Patent ID: 12256497

DESCRIPTION OF EMBODIMENTS

First Embodiment

An optical module according to a first embodiment will be described with reference toFIGS.1to4.

Note that, in the drawings, the same reference numerals denote the same or corresponding parts.

An optical module targeted by the present disclosure is a CAN package type optical module of an optical transmission module on which a semiconductor laser for optical communication as a light-emitting element is mounted, an optical reception module on which a photodiode for optical communication as a light-receiving element is mounted, or an optical transmission and reception module on which the semiconductor laser for optical communication and the photodiode for optical communication are mounted.

In the first embodiment, the optical transmission module will be described as an example, but a relationship among a stem, a flexible printed circuit (FPC), a signal lead pin, a ground pin, and a plate is the same also in the optical reception module and the optical transmission and reception module.

The optical module includes an optical module body1, a flexible printed circuit3, and a plate4.

The optical module body1includes a stem10, a lens cap11, a lens12, a signal lead pin13, a ground pin14, a thermoelectric cooler15, a base16, a submount17, a semiconductor light-emitting element18which is a semiconductor laser, a termination resistor19, and a dielectric substrate20.

The stem10is made of a disk-shaped metal, has an inner flat surface10aand an outer flat surface10b, and has a through hole10cpenetrating between the inner flat surface10aand the outer flat surface10b.

The stem10functions as a heat sink of the semiconductor light-emitting element18, and the inner flat surface10ais a region for component mounting.

Note that the stem10is not limited to the disk shape, and may have a circular column shape or a square column shape, and is only required to be a flat plate shape having the inner flat surface10aand the outer flat surface10bparallel to the inner flat surface10a.

The lens cap11is formed of a cylindrical metal with an open end and having a bottomed portion and a side wall portion. In the bottomed portion of the lens cap11, a lens attaching opening is formed, through which the lens12that is spherical and made of glass is mounted, that is, attached. The lens12is attached in the lens attaching opening of the bottomed portion in such a way that airtightness is maintained inside and outside the lens cap11.

An end surface of the side wall portion of the lens cap11, that is, an end surface with the open end is in contact with a peripheral end portion of the inner flat surface10aof the stem10and fixed by a solder or the like. The end surface with the open end of the lens cap11is fixed to the inner flat surface10aof the stem10in such a way that airtightness is maintained inside and outside the lens cap11, also in the end surface with the open end. This fixing and attaching are performed at the end of the manufacturing process.

The stem10and the lens cap11constitute a CAN type package.

The signal lead pin13penetrates the through hole10cof the stem10, and is fixed to the stem10by an insulating glass21that is filled and solidified between the signal lead pin13and the through hole10c. The insulating glass21electrically insulates the signal lead pin13from the stem10, and seals the through hole10cof the stem10to maintain airtightness in the CAN type package.

The signal lead pin13includes an inner lead portion13aprojecting from the inner flat surface10aof the stem10and an outer lead portion13bprojecting from the outer flat surface10bof the stem10.

Although only the semiconductor light-emitting element18is illustrated in the drawing, a light-receiving element which is a photodiode that receives back surface light of the semiconductor light-emitting element18and monitors output light, and a temperature adjusting device that adjusts the temperature of the semiconductor light-emitting element18are also mounted in the CAN type package.

In addition, although not illustrated, there is also a power supply pin for the semiconductor laser18, the light-receiving element, and the like, and the power supply pin is electrically insulated from the stem10and fixed similarly to the signal lead pin13.

The ground pin14includes a pin portion14aand a joint portion14bhaving a diameter larger than a diameter of the pin portion14aat an end of the pin portion14aand joined to the outer flat surface10bof the stem10. The diameter of the pin portion14ais the same as the diameter of the signal lead pin13.

The ground pin14has a step between the pin portion14aand the joint portion14b, and the joint portion14bis a step portion with respect to the pin portion14a.

The joint surface of the joint portion14bof the ground pin14and the outer flat surface10bof the stem10are joined by welding.

The thermoelectric cooler15is mounted on the inner flat surface10aof the stem10and cools the semiconductor light-emitting element18. Heat that has cooled the semiconductor light-emitting element18is dissipated from the stem10to the outside. The thermoelectric cooler15is, for example, a Peltier element as a cooling element. Note that the thermoelectric cooler15is not necessarily required.

The tabular base16is vertically erected and fixed on the thermoelectric cooler15. When the thermoelectric cooler15is not required, the base16is fixed upright perpendicular to the inner flat surface10aof the stem10.

The submount17is mounted, that is, attached on one flat surface of the base16. The submount17is a ceramic substrate made of aluminum nitride having a thermal linear expansion coefficient close to that of the semiconductor light-emitting element18.

The semiconductor light-emitting element18is mounted on one flat surface of the submount17.

The semiconductor light-emitting element18is mounted, by die bonding with a solder, a conductive adhesive, or the like, on a first electrode connection region provided on the one flat surface of the submount17by vapor deposition or the like, and is placed and fixed on the one flat surface of the submount17.

Thus, one electrode, that is, one signal terminal of the semiconductor light-emitting element18is electrically connected to the first electrode connection region.

Further, the other electrode, that is, the other signal terminal of the semiconductor light-emitting element18is electrically connected, by a gold wire22a, to a second electrode connection region provided on the one flat surface of the submount17by vapor deposition or the like.

The termination resistor19is provided on the one flat surface of the submount17by vapor deposition or the like.

The termination resistor19is a resistor for impedance matching with an IC that drives the semiconductor light-emitting element18, and is connected to the other signal terminal of the semiconductor light-emitting element18by a gold wire22b.

The dielectric substrate20is mounted in the CAN type package, that is, disposed on the inner flat surface10aof the stem10, and a high frequency line connecting the semiconductor light-emitting element18and the signal lead pin13for the semiconductor light-emitting element18is formed by vapor deposition or the like.

The dielectric substrate20serves as a bridge substrate between the semiconductor light-emitting element18and the signal lead pin13.

That is, the dielectric substrate20includes: a first signal line region connected, via a gold wire22c, to the first electrode connection region to which the one signal terminal of the semiconductor light-emitting element18is connected; and a second signal line region connected, via a gold wire22d, to the second electrode connection region to which the other signal terminal of the semiconductor light-emitting element18is connected, and the first signal line region and the second signal line region are connected to respective different signal lead pins13via gold wires (not illustrated).

The first signal line region and the second signal line region are different high frequency lines.

The semiconductor light-emitting element18receives a modulation signal from the signal lead pin13and emits laser light corresponding to the modulation signal. The laser light emitted from the semiconductor light-emitting element18is condensed or converted into parallel light via the lens12, and is emitted to the outside.

The dielectric substrate20is not necessarily required. In a case where the dielectric substrate20is not required, the first electrode connection region to which the one signal terminal of the semiconductor light-emitting element18is connected and the second electrode connection region to which the other signal terminal of the semiconductor light-emitting element18is connected are connected directly to the respective different signal lead pins13via gold wires.

The flexible printed circuit3includes a flexible insulating substrate31of polyimide or the like, a wiring pattern32formed on a front surface of the insulating substrate31by vapor deposition or the like, a ground pattern33formed on a back surface of the insulating substrate31by vapor deposition or the like, a power supply wiring layer (not illustrated) formed on the front surface of the insulating substrate31by vapor deposition or the like, a front surface protective film34, and a back surface protective film35.

The wiring pattern32includes a plurality of signal wiring layers for transmitting a high frequency signal. A surface of the wiring pattern32is covered and protected by the front surface protective film34.

In the insulating substrate31, a first through hole36is formed at a position facing the signal lead pin13in the wiring pattern32. As for the first through hole36, as illustrated inFIG.4, three first through holes36ato36care arranged along a circumference in the first embodiment.

That is,FIG.4illustrates an example in which the semiconductor light-emitting element18, the light-receiving element, and the temperature adjusting device are mounted in the CAN type package, the signal lead pins13for the semiconductor light-emitting element18, the light-receiving element, and the temperature adjusting device are provided, and the first through holes36corresponding to the respective signal lead pins13are formed.

Note that subscripts of reference numerals in the first through holes36ato36cmay be omitted for simplicity of description.

In the first embodiment, the through hole has a conductive portion on an inner wall of the hole formed in the substrate, a front surface land on the front surface of the substrate, and a back surface land on the back surface, and the front surface land and the back surface land are electrically conducted by the conductive portion.

The outer lead portion13bof the signal lead pin13penetrates the first through hole36in contact with the conductive portion, and a tip portion of the outer lead portion13bof the signal lead pin13is electrically connected to the wiring pattern32.

The tip portion of the outer lead portion13bis fixed to the front surface land of the first through hole36by a solder39, thereby electrically connecting the signal lead pin13to the wiring pattern32via the first through hole36.

The ground pattern33is formed on substantially the entire back surface of the insulating substrate31. The ground pattern33has an exposed surface at a position facing the outer flat surface of the stem10, and a front surface excluding the exposed surface is covered and protected by the back surface protective film35.

In the insulating substrate31, a second through hole37is formed at a position facing the ground pin14on the exposed surface of the ground pattern33.

The pin portion14aof the ground pin14penetrates the second through hole37in contact with the conductive portion, and a tip portion of the pin portion14aof the ground pin14is fixed to the front surface land of the second through hole37by a solder40.

Consequently, the ground pin14is electrically connected to the ground pattern33via the front surface land, the conductive portion, and the back surface land of the second through hole37.

In the insulating substrate31, a third through hole38is formed at a position where the power supply pin faces.

An outer lead portion of the power supply pin penetrates the third through hole38in contact with the conductive portion, and a tip portion of the outer lead portion of the power supply pin is electrically connected to a power supply pattern.

The tip portion of the outer lead portion of the power supply pin is fixed to the front surface land of the third through hole38by a solder, thereby electrically connecting the power supply pin to the power supply pattern via the third through hole38.

The plate4is a flat plate-shaped metal having a flat front surface and back surface, and the back surface is joined to the outer flat surface10bof the stem10, and the front surface is joined to the exposed surface of the ground pattern33of the flexible printed circuit3.

As illustrated inFIG.4, a planar shape of the plate4is a shape whose outer shape conforms to an outer shape of the outer flat surface10bof the stem10, and from which a surface through which the signal lead pin13and the ground pin14pass separately is removed.

That is, the plate4is formed by continuously hollowing a disk-shaped metal at a portion through which the signal lead pin13, the ground pin14, and the power supply pin pass. Note that the plate4may be made of a disk-shaped metal with a hole formed in a portion through which each of the signal lead pin13, the ground pin14, and the power supply pin passes.

FIG.4illustrates the first through hole36, the second through hole37, and the third through holes38.

The back surface of the plate4and the outer flat surface10bof the stem10are joined by a conductive tape5. By the conductive tape5, the plate4is fixed to the stem10, and the plate4and the stem10are electrically connected.

Note that the back surface of the plate4and the outer flat surface10bof the stem10may be joined and fixed by another conductive material instead of the conductive tape5.

The front surface of the plate4and the exposed surface of the ground pattern33of the flexible printed circuit3are bonded by a conductive adhesive6. The plate4is fixed to the flexible printed circuit3by the conductive adhesive6, and the plate4and the ground pattern33are electrically connected.

Note that, instead of the conductive adhesive6, the front surface of the plate4and the exposed surface of the ground pattern33of the flexible printed circuit3may be bonded and fixed by another conductive material.

The stem10is electrically connected to the ground pattern33of the flexible printed circuit3via the conductive tape5, the plate4, and the conductive adhesive6, and the stem10and the ground pattern33have a common ground.

As described above, the optical module according to the first embodiment is the optical module including the ground pin14in which the tip portion of the pin portion14ais electrically connected to the ground pattern33of the flexible printed circuit30, and which includes the joint portion14bhaving the diameter larger than the diameter of the pin portion14aat an end of the pin portion14aand joined to the outer flat surface10bof the stem10, in which the stem10and the exposed surface of the ground pattern33are electrically and mechanically connected with the plate4made of metal interposed between the stem and the exposed surface, so that the diameter of the through hole37for the ground pin14can be set to a size that matches the diameter of the pin portion14a, and the degree of freedom in wiring design in the flexible printed circuit30is not impaired.

That is, it is not necessary to increase the diameter of the through hole37for the ground pin14to match the joint portion14bhaving a diameter larger than the diameter of the pin portion14a, and the degree of freedom in wiring design is not hindered.

The tip portion of the outer lead portion13bof the signal lead pin13is fixed to the front surface land of the first through hole36by the solder39, the tip portion of the pin portion14aof the ground pin14is fixed to the front surface land of the second through hole37by the solder40, whereby the flexible printed circuit30, the plate4, and the stem10are firmly adhered to each other.

As a consequence, by using the conductive tape5and the conductive adhesive6, the electrical and mechanical connection between the stem10and the ground pattern33can be surely and firmly maintained.

The plate4is bonded to the exposed surface of the ground pattern33of the flexible printed circuit30with the conductive adhesive6, the conductive tape5is attached to the front surface of the plate4bonded to the flexible printed circuit30, and the stem10is bonded to the plate4with the conductive tape5, so that the optical module can be assembled without adding a hand to the optical module body1and the flexible printed circuit3.

Moreover, since the stem10is fixed to the flexible printed circuit3with the conductive tape5and the conductive adhesive6, it is easy to perform soldering39of the tip portion of the outer lead portion13bof the signal lead pin13and the front surface land of the first through hole36, and soldering40of the tip portion of the pin portion14aof the ground pin14and the front surface land of the second through hole37.

Furthermore, since the stem10and the ground pattern33of the flexible printed circuit30are electrically connected to the ground potential by the plate4made of metal, the ground potential near the signal lead pin13is strengthened, and parallel plate resonance due to the stem10and the ground pattern33of the flexible printed circuit30can be suppressed.

In order to verify that the parallel plate resonance is suppressed, a pass characteristic S21with respect to the frequency in the optical module according to the first embodiment has been calculated.

For comparison, the pass characteristic S21with respect to the frequency in the optical module in which not the plate4made of metal but an insulator plate made of polyimide is used has been also calculated.

The calculation results are illustrated inFIG.5.

InFIG.5, a horizontal axis represents the frequency, a vertical axis represents the pass characteristic S21, a solid line represents a calculation result in the optical module according to the first embodiment, and a dotted line represents a calculation result in a comparative example.

As can be understood fromFIG.5, it can be seen that the pass characteristic S21with respect to the frequency in the optical module according to the first embodiment is better than the pass characteristic S21with respect to the frequency in the comparative example.

That is, in the optical module according to the first embodiment, the stem10and the exposed surface of the ground pattern33of the flexible printed circuit30are electrically and mechanically connected with the plate4made of metal interposed between the stem and the exposed surface, so that resonance and multiple reflection between the stem10and the ground pattern33can be suppressed, and good frequency characteristics are obtained.

Note that, in the present invention, it is possible to modify any component of the embodiment or omit any component in the embodiment within the scope of the invention.

INDUSTRIAL APPLICABILITY

As shown in the first embodiment, an optical module according to the present disclosure can be used as an optical transmission module for optical communication, and can be used as an optical reception module for optical communication on which a light-receiving element is mounted, and as an optical transmission and reception module on which both a light-emitting element and a light-receiving element are mounted.

REFERENCE SIGNS LIST

1: optical module body,10: stem,10a: inner flat surface,10b: outer flat surface,10c: through hole,13: signal lead pin,13a: inner lead portion,13b: outer lead portion,14: ground pin,14a: pin portion,14b: joint portion,18: semiconductor light-emitting element,20: dielectric substrate,3: flexible printed circuit,31: insulating substrate,32: wiring pattern,33: ground pattern,36ato36c: first through hole,37: second through hole,4: plate,5: conductive tape,6: conductive adhesive