JP2000022279A - Mounting structure for optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element mounting structure in which the optical axes of an optical element and a light transmitting path can be aligned accurately through an extremely convenient arrangement without requiring any adjustment. SOLUTION: An optical element 31 to be coupled optically with a light transmitting path is arranged through a solder 3 on a metal pattern 2a where parts 4a, 4b for punching a pattern are formed at positions symmetric to the projection L of the optical axis of the light transmitting path on a substrate 1. Optical axis of the optical element 31 is aligned with that of the light transmitting path by surface tension of the solder 3 fused on the metal pattern 2a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical module used for optical transmission, optical communication, and the like, and more particularly, to an optical module mounting structure.

[0002]

2. Description of the Related Art In the telecommunications field, with the increase of information capacity,
The transition from communication to optical communication, which is advantageous for increasing the capacity, is progressing from electric signals. Application of optical communication to general subscriber systems is also being considered. Therefore, there is a demand for a low price optical device for optical communication.

However, in the manufacture of an optical device, it is necessary to mount the optical axis of an optical element on a substrate with high accuracy, and a great deal of effort is required for adjusting the optical axis. Therefore, a method of mounting an optical element on a substrate without adjustment has been studied for cost reduction.

As an example of a non-adjustment mounting method, there is a method using a solder bump as follows. For example, FIG.
As shown in (a) to (c), a circular electrode pad 2a is formed on a substrate 1 and a solder bump 3 is supplied on the substrate 1,
The optical element 31 is temporarily placed on the solder bump 3 and the solder bump 3 is heated and melted. In the drawing, reference numeral 41 denotes an optical transmission line such as an optical fiber or an optical waveguide, and reference numeral 11 denotes an optical axis thereof.

[0005] Here, the optical element 31 is soldered by its surface tension.
In order to change the shape so that the surface area is minimized in the state in which the optical elements 31 are joined, the optical element 31 is moved by the surface tension of the solder, and the optical element 31 is positioned so as to be directly above the solder bump 3.

Conventionally, a circular electrode pad is formed on a silicon substrate, a solder bump is formed on the electrode pad, and the electrode pad prepared on the laser diode side is mounted on the solder bump to perform horizontal positioning. Proposed. Further, for positioning in the vertical direction, it has been proposed to form a positioning table made of an insulator near a solder pad and perform positioning in the height direction by applying a laser diode. This is because the positioning in the vertical direction tends to vary depending on the supplied amount of solder (for example, see Japanese Patent Application Laid-Open No. 7-235566).

The electrode pads for supplying the solder bumps are formed in a rectangular shape instead of a circle, and the area of the electrode pads is increased to reduce the variation in bump height due to the variation in the amount of solder to be supplied. And the like have been proposed to increase the accuracy of the image. 7 to 9 show these examples.

According to these methods, first, the optical waveguide 41
An electrode pad 2a for bonding the core of the waveguide 41 or the core of the optical fiber 51 to the optical element 31 is formed by photolithography on the Si substrate 1 on which the V-groove 52 for fixing the optical fiber is formed. Next, the solder bumps 3 are formed on the electrode pads 2a.

On the other hand, the electrode pad 2
An electrode pad having the same shape as a is formed. Next, the optical element 31 is temporarily fixed on the solder bumps 3 with solder interposed between the electrode on the back surface of the optical element and the electrode pad 2a, and is joined by melting the solder. Positioning is performed with high accuracy without adjustment by the self-alignment effect of tension. Thereby, optical axis alignment between the active layer of the optical element 31 and the core of the optical waveguide 41 or the optical fiber 51 is achieved. In the figure, reference numeral 53 denotes a fiber stopper groove.

As a method for simultaneously and accurately positioning in the horizontal and vertical directions, the shape of the solder pad is formed in a rectangular shape so that the positioning in the vertical direction does not vary even if the amount of supplied solder varies. It has been proposed to. In this way, a rectangular bump can secure a larger bonding area than a circular bump, so that heat dissipation and
The bonding strength is somewhat improved (see, for example, JP-A-8-179154).

[0011]

In the above-mentioned conventional method for mounting an optical element using solder bumps, the positioning accuracy in the horizontal direction with respect to the substrate is good. However, in order to position the vertical direction to the required accuracy of ± 1 μm required for mounting, it is difficult to use a simple circular electrode pad. Therefore, a vertical positioning table is prepared near the substrate-side electrode pad, and the optical element is pressed against the vertical position. It is necessary to adjust the optical axis, and the spherical solder bump must have a large diameter in terms of bonding strength, but the height from the Si substrate surface to the core of the optical waveguide must be 20 μm or less. Because of the large number, the diameter is restricted, and the problem of a decrease in bonding strength and a decrease in heat dissipation arises.

To avoid this problem, it is conceivable to increase the number of spherical solder bumps to be formed. However, variations in the amount of solder to be supplied cause variations in the height of the solder bumps. Make positioning difficult.

In order to avoid this problem, in a rectangular bump structure, by increasing the supply amount of solder per bump, it is possible to improve the variation in the height direction due to the variation in the supply amount of solder. In addition, the bonding area is larger than that of the conventional spherical solder bump, and the bonding strength and heat dissipation are improved, but are insufficient.

Further, in the case of a spherical or rectangular solder bump,
Since the positioning is performed by using the surface tension of only the outer periphery of the solder bump, when the electrode is taken out to a portion for making contact with the outside other than the optical element 31 mounting portion as an electrode structure, a part of the solder is melted when the solder is melted. It flows into an electrode for taking out a contact with the outside, so that the shape of the circle or rectangle is broken, and problems such as unevenness in the amount of solder and reduction in alignment accuracy arise.

In view of the above, according to the present invention, the mounting of an optical element capable of adjusting the optical axis of the optical element and the optical axis and the position (optical axis) of the optical transmission line with high precision without adjustment is performed with a very simple configuration. The purpose is to provide a structure.

[0016]

In order to solve the above-mentioned problems, in the mounting structure of the optical element according to the present invention, a cutout portion of a pattern is formed at a position symmetrical to an optical axis projection of an optical transmission line on a substrate. An optical element to be optically connected to the optical transmission line is disposed on a metal pattern with solder interposed therebetween, and the optical axis of the optical element is set to the optical transmission path by the surface tension of the solder melted on the metal pattern. In alignment with the optical axis. The optical element may be an optical semiconductor element such as a light emitting diode for emitting or receiving light, a semiconductor laser element, a light receiving element, or the like.

In this manner, a structure is provided which has a larger bonding area, high positioning accuracy, and minimizes misalignment during solder melting. This makes it possible to position the optical element in the horizontal direction by the outer periphery of the solder bump and the cavity formed in the solder bump.

For example, in order to secure a sufficient bonding area between the substrate-side electrode pad (metal pattern) and the electrode pad provided on the back surface of the optical element, an optical element mounting portion of the substrate-side electrode pad and the electrode pad on the back surface of the optical element are required. Make the same shape. For example, a cut pattern formed by combining rectangles is formed inside the electrode pad.

Compared with the conventional circular or rectangular solder pad, the side having the self-alignment effect due to the surface tension of the solder becomes the outer peripheral portion and the outer peripheral portion of the punch pattern by forming the punch pattern on the electrode pad. Since the number is larger than that of the conventional structure, the alignment effect is larger.

In consideration of only the alignment effect, in the case of a circular solder bump, the smaller the size of the solder bump, the better. However, if the solder bump is small, the joint strength and heat dissipation will be reduced due to a decrease in the joint area. Occurs. For example, in the case of a rectangular solder bump, the narrower the width is, the better the alignment effect is, but the problems of the bonding strength and heat dissipation also arise.

In the case of the punched pattern, the width of the solder bump between the outer peripheral portion and the punched pattern can be reduced by bringing the position of the punched pattern closer to the outer peripheral portion without changing the area of the electrode pad. In addition, the alignment effect can be improved without impairing the heat radiation.

Next, solder is supplied to the substrate-side electrode pads. At the time of mounting the optical element, temporary fixing is performed by matching the pattern of the substrate-side electrode pads and the optical element-side electrode pads. The optical axis in the horizontal direction is adjusted with respect to the substrate of the optical element by the surface tension around the cut pattern.

Regarding the positional accuracy in the vertical direction, the amount of solder supplied on the electrode pad is increased, so that even if the amount of the supplied solder pad varies, the variation in the positional accuracy in the vertical direction can be reduced. By making the area of the punched pattern smaller than the area of the electrode pad, a sufficient bonding area can be ensured, and problems relating to heat dissipation and bonding strength are eliminated.

According to the present invention, the solder interposed between the optical element side electrode pad formed on the back surface of the optical element and the substrate side electrode pad formed on the surface of the substrate is joined by melting the solder, which is generated when the solder is melted. This is a mounting structure of an optical element capable of performing joint positioning by surface tension and accurately aligning the optical axis of the optical element with the optical axis of the optical transmission path.

In particular, when the surface of the solder is applied in the optical axis direction and in the direction perpendicular to the optical axis, the optical element mounting portion of the substrate-side electrode pad has a cutout pattern formed by combining rectangles. Good. When the optical element is a light emitting element, in order to improve the heat radiation efficiency, both the optical element side electrode pad and the substrate side electrode pad are formed with an electrode part of the electrode pad in a lower region of the active layer of the light emitting element. Is also good.

Further, it is preferable that the shape of the cut pattern in the electrode pad is line-symmetric with respect to the optical axis so that positioning can be performed with high accuracy in a direction perpendicular to the optical axis.

It is more preferable that the area of the punched pattern is not more than half the area of the electrode pad including the punched pattern for the purpose of securing a sufficient bonding area and improving heat dissipation and bonding strength.

[0028]

The self-alignment of the optical element on the substrate-side electrode having the cutout pattern in the optical element mounting portion can be performed by the surface tension of the solder. In addition, by reducing the area of the cutout pattern of the optical element mounting portion, a sufficient bonding area can be obtained, and problems with heat dissipation and bonding strength can be avoided. Further, by providing the hollow portion inside the solder bump, the optical element is positioned not only by the surface tension of the outer periphery of the solder bump but also by the surface tension of the solder bump on the outer periphery of the internally formed hollow portion. Therefore, the electrodes can be routed from the optical element mounting portion to the outside.

[0029]

Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in FIG. 1, the mounting structure of the optical element 31 according to the present invention comprises a metal pattern in which pattern cutouts 4a and 4b are formed at symmetric positions with respect to the optical axis projection L of the optical transmission path on the substrate 1. An optical element 3 for optically connecting to an optical transmission line on 2a
1 is arranged with the solder 3 interposed therebetween, and the optical axis of the optical element 31 is aligned with the optical axis of the optical transmission path by the surface tension of the solder 3 melted on the metal pattern 2a.

Specifically, on the thermally oxidized Si substrate 1,
Electrode pad 2a such as Cr / Au or Ti / Pt / Au
Is formed by photolithography, vapor deposition, sputtering and the like. The electrode pad 2a has rectangular removal patterns 4a and 4b in the optical axis direction and the direction perpendicular to the optical axis 11.
The positions and shapes of the cutout patterns are formed line-symmetrically with respect to the optical axis.

Here, as shown in FIGS. 1 and 2, the total area of the cutout patterns 4a, 4b, and 4c is set to be less than half the area of the optical element mounting portion of the electrode pad 2a. As a result, the bonding area is increased, and sufficient bonding strength and heat dissipation are obtained. It should be noted that the cutout pattern 4c may be a combination of a rectangular cutout pattern 4a whose longitudinal direction is the optical axis direction and a rectangular cutout pattern 4b whose longitudinal direction is perpendicular to the optical axis.

Next, a eutectic alloy solder of 80% by weight of Au—20% by weight of Sn is supplied to the optical element mounting portion of the electrode pad on the substrate 1 side by a vapor deposition method, a plating method, a press punching method of punching out an AuSn foil, or the like, and melting. By doing so, the solder bumps 3 are formed.

The optical element 31 is temporarily fixed on the solder bump 3 with the solder bump 3 interposed between the substrate-side electrode pad 2a and the optical element-side electrode pad 2b. On the back surface of the optical element 31, an electrode pad 2b having the same shape as the substrate-side electrode pad is formed.

Finally, bonding is performed by heating in a nitrogen atmosphere to melt the solder. At this time, the optical element 31 can be mounted with high precision by the self-alignment effect of the solder.

According to the present invention, a sufficient bonding area between the substrate-side electrode pad 2a and the optical element-side electrode pad 2b can be ensured. In addition, the bonding area is wider than before, the heat conduction from the optical element 31 to the solder is good, the heat dissipation is improved, and the light emission intensity of the optical element 31 can be increased and stable operation at high temperatures can be performed. In addition, since the bonding strength can be obtained in proportion to the bonding area ratio, the bonding area is about four times as large as the conventional one, so that about four times the bonding strength can be obtained and a highly reliable structure can be obtained. it can.

[0037]

Next, specific examples of the method of mounting an optical element and the structure thereof according to the present invention will be described.

First, on the thermally oxidized Si substrate 1, Ti /
A Pt / Au electrode pad 2a was formed by photography and vapor deposition. The size of the electrode pad 2a was 400 microns in the optical axis direction and 300 microns in width according to the outer shape of the optical element 31 to be mounted.

The electrode pad 2a has a length of 200 in the optical axis direction.
It has a cutout pattern 4a having a width of 30 microns and a cutout pattern 4a having a length of 100 microns and a width of 30 microns in a direction perpendicular to the optical axis 11. The same pattern as the substrate-side electrode pad 2a was formed on the optical-element-side electrode pad 2b.

Since the optical element 31 used in this embodiment is a light emitting element, no pattern is formed in a portion immediately below the active layer region in consideration of heat dissipation.

In the optical element mounting portion of the substrate-side electrode pad 2a,
A eutectic alloy solder of 80 wt% Au-20 wt% of Sn was supplied by vapor deposition and melted to form a solder bump 3. Then, the optical element 31 is temporarily fixed on the solder bump 3 with the solder bump 3 interposed between the substrate-side electrode pad 2a and the optical element-side electrode pad 2b, and heated in a nitrogen atmosphere.
Bonding was performed by melting the solder at 300 ° C.

FIG. 2 shows the optical axis 11 (or the optical axis projection (direction)).
L) illustrates an example of a cutout pattern 4c in which a rectangle whose major axis direction is perpendicular to the rectangle and a rectangle whose major axis direction is optical axis are combined.

FIGS. 3 (a) to 3 (c) and FIGS.
As shown in (a) to (f), an example of a combination of a rectangle whose major axis direction is perpendicular to the optical axis 11 and a cutout pattern of a rectangle whose major axis direction is the optical axis direction will be described. Alignment in the direction perpendicular to the optical axis and in the optical axis direction can be performed simultaneously by combining the rectangles.

For easy understanding, FIG. 5 shows an example of the mounting structure of the optical element 31 in the substrate 1 having the optical waveguide 41. FIG. 6 shows the substrate 1 having the optical fiber 51 mounted in the optical fiber fixing V-groove 52. 3 shows an example of a mounting structure of the optical element 31 in FIG.

[0045]

As described in detail above, according to the present invention,
For example, by making rectangular removal patterns that are line-symmetric with respect to the optical axis in the optical axis direction and the direction perpendicular to the optical axis in the optical element side electrode pad and the substrate side electrode pad, the surface tension of the solder during the optical element mounting By having a horizontal self-alignment function and increasing the bonding area as compared with conventional spherical solder bumps or rectangular solder bumps, heat dissipation and bonding strength can be improved.

As for the accuracy in the height direction, if the amount of solder to be supplied is large, even if there is a slight variation in the amount of supply, the height accuracy is hardly affected. it can.

Further, the positioning can be performed without relying on the surface tension of only the outer shape of the solder bump, and the electrode can be taken out of the portion other than the optical element mounting portion.

[Brief description of the drawings]

1A and 1B are diagrams for explaining a mounting structure of an optical element according to the present invention, wherein FIG. 1A is a plan view, FIG. 1B is a cross-sectional view taken along the line BB of FIG. It is CC sectional drawing.

2A and 2B are diagrams illustrating a mounting structure of another optical element according to the present invention, wherein FIG. 2A is a plan view, FIG. 2B is a cross-sectional view taken along the line BB of FIG. () Is a sectional view taken along line CC.

FIGS. 3A to 3C are plan views each illustrating a modification of the metal pattern according to the present invention.

FIGS. 4A to 4F are plan views each illustrating a modified example of the metal pattern according to the present invention.

5A and 5B are diagrams showing coupling between an optical element and an optical transmission line in the optical element mounting structure according to the present invention, wherein FIG.
(B) is a sectional view taken along the line BB of (a), and (c) is a sectional view of C of (a).
FIG. 4 is a sectional view taken along line C of FIG.

6A and 6B are diagrams showing coupling between an optical element and an optical transmission line in a mounting structure of the optical element according to the present invention, wherein FIG.
(B) is a sectional view taken along the line BB of (a), and (c) is a sectional view of C of (a).
FIG. 4 is a sectional view taken along line C of FIG.

7A and 7B are diagrams showing coupling between an optical element and an optical transmission line in a conventional optical element mounting structure, where FIG. 7A is a plan view and FIG.
5A is a cross-sectional view taken along the line BB of FIG. 5A, and FIG. 5C is a cross-sectional view taken along the line CC of FIG.

8A and 8B are diagrams showing coupling between an optical element and an optical transmission line in a conventional optical element mounting structure, where FIG. 8A is a plan view and FIG.
5A is a cross-sectional view taken along the line BB of FIG. 5A, and FIG. 5C is a cross-sectional view taken along the line CC of FIG.

9A and 9B are diagrams showing coupling between an optical element and an optical transmission line in a conventional optical element mounting structure, where FIG. 9A is a plan view and FIG.
5A is a cross-sectional view taken along the line BB of FIG. 5A, and FIG. 5C is a cross-sectional view taken along the line CC of FIG.

10A and 10B are diagrams showing coupling between an optical element and an optical transmission line in a conventional optical element mounting structure, wherein FIG.
(B) is a sectional view taken along the line BB of (a), and (c) is a sectional view of C of (a).
FIG. 4 is a sectional view taken along line C of FIG.

[Explanation of symbols]

 1: substrate 2a, 2b: electrode pad (metal pattern) 3: solder pad 4a, 4b, 4c: blank pattern 11: optical axis 31: optical element (laser diode) 41: optical waveguide 51: optical fiber 52: optical fiber fixed V-groove 53: Rectangular groove for optical fiber stopper

Claims (1)

[Claims] An optical element to be optically connected to an optical transmission line is disposed on a metal pattern having a pattern cutout formed at a position symmetrical to an optical axis projection of the optical transmission line on a substrate, with solder interposed therebetween. An optical element mounting structure in which the optical axis of the optical element is aligned with the optical axis of the optical transmission path by the surface tension of the solder melted on the metal pattern.