagram of a paste window.

FIG. 10 is a flowchart of an algorithm for determining whether the paste is good or bad.

FIG. 11 is a flowchart of the operation of the entire apparatus.

[Explanation of symbols]

 101 ... TV camera, 102 ... Slit light projector, 103 ... Galvano mirror, 104 ... Inspection target substrate, 105 ... XY table, 106 ... Optical control circuit, 107 ... XY table control circuit, 108 ... Image input circuit, 109 ... Optical Cutting line extraction circuit, 110 ... CPU, 111 ... Memory, 112 ... System bus, 113 ... Image processing system.

Claims (9)

[Claims] 1. A solder paste comprising a slit light projector for generating a line pattern on a printed circuit board, a TV camera for capturing the line pattern, and an image processing device for analyzing an image captured by the TV camera. 1 is the inspection target in the device for inspecting the coating state of
Slit light irradiated so that a line pattern is scanned perpendicularly to the horizontal direction of the line pattern with respect to a predetermined application region of one or a plurality of solder pastes, and the line pattern is formed at the end portion of the predetermined application region. A solder paste application state monitoring device characterized by obtaining a height position of a printed circuit board at a position where a twisted line pattern is formed. 2. The monitor device according to claim 1, wherein when the height position of the printed circuit board is detected, the device has a predetermined application area of one or a plurality of solder pastes having positional information, or the vicinity thereof. When the line pattern is irradiated, the height position of the printed circuit board is obtained based on the line pattern irradiated to the leftmost and right end portions of the coating area, which are not the coating area. Solder paste application status monitor. 3. The monitor apparatus according to claim 1, wherein the height of the printed circuit board at a position irradiated with another line pattern is higher than the line pattern used for obtaining the height position of the printed circuit board according to claim 1. A solder paste application state monitoring device characterized in that the height position is obtained by interpolation. 4. A monitor device capable of measuring height information at an arbitrary or a specific position on a printed circuit board, the measured capacity of the solder paste applied to a portion corresponding to a hole of a solder paste print mask on the printed circuit board. And a solder paste application state monitoring device for evaluating the application state of the solder paste based on the ratio of the capacity of the ideal shape of the solder paste assumed to be a rectangular parallelepiped having the bottom of the area of the predetermined solder paste application area. .. 5. The monitor device according to claim 4, wherein a certain area is provided outside a portion corresponding to a predetermined solder paste application area, and the solder paste in this area or in an area obtained by dividing this area into a plurality of areas. It is possible to evaluate the applied state of the solder paste from the ratio of the measured capacity of the above and the capacity when the paste is applied at the height of the rectangular parallelepiped which is assumed to have an ideal shape in this region. Characteristic solder paste application condition monitoring device. 6. The monitor device according to claim 4, wherein when a solder paste is inspected, a certain reference height is provided, and the solder paste applied to a certain predetermined application area has a height exceeding the reference height. A solder paste application state monitoring device, characterized in that the application state of the solder paste is evaluated from the ratio of the area of the area of (1) to the area of a specific application area. 7. The solder paste application state according to claim 4, wherein the application state of the solder paste is evaluated by using any one of claims 4, 5 and 6 alone or by combining some of them. Monitor device. 8. A hole in a solder paste printing mask corresponding to a paste to be inspected in a predetermined application area according to claim 1, 2, 4, 5, 6 in a monitor device according to claim 1 or 4. A solder paste application state monitoring device, which is determined by the above. 9. The state of the solder paste printing machine is evaluated from the result of the evaluation of the solder paste application state as described in claim 7, and the state of the printing machine is notified to the paste printing machine or a worker of the printing machine. A solder paste application state monitoring device characterized by the above.