JP2002299486A - Package for storing optical semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance mounting reliability for an external circuit board having a relatively large coefficient of thermal expansion and for the package of an optical semiconductor element. SOLUTION: The package for storing an optical semiconductor element comprises an insulating board and a wiring conductor layer, a ceramic wiring board having an optical semiconductor element mounting part on the upper surface of the insulating board, a frame fixed onto the wiring board while surrounding the optical semiconductor element mounting part and provided with a part for introducing an optical signal, a cover member fixed to the upper surface of the frame and sealing the optical semiconductor element, and a terminal for connection with an external circuit board provided on the side of the insulating board opposite to the optical semiconductor element mounting part wherein the coefficient of thermal expansion on the side of the insulating board provided with the connection terminal is set larger than that on the optical semiconductor element mounting side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor element housing package for housing an optical semiconductor element therein.

[0002]

2. Description of the Related Art Conventionally, an optical semiconductor element housing package for housing an optical semiconductor element generally seals a concave metal container such as an Fe / Ni / Co alloy or a Cu / W alloy and an opening of the container. It consists of a metal lid for
A mounting portion for mounting and fixing the optical semiconductor element is provided at the center of the bottom of the metal container. In addition, on the side wall portion of the metal container, a wiring board provided with a wiring conductor layer on the surface of an insulating substrate made of ceramics such as alumina and an introduction portion for introducing an optical fiber are provided through the side wall portion. It has a structure in which a signal sent from an optical fiber is converted into an electric signal by an optical semiconductor element and transmitted to an external circuit through a wiring board.

In recent years, with the reduction in the weight of components, a form in which an optical semiconductor element housing package is mounted on a predetermined external circuit board has been required. In response to this demand, recently, using a conventionally known multilayer ceramic processing method,
Forming a wiring conductor layer made of tungsten on the surface or inside of a ceramic insulating substrate such as alumina, forming an optical semiconductor element mounting part on the surface, attaching a frame so as to surround this mounting part, forming a cavity, A package in which this is sealed with a lid has also been proposed. In this package, lead terminals are attached to the side and bottom of the wiring board and mounted by soldering, or pin terminals are attached to the bottom and mounted on the external circuit board by vertically inserting pins into the external circuit board It has also been suggested.

[0004]

With the recent expansion of optical communication, it has been required to automate the mounting of the optical semiconductor element housing package on an external circuit board. In the case of the package used, the lead terminals are usually set to be long to reduce the generation of stress in the mounting of the package and the external circuit board. There is a problem that the transmission of the high-frequency signal fluctuates due to a shift due to a problem that the amount of solder cannot be made constant. Further, in the case where the pin terminal is used, there is a problem that the inserted pin protrudes from the external circuit board, thereby increasing the reflection loss of the high-frequency signal.

In order to solve these problems, it is conceivable to mount directly by soldering in a ball shape or the like instead of the lead terminal or the pin terminal.

On the other hand, an external circuit board is generally made of an organic resin as an insulating material, and an optical semiconductor element has a thermal expansion coefficient of 5 to 7 × 10
⁻⁶ / ° C., while the external circuit board contains an organic resin as an insulating material and has a coefficient of thermal expansion of 10 to 15
It consists of a so-called printed wiring board of × 10 ^-6 / ° C. Therefore, when the package is formed of ceramics such as alumina, the alumina ceramics has a thermal expansion coefficient of 6 to 7 × 10 ⁻⁶ / ° C., which is close to that of the optical semiconductor element, so that the mounting reliability for the optical semiconductor element is high. However, since the thermal expansion difference between the external circuit board and the external circuit board is large, there is a problem in reliability of mounting on the external circuit board.

To solve this problem, if the package is formed of ceramics having a high thermal expansion, the reliability of mounting the package on an external circuit board is improved, but the difference in thermal expansion between the package and the optical semiconductor element is increased. The mounting reliability is reduced, and a stress is generated in the optical semiconductor device mounted on the package due to a difference in thermal expansion, and the stress causes a displacement between the optical semiconductor device and the optical semiconductor device. However, there is a problem in that the conversion efficiency of the signal is reduced.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical semiconductor device housing package having improved mounting reliability for an external circuit board having a relatively large coefficient of thermal expansion and mounting reliability for an optical semiconductor device package. It is assumed that.

[0009]

Means for Solving the Problems As a result of repeated studies on the above-mentioned problems, the present inventors have found that when mounting an optical semiconductor element in a package, a ceramic insulating member for mounting the optical semiconductor element on a ceramic wiring board is used. On the board, the surface on which the connection terminals are provided is matched to the thermal expansion of the external circuit board,
The surface on which the optical semiconductor element is mounted is matched to the thermal expansion of the optical semiconductor element, and the thermal expansion coefficient of the ceramic wiring board is increased by changing the coefficient of thermal expansion in the insulating substrate stepwise or continuously. It is found that even when the thermal expansion of the optical semiconductor device is approximated, a highly reliable package for storing the optical semiconductor device can be obtained without deteriorating the signal conversion efficiency without affecting the mounting of the optical semiconductor device. This has led to the present invention.

That is, a package for storing an optical semiconductor element according to the present invention comprises a ceramic wiring board having an insulating substrate and a wiring conductor layer, and having an optical semiconductor element mounting portion on the upper surface of the insulating substrate; A frame body mounted on the wiring board so as to surround and provided with an introduction portion for introducing an optical signal; and a lid member attached to an upper surface of the frame body for sealing the optical semiconductor element. And a connection terminal for connecting to an external circuit board is provided on a surface of the insulating substrate opposite to the optical semiconductor element mounting portion, and the connection of the insulating substrate is provided. The coefficient of thermal expansion of the surface on which the terminals are provided is larger than the coefficient of thermal expansion of the optical semiconductor element mounting surface,
As a result, the primary mounting reliability of the optical semiconductor element of the package on the wiring board and the secondary mounting reliability of the package on the external circuit board can be improved.

In order to improve the primary mounting reliability, the difference in thermal expansion coefficient between 25 and 200.degree.
It is 0 ^-6 / ° C. or less, and it is desirable thermal expansion coefficient at 25 to 200 ° C. of the optical semiconductor element mounting surface of the insulating substrate in the wiring substrate is 9 × 10 ^-6 / ℃ or less.

In order to enhance the reliability of the secondary mounting, the difference in the coefficient of thermal expansion between 25 and 200 ° C. between the surface of the wiring board on which the connection terminals are provided and the external circuit board is 3 × 10 ^−6.
/ ° C or less, and particularly, the coefficient of thermal expansion at 25 to 200 ° C of the surface of the insulating substrate on which the connection terminals are provided is 9 × 10 ⁻⁶ /
Desirably, it is higher than ° C.

Preferably, the coefficient of thermal expansion of the insulating substrate changes stepwise or continuously from the surface on which the optical semiconductor element is mounted to the surface on which the connection terminals are provided.

Further, the insulating substrate of the wiring board is
Since the wiring conductor layer can be formed of a low-resistance metal such as copper or silver by being formed of a low-temperature fired ceramic material that can be fired at a temperature of not more than 0 ° C., it is suitable for handling high-frequency signals.

According to the package for housing an optical semiconductor element of the present invention, as described above, the thermal expansion on the side on which the optical semiconductor element is mounted and the side on which the connection terminals are provided in the insulating substrate of the wiring board are changed. Since the difference in thermal expansion between the external circuit board and the package and the difference in thermal expansion between the optical semiconductor element and the package can be reduced, the generation of stress due to the difference in thermal expansion is suppressed, and the optical semiconductor Primary mounting reliability of the element and secondary mounting reliability of the package on the external circuit board can be achieved at the same time.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view for explaining an example of an optical semiconductor element housing package A of the present invention.
In the figure, 1 is a ceramic wiring board, 2 is a frame, and 3 is a lid member. A cavity is formed by the wiring board 1, the frame 2, and the lid member 3, and the optical semiconductor element 4 is housed in the cavity.

The wiring board 1 includes an insulating substrate 5 and a wiring conductor layer 6.
A mounting portion for mounting the optical semiconductor element 4 is formed substantially at the center of the upper surface of the wiring substrate 1 on the cavity side. A conductor layer 7 for bonding and fixing the optical semiconductor element 4 is formed on the mounting portion. For example, an optical semiconductor in which a photoelectric conversion element section 4b is formed on an optical semiconductor element substrate 4a made of silicon or the like. The element 4 is bonded and fixed to the conductor layer 7 with a solder material (not shown) such as gold-germanium.

The frame 2 is made of ceramics or metal. In order for the optical signal from the optical fiber 8 to reach the photoelectric conversion element 4b, the frame 2 has an introduction section 9 for introducing the optical fiber 8. Are formed. For example, a through hole 10 that penetrates the frame 2 is formed in the introduction portion 9, and the optical fiber 8 is formed in the through hole 10.
Is fixed to the outer surface of the through hole 10 with a brazing material. A conductor layer (not shown) is previously formed on the attachment surface of the fixing member 11 of the frame 2, and a nickel plating layer or a gold plating layer is applied to the surface of the conductor layer, and the fixing member 11 is brazed. The fixing member 11 is firmly fixed to the frame body 2 with enhanced properties.

The optical fiber 8 is supported so as to pass through the cylindrical fixing member 11, is introduced into the cavity through the through hole 10, and is arranged so that an optical signal can be transmitted and received between the optical semiconductor elements 4. Have been. In addition, the cylindrical fixing member 1
The optical fiber 1 and the optical fiber 8 are fixed by a solder material, resin sealing or the like.

On the upper surface of the frame 2, for example, Fe-N
A cover member 3 made of a metal material such as an i-Co alloy or an Fe-Ni alloy is joined by welding such as a seam welding method,
The inside of the cavity is hermetically sealed.

Further, connection terminals 13 are attached to the lower surface of the wiring board 1 via connection pads 12. In this example, a ball-shaped solder is attached as the connection terminal 13.

The package A is mounted on an external circuit board B. The external circuit board B includes an insulating base 14.
Pad 15 for mounting package A on the surface of
Are formed, and as shown in FIG.
Means that the connection pads 12 on the package A side are connected to the external circuit board B
Connection pad 15 and connection terminal 13 made of ball-shaped solder
The connection is fixed.

According to the present invention, the connection terminals 13 of the package for housing an optical semiconductor element are formed by soldering such as ball solder as described above, and the connection pads 1 on the package A side are formed.
2 and the connection pads 15 on the external circuit board B side are directly connected by soldering, because the height between the connection pads between the package A and the external circuit board B is very low, the difference is caused by the difference in thermal expansion between the two. Stress cannot be absorbed by the solder,
Cracks and the like are generated around the solder and the connection pad serving as the connection terminal 13, so that the connection resistance is increased and the mounting reliability is impaired.

In order to improve the reliability of mounting the package A on the external circuit board B when the connection terminals 13 are made of solder as described above, the coefficient of thermal expansion of the insulating base 14 constituting the external circuit board is increased. It is desirable to approximate the thermal expansion coefficient between the substrate and the insulating substrate 5 in the optical semiconductor element housing package.

In the package A on which the optical semiconductor element 4 according to the present invention is mounted, it is very important to prevent the occurrence of displacement between the optical fiber 8 and the photoelectric conversion element 4a in order to increase the signal conversion efficiency. . This displacement is determined by the reliability of the mounting on the conductor layer 7 on the insulating substrate 5 in the package A on which the optical semiconductor element 4 is directly mounted.

In order to increase the reliability of the secondary mounting of the package A on the external circuit board B, the thermal expansion coefficient of the insulating substrate 5 tends to increase. Therefore, distortion occurs in the mounting portion of the optical semiconductor element, and the optical semiconductor element is displaced from the optical fiber, thereby deteriorating the signal conversion efficiency.

Therefore, according to the present invention, the thermal expansion coefficient of the surface of the insulating substrate on which the connection terminals are provided (hereinafter referred to as the connection terminal installation surface) is set to be larger than the thermal expansion coefficient of the optical semiconductor element mounting surface. By adjusting, the connection terminal installation surface can be matched to the thermal expansion of the external circuit board, and the optical semiconductor element mounting surface can be matched to the thermal expansion of the optical semiconductor element.

In particular, in terms of the matching of the thermal expansion, the difference in the thermal expansion coefficient between the optical semiconductor element mounting surface side of the insulating substrate and the optical semiconductor element, and the thermal expansion coefficient between the connecting terminal installation surface side of the insulating substrate and the external circuit substrate. The expansion coefficient difference is desirably 3 × 10 ⁻⁶ / ° C. or less, particularly 2 × 10 ⁻⁶ / ° C. or less.

The thermal expansion coefficient of the optical semiconductor element mounting surface of the insulating substrate is preferably 9 × 10 ⁻⁶ / ° C. or less, particularly preferably 8 × 10 ⁻⁶ / ° C. or less.

On the other hand, the external circuit board B has a name of FR-4.
Epoxy on woven or non-woven fabric such as glass
Organic resin impregnated with thermosetting resin such as resin
The wiring circuit layer is formed by metal foil on the insulating substrate containing
Is used. Such an external circuit board is commonly used.
Usually, the coefficient of thermal expansion at 20 to 200 ° C. is 10 to 15 ×.
10^-6/ ° C. Therefore, the optical semiconductor device housing of the present invention
On the connection terminal installation side of the insulating substrate 5 in the package A
The coefficient of thermal expansion at 25 to 200 ° C. is 9 × 10 ^-6/ ℃
Greater than, especially 10 × 10^-6/ ° C or higher
No.

In the ceramic insulating substrate 5,
The optical semiconductor element mounting surface and the connection terminal installation surface have different thermal expansion coefficients, and it is desirable that the thermal expansion coefficient in the insulating substrate 5 changes stepwise or continuously.

Accordingly, the ceramic insulating substrate 5 is formed as shown in FIG.
As shown in (a), when formed by two insulating layers 5a and 5b having different thermal expansion coefficients, the insulating layers 5a and 5b
When b is formed by simultaneous firing, an intermediate layer having an intermediate composition of the insulating layers 5a and 5b is naturally formed at the interface, and a graded or continuous gradient structure with a thermal expansion coefficient is formed. When the difference between the thermal expansion coefficients of the insulating layers 5a and 5b is large, as shown in FIG.
It is desirable to provide an intermediate layer 5c having an intermediate thermal expansion characteristic between the insulating layers 5a and 5b between the insulating layers 5a and 5b, thereby suppressing generation of stress due to a difference in thermal expansion between the insulating layers 5a and 5b. Can be. This intermediate insulating layer is not limited to one layer, and may have two or more layers. (Insulating substrate) According to the package of the present invention, the wiring substrate 1
The ceramic insulating substrate 5 is made of a conventionally known ceramic insulating substrate material, and is made of alumina, mullite,
It can be formed of at least one selected from the group consisting of forsterite, aluminum nitride, silicon nitride, and glass ceramics.

According to the present invention, it is necessary to change the thermal expansion in the insulating substrate 5. In order to change the thermal expansion coefficient between the optical semiconductor element mounting surface of the insulating substrate 5 and the connection terminal mounting surface, insulating layers having different thermal expansion coefficients can be formed and then joined. Insulating substrate 5
It is necessary to form a circuit in the wiring conductor layer 6 inside,
Moreover, since it is desirable that the coefficient of thermal expansion changes stepwise or continuously in the insulating substrate, it is desirable that all of these are formed by simultaneous firing.

As a ceramic material which can be co-fired and whose thermal expansion coefficient can be controlled in a wide range, ceramics which can be fired at a low temperature of 1000 ° C. or lower so as to be able to co-fire with the above-mentioned Cu or Ag are used. Preferably used,
In particular, glass ceramics generally have low dielectric loss,
Dielectric constant can be arbitrarily controlled from low dielectric constant to high dielectric constant,
Furthermore, it is particularly useful for the package of the present invention in that the coefficient of thermal expansion can be arbitrarily controlled.

This glass ceramic has a glass component,
Alternatively, it is obtained by firing a mixture of a glass component and a filler component. In particular, in order to enhance the strength of the wiring board, the filler component is used in the form of glass: filler of 5:95 to 9: 9.
A composition obtained by calcining a composition mixed at a volume ratio of 5: 5 is suitably used.

As the glass component used, at least
Also SiO_TwoContaining, Al_TwoO_Three, B_TwoO _Three, ZnO, Pb
O, alkaline earth metal oxide, alkali metal oxide
At least one or more of them, and
Even if it is amorphous,
Cellite, mullite, anorthite, Sergien, spi
Flannel, garnite, willemite, dolomite, petara
Precipitates at least one type of crystal of a site or its substituted derivative
Crystallized glass is used.

As the filler component, calcium zirconate, strontium silicate, calcium titanate, strontium titanate, barium titanate, alumina, quartz, cristobalite, quartz glass, mullite, forsterite, zirconia, spinel, cordierite, anorthite It is preferable to use crystallized glass that precipitates at least one kind of crystal of Celsian, garnite, willemite, dolomite, petalite or a substituted derivative thereof, from the viewpoint of exhibiting good electric characteristics and improving strength.

The ceramics having a density of less than 9 × 10 ⁻⁶ / ° C. can be formed by adding a filler such as alumina, mullite, aluminum nitride or the like to borosilicate glass or the like.

As ceramics having a coefficient of thermal expansion exceeding 9 × 10 ⁻⁶ / ° C., for example, BaO is 5 to 60% by weight.
A low-softening point, high thermal expansion BaO-based glass, and others, such as lithium silicate-based glass described in the specification of Japanese Patent Application No. 8-322038.
For high thermal expansion glass components such as PbO-based glass and ZnO-based glass, SiO ₂ (quartz), enstatite, forsterite, MgO, ZrO ₂ ,
It can be easily produced by baking a mixture of various high thermal expansion ceramic filler components such as petalite and controlling the ratio thereof.

According to the present invention, when the frame 2 is formed of ceramics, if the frame 2 is formed of ceramics that can be fired at the same firing temperature as the wiring board 1, the wiring board 1 and the frame 2 are integrally fired. Can be (Conductor Material) The conductor layer 7 for fixing the optical semiconductor element 4 and the wiring conductor layer 6 and the connection pads 12 in the wiring board 1 are made of W, Mo, a conventionally known conductor material.
It is formed of a conductor material mainly containing at least one selected from the group consisting of Mn, Cu, and Ag.
Ceramics that can be fired at a temperature of 00 ° C. or less are selected, and can be formed of a conductive material mainly composed of a low-resistance metal such as Cu or Ag in order to enhance the transmission of high-frequency signals.
The conductor layer 7 and the connection pad 12 are made of a metal having excellent corrosion resistance and good wettability to a brazing material, specifically, a Ni layer having a thickness of 1.5 to 6 μm and a thickness of 0.2 to If a 5 μm Au layer is sequentially applied by a plating method, the oxidative corrosion of the wiring substrate 1 can be effectively prevented, and the optical semiconductor element 4 on the upper surface of the wiring substrate 1 is firmly adhered and fixed with a brazing material. Can be.

[0041]

EXAMPLES The following experiments were conducted to confirm the effects of the present invention. As an insulating substrate material for forming a wiring board in a package, 25-
A glass ceramic material having a thermal expansion coefficient at 200 ° C. of 8 to 12 × 10 ⁻⁶ / ° C. was used. The wiring conductor layer in the wiring substrate and the conductor layer for mounting the optical semiconductor element were formed by simultaneous firing at 950 ° C. with the insulating substrate using copper metallization.

A ball solder terminal made of eutectic solder was attached to the connection pad on the bottom surface of the wiring board. Then, an optical semiconductor element having a photoelectric conversion element (α = 6 × 10 ⁻⁶ ) formed on a silicon substrate with a coefficient of thermal expansion was bonded using eutectic solder on the conductor layer.

An insulating substrate (FR-4, α = 14 × 10 ^{−6) obtained} by impregnating this package with a glass woven fabric and an epoxy resin.
(/ ° C.) The above package was mounted on the surface of a printed wiring board having connection pads made of copper foil formed on the surface, and was surface-mounted using eutectic solder.

The optical coupling loss of the manufactured optical semiconductor device package was measured with an optical power meter. In addition,
The optical coupling loss was measured by setting the positions of the light emitting source and the optical fiber in advance and stabilizing the fiber output at 0.2 mW. The package mounted on a printed wiring board was subjected to a thermal cycle of −40 ° C. and 85 ° C. repeatedly, and the resistance between the connection pads via the connection terminals was measured every 100 cycles. Table 1 shows the number of cycles at the time of deterioration of 10% or more as a limit value.

[0045]

[Table 1]

[0046]

[Table 2]

As shown in Table 1, by controlling the thermal expansion coefficient between the optical semiconductor element mounting surface and the connection terminal mounting surface according to the present invention, the optical coupling loss can be reduced to 0.2 dB or less and the secondary coupling loss can be reduced. The mounting reliability was high without any change even after 500 cycles.

On the other hand, a sample N formed of a single ceramic having an insulating substrate aligned with an optical semiconductor element was used.
o. In No. 1, the optical coupling loss was good, but the secondary mounting reliability was poor. Conversely, the sample No. formed by a single ceramic matched to the external circuit board. In No. 2, the heat cycle test was good, but the optical coupling loss was low.

[0049]

As described above in detail, according to the package for housing an optical semiconductor device of the present invention, the optical semiconductor device and the electric signal can be smoothly transmitted from the optical fiber, and the primary mounting reliability and the secondary The mounting reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a development view showing an embodiment of an optical semiconductor element housing package of the present invention.

FIGS. 2A and 2B are schematic cross-sectional views illustrating the structure of an insulating substrate according to the present invention, wherein FIG. 2A illustrates one example and FIG. 2B illustrates another example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic wiring board 2 Frame 3 Cover member 4 Optical semiconductor element 4a Optical semiconductor element substrate 4b Photoelectric conversion element 5 Insulating substrate 6 Wiring conductor layer 7 Conductor layer 8 Optical fiber 9 Introducing part 10 Through hole 11 Fixing member

Claims (8)

[Claims] A ceramic wiring board comprising an insulating substrate and a wiring conductor layer, wherein the ceramic wiring board has an optical semiconductor element mounting portion on the upper surface of the insulating substrate, and is mounted on the wiring substrate so as to surround the optical semiconductor element mounting portion; And a frame provided with an introduction portion for introducing an optical signal, attached to the upper surface of the frame,
A cover member for sealing the optical semiconductor element, and a connection terminal for connecting to an external circuit board is provided on a surface of the insulating substrate opposite to the optical semiconductor element mounting portion. An optical semiconductor element housing package according to claim 1, wherein a thermal expansion coefficient of a surface of said insulating substrate on which said connection terminal is provided is larger than a thermal expansion coefficient of an optical semiconductor element mounting surface. 2. A thermal expansion coefficient difference between the optical semiconductor element mounting surface of the insulating substrate and the optical semiconductor element at 25 to 200.degree.
2. The package for housing an optical semiconductor element according to claim 1, wherein the temperature is not higher than × 10 ⁻⁶ / ° C. 3. An optical semiconductor device mounting surface of the insulating substrate.
3. The package for housing an optical semiconductor element according to claim 1, wherein a thermal expansion coefficient at a temperature of from 200 to 200 [deg.] C. is 9 * 10 < ^-6 > / [deg.] C. or less. 4. A thermal expansion coefficient difference between the surface of the insulating substrate on which the connection terminals are provided and the external circuit substrate at 25 to 200.degree.
^{4. The} package for accommodating an optical semiconductor element according to claim 1, wherein the temperature is not higher than × 10 ⁻⁶ / ° C. 5. A semiconductor device according to claim 5, wherein said insulating substrate has connection terminals on a surface on which connection terminals are provided.
The package for housing an optical semiconductor element according to any one of claims 1 to 4, wherein a thermal expansion coefficient at -200 ° C is larger than 9 × 10 ^-6 / ° C. 6. The optical semiconductor device according to claim 1, wherein the thermal expansion coefficient of the insulating substrate changes stepwise or continuously from the surface on which the optical semiconductor device is mounted to the surface on which the connection terminals are provided. Package for storage. 7. The package for housing an optical semiconductor device according to claim 1, wherein said connection terminals are made of solder. 8. The package according to claim 1, wherein said insulating substrate is made of a low-temperature fired ceramic material fired at 1000 ° C. or lower.