JP2010040647A - Optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical module for mounting and hermetically sealing a photoelectric converting element, or the like, to which a high voltage is applied in a package adhered by resistance welding, and by which faults do not occur for a long period. <P>SOLUTION: An optical module has a stem on which a circuit element, including a photoelectric converting element is mounted, and a cap 4 which is attached to the stem by resistance welding to cover the circuit element and hermetically seals the circuit element, in cooperation with the stem. The cap 4 has two or more closed annular projections 4e for resistance welding. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical module including a photoelectric conversion element for transmitting or receiving an optical signal.

  Some optical modules use a coaxial CAN package configured by sealing a cap on a stem on which a photoelectric conversion element is mounted (see, for example, Patent Document 1). A flat glass or a condensing lens as an optical window is attached to the cap. In such an optical module, a hermetic seal (airtight sealing) is ensured by the CAN package. Further, as a level of hermetic sealing of the optical module, a helium (He) leak rate of 5E-8 atmcc / sec or less is required according to the specification of Telcordia GR-468-CORE or MIL-STD750D.

  A cap used for hermetic sealing has a cap shell to which the optical window is attached, and the cap shell is manufactured by press molding or cutting. Both the cap shell by press molding and the cap shell by cutting are resistance-welded to the stem for hermetic sealing of the element as described above. In these resistance welding processes, moisture adsorbed on the stem or the like is removed by heat-treating the stem or cap at a high temperature in advance, and then the stem and cap are placed in a glove box filled with an inert gas such as nitrogen. Resistance welding the cap. As a result, hermetic sealing is achieved in a state where the inside of the CAN package (that is, around the photoelectric conversion element) is kept at a low moisture content. Note that projection welding is often used for resistance welding.

As an optical module, there is an optical receiver module for long-distance communication, in which an avalanche photodiode (APD) is mounted as a photoelectric conversion element. The APD is used by applying a high voltage of about 30 to 70 V so that a sufficient multiplication state can be obtained. It has been reported that such an APD has a problem when it operates when the surrounding water content is as high as 5000 ppm or more (for example, see Non-Patent Document 1).
Further, according to a recent study, MIL-STD specifies that the internal moisture of the module (Internal Moisture) satisfies the condition of 5000 ppm or less.
JP 2007-134644 A Comizzoli, 6 others, “Failure Mechanism of Avalanche Photodiodes in the Presence of Water Vapor”, Journal of Lightwave Technology ), The Optical Society of America, February 2001, Vol. 19, No. 2, pp. 252-265.

  As in the optical module disclosed in Patent Document 1, one projection is provided on the cap side and sealed by projection welding, so that the current product guarantee level is 1E-8 atmcc / sec or 1E-9 atmcc / sec. Such a leak rate can be secured. However, according to the calculation, for example, in the case of 1E-9 atmcc / sec which is a past acceptable level, it is known that the gas in the cap is replaced with the atmosphere in about 10 to 100 days. The moisture content in the package cannot be kept below 5000 ppm for a long time. That is, in the conventional optical module, when an element to which a high voltage such as APD is applied is used, the period of time during which the moisture content in the package can be maintained at 5000 ppm or less is short. high.

  The present invention has been made in view of the above circumstances, and is an optical module that is mounted with a photoelectric conversion element or the like to which a high voltage is applied and hermetically sealed, and does not cause problems over a long period of time. The purpose is to provide.

  In order to solve the above-described problems, an optical module of the present invention includes a stem on which a circuit element including a photoelectric conversion element is mounted, and is attached by resistance welding so as to cover the circuit element. A cap hermetically sealed, wherein the cap has two or more closed annular projections for resistance welding.

According to the optical module of the present invention, multiple projections for resistance welding to the stem are provided on the cap, and the area of the fusion part between the stem and the cap for hermetically sealing the circuit element including the photoelectric conversion element is increased. Therefore, the leak rate from the hermetic sealing portion of the circuit element can be suppressed.
Therefore, since the moisture content in the hermetic sealing portion of the circuit element can be kept low for a long period of time, it is possible to prevent the circuit element from being damaged by applying a high voltage in a high moisture environment.

1A and 1B are diagrams for explaining an example of an optical module of the present invention. FIG. 1A is a perspective view of an optical module with a cap omitted, and FIG. 1B is a partial cross-sectional view of the optical module. . FIG. 2 is a view for explaining the cap of the optical module of FIG. 1, FIG. 2 (A) is a cross-sectional enlarged view of the main part of the cap before resistance welding, and FIG. 2 (B) is a bottom view of the cap. .
As shown in FIG. 1, the optical module 1 of this example includes a stem 3 on which an element such as an avalanche photodiode (APD) 2 that is a photoelectric conversion element is mounted, and a cap 4 that covers the stem 3. The coaxial package forming the outer shape of the optical module 1 is configured by attaching a cap 4 to a stem 3 by resistance welding (projection welding). In the optical module 1, elements such as the APD 2 are hermetically sealed in a space formed between the stem 3 and the cap 4.

  First, the stem 3 will be described. The stem 3 is a substantially disk-shaped member made of metal, and various elements such as the APD 2 are mounted on the upper surface 3a that functions as an element mounting portion. The stem 3 can be obtained, for example, by extruding a Ni / Au plated metal plate such as Kovar (Fe—Ni—Co alloy) or thin sheet cold rolled steel (SPC). On the upper surface 3 a of the stem 3, an APD 2 is mounted via a bypass capacitor 5 for the APD 2, and elements such as a preamplifier IC 6 for amplifying a photocurrent generated by the APD 2 and a bypass capacitor 7 for the preamplifier IC 6 are mounted. The

  In addition, lead pins 8 for electrical connection with an external electric circuit are attached to the stem 3 by glass sealing or the like. The APD 2 on the stem 3 and the preamplifier IC 6 are electrically connected via a wire (not shown). The APD 2 and the lead pin 8, and the preamplifier IC 6 and the lead pin 8 are electrically connected via a wire, a bypass capacitor 7, and a stem upper surface 3a. By such electrical connection, the optical module 1 photoelectrically converts an optical signal received through an optical window such as a condensing lens described later by the APD 2 and amplifies the obtained electrical signal by the preamplifier IC 6. It can be output to an external electric circuit via the lead pin 8 or the like.

Next, the cap 4 will be described. The cap 4 covers the upper surface 3a of the stem 3, and includes a condenser lens 4a as an optical window and a cap shell 4b that holds the condenser lens 4a. The cap shell 4b has a condensing lens 4a fixed to the opening 4c at the upper center of the cap shell 4b by sealing glass or the like, and is resistance-welded to the stem 3 at a flange portion 4d at the lower portion.
Projection 4e for projection welding for hermetic sealing is provided in the inner and outer multiples (double in this example), as shown in FIG. 4 has two or more closed annular projections 4e. For example, as shown in FIG. 2B, these projections 4e are formed concentrically around the central axis of the coaxial package.

  In the process of attaching the cap 4 to the stem 3, the stem 3 and the cap 4 are heat-treated at a high temperature before resistance welding, thereby removing moisture adsorbed on each component. Thereafter, the cap 4 and the stem 3 are projection welded so as to hermetically seal the element such as the APD 2. This projection resistance welding is performed in a low moisture content (1 ppm or less) glove box filled with an inert gas such as N2. By welding in this way, the moisture concentration of the hermetic sealing portion V of the element after welding can be lowered.

In the optical module 4, the projections 4e on both the inside and outside of the cap shell 4b are melted and fused to the stem 3, so that compared with the conventional case of resistance welding using a single projection, the fusion part The area can be increased, and the leak rate from the hermetic sealing portion of the element can be suppressed. Therefore, in the optical module 20, the moisture concentration inside the hermetic sealing portion V of the element can be kept low for a long period. Therefore, it is possible to prevent a failure due to applying a high voltage to an element such as APD2 in a high moisture concentration atmosphere for a long period of time.
Thus, by performing double (plural) resistance welding (projection) with one cap, it is possible to ensure high airtightness while preventing an increase in the size of the optical module.

  The cap shell 4b is manufactured by press molding using, for example, an FeNi50 material or a Kovar material, and the surface thereof is protected by Ni plating (Au plating may be added). If the surface is protected by Ni plating in this way, the Ni plating contributes as a part of the brazing material, so resistance welding is relatively easy and the range of welding conditions such as end pressure and welding current is widened. That is, the resistance weldability can be improved.

Further, the cap shell 4b may be made by cutting molding using SF20T of ferritic stainless steel or SUS304 of austenitic stainless steel having good machinability and YAG weldability. This is preferable when a sleeve for receiving an optical connector is attached to the optical module package by YAG welding, that is, when the optical module is used as an optical sub-assembly (OSA) with the sleeve attached. It is.
In the example of FIGS. 1 and 2, the condenser lens is attached to the optical module. However, when a condensing lens is provided on the sleeve when the sleeve is attached to the optical module, it is not necessary to attach the condensing lens to the optical module 1, and a flat glass is attached to the cap shell as an optical window. Just do it.

  In the above description, the present invention has been described with reference to an example in which an APD is mounted as a photoelectric conversion element. However, the present invention is applied to an optical module in which a laser diode or a PIN type PD is mounted as a photoelectric conversion element. You can also

It is a figure explaining an example of the optical module of this invention. It is a figure explaining the cap of the optical module of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical module, 2 ... APD, 3 ... Stem, 4 ... Cap, 4a ... Condensing lens, 4b ... Cap shell, 4c ... Opening, 4d ... Flange part, 4e ... Projection, 5, 7 ... Bypass capacitor, 6 ... Preamplifier IC, 8 ... lead pin.

Claims (1)

A stem on which circuit elements including photoelectric conversion elements are mounted;
A cap attached by resistance welding so as to cover the circuit element and hermetically sealing the circuit element in cooperation with the stem;
The cap has two or more closed annular projections for resistance welding.

Images