JPH0786320A - Paste inspection method - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a paste inspection method capable of accurately inspecting the state of the paste applied to the lead frame without being affected by the metallic luster of the lead frame. [Structure] When the upper surface of a lead frame LF coated with a paste P is imaged by a CCD camera 1, illumination light L _2A or L _2B is emitted from the lighting device 2A or 2B onto the upper surface of the lead frame LF in a substantially horizontal oblique direction The illumination light applied to the portion where the paste P is not applied is reflected by the surface of the lead frame LF so as not to enter the CCD camera 1, and the illumination light applied to the portion where the paste P is applied. Only the CCD camera 1 is made incident on the CCD camera 1.

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 paste applied to a lead frame in a die bonding process for semiconductor chips.

[0002]

2. Description of the Related Art As a method of fixing a semiconductor chip to a lead frame made of metal, a conductive adhesive called a paste is applied to the upper surface of the lead frame, and the semiconductor chip is die-bonded on the adhesive. There is a method of adhesively fixing a semiconductor chip to a lead frame.

When the semiconductor chip is fixed to the lead frame by such a method, it is necessary to inspect the application position and the application amount of the paste applied to the lead frame from the viewpoint of quality control. A method of inspecting the state of the paste by imaging the upper surface of the lead frame coated with the paste with an imaging device such as a CCD and performing image processing on the image signal output from the imaging device has been considered.

[0004]

However, it has been found that the following problems are encountered when carrying out such an inspection method. In other words, when the lead frame is irradiated with illumination light from above when the top surface of the lead frame coated with the paste is imaged by the imaging device, the illumination light reflected by the surface of the lead frame not coated with the paste is applied with the paste. The incident light enters the image pickup device more than the illumination light reflected by the part. Therefore, the image picked up by the image pickup device is affected by the metallic luster of the lead frame, and it becomes difficult to clearly distinguish the portion where the paste is applied and the portion where the paste is not applied. There is a problem that the paste state cannot be accurately inspected even if the processed image signal is subjected to image processing.

The present invention has been made in view of such circumstances, and a paste inspection method capable of accurately inspecting the state of the paste applied to the lead frame without being affected by the metallic luster of the lead frame. The purpose is to provide.

[0006]

In order to solve the above-mentioned problems, the present invention irradiates a lead frame coated with a paste with an illuminating light from an oblique direction which is almost horizontal when the lead frame is imaged by an imaging device. It is characterized by doing.

[0007]

According to such a method, the illumination light reflected at the portion where the paste is not applied hardly enters the image pickup device, and only the illumination light reflected at the portion where the paste is applied enters the image pickup device. , It becomes possible to distinguish between the part where the paste is applied and the part where the paste is not applied. Therefore, the state of the paste applied to the lead frame can be accurately inspected without being affected by the metallic luster of the lead frame.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A paste inspection method according to the present invention will be described below with reference to FIG.
It will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of a paste inspection apparatus to which the paste inspection method according to the present invention is applied. As shown in FIG. 1, the paste inspection apparatus is provided on the upper surface of a lead frame LF coated with a paste P. CCD camera 1 as an imaging device for imaging from above
And illuminating devices 2A and 2B for irradiating the lead frame LF with illumination light from an oblique direction which is almost horizontal.
The CCD camera 1 and the illumination devices 2A and 2B are
Each is connected to the inspection device main body 3 via a cable, and the inspection device main body 3 is provided with a display unit 4 for displaying inspection results and an operation panel 5.

The display section 4 and the operation panel 5 are connected to the control section of the inspection apparatus body 3. This controller is
As shown in FIG. 2, a central processing unit 6 (hereinafter abbreviated as CPU), a read only memory 8 (hereinafter abbreviated as ROM), a random access memory 9 (hereinafter abbreviated as RAM) and an I / O port. I and 10
A display unit 4 and an operation panel 5 are connected to the / O port 10, and a camera control circuit 11 that controls driving of the CCD camera 1 and lighting control circuits 12A and 12B that control lighting of the lighting devices 2A and 2B are connected. ing.

In such a structure, when the inspection switch provided on the operation panel 5 is turned on by the CPU 6, FIG.
It operates according to the flowchart shown in FIG. 1 and first sends a lighting signal to the illumination control circuit 12A (step S1). As a result, the illumination device 2A is turned on for a predetermined time (for example, 3 seconds), and the illumination light is emitted from the illumination device 2A to the lead frame LF.

Next, the CPU 6 sends an image pickup command to the camera control circuit 11 while the illumination device 2A is on (step S2). This drives the CCD camera 1,
The image captured by the CCD camera 1 is captured by the inspection device body 3.

FIG. 4B is a diagram showing the illumination light emitted from the illumination device 2A to the lead frame LF when the CCD camera 1 takes an image of the upper surface of the lead frame LF coated with the paste P. As shown in FIG. 5, when the upper surface of the lead frame LF coated with the paste P is irradiated with the illumination light L2A from the illumination device 2B from an oblique direction which is substantially horizontal, the illumination light reflected by the portion not coated with the paste P is CCD. The CCD camera 1 receives only the illumination light that is incident on the camera 1 and is reflected at the portion where the paste P is applied.
Incident on. Therefore, in the lead frame LF imaged by the CCD camera 1 at this time, as shown in FIG. 5A, only a portion where the paste P is applied is a white image, and a portion where the paste P is not applied is a black image. Becomes

Next, the CPU 6 stores the image taken in the inspection apparatus main body 3 in the RAM 9 and then the illumination control circuit 12
A lighting signal is sent to B (steps S3 and S4). As a result, the illumination device 2B is turned on for a predetermined time (for example, 3 seconds), and the illumination light is emitted from the illumination device 2B to the lead frame LF.

Next, the CPU 6 sends an image pickup command to the camera control circuit 11 while the lighting device 2B is on (step S5). This drives the CCD camera 1,
The image captured by the CCD camera 1 is captured by the inspection device body 3. The image signal from the CCD camera 1 taken into the inspection apparatus main body 3 at this time is stored in the RAM 9 (step S6).

FIG. 4C is a diagram showing the illumination light emitted from the illumination device 2B to the lead frame LF when the CCD camera 1 captures an image of the upper surface of the lead frame LF coated with the paste P. As shown in, when the upper surface of the lead frame LF coated with the paste P is irradiated with the illumination light L _2B from the illumination device 2B from an oblique direction which is substantially horizontal,
The illumination light reflected by the portion not coated with the paste P hardly enters the CCD camera 1, and only the illumination light reflected by the portion coated with the paste P enters the CCD camera 1. Therefore, the lead frame LF imaged by the CCD camera 1 at this time is, as shown in FIG.
Only the part where the paste P is applied becomes a white image, and the part where the paste P is not applied becomes a black image.

Next, the CPU 6 stores 2 data stored in the RAM 9.
After combining two images into one image as shown in FIG. 6 (step S7), the following image processing is performed to allow the position, number and application amount of the paste P applied on the upper surface of the lead frame LF. Check if it is in range.

That is, the CPU 6 first labels the composite image shown in FIG. 6 to determine how many application points of the paste P are in the composite image (step S8,
S9). Then, it is determined whether or not the application point of the paste P matches a preset value, and if it does not match the set value, the fact is displayed on the display unit 4.

Next, the CPU 6 obtains the center coordinates of the paste P applied on the upper surface of the lead frame LF, and calculates how much the center coordinates deviate from the preset position (steps S10 and S11). Then, the paste P is compared by comparing the shift amount of the center coordinates with the set value.
It is determined whether the application position of the paste P is within the allowable range. If the application position of the paste P is outside the allowable range,
The fact is displayed on the display unit 4 (step S12).

As a method for obtaining the center coordinates of the paste P, for example, as shown in FIG. 7, circumscribing rectangles A ₁ , A ₂ , A ₃ , and A ₄ circumscribing the application points of the paste P are shown in FIG.
Of the circumscribed quadrangle A ₁ , A ₂ , A ₃ , A
X-direction of the straight line x _A1 passing through the center of the _{4, x A2, x A3,} x A4 and y direction of the straight line _{y A1, y A2, y A3} , paste from y _A4 Metropolitan P
The center coordinates of can be obtained.

Next, the CPU 6 obtains the coating amount of the paste P and determines whether the coating amount is within the allowable range. If the applied amount of the paste P is out of the allowable range, the fact is displayed on the display unit 4 (step S1).
3, S14).

As a method of determining the coating amount of the paste P, the number of pixels in the white portion existing inside the circumscribing quadrangle A ₁ , A ₂ , A ₃ , A ₄ is determined, and this number of pixels and the circumscribing quadrangle are The application amount of the paste P can be obtained from the ratio with the number of pixels.

As described above, when the CCD camera 1 captures an image of the upper surface of the lead frame LF coated with the paste P, if the lead frame LF is irradiated with illumination light from a substantially horizontal oblique direction, the paste P is coated. The irradiation light reflected on the surface of the unleaded lead frame LF hardly enters the CCD camera 1, and only the illumination light reflected on the portion where the paste P is applied enters the CCD camera 1, so the paste P is applied. The inspection device body 3 can discriminate between the portion where the paste P is applied and the portion where the paste P is not applied. Therefore, when the image captured by the CCD camera 1 is subjected to image processing to inspect the state of the paste P applied to the lead frame LF, the lead frame LF
The state of the paste P can be accurately inspected without being affected by the metallic luster of.

[0023]

As described above, according to the present invention, the paste inspection in which the lead frame coated with the paste is imaged by the image pickup device and the image picked up by the image pickup device is subjected to the image processing to inspect the state of the paste. In the method, when the lead frame is imaged by the imaging device, the lead frame is irradiated with illumination light from an oblique direction which is substantially horizontal. Therefore, the irradiation light reflected by the surface of the lead frame not coated with the paste hardly enters the imaging device, and only the illumination light reflected by the portion coated with the paste enters the imaging device. A paste inspection method capable of accurately inspecting the state of the paste applied to the lead frame without being affected by the gloss can be provided.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a paste inspection apparatus to which a paste inspection method according to the present invention is applied.

FIG. 2 is a block configuration diagram of the inspection apparatus.

FIG. 3 is a flowchart showing a control operation of a CPU of the inspection apparatus.

FIG. 4 is an operation explanatory view for explaining the operation of the paste inspection method according to the present invention.

5 is a diagram showing an image taken by a CCD camera of the paste inspection apparatus shown in FIG.

FIG. 6 is a view showing an image obtained by combining two images stored in a RAM of the inspection apparatus.

FIG. 7 is an explanatory diagram for explaining a method of calculating center coordinates of paste.

[Explanation of symbols]

 LF ... Lead frame P ... Paste 1 ... CCD camera 2A, 2B ... Illumination device 3 ... Inspection device body 4 ... Display unit 5 ... Operation panel 6 ... CPU 8 ... ROM 9 ... RAM 10 ... I / O port 11 ... Camera control circuit 12A, 12B ... Lighting control circuit

Claims (1)

[Claims] 1. A paste inspecting method for inspecting a paste state by imaging an image of a lead frame coated with paste with an imaging device and performing image processing on an image captured by the imaging device. The method for inspecting a paste is characterized in that the lead frame is irradiated with an illumination light from an oblique direction which is substantially horizontal when the image is picked up.