Optical waveguides – Integrated optical circuit
Reexamination Certificate
2001-09-24
2003-12-09
Chang, Audrey (Department: 2872)
Optical waveguides
Integrated optical circuit
C385S092000, C385S129000
Reexamination Certificate
active
06661939
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical module for use in optical communication modules or the like, more particularly to an optical module obtained by flip-chip mounting a surface-operating optical element on an electric circuit substrate having an optical waveguide formed thereon and filling underfill resin in between the optical element and the substrate, wherein the electrical, optical, and mechanical mounting reliability of the optical element is successfully improved and a method for manufacturing such an optical module.
2. Description of the Related Art
As a method for mounting a semiconductor element on an electric circuit substrate, there has conventionally been known a so-called flip-chip mounting method whereby a semiconductor element is mounted via a conductor bump on an electric circuit substrate. Generally, in the flip-chip mounting, after an electric circuit substrate and a semiconductor element are electrically connected and fixed to each other via a conductor bump, such a solder bump, underfill resin is filled in between the electric circuit substrate and the semiconductor element. By doing so, the bump-connected portion between the electric circuit substrate and the semiconductor element is sealed, and the other portions thereof are fixed to each other, so that the mechanical and electrical mounting reliability improve.
Meanwhile, the flip-chip mounting is adopted for mounting an optical element. For example, in the construction proposed in Japanese Unexamined Patent Publication JP-A 7-183570 (1995), as shown in
FIG. 3
in section, a compound semiconductor chip
22
including a light-emitting element
25
and a silicon semiconductor chip
23
including a light-receiving element
26
are each mechanically and electrically connected to a silicon substrate
21
via a gold-made conductor bump
24
. According to this proposal, the light emitted from the light-emitting element
25
is introduced into an optical waveguide
27
, and then has its traveling direction changed by a reflecting surface
28
so as to enter the light-receiving element
26
.
Also in a case where an optical element is flip-chip mounted, to attain sufficiently high mechanical and electrical mounting reliability, it is preferable that underfill resin is filled in between the optical element and the mounting substrate. Moreover, if there exists a gap between the optical element and the mounting substrate, there is the possibility of accidental intrusion of foreign material between the optical element and the mounting substrate, which is detrimental to establishment of optical connection. To avoid this, it is preferable to fill underfill resin in between the optical element and the mounting substrate.
However, in the case where underfill resin is filled in between the optical element and the mounting substrate having an optical waveguide formed thereon, not only it is necessary to achieve improvement in mechanical and electrical mounting reliability as conventionally intended, but it is also necessary to transmit light between the optical element and the optical waveguide with efficiency. Specifically, although it is needless to say that the underfill resin needs to exhibit light transmittability, in a case where, in the optical waveguide, the upper clad portion covering the core portion is made thin, if the refractive index of the underfill resin covering the upper clad portion is larger than the refractive index of the upper clad portion, specific light, which is basically guidedly transmitted through the optical waveguide while being trapped in the core portion having a refractive index larger than that of the clad portion, inconveniently leaks to the underfill resin arranged on the outer side of the clad portion. This makes it impossible to achieve proper light transmission.
Moreover, light leakage usually occurs between the optical waveguide and the optical element to one degree or another. In this connection, a so-called multichip module obtained by mounting a plurality of optical element chips on a single substrate faces a problem in that such leakage of light becomes stray light and couples with another optical element or optical waveguide to cause crosstalk.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above stated problems with the conventional art, and has its object to provide an optical module obtained by flip-chip mounting an optical element face-down on a substrate having an optical waveguide formed thereon, and thereafter filling underfill resin in between the substrate on which the optical waveguide is formed and the optical element, wherein the mechanical, electrical, and optical mounting reliability of the optical element is successfully improved.
The invention provides an optical module comprising:
a substrate having an electric circuit formed thereon;
a surface light receiving optical element or surface light emitting optical element flip-chip mounted on the substrate with its light-receiving surface or light-emitting surface facing the substrate side;
an optical waveguide formed on the substrate, the optical waveguide having a core portion and a clad portion optically connected to the surface light receiving optical element or the surface light emitting optical element; and
underfill resin filled in between the substrate and the light-receiving surface or between the substrate and the light-emitting surface, the underfill resin covering an optical junction between the surface light receiving optical element or the surface light emitting optical element and the optical waveguide,
wherein the underfill resin is an electrically insulating material and has a refractive index equal to or smaller than a refractive index of the clad portion of the optical waveguide.
The invention further provides a method for manufacturing an optical module comprising the steps of:
forming an optical waveguide having a core portion and a clad portion on a substrate on which an electric circuit is formed;
flip-chip mounting a surface light receiving optical element or a surface light emitting optical element on the substrate with its light-receiving or light-emitting surface facing the substrate side; and
filling and curing an underfill resin of an electrically insulating material and having a refractive index equal to or smaller than a refractive index of the clad portion of the optical waveguide, in between the substrate and the light-receiving surface or between the substrate and the light-emitting surface.
According to the invention, the underfill resin, which is filled in between the light-receiving surface of the surface light receiving optical element (or the light-emitting surface of the surface light emitting optical element) flip-chip mounted on the substrate having an electric circuit formed thereon and the substrate, and covers the optical junction between the surface light receiving optical element (or the surface light emitting optical element) and the optical waveguide formed on the substrate, is of an electrically insulating material and has a refractive index equal to or smaller than the refractive index of the clad portion of the optical waveguide. Thus, the optical element can be flip-chip mounted with improved mechanical and electrical mounting reliability. Moreover, since there is no possibility of accidental intrusion of foreign material between the optical element and the mounting substrate, satisfactory optical connection can be maintained. Further, even in a case where, for example, the upper clad portion of the optical waveguide covering the core portion is made thin, it never occurs that light which is guidedly transmitted through the optical waveguide while being trapped in the core portion of the optical waveguide leaks to the underfill resin arranged on the outer side of the clad portion in the optical junction between the path and the optical element. This allows satisfactory light transmission between the optical element and the optical waveguide.
In the invention, it is preferable
Kaneko Katsuhiro
Tanahashi Shigeo
Allen Denise S.
Chang Audrey
Hogan & Hartson
Kyocera Corporation
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