JP2001053436A - Printed wiring board and method for inspecting printing of cream solder printed thereon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed wiring board for reflow soldering which is equipped with a pair of large and small test lands for inspecting the film thickness state of cream solder printed on the printed wiring board, and to manage the film thickness of cream solder by using a two-dimensional picture inspecting device. SOLUTION: A printed wiring board 1 is provided with a pair of test lands 9 and 11 constituted of a large area test land 5 and a small area test land 6. The area of the large area test land 5 is made larger than the area of a large area metallic foil 2 to be used for a normal printed wiring board, and the area of the small area test land 6 is made smaller than the area of the small area metallic foil 2 to be used for the normal printed wiring board. The printed state of cream solder 3 on the pair of test lands 9 and 11 is fetched in a two-dimensional picture inspecting camera 4 so that the printed film thickness of the cream solder 3 can be managed. Thus, soldering with high reliability and high quality can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board for reflow soldering, and a method for inspecting a thickness of a printed solder printed on the printed wiring board.

[0002]

2. Description of the Related Art In recent years, high-density mounting of printed wiring boards has been promoted.
High integration of semiconductor mounted components has been remarkable, and the number of pins and the pitch of soldered portions of mounted components have been reduced.

FIG. 3 is an enlarged view of a main part for explaining a conventional method for inspecting a printed wiring board on which cream solder is printed. FIG. 3A is a front view of a printed wiring board, and FIG.
Denotes a cream solder print inspection apparatus viewed from the cross section of the printed wiring board BB '.

In FIG. 3, reference numeral 101 denotes a printed wiring board;
102 is a metal foil connected to the terminal electrode of the mounted component, 103
Denotes a printed cream solder, and 104 denotes a camera.
Cream solder 10 printed on all metal foils 102
Reference numeral 3 denotes a camera 10 provided above the printed wiring board 101.
At 4, the image is captured as a two-dimensional monitor image. The monitor image taken in for inspection was subjected to multi-value processing of the density of the image to determine the quality of the printing of the cream solder on each metal foil 102.

A conventional method for judging the quality of a printed printed wiring board based on a monitor image of cream solder printed on a metal foil 102 will be described with reference to FIG.

FIG. 4A shows a monitor image in which the cream solder 103 is correctly printed on the metal foil 102, FIG. 4B shows an image printed in a displaced position, and FIG. 4D is a defective image in which no cream solder is printed, and FIG. 4D is a printed faint image in the center of the metal foil 102. According to the conventional two-dimensional monitor image, FIG.
FIG. 4D shows that the printing was determined to be defective. However, as for the image printed almost uniformly at the correct position as shown in FIG. 4A, the applied thickness of the cream solder 103 could not be measured, and thus all were judged as good.

As a result, when the printing film pressure changes due to variations in the accuracy of the cream solder printing equipment, etc., the change cannot be inspected despite the change in the cream solder printing amount. However, when the printed film thickness is increased, the degree of occurrence of short-circuit failure is increased, and when the printed film thickness is reduced, the degree of occurrence of open failure is increased. .

In order to solve the above problems, an inspection method using a three-dimensional image analysis device has been proposed. However, the three-dimensional image analysis device is expensive and has a low processing speed, so that it is difficult to use it at a manufacturing site. Was inappropriate.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a printed wiring board capable of inspecting a proper printed film thickness of cream solder by applying a conventional inspection using a two-dimensional monitor image. And an inspection method for inspecting the thickness of the cream solder printed on the printed wiring board. According to the cream solder printing inspection method of the present invention, the absolute film thickness of the cream solder cannot be measured, but it can be determined whether or not the cream film is in an allowable film thickness range that does not cause a short-circuit defect or an open defect.

[0010]

According to the present invention, there is provided a method for inspecting the thickness of a cream solder, comprising: a step of judging whether or not the thickness of the cream solder is within a range in which a short-circuit defect or an open defect does not occur. Are provided on a printed wiring board.
By configuring so that the electrode for terminal connection and the cream solder on the test land are simultaneously inspected after the cream solder printing, the area and shape of the conventional cream solder printing section, and the positional relationship between the cream solder printing section and the metal foil In addition to the inspection, by inspecting the allowable print film thickness, high reliability and high quality soldering can be achieved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a narrow pitch metal foil connected to a mounting component having a narrow pitch terminal electrode and a large pitch metal connected to a mounting component having a large pitch terminal electrode. A foil, a first test land having an area smaller than the area of the narrow-pitch metal foil, and a second test land having an area larger than the area of the large-pitch metal foil. By arranging the test lands on the wiring board, using a two-dimensional image inspection machine conventionally used in the manufacturing process,
It is configured so that the printed film thickness of cream solder can be inspected.

According to a second aspect of the present invention, in the first aspect, the first test land and the second test land are arranged as an adjacent pair. In addition, since the printing conditions of the first test land and the second test land and the capturing condition of the monitor image are the same, it is possible to accurately estimate the cream solder film thickness.

According to a third aspect of the present invention, in the second aspect, a pair of the first test land and the second test land is arranged at a diagonal position of the printed wiring board. Since the test lands are arranged at positions where the printing conditions of the cream solder are the most different, the allowable film thickness of the cream solder can be strictly determined.

According to a fourth aspect of the present invention, in the first aspect, the first test land has an area of 0.05 to 3 mm 2 and the second test land has an area of 4 to 50 mm 2. It is characterized by millimeters, and it is possible to inspect a medium density printed wiring board from a high density printed wiring board.

According to a fifth aspect of the present invention, a step of printing cream solder on the first test land and the second test land on the printed wiring board according to the first aspect, and the first test land And a step of capturing a two-dimensional image of the cream solder printed on the surface of the second test land with a camera from above the printed wiring board, and a calculation step of performing a multi-value processing of the density of the two-dimensional image, It is characterized by judging the suitability of the print thickness of the cream solder based on the uniformity of the image density on the first test land and the second test land subjected to the multi-value processing, the conventional two-dimensional Using an image inspection machine, the three-dimensional height inspection device can be used to inspect the printed film thickness, which was required. With this configuration, the amount of solder printing can be inspected and managed using the conventional two-dimensional image inspection,
High reliability and high quality soldering are possible.

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, both the multi-valued processed image densities in the first test land and the second test land are set in a predetermined density range. In this case, it is determined that the printed film thickness of the cream solder is within the allowable film thickness, and high-speed and highly accurate determination is possible.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1, 2 and Table 1.

(Embodiment) FIG. 1A is a front view of a printed wiring board according to an embodiment of the present invention, and FIG.
FIG. 2A is a cross-sectional view of the printed wiring board, and FIG.
2B is a cross-sectional view in which cream solder is applied using a metal mask 7 and a solder squeegee 8, FIG. 2C is a cross-sectional view in which the metal mask 7 is separated from a printed wiring board, and FIG.
FIG. 3 is a cross-sectional view of inspecting cream solder printed by a camera. Table 1 is a correlation table showing the printing state of the squeegee pressure and the cream solder.

In FIG. 1, 1 is a printed wiring board, 2 is a metal foil for connecting leads of mounted components, 5 is a large area test land, 6 is a small area test land, 9 and 11 are test land pairs, 3 Is a cream solder, and 4 is a camera.

First, the cream solder printing for printing the cream solder 3 on the metal foil 2 using the metal mask 7 will be described. In FIG. 2B, the metal mask 7 is formed.
Then, the cream solder 3 is scraped off by the solder squeegee 8 while applying pressure to the solder squeegee 8 while placing the cream solder 3 on the metal mask 7. The cream solder 3 fills the opening 10. Next, when the metal mask 7 is peeled off from the printed wiring board 1, the cream solder 3 is formed on the metal foil 2 (FIG. 2c).

As shown in FIG. 2 (c), the cross-sectional shape of the printed cream solder 3 is such that the tip of the solder squeegee 8 is elastic at the center of the metal foil 2 so that the coating thickness becomes thin, and At the end, the tip of the solder squeegee 8 is supported by the edge of the opening of the metal mask, so that the tip of the solder squeegee 8 and the metal mask 7 have the same height. That is, the cross section of the printed cream solder 3 is generally thin at the center and thick at the edges. This tendency is more remarkable as the area of the metal foil 2 is larger (that is, as the opening 10 of the metal mask 7 is larger), and when the size of the opening 10 exceeds a certain limit, the solder squeegee 8
Are brought into contact with the metal foil 2, and the metal foil 2 is exposed at the center. Conversely, when the area of the metal foil 2 is small, the tip of the solder squeegee 8 has a small deflection, and it is difficult for the cream solder 3 to fill the opening 10. That is, even when the pressure of the solder squeegee 8 is constant, the shape of the printed film thickness of the cream solder 3 differs between the large-area and small-area metal foils 2 due to the elasticity of the solder squeegee 8. Therefore, in order to eliminate the solder defect caused by the variation in the amount of the printed cream solder such as the short-circuit defect and the open defect, the pressure of the solder squeegee 8 is adjusted so that the large-area metal foil 2 and the small-area metal foil 2 It is necessary to make the film thickness as equal as possible.

At present, the area of the metal foil 2 in a printed wiring board for electronic equipment generally used is 0.5 to 0.5%.
It is about 5 square millimeters. Therefore, conventionally, the pressure of the solder squeegee has been adjusted so that the appearance density of the metal foil 2 in the range of about 0.5 to 5 mm 2 is constant.

In the present embodiment, the area of the small area test land 6 is preferably 0.05 to 0.5 mm 2, and the area of the large area test land 5 is preferably 5 to 50 mm 2. That is, the area of the small-area test land 6 in the present invention is smaller than the area of the small-area metal foil 2 normally used for a printed wiring board,
Is larger than the area of the large-area metal foil 2.

When the pressure of the solder squeegee 8 is too large, the solder squeegee cuts into the opening of the metal mask and the cream solder is scraped off. Is set so that no cream solder remains and the metal foil is exposed.
Also, the area of the small area test land 6 is sufficiently printed on the metal foil 2 because the solder squeegee does not sufficiently fill the opening of the metal mask with the cream solder when the pressure of the solder squeegee is too small. And the dimensions are set so that the metal foil is exposed.

In FIG. 1A, a small-area test land 6 and a large-area test land 5 are arranged on the printed wiring board 1 as adjacent test land pairs 9. Also,
A test land pair 11 is arranged at the diagonal of the test land pair 9, and the inspection is performed at a place where the printing condition and the monitor image capturing condition are different. In FIG. 1A, the small-area test land 6 is rectangular and the large-area test land 5 is square. Generally, the small-area metal foil 2 has many rectangular shapes, and the large-area metal foil 2 has many squares. However, the shape, arrangement, arrangement, and the like are not limited. The periphery of the test land metal foils 5 and 6 may be either a substrate resist or a substrate background.

Next, a method of inspecting the printed film thickness of the cream solder using the test land 9 will be described with reference to Table 1.

[0027]

[Table 1]

The squeegee pressure in Table 1 is the pressure at which the solder squeegee 8 presses the metal mask 7 in FIG. 2B, and can be changed by adjusting the amount of the solder squeegee 8 pressed into the metal mask 7. . The squeegee pressure is appropriate when the cream solder 3 is printed with the pressure and the cream solder 3 is exposed on both the small area test land 5 and the small area test land 6 without exposing the metal foil.
Is the pressure at which printing is OK. The small squeegee pressure means that when the cream solder 3 is printed with the pressure, the cream solder 3 is printed uniformly on the small area test land 6 and is OK, but the large area test land 5 has one metal foil due to insufficient pressure. The pressure at which the part is exposed and becomes NG. On the other hand, a large squeegee pressure means that when the cream solder is printed with the pressure, the pressure is too strong on the small-area test land 6, so that the cream solder 3 is scraped off at the center to expose the metal foil and N
G means the pressure at which the cream solder 3 is sufficiently printed on the large-area test land 5 to be OK. The experimental results in Table 1 show that the area of the large-area test land 5 is 10 to 35 mm 2 and the area of the small-area test land 6 is 0.1 to 35 mm 2.
2.0 square millimeters, and the appropriate squeegee pressure is expressed as 0 to 0.
It was 10 mm. In the case of the printed wiring board without the test lands 5 and 6, the metal foil 2 was not exposed when the amount of pushing the solder squeegee was between -0.10 and 0.30 at the same pressure.

Note that the pushing amount of 0 means the solder squeegee 8
Is in light contact with the surface of the metal mask 7 (the squeegee pressure is ~ 0), and the plus side is the solder squeegee 8
Indicates a state where the tip of the button is biting, and a minus side indicates a state where the tip is floating. The amount of indentation is -0.10mm.
0.10 mm between the tip of the metal mask 7 and the surface of the metal mask 7.
There is a gap.

A value of 0 to 0.10 and -0.10 to 0.3
As is clear from the comparison of the value range of 0, the cream solder 3 on the small area test land 6 and the large area test land 5
Inspection of the printing state of the above by a two-dimensional inspection apparatus makes it possible to narrow the printing pressure range to a narrow range.

The cream solder printing inspection method of the present invention comprises:
The steps up to the inspection are the same as the conventional method. That is, the cream solder 3 is uniformly applied by screen printing on the metal foil 2 including the test pair lands 9 and 11 on the printed wiring board 1 on which the test land pairs 9 and 11 are provided.
Next, the cream solder 3 printed on all the metal foils 2 including the test lands is inspected from above the printed wiring board 1 using the two-dimensional image inspection camera 4. Inspection items include a conventional item relating to the positional accuracy of the metal foil 2 and the cream solder 3, an item relating to the uniformity of the concentration of the cream solder 3 on the metal foil 2, and a new concentration for the test land pairs 9 and 11. This is an item related to the uniformity (whether or not the metal foil is exposed). by this,
If the amount of cream solder printed is managed by a three-dimensional inspection device, the same management becomes possible, and high-reliability and high-quality soldering becomes possible.

[0032]

As described in detail above, in the print inspection of cream solder, the printed film thickness of cream solder is managed by managing the test land pair provided on the printed wiring board by the two-dimensional image inspection apparatus. And more reliable and high quality soldering can be performed.

Also, by using the printed wiring board of the present invention, a conventional two-dimensional image inspection apparatus can be used, and there is no need for new capital investment.

[Brief description of the drawings]

FIG. 1A is a front view of a printed wiring board according to an embodiment of the present invention. FIG. 1B is a cross-sectional configuration diagram of an inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a printed wiring board in a cream solder printing / inspection method according to an embodiment of the present invention; FIG. 2B is a cross-sectional view of printing a cream solder from above a metal mask; Sectional view of peeled printed wiring board (d) Sectional view for two-dimensional image inspection

FIG. 3A is a front view of a conventional cream solder printed wiring board. FIG. 3B is a cross-sectional view of a conventional two-dimensional image inspection apparatus for inspecting a printing state of cream solder.

FIG. 4 is a diagram showing an example of a two-dimensional image for determining whether the printing state of cream solder is good or not using a conventional two-dimensional image inspection apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 101 Printed wiring board 2, 102 Metal foil 3, 103 Cream solder 4, 104 Camera 5 Large area test land 6 Small area test land 7 Metal mask 8 Solder squeegee 9, 11 Test land pair 10 Metal mask opening

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[Procedure amendment]

[Submission date] December 14, 1999 (1999.12.
14)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

[0027]

[Table 1]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction contents]

The squeegee pressure in Table 1 is the pressure at which the solder squeegee 8 presses the metal mask 7 in FIG. 2B, and can be changed by adjusting the amount of the solder squeegee 8 pressed into the metal mask 7. . The squeegee pressure is appropriate when the cream solder 3 is printed with the pressure and the cream solder 3 is not exposed on both the large- area test land 5 and the small-area test land 6 without exposing the metal foil.
Is the pressure at which printing is OK. The small squeegee pressure means that when the cream solder 3 is printed with the pressure, the cream solder 3 is printed uniformly on the large area test land 5 and is OK, but the small area test land 6 has one metal foil due to insufficient pressure. The pressure at which the part is exposed and becomes NG. On the other hand, a large squeegee pressure means that if cream solder is printed at the pressure, the large area test land 5 has too strong pressure, so that the cream solder 3 is scraped off at the center and the metal foil is exposed and N
G means the pressure at which the cream solder 3 is sufficiently printed on the small- area test land 6 to be OK. The experimental results in Table 1 show that the area of the large-area test land 5 is 10 to 35 mm 2 and the area of the small-area test land 6 is 0.1 to 35 mm 2.
2.0 square millimeters, and the appropriate squeegee pressure is expressed as 0 to 0.
It was 10 mm. In the case of the printed wiring board without the test lands 5 and 6, the metal foil 2 was not exposed when the amount of pushing the solder squeegee was -0.10 to 0.30 mm at the same pressure.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0029

[Correction method] Change

[Correction contents]

The pushing amount of 0 mm refers to a state in which the tip of the solder squeegee 8 is lightly in contact with the surface of the metal mask 7 (the squeegee pressure is up to 0 g / cm ). The state, the minus side indicates a floating state. The pushing amount of −0.10 mm is a state where there is a gap of 0.10 mm between the tip of the solder squeegee 8 and the surface of the metal mask 7.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0030

[Correction method] Change

[Correction contents]

A value between 0 and 0.10 mm and between -0.10 and
As is clear from comparison of the value range of 0.30 mm, the printing pressure range is narrowed by inspecting the printing condition of the cream solder 3 on the small area test land 6 and the large area test land 5 with a two-dimensional inspection device. You can narrow down to a range.

Claims (6)

[Claims] A small-pitch metal foil connected to a mounting component having a narrow-pitch terminal electrode, a large-pitch metal foil connected to a mounting component having a large-pitch terminal electrode, and an area smaller than an area of the narrow-pitch metal foil. A printed wiring board comprising: a first test land; and a second test land having an area larger than an area of the large pitch metal foil. 2. The printed wiring board according to claim 1, wherein the first test land and the second test land are arranged as an adjacent pair. 3. The printed wiring board according to claim 2, wherein pairs of the first test lands and the second test lands are arranged at diagonal positions of the printed wiring board. 4. The printed wiring board according to claim 1, wherein the area of the first test land is 0.05 to 3 mm 2, and the area of the second test land is 4 to 50 mm 2. 5. A step of printing cream solder on a first test land and a second test land on the printed wiring board according to claim 1, and printing on a surface of the first test land and the second test land. A step of capturing the two-dimensional image of the cream solder by a camera from above the printed wiring board, and a calculating step of performing a multi-value processing on the density of the two-dimensional image, wherein the first test after the multi-value processing is performed. A method for inspecting a printed circuit board, comprising determining whether the print thickness of the cream solder is appropriate based on the uniformity of the image density between the land and the second test land. 6. A determination is made that the printed film thickness of the cream solder is within an allowable film thickness when both multi-valued processed image densities in the first test land and the second test land are within a predetermined density range. The method for inspecting a printed circuit board according to claim 5, wherein