JPH04303669A - Image device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to image devices such as light emitting diode printer heads and image sensors, and particularly to wire bonding thereof.

0002

2. Description of the Related Art One of the characteristics of image devices is that they require high-density wiring and high-density wire bonding. FIG. 6 shows an example of such an imaging device. In the figure, reference numeral 2 denotes an image element array, in which a large number of light receiving and emitting surfaces 4 are linearly arranged on a substrate made of, for example, Ga-As, and each of the light receiving and emitting surfaces 4 is connected to an individual electrode 6. A common electrode is provided on the back surface of the image element array 2, and is connected to a common electrode wiring 12 through a through hole in an insulating film 10 provided on a substrate 8. Reference numeral 14 denotes wiring provided on the substrate 8, which is wire-bonded to the individual electrodes 6 using lead wires 16. 17 is an electrode pad for bonding.

[0003] When considering the degree of integration of image devices, for example, A
4 specification with a resolution of 300 dots/inch (DPI), the total number of receiving and emitting surfaces 4 reaches 2560, which is increased to 300 dots/inch (DPI).
They will be arranged at a density of dots/inch. As a result, the wiring 14 becomes a high-density wiring, and the wire bonding also becomes high-density. Ultrasonic bonding is usually used for wire bonding. For example, heating is performed from the back side of the substrate 8, the capillary is ultrasonically vibrated, and the lead wire 16 is heated.
Crimp.

As shown in FIG. 7, the common electrode is connected to the common electrode wiring on the substrate 8 using a conductive paste 18 such as silver paste. In order to prevent short-circuiting of each image element array 2, conductive paste 18 is not filled on both ends of the back surface of the image element array 2. If wire bonding is performed in the regions A at both ends, since there is no conductive paste 18 here, the heat from the back surface of the substrate will not be transmitted, making bonding difficult. In order to avoid this, if the ultrasonic energy is increased, damage such as cracks will occur in the image element array 2.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to enable wire bonding to be performed with high reliability even in both end regions of an image element array.

[0006]

[Structure of the Invention] This invention has a plurality of image element arrays formed on a substrate, each having a large number of light receiving/emitting surfaces and individual electrodes connected to each light receiving/emitting surface formed on the front surface, and a common electrode formed on the back surface. In an image device mounted in a straight line, a conductive paste is filled between the back side of each image element array and the substrate, leaving both ends of the image element array, and an insulating paste is filled at both ends of the back side of the image element array. It is characterized by being filled.

[0007]

Embodiment In order to prevent bonding defects at both end regions of the image element array 2, the configuration shown in FIG. 1 was adopted. In the figure, 1 is a common electrode, which is provided on the back surface of the image element array 2, and 30 is an insulating paste such as an insulating adhesive, which is filled in both end areas of the back surface of each image element array 2. If wire bonding is performed in this state, the regions at both ends will also be heated from the back surface of the substrate 8, and the ultrasonic vibrations of the capillary will be transmitted evenly without escaping, allowing wire bonding to be performed without changing from other parts.

[0008] This is not the only problem with wire bonding; there is also short-circuiting due to high-density wiring. For example, as shown in FIG. 8, when the lead wire 16 hangs down and becomes a broken line, the lead wire 16 tends to come into contact with the electrode pad 17 of the adjacent wiring. This is because the electrode pads 17 cannot be spaced apart. Note that 20 is a ball at the end of the lead wire 16, and 22 is a wedge at the other end. The lead wire 16 hangs down from the second lead wire 16 from the left in FIG.
7 shows a short circuit state. Further, the second lead wire 16 from the right is shown curled to the left and short-circuited to the third lead wire 16 adjacent thereto. If the wire bonding to the electrode pad 17 is defective, the pressure and ultrasonic waves during bonding will be transmitted to the individual electrodes 6 via the lead wires 16, causing cracks in the image element array 2, a drop in reverse voltage, etc. Become.

FIG. 10 shows wire bonding conditions in a conventional example. The feature here is that the bonding load (Fo
rce) and bonding energy (USPower)
The purpose is to keep the voltage constant on both the individual electrode 6 side and the wiring 14 side.

Next, the inventor investigated the cause of the bonding defects as shown in FIGS. 8 and 9, and found that the cause was the wobbling or bouncing of the capillary housing the lead wire 16. For example, suppose that the image element array 2 side, which has lower strength, is bonded first, and then the wiring 14 side is bonded. Then, a ball 20 can be formed and placed on the side of the image element array 2 using a torch or the like before bonding. As a result, the capillary lead wires 16 come into soft contact with the image element array 2, and it is possible to prevent shaking or bouncing due to sudden pressure applied at the time of contact. On the other hand, the ball 20 cannot be provided on the side of the wiring 14, and the bonding state becomes wedge-shaped as shown in FIG. The capillary lead wire is attached to the electrode pad 17 as it is.
If you touch the capillary, the bonding load will be applied rapidly, causing the capillary to shake or bounce.

[0011] If the contact between the capillary and the electrode pad 17 is simply to be softened, the thickness of the pad 17 may be increased. However, this reduces the etching accuracy of the wiring 14 and makes high-density wiring impossible.

In contrast, the inventor has proposed that the electrode pad 17
At the start of bonding to the pad 17, the load or bonding energy at the start of contact with the pad 17 is reduced,
They found that increasing the load and energy afterwards yielded better results. That is, at the start of bonding, weak bonding is performed with a small pressing force (load) or small bonding energy, for example, a tensile strength of about 2 g (generally 1 g or more). This fixes the position of the capillary. After the capillary is fixed, the bonding is progressed by increasing the pressure and energy, and bonding is performed with a tensile strength of, for example, about 6 g. In this way, bonding can be performed while fixing the position of the capillary, so bonding defects such as short circuits do not occur, and damage to the image element array 2 can also be prevented.

FIG. 2 shows the bonding process in this example. In the first bonding (1st bond), bonding is performed to the image element array 2. Note that bonding to the electrode pads 17 may be performed first, but this is not preferable because it would result in forced bonding to the weak image element array 2. First, a lead wire 16 made of gold, aluminum, copper, etc. (in this case, a gold wire with a diameter of 20 μm) with a ball 20 formed at its tip using a torch is moved with respect to each capillary to search for the position of the individual electrode 6. Capillary is individual electrode 6
When it comes into contact with the capillary, ultrasonic waves are applied to the capillary while heating it from the back side of the substrate 8 using an electric heater or the like, and the lead wire 16 is thermocompressed by the load applied to the capillary. After the bonding is completed, the capillary is raised and the wiring 1 of the substrate 8 is removed.
A second bonding is performed on the electrode pad 17 provided at 4 (2nd bond). Here, bonding is started with a low load or low ultrasonic energy, and then the load or energy is increased and bonding is performed.

FIG. 3 shows an example of bonding conditions in which the weight is increased midway through. The parameters used are shown in Table 1.

[0015]

[Table 1] Bonding parameters
1st bond 2nd bond

Level 1 Level 2 Ultrasonic application time
20~40 12~17 (msec
) 30
15 (Ultrasonic waves are common to levels 1 and 2) Weighting
50-70
50-30 50-70 (g)
60
40 60 ultrasonic energy
0.19~0.27 0.15~0.23 (W)
0.23
0.19 (Ultrasonic waves are common to levels 1 and 2) Substrate temperature 17
0±10°C (common) *The upper row shows the preferred range, and the lower row shows the optimal value.

The reason for doing this is to first perform weak bonding to prevent the capillary from wobbling or bouncing, and then complete the wire bonding after fixing the capillary position. Here, the inventor found that the first necessary wire bonding condition is 1 g or more in terms of the tensile strength of the lead wire 16. To perform bonding to fix the capillary position, for example, even if the initial value of ultrasonic energy is small,
Alternatively, the initial values of both the ultrasonic energy and the bonding weight may be reduced. Of course, the ultrasonic energy and weight may be increased continuously from a low initial value. Figure 4 shows an example of changing ultrasonic energy (parameters are in Table 2), the upper part of Figure 5 shows an example of changing both ultrasonic energy and bonding weight (parameters are in Table 3), and the lower part shows an example of changing ultrasonic energy and bonding weight. An example of continuously changing the weighting is shown in Table 4 (parameters are shown in Table 4). Under these conditions, the inventor reduced the bonding defect rate to 10pp.
It was confirmed that the temperature could be kept below m. In the case of an imaging device that uses 2560 light receiving and emitting elements, the defective rate is 0.04%.
In this case, the defective rate of the image device is 100%. Figure 1 for reference
Table 5 shows the parameters for the conventional example.

[0017]

[Table 2] Bonding parameters
1st bond 2nd bond

Level 1 Level 2 Ultrasonic application time
20-40 3-7
7-13 (msec)
30 5
10 weight 50~
70 50-70 (g)
60 60(
Weighting is common to levels 1 and 2) Ultrasonic energy 0.1
9~0.27 0.10~0.14 0.15
~0.23(W)
0.23 0.12
0.19 substrate temperature
170±10°C (common) *The upper row shows the preferred range, and the lower row shows the optimal value.

[0018]

[Table 3] Bonding parameters
1st bond 2nd bond

Level 1 Level 2 Ultrasonic application time
20-40 3-7
7-13 (msec)
30 5
10 weight 50~
70 30~50 50~70(
g) 60
40 60 Ultrasonic energy 0.19~0.27 0.11~0
．． 18 0.15~0.23(W)
0.23 0
．． 15 0.19 Substrate temperature
170±10℃ (
Common) *The upper row shows the preferred range, and the lower row shows the optimal value.

[0019]

[Table 4] Bonding parameters
1st bond 2nd bond

Level 1 Level 2 Ultrasonic application time
20-40 4-10
7-13 (msec)
30 7
10 weight 50~
70 0~60 50~70(
g) 60
60 Ultrasonic energy 0.19~0.27 0~0
．． 19 0.15~0.23(W)
0.23
0.19 substrate temperature
170±10℃ (
Common) *The upper row shows the preferred range, and the lower row shows the optimal value.

[0020]

[Table 5] Bonding parameters (conventional example) 1st bond 2nd bond Ultrasonic application time 20-40
10-20 (msec) Weight (g) 50-70
50-70 Ultrasonic energy 0.19-0.27
0.15-0.23 (W) Substrate temperature 1
70±10℃ (common)

Specific bonding parameters are shown here, but these include the wire diameter and wire material of the lead wire 16, the individual electrodes 6 and the electrode pads 17.
It should be changed depending on the type, and is not particularly limited. Moreover, although ultrasonic bonding was used for bonding, the type of bonding itself is arbitrary.

[0022]

According to the present invention, wire bonding can be performed with high reliability even in both end regions of the image element array. As a result, the reliability and yield of the imaging device can be improved.

[Brief explanation of drawings]

FIG. 1 is a plan view of essential parts of an image forming apparatus according to an embodiment.

FIG. 2 is a process diagram of wire bonding in the image forming apparatus of the embodiment.

FIG. 3 is a diagram showing the operation timing of the wire bonding process of the image forming apparatus of the embodiment.

FIG. 4 is a diagram showing the operation timing of a wire bonding process of an image forming apparatus according to a modified example.

FIG. 5 is a diagram showing the operation timing of a wire bonding process of an image forming apparatus according to a modified example.

FIG. 6 is a perspective view of main parts of a conventional image forming apparatus.

FIG. 7 is a plan view of main parts of a conventional image forming apparatus.

FIG. 8 is a side view showing problems in wire bonding of a conventional image forming apparatus.

FIG. 9 is a diagram illustrating problems in wire bonding of a conventional image forming apparatus.

FIG. 10 is a diagram showing the operation timing of a wire bonding process of a conventional image forming apparatus.

[Explanation of symbols]

1 Common electrode 2 Image element array 4 Receiving and emitting surface 6 Individual electrodes 8 Board 14 Wiring 16 Lead wire 17 Electrode pad 18 Conductive paste 30 Insulating paste

Claims (1)

[Claims] Claim 1: A plurality of image element arrays are mounted linearly on a substrate, each having a large number of light receiving and emitting surfaces and individual electrodes connected to each light receiving and emitting surface formed on the front surface, and a common electrode formed on the back surface. In the image device, conductive paste is filled between the back surface of the image element array and the substrate, leaving both ends of the image element array, and both ends of the back surface of the image element array are filled with insulating paste. An imaging device.