News Column

"Optical Module" in Patent Application Approval Process

February 12, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent application by the inventors YAMADA, Osamu (Hiratsuka, JP); AKASHI, Mitsuo (Fujisawa, JP); OKAYAMA, Shinichi (Hamamatsu, JP); KAGAYA, Osamu (Tokyo, JP); ISHII, Hiroyoshi (Yokohama, JP), filed on June 4, 2013, was made available online on January 30, 2014, according to news reporting originating from Washington, D.C., by VerticalNews correspondents.

This patent application has not been assigned to a company or institution.

The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention relates to an optical module.

"An information transmission amount of an optical communication network grows steadily, and in particular for middle or long-distance transmission, transmission devices having a transmission speed of 40 Gbit/s, 100 Gbit/s are increasing. An optical module used for these transmission devices is demanded to be compact, consume less power, and cost less, and integration of such an optical module has been progressed. For example, a technique for making an optical module compact is described in JP 2008-28309 A.

"For a receiving module used in an optical module, industrial standardization by OIF (Optical Internetworking Forum), which is an industry group, has been progressed. According to the standard, for example, the size of a receiving module of 40 Gbit/s or 100 Gbit/s is 45.times.27.times.8 mm, which is large. From the study of the inventors, a receiving module has a weight more than 10 g when a PKG is configured using kovar alloy in order to hold an optical element and an optical system inside thereof and to secure heat dispersion. A metal PKG (receiving module) of this type, which is comparatively large and has a comparatively large weight, is usually mounted on a printed circuit board using four screws in order that the PKG withstands mechanical vibration and impact force during transportation or during use, and heat dispersion from the PKG bottom surface to the printed circuit board is improved.

"In order to transmit a signal received by a receiving module to the printed circuit board, a lead portion for extracting an electrical signal from the receiving module and an electrode pad of the printed circuit board are soldered. It is desirable that the shape of the lead portion is almost straight and a gap between the lead portion and the electrode pad is as small as possible in order to avoid deterioration of transmission characteristics of a high-frequency signal. For example, the thickness of the lead portion is about 0.15 mm, which is thin, and an interval (lead pitch) between leads in the lead portion is about 1 mm.

"However, if the lead portion and the electrode pad are soldered when they are close enough not to leave a gap therebetween, a very thin portion is generated in the solder that connects the lead portion and the electrode pad. Then, there has been a case where a crack/disconnection is generated in the very thin portion of the solder in a given temperature cycling test, and thus transmission characteristics of a high-frequency signal is significantly deteriorated. Note that the given temperature cycling test is a test to be performed on an optical module obtained by soldering a receiving module on a printed circuit board, and it is required to pass 100 cycles, which is a target in the industry (based on a required value related to a temperature cycle for an optical integration module provided in Table 4-4 in 3.3.2.2 of Telcordia GR-468-CORE 'Generic Reliability Assurance Requirements for Optoelectronic Devices Used in Telecommunications Equipment') of the temperature cycling test.

"The present invention is made in view of the above-described problems, and an object thereof is to provide an optical module which makes a crack/disconnection less likely occur in a connection portion between an optical receiving module and a printed circuit board."

In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "To achieve the above-described object, an optical module according to the present invention includes: an optical receiving module provided with a plurality of leads for transmitting an electrical signal at 15 Gbit/s or more; a printed circuit board provided with a pad that is connected with the plurality of leads by solder; and a metal thin plate that is provided between the printed circuit board and the optical receiving module when the optical receiving module is mounted on the printed circuit board, wherein a thickness of the metal thin plate is defined in such a manner that distance between the plurality of leads and the pad is in the range of 50 to 500 .mu.m after the optical receiving module is mounted on the printed circuit board.

"In an aspect of the present invention, in the optical module, the printed circuit board, the metal thin plate, and the optical receiving module may be fastened by a plurality of screws that are inserted through the printed circuit board, the metal thin plate, and the optical receiving module respectively, and the plurality of leads and the pad may be thereafter connected by the solder.

"In an aspect of the present invention, in the optical module, the metal thin plate may have a surface of a shape that is substantially identical to a surface of the optical receiving module, the surfaces facing each other.

"In an aspect of the present invention, in the optical module, the metal thin plate may be made of stainless steel.

"In an aspect of the present invention, in the optical module, the plurality of leads may be provided near a bottom surface of the optical receiving module on a side surface thereof, and an area where the optical receiving module is mounted in the printed circuit board and the pad may be in an identical surface.

"In an aspect of the present invention, in the optical module, the optical receiving module may include the plurality of leads that transmit an electrical signal at 20 Gbit/s or more, and the thickness of the metal thin plate may be defined in such a manner that a distance between the plurality of leads and the pad is 50 to 300 .mu.m when the optical receiving module is mounted on the printed circuit board.

"In an aspect of the present invention, in the optical module, the optical receiving module may include the plurality of leads that transmit an electrical signal at 30 Gbit/s or more, and the thickness of the metal thin plate may be defined in such a manner that a distance between the plurality of leads and the pad is 50 to 200 .mu.m when the optical receiving module is mounted on the printed circuit board.

"According to an aspect of the present invention, it is possible to make a crack/disconnection less likely occur in a connection portion between the optical receiving module and the printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 is a view illustrating one configuration example of an optical module according to a first embodiment;

"FIG. 2 is a view for describing an assembled state of an optical receiving module, a printed circuit board, and upper and lower metal cases;

"FIG. 3 is a side view of the optical receiving module according to the first embodiment;

"FIG. 4 is a plan view of the optical receiving module according to the first embodiment;

"FIG. 5 is a view showing a relationship between the thickness (.mu.m) of a metal thin plate and the lifetime cycle (number of times) in a temperature cycling test;

"FIG. 6 is a view showing a relationship between the thickness (.mu.m) of the metal thin plate and the reflectance loss (dB) of the high-frequency transmission characteristics of the optical receiving module;

"FIG. 7 is a side view of an optical module according to a second embodiment;

"FIG. 8 is a side view of an optical module according to a third embodiment;

"FIG. 9 is a plan view of the optical module according to the third embodiment;

"FIG. 10 is a view illustrating a configuration example of a case where the optical receiving module is directly provided on a printed circuit board; and

"FIG. 11 is a cross-section view of lead connecting solder in the configuration illustrated in FIG. 10."

URL and more information on this patent application, see: YAMADA, Osamu; AKASHI, Mitsuo; OKAYAMA, Shinichi; KAGAYA, Osamu; ISHII, Hiroyoshi. Optical Module. Filed June 4, 2013 and posted January 30, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3543&p=71&f=G&l=50&d=PG01&S1=20140123.PD.&OS=PD/20140123&RS=PD/20140123

Keywords for this news article include: Patents, Electronics, Circuit Board.

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Source: Electronics Newsweekly


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