JP2006064989A - Joint structure, optical isolator using this structure and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of failure such as the cracking of an optical element and the deterioration of optical characteristicsby preventing thermal stress from being caused in the optical element with respect to an optical isolator which is used for optical communication, optical information processing and an optical sensor or the like. <P>SOLUTION: In the joint structure, on which optical elements are alinged and fixed on a substrate, a metallic bump is formed on one of the optical element or the substrate and a metalized film is formed on the other and both of them are joined by ultrasonic joining , thereby suppressing the thermal stress to provide the joint structure and the joining method excellent in reliability and optical characteristics. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an optical isolator used for optical communication, optical information processing, an optical sensor, and the like.

  Light emitted from a light source such as a laser light source is incident on various optical elements and optical fibers, but some of the incident light is reflected and scattered when passing through the various optical elements and optical fibers. A part of the reflected or scattered light returns to the light source side, and an optical isolator is used to block this return light.

  As shown in FIG. 6, the miniaturized optical isolator has polarizers 3 and 4 and a Faraday rotator 5 on a substrate 2 and a magnet 6 for applying a saturation magnetic field to the Faraday rotator. A structure having a different structure has been proposed (see Patent Document 1).

  The structure of the optical isolator 1 as shown in FIG. 6 is mainly for a laser light source module and is surface-mounted together with a semiconductor laser element in a package.

  Here, the polarizers 3 and 4 have a function of absorbing a polarization component in one direction of transmitted light and transmitting a polarization component orthogonal to the polarization component, and the Faraday rotator 5 has a saturation magnetic field strength. 1 has a function of rotating the polarization plane of light of a predetermined wavelength by about 45 degrees. The two polarizers 3 and 4 are arranged so that their absorption or transmission polarization directions are deviated by about 45 degrees. The arrow in the figure represents the transmission polarization direction, and the transmission polarization direction of the polarizer 3 is parallel to the bottom surface of the substrate 1, while the transmission polarization direction of the polarizer 4 is inclined by about 45 degrees. .

  Next, the operation of the optical isolator 1 will be described. The direction of the arrow shown on the optical axis L is the forward direction, and the angle is + in the clockwise direction. The light emitted from the LD travels in the forward direction, and the light generally becomes TE mode oscillation and enters the optical isolator 1 in a polarization direction parallel to the transmission polarization direction of the polarizer 3. The light passes through the polarizer 3, rotates its polarization direction by +45 degrees with the Faraday rotator 5, and enters the polarizer 4. Since the transmission polarization direction of the polarizer 4 is arranged at an angle of +45 degrees with respect to the transmission polarization direction of the polarizer 3, the light traveling in the forward direction is transmitted through the polarizer 4.

  The reflected return light incident from the opposite direction has an indefinite polarization, but the polarizer 4 transmits only the light having the polarization direction of +45 degrees, and the other is blocked. The light in the reverse direction transmitted through the polarizer 3 is further rotated by +45 degrees in the polarization direction by the Faraday rotator 5 and is incident on the polarizer 3. Here, the reverse direction light incident on the polarizer 4 has a polarization direction of +90 degrees and is crossed Nicol with the polarizer 3, so that it is blocked by the polarizer 3 and the reflected return light does not return to the LD. In this way, the optical isolator 1 functions by arranging the transmission polarization directions of the polarizer 3 and the polarizer 4 so as to be shifted by 45 degrees.

  In addition, when the optical elements such as the polarizers 3 and 4 and the Faraday rotator 5 and the magnet 6 are bonded on the substrate, an organic system is used so as not to cause degradation of the semiconductor laser element due to decomposition products such as outgas. The bonding member is not used, but an inorganic bonding member such as solder or low-melting glass is used.

  FIG. 7 shows the bonding of the optical element and the magnet 6 onto the substrate 2 using the solder 8. Here, only a portion where the optical element 7 made of a polarizer or a Faraday rotator is bonded to the substrate 2 is shown. The metallized film 9 is processed in advance on the bonding surface of each member, and a flux is applied to remove the oxide film on the surface of the metallized film 9 and the surface of the solder 8 generated at the time of bonding. When bonding, the substrate 2 is heated in accordance with the melting point of the solder 8 to be used, and the solder 8 is melted, and then the optical element 7 is pressure-bonded to the substrate 2.

  Note that the method of removing the oxide film on the surface of the metallized film 9 or the surface of the solder 8 can be realized by performing a scrub work instead of using a flux. This is because when the optical element 7 is mounted, the substrate 2 is heated to a predetermined temperature in an atmosphere of an inert gas such as nitrogen, the solder 7 is applied and melted, and then the optical element 7 is pressed against the molten solder 8. By swinging, the oxide film on the surface of the solder 8 is destroyed.

  As a method for joining the substrate 2 and the optical element 7, solder plating 10 is applied to both surfaces as shown in FIG. 8, ultrasonic waves are applied after the two are pressed, and solder plating is performed by the generated thermal energy. A method of performing metal bonding by melting 10 is also devised (see Patent Document 2).

In addition, when joining with the low melting glass 11 as shown in FIG. 9, a paste of the low melting glass 11 is applied on the substrate 2 in advance and once sintered and solidified at a high temperature, the low melting glass 11 is cut. Or, it is polished and adjusted so that the thickness is constant. When bonding, the substrate 2 is heated in accordance with the working temperature of the low-melting glass 11 to be used to melt the low-melting glass 11, and then the optical element 7 is pressure-bonded to the substrate 2.
See JP-A-1998-227996 See JP-A-1998-11779

  However, in the optical isolator 1 as shown in FIGS. 7 and 9, optical elements such as the polarizers 3 and 4 and the Faraday rotator 5 and the magnet 6 are placed on the substrate 2 with heat such as solder 8 and low melting point glass 11. When joining using a plastic joining member, a thermal stress arises by the difference in the thermal expansion coefficient of each member.

In particular, the polarizers 3 and 4 constituting the optical isolator 1 are generally formed by dispersing fine metal particles facing back in a certain direction in an optical glass, and have an expansion coefficient of about 60 × 10 ^−7. It is. On the other hand, the Faraday rotator 5 is generally made of bismuth-substituted garnet and has an expansion coefficient of about 100 × 10 ⁻⁷ . Therefore, it is difficult to make the thermal expansion coefficient of the substrate 2 coincide with the thermal expansion coefficient of both.

  Therefore, thermal stress is generated in some optical elements, but since the optical elements are brittle materials, cracks and cracks may occur. Further, when thermal stress is applied to the Faraday rotator 5, the extinction ratio of light passing through the Faraday rotator 5 deteriorates, and various characteristics of the optical isolator 1, particularly the isolation characteristics, deteriorate.

  Further, when the optical element 7 is bonded to the substrate 2 with the solder 8 as shown in FIG. 7, if flux is used as a method for removing the oxide film on the surface of the solder 8, corrosion of the solder 8 due to the flux is prevented. In addition, it is necessary to clean the flux so as not to cause degradation of the semiconductor laser element due to decomposition products such as outgas generated from the flux. However, as shown in FIG. 7, the gap between the optical elements 7 is narrow, and it is difficult to remove the flux residue even if ultrasonic cleaning or the like is performed using an organic solvent.

  Further, when scrubbing is performed as a method of removing the oxide film on the surface of the solder 8, the solder 8 pushed away by swinging the optical element 7 flows into the light transmitting portion of the optical element 7, and the optical isolator 1 Degradation occurs in insertion loss characteristics.

  Further, as shown in FIG. 8, in the method of applying solder plating 10 to both the substrate 2 and the optical element 7 and applying ultrasonic waves while pressure-welding both, the bonding strength between the solder plating 10 and the substrate 2 or the optical element 7 is high. When weak, both joint strengths deteriorate. Further, when the solder plating 10 is performed by dipping, the flatness of the surface is poor, and the bonding is performed only at the protruding portion of the surface of the solder plating 10. In this case, when stress is applied to the optical element 7 from the outside, local stress concentration occurs at the joint location, so that the joint strength becomes unstable and the optical element 7 may drop off.

  In addition, when the optical element 7 is bonded to the substrate 2 with the low melting point glass 11 as shown in FIG. 9, the pressed low melting point glass 11 transmits light of the optical element 7 when the optical element 7 is bonded to the substrate 2. The insertion loss characteristic of the optical isolator 1 is deteriorated.

  Furthermore, when the optical isolator 1 is used in a laser light source module, it is necessary to join the package with solder or the like, and processing at a high temperature is required. Here, when a thermoplastic bonding member such as solder 8 or low-melting glass 11 is used as shown in FIGS. 7 and 9 when the optical isolator 1 is manufactured, deformation of the bonded portion is caused in an environment of the respective melting temperatures or higher. The danger of etc. arises.

  Further, many of the solder 8 and the low-melting glass 11 contain lead, and when a product using these is discarded, special care must be taken, such as special treatment.

  In view of the above problems, the present invention provides a bonding structure in which an optical element is aligned and fixed on a substrate, and has a metal bump on one of the optical element and the substrate, a metallized film on the other, and both the metal bump and the metal bump. It is characterized by being metal-bonded with a metallized film.

  Further, in an optical isolator in which an optical element including a flat Faraday rotator and a flat polarizer is aligned and fixed on a substrate, the optical element and the substrate have metal bumps on one side and a metallized film on the other side, and Both are metal-bonded by the metal bump and the metallized film.

Further, with respect to the height H of the metal bump and the area S of the contact surface between the metal bump metallized film, the value of H / (S ^0.5 ) is 0.25 to 1.0. To do.

  Further, the metal bump is made of gold having a hardness of 175 Hv or less, and the outermost surface of the metallized film is made of gold.

  Furthermore, the metal bump is made of nickel, and the outermost surface of the metallized film is made of nickel.

  In addition, a metallized film is formed on the surface of the optical element facing the bonding surface with the substrate.

  Further, the metal bump and the metallized film according to claims 1 to 6 are bonded by ultrasonic bonding.

  Hereinafter, the structure of the optical isolator 1 according to the present invention will be described with reference to FIG.

  The optical isolator 1 of the present invention has a structure in which a flat plate polarizers 3 and 4, a Faraday rotator 5, and a magnet 6 for applying a saturation magnetic field to the Faraday rotator 5 are aligned and fixed on a substrate 2. . Here, the polarizers 3, 4 and the Faraday rotator 5 are bonded to the substrate 2 at the side surface perpendicular to the light transmission surface, and the magnet 6 is a rectangular parallelepiped and sandwiches the Faraday rotator 5 between the substrate 2 and the magnet 2. It is joined to both sides.

  The polarizers 3 and 4 are made of, for example, polarizing glass having a structure in which ellipsoidal metal particles are dispersed in glass. This polarizing glass is a glass having polarization characteristics by arranging long stretched metal particles in one direction in the glass itself, light having a polarization plane perpendicular to the stretch direction of the metal particles is transmitted, Light with a parallel polarization plane is absorbed. Here, the transmission polarization direction of the polarizer 3 is arranged to have an angle of approximately +45 degrees with respect to the transmission polarization direction of the polarizer 4.

  The Faraday rotator 5 is, for example, a bismuth-substituted garnet crystal, and the thickness thereof is set so that the polarization plane of incident light rotates 45 degrees. In general, in order to rotate the plane of polarization, it is necessary to apply a sufficient magnetic field in the direction of the optical axis L of incident light. Further, if the self-bias type Faraday rotator 5 is used, the optical isolator 1 operates without the magnet 6, so the magnet 6 becomes unnecessary.

  Here, the optical element 7 including the polarizers 3 and 4 and the Faraday rotator 5 has a metallized film formed on the bonding surface with the substrate 2. The metallized film 9 is made of chromium, titanium or the like in the lower layer to improve adhesion, and tungsten, copper, nickel or the like in the intermediate layer to prevent metal diffusion. Further, gold, nickel or the like is applied to the upper layer.

  The metallized film 9 may be formed by a known method, such as sputtering, vacuum deposition, or CVD. The sputtering method is performed according to the following principle. First, a film material (target) is placed in the vicinity of the sample to be coated in a vacuum processing container, and a voltage is applied between the sample and the target to move electrons and ions at high speed and collide with the target. Let Ions that collide with the target repel target particles. (Sputtering phenomenon) The repelled raw material particles collide and adhere to the sample to form a film. In vacuum deposition, a film target is placed in the vicinity of a sample to be coated in a vacuumed processing vessel, and the target is opposed to the sample to be coated in a vacuumed processing vessel. A film is formed by colliding the heated, evaporated and vaporized raw material with the sample. In the CVD method, a sample is placed in an atmosphere of a gas raw material, and a high-purity thin film is formed on the sample surface by a chemical reaction.

  When the metallized film 9 is formed, the metallized film 9 is shielded by using a resist or a protective member instead of the resist so that the metallized film 9 is not formed on the optical surface of the optical element 7.

  The surface of the magnet 6 is plated. The plating process has the purpose of maintaining the magnet shape in addition to the purpose of being used for bonding to the substrate 2. In general, since the magnet used for the optical isolator 1 is small and is often processed at a high temperature, the material is a samarium cobalt magnet that has excellent magnetic properties and is difficult to demagnetize at a high temperature. ing. Since samarium cobalt magnets have low mechanical strength, it is common to perform plating treatment to prevent cracks and cracks.

  As for the material of the substrate 2, it is preferable to use an inorganic material such as metal or ceramic so that a degradation product such as outgas does not cause deterioration of the semiconductor laser element. The material and the surface treatment of the bottom of the substrate 2 are selected by means for mounting in the package. For example, when metal bonding is performed by soldering, a metallized film is formed on the back surface of the substrate 2, and a material having a thermal expansion coefficient matched to a portion where an optical isolator is to be attached is used. Moreover, when fixing by YAG welding, a material with good weldability such as SUS304 is used. When the optical element 7 is bonded to the substrate 2 according to the present invention, since the bonding is performed at a low temperature, it is not necessary to consider the thermal stress generated in the optical element 7. Therefore, it is not necessary to make the thermal expansion coefficients of the optical element 7 and the substrate 2 coincide with each other, and the material of the substrate 2 can be freely selected. However, a non-magnetic material is selected for the substrate 2 so that the magnetic field applied to the Faraday rotator 5 is not weakened by the magnet 6 disposed on the substrate 2 being magnetized in the opposite direction to the magnet 6. It is desirable to do.

  Further, bumps 12 are formed on the substrate 2 at predetermined positions where the optical element 7 and the magnet 6 are joined. This is illustrated in FIG. The bumps 12 referred to here are the same as the solder bumps used for flip-chip mounting or the like, and are used to form a metal thin film consisting of a single layer or a plurality of layers in several islands on the substrate. The bump 12 only needs to have a thickness equal to or greater than the flatness of the surface of the substrate on which the bump is formed, and the substrate 2 and the member to be joined are joined only through the bump. Note that the size of the bump 12 is appropriately determined according to the size of the member to be bonded and the required bonding strength, and the bonding strength can be increased by using a plurality of bumps 12 for each bonding member.

  The formation process of the bump 12 includes an electroplating method, a stud bump method, a printing method, and a vapor deposition method. Electroplating is the mainstream for forming gold bumps, and the stud bump method is used in part.

  From the viewpoint of microfabrication of the bumps 12, an electroplating method and a vapor deposition method that employ a lithography process are advantageous. In the electroplating method, a barrier metal is first formed by sputtering or vapor deposition, a resist film is applied on the barrier metal, exposure and development are performed, and an opening is formed. After a bump material is grown on the opening by electroplating, the resist film is removed leaving the bump. The vapor deposition method is performed using a vacuum vapor deposition method when a bump material is grown in the opening after the same pre-process as the electroplating method.

  As the barrier metal, chromium, titanium, or the like is applied to the lower layer to improve adhesion, and tungsten, copper, nickel, or the like is applied to the upper layer to prevent metal diffusion. Note that when the adhesion to the barrier metal is good depending on the substrate material, the lower layer treatment is not required. As the material of the bump 12, gold, nickel, or the like can be selected.

  When the polarizers 3 and 4, the Faraday rotator 5, and the magnet 6, which are the members to be bonded, are bonded onto the substrate 2, as illustrated in FIG. Is held on the anvil 15, the member 13 to be bonded is seated on the bump 12 of the substrate 2, and ultrasonic waves are applied for several seconds while pressing the member 13 to be bonded by the tool 16. The ultrasonic wave is generated by the ultrasonic vibrator 17, then the amplitude is increased via the horn 18, and then propagated to the tool 16. The ultrasonic vibration forms a standing wave at the horn 18 and the tool 16 portion. By using the portion that pressurizes the member 13 to be antinode of vibration, the ultrasonic vibration can be efficiently transmitted to the member 13 to be bonded. it can. The applied pressure needs to be optimized depending on the material of the bumps 12, but when gold is used as an example, about 150 gf per bump 12 is appropriate.

  In the initial stage of ultrasonic bonding shown here, the metallized film 9 and the plating film applied to the member to be bonded 13 and the surface of the bump 12 formed on the substrate 2 cause friction by ultrasonic vibration, and the metal surface The oxide film and adsorbate are destroyed, and the joint surface is mechanically cleaned. In addition, the joining surface is smoothed and adhesion nuclei are generated. In the latter stage of ultrasonic bonding, the bonding surfaces are sufficiently close to each other, a cohesive force is generated, and a rapid composition flow is generated to expand the bonding surface. The destroyed metal surface film is diffused and present in the vicinity of the joint surface.

  In addition, about the form of the joining layer in the joining interface by ultrasonic joining, since a molten structure is not recognized in a junction part, it is thought that it is a solid-phase joining by the diffusion between mutual metals.

  In order to increase the bonding strength by ultrasonic bonding, a heater 19 is added to the anvil 15 portion, the substrate 2 is preheated at a low temperature of about 150 to 200 ° C., and the substrate 2 is heated to a predetermined temperature. It is preferable to perform bonding.

  Further, the ultrasonic bonding method shown in FIG. 3 has a structure in which the member to be bonded 13 is adsorbed and held by the collet 14, but when the member to be bonded 13 is a brittle material, mechanical strength is obtained. Therefore, there is a concern that cracks may occur in the bonded member 13 when the collet 14 that has undergone ultrasonic vibration comes into contact. This can be prevented by applying an element protecting metallized film 20 on the contact portion of the member 13 to be contacted with the collet 14, that is, on the opposite surface of the bonding surface of the member 13 to be bonded to the substrate 2. When the member 13 to be joined is a brittle material such as an optical element, if the metallized film 20 is processed, microcracks in the outer periphery of the optical element generated when the optical element is cut into small pieces are filled, and the optical element Since compressive stress is applied from the outer peripheral portion, the mechanical strength of the optical element is improved. Since the metallized film 20 may be processed in the same structure as the metallized film 9 used for bonding to the substrate described above, both metallized films can be formed in a lump.

  Further, the degree of contamination of the substrate 2 and the member 13 to be joined greatly affects the joining strength. Therefore, the substrate 2 and the member to be bonded 13 need to be cleaned in advance. The cleaning treatment includes ultrasonic cleaning that is wet cleaning, ultraviolet ozone cleaning that is dry cleaning, plasma cleaning, cleaning by laser irradiation, and the like. It is also effective to use these in combination.

  As an example, good bonding strength can be obtained by performing ultrasonic cleaning after ultrasonic cleaning in an organic solvent such as IPA or ethanol.

  Furthermore, the surface roughness and flatness of the base material to which the metallized film 9 is to be applied and the height variation of the bumps 12 have a great influence on the bonding strength and the destruction and deformation of the product. If the surface roughness of the metallized film 9 is rough, the proximity of the metal surfaces becomes insufficient at the time of bonding, and the bonding strength decreases. Moreover, there is a risk that the application time of the ultrasonic wave becomes long and the product is destroyed. Further, when the flatness of the metallized film 9 is poor and the height of the bumps 12 varies, a part of the bumps 12 does not come into contact with the metallized film 9 on the bonded member 13 side, leading to deterioration of bonding strength. Further, when the substrate 2 is pressed toward the member to be bonded 13, the substrate 2 is bent and internal stress is generated on the bonding surface, which causes the bonded portion to be broken. The surface roughness of the metallized film 9 is preferably Ra 1.6 μm or less, and the flatness of the metallized film 9 and the height variation of the bumps 12 are preferably about 2 μm or less. When the bumps 12 are formed, it is relatively easy to realize processing accuracy, and a stable joining operation can be performed.

  Further, in ultrasonic bonding, a technique is adopted in which the surface roughness of the tip of the tool 16 is increased in order to increase the contact resistance between the collet 14 and the components held by the collet 14. This also has the purpose of preventing the joint between the collet 14 and the product held thereby. Note that adding a clamping mechanism to the tip of the collet 14 is also effective for increasing the contact resistance between the collet 14 and the member 13 to be joined.

  Furthermore, in ultrasonic bonding, the vibration speed is an important factor, and this is represented by the product of the ultrasonic frequency and the vibration amplitude. Therefore, when joining a very small sample as in this example, the vibration amplitude should be reduced and the frequency should be increased in order to suppress destruction and deformation of the product. Here, the frequency is specifically about 20 to 80 kHz.

  Further, the hardness of the bump 12 part affects the time for applying ultrasonic waves during bonding. FIG. 10 is a table showing the relationship between the ultrasonic application time and the bonding strength according to the hardness of the gold bump 12 when the magnet 6 is bonded to the gold bump 12 formed on the alumina substrate 2 shown in FIG. is there. The gold bumps 12 were formed by first applying a molybdenum manganese metallized paste on the alumina substrate 2 and then firing in a reducing atmosphere to form a conductive film. Thereafter, a barrier metal layer composed of a chromium layer of 0.3 μm and a nickel layer of 0.35 μm was formed by electroplating. Then, after applying a resist film, an opening was formed at a bump 12 formation location through a lithography process, and a bump material was grown by 50 μm by electroplating. Further, a nickel layer of 5 μm and a gold layer of 0.2 μm were formed on the surface of the magnet 6 by electroplating. The magnet was bonded to the substrate by a total of six bumps, the ultrasonic frequency was 30 kHz, the applied pressure was 150 gf per bump, and the members were bonded while heating the members to 150 ° C.

  According to FIG. 10, as the hardness of the gold bump 12 is lower, a sufficient bonding strength is obtained even when ultrasonic waves are applied for a short time. When a bump having a hardness of 154 Hv is used, the bonding strength is saturated in about 45 seconds. On the other hand, when the gold bump 12 having a hardness of 185 Hv was used, the bonding strength was not saturated even when the ultrasonic application was performed for 120 seconds. The reason for this tendency is considered to be that if the hardness of the metal forming the gold bump 12 is low, the gold bump 12 is deformed in a short time and the bonding area with the metallized film 9 is sufficiently widened. In consideration of the time required for bonding in practice, if the ultrasonic application time is 60 seconds or less, the hardness of the gold bump is considered to be 175 Hv or less. When gold is used for the bump material, the hardness depends on the purity of the gold, and the hardness decreases as the purity increases. When nickel is used for the bump 12, the hardness of the bump 12 varies depending on plating conditions such as a plating method and a plating solution composition when the nickel bump 12 is formed. In general, when a Watt bath is used in electroplating, the hardness of the bump 12 is most softened, and a hardness of about 150 Hv is obtained. Further, when a sulfamic acid bath is used, only a hardness of about 200 Hv can be obtained. Therefore, it is appropriate to form the nickel bumps 12 by electroplating using a watt bath.

Furthermore, the ratio of the height of the bump 12 portion and the size of the bump 12 bonding surface affects the bonding strength. FIG. 11 is a table showing the relationship between the height H of the bump 12 portion and the area S of the bump 12 bonding surface with the A value obtained by H / (S ^0.5 ).

  In addition, the sample used for the joining test used the thing which formed the gold bump 12 on the alumina substrate 2 as mentioned above, and the thing which gave the gold plating to the magnet 6 surface. In addition, it joined by the bump 12 of a total of six places, the gold bump 12 used the thing of hardness 154Hv, and applied the ultrasonic wave for 60 seconds.

  According to FIG. 11, when the A value became 0.25, the joining strength was almost saturated, and conversely, the joining strength tended to deteriorate thereafter. For this reason, when the A value is small, the contact area between the bump 12 and the metallized film 9 is large, the pressure per unit area of the contact surface is reduced, and the bump 12 is thin, so the bump 12 is not deformed. This is probably because the area of the contact interface between the bump 12 and the metallized film 9 could not be obtained sufficiently. In addition, when the A value is large, the bump 12 is formed by plating when the bump 12 is formed, the height of the bump 12 is bent, the substrate bends during bonding, and a stress is applied between the bump 12 and the metallized film 9 in the peeling direction. It is considered a thing. Thus, the A value is considered to be appropriate from 0.25 to 1.0.

  In FIG. 3, ultrasonic waves are applied to the bonded member 13 side and pressed onto the substrate 2 held on the anvil 15. On the contrary, ultrasonic waves are applied to the substrate 2 and held on the anvil 15. A method of pressure-bonding on the bonded member may be taken.

  1 to 3, the bump 12 is formed on the substrate 2 side, and the metallized film 9 is formed on the bonded member side composed of the optical element 7 and the magnet 6, but this is conversely metallized on the substrate 2 side. The film may be formed with bumps 12 on the bonded member side.

  As described above, in the optical isolator 1 of the present invention, the bonding between the substrate 2 and the member to be bonded such as the optical element 7 and the magnet 6 including the polarizers 3 and 4 and the Faraday rotator 5 is as low as about 150 to 200 ° C. Therefore, the occurrence of thermal stress due to the difference in thermal expansion coefficient of each member is extremely small, and the optical element 7 which is a brittle material is not cracked, and the extinction ratio of the Faraday rotator 5 is not deteriorated. . Therefore, an optical isolator excellent in reliability and excellent in optical characteristics, particularly in isolation characteristics can be manufactured.

  Further, when the optical element 7 or the magnet 6 and the substrate 2 are ultrasonically bonded, the flux for removing the oxide film on the surface of the metallizing film 9 for bonding and the bump 12 is unnecessary, and the work of cleaning the flux after the bonding work is also required. It is unnecessary.

  Furthermore, since ultrasonic bonding is solid phase bonding, there is no substance that melts during the bonding operation. Therefore, there is no substance that shields the light transmission part of the optical element 7, and the insertion loss characteristic of the optical isolator 1 is always good.

  Further, the place where the substrate 2 and the member to be joined are joined is limited to the place where the bump 12 is formed. For this reason, by dispersing the locations where the bumps 12 are formed, when stress is applied to the members to be joined from the outside, it is possible to disperse the stress concentration at the joint locations. Further, since it is easy to increase the flatness of the metallized film 9 and the height accuracy of the bumps 12, the bonding strength itself between the metallized film 9 and the bumps 12 can be stabilized.

  In addition, since the metallized film 9 and the bump 12 are directly bonded to each other between the substrate 2 and the member to be bonded, the heat resistance of the bonded portion depends on the melting point of the material forming the metallized film 9 and the bump 12 part. Become. For example, if nickel and gold are used as the material of the metallized film 9, the melting points thereof are gold 1064 ° C. and nickel 1453 ° C., and sufficient heat resistance as the optical isolator 1 can be secured.

  Furthermore, since the metallized film 9 and the bumps 12 are directly bonded to each other between the substrate 2 and the member to be bonded, a bonding member using lead or the like is unnecessary, and an excellent product in terms of environment is provided. It is possible.

  An embodiment of the present invention will be described with reference to FIG.

  The metallized film 9 and the bumps 12 are formed on the substrate of the optical isolator 1 by batch processing on a large flat substrate material and then cutting into small pieces by dicing and then manufacturing a large number. did.

  The substrate 2 was made of alumina, and the surface was polished to have a flatness of 2 μm or less before use. In forming the bumps 12, first, a molybdenum manganese metallized paste was applied, and then fired in a reducing atmosphere to form a conductive film. Thereafter, a barrier metal layer composed of a chromium layer of 0.3 μm and a nickel layer of 0.35 μm was formed by electroplating. Then, after applying a resist film, an opening was formed in a bump formation portion through a lithography process, and a bump 12 material was grown by electroplating. In addition, gold | metal | money was selected as a material of bump 12, The thickness was 50 micrometers.

  In addition, the board | substrate 2 and the optical element 7 were joined with the bump 12 of 4 places, respectively, and the board | substrate 2 and the magnet 6 were joined with the bump 12 of 6 places. The dimensions of each member constituting the product are shown in FIG. 4, and the size and position of each bump 12 are shown in FIG.

  Further, as the polarizers 3 and 4, a polar core 1550HC manufactured by Corning is used, and as the Faraday rotator 5, YTd5V manufactured by Sumitomo Metal Mining is used, and the metallized film 9 of each optical element 7 and the metallized film 20 for element protection are used. In this processing, a chromium layer of 0.3 μm, a nickel layer of 0.35 μm, and a gold layer of 0.2 μm were formed by a sputtering method. In addition, when performing the formation process of a metallization film so that a metallization film may not be formed on the optical surface of each optical element 7, a resist film is formed on the optical surface of each optical element 7, and after the formation process of the metallization film, in an organic solvent This was removed by ultrasonic washing with.

  Further, samarium cobalt was used as the material of the magnet 6, and a nickel layer of 5 μm and a gold layer of 0.2 μm were formed on the surface by electroplating.

  When the optical element 7 and the magnet 6 are bonded on the substrate 2, as shown in FIG. 3, the bonded member 13 made of the optical element and the magnet is attracted and held by the collet 14, while the substrate 2 is held on the anvil 15. Then, the member to be bonded 13 was seated on the bump 12 of the substrate 2, and ultrasonic waves were applied while pressing the member to be bonded 13 with the tool 16. Here, the frequency of ultrasonic waves was adjusted to 30 kHz, and the applied pressure was adjusted so that 150 gf was applied to each bump 12. Further, the anvil 15 portion was heated to 150 ° C. by the heater 19 and joined.

  When performing ultrasonic bonding under the above processing conditions, the ultrasonic application time was determined based on the change in bonding strength at each bonding location. As shown in FIG. 12, when the optical element 7 and the substrate 2 are bonded, the bonding strength is almost saturated when the ultrasonic wave application time is 45 seconds or more. Further, when the magnet 6 and the substrate 2 are bonded, the bonding strength is almost saturated when the ultrasonic wave application time is 75 seconds or more. Therefore, it was decided to apply ultrasonic waves at these times.

  In addition, the following 2 types were produced as the product produced according to the Example and the comparative example with respect to this.

  As a first comparative example, as shown in FIG. 7, a member obtained by applying a metallized film 9 to a bonding surface between a substrate 2 and a member to be bonded such as an optical element 7 or a magnet is bonded using gold-tin solder 8. Prepared.

  Note that alumina is selected as the material of the substrate 2, and the metallized film 9 is formed by performing molybdenum manganese treatment on the substrate to form a conductive film, and then forming a chromium layer 0.3 μm, a nickel layer 0.35 μm, and a gold layer 0. .2 μm was applied by electroplating. The optical element 7 and the magnet were the same as those used in the examples of the present invention.

  Gold-tin solder 8 was used when the optical element 7 and the magnet were joined on the substrate 2. First, the substrate 2 was placed on a hot plate and heated to 280 ° C., which is the melting point of the gold-tin solder 8, and then the solder foil was placed on the substrate 2 and melted. Thereafter, the members to be joined were pressed onto the substrate 2 and subjected to scrubbing to perform joining. In addition, this time, the flux was not used as a method for removing the oxide film on the surface of the solder 8 but scrub treatment was used. This is because it is difficult to remove the flux after joining. Further, in order to prevent an oxide film from being formed on the surface of the solder 8, nitrogen gas was blown onto the product.

  Further, as a second comparative example, as shown in FIG. 10, a soldered plate 10 was applied to the bonding surface between the optical element 7 and a member to be bonded such as a magnet and the substrate 2 and then ultrasonic bonding was prepared. The material of the solder 8 was lead-tin eutectic solder 8.

  Alumina is selected as the material of the substrate 2 and the solder plating 10 is formed by performing molybdenum manganese treatment on the substrate 2 to form a conductive film, and then forming a chromium layer 0.3 μm, a nickel layer 0.35 μm, and a solder layer 5 μm was formed by electroplating.

  Further, a chromium layer 0.3 μm, a nickel layer 0.35 μm, and a solder layer were formed by a sputtering method at a joint portion between the optical element 7 and the substrate 2. In order to prevent the metallized film and the solder plating from being formed on the optical surface of each optical element 7, a resist film is formed on the optical surface of each optical element 7 during the processing, and after the solder plating is formed, the resist film is formed in an organic solvent. This was removed by sonic cleaning.

  Further, samarium cobalt was used as a magnet material, and a nickel layer of 5 μm and a solder plating of 5 μm were formed on the surface by electroplating.

When the optical element 7 and the magnet were bonded on the substrate 2, the ultrasonic bonding method used in the example of the present invention shown in FIG. 3 was used. As working conditions, the ultrasonic frequency was 30 kHz, and the applied pressure was 1500 gf / mm ² per unit area of the joint surface, which was the same as the applied pressure per unit area applied to each bump 12 in the embodiment of the present invention. It adjusted so that it might become. Further, the anvil 15 part was heated to 150 ° C. by the heater 19 and joined. The ultrasonic wave application time was 3 minutes for the optical element 7 and 4 minutes for the magnet 6. In addition, this time, flux was used as a method for removing the oxide film of the solder plating 10. This is because the oxide film of the solder plating 10 is strong and the solder plating layers are not joined to each other even when the scrub treatment is performed in a nitrogen atmosphere.

50 samples were prepared for each, and the average peak value and insertion loss value of the isolation were compared, and the standard deviation indicating the variation was compared. The results are shown in Table 1.

  Thus, in contrast to the first and second comparative examples, in the examples according to the present invention, the peak isolation value was high and the standard deviation was small, and a stable value could be obtained. This is because in the embodiment according to the present invention, the heating temperature at the time of bonding between the member to be bonded and the substrate is lower than that of the comparative example, so that the generated thermal stress, particularly the thermal stress applied to the Faraday rotator is reduced. This is considered to be a result of good specific characteristics. In the second comparative example, the insertion loss value significantly deteriorated. This is presumably because the solder flowed between the optical elements consisting of the polarizer and the Faraday rotator, and the solder covered the optical surface, and the flux could not be completely removed.

In addition, for each of the 10 samples, the shear bonding strength of the member to be bonded, particularly the magnet 6 portion, and their standard deviation were compared. The results are shown in Table 2.

  As described above, in the examples of the present invention, although not reaching the first comparative example, the shear bonding strength was relatively large, and the standard deviation was small and a stable value could be obtained. On the other hand, in the second comparative example, the bonding strength was small and the standard deviation was large. In addition, in the second comparative example, the broken part may be between the nickel layer on the surface of the magnet and the solder plating 10 layer in addition to the joint portion between the solder plating 10 layers, and the peel strength between the metallized films is reduced. It is thought that this led to a decrease in bonding strength.

The perspective view which shows embodiment of the optical isolator by this invention. The perspective view which shows each member structure of the optical isolator by this invention. It is sectional drawing which shows the ultrasonic bonding method by this invention. It is a three-way figure which shows the dimension of the product produced in the Example by this invention. It is a top view which shows the dimension of the bump provided on the board | substrate. It is a perspective view which shows the conventional optical isolator. It is sectional drawing of the optical isolator which joins a member with solder | pewter. It is sectional drawing of the optical isolator which joins a member by ultrasonic joining of solder plating. It is sectional drawing of the optical isolator which joins a member with low melting glass. It is the graph which showed the relationship between ultrasonic application time and joining strength for every hardness of gold bumps. It is the graph which showed the relationship between A value and joint strength. 3 is a graph showing a relationship between ultrasonic application time and bonding strength.

Explanation of symbols

1: Optical isolator 2: Substrate 3, 4: Polarizer 5: Faraday rotator 6: Magnet 7: Optical element 8: Solder 9: Metallized film 10: Solder plating 11: Low melting glass 12: Bump 13: Bonded member 14 : Collet 15: Anvil 16: Tool 17: Ultrasonic vibrator 18: Horn 19: Heater 20: Metallization film for element protection

Claims (7)

In a bonding structure in which optical elements are aligned and fixed on a substrate, one of the optical element and the substrate has a metal bump and the other has a metallized film, and both are metal-bonded by the metal bump and the metallized film. Joining structure characterized by In an optical isolator in which an optical element including a flat Faraday rotator and a flat polarizer is aligned and fixed on a substrate, one of the optical element and the substrate has a metal bump, and the other has a metallized film. An optical isolator, wherein the metal bump is metal-bonded to the metallized film. The value of H / (S ^0.5 ) is 0.25 to 1.0 with respect to the height H of the metal bump and the area S of the contact surface between the metal bump metallized film. Item 3. The optical isolator according to Item 2. 3. The optical isolator according to claim 2, wherein the metal bump is made of gold having a hardness of 175 Hv or less, and the outermost surface of the metallized film is made of gold. 3. The optical isolator according to claim 2, wherein the metal bump is made of nickel and the outermost surface of the metallized film is made of nickel. The optical isolator according to claim 2, wherein a metallized film is formed on a surface of the optical element facing the joint surface with the substrate. The method for manufacturing an optical isolator, wherein the metal bump and the metallized film according to claim 1 are bonded by ultrasonic bonding.

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