JP2830841B2 - Surface emitting element mounting method and surface emitting element mounting board - 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 mounting a surface light emitting element and a surface light emitting element mounting board.

[0002]

2. Description of the Related Art In order to apply the parallelism and spatial propagation properties of light to data links between boards, information processing, and the like, it is desired to integrate light emitting elements two-dimensionally in a plane direction. The surface emitting element can satisfy such a demand, and an increase in parallel information processing capacity can be expected. Also,
Since a cleavage process is not required for the formation of a surface-emitting device and a characteristic test can be performed in the state of a wafer, it is suitable for mass production compared to an edge-emitting device. But it is advantageous.

[0003] Pioneering research has been carried out by Iga et al. On such planar semiconductor devices, and a series of their research results has been published in 1988 by Iga et al., Journal of Quantum Electronics.
antnm Electronics) Vol. 24, No. 18
The papers on pages 45 to 1855 are summarized, including their historical background.

When incorporating the above-mentioned surface light emitting device into an actual system or the like, it is necessary to mount the surface light emitting device on a wiring board in some form and use it together with a drive circuit. As a method of mounting a surface emitting element on a wiring board, a method in which a surface emitting element is also directly formed on a substrate on which a driving circuit or the like is formed, or a method in which a driving circuit or the like and a surface emitting element are separately manufactured. , And a method of implementing it in a hybrid.

FIG. 3 is a schematic cross-sectional view of a conventional surface light emitting device mounting substrate in which a surface light emitting device is formed on the same substrate as a drive circuit and the like. In the figure, reference numeral 30 denotes an electronic circuit, 31 denotes a substrate, 32 is a surface light emitting element. As an example of the former, FIG.
A surface emitting device 32, which is a surface emitting laser, is formed by crystal growth on a Si substrate 31 as shown in FIG.
There is something that forms. In this method, lasers and circuits are formed monolithically, so that alignment between them is not required.

FIG. 4 is a schematic cross-sectional view of a conventional surface light emitting element mounting board in which a substrate on which a surface light emitting element is formed and a wiring board are joined by soldering. Is a p-type electrode pad, 51 is a wiring board, and 52 is a solder bump. As an example of the latter, solder bumps 52 corresponding to the positions of the surface emitting elements 42, each of which is a surface emitting laser, are formed on a wiring board 51 as shown in FIG. When the surface emitting laser array substrate 41 on which the p-type electrode pads 47 are formed is roughly positioned on the wiring substrate 51 and reflowed, the p-type electrode pads 47 of the surface emitting element 42 are pulled by the molten solder bumps 52. And the solder bumps 52 are self-aligned. Since alignment is only performed roughly at the beginning, high accuracy such as submicron is not required, and the influence on cost is small.

[0007]

However, several problems are pointed out in the above-mentioned conventional embodiment. First, in the first conventional example, since the material system of the surface emitting laser is mainly a GaAs system and the lattice constant is inconsistent with that of Si as a substrate, crystal growth thereof becomes technically very difficult. Since the lattice mismatch causes defects, the defects significantly reduce the life of the laser, and the characteristics of the laser itself have not reached a practical level. The life of a laser is a very important factor in commercialization, and the above-mentioned difficulties are fatal since it is necessary to ensure that the laser can be used for a long time.

Also, in the second conventional example, since the thermal expansion coefficients of the gold pad used as the electrode of the surface light emitting element and the solder bumps on the wiring board side and the wiring board are greatly different, the reflow is difficult. Due to the rise in temperature, distortion due to a difference in thermal expansion between the two is applied to the surface light emitting element, resulting in a decrease in element characteristics or life of the element. Also,
When using gold tin instead of solder bumps, the difference in thermal expansion coefficient may be small and the effect of distortion may be avoided, but the difference from the thermal expansion coefficient with the wiring substrate still remains, Since the temperature rise during reflow is considerably high at 300 ° C, compared to 200 ° C for solder bumps,
There is a problem that the element is deteriorated by heat. If the life and characteristics of such devices cannot be guaranteed, it is difficult to play a role as a stable light source, and a surface emitting device mounting method and a surface light emitting device mounting substrate capable of stably supplying them have been widely desired. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for mounting a surface light emitting element having stable characteristics and a long life with a small increase in cost, and a surface light emitting element mounting substrate.

[0010]

According to a method of mounting a surface light emitting element of the present invention, in a step of mounting a plurality of surface light emitting elements on a wiring board, the method for mounting the surface light emitting element provided on the substrate on which the surface light emitting element is formed is provided. Forming a bonding pad electrically connected to the electrode pad adjacent to the electrode pad, a solder bump provided at a position corresponding to the bonding pad on the wiring board;
The surface emitting element is mounted on the wiring substrate by bonding the bonding pad and the bonding pad by reflow .

Further, on provided with the electrode pads of the substrate which is formed of the surface-emitting device surface, it is not preferable that the dielectric film except the bonding pad upper surface is formed.

In the surface light emitting element mounting substrate of the present invention, a plurality of surface light emitting elements are formed, and an electrode pad of the surface light emitting element and a bonding pad adjacent to the electrode pad and electrically connected to the electrode pad are the same. A substrate provided on the surface, and a wiring substrate provided with solder bumps connected to pads of an electronic circuit formed on the substrate at positions corresponding to the bonding pads,
The bonding pad and the solder bump are bonded by reflow .

According to the present invention, since the electrode pad of the surface light emitting element and the bonding pad for the solder bump are provided independently of each other, the position of the electrode pad with the surface light emitting element and the solder bump on the wiring board side are provided. Unlike the position, the surface light emitting element is not directly subjected to the distortion due to the difference in thermal expansion coefficient, and the adverse effect due to the distortion can be avoided.

Further, the pad of the surface emitting element can function only as a heat sink and a heat escape path.
By covering with a dielectric film for the purpose of preventing the solder bumps from flowing around the dielectric film, the dielectric film can also serve as a passivation film of the pad itself.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a substrate on which a surface light emitting element according to an embodiment of the present invention is formed, and FIG. 2 is a view for explaining a bonding step between a substrate on which the surface light emitting element is formed and a wiring substrate. 3A is a schematic cross-sectional view, FIG. 3A shows a state in which both substrates are opposed, FIG. 3B shows a state in which both substrates are aligned, and FIG. 3C shows a state in which solder bumps are reflowed. In the figure, reference numeral 10 denotes a laser beam, 11 denotes a substrate, 12 denotes a surface emitting element, 13 denotes an active layer, and 14 denotes an n-type DB.
R and 15 are p-type DBRs, 16 is an n-type electrode, 17 is a p-type electrode pad, 18 is a bonding pad, 19 is a dielectric film, 21
Is a wiring board, and 22 is a solder bump.

Substrate 1 on which surface emitting array elements are two-dimensionally arranged
The surface light emitting element 12 on one side has a structure as shown in FIG. 1, and the active layer 13 is formed of an n-type DBR 14 and a p-type DBR 15
To form a resonator. DBR (Multilayer Reflector, Distributed Bragg Reflect)
(tor) is, for example, about 15 to 20 cycles of AlAs and GaAs alternately laminated with a thickness of λ / 4. Each surface light emitting element is electrically separated by a high resistance region formed by proton injection or the like. The n-type electrode 16 is etched from the surface and plated with gold to form an electrode pad on the surface together with the p-type electrode pad 17. It is formed as. When the electrode pad 17 is formed in the gold plating process, a bonding pad 18 for bonding to the solder bump 22 on the wiring board 21 side is formed at the same time. If the electrode pad 17 has a size of, for example, 30 μm square and the bonding pad 18 has a size of, for example, 50 μm square, the p-type electrode pad 17 is sufficient to perform the function of the heat sink, and the bonding pad 1
Numeral 8 is large enough to be self-aligned with the solder bump 22. The plating thickness can be from 3 microns to 10 microns. After forming the p-type electrode pad 17 and the bonding pad 18, first, the surface of the surface light-emitting element side of the substrate 11 is used to prevent the inflow of solder when the p-type electrode pad 17 is bonded and the bonding pad 18 and the solder bump 22 are bonded. A dielectric film 19 such as SiO ₂ is deposited on the entire surface by a thermal CVD device or the like. Thereafter, only the portion of the bonding pad 18 is removed with buffered hydrofluoric acid. On the other hand, on the wiring board 21, the solder bumps 22 are formed in accordance with the positions of the bonding pads 18 on the board 111, as shown in FIG. The size of the solder bump 22 may be 50 microns if the pitch between the surface light emitting elements 12 is 250 microns. If it is too small, self-alignment will not be performed, and if it is too large, there is a possibility that adjacent circuits will be short-circuited.
Various circuits necessary for driving the surface emitting element are arranged on the wiring board side. For example, a driving circuit or a surface light emitting element selection circuit depending on the system may be used. The substrate 11 and the wiring board 21 thus obtained are arranged under an infrared microscope such that the bonding pads 18 are almost over the solder bumps 22 as shown in FIG. afterwards,
When both of them are reflowed at a temperature of 200 ° C., as shown in FIG. 2C, the tension is applied to the solder bumps 22 and the bonding pads 18 and the solder bumps 22 are self-aligned and bonded. At this time, if the flux is applied to the solder bumps 22, the bonding can be performed smoothly. Alternatively, the bonding may be performed in an atmosphere in which oxygen is completely blocked. After about 30 seconds from the temperature rise, the temperature is lowered and returned to room temperature. After bonding, if possible, wash away the flux with an organic solvent such as acetone.

Through the above steps, mounting without deterioration of the surface emitting element can be performed. High alignment accuracy is not required, so there is almost no effect on the cost. Also, in the process of fabricating the surface emitting element, the number of processes that do not require precision, such as dielectric deposition and-part separation, only increases, which greatly affects the cost. do not do.

The configuration of the surface emitting element described in the above embodiment of the present invention does not necessarily have to be in accordance with the present embodiment, but can be arbitrarily selected. Further, the scale of each component can be appropriately changed. The reflow temperature also depends on the alloy composition of the solder bump.

[0019]

As described above, according to the present invention, the surface light emitting device can stably supply the characteristics and the life of the surface light emitting device by a simple method without substantially changing the manufacturing cost of the surface light emitting device module. An element mounting method can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a substrate on which a surface-emitting element according to an embodiment of the present invention is formed.

FIG. 2 is a schematic cross-sectional view illustrating a step of joining a substrate on which a surface light emitting element is formed and a wiring substrate. (A)
Indicates a state in which both substrates are opposed to each other. (B) shows the state of alignment of both substrates. (C) shows a state where the solder bumps are reflowed.

FIG. 3 is a schematic cross-sectional view of a surface emitting element mounting substrate in which a conventional surface emitting element is formed on the same substrate as a drive circuit and the like.

FIG. 4 is a schematic cross-sectional view of a conventional surface light emitting element mounting substrate in which a substrate on which a surface light emitting element is formed and a wiring board are joined by soldering.

[Explanation of symbols]

 Reference Signs List 10 laser beam 11, 31, 41 substrate 12, 32, 42 surface emitting element 13 active layer 14 n-type DBR 15 p-type DBR 16 n-type electrode 17, 47 p-type electrode pad 18 bonding pad 19 dielectric film 21, 51 Wiring board 22, 52 Solder bump 30 Electronic circuit

Claims (3)

(57) [Claims] 1. A step of mounting a plurality of surface light emitting elements on a wiring board, wherein the plurality of surface light emitting elements are electrically connected to and adjacent to the electrode pads of the surface light emitting elements provided on the substrate on which the surface light emitting elements are formed. Forming a bonding pad to be connected to the wiring board, and reflowing the solder pad provided at a position corresponding to the bonding pad on the wiring board and the bonding pad.
A method for mounting a surface light emitting element, wherein the surface light emitting element is mounted on the wiring substrate by bonding with each other. 2. The surface according to claim 1, wherein a dielectric film is formed on a surface of the substrate on which the surface light emitting element is formed, on a surface on which the electrode pads are provided, except for an upper surface of the bonding pad. Light emitting element mounting method. 3. A substrate on which a plurality of surface light emitting elements are formed, and an electrode pad of the surface light emitting element and a bonding pad adjacent to the electrode pad and electrically connected to the electrode pad are provided on the same surface. A wiring board provided with solder bumps connected to pads of an electronic circuit formed on the board at positions corresponding to the bonding pads, wherein the bonding pads and the solder bumps are reflowed;
Surface light-emitting element mounting substrate, characterized by being joined Ri.