JPH01143940A - Method and device for inspecting defect of sheet-like etching precision component - Google Patents

Abstract

PURPOSE:To surely discriminate and detect a defect of a through-hole, etc. and a defect of half etching by setting a level ratio of illuminating light beams from the reverse side of etching precision parts and reflecting light beams of the illuminating light beams from the surface side to a specific value and synthesizing said both light beams. CONSTITUTION:A lead frame 1 to be inspected is placed on a transparent placing base 2 such as a glass plate, etc., and the surface of the lead frame 1 is irradiated vertically through a projection lens 4a and a half mirror 7 from a light source 3a. Subsequently, the reverse side is irradiated vertically through a projection lens 4b from a light source 3b provided on the reverse side. Next, a ratio of intensity of transmission light beams of the illuminating light beams of the reverse side by the lead frame 1 and intensity of reflecting light beams by the illuminating light beams of the surface side is set so as to become about 1:0.5 and said both light beams are synthesized, and photodetected in common by the same photodetector 8. In such a way, from two pieces of digital signals obtained by detecting an analog signal to the lead frame 1 outputted from the photodetector, by two pieces of signal detectors 9-1, 9-2 to which the respective different threshold levels have been set, a defect such as a through- hole existing in the lead frame 1, a short circuit, etc., and a defect caused by half etching are discriminated and detected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method and apparatus for inspecting defects in sheet-like etched precision parts such as lead frames for wiring of IC chips, and more particularly, to The present invention provides a method and apparatus for distinguishing and detecting defects such as through holes and short circuits caused by etching, and half-etching defects caused by poor etching.

[Prior Art] An IC device of a semiconductor product has a frame island 1 located approximately in the center of a lead frame 1, an example of which is shown in FIG. 3(a).
An IC chip is mounted on the substrate 1a, and the IC chip is connected to the lead wire 1a. The lead frame 1 is made by drawing a lead v&lb pattern on a thin metal plate and etching it. Lead wires are extremely thin, and defects can occur for some reason during the etching process. An example is shown in Fig. 3(b), (A) is a through hole, (IT) is a defect with an end (hereinafter, (A), (U), etc. are collectively referred to as a defect), (8) is a short circuit between the lead wires. These are all defects that were properly etched, but corresponding to them are ), (,1), and (to).
Due to poor etching (half etching), the thickness of the shaded area is thinner to some extent, which is also a defect. (However, the flaw is that (to) is short).

Conventionally, the defects in the lead wires described above have been visually inspected, but this is naturally inefficient. On the other hand, since optical inspection methods are effective, it is conceivable to apply a printed circuit board appearance inspection method or various surface defect inspection apparatuses that are already in practical use. However, these inspection methods have difficulties in detecting defective etched areas. This will be explained below with reference to the drawings.

Optical systems in conventional inspection apparatuses for printed circuit boards or various surface defects can be roughly divided into transmitted light systems and reflected light systems. 4th f(a) is a diagram showing the principle of the transmitted light method, in which an object to be inspected 1' is placed on a transparent mounting table 2, and a light source 3 irradiates the object with light through a projection lens 4. . The light beam transmitted through the object to be inspected is scattered by a pattern or defect of the object to be inspected by a light receiving lens 5, and is received by a gold receiver 6. Now, using the lead wire 1a of the lead frame as the object to be inspected, scanning as indicated by arrow C is performed using an appropriate means, and the defect shown in the lower part of the waveform distribution diagram of the light reception signal of the light receiver corresponding to the defect is shown in FIG. Taking (a) and (d) shown in (b) as an example, (T) is obtained as the analog waveform of the light reception signal for each. In other words, since the hole (a) is penetrating, the corresponding part is detected at the same level S as where there is no lead wire. However, defects due to poor etching (
In (d), there is no transmitted light because the metal remains, and the corresponding signal waveform is not detected. This waveform (T) is identified using an appropriate threshold, and the polarity is further inverted to create a digital signal [D
] (hereinafter referred to as [detail]) is obtained, and the width dimension Tl of the lead wire 1a and the dimension T2 of the through hole (A) are obtained.
can be measured. It is also possible to determine the defect (a) by comparing this signal with the signal of a reference lead frame. However, no signal indicating defective etching (d) can be obtained regardless of the magnitude of the threshold value.

Next, FIG. 4(b) shows a reflection type optical system. Diagram (a)
A light source 3 and a mounting table 2 similar to the above are used, and the reflected light from the object 1' to be inspected is received by a light receiver 6 by a light receiving lens 5 provided on the same side as the light source. In this case as well, assuming the same defects (a) and (d) as above, the waveform of the received light signal for them is (R). Since there is no level, the level is detected as 0. However, (d)
Due to poor etching, the surface of the lead wire has lost its luster and has a rough surface, resulting in a decrease in reflection performance and a correspondingly concave waveform. When the waveform is identified using the threshold value Da to detect this depression, the signal [Da] is changed, but the difference between () and () cannot be distinguished, and it is detected as a through hole. This is inconvenient. Also, if you change the threshold and identify Db"C which is smaller than the concavity in (d), it is a signal of [Dbl, but it is the same as [D] in figure (a), and (d) is not detected. In this way, Defects due to poor etching are either not detected by either the transmitted light method or the reflected light method, or are mistakenly detected as through holes.In addition, in the above example, (a) and (d) in Figure 3 are used as defects. However, other arbitrary etching defects such as (book) and (to) cannot be detected in the same way, or are erroneously detected as missing defects or short circuits.

Regarding the above, although it is possible to extract the dents caused in (R) using a highly complex waveform processing technique, such a method is not necessarily suitable for quickly inspecting a large number of lead frames. This is why a simple and reliable testing method and device is desired.

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and it is possible to eliminate defects such as through-holes and short-circuit defects that occur in the lead wires of lead frames, as well as defects caused by poor etching using a simple optical system. It is an object of the present invention to provide a lead frame inspection method and apparatus that can distinguish and detect lead frames by signal processing.

[Means for Solving the Problems] The present invention provides a method and apparatus for inspecting defects in lead frames for wiring of IC chips, and the method will first be described. Illumination light is irradiated perpendicularly to the lead frame to be inspected from its back side and front side, and the intensity of the transmitted light of the illumination light on the back side by the lead frame and the reflected light from the front side illumination are measured. Strength ratio approximately 1:0.5
The signals are set and combined so that the light is received in common by the same receiver, and the analog signal for the lead frame output from the receiver is detected by two signal detectors each set to a different value. This method is characterized by distinguishing and detecting defects such as through holes and short circuits existing in the lead frame and defects due to poor etching (half-etching) from the two digital signals obtained.

Next, in the apparatus according to the present invention, with respect to the lead frame to be inspected placed on a transparent mounting table such as glass,
A first light source and a half mirror are provided on the front side of the lead frame, and a half mirror that converts the projected light from the first light source into a right angle direction and irradiates the lead frame perpendicularly, and on the back side of the lead frame. A second light source that irradiates the lead frame perpendicularly is provided. the intensity of the transmitted light from the second light source;
The intensity ratio of the light reflected by the first light source is set to approximately 1:0°5, and the light is combined by the half mirror, and the common light receiver receives the combined light, and the common light receiver outputs the light to the lead frame. Two signal detectors inputting analog signals, each having a different threshold value, and 2111 digital signals output from the two signal detectors detect defects such as through holes and short circuits existing in the lead frame, It is comprised of a signal processing section that distinguishes and detects defects caused by etching defects (half etching).

[Function] In the lead frame defect inspection method according to the present invention, since the ratio of the intensity of the illumination light from the two light sources to the intensity of the light transmitted by the lead frame and the reflected light is approximately 1:0.5, the lead wire Assuming that the received light intensity of the transmitted light in other parts is 1.0, it is also 1.0 because it is completely transmitted in parts other than the lead wire and in transparent parts such as through holes and defective parts.
In addition, in the defect-free portion and half-etched portion of the lead wire, there is no transmitted light at all. On the other hand, the received intensity of the reflected light is 0 in areas other than the lead wires and through-holes with no reflection, but it is 0.5 in the lead wire areas, and on the other hand, the half-etched areas have lost their luster. It has a hue similar to that of lead oxide, and its reflective performance is low, at least less than half of the lead wire portion, so the intensity of this portion is about 0.25 or less. As a result, the received light intensity of the combined light of transmitted light and reflected light is 1.0 in the transparent part, 0.5 in the defect-free part of the lead wire, and 0.2 in the half-etched part.
5 or less, the analog signal waveform detected by the photoreceiver undergoes a corresponding change. Therefore, this signal is input to two signal detectors in parallel, and the threshold value of one of the detectors is set to, for example, 0.
A digital signal of the through hole is obtained as 75, and a digital signal of the half-etched part is obtained by setting the threshold value of the other detector to about 0.4. In other words, through-holes and half-etching can be detected separately.

Next, in the apparatus for the above, the lead frame to be inspected is placed on a transparent RW table made of glass or the like, and the light emitted from the first light source provided on the front side of the lead frame is
The light is converted into a right angle direction by a half mirror, is irradiated perpendicularly to the lead frame, and is reflected to become reflected light. Further, the illumination light from the second light source on the back side is irradiated perpendicularly to the lead frame, and since the transmitted light is coaxial with the above-mentioned reflected light, it is combined by the half mirror and input to the common light receiver. Here, the necessary condition, that is, the method of setting the intensity ratio of the transmitted light and the reflected light at the common receiver to approximately 1:0°5, is based on experiments or the like. This is not possible at this stage because the intensity changes in both cases.

The analog signal obtained by the common receiver is outputted as a digital signal by the above-mentioned two signal detectors each having a different threshold value, and in the signal processing section, it is processed as a missing defect, a short defect, Half-etching defects are distinguished. Note that the optical system of the above device is equipped with necessary lenses.

[Example] FIG. 1 illustrates the signal waveforms of transmitted light and reflected light received by a common light receiver and their combined waveform in a lead frame defect detection method according to the present invention. When the object to be inspected is the through hole (A) and the circular half-etched part, the intensity of the transmitted light in the transmitting part is set to 1.0 to change the waveform of (T). On the other hand, the intensity of the reflected light from the defect-free area is set to 0.
5, the waveform (R) of the reflected light can be obtained. (R)
In the half-etched portion (d), due to a decrease in the reflective performance of its surface, it becomes a concave portion of 0.5 or less of the defect-free portion, that is, α<0.25 in the figure. Furthermore, these combined waveforms are shown as (T) + (R), and two threshold values D1 (approximately 0.75) and D2 are applied to this.
(approximately 0.4) and are converted into digital signals [Dtl and [D21], respectively. Furthermore, if necessary, reverse the respective polarities to create −[0+] and −[D21
Then, in an appropriate signal processing unit, the through hole (A) is detected as mentioned above using T, . It detects and determines its size.

FIG. 2 shows the overall structure of an embodiment of the lead frame defect detection apparatus according to the present invention, in which a lead frame 1 to be inspected is placed on a transparent stand 2 such as a glass plate.
place A first light source 3a is provided on the front side (upper side in the figure).
A projection lens 4a and a half mirror 7 for converting the projection light into three directions are provided to vertically illuminate the surface of the lead frame. - On the other hand, a second light source 3b provided on the back side irradiates the back surface vertically through a projection lens 4b, and the transmitted light travels straight upward. This and the reflected light from the irradiated light on the surface side are:
They are combined by a half mirror 7 as a coaxial light receiving lens 5.
The image of the lead frame is connected to the common light receiver 8. Here, the mounting table 2 moves in the direction of arrow C and the direction perpendicular to it, and the lead frame 1 is scanned, and the received light image moves sequentially. A time-varying light reception signal is output.

A linear sensor is used as the light receiver 8. in this case,
As mentioned above, the light intensity of the first light source and the second light source is Nl.
! Then, by setting the intensity ratio of the transmitted light and the reflected light in the common light receiver 8 to approximately 1:0.5, the composite waveform (T)+(R) of the light reception signal shown in FIG. 1 is obtained. This analog signal is sent to two signal detectors 9-1.9 with thresholds Dl and D2, respectively.
-2 in parallel to the digital signal [Dl] in Figure 1.
and [D21 are output, and if necessary, they are further inverted by phase inverters 10-1 and 10-2 to become -[Dtl
, -[D21, and both are input to the signal processing unit 11 to perform predetermined defect detection and size determination.

As has been explained above, in the embodiments, an example of a lead frame is given, but the present invention is applicable to not only lead frames but also lead frames.
For example, it can be applied to sheet-like precision electronic parts such as mesh-like razor blades, precision mechanical parts such as encoders, etc. In these materials, the manner in which defects occur after etching is almost similar to that in lead frames.

Note that the inspection device or the inspection method of the present invention is not limited to lead frames, but particularly when applied to lead frames, it produces the effect of being able to perform inspections that fully satisfy the product standards of lead frames. .

[Effects of the Invention] As is clear from the above explanation, in the defect detection method for sheet-like etched precision parts according to the present invention, the transmitted illumination light from the back side of the etched precision part and the illumination light from the front side are separated. By combining the reflected light with a level ratio of approximately 1:0.5 and using the received light signal obtained by a common receiver for the combined light, defects such as through holes, which were impossible with conventional reflected light or transmitted light methods, can be detected. By reliably distinguishing and detecting half-etching defects and half-etching defects, and performing corresponding processing if necessary, their sizes can also be determined. The configuration of this device is simply a combination of the conventional reflected light method and transmitted light method. As described above, the defect inspection method and apparatus for etched precision parts according to the present invention have a major feature of being simple and do not require complex signal processing, and can be used not only for inspecting etched precision parts but also for inspecting similar workpieces. It has great potential to contribute to inspection technology for various parts.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram for explaining the received signal waveforms of reflected light, transmitted light, and their combined light in the lead frame defect inspection method according to the present invention, and the principle by which through-holes and half-etching can be distinguished. 3(a) and 3(b) are plan views showing the external appearance of the lead frame and examples of defects occurring in the lead wires. Figure (1
) and (b) are light reception signal waveform diagrams illustrating lead frame defect detection signals by the conventional transmitted light method and reflected light method, respectively, and the fact that half etching cannot be detected. 1--Lead frame, 1a...-Lead wire, 1
b...IC chip, 1'...Test object, 2...
-31 mounting stand, 3...-light source, 4...-light emitting lens, 5...-light receiving lens, 6...-light receiver,
7...Half mirror-18...Common receiver,
9--signal detector, 10--phase inverter,
II.-Signal processing section.

Claims (4)

[Claims] (1) Illumination light is irradiated perpendicularly to the sheet-like etched precision part to be inspected from the back side and the front side of the etched precision part, and the illumination light from the back side is transmitted by the etched precision part. The light and the reflected light from the surface side are combined, and the ratio of the intensity of the transmitted light to the intensity of the reflected light is set to approximately 1:0.5, and the light is commonly received by the same receiver. , from the two signal waveforms obtained by detecting the analog signal for the etched precision part output from the light receiver with two signal detectors each having a different threshold value, the through hole existing in the etched precision part is detected. ,
A defect inspection method for sheet-shaped etched precision parts, which distinguishes and detects defects such as short circuits and defects due to poor etching such as half etching. (2) The defect inspection method for a sheet-like etched precision part according to claim 1, wherein the etched precision part is a lead frame. (3) A first light source is placed on the surface side of a sheet-like etched precision part to be inspected that is placed on a transparent mounting table such as a glass plate, and the light emitted from the first light source is directed at right angles. a half mirror that irradiates the etched precision part perpendicularly, and a second light source that irradiates the etched precision part perpendicularly on the back side of the etched precision part; The ratio of the intensity of the transmitted light of the etched precision part by the light source and the reflected light of the etched precision part by the first light source is set to approximately 1:0.5, and the light is combined by the half mirror, and the combined light is received. two signal detectors, each having a different threshold value, into which the analog signals for the etched precision parts output from the common light receiver are input in parallel; and two digital signals detected by the two signal detectors. A sheet-like etching device comprising a signal processing unit that distinguishes and detects defects such as through holes and short circuits existing in the etched precision parts and defects due to poor etching such as half etching based on signals. Defect inspection equipment for precision parts. (4) The defect inspection device for sheet-like etched precision parts according to claim 3, wherein the etched precision parts are lead frames.