JP2960301B2 - Inspection method of circuit element joint - 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 a bonding portion of a circuit element such as an integrated circuit, and more particularly to a method suitable for inspecting a bonding state between an inner lead or an outer lead of a semiconductor chip and a bump.

[0002]

2. Description of the Related Art Conventionally, as a technique for inspecting a solder joint of an electronic circuit, there is a technique disclosed in Japanese Patent Application No. 62-141182, for example. This is due to the temperature distribution image obtained by imaging the infrared radiation emitted from the solder joint when irradiating the laser beam to the solder joint of the electronic circuit,
The thermal conduction status of the solder joint between the lead of the electronic component and the conductive pattern of the circuit board is known, and based on the result, the quality of the solder joint is judged.

[0003]

According to this technique, a laser beam is directly applied to a solder joint to apply heat energy, and infrared rays emitted from the solder joint are received by an infrared camera, and an electronic circuit is used. The solder joint between the lead portion and the conductive pattern of the circuit board is regarded as a temperature distribution image, that is, a surface image, and good or bad is determined from the state of the solder between the lead portion and the conductive pattern.

[0004] Soldering defects include voids inside solder joints, bridges formed between adjacent leads, and solder balls. Of these, in the bridge, adjacent leads bridge in a thin line state or a thick line state to cause a short circuit, and solder balls also vary in size, and external defect phenomena are represented as thermal image distribution on the surface. The person who caught it can be distinguished more accurately.

On the other hand, bonding without using solder, for example, TAB bonding in which inner leads are bonded to bumps of a silicon chip in a circuit element,
The thermocompression bonding does not cause defects such as soldering such as bridges and solder balls. The quality of the bonding state is determined solely by the size of the area of the bonding surface.

In this circuit element, a lead is connected to an aluminum pad provided on one surface of a silicon chip via a bump, and the other end of the lead is similarly connected to a pattern on a circuit board via a bump. Here, as shown in FIG. 8, the circuit element has a face-up type in which the surface on which the aluminum pads and bumps are provided faces the back of the circuit board and the joints are exposed (FIG. 8B). And a face-down type in which the same surface is opposed to the circuit board and the junction is covered with a silicon chip (FIG. 7A).

In the face-up type, a laser beam can be directly applied to a junction between a silicon chip and a lead. However, since the tip of the heater chip pressed into contact with the joining portion at the time of joining may be uneven, direct irradiation with a laser beam may cause irregular reflection and irregularity. Therefore, by irradiating a laser beam to a part of the lead close to the joint, heat energy can be input regardless of whether the joint is uneven.

On the other hand, in the face-down type, since the bonding portion is provided behind the silicon chip of the integrated circuit in the mounted state, the laser beam cannot be directly applied to the bonding portion from the structural point of view. However, the silicon constituting the silicon chip transmits the laser beam. However, as shown in FIG. 9, the aluminum pad between the bump and the silicon chip reflects the irradiated laser beam as shown in FIG.
The joint cannot be inspected.

The present invention has been made in consideration of the above points, and has as its object to provide a method of inspecting a circuit element junction which can determine the quality of various electronic circuit junctions.

[0010]

In order to achieve the above object, according to the present invention, a circuit element to be measured is provided in a method for inspecting a circuit element bonding portion for bonding a circuit element to a circuit board according to claim 1. Measure the temperature of the environment in which the junction is located, and determine the closest to the bump of the silicon chip as the circuit element or the lead portion suitable for applying thermal energy, or the closest to the bump and covered with the silicon chip. In addition, thermal energy is applied to a lead portion for connecting the silicon chip to the circuit board, infrared rays radiated from the lead portion are received, a thermal image of the lead portion is taken out, and a surface of the lead portion is taken out. The temperature of the lead portion is calculated from the thermal image of the above, the calculated temperature is compared with the temperature of the environment, and the quality of the junction is determined based on the magnitude of the difference. 2. The method according to claim 1, wherein the bonding is performed by bonding the lead bonded to the tape to a bump formed on an aluminum pad of a silicon chip. It is an object of the present invention to provide a method for inspecting a circuit element joined by a TAB process of bonding.

[0011]

In the method according to the first aspect, a portion most suitable for inspecting a bonding state between a bump and a lead portion of a silicon chip, which is a circuit element to be bonded to a circuit board, that is, a lead portion closest to the bump. Alternatively, thermal energy is applied to a lead portion for connecting the silicon chip to the circuit board, which is closest to the bump and not covered with the silicon chip, and receives infrared rays radiated from the lead portion. Then, a thermal image of the lead portion is taken out based on the received infrared light, the temperature of the lead portion is calculated from the thermal image of the surface of the lead portion, the calculated temperature is compared with the temperature of the environment, and bonding is performed based on the difference between the temperatures. The quality of the part is determined.

According to the second aspect of the present invention, the joint between the lead and the bump is determined by applying the method to the TAB method.

[0013]

[0014]

In the method according to the first aspect, a lead portion closest to a bump of a silicon chip as a circuit element and suitable for inputting thermal energy, or a lead portion closest to the bump and not covered by the silicon chip, Heat radiation is applied to the leads for connecting the chip to the circuit board to receive infrared rays emitted from the leads, so that the heat transfer status between the bumps and the leads can be accurately taken out. . Moreover, the joints face up,
Any face-down can be taken out similarly.

According to a second aspect of the present invention, the present invention provides a
Since the method is applied to the system, quick and accurate inspection can be performed during mass production.

[0017]

[0018]

[0019]

FIG. 1 shows a method of irradiating thermal energy in one embodiment of the present invention. FIG. 1 shows a face-down type integrated circuit, in which aluminum pads (not shown) serving as bonding portions are provided on the lower surface of a silicon chip 1.
And a lead 2 made of copper is bonded to this aluminum pad via a bump (not shown). The leads 2 are bonded to the bumps by, for example, TAB (Tape Automated Bonding) technology which is widely used as a high-density mounting technology. The tips of the leads 2 are connected to the silicon chip 1 at positions hidden by the silicon chip 1. They are joined and the proximal end is visible.

The visible portion is irradiated with a laser beam as thermal energy as shown by a grain pattern in the figure. As a result of heating the lead by the irradiation of the laser beam, infrared rays are emitted from the lead toward the surroundings, and heat is conducted inside the lead toward both ends.

FIGS. 2 (a) and 2 (b) are diagrams for explaining the heat conduction. FIG. 2 (a) shows a state where the bonding is good, and FIG. 2 (b) shows a state where the bonding is bad. I have.
That is, in FIG. 3A, heat is conducted from the lead 2 toward the silicon chip 1 via the bonding interface,
The temperature of the lead 2 does not rise rapidly.

On the other hand, in FIG. 2B, since the bonding interface does not exist, the heat of the lead 2 is not conducted to the silicon chip 1, and the temperature of the lead 2 instantaneously rises.

FIG. 3 shows how the temperature of the leads and the silicon chip rises with the lapse of time during the irradiation of the thermal energy. Here, the temperature of the silicon chip is used as an example of the environmental temperature. Then, FIG.
Shows that when the bonding is good, the temperature of the lead and the chip are almost the same even after a lapse of time,
FIG. 2A shows a state in which the temperature of the lead and the temperature of the chip are separated over time when the bonding is poor.

From this, it can be understood that the state of heat transfer from the leads to the silicon chip can be grasped by comparing the temperature rise of the leads with the temperature of the silicon chip as the environmental temperature. That is, since the heat capacity of the lead is small, when the lead is not bonded to the silicon chip, the temperature rises instantaneously. On the other hand, the lead
When bonded to the chip, the heat applied to the leads escapes to the silicon chip, so that the leads do not heat up as much.

Therefore, when the bonding is defective, the temperature of the lead gradually departs from the temperature of the silicon chip as time passes, as shown in FIG. On the other hand, when the bonding is good, the temperature of the lead and the temperature of the silicon chip remain almost the same even after a lapse of time, as shown in FIG.

FIG. 4 is a cross-sectional view showing the temperature distribution at the junction between the silicon chip 1 and the lead 2. That is, as shown in FIG. 3A, when the bonding state of the bonding portion is good, when the left portion of the lead 2 receives thermal energy and the temperature rises, the rightward portion of the lead 2 becomes closer to the right. Although the temperature decreases, the temperature itself increases. The silicon chip 1 that receives heat from the lead 2 via the bonding portion, that is, the bump 3, has a low heat because of its large heat capacity, but the temperature change is continuous from the left side of the lead 2 to the silicon chip 1 in the drawing. is there.

On the other hand, as shown in FIG. 2B, when the bonding portion is defective, the temperature of the lead 2 rises, but the heat is not transmitted to the silicon chip, and the chip part 1 can be said to be completely. The temperature does not change as much.

FIG. 5 shows a state in which the lead 2 is bonded to the silicon chip 1, and FIG. 5 (a) is a plan view,
FIG. 2B is a side view. 4000μm × 4000μ
The right end of the lead 2 is joined to the center of the left side of the silicon chip 1 shown by a square having a size of m. A length of about 100 μm on the right end of the lead 2 is placed at a position overlapping the silicon chip 1, and the silicon chip 1 and the lead 2 are joined to the center of the overlapping portion via a bump 3 shown by a broken line. . The left end of the bump 3 is located at a position about 50 μm from the left end of the silicon chip 1.

As described above, the laser beam is applied to the lead 2 bonded to the silicon chip 1. The irradiation position is appropriately closer to the left end of the silicon chip because it is closer to the bonding portion, but the bonding portion can be determined by irradiating a position distant to some extent.

This is the reason why the junction of both the face-up type and the face-down type integrated circuits can be determined.

FIG. 6 shows the distance from the laser beam irradiation point on the lead 2 and how the temperature rises. In the figure, the horizontal axis represents the distance from the end of the bump, and the vertical axis represents the temperature. The abscissa represents the result of measurement from a bump on a silicon chip or a circuit board to a point 5 mm from the bump. As can be seen from this figure, as the distance from the joint increases, the difference between good and poor joints decreases.

That is, the difference in temperature between the case where the bonding is good and the case where the bonding is bad is small when the distance from the bonding portion is large. Therefore, in order to accurately detect a defective joint, it is better to measure the temperature near the joint. This indicates that it is desirable that the position where the thermal energy is applied is also near the joint. This is based on the fact that the degree of heat conduction when the joint is good is closer to the joint.

As can be seen from the measurement results of FIG. 6, there is a difference of about 40 ° C. from the starting point to a range of 2 mm.
It can be determined unambiguously.

FIG. 7 shows the structure of an apparatus used to carry out the method of the present invention. In the figure, a laser beam is irradiated from a laser 10 via a dichroic mirror onto an upper surface of a lead 2 projecting leftward from a left end of a silicon chip 1 in the figure. The infrared rays emitted from the lead 2 heated by the laser beam are received by the infrared camera 11 via the dichroic mirror at the same position as the laser beam to form a signal, which is given to the image processor 12.

The image processor 12 gives the processed data to the computer 13 by signal processing. The computer 13 calculates the temperature rise value of the lead from the obtained data, compares it with the previously measured environmental temperature, and, based on the magnitude of the difference, determines the bonding state between the lead and the silicon chip at the same position as the laser beam. A pass / fail judgment is made, and an image is further displayed on the display 14. In this case, the computer 13 performs the following processing.

With respect to the thermal image taken in the image processor 12, a window is provided in a lead portion which is a temperature observation surface, and an average luminance value in the window is obtained. That is, ^{the sum of the} luminance values in the ^window = ^{the total number} of ^{images in the} average luminance value ^window . The average luminance value is converted into a temperature using a luminance-temperature conversion table and is taken into the computer 13 to obtain a difference from the ambient temperature. The luminance-temperature conversion table may be prepared in advance in consideration of the fact that the emissivity differs depending on the substance.

The average luminance value may be replaced by the maximum luminance value in the window. The maximum luminance value is four pixels or more, and less than four pixels is noise.

The ambient temperature may be measured or calculated using the above-mentioned square method for obtaining the lead temperature.

The result of the judgment by the computer 13 is given to, for example, a sorting mechanism (not shown) to be used for discarding a defective chip or for recording.

In the above embodiment, the inner lead bonding TA for joining the lead connected to the tape to the bump formed on the aluminum pad of the silicon chip is used.
Although the method for inspecting the joined portions joined by the B process has been described, the present invention can be similarly applied to the TAB process for joining the outer leads to the circuit board.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a method for irradiating thermal energy in one embodiment of the present invention.

2A and 2B are explanatory diagrams of heat conduction by the method of FIG. 1, wherein FIG. 2A shows a case where a joint is good, and FIG. 2B shows a case where a joint is bad.

FIGS. 3A and 3B are diagrams showing how the temperature of a lead and a silicon chip rises with the lapse of time during irradiation of thermal energy. FIG. 3A shows a case where a joint is defective, and FIG. The figure which showed the case where a part was good.

FIG. 4 is an explanatory diagram showing a temperature distribution in a cross section at a junction between the silicon chip 1 and the lead 2;

5A and 5B are diagrams for explaining irradiation points of a laser beam on a lead 2, FIG. 5A is a plan view, and FIG. 5B is a side view thereof.

FIG. 6 is a characteristic diagram showing a distance from a laser beam irradiation point on a lead 2 and a state of temperature rise.

FIG. 7 is a block diagram showing an apparatus configuration for implementing the method of the present invention.

8A and 8B show connection states of the integrated circuits. FIG. 8A shows a face-down integrated circuit, and FIG. 8B shows a face-up integrated circuit.

FIG. 9 is an explanatory diagram of a joint between a silicon chip and a bump in an integrated circuit.

FIG. 10 is a diagram showing a state when a laser beam is irradiated to a lead portion of an integrated circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon chip 2 Lead 3 Bump 10 Laser 11 Camera 12 Image processor 13 Computer 14 Display

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-202048 (JP, A) JP-A-63-305238 (JP, A) JP-A-6-85027 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H01L 21/66

Claims (2)

(57) [Claims] In a method for inspecting a circuit element junction for joining a circuit element to a circuit board, a temperature of an environment where the circuit element junction to be measured is placed is measured, and the silicon element as the circuit element is measured. A lead portion closest to the bump of the chip and suitable for inputting thermal energy, or a lead portion closest to the bump and not covered by the silicon chip, for connecting the silicon chip to the circuit board. Irradiating energy, receiving infrared rays radiated from the lead portion, extracting a thermal image of the lead portion, calculating a temperature of the lead portion from a thermal image of the surface of the lead portion, and calculating the calculated temperature A method for inspecting a circuit element junction, which compares the temperature with the environment and determines the quality of the junction based on the magnitude of the difference. 2. The method according to claim 1, wherein the joint comprises a lead bonded to a tape made of silicon.
A method for inspecting a circuit element which is bonded by a TAB process of inner lead bonding for bonding to a bump formed on an aluminum pad of a chip.