JPH10239245A - Visual inspection method for lead - Google Patents

Abstract

PROBLEM TO BE SOLVED: To establish a method in which a visual inspection is automated and in which a flaw and a surface irregularity are detected without an erroneous detection by a method wherein a plurality of black points inside a lead are set as foreign-body candidates and only a foreign body is detected from the candidates by making use of the difference in a feature between the foreign body and the flaw. SOLUTION: The image signal, of an object 1 to be inspected, which is input from an image imaging part 2 is read out by an image storage part 7 as gray level data, it is computed and processed by a processing and judgment part 8, it is compared with a judgment value which is set in advance in a judgment-value storage part 10, and whether an outward- appearance defect exists or not is judged. A plurality of foreign-body candidate points are set with reference to the outer shape of a detected lead. When the size of a candidate point does not exceed a judgment value J1, a nondefective is judged. A first-order differential value is computed on the basis of a density distribution near a boundary. When its mean value D1 does not exceed a judgment value J2, a flaw is judged. A first-order differential value D2 is computed regarding all leads. When its ratio to the mean value D1 does not exceed a judgment value D3, an irregularity is judged. When the ratio regarding the gray-level- value mean of a reinforcing lead to an adjacent lead does not exceed a judgment level 4, a foreign body is judged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for inspecting the appearance of leads of a semiconductor device or other electronic parts.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No. 6-66533 discloses an example of a technique for inspecting the appearance of leads.

In the manufacture of semiconductor devices and the like, the appearance of a package often greatly affects quality. In other words, when a package defect including a lead occurs in the product, not only is the visual impression bad, but also the characteristic is likely to be deteriorated due to a mounting defect or penetration of moisture. Therefore, at the final stage of the manufacturing process, an appearance inspection step is performed to inspect whether or not these appearances meet a certain standard. Conventionally, such visual inspection has been performed visually by a human, but in recent years automation has been advanced and an inspection device has been developed. However, as described in the above-mentioned publications, the devices have been implemented only for inspection of defects related to shapes such as bending or floating of leads of IC packages or mark inspection.

[0004]

As described above, there is an example in which the method of detecting a shape defect is described, and there is an automated example. However, in a visual inspection device, there is no device capable of inspecting foreign matter adhering to a lead. Did not. In particular, there is a problem that foreign matter adhered to the back surface of the lead causes a contact failure with a land on the substrate or a writing terminal when mounting the semiconductor device on the substrate or writing data to the semiconductor device. After the lead shape is inspected by the visual inspection device, it is necessary for a human to visually inspect again.
However, in order to inspect the back of the lead, it is necessary to turn the package upside down and look at the package. Therefore, the inspection is limited to a specific type for a specific customer or is performed as a sampling inspection. In addition, the size of foreign matter to be detected has become smaller in conjunction with the finer lead pitch accompanying the increase in the number of leads, which makes detection difficult for the human eye. This is a laborious inspection.

In order to reduce the number of steps in the appearance inspection process as described above, it is essential to develop a device capable of automatically detecting foreign matter adhering to the back surface of the lead, but the state of the back surface of the lead at the final stage of the manufacturing process is as follows. In many cases, a plurality of indentations or scratches on the terminals remain or the surface is uneven due to the test process or the like that has been performed up to that time. Since these flaws do not adversely affect the operation of the semiconductor device, they are good for inspection.However, in the image for performing the automatic inspection for the black foreign matter, the flaws or a part of the unevenness appear black, and the image With only the binarization method, there is a problem that these are erroneously detected as foreign substances.

SUMMARY OF THE INVENTION An object of the present invention is to automate the appearance inspection at the final stage in the manufacturing process of a semiconductor device or the like or at each stage after the lead cutting and molding process. An object of the present invention is to provide a method for detecting flaws and uneven surface without erroneous detection.

[0007]

In order to solve the above-mentioned problems, the present invention has devised a method for determining a minute foreign matter as shown in FIG.

First, with respect to the input lead grayscale image,
Binarization is performed so as to detect both foreign matter and flaws, and a plurality of black points in the lead are set as foreign matter candidates. Next, from among these candidate points, selection for finally detecting only the foreign matter is performed using the difference in the characteristics between the foreign matter and the flaw.

[0009] The characteristics of foreign matter and flaws include the following differences. First, there is a difference in brightness change. As shown in FIG. 4, in the case of the foreign matter, the brightness is sharply darkened with respect to the lead around the foreign matter, and the difference in brightness between the foreign matter and the periphery is clear. In contrast, in the case of a flaw, the brightness gradually decreases from the brightness of the lead, and the change in brightness is often smaller than that of the foreign matter. On the other hand, when the surface condition of the lead is poor, regardless of the presence or absence of foreign matter, the brightness of the entire lead portion greatly changes, and particularly a dark portion tends to be a foreign matter candidate point.

Furthermore, in the case of indentation or rubbing of the terminal remaining in the test process or the like, not only a specific lead having a foreign matter candidate point but also an adjacent lead has a similar position as shown in FIG. The flaw exists continuously. It is rare that a foreign substance is attached in such a manner, and usually one foreign substance is present alone, so that it is possible to distinguish it by comparison with an adjacent lead.

As means for realizing these processes, a processing determining unit for performing image processing and determining the presence or absence of a foreign substance, a determination value input unit for inputting and changing a determination value, and a determination value inputting unit. This problem can be solved by providing the storage unit and executing the inspection process shown in FIG.

[0012]

FIG. 1 is a flow chart showing a method for judging a minute foreign matter on a lead according to an embodiment of the present invention, FIG. 2 is a block diagram of an inspection section, FIG. 3 is a block diagram of an inspection apparatus, and FIG. FIG. 5 is an explanatory view showing a difference in brightness change between a foreign matter and a lead, FIG. 5 is an explanatory view showing a difference in appearance of a foreign matter, and FIG. 6 is an identification diagram of a minute foreign matter based on a change in brightness of a foreign matter. FIG. 7 is an explanatory view showing a method, and FIG. 7 is an explanatory view showing a method for identifying a minute foreign matter based on a difference in how a foreign matter and a scratch are attached.

As shown in FIG. 3, the appearance inspection apparatus according to the present embodiment includes an apparatus main body 12, an inspection unit 15, and a control unit 17 including a personal computer system for controlling these units. Indicates an external storage device 19 such as a magnetic disk in addition to a display unit 18 for displaying control information.
Is provided.

The inspection section 15 of the appearance inspection apparatus will be described with reference to FIG. First, an image signal of the inspection target 1 input from the image capturing unit 2 such as a camera
After being A / D-converted by the / D conversion unit 6, it is stored in the image storage unit 7. After the grayscale data is read from the image storage unit 7 and subjected to arithmetic processing by the processing determination unit 8, the calculation result is compared with a determination value preset in the determination value storage unit 10 to determine the presence or absence of appearance defects. You. The judgment value is input to the judgment value input unit 9
Is input, changed, and set in the judgment value storage unit 10. The image and the processing result are D / A-converted by the D / A conversion unit 11, and then displayed on the image display unit 4. The defective data is transferred to the control unit 17 shown in FIG. 3, then displayed on the display unit 18 and stored in the external storage device 19.

When the back surface image of the inspection object 1 is picked up by the image pick-up unit 2, the illuminating unit 5 may be used as a method for dark-field illumination for brightening the surface of the lead, or for bright field having an effect for brightening flaws on the lead. Various lighting methods such as lighting and a combination thereof are conceivable.

The inspection object 1 is supplied from the loader 13 shown in FIG.
A predetermined inspection is performed in the inspection unit 15 and the transport unit 14
Is returned to the unloader 20. The unloader 20 stores non-defective products and defective products in different trays based on the inspection result of the inspection unit 15.

The movement of the inspection object 1 such as a semiconductor device is performed by a transporting means such as a conveyor, for example.
Is controlled by the drive mechanism control unit 16 shown in FIG. Each of the inspection units 15 is processed by the image processing unit 3 and can be visually monitored by an operator by the image display unit 4. In the inspection unit 15, since it is necessary to capture the image of the inspection target 1 from the back surface, for example, while the inspection target 1 is being transported, an image is input from the imaging unit 2 installed below, or a reversing mechanism is provided. A method of inputting an image using the imaging unit 2 installed above or on the side may be considered.
The drive mechanism control unit 16 and the inspection unit 15 are configured to be controlled by the control unit 17.

FIG. 1 shows the flow of the inspection method of the present invention.
Although the basic concept of foreign substance identification has already been described, a lead shape inspection is first performed before the foreign substance inspection.

An image of the inspection object 1 is input from the back surface, and the outer shape is detected for all leads. From the detected data, the shape of the lead width, lead length, lead pitch, etc. is calculated, and the difference with respect to the predetermined shape value, such as the lead pitch, lead irregularity, etc., is calculated.
If not, it is determined to be defective. In the case of a defective product, it is stored in a defective product tray by the unloader 20. In the case of a non-defective product, a lead foreign matter inspection is performed subsequently.

First, for the detected lead outer shape, the range of the mounting surface grounded to the substrate when mounting the inspection target 1 is set as the inspection range. In order to eliminate oversight of foreign matter, a threshold value is set so that a plurality of foreign matter candidate points are included in the inspection range, and binarization is performed. The following processing is performed for each of these candidate points to determine whether or not the candidate point is a foreign substance.

First, if the candidate point size does not exceed a certain judgment value J1, it is judged as a non-defective item and is excluded from the candidate points. As shown in FIG. 6C or FIG. 6D, the remaining candidate points are shifted from the foreign object candidate point shown in FIG. 6A or FIG. The distribution of the density (brightness: f (x)) is obtained, and the first-order differential value (brightness change: g (x) = | f (x)) is obtained as shown in FIG. −f (x−1) |), and further obtains the average value D1. If this value does not exceed a certain determination value J2, this candidate point is determined to be a flaw and is excluded from the candidates.

For the remaining candidate points, the primary differential value D2 is calculated for the entire lead where the candidate point exists. When the surface condition of the lead is poor, the entire lead has unevenness, and the difference between the light and dark portions is large, so that the differential value D2 also takes a large value. This differential value D2,
Ratio of differential value D1 near the boundary between foreign object candidate points (D1 / D2)
Does not exceed the determination value J3, this candidate point is determined to be part of the unevenness of the lead surface, and is excluded from the candidates.

For the remaining candidate points, a data acquisition range including the candidate points is set from the lead L1 as shown in FIG. 7, and the average M1 of the gray values within the range is obtained. Next, two adjacent leads (one in the case of an end lead) L
With respect to 2 and L3, the averages of gray values M2 and M3 are calculated at the same position and the same range as L1. As shown in FIG. 7 (b), when these leads have dark portions equivalent to the leads L1, that is, indentations or scratches on the terminals, the average gray values M2 and M3 also have values close to the average gray value M1 of the leads L1. However, when there is no dark part, the value becomes larger than M1. Therefore, the ratio of the average of the gray values of the leads (M1 / MIN (M2, M3)) is calculated, and if the value does not exceed the determination value J4, that is, if the adjacent lead is sufficiently bright, the candidate point is determined to be a foreign substance. judge.

The above-described method is an algorithm of a thinking process when a human distinguishes a foreign matter or a flaw. The judgment values J1 to J
It is difficult to obtain 4 theoretically. Therefore, to set these values, a method of adjusting the determination result as close as possible to human judgment by repeating trial and error in order to minimize false reports that a foreign object is not overlooked and that a non-defective product is determined to be defective. It is a target.

Although the present invention has been described in detail with reference to the embodiments, it is needless to say that the present invention is not limited to the embodiments and can be variously modified without departing from the gist thereof. In particular, in the above invention, the case where the invention made mainly by the present inventor is applied to the field of application, that is, the so-called visual inspection technique after package assembly in the manufacture of a semiconductor device, has been described. It can be widely applied as a visual inspection method for other electronic components such as VTR head position adjustment and inspection.

[0026]

According to the present invention, minute foreign matter adhering to a lead of a semiconductor device or the like is stably detected without being affected by the surface condition such as a scratch mark on the lead. This makes it possible to automate the inspection of foreign matter on the lead.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a method for determining a minute foreign matter on a lead according to an embodiment of the present invention.

FIG. 2 is a block diagram of an inspection unit.

FIG. 3 is a block diagram of an inspection device.

FIG. 4 is an explanatory diagram showing a difference in brightness change between a foreign matter and a flaw on a lead.

FIG. 5 is an explanatory view showing a difference in how a foreign matter and a scratch are attached.

FIG. 6 is an explanatory diagram showing a method for identifying a minute foreign matter based on a change in brightness caused by a foreign matter and a fog;

FIG. 7 is an explanatory diagram showing a method for identifying a minute foreign matter based on a difference between a foreign matter and a scratch.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Inspection object, 2 ... Image pick-up part, 3 ... Image processing part, 4 ... Image display part, 5 ... Lighting part, 6 ... A / D conversion part.

Claims (1)

[Claims] An image pickup unit for inputting an image of an inspection object and an image input from the image pickup unit are processed to perform a foreign substance inspection on a lead of a semiconductor product or an electronic component. In an inspection apparatus having a processing determination unit for performing, a determination value input unit for inputting and changing a determination value, and a determination value storage unit, a candidate point boundary partial differential value for a defective candidate point on a lead in an image The presence / absence of a foreign object is determined by comparing the ratio of the boundary differential value to the overall lead differential value, and the ratio of the average gray value in the vicinity of the candidate point to the average of the same partial gray value in the adjacent lead, with predetermined determination values. A lead appearance inspection method, characterized in that: