JP2907605B2 - Inspection method of soldering state by X-ray - 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 inspecting the state of soldering by X-rays, and obtains a concentration distribution in a longitudinal direction of solder for fixing an electrode of an electronic component to a substrate. Is determined.

[0002]

2. Description of the Related Art After an electronic component is fixed to a substrate by soldering, an inspection for judging the quality of a soldered state is performed. Conventionally, this inspection has been performed by visual inspection of an operator, but in recent years, automatic inspection using an optical device such as a camera or a laser device has been gradually spread.

[0003] In a camera or a laser device, the appearance of the solder exposed to the outside can be inspected. However, the solder hidden under the electrodes of the electronic components cannot be irradiated with illumination light or laser light. There was a problem that inspection was not possible.

Therefore, it has already been proposed to inspect the soldering state using an X-ray apparatus. Since the X-rays penetrate the substance, by obtaining a transmission image thereof, it is possible to inspect solder that is not exposed to the outside, such as the solder hidden under the electrodes as described above.

[0005]

However, at present, a specific method for accurately judging the quality of a soldering state based on an X-ray transmission image has not yet been sufficiently determined.

Incidentally, when X-rays pass through a substance, the intensity is attenuated, and the degree of the attenuation depends on the type and thickness of the substance. In electronic circuit boards, solder is the most likely to attenuate X-rays compared to other components. Therefore, by controlling the transmission capacity by adjusting the tube voltage, etc., substances other than solder, such as glass epoxy boards and resins It is possible to transmit the light through a mold or the like and selectively obtain only the solder portion as an image. Using this solder image, it is possible to inspect the bonding state from the presence or absence of solder and the distance measurement in the planar direction of the board.

[0007] Further, for the thickness of the solder, by utilizing the fact that the X-ray intensity attenuates exponentially, the density of the transmitted image is divided into gradation levels, and an upper limit level and a lower limit level are set. Insufficient or excessive solder can be inspected.

Accordingly, an object of the present invention is to provide a method for accurately judging the quality of a soldered state from an X-ray transmission image.

[0009]

According to the present invention, an electronic component mounted on a substrate is irradiated with X-rays to obtain a concentration distribution in a longitudinal direction of a solder for fixing an electrode of the electronic component to the substrate. A reference density level that intersects the distribution is set, an intersection between the density distribution and the reference density level is determined, and the quality of the soldering state is determined from the length of the distance between the intersections.

[0010]

According to the above configuration, the quality of the soldering state can be easily determined from the length of the distance between the intersections of the density distribution and the reference density level.

[0011]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a front view of the X-ray inspection apparatus. Reference numeral 1 denotes a substrate to be inspected, on which a rectangular electronic component 11 and an electronic component 12 with leads are mounted. The rectangular electronic component 11 includes a capacitor chip and a resistance chip, and the electrode E
Are fixed to the substrate 1 by solder S. The electronic components 12 with leads include QFP, SOP, and TAB devices, and the leads L, which are electrodes, are fixed to the substrate 1 by solder S.

The substrate 1 is placed on an XY table 2 and moves in the XY directions. X above the XY table 2
A radiation source 3 is provided, and irradiates the substrate 1 with X-rays. X
An aperture unit 4, an X-ray detector 5, an optical unit 6, and a camera 7 are provided below the Y table 2, and the transmitted image of the X-ray transmitted through the substrate 1 is taken into the camera 7.

FIG. 2 is an explanatory diagram for judging whether or not the soldering state of the rectangular electronic component 11 is good. In the figure, column A shows a side view of the rectangular electronic component 11. Column B is camera 7
3 shows an X-ray transmission image captured in FIG. Column C is the concentration distribution GL (GLa to GLh) along the vertical line NA of column B.
And a histogram HG of the inspection area. In column C, SL indicates a reference density level, and P, Q1, and Q2 indicate distances between intersections of density distributions GL (GLa to GLg) and the reference density level SL. Lmin is the lower limit set concentration.
Column D shows a pass / fail judgment formula.

Column a shows good solder. Column b shows missing parts, column c shows displacement, column d floats, column e stands, the right side of column f shows too little solder, and the right side of column g shows too much solder. Column h shows the case where a solder bridge Sa has occurred. Column i shows the case where a solder ball Sb has occurred. Aa to Ag and Ai are electronic components 1
1 is a side view, and Ah shows a plan view of the electronic component 11. In this embodiment, the solder S in column a is good, and the solder S in columns b to i are all bad. Next, referring to FIG.
The pass / fail judgment method will be described in detail.

The solder S of the electronic component 11 indicated by Aa has the electrode E firmly fixed to the substrate 1, and this solder S is a good product. Ba is an image of the electronic component 11, and the solder S is observed dark. Ca is N which traverses the solder S
The density distribution GLa along the A line is shown. As shown in the figure, since the X-rays hardly penetrate the solder S, the concentration level of the portion corresponding to the solder S is extremely low. in this case,
The distances P, Q1, and Q2 between the intersections of the density distribution GLa and the reference setting level SL satisfy all the expressions of Da. Note that Pmin and Qmin are lower limit values, Pmax and Qmax are upper limit values, and Lmin is a lower limit set concentration, which are arbitrarily set, but the values are slightly different depending on required accuracy. The minimum value GLamin of the density distribution GLa is larger than the lower limit set density Lmin. If all the formulas shown in Da are satisfied, the solder is determined to be good. The distance P is the length K of the electronic component 11 (see Aa).
If they are approximately equal, it can be determined that they are non-defective.

Further, in the case of Ab, no electronic component exists on the solder S. Such a shortage occurs when the chip mounter fails to mount the electronic component on the substrate 1. In this case, the image is as shown by Bb, and the density distribution GLb is as shown by Cb. D-
If the expression shown in b is satisfied, it is determined to be defective.

In Ac, the electronic component 11 is displaced from the set position. In this case, the image is as shown in Bc, and the density distribution GLc is as shown in Cc. The pass / fail judgment formulas are as shown in Dc. If these formulas are satisfied, it is judged that the test is defective. A
The electronic components 11 indicated by −d, Ae, Af, and Ag are also determined to be good or defective by the same method as in the above-described case, and thus detailed description is omitted.

Ah shows the case where the solder bridge Sa has occurred. In this case, as shown in Bh, an inspection line NB is set between the electronic components 11 and
-H is obtained. Then, when the boundary density level BL is set and the determination expression of Dh is satisfied, it is determined that the solder bridge Sa exists.

A-i shows a case where the solder ball Sb is generated. In this case, as shown in Bi, the electronic component 1
Inspection areas CA1 and CA2 are set on the side of No. 1 and C-i
As shown in the figure, a histogram HG of the density of the inspection areas CA1 and CA2 is obtained. TH is a threshold value. If the number N of low-luminance pixels equal to or less than the threshold value TH is equal to or greater than the set number Nmin, it is determined that the solder ball Sb exists.

FIG. 3 shows the leads L of the electronic component 12 with leads.
2 shows a method of inspecting solder S for fixing semiconductor device 1 to substrate 1. Also in this case, the quality of the soldered state is determined by the same method as in the case of FIG. That is, Aa is a side view of the lead L in a good soldered state. Ba-a is a transmission image of the solder S. The rear part S1 (called a back fillet) of the solder S is sucked more sufficiently by the lead L than the front part S2 (called a toe fillet), and just above the back fillet S1. , The lead L is bent,
Since the transmission distance W of the X-ray lead L is long, the image of the rear part S1 is darker than the image of the front part S2 (Ba, Ca).
reference).

Da indicates a pass / fail judgment formula. In this case, upper and lower levels P′max, Q′max and P′min,
Set Q'min. And each minimum value BF,
If TF satisfies the determination formula of Da, the soldering state is determined to be good. That is, in the case of the rectangular electronic component 11 shown in FIG. 2, as described with reference to the C and D columns,
Although the pass / fail was determined based on the distances P and Q between the intersections, in the case of the leaded electronic component 12 shown in FIG. 3, the minimum values BF and TF of the rear part S1 and the front part S2 of the solder S were set to the upper limit level P′max,
The quality is determined by comparing with Q′max and the lower limit levels P′min and Q′min.

Ab is a missing item, and Ac is a displacement.
The lead L of Ac is a plan view. Ad is completely floating, Ae is partially floating, Af is too little solder, Ag
Is too much solder.

Ah denotes a solder bridge Sa, and an inspection line NB is set between the leads L.
As in the case of Ah, the presence or absence of the solder bridge Sa is determined. Note that the solder balls Sb are also inspected by the exactly same method as in FIG. 2A-i, and a description thereof will be omitted.

As described above, according to the present method, the quality of the soldered state can be easily inspected from the transmission image obtained by irradiating the electronic component with X-rays. Since all of the solder S shown in FIG. 2 is exposed, the quality of the solder S can be determined by a camera, a laser position, or the like. However, the solder S shown in FIG. Therefore, observation and measurement cannot be performed using a camera or a laser position, and pass / fail determination can be performed based on X-rays transmitted through the lead L. Alternatively, it is also possible to obtain a clear image or a density distribution while changing the X-ray irradiation angle by, for example, tilting the substrate 1 to determine the quality of the soldered state.

[0026]

As described above, the present invention can be applied to a substrate.
The mounted electronic components are irradiated with X-rays, and the electrodes of the electronic components are exposed.
The concentration distribution of the solder that adheres to the substrate in the longitudinal direction was determined, and this was determined.
Set a reference density level that intersects the density distribution
Find the intersection between the density distribution and the reference density level, and calculate the distance between the intersections.
It is a simple method to judge the quality of the soldered state from the separation length
By the method, the quality of the soldering state can be accurately determined.

[Brief description of the drawings]

FIG. 1 is a front view of an X-ray inspection position according to the present invention.

FIG. 2 is an explanatory diagram for judging the quality of the soldered state of the rectangular electronic component according to the present invention.

FIG. 3 is an explanatory diagram for judging the quality of a soldered state of an electronic component with leads according to the present invention.

[Explanation of symbols]

 1 Board 11 Electronic component 12 Electronic component S Solder GL Concentration distribution SL Reference concentration level P Distance between intersections Q Distance between intersections BF Minimum value TF Minimum value P'min Lower limit level Q'min Lower limit level P'max Upper limit level Q ' max upper limit level

Claims (1)

(57) [Claims] An X-ray is applied to an electronic component mounted on a substrate to determine a concentration distribution in a longitudinal direction of solder for fixing an electrode of the electronic component to the substrate, and a reference concentration level intersecting with the concentration distribution is determined. A method for inspecting a soldering state by X-rays, wherein an intersection between the density distribution and a reference density level is set, and the quality of the soldering state is determined from the length of the distance between the intersections.