JPH0666401B2 - Inspection method for lead frame - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for inspecting a lead frame, which is a component of a semiconductor device such as an IC or LSI, and more specifically, in-plane of each part of the lead frame. Deformation (hereinafter horizontal deformation) and deformation in the direction perpendicular to the surface (hereinafter vertical deformation),
The present invention relates to a method for inspecting a defective position of a partial plating portion.

[Background of the Invention]

Lead frame is made by etching method or pressing method.
Process a metal plate of 100-300 μm into the shape shown in the second illustration,
The tip of the island 1 and the inner lead 2 is partially plated with metal such as gold and silver. A reaction body chip is attached to the island 1 of the lead frame (damping), and the tip of the inner lead and the semiconductor chip are further attached. The electrodes are connected with thin metal wires such as gold and aluminum (wire bonding) to manufacture a semiconductor device. In FIG. 2, 3 is a dam, 4 is an outer lead, 5 is an outer frame, and 6 is a partial plating area.

Although the lead frame has been described above, the lead frame itself has a small plate pressure as described above, and the inner lead 2
Since the width of each part is as thin as 100 to several hundreds of μm, it may be deformed during manufacturing, and the positioning accuracy of the partial plating area 6 may be defective due to malfunction of the manufacturing equipment. Incorrect defective products may be mixed. If such defective products are used, defective products may be generated in the die bonding or wire bonding process and the reliability of the completed semiconductor device may be deteriorated. Is essential.

Conventionally, inspection of such a lead frame is usually conducted by naked eyes or visual observation using a microscope, but it takes a lot of manpower to inspect a large number of products, and Since it was a sensory test, there was a problem in inspection accuracy and reliability.

In order to solve such a problem, for example, regarding a method for inspecting the lateral deformation of the lead frame, a video signal obtained by shooting the lead frame with transillumination using ITV is similarly used as a reference pattern or an adjacent pattern. A method of detecting the deformation by comparing with the signal obtained by photographing, and for the inspection of the partial plating portion, a method of performing a similar process using reflected illumination to detect a defective position of the plating portion, and Regarding the inspection of the vertical deformation, a method using an optical non-contact height measuring device, etc. have been proposed.

However, according to these methods, the method is different for each inspection item although the purpose is achieved individually, so the inspection process becomes complicated, and the method using ITV, There is a case of detecting defects that do not cause defects such as dust and scratches adhering to the lead frame, and it may be judged as defective, and further, in the method using the non-contact height measuring device,
There were many problems in terms of reliability, such as the measurement values becoming unstable when the measurement point was on the edge of the pattern, and practical application was difficult.

[Object of the Invention]

The object of the present invention is to perform all inspections of the surface condition such as lateral deformation, vertical deformation of the lead frame and the presence or absence of plating in a single process with high reliability, except for the above-mentioned drawbacks of the prior art. It is to provide a method of inspecting a lead frame that can be performed.

[Outline of Invention]

In order to achieve this object, the present invention scans the surface of the lead frame to be inspected with an optical spot, detects the lateral deformation of the lead frame by the transmitted light and the scanning position at this time, and reflects by the lead frame at this time. The surface condition of the lead frame is detected by the amount of light, and the image of the optical spot on the lead frame at this time is projected and imaged in a direction oblique to the irradiation optical axis of the optical spot. The feature is that the vertical deformation of the lead frame is detected by the measurement based on the optical triangulation method based on the displacement of the image position.

Example of Invention

Hereinafter, a lead frame inspection method according to the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 shows an embodiment of the present invention. In the figure, 7 is a light source side detection unit, 8 is a semiconductor laser that acts as a point light source, 9 is a lens for illuminating a light spot, and 10 is an image of the light spot. Lens, 11 is a PSD that acts as a one-dimensional incident position detection element
(Semiconductor position detecting element), 12 is a signal processing section for processing the signals S ₁ and S ₂ from the PSD 11, 13 is a transmission detecting section, 14 is a condenser lens, 15 is a photodiode, an optical element, etc. A light receiving element, 16 is a signal processing unit for the signal T of the light receiving element 15, 17 is a waveform storage device including a digital memory, 18 is a control determination unit including a computer, 19 is an XY stage for scanning,
20 is a motor for driving the XY stage 19, 21 is a linear encoder for detecting the position of the XY stage, and 22 is a lead frame to be inspected.

Next, the operation of this embodiment will be described.

First, the light emitted from the semiconductor laser 8 in the detecting portion 7 forms an optical spot having a diameter of about 100 μm on the lead frame 22 by the lens 9. The reflected and scattered light of this optical spot is a light-receiving lens 10 whose optical axis is at an angle of 40 ° with respect to the irradiation optical axis.
The image of the light spot is formed on the PSD 11 for one-dimensional position detection by. The PSD11 has two output terminals, and the signals S ₁ and S ₂ obtained from them have the light intensity information of the light spot imaged on the PSD and the image formation position information on the PSD, (S ₁ + S ₂ ) Is the light intensity, and (S ₁ −S ₂ ) / (S ₁ + S ₂ ) is the position signal. Therefore, the signal processing unit 12 connected to the PSD 11 performs the above calculation based on the PSD signals S ₁ and S ₂ and then corrects the light receiving characteristics of the optical system and the PSD 11 itself, and the lead frame 2
Outputs a signal proportional to the height of the light spot on 2 and the scattered light intensity.

On the other hand, the transmitted light detector 13 causes the light passing through the lead frame pattern of the irradiation light to be incident on the light receiving element 15 by the lens 14, and the signal processing 16 outputs a signal S _T that is proportional to the transmitted light amount.
And output to 18.

FIG. 3 is a diagram showing the positional relationship between the lead tip 2a and changes in the signals of the detectors 12 and 16 when the optical spot S scans the tip 2a of the inner lead 2. 2a
The shaded area on the bottom shows that it has been plated. Further, in this figure, T indicates a change in the amount of transmitted light, a solid line indicates a signal when scanning a portion with lateral deformation of the lead, a broken line indicates a signal when scanning a corresponding portion without deformation, and T _S is both. , R represents the reflected light amount signal, and H represents the height signal.

The transmitted light amount signal T has both horizontal position information of the pattern and positional relationship information of the light spot and the pattern edge,
Signal when scanning part A with horizontal deformation (solid line)
And the data (broken line) stored by scanning the corresponding portion B of the lead frame which is not deformed in advance, the signal whose value is increased only in the deformed portion as shown by T _S. It is possible to detect whether or not there is horizontal deformation by comparing this with a predetermined slice level.

On the other hand, in areas such as the island 1 where the amount of displacement is a problem, the edge coordinates of the pattern are detected by the stage coordinate signal at the point where the amount of transmitted light is 50%, and the amount of deformation is compared with the reference value such as the design value. Can be detected. Further, it is possible to recognize that all or most of the light spots are on the pattern at the position where the amount of transmitted light is 0 or less than a predetermined slice level, so that it is possible to know the timing at which the inspection by the PSD 11 is performed correctly. That is, the reflected light amount signal R has a large value on the non-meta surface and a small value on the non-meta surface due to the difference in surface roughness between the non-meta surface and the non-meta surface, and has information on the presence or absence of the mat. However, by simply comparing the reflected light amount signal with a certain level, if the optical spot is in the middle of the lead, it becomes a signal with no plating, and if it is on the pattern edge, even if it is a non-plating portion, it is Since the light scattering causes a signal with a scattering, as described above, the intermediate value of the reflected light amount level of the non-spotted portion is set by the transmitted light amount signal T on condition that all or most of the light spots are on the pattern. By comparing the slice levels, it is possible to reliably detect the presence or absence of a mesh. For example, if a signal indicating no mesh is detected while scanning the inside of the boundary line of the partial mesh designated area, it means that the defective position of the mesh is detected. .

Similarly, as shown in the figure, the height signal H has an indefinite value when the light spot is between the patterns, and on the edge, the influence of the reflected light from the end face and the brightness distribution of the light spot imaged on the PSD are A measurement error occurs due to the change, but as in the case of detecting the presence or absence of the above-mentioned mess, if the height is detected on condition that all or most of the optical spots are on the pattern, an accurate value is always obtained. The vertical deformation can be detected by comparing with a reference value, for example, the height of the dam central portion.

Here, the principle of vertical deformation detection by the PSD 11 will be described in more detail.

As shown in FIG. 4, the image of the light spot emitted from the semiconductor laser 8 to the beam tip 2a through the lens 9 is formed by the lens 10 at the position (a) on the detection surface of the PSD 11.

If the lead tip 2a moves from the solid line position to the broken line position in this state, the position of the optical spot image on the PSD 11 is displaced to (b) at this time.

Therefore, if the PSD 11 detects the moving distance 1 of the optical spot image, the vertical deformation h of the lead frame can be measured.

By the way, the angle θ formed by the optical axes L ₁ and L ₂ at this time must be kept below 90 degrees, and in practice, as in the above-mentioned embodiment,
It is desirable to set it to around.

In addition, PS as such one-dimensional light entering position detection means
D is known, for example, from "Electronic Materials" February 1980 issue.

The above is the description of the method for detecting vertical deformation, lateral deformation, and defective plating position according to the embodiment of the present invention.

Next, a more specific operation in the case of inspecting the lead frame according to the embodiment of the present invention will be described. FIG. 5 shows an example in which the pattern of the lead frame 22 is scanned to inspect for deformation and defective plating position, and the shaded area in the drawing indicates the area where the plating is performed.

In this figure, 30 to 46 are points indicating scanning paths, and
30 is the scanning start point, and the X coordinate of both ends of the dam at points 30-31,
Detect the Y coordinates of both ends of the inner lead 2 at points 31-32.
The respective midpoints are obtained and used as the origin coordinates of the lead frame, and correction is performed so that the subsequent scanning path becomes the path defined by the lead frame coordinate system. In addition, the height of the scanning Dedham portion at points 30-31 is measured and used as the height reference value. Point 33−34−35
The path of -36-33 is a part to detect horizontal and vertical deformation of the tip of the inner lead.
Moving distance 10 from the coordinates of
The transmitted light amount signal for each μm is compared with the transmitted light amount data at the same location obtained by scanning the same path of the lead frame without deformation in advance, and a portion where the difference is equal to or higher than a predetermined level is determined to be defective.

Regarding vertical deformation, a portion in which the difference between the height signal and the reference value when the transmitted light amount level is equal to or lower than the predetermined level is equal to or higher than the predetermined level is determined to be vertical deformation failure.

Next, the route of points 37-38-39-40-41 is the route for inspecting the metallurgical part, and it is 100μ of the specified metallurgical region boundary line.
Scan inside about m. In this path, when the amount of transmitted light is below a predetermined level and the amount of reflected light is below the level of determination of presence / absence of a defect, it is determined that the defective position of the defect is defective.

Further, point 41-42-43-44-45-46 is an inspection route of the island portion, and the difference between the average value of the two X-coordinates detected at points 41-42 and 45-46 and the reference value is the island. The amount of deformation is in the X direction, and the difference between the two X coordinates is the amount of rotation of the island.

On the other hand, the difference between the average value of the two Y coordinates detected at points 42-43 and 44-45 and the reference value is the amount of deformation in the Y direction.

Furthermore, the difference between the average value of the heights of the four corners of the island measured in the scanning of points 41-45 and the reference value is the amount of vertical deformation of the island.
The height of the corner and the difference between the maximum value and the minimum value become the amount of inclination of the island, and the deformation amounts of the islands are compared as intersections to determine whether the shape is good or bad.

By the way, the above example shows the case of inspecting the deformation of the inner lead and the island portion and the defective plating position, but in addition to this, if the outer lead, the outer frame portion, etc. are set in the scanning path, the lead The entire warp and twist of the frame can be detected, and the inspection time can be shortened by omitting unnecessary portions for inspection.

〔The invention's effect〕

As described above, according to the present invention, the deformation of the lead frame and the defective plating position can be automatically inspected by one set of detection systems, and can be inspected in one step, and since the line scanning is performed, dust, The probability of false detection due to scratches is very small, and it is easy to improve inspection accuracy and reliability.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the lead frame inspection method according to the present invention, FIG. 2 is a plan view showing an example of the lead frame, and FIG. 3 is a waveform showing the operation of the embodiment of the present invention. 4 and FIG. 4 are explanatory diagrams showing the principle of vertical deformation detection in one embodiment of the present invention, and FIG. 5 is an explanatory diagram more specifically showing the operation in one embodiment of the present invention. 1 ... Island, 2 ... Inner lead, 3 ... Dam, 4 ... Outer lead, 5 ... Outer frame, 6 ... Partial plating area, 7 ... Light source side detection section, 8 ... Semiconductor laser,
9,10,14 …… Lens, 11 …… PSD, 12 …… Signal processing unit, 13
...... Transmitted light amount detector, 15 ...... Light receiving element, 16 ...... Signal processing unit, 17 ...... Waveform storage device, 18 ...... Control determination unit, 19 ...... XY
Stage, 20 …… Motor, 21 …… Linear encoder, 22
...... Lead frame, L ... Optical spot, A ... Deformed inner lead, B ... Undeformed inner lead, T ... Transmitted light amount signal, R ... Reflected light amount signal, H ...
Height signal, T _S …… Transverse deformation signal, 30 to 46 …… Scanning points on the lead frame.

Claims (2)

[Claims] 1. A method for inspecting a lead frame which optically detects the shape and surface condition of the lead frame,
Light source means for irradiating a light spot perpendicular to the surface of the lead frame to be inspected, and light receiving means positioned on the optical axis of the light spot extending on the side opposite to the light source means with the lead frame sandwiched therebetween. And image forming optical means for forming an image of the light spot irradiated on the lead frame at a predetermined position in a predetermined angle direction of less than 90 degrees with respect to the irradiation optical axis of the light spot, and the image forming means. One-dimensional light incident position detecting means located near the image forming position of the image of the optical spot by the optical means, scanning means for relatively moving the optical axis of the optical spot along the surface of the lead frame, and The measuring means for detecting the relative movement amount by the scanning means is provided, and the deformation in the in-plane direction of the lead frame is detected by the output signal of the light receiving means and the output signal of the measuring means,
A method of inspecting a lead frame, which is configured to detect a deformation and a surface state in a direction perpendicular to a surface direction of the lead frame by an output signal of the one-dimensional light incident position detecting means. 2. A lead frame inspection according to claim 1, wherein the light source means is a semiconductor laser and the one-dimensional light incident position detecting means is a semiconductor position detecting element. Method.