JP3314406B2 - How to measure the height of cream solder - Google Patents

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 of a cream solder, and more particularly to a method for measuring the height of a cream solder based on the upper surface of a circuit pattern having good flatness covered with a solder resist. Is measured by a laser beam, and based on the measured value, the quality of the applied amount of the cream solder is inspected.

[0002]

2. Description of the Related Art Chips such as ICs and LSIs are bonded to electrodes on a substrate by soldering. This soldering is performed by applying cream solder to the electrodes of the substrate using a screen printing device, landing the chip leads on the cream solder, and then heating the cream solder using a reflow device.

[0003] By the way, if the amount of cream solder applied is not proper, soldering is likely to be defective. Therefore, before mounting a chip on a substrate by a chip mounter, an inspection for judging whether the amount of cream solder applied is proper or not is performed. Will be As this inspection method, it is known that the height of the cream solder is measured using a laser device, and the quality of the applied amount of the cream solder is determined based on the result.

The height is measured by irradiating the cream solder applied to the electrodes of the substrate with laser light from the light emitting section and receiving the reflected light at the light receiving section. In this case, the cream solder is used. Height standards must be set. Therefore, conventionally, the height of the upper surface of the electrode on which the cream solder is applied is measured by a laser beam, and the height of the upper surface is used as a reference for the height.

[0005]

On the upper surface of the electrode, a solder coating portion is formed by a solder leveler, solder plating or the like in order to improve the wettability of the cream solder. The reference for the actual height is the upper surface of the solder coating. However, since the upper surface of the solder coating portion is rough and has significant irregularities, when the height is measured by irradiating a laser beam, the measurement result tends to vary. For this reason, in the conventional means using the solder coating portion as a reference for the height, there has been a problem that the reliability of the measurement result of the cream solder height is low, and that the determination of the quality of the application amount of the cream solder is liable to occur.

[0006] The substrate is coated with a solder resist so that solder does not adhere to portions other than the electrodes.
This solder resist is transparent or translucent, and transmits laser light. The circuit pattern formed simultaneously with the electrodes by etching means is covered with solder resist, but its upper surface is a smooth surface with relatively few irregularities and is protected by solder resist, so it has a relatively flat surface. Is good.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a cream solder height measuring method capable of improving measurement accuracy by a laser beam.

[0008]

For this purpose, the present invention provides a method of irradiating a circuit pattern covered with a solder resist on the side of an electrode with a laser beam, measuring the height of the upper surface thereof, and measuring the measured height. Is used as a height standard, and the height of the cream solder is measured by a laser beam.

[0009]

According to the above arrangement, when laser light is irradiated from the light emitting portion to the circuit pattern on the side of the electrode, the laser light is transmitted through the transparent or translucent solder resist and is irradiated on the upper surface of the circuit pattern. The reflected light is received by the light receiving section to detect the height of the upper surface of the circuit pattern. Then, the cream solder applied to the electrodes of the substrate is irradiated with laser light, and the reflected light is received by a light receiving portion to measure the height of the cream solder. In this case, the upper surface of the circuit pattern is a smooth surface. Moreover, since it is covered and protected by solder resist,
The flatness is relatively good, and the reliability as a height standard is extremely high. Therefore, by using the height of the upper surface of the circuit pattern as a reference for the height of the cream solder, a highly reliable measurement result can be obtained, and based on this, the quality of the cream solder is appropriately determined. be able to.

[0010]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a front view of the cream solder height measuring device. 1 is a substrate, 2 is an electrode formed on the substrate 1, 3
Is a cream solder applied to the upper surface of the electrode 2 by a screen printing device, 4 is an X table, and 5 is a Y table. Reference numeral 6 denotes a light emitting unit of the laser light B, 7 denotes a light receiving unit that receives the laser light B emitted from the light emitting unit 6 and reflected by the object,
Reference numeral 8 denotes a bracket for attaching the light emitting unit 6 and the light receiving unit 7 to the Y table 5, and 9 and 10 denote motors for driving the XY tables 4 and 5. The light emitting unit 6 and the light receiving unit 7 move integrally in the XY directions. I do. Reference numeral 11 denotes a CCD camera provided on the Y table 5 for observing the cream solder 3.

FIG. 2 is a cross-sectional view of the substrate 1 in which the cream 2 is applied to the electrode 2. A circuit pattern 12 connected to the electrode 2 is formed on the upper surface of the substrate 1. The electrode 2 and the circuit pattern 12 are formed at the same time by a copper foil etching means or the like, and their surfaces are smooth surfaces with relatively few irregularities. Reference numeral 13 denotes a solder resist that covers portions of the circuit pattern 12 other than the electrodes 2. The solder resist 13 is made of a transparent or translucent resin, and transmits the laser beam B so that the height of the upper surface of the circuit pattern 12 can be measured. Reference numeral 14 denotes a solder coating formed on the upper surface of the electrode 2 in order to improve the wettability of the cream solder 3. The solder coating portion 14 is formed by a solder leveler, solder plating, or the like, and the upper surface thereof is a rough surface having irregularities as described above.

Next, the cream solder 3 using this measuring device
An inspection method will be described. In the present embodiment, the quality of the planar shape of the cream solder 3 is inspected by the camera 11 and the laser light B
Inspection of the height of the cream solder 3 is performed, and if both the tests pass, the application amount of the cream solder 3 is determined to be good.

First, a quality inspection of the planar shape of the cream solder 3 by the camera 11 is performed. FIG. 3 is an explanatory diagram for determining whether or not the planar shape of the cream solder 3 by the camera 11 is good. In the figure, column A shows a planar image of the electrode 2 obtained by binarizing the CCD image captured by the camera 11. The electrode 2 made of a copper foil is observed dark, and the cream solder 3 made of an alloy of lead and tin is observed bright. Also B
The column shows a determination diagram of the quality. Column a shows non-defective cream solder 3, column b shows displacement, column c is missing, and column d shows defective cream solder 3 due to bleeding. Next, a method of determining the quality of the cream solder 3 in the planar shape will be described in detail.

An appropriate amount of cream solder 3 indicated by Aa is applied to the center of the electrode 2. Ba shows a quality judgment diagram of the cream solder 3. The determination of the quality of the cream solder 3 is made based on the design area of the electrode 2. That is, the area of the non-applied portion obtained by subtracting the area of the cream solder 3 from the design area S1 of the electrode 2 (that is, the area of the portion shaded in the column A-a) S2 falls within the preset area. It is determined by whether or not there is. L (LOW)
Is the lower limit of the area, and H (HIGH) is the upper limit of the area. The lower limit L and the upper limit H are set according to the required accuracy. In the section Ba, S2 is between the lower limit value L and the upper limit value H, and is therefore determined to be non-defective. The design area S1 of the electrode 2 is known in design and is registered in a computer (not shown) in advance. The area S2 can be easily obtained by well-known image processing based on a luminance distribution.

In addition, in Ab, the cream solder 3 is formed on the electrode 2 so as to be displaced to the upper right. Such a displacement occurs when there is a displacement between the screen mask and the substrate 1 when the cream solder 3 is printed by the screen printing apparatus. In this case, the area of the cream solder 3 is reduced by the amount protruding from the electrode 2, and therefore, as shown by Bb, the area S2 of the non-applied portion is set to the upper limit H
Is determined as a defective product.

In A-c, the cream solder 3 lacks the left end. Such chipping occurs when a part of the pattern holes formed in the screen mask of the screen printing apparatus is clogged. The area is reduced by the amount of the cream solder 3 being chipped, and the non-applied area S2 exceeds the upper limit H as shown by B-c, so that it is determined to be defective.

In Ad, the cream solder 3 is the electrode 2
Oozes out near the outer edge. This bleeding occurs when a large amount of cream solder 3 is applied to the electrode 2. The area of the cream solder 3 increases by the amount of the oozing, and therefore, as shown in Bd, the uncoated area S2
Is smaller than the lower limit L, so that it is determined to be defective. As described above, by using the design area S1 of the electrode 2 as a criterion, the quality of the cream solder 3 in the planar shape can be easily determined.

The board 1 on which the cream solder 3 determined to be defective is formed by inspection of the planar shape with the camera 11 is removed, and only the board 1 for which all cream solders 3 are determined to be non-defective is described below. As described above, the inspection of the height of the cream solder 3 by the laser beam B is performed.
This inspection is performed by scanning the laser beam B in the direction (arrow X direction) that traverses the electrode 2 in FIG. 4 to measure the height distribution of the cream solder 3 in the longitudinal direction, and the direction traversing the electrode 2. And scanning the laser beam B in the direction of the arrow Y to measure the height distribution of the cream solder 3 in the width direction.

First, in the longitudinal direction (X
The inspection for measuring the height distribution in the (direction) will be described in detail. FIG. 5 is an explanatory diagram of the quality judgment of the cream solder 3. FIG.
In the column A, the substrate 1 in which the cream solder 3 is applied to the electrode 2 is shown.
, A column B shows a determination diagram of the quality of the cream solder 3, and a column C shows a determination formula of the quality. In addition, the column a of FIG. 5 shows a non-defective cream solder 3, the column b of FIG. 5 shows a cream solder 3 of an inferior product due to an insufficient amount, and the column c of FIG.

The laser beam B is scanned in the X direction to obtain the height distribution of the cream solder 3 in the longitudinal direction indicated by Ba. Then, a preset upper limit value H (HI
GH) and the length L1, which falls within the range of the lower limit L (LOW).
The sum L of L2 and L3 is obtained, and pass / fail is determined based on whether or not the sum L is within a range between a preset lower limit Lmin and an upper limit Lmax. In this example, Lmin <
L <Lmax, and it is determined that the product is good.

In Ba, S.D. L is a reference for height, and as shown in FIG. 2, a circuit pattern 12 covered with a solder resist 13 on the side of the electrode 2 by a laser beam B.
Is set by measuring the height of the upper surface of the. As described above, since the upper surface of the circuit pattern 12 is smooth and covered with the solder resist 13, the planarity thereof is extremely good. The reliability of the measurement result at the height of 3 is extremely high, and accurate pass / fail judgment can be made. Note that M (M
AX) is the maximum limit height of the cream solder 3 set at a position exceeding the upper limit H. Even if the determination formula of Ca is satisfied, if a part of the cream solder 3 exceeds this, it is determined to be defective. Is done.

In FIG. 5A-b, only a small amount of the cream solder 3 is applied to the electrode 2 and the height thereof is low. In this case, as shown in Bb, L is only L1, and therefore, as shown in Bc, L is smaller than Lmin.

In FIG. 5A-c, a large amount of the cream solder 3 is applied to the electrode 2 and is high. in this case,
As shown by Bc, the sum L of L1, L2, and L3 becomes small, and therefore, as shown by Cc, L becomes smaller than Lmin.

Inspection of the height distribution of the cream solder 3 in the longitudinal direction by the laser beam B removes the substrate 1 having the cream solder 3 determined to be defective, and all the cream solder 3 are determined to be non-defective. An inspection of the height distribution of the cream solder 3 in the width direction is performed on only the substrate 1 as described below.

Next, the inspection of the height distribution in the width direction of the cream solder 3 will be described with reference to FIG. FIG. 6 is an explanatory diagram of the quality judgment of the cream solder 3. 6A is a cross-sectional view of the substrate 1 in which the cream solder 3 is applied to the three electrodes 2, FIG. 6B is a diagram showing the determination of the quality of the cream solder 3, and FIG. 6C is the determination of the quality of the cream solder 3. The equation is shown. Also,
6A shows a good cream solder 3 and FIG. 6B shows a bad cream solder 3 due to bleeding.

The laser beam B is scanned in the Y direction of FIG. 4 to obtain the height distribution of the cream solder 3 in the width direction shown by Ba. And the height standard S.M. The widths D1, D2, and D3 of the cream solder 3 in L are measured, and these D1, D2, and D3 are set to a predetermined lower limit value Dmin.
Pass / fail is determined based on whether it is within the range of the upper limit value Dmax. In this example, as shown by Ca, Dmin <D1 <Dma
x, Dmin <D2 <Dmax, and Dmin <D3 <Dmax, and are determined to be non-defective.

In FIG. 6Ab, a large amount of the cream solder 3 at the center is applied to the electrode 2 and oozes to the outer edge of the electrode 2, and as shown at Bb, the cream solder 3 at the center is removed. The width D2 on the height reference plane is longer. For this reason, as indicated by Cb, D2 is larger than Dmax and is determined to be defective.

The board 1 on which the cream solder 3 determined to be defective is formed by inspection of the height distribution of the cream solder 3 in the width direction with the laser beam B is removed, and the planar shape inspection by the camera 11 and the laser In the inspection of the height of the cream solder 3 in the X direction and the Y direction by the light B, only the substrate 1 in which all the cream solders 3 are determined to be good is sent to a post-process such as reflow.

This means measures the height of the cream solder 3 using the upper surface of the circuit pattern 12 as a reference for the height as described above. In this case, the upper surface of the circuit pattern 12 is smooth and the solder resist 13 is used. , The flatness is relatively good, and the reliability as a height standard is high. Accordingly, by using the height of the upper surface of the circuit pattern 12 as a reference for the height of the cream solder 3, the rough solder coating portion 1 having poor flatness as in the prior art.
4. A highly reliable measurement result can be obtained as compared with the case where the upper surface of the electrode 2 of the substrate 1 covered by the solder 4 is used as a reference for the height. The judgment can be made accurately.

In the embodiment, the cream solder 3 determined to be defective by the inspection of the planar shape by the camera 11 is used.
Is removed, and all the cream solder 3 is removed.
The inspection of the height of the cream solder 3 by the laser beam B is performed only on the substrate 1 which has been determined as a non-defective product. By removing the substrate 1 of the defective cream solder 3 by the inspection, the inspection time can be shortened, and the inspection accuracy of the appearance inspection of the cream solder 3 can be improved.

[0031]

As described above, in the present invention, the height and width of the cream solder are measured using the upper surface of the circuit pattern as a reference for the height, so that the rough solder coating portion having poor flatness as in the prior art is used. The accuracy of measuring the height of the cream solder can be improved as compared with the case where the upper surface of the electrode of the substrate covered with the solder is used as a reference for the height.

[Brief description of the drawings]

FIG. 1 is a front view of a cream solder measuring apparatus according to the present invention.

FIG. 2 is a cross-sectional view of a substrate coated with cream solder according to the present invention.

FIG. 3 is an explanatory diagram for judging the quality of the planar shape of the cream solder according to the present invention.

FIG. 4 is a plan view of a substrate to which the cream solder according to the present invention has been applied;

FIG. 5 is an explanatory diagram for determining the quality of the height distribution in the length direction of the cream solder according to the present invention.

FIG. 6 is an explanatory diagram for judging the quality of the height distribution in the width direction of the cream solder according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 electrode 3 cream solder 6 light emitting part 7 light receiving part 12 circuit pattern 13 solder resist 14 solder coating part B laser light

Claims (1)

(57) [Claims] 1. A laser beam is emitted from a light emitting portion to a cream solder applied to a solder coating portion formed on an electrode of a substrate, and the reflected light is received by a light receiving portion to measure the height of the cream solder. Then, in inspecting the quality of the applied amount of cream solder based on the measured height, the circuit pattern covered with the solder resist on the side of the electrode is irradiated with laser light to measure the height of the upper surface thereof. A method for measuring the height of the cream solder, wherein the height of the upper surface is used as a reference for the height of the cream solder.