JPH0416953B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Technical Field The present invention relates to an optical device package for housing an optical device such as a light emitting diode or a photodiode.

The technical requirements for an optical device package are: (1) It must have a light introduction structure that is transparent to light.

(2) Wiring the optical element using diamond bonding, wire bonding, etc., and taking out the electrode terminals from the optical element.

(3) The optical element must be hermetically sealed.

(4) High coupling efficiency with optical fiber.

The end faces of the light emitting diode chip or photodiode chip and the optical fiber are sufficiently close to each other, and the aperture angle is wide.

The present invention particularly meets the requirement (4).

(a) Prior art (top type) FIG. 15 is a sectional view of a photodiode package according to a conventional example. This is the most common type where the fiber optic light enters from the top.

TO18 type package 40 is package body 4
1, and a cap 42 that covers the upper surface of the cap. The center of the upper surface of the cap 42 is an opening, and a window 43 made of transparent Kovar glass is provided.

A photodiode chip 44 is die-bonded to the bottom plate of the package body 41.

A lead 45 is provided on the bottom plate of the main body 41.
The lead 46 and the electrode on the photodiode chip 44 are wire-bonded by a gold wire 47. An optical fiber 48 is provided outside the window 43 so as to face the photodiode chip 44.

Cap 42 and main body 41 are welded together. This package is a hermetically sealed type that has a long track record.

This package is wire bonded (gold wire 4
7), the distance between the top surface of the photodiode chip 44 and the window 43 becomes too long. For this reason, there was a drawback that the coupling efficiency with the optical fiber 48 could not be improved.

FIG. 16 shows the same top type optical device package as FIG. 15. Instead of the transparent Kovar glass 43, a window made of sapphire plate 43' is provided.

This is also wire-bonded gold wire 47, so the photodiode chip and sapphire plate 4
3' are separated from each other, and the coupling efficiency with the optical fiber 48 is poor.

(c) Conventional technology (lower surface through-hole type) In order to bring the optical fiber and the chip close together, there is a limit to the upper surface where the wires are located, and it is thought that it is better to use the lower surface.

Therefore, a package for an optical element having a through-hole type on the bottom surface as shown in FIGS. 17 to 19 was manufactured.

The same reference numerals have been used for parts common to FIG. 15. In FIG. 17, cap 42 has no window. A wide through hole 50 in the axial direction is bored in the package body 41 at a portion corresponding to the lower part of the photodiode chip 44.

The optical fiber 48 is provided so that its end face faces the through hole 50 in the lower part of the package body 41.
Light from the optical fiber 48 enters the photodiode chip 44 from the back side through the through hole 50.

In the example shown in FIG. 18, the through hole 50 is made wider,
The tip of the optical fiber 48 is inserted and fixed into the through hole 50. a photodiode chip 44;
The distance between the end faces of the optical fiber 48 can be narrowed.

However, in this example, when the tip of the optical fiber 48 is inserted into the through hole 50, it may come into contact with the photodiode chip 44 and damage it. Furthermore, it is difficult to fix the optical fiber 48.

The example in FIG. 19 shows a package in which the through hole 50 is sealed with Kovar glass 51.

The disadvantages of these bottom through-hole type optical device packages will be explained with reference to enlarged sectional views of FIGS. 20 and 21.

The pn junction of the photodiode chip 44 becomes the light receiving section 52. Light enters the light receiving section 52 from below the through hole 50. Limited by the edge 53 of the through hole 50, only light rays within a small aperture angle θ reach the light receiving portion 52.

Even if the end surface of the optical fiber 48 is brought into contact with the lower surface of the package body 41, the aperture angle θ is limited.

Next, there is the problem of difficulty in installation.

The through hole 50 is a round hole, and the photodiode chip 44 is die-bonded at a contact portion 54 other than the through hole 50. The chip is small and the through hole 50 is also small. For this reason, alignment is difficult.

When the central axis of the through hole 50 and the light receiving section 52 are shifted laterally, the aperture angle θ becomes narrower on the shifted side, as shown in FIG. In this figure, the chip is shifted to the right, making it difficult for light to reach the right portion of the light receiving section 52. Since the amount of light incident on the photodiode decreases, detection sensitivity decreases.

In order to increase the aperture angle of light incident on the light receiving section 52, the through hole 50 must be shortened and its cross-sectional area must be increased.

The length of the through hole 50 is equal to the thickness of the bottom plate of the package body 41. If this is made too thin, the mechanical strength will be insufficient. The main body 41 is made of metal or ceramic, but there is a limit to how thin it can be. The main body is
This is because it is the mechanical center that supports chips, leads, caps, etc.

Increasing the diameter of through hole 50 also requires increasing the size of photodiode chip 44. The larger the size of the semiconductor, the higher the cost and the lower the strength of the chip.

(D) Prior art (Sapphire substrate type) Therefore, the present inventor provided a die-bonding pad having a defective part on a Sapphire substrate, die-bonded an optical element onto the pad, and attached an optical fiber end face to the back side of the Sapphire substrate. Invented a package for optical devices that faces each other.

FIG. 1 is a plan view of such a package for an optical device, and FIG. 2 is a sectional view taken along the line "--" in FIG. FIG. 3 shows a cross-sectional view of a photodiode chip that has been die-bonded and a gold wire or the like that has been wire-bonded.

A lower frame 2 is bonded onto a sapphire substrate 1. The lower frame 2 only needs to be an insulator, and here, an alumina sintered body was used. Saffire board 1 and lower frame 2
The adhesion is, for example, brazing.

At the center of the sapphire substrate 1, a conductive die bonding pad 3 having a cutout 4 is provided by metallization. The die bonding pad 3 extends beyond one side of the lower frame 2 to the end.

The defective portion 4 is a portion through which light passes, and is rounded in this example. However, it does not have to be round, and may be square.

An upper frame 5 is glued onto the lower frame 2. In this example, the upper frame 5 is also made of alumina. Upper frame 5 and lower frame 2
It is attached with an insulating adhesive.

A lead 6 is soldered to the extended side of the die bonding pad 3.

Wire bonding pads 8 are metallized on opposite sides of the lower frame 2. A lead 7 is soldered to the extended side of the wire bonding pad 8.

As shown in FIG. 3, an optical element chip 9 such as a photodiode or a light emitting diode is bonded to such a package.

The optical element chip 9 is placed on the die bonding pad 3. At this time, the center of the defective part 4 and
Align so that the center of the optical element chip 9 coincides with the center.

The pad 3 is, for example, a ring solder such as AuSn eutectic. When the optical element chip 9 is pressed down and energy such as ultrasonic waves is applied, the solder melts and the chip 9 is fixed on the pad 3.

Furthermore, wire bonding 10 is performed using a gold wire or the like to connect the wire bonding pad 8 and the electrode portion of the optical element chip 9.

Usually, an alumina cap is further bonded onto the upper frame 5 to seal the internal space.

FIG. 4 is an enlarged plan view of only the vicinity of the defective part 4 of the die bonding pad 3.

FIG. 5 is a - sectional view in FIG. 4.

In an ideal case, as shown here, the sapphire substrate 1 is flat and the die bonding pad 3 is flat.

If the pad 3 is truly flat, the optical element chip can be fixed exactly in place and in a stable state.

However, in reality, the die bonding pad 3 is not flat.

After considering this reason, we found the following.

FIG. 6 is a cross-sectional view of a state in which conductive (for example, gold) paste is printed on a sapphire substrate.
Since this is thick film printing, a thin screen with holes cut out to match the shape of the pad is placed on the sapphire substrate 1.
Gold paste 13 is applied on top of it. In this state, the top surface of the gold paste is flat.

Next, in order to solidify the gold paste, the sapphire substrate 1 is placed in a furnace and fired.

During the firing process, the ends 14 of the gold paste 13 bulge due to surface tension. For this reason, the end 14
is high and other parts are low. After taking it out of the furnace, it solidifies in such an amorphous shape.

FIG. 7 is a sectional view showing the state of the pad after such firing.

FIG. 8 is a cross-sectional view showing the optical element chip 9 die-bonded onto the pad. The upper surface of the paste has many irregularities due to expansion and contraction of the paste during firing. It is impossible to glue a flat optical element chip 9 on top of this. This is because the chip 9 may peel off due to weak vibrations or the like.

(e) Structure of the present invention The present invention solves the problem of metallization of the die bonding pad 3 in an optical device package as shown in FIG. By firing,
Because the gold paste is raised at the edges,
The sapphire substrate may be shallowly shaved in advance to accommodate the raised portion.

This will be explained with reference to cross-sectional views of the sapphire substrate 1 shown in FIGS. 9 to 12.

FIG. 9 is a sectional view of the sapphire substrate 1. It is flat and transparent. The thickness is 0.2 mm in this example.

In FIG. 10, a flat sapphire substrate 1 is provided with a shallow tapered portion 16 and a concave portion 17 continuing therefrom. The tapered portion 16 and the depression 17 are processed using an Ar laser. It can also be processed mechanically.

The difference between the upper surface 15 of the sapphire substrate 1 and the depression 17 was 5 to 10 μm.

Next, as shown in FIG. 11, a conductive paste 18 such as gold paste is screen printed in the shape of the die bonding pad 3. Then, as shown in FIG. Hollow 1
7 corresponds to the missing part 4 of the pad 3. End portion 19 corresponding to the defective portion 4 of the paste 18
slopes gently toward the depression 17.

The screen-printed material is dried, then placed in a furnace and fired. FIG. 12 is a cross-sectional view of the sapphire substrate and paste after firing.

By firing, the paste end 19 is raised. However, the height of the protuberance is at most 5 μm.
It is. Since the end of the paste overlaps the tapered portion 16, even if there is a bump, it will not be higher than the other portion of the gold paste 18.

Such a die bonding pad 3,
The optical element chip 9 is die-bonded. Since the ridges at the ends are low, they do not unevenly lift the bottom surface of the chip 9.

From this point on, follow the steps already described.
An optical device package as shown in FIGS. 2 and 2 is produced. Then, as shown in FIG. 3, the optical element chip 9 is die-bonded, wire-bonded 10, and cap-sealed to form an optical element.

(F) Effect (1) Increased safety of die bonding of optical device chips.

When the gold paste is fired, the protuberances formed at the edges are low and do not touch the surface of the optical device chip. This is because only the flat side of the gold paste contacts the backside of the chip, creating a smooth contact surface.

(2) The packaging of this optical element chip is
Unlike the bottom through-hole type shown in Figure 4, there is no strong restriction on the opening angle. In the packaging structure of the present invention shown in FIG. 15, the light reaching the light receiving portion 52 passes through the cutout portion 4 of the pad 3. As shown in FIG. The defective part 4 is in contact with the chip 9,
Moreover, it is extremely thin. Therefore, light included in the wide aperture angle θ can be made to enter the light receiving section 52.

[Brief explanation of drawings]

FIG. 1 is a plan view of the optical device package of the present invention. FIG. 2 is a sectional view taken in FIG. 1. FIG. 3 is a cross-sectional view of an optical device chip die-bonded into an optical device package. FIG. 4 is an enlarged plan view of the die bonding pad. FIG. 5 is a sectional view taken in FIG. FIG. 6 is a sectional view showing a state in which gold paste is screen printed on a sapphire substrate. FIG. 7 is a cross-sectional view showing the state of gold paste on the sapphire substrate after firing. FIG. 8 is a sectional view showing a state in which an optical element chip is placed on gold paste. FIG. 9 is a cross-sectional view of the sapphire substrate. FIG. 10 is a cross-sectional view of a sapphire substrate with a tapered portion and a depression. FIG. 11 is a cross-sectional view of a state in which gold paste is screen printed so that the end portion is located on the tapered portion. FIG. 12 is a sectional view showing the state of the gold paste after firing. FIG. 13 is a sectional view illustrating the relationship between the light receiving portion of the chip and the aperture angle in the optical device package of the present invention. FIG. 14 is a sectional view illustrating the relationship between the chip light-receiving portion and the aperture angle in a conventional bottom-through-hole type package. FIG. 15 is a sectional view of a known top-surface type optical device package. An example with a glass window. FIG. 16 is a sectional view of a known top-surface type optical device package. An example with a sapphire window. FIG. 17 is a cross-sectional view of a conventional optical device package with a through-hole type on the bottom surface. FIG. 18 is a sectional view of a conventional optical device package with a through-hole type on the bottom surface. FIG. 19 is a cross-sectional view of a conventional optical device package with a through-hole type on the bottom surface. FIG. 20 is an enlarged cross-sectional view showing the range of light incident on the lower surface through-hole type light receiving section. FIG. 21 is an enlarged cross-sectional view showing the range of light incident on the light receiving section in the case where the mounting position of the chip is shifted in the optical device package of the bottom through-hole type. 1...Sapphire substrate, 2...Bottom frame, 3...Die bonding pad, 4...Defected part, 6,7
... Lead, 8 ... Wire bonding pad, 9 ... Optical element chip, 10 ... Bonding wire, 13 ... Gold paste, 14 ... End of gold paste.

Claims (1)

[Claims] 1 An optical element chip consisting of a sapphire substrate 1, a die bonding pad 3 having a defective part 4 obtained by printing and baking a conductive paste on the sapphire substrate 1, and a light emitting or light receiving element die-bonded onto the die bonding pad 3. 9, a lower frame 2 fixed on the sapphire substrate 1, a wire bonding pad 8 provided on the lower frame 2 and wire bonded to the optical element chip 9, a die bonding pad 3, and a wire bonding pad 3. It includes leads 6 and 7 connected to the pad 8 and an upper frame 5 fixed on the lower frame 2, and the light is transmitted to the sapphire substrate 1.
In the optical device package which is designed to enter and exit the optical device chip 9 through the defective portion 4 of the die bonding pad 3, a shallow taper portion 16 is provided in advance on the sapphire substrate 1 so as to hit the defective portion 4 of the conductor paste. A package for an optical device characterized in that an end portion is located above a tapered portion 16.