Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2001-03-08
2002-10-08
Ullah, Akm E. (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S147000
Reexamination Certificate
active
06461059
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photo-electronic device (semiconductor optical module) and a method of producing thereof, particularly to a technology effectively applied to a technology of producing a photo-electronic device capable of preventing breakage of an optical fiber core line comprising a core and a clad and extended in a package and capable of preventing a deterioration in transmission efficiency of light.
There is used a photo-electronic device integrated with a semiconductor laser (semiconductor laser element: semiconductor laser chip) as a light source for an information processing apparatus or a light source for optical communication. As an example of a photo-electronic device, there is disclosed, in Japanese Patent Laid-Open No. 282369/1998 or Japanese Patent Laid-Open No. 307235/1998, an optical communication apparatus (semiconductor laser module) forming a package by a case and a lid (cap) comprising plastics (resin) formed by a transfer mold process, containing a semiconductor laser (laser diode) or a photo detector (photo diode) and extending an optical fiber to inside and outside of the package.
Further, portions of a pad (pad portion) and a lead frame for fixing a silicon substrate, are embedded in the case simultaneously with the transfer mold operation. The silicon substrate is fixed with the semiconductor laser. The optical fiber extended to inside and outside of the package is constructed by a structure in which the optical fiber core line is covered with a cover member up to a middle of the package and a front end thereof is a bare optical fiber at which the optical fiber core line is exposed by removing the cover member. The optical fiber core line is constituted by the core and the clad covering the core and both of them comprise, for example, quartz and are brittle and easy to break by external force.
Further, in the package, the semiconductor laser is covered with transparent gel-like resin comprising silicone resin.
SUMMARY OF THE INVENTION
The applicants have investigated to use a copper frame having excellent thermal conductivity (thermal expansion coefficient &agr;=17×10
−6
/° C.) as a lead frame for radiating heat generated at a semiconductor laser element to outside of the package in developing a photo-electronic device integrated with the semiconductor laser.
However, according to the structure, it has been found that exfoliation of an optical fiber is caused by a mounting test by solder reflow (10 seconds at 260° C).
In producing a photo-electronic device, a case is formed to embed a portion of a lead frame by transfer mold. A base plate (pad) comprising a copper plate is formed at an inner bottom face of a case and a silicon substrate (thermal expansion &agr;=3.0×10
−6
/° C.) is fixed onto the base plate. A semiconductor laser element, a light receiving element, an optical fiber and the like are fixed onto the silicon substrate. A front end portion of an optical fiber is positioned to face an emitting face of the semiconductor laser element and a front end portion thereof is adhered to the silicon substrate by an adhering agent. Further, a portion at a middle of the optical fiber is fixed to the case by an adhering agent.
Here, the optical fiber indicates also an optical fiber core line formed by a core and quartz covering the core and the optical fiber cable covering the optical fiber core line by a cover member of a jacket. When the optical fiber core line or the optical fiber cable may not be specified particularly or may not preferably be specified, these are referred to simply as optical fiber in the following.
When a constitution of supporting an optical fiber (optical fiber core line) is constructed by two points support constitution of fixing a front end portion of the optical fiber and a middle portion thereof, tensile force is operated to the optical fiber core line by thermal deformation of the base plate caused by heat in the solder mount test and the tensile force exceeds force of adhering the silicon substrate and the optical fiber core line and the optical fiber core line is exfoliated. Exfoliation of the optical fiber at the front end portion of the optical fiber causes a phenomenon in which a deterioration is caused in transmission and reception efficiency of light to and from the semiconductor laser element or light is not inputted at all from the front end.
In order to resolve such a problem, the applicants have investigated to form the lead frame by a material the thermal expansion coefficient of which is proximate to that of silicon. As a material the thermal expansion coefficient is proximate to that of silicon, there are kovar, 42 alloy and the like. Hence, the applicants have formed the lead frame by 42 alloy (&agr;=5×10
−6
/° C.). Therefore, the base plate and the lead integrated to the case are made of 42 alloy. The thermal conductivity of 42 alloy is as small as 13.4 W/m·k in comparison with 146 W/m·k of Cu and achieves an effect of capable of restraining temperature rise of the base plate per se and restraining deformation of the base plate. Thereby, there is provided a structure in which the optical fiber is difficult to exfoliate.
Meanwhile, the applicants have investigated also on adaptability of resin constituting the case. Since the case is exposed to high temperature even in a short period of time, as a resin constituting the case, the resin having heat resistant temperature of 200° C. or higher has been investigated. Although as resins, there are thermoplastic resin and thermosetting resin, thermoplastic resin is used since thermosetting resin is provided with a drawback in which the time period of molding thereof is long and the resin is not reproducible. Thermoplastic resin is widely used as engineering plastic.
As resin having the heat resistant temperature equal to or higher than 200° C., there are polyphenylene sulphide (PPS), polyether sulfone (PES), polyetherketone (PEEK) and liquid crystal polymer (LCP).
PES, PEEK and LCP are expensive and PPS is balanced in view of heat resistance and price.
Although the price is high, the liquid crystal polymer (LCP) is featured in high heat resistance (thermal deformation temperature equal to or higher than 260° C.) and high bending strength (bending strength: 21.2 kg/mm
2
at 25° C.). Further, the liquid crystal polymer is particularly featured in small linear expansion coefficient in a direction of flow of resin in molding thereof. The linear expansion coefficient of the resin in the flow direction is 2.0×10
−6
/° C. and the linear expansion coefficient in a direction orthogonal to the flow is 66×10
−6
/° C.
Hence, the applicants have conceived to prevent breakage caused by the thermal stress of the optical fiber core line by molding the case by making the resin flow in the direction of extending the optical fiber core line and approximating the thermal expansion coefficient of the case in the direction of extending the optical fiber core line to the thermal expansion coefficient of the optical fiber core line.
However, in the case of the liquid crystal polymer, the thermal conductivity is as small as 0.4 W/m·k and the tensile strength of weld after molding is smaller than 25 MPa in comparison with 55 MPa or more of various engineering plastics. In order to improve the heat radiating performance, the thinner the resin thickness below the base plate fixed with the semiconductor laser element, that is, the thickness of the bottom of the case, the more preferable. However, as mentioned above, the liquid crystal polymer is provided with the low tensile strength of weld and the bottom of the case becomes brittle. Hence, the inventors have conceived to increase the strength by partially thickening the bottom of the case.
Meanwhile, it has been found that there is a case of breaking the optical fiber core line from the following reason by analysis and investigation by the inventors.
FIG. 21
is an enlarged sectional view showing a portion of a package
Ando Kazunori
Naka Hiroshi
Takahashi Shoichi
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Ullah Akm E.
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