JPH05149733A - Method for measuring height distribution and volume of cream-soldered section - Google Patents

Abstract

PURPOSE:To obtain a means which can accurately and quickly measure the height and volume of a cream-soldered section. CONSTITUTION:The height information about part of a cream-soldered section 3 formed on a substrate 1 is found by trigonometrical survey using a laser beams and, at the same time, a picture of transmitted X rays is obtained by irradiating the substrate 1 with X rays. Then calibration is performed by correlating the density distribution of the X-ray picture with the height information. By utilizing the calibrated results, the height distribution of the soldered section is found from the density distribution of the X-ray picture. In addition, the volume of the soldered section is found by multiplying the found height distribution by the area of the soldered section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the height distribution and volume of cream solder, and more particularly, it combines the height distribution of cream solder with the density distribution of X-ray transmission images. The present invention relates to means capable of accurately and quickly measuring distribution and volume.

[0002]

2. Description of the Related Art Prior to mounting electronic components on a board, cream solder is generally applied to the electrodes of the circuit pattern on the board by a screen printing device. In this screen printing, a screen mask having a pattern hole is brought close to the upper surface of the substrate, and a squeegee is slid on the screen mask to apply cream solder through the pattern hole, and then separate the screen mask and the substrate. By doing so, the cream solder in the pattern hole is transferred onto the electrode.

However, the cream solder in the pattern holes is not always completely transferred. For example,
When the pattern holes are clogged or the cream solder oozes out to the back surface of the screen mask, the volume of the cream solder part on the electrode is insufficient, or the height of the surface of the cream solder part becomes inappropriate. As a result, defects such as mounting of electronic components, joining state after soldering, floating of electrodes, solder bridges, solder balls, and standing of chips may occur.

Therefore, it is necessary to accurately and quickly measure the height distribution and volume of the cream solder portion and inspect the quality of the solder application state. However, under the present circumstances, this measurement is generally performed by visual observation, which is inaccurate. Therefore, the following means have been tried as a measuring means that does not rely on visual observation.

[0005]

First, there is a means for observing the cream solder portion from above with a camera. However, with this means, only the planar image of the cream solder portion can be obtained, and the height of the cream solder portion cannot be known. Also, the cream solder part is in a mixed state of the solder alloy powder and the flux, and its surface is usually covered with the flux, but this flux shines and becomes noise in the image of the camera, and the planar shape of the cream solder part becomes unclear. There is a problem that it tends to be clear.

Second, there is means by laser triangulation. However, laser triangulation can basically measure the height of only one point. Therefore, in order to measure the height of all points on the surface of the cream solder portion having irregularities on the surface with sufficient accuracy, for example, scanning along the longitudinal direction of the cream solder portion needs to be repeated a great number of times in the perpendicular direction. is there.
Therefore, this method has a problem that it takes a lot of time for measurement and is difficult to put into practical use.

Thirdly, there is means for measuring only the density distribution of the X-ray transmission image. This means that X-rays are hard to pass through where cream solder is high (thick), so the image becomes dark, and where it is low (thin) the image becomes bright, making use of the density distribution (density level) of the image. From this, the height of the cream solder part is obtained and the volume is measured. However, the density level of this image merely indicates the relative height of the cream solder part, and the absolute height (thickness) of the portion having the density level is uniquely determined depending on the density level. It is very difficult to decide.

Therefore, it is an object of the present invention to provide means for accurately and quickly measuring the height distribution and volume of the cream solder portion.

[0009]

According to the present invention, the height information of a part of a cream solder portion formed on a substrate is obtained by laser triangulation, and the substrate is irradiated with X-rays to obtain an X-ray transmission image. A step, a step of performing a calibration in which the density distribution of the X-ray transmission image is associated with the height information, and a result of the calibration,
It comprises a step of obtaining the height distribution of the cream solder portion from the density distribution of the X-ray transmission image.

[0010]

According to the above construction, it is not necessary to repeat the laser triangulation many times, and the X-ray transmission image can be obtained in a short time, so that the predetermined measurement can be performed quickly. In addition, since the density distribution of the X-ray transmission image uniquely corresponds to the absolute value of the height by the calibration, the absolute height distribution and volume of the cream solder portion can be accurately known.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a front view of the X-ray apparatus. 1 is the substrate
Reference numeral 2 is an electrode formed on the substrate 1, and 3 is a cream solder portion applied to the upper surface of the electrode 2 by a screen printing device. An X-ray source 4 irradiates the substrate 1 with white X-rays.
Reference numeral 5 is an aperture unit provided below the substrate 1, 6 is an X-ray detector, 7 is an optical unit, and 8 is a camera. When the substrate 1 is irradiated with X-rays from the X-ray source 4, the X-ray transmission image is captured by the camera 8 and its concentration distribution can be obtained.

Reference numeral 9 is an X table, 10 is a Y table, and these XY tables 9 and 10 are provided so as to be parallel to the substrate 1. Reference numeral 11 is a laser irradiator, 12 is a light receiver that receives the laser light B that is emitted from the laser irradiator 11 and reflected by the cream solder portion 3, and 13 is a laser irradiator 11 and a light receiver 12 fixed to the Y table 10. The brackets 14 and 15 are motors for driving the XY tables 9 and 10. By moving the laser irradiator 11 and the light receiver 12 integrally, the cream solder portion 3 can be scanned in the XY directions. That is, the height information (absolute value) of an arbitrary point of the cream solder portion 3 formed on the substrate 1 can be obtained by laser triangulation.

FIG. 2 shows the cream solder portion 3 applied on the electrode 2 of the substrate 1. The surface of the cream solder portion 3 is not flat but has irregularities, and the height t thereof is not uniform. Here, the driving motors 14 and 15 for the XY tables 9 and 10
Is driven to irradiate the laser beam B from the laser irradiator 11, and the laser beam B is scanned so as to follow the longitudinal direction of the cream solder portion 3 and pass through the apex of the cream solder portion 3, Information on the absolute height t of a part of 3 (about the ridge line that crosses the cream solder portion 3 in its longitudinal direction) is obtained. It is desirable that the laser beam B be made slightly thicker in order to stabilize the measured value.

Next, the substrate 1 is irradiated with X-rays by the X-ray apparatus to obtain an X-ray transmission image. FIG. 3 shows a density distribution of an X-ray transmission image in which the cream solder portion 3 shown in FIG. 14 is a pixel of the light receiving part of the camera 8, L
(L0 to L5) are the density levels of this image. However,
It indicates that the density level L gradually darkens toward L0 to L5. That is, at the concentration level L1, the cream solder portion 3 is low and the X-rays are easily transmitted, so that it becomes bright, and at the concentration level L5, the cream solder portion 3 is high and the X-rays are hardly transmitted, so that it becomes dark.

Next, the calibration for associating the density distribution of the X-ray transmission image with the height information of laser triangulation will be described. By the way, generally, the following basic formula is established for the permeation of monochromatic X-rays.

I = I0 exp (-μt) where I is the X-ray transmission intensity, I0 is the incident X-ray intensity, μ is the linear absorption coefficient, and t is the height of the transmitting substance. Here, if the logarithm of both sides of the above equation is taken and the vertical axis is logI and the horizontal axis is height t, a graph is drawn to show a straight line to the right (however, I
0 is constant, and μ is determined by the type of transparent material and the wavelength of monochromatic X-rays). However, in the present embodiment, X that emits white X-rays is used.
Since the radiation source 4 is used, the wavelength of X-rays has a distribution, and the X-ray detector 6 detects scattered rays due to the large X-ray flux. The curve is convex downward. It should be noted that this curve is obtained in advance for cream solder. Here, the density level L0 corresponds to the case where the X-ray transmission intensity I is large, and the density level L5 is X.
This corresponds to the case where the line transmission intensity I is small.

Then, as described above, the calibration is performed using the information on the height (absolute value) obtained by the laser triangulation. Desirably, as shown in FIG. 4, the height (absolute value) of the apex of the cream solder portion 3 is obtained from the result of laser triangulation, and the density levels L and logI of this apex are obtained from the X-ray transmission image. Is plotted on the graph (point P). Then, a solid curve that passes through the point P and is moved by Δt in parallel with the horizontal axis is obtained. This solid curve is the characteristic line after calibration. Next, the absolute value of the height t with respect to each log I and the density level L is obtained from this characteristic line.

Next, using the result of the above calibration, the height distribution of the cream solder portion is obtained from the density distribution of the X-ray transmission image. FIG. 5 is a relational diagram in which the results of the above calibration are summarized.
The relationship between the height t, the density level L, and the number N of pixels is shown. Note that t0 to t5 are heights t corresponding to the density levels L0 to L5, and N0 to N5 are the number of pixels N corresponding to the density levels L0 to L5. That is, by the above calibration, the density distribution of the X-ray transmission image uniquely corresponds to the distribution of the height (absolute value) of the cream solder portion 3. That is, with reference to FIGS. 3 and 5, the distribution of the height (absolute value) of the cream solder portion 3 can be immediately known.

Further, the volume V of the cream solder portion 3 can be obtained from the integration of the height t and the number of pixels N, that is, V = ΣtN. Then, based on this result, the quality of the applied state of the cream solder portion is determined.

Thereafter, a new object to be measured (cream solder portion on the substrate) can be measured more simply and quickly than the above. That is, if an X-ray transmission image is obtained under the same conditions as described above, the density distribution of this image shows an absolute height distribution from the result of the above calibration without performing laser triangulation. It is possible to immediately measure the absolute height distribution and volume of this cream solder portion which is newly measured.

[0021]

As described above, according to the present invention, the height information of a part of the cream solder portion formed on the substrate is obtained by laser triangulation, and the substrate is irradiated with X-rays to obtain an X-ray transmission image. The step of obtaining and the step of performing a calibration in which the density distribution of the X-ray transmission image and the height information are associated with each other, and the result of this calibration is used to calculate the cream solder from the density distribution of the X-ray transmission image. Since the step of obtaining the height distribution of the portion is configured, it is not necessary to repeat the laser triangulation many times, and the X-ray transmission image can be obtained in a short time, so that the measurement can be performed quickly. Further, since the height distribution can be uniquely obtained from the density distribution of the X-ray transmission image by the calibration, the height distribution and the volume of the cream solder portion can be accurately known.

[Brief description of drawings]

FIG. 1 is a front view of a measuring device of the present invention.

FIG. 2 is a perspective view of the cream solder part.

FIG. 3 is a density distribution diagram of the X-ray transmission image.

FIG. 4 is an explanatory diagram of the calibration.

FIG. 5 is a relationship diagram of the same height, the density level, and the number of pixels.

[Explanation of symbols]

 1 substrate 3 cream solder part t height

Claims (2)

[Claims] 1. A step of obtaining height information of a portion of a cream solder portion formed on a substrate by laser triangulation and irradiating the substrate with X-rays to obtain an X-ray transmission image, and then the X-rays. A step of performing a calibration in which the density distribution of the transmission image is associated with the height information, and a step of obtaining the height distribution of the cream solder portion from the density distribution of the X-ray transmission image using the result of the calibration. A method for measuring the height distribution and the volume of a cream solder part, which comprises: 2. A method for measuring the height distribution and the volume of the cream solder portion, wherein the area is integrated with the height distribution of the cream solder portion obtained by the height measuring method according to claim 1.