Optical module mounted body and securing method of optical module

1. Field of the Invention

The present invention relates to an optical module mounted body and a method of securing an optical module to a mounting board.

2. Related Art

Optical modules having an optical semiconductor element such as a semiconductor laser diode (hereinafter referred to as LD) are generally mounted on a mounting board formed with a predetermined wiring patterns.

FIG. 1-16 shows an example of the optical module mounted on a mounting board, which is disclosed in U.S. Pat. No. 6,522,486.

In this prior art, the optical module is placed directly on a mounting board. A securing member is placed over a package of the optical module and fastened to the mounting board by use of screws on the bottom end flanges of the securing member. The optical module is held between the securing member and the mounting board, thereby fixedly pressed against the mounting board. The heat generated by an LD inside the optical module is dissipated through a bottom face of the package to the mounting board and ultimately into the air.

In this securing method of the optical module, however, if a turning torque of the screws is not sufficient, the optical module and the mounting board are not in properly close contact with each other, while if the torque is excessive, the mounting board or the securing member may be deformed or damaged, leading also to an improper contact. Thus, a reduced heat transferring efficiency between the optical module and the mounting board results in both cases.

It is for this reason that the prior art requires a turning torque of the screws to be strictly controlled.

In addition, the prior art securing method requires flanges at which the securing member is fastened to the mounting board. Those flanges project beyond the main body and inevitably occupy some space on the mounting board. However, the package should be free of such flanges in pursuing downsizing of the optical module and of the mounting board mounted with the optical module.

Further, in adopting an easy method of securing the optical module to a mounting board, a care should be paid to ensure or to enhance the heat dissipation from the LD to the mounting board.

In general, in one aspect, the present invention relates to an optical module mounted body. The optical module mounted body comprising: a mounting board having a mounting surface with a plurality of holes formed thereon; an optical module placed on the mounting surface; and a securing member configured to secure the optical module, the securing member including an upper portion, a plurality of legs extending from the upper portion and a plurality of engagement portions formed at ends of the plurality of legs, wherein the optical module is held between the mounting board and the securing member such that the upper portion of the securing member abuts on an upper surface of the optical module, and wherein the plurality of legs are inserted in the plurality of holes, the plurality of engagement portion engaging with the mounting board.

In general, in one aspect, the present invention relates to a securing method of an optical module. The securing method of an optical module comprising: placing the optical module on a mounting surface of a mounting board; placing a securing member over the optical module, the securing member including an upper portion to abut on an upper surface of the optical module, a plurality of legs extending from the upper portion generally alongside of the optical module, and a plurality of engagement portions being formed at ends of the plurality of legs; and attaching the securing member to the mounting board, the plurality of legs being inserted in a plurality of holes formed on the mounting board and the plurality of engagement portions being engaged with the mounting board.

In general, in one aspect, the present invention relates to an optical module mounted body. The optical module mounted body comprising: means for mounting the optical module; and means for engaging a securing member with the mounting board, the optical module being secured therewith on the mounting board.

In general, in one aspect, the present invention relates to a mounting board. The mounting board comprises: a plate member having a mounting surface and an undersurface opposite the mounting surface; and at least one heat conducting member embedded in the plate member and connecting continuously the mounting surface and the undersurface of the plate member, wherein each of the at least one heat conducting member are exposed on each one of the mounting surface and the undersurface.

Other aspects and advantages of the invention will be apparent from the following description and the appended claims.

FIG. 1-1 is an explanatory diagram showing a first embodiment of the present invention, illustrating a method of securing an optical module to a mounting board by use of a securing member.

FIG. 1-2 is a sectional view showing an optical module mounted body according to the first embodiment of the present invention.

FIG. 1-3 is a perspective view showing a securing member used in the first embodiment of the present invention.

FIG. 1-4 is a sectional view showing an optical module mounted body according to the first embodiment of the present invention, with the engagement portion bent contrarily to the case of FIG. 1-2 .

FIG. 1-5 is a perspective view showing a securing member used in the example of FIG. 1-4 .

FIG. 1-6 is a sectional view showing a modified example of the first embodiment of the present invention.

FIG. 1-7 is a perspective view showing the securing member used in the modified example of FIG. 1-6 .

FIG. 1-8 is an explanatory diagram showing another example of the securing method according to the first embodiment of the present invention.

FIG. 1-9 is an explanatory diagram showing a second embodiment of the present invention, illustrating a method of securing an optical module to a mounting board by use of a securing member.

FIG. 1-10 is a plan view showing an optical module mounted body according to the second embodiment of the present invention.

FIG. 1-11 is a sectional view showing an optical module mounted body of a modified example according to the second embodiment of the present invention.

FIG. 1-12 is a perspective view showing the securing member used in the modified example of FIG. 1-11 .

FIG. 1-13 is an explanatory diagram showing an example of the securing method using the securing member.

FIG. 1-14 is a sectional view showing an optical module mounted body according to a third embodiment of the present invention.

FIG. 1-15 is a plan view showing a mounting board used in the third embodiment of the present invention.

FIG. 1-16 is a diagram showing an optical module mounted body according to prior art.

FIG. 2-1 is a plan view showing a first example of the mounting board used in the third embodiment of the present invention.

FIG. 2-2 is a sectional view taken along the line I—I in FIG. 2-1 .

FIG. 2-3 is an explanatory diagram illustrating a manufacturing process of the mounting board of the first example.

FIG. 2-4 is a diagram showing another example of heat conducting portion of the mounting board.

FIG. 2-5 is a diagram showing still another example of heat conducting portion of the mounting board.

FIG. 2-6 is a diagram showing still another example of heat conducting portion of the mounting board.

FIG. 2-7 is a diagram showing still another example of heat conducting portion of the mounting board.

FIG. 2-8 is a sectional view showing a second example of the mounting board, or multiplayer wiring board, used in the third embodiment of the present invention.

FIG. 2-9 is a diagram showing an example of the optical module mounted body using the mounting board.

FIG. 2-10 is a diagram showing another example of the optical module mounted body using the mounting board.

(First Embodiment)

An optical module mounted body according to first embodiment of the present invention is shown in FIG. 1-1 and FIG. 1-2 . FIG. 1-1 is an explanatory diagram illustrating a securing method of an optical module to a mounting board by use of a securing member which will be described later. FIG. 1-2 is a sectional view showing an optical module mounted body according to the first embodiment of the present invention.

In the first embodiment of the present invention, a mounting board 1 A is formed with through holes 1 c each having a long rectangular aperture exposed on each side of the portion where an optical module 2 A is mounted (or the portion 2 C, enclosed by two-dot chain lines in FIG. 1-1 , hereinafter referred to as mounting portion) on a mounting surface. In addition, a plurality of (4 on one side, in the figure) wiring through holes 1 d , for receiving lead pins 2 d of the optical module 2 A, are formed on the portion between the mounting portion 2 C and the through holes 1 c.

An optical module 2 A of so-called a DIP (dual inline package) type, having a plurality of lead pins 2 d extending downwards from two opposing sides 2 b thereof, is mounted on the mounting portion 2 C of the mounting board 1 A. The plurality of lead pins 2 d are inserted into the wiring through holes 1 d and fixed therein by a low-melting point metal 4 and electrically connected to wiring terminals 1 j on the mounting board 1 A.

Thereafter, a securing member 3 A is placed over the optical module 2 A, with two legs 3 b thereof located alongside of the two opposing sides 2 b of the optical modules 2 A, and engagement portions 3 c , or backs of hook-shaped ends of the legs 3 b , being inserted into the through holes 1 c of the mounting board 1 A. The engagement portions 3 c are lead out on an undersurface 1 b of the mounting board 1 A, where the engagement portions 3 c engage with the lower edges of the through holes 1 c.

Thus, the optical module 2 A is secured on the mounting board 1 A, as shown in FIG. 1-2 , being held between the securing member 3 A and the mounting board 1 A.

In the sectional view of FIG. 1-2 , since the bottom face 2 c of the optical module 2 A is in close contact with an upper face 1 a of the mounting board 1 A by means of the securing member 3 A, the heat transfer from the optical module 1 A through the bottom face 2 c to the mounting board 1 A is enhanced. The top face 2 a of the optical module 2 A is in close contact with nearly entire lower face of the upper portion 3 a of the securing member 3 A. The both legs 3 b of the securing member 3 A extend alongside the two opposing sides 2 b of the optical module 2 A, and the engagement portions 3 c formed at the ends of the legs 3 b are inserted through the respective through holes 1 c to engage with the corner 1 e on the lower surface 1 b of the mounting board 1 A.

For the purpose of enhancing heat dissipation, the optical module 2 A needs to be pressed against the mounting board 1 A so as to be in close contact with the mounting board 1 A. In the present invention, the legs 3 b of the securing member 3 A is resilient, exerting a restoring force F 1 (see FIG. 1-2 ) orienting inward (i.e. toward the optical module) when the engagement portions 3 c engage with the corners 1 e on the lower face 1 b in the respective through holes 1 c.

By properly setting the length of the legs 3 b , the corner 1 e of the through hole 1 c on the lower face 1 b of the mounting board 1 A and a neck portion 3 e of the engagement portion 3 c (or, a connection point of the roundly formed end portion and the rectilinear portion of the legs 3 b in FIG. 1-2 ) are able to come into contact with each other, each exerting a force F 1 against other, and consequently generating a diagonally upward force F 2 at the corner 1 e . Therefore, upward component F 3 of the force F 2 works on the mounting board 1 A (see FIG. 1 - 2 ). It is needless to say that the reactive force having the same magnitude works on the legs 3 b.

The force F 3 thus exerted by the engagement portion 3 c on the corner 1 e of the mounting board 1 A acts to lift the bottom face 2 c of the optical module 2 A while the opposing force having the equivalent magnitude F 3 exerted by the upper portion 3 a of the securing member 3 A on the top face 2 a of the optical module 2 A acts to hold back the optical module 2 A. Consequently, the optical module 2 A is fixed on the mounting board 1 A with the pressing force F 3 . (Note that since the securing member 3 A of the present embodiment has two legs 3 b , the optical module 2 A is fixed to the mounting board 1 A with a pressing force F 4 , which is twice as large as the force F 3 .)

The mounting board 1 A and the securing member 3 A used in the above embodiment will be explained in detail below.

As shown in FIG. 1-1 , the mounting board 1 A is formed with two through holes 1 c , 1 c , spaced by a distance L 1 . Each through hole 1 c has a long rectangular aperture, with its two opposing longer sides being longer than the longitudinal length of the leg 3 b of the securing member 3 A and its two opposing shorter sides being slightly wider than the width of the engagement portion 3 c as viewed in its cross section, for allowing the insertion of the engagement portions 3 c.

In addition, the mounting board 1 A is formed with a plurality of wiring through holes 1 d , a plurality of wiring terminals 1 j , and a predetermined wiring patterns for electrical connection to outside.

FIG. 1-3 is a perspective view showing an example of the securing member 3 A.

The securing member 3 A is made from a resilient plate member formed of a material such as stainless steel, resin or engineering plastics. The thickness of the plate member made of the material is selected so as to enable the resultant legs 3 b to exert a proper magnitude of pressing force arising from the restoring force when deformed in being attached to secure an optical module. In the example shown in FIGS. 1-1 to 1 - 3 , the upper portion of the securing member 3 A is made flat. The upper portion 3 a and the leg portion 3 b are integrally formed, with a stepwise intermediate portion 3 d interposed between them. The leg 3 b extends vertically downward from a lateral end of the intermediate portion 3 d . A lateral width L 3 of the upper portion 3 a of the securing member 3 A is made slightly larger than a lateral width L 4 of the top face 2 a of the optical module 2 A (see FIG. 1 - 1 ), allowing the top face 2 a of the optical module 2 A and the lower face of the upper portion 3 a of the securing member 3 A to be in contact with each other in an accurate and stable manner.

The distance between the two intermediate portions 3 d are made nearly equal to or slightly larger than the distance L 1 between the two through holes 1 c of the mounting board 1 A. The separation between the two opposing legs 3 b , 3 b are made smaller as it approaches to the engagement portions 3 c formed on their respective ends, wherein the separation L 2 of the two legs 3 b just above the engagement portions 3 c is smaller than the distance L 1 between the through holes 1 c of the mounting board 1 A to ensure that a proper magnitude of restoring force is exerted by the legs 3 b.

The engagement portion 3 c formed at each end of the legs 3 b is formed by roundly bending a tip end of the rectilinear leg 3 b , and projecting inward of the securing member 3 A. Each of the engagement portions 3 c has a neck portion 3 e where the roundly formed end portion and the rectilinear portion of the leg 3 b meet, wherein the neck portion 3 e is formed so as to engage with the corner 1 e of the through hole 1 c on the lower face 1 b of the mounting board 1 A when attaching the securing member 3 A to the mounting section is smaller than a length of the shorter side of the rectangular through hole 1 c , so that the engagement portion 3 c is accessible to the lower face 1 b of the mounting board 1 A via the through hole 1 c.

In the present embodiment of the invention, the optical module 2 A can be fixedly pressed to the mounting board 1 A by using the compact securing member 3 A which is formed to fit the outer shape of the optical module 2 A and to have resilient legs 3 b , facilitating attachment and detachment of the optical module 2 A to the mounting board 1 A. Therefore, in the present invention, it is possible to mount optical modules in a reduced time. In addition, the present invention eliminates the need of flanges to fasten the optical module by screwing, occupying a reduced space when the optical module is mounted on the mounting board 1 A.

Note that in case of replacing the optical module 2 A, it can be detached easily from the mounting board 1 A simply by expanding apart the engagement portions 3 c , withstanding the pressing force F 1 , and drawing the securing member 3 A upward.

In the above embodiment, the engagement portions 3 c engage with the inner corners 1 e of the through hole 3 c , as shown in FIG. 1-2 . However, the securing member 3 A may be formed such that the engagement portions 3 c engage with outer corners 1 e′ of the through hole 1 c on the lower face 1 b of the mounting board 1 A, as shown in FIG. 1-4 . In this case, the distance L 2 (see FIG. 1-5 ) between the two legs 3 b just above the engagement portions 3 c is made larger than the distance between the through holes 1 c . The engagement portion 3 c may be formed as a hook-shaped end of the leg 3 b , the round bending of the hook-shape projecting outward to serve as the engagement portion. The optical module 2 A in this case can be fixed to the mounting board 1 A easily, by pressing the two legs 3 b of the securing member 3 A inward, inserting the engagement portions 3 c into the through holes 1 c and releasing the two legs 3 b to cause the engagement portions 3 c to engage with the outer corners 1 e′ of the through holes 1 c on the lower face this case can be detached from the mounting board 1 A simply by pressing inward the two legs 3 b of the securing member 3 A to disengage the engagement portions 3 c with the outer corner 1 e′ of the through hole 1 c , and drawing the securing member 3 A upward.

In the securing method of the present invention, the optical module 2 A is fixed with a force worked by a securing member 3 A along a longitudinal range where the engagement portion 3 c and the corner 1 e ( 1 e′ ) of the mounting board 1 A are in contact. Therefore, as opposed to the case of an optical module being fixed with screws, the optical module 2 A is free from concentration of strain on any particular portion of the optical module. Hence, the optical module is immune from optical misalignment of the LD and the optical fiber, and consequent decrease in optical output as well. In addition, in the present invention, efficient heat transfer from the bottom plate 2 c of the optical module to the mounting board 1 A can be ensured by the pressing force uniformly worked on the optical module.

FIG. 1-6 is a sectional view showing a modified example of the first embodiment of the present invention.

The modified example is similar to the above embodiment except for a securing member 3 B having a different shape of upper portion. As shown in FIG. 1-7 , the securing member 3 B of this modified example has the upper portion 3 a 1 which is convex downward such that a center portion of the upper portion 3 a 1 abuts against the top surface 2 a of the optical module 2 A. Like in the example shown in FIG. 1-2 , the resilient nature of the legs 3 b can give rise to the force F 5 , as depicted by the upward arrow in FIG. 1-6 . The upward force F 5 in turn causes the upper portion 3 a 1 of the securing member 3 B to deform elastically, giving rise to the force of the same magnitude F 5 , that press the optical module 2 A against the mounting board 1 A, as depicted by the downward arrow in FIG. 1-6 .

In the above securing methods, the securing member 3 A or 3 B was attached over the optical module 2 A after the lead pins 2 d were adhered within the wiring through holes 1 d and to the wiring terminals 1 j . However, the securing member 3 A or 3 B may be attached before the lead pins 2 b are adhered.

FIG. 1-8 is an explanatory diagram showing another example of the securing method according to the first embodiment of present invention, in which a plurality of the lead pins 2 d are received within a DIP socket 5 .

In the example, an optical module 2 A is placed on a mounting portion of the mounting board 1 A, with its plurality of lead pins 2 d being inserted into the corresponding wiring through holes 1 d (see FIG. 1 - 8 A). Then, a securing member 3 B with a convex top surface 3 a 1 is placed over the optical module 1 A to fix it to the mounting board 1 A (see FIG. 1 - 8 B). Thereafter, ends of the plurality of lead pins 2 d are mated with corresponding female contacts of the DIP socket 5 arranged on the lower face 1 b of the mounting board 1 A, whereby electric connection to outside is established (see FIG. 1 - 8 C).

In the above method, the use of the DIP socket for electrical connection eliminates the need of soldering process of the lead pins 2 d , thereby further simplifying the attachment or detachment of the optical module 2 A. Furthermore, since the optical module 2 A is not soldered in this method, it is easy to replace the optical module with a new one by simply detaching the securing member.

(Second Embodiment)

In the above-described optical module mounted body, the optical module was of DIP type, having a plurality of lead pins extending downwards from two opposing sides of the optical module 2 A. However, as will be explained below, the present invention may be applicable to an optical module 2 B of so-called a butterfly-type, wherein a plurality of lead pins are protruding from two opposing sides of the optical module and are to be arranged parallel to the mounting board.

FIG. 1-9 is an explanatory diagram showing a second embodiment of the present invention, illustrating a method of securing an optical module 2 B to a mounting board 1 B by use of a securing member 3 C. FIG. 1-10 is a plan view showing an optical module mounted body according to the second embodiment of the present invention.

The mounting board 1 B is formed with a long rectangular through hole 1 f 1 adjacent to one longitudinal side of a mounting portion 2 D on which the optical module 2 B is to be mounted, and two rectangular through holes 1 f 2 , 1 f 3 adjacent to the other longitudinal side from which an optical fiber is to be arranged. As shown in FIG. 1-9 , the latter two rectangular through holes 1 f 2 , 1 f 3 are shorter in length of longer side than the through hole 1 f 1 . In addition, a plurality of wiring terminals 1 j , for electrical connection of the plurality of lead pins 2 e to outside, are formed on both lateral sides of the mounting portion 2 D, to which the plurality of lead pins 2 e are to protrude from the optical module 2 B.

The optical module 2 B is disposed on the mounting portion 2 D of the mounting board 1 B, with its plurality of protruding lead pins 2 e resting on the respective wiring terminals 1 j . Then, the lead pins 2 e are soldered to the wiring terminals 1 j by use of a low melting point metal 4 , whereby electrical connection is established.

Thereafter, a securing member 3 C is placed over the optical module 2 B, with its three legs 3 f 1 , 3 f 2 , 3 f 3 lying alongside of the two opposing longitudinal sides of the optical module 2 B. Engagement portions 3 c formed on respective ends of the three legs are inserted through respective through holes 1 f 1 , 1 f 2 , 1 f 3 , so that they engage with the mounting board 1 B on the lower face thereof.

Thus, the optical module 2 B is secured on the mounting board 1 B, as shown in FIG. 1-10 .

In the second embodiment of the present invention, the legs 3 f 1 to 3 f 3 are formed on both longitudinal ends of the securing member 3 C, allowing the optical module 2 B having the laterally protruding lead pins 2 e from its two opposing lateral sides to be fixed on the mounting board 1 B.

In the second embodiment, the pressing force of the optical module 2 B against the mounting board 1 B is generated in the similar manner to the case of the first embodiment.

Note that the magnitude of the pressing force is nearly proportional to the lateral width of the legs, so preferably, the three legs may be formed such that the restoring force arising from the solitary leg 3 f 1 and the combined restoring force of the legs 3 f 2 and 3 f 3 are substantially equivalent.

The details of the mounting board 1 B and the securing member 3 C, which are used in the above securing method in the second embodiment, will be described below.

In FIG. 1-9 the three through holes 1 f 1 to 1 f 3 are formed so as to allow three engagement portions 3 c of the three legs 3 f 1 to 3 f 3 to be inserted, i.e., the longer side of the through hole 1 f 1 being longer than the lateral width of the leg 3 f 1 , those of the through holes 1 f 2 and 1 f 3 being longer than that of the legs 3 f 2 and 3 f 3 , and the shorter side of all the through holes being wider than the width in cross section of the engagement portion 3 c.

The distance L 1 between the through holes are selected to be nearly equal to or smaller than the distance between the legs at the position near the upper portion 3 a 2 of the securing member 3 B, so that the legs 3 f 1 to 3 f 3 exert a proper magnitude of restoring forces.

The upper portion 3 a 2 of the securing member 3 C is convex toward the top surface 2 a 1 of the optical module 2 A. The three legs 3 f 1 to 3 f 3 extends vertically downward from longitudinal ends of the upper portion 3 a 2 of the securing member 3 C, correspondingly to the three through holes 1 f 1 to 1 f 3 of the mounting board 1 B.

In addition, the securing member 3 C is formed with a cutout 3 g between the two legs 3 f 2 and 3 f 3 on the front end (right-side end in FIG. 1-9 ) from which the optical fiber extends. The cutout 3 g is adapted to receive an optical fiber feed-through pipe 2 f . Engagement portions 3 c are formed on respective ends of the legs 3 f 1 to 3 f 3 .

For the purpose of obtaining a restoring force from the legs, the distance between the leg 3 f 1 and the legs 3 f 2 / 3 f 3 is smaller as it approaches to the engagement portions 3 c , and the distance L 2 just above the engagement portion 3 c is smaller than the distance L 1 between the through holes of the mounting board 1 B.

In the second embodiment of the present invention, the securing member 3 C, having the legs 3 f 1 to 3 f 3 extending downward from the longitudinal ends of the upper portion 3 a 2 , was used to fix the optical module 2 B of so-called a butterfly-type to the mounting board 1 B. For the purpose of fixing the butterfly-type optical module, however, the securing member 3 C may be replaced by one obtained by forming on each leg 3 b 1 of the securing member 3 B, which is shown in FIG. 1-7 of the first embodiment, a cutout for avoiding interference with the laterally-protruding lead pins. Such a modified example of the optical module mounted body according to the second embodiment of the present invention is shown in FIG. 1-11 in its sectional view. FIG. 1-12 is a perspective view showing the securing member 3 D used in the modified example.

As shown in FIG. 1-12 , the securing member 3 D used in the modified example has a cutout 3 b 3 in each of the legs formed on both lateral ends of the upper portion 3 a 1 , for avoiding interference with the lead pins laterally protruding from the two opposing lateral sides of the optical module. As shown in FIGS. 1-11 and 1 - 12 , the securing member 3 D is placed over the optical module 2 B such that a plurality of the laterally protruding lead pins 2 e are received within the cutout 3 b 3 of the securing member 3 D, with the through hole 1 c and engaging with the lower face 1 b of the mounting board 1 C. The mounting board 1 C in this example is formed with a plurality of wiring terminals 1 j , instead of the plurality of the wiring through holes 1 d of the first embodiment. Each of the lead pins 2 e are soldered to each of the wiring terminals 1 j.

The number of the through holes 1 c of the mounting board 1 C may be four correspondingly to the number of the legs 3 b 2 of the securing member 3 D, such that each through hole 1 c receives each of the engagement portion 3 c of the leg 3 b 2 .

Note that the securing members explained in the first and second embodiments may be used to temporarily fix an optical module to the mounting board.

Referring now to FIG. 1-13 , an optical module 2 A is disposed on a mounting portion 2 C on a mounting board 1 A, and a plurality of lead pins 2 d extending downwards are inserted in the wiring through holes 1 d of the mounting board 1 A (see FIG. 1 - 13 A).

Then, a securing member 3 B is placed over the optical module 2 A and attached to the mounting board 1 A, whereby the optical module 2 A is fixed (see FIG. 1 - 13 B).

Thereafter, each lead pins 2 d of the optical module 2 A are soldered within each wiring through holes 1 d and to each wiring terminals 1 j of the mounting board 1 A by a low-melting point metal 4 (see FIG. 1 - 13 C).

Finally, the securing member 3 B is detached from the mounting board 1 A (see FIG. 1 - 13 D).

With the above securing method, the lead pins 2 d of the optical module 2 A are adhered to the mounting board in the state that the optical module is firmly fixed to the mounting board 1 A, whereby the work of fixation of optical modules can be done in a stable manner and it is possible to maintain the state of close contact of the optical module to the mounting board after the securing member 3 B is removed.

In the first and second embodiment, heat-conducting material such as heat-conducting grease, a plating layer, or a sheet of indium can be preferably interposed between a bottom face 2 c of the optical module and an upper face 1 a of the mounting board for the purpose of enhancing the heat transfer.

(Third Embodiment)

FIG. 1-14 is a sectional view showing an optical module mounted body according to a third embodiment of the present invention.

The optical module mounted body according to the third embodiment differs from the first or second embodiment in that the mounting board comprises a plurality of heat conducting member in a mounting portion.

FIG. 1-15 is a plan view showing a mounting board 1 D used in the third embodiment. The plurality of heat conducting member 7 are provided in the mounting portion of an optical module 2 A, which is depicted with two-dot chain lines 2 C. The other constituents including the through holes 1 c , and the wiring through holes 1 d are similarly formed to the mounting board 1 A. The heat-conducting members 7 are embedded in the mounting portion 2 C. Both ends 7 a , 7 b of the heat-conducting members are exposed on both side 1 a (upper surface, or mounting surface), 1 b (lower surface) of the mounting board 1 D, wherein at least one ends 7 a of the heat-conducting member 7 are in contact with the bottom face 2 c of the optical module 2 A.

The heat transferred from the optical module 2 A is efficiently conducted through the heat-conducting members 7 to the lower face 1 b of the mounting board 1 D, wherefrom the heat is dissipated into the air.

Thus, in the third embodiment of the present invention, it is possible not only to fix optical modules easily; compactly and surely to a mounting board by use of the securing member, but also to enhance heat dissipation by the heat-conducting members embedded in the mounting board and continuously connecting the mounting surface and the lower surface opposite the mounting surface.

Detailed explanations of some examples of such mounting boards (or, heat-conducting mounting board), which are applicable in the third embodiment, will be given below.

(First Example of Heat-Conducting Mounting Board)

FIGS. 2-1 and 2 - 2 show a first example of the mounting board that is applicable to the third embodiment of the present invention. FIG. 2-1 is a plan view showing the first example of a wiring board which is used as the mounting board in the present invention, and FIG. 2-2 is a sectional view taken along the line I—I in FIG. 2-1 .

The wiring board 11 A has heat-conducting portions 14 , as enclosed by dashed lines in FIG. 2-2 . The heat-conducting portions 14 pierce the wiring board 11 A, connecting one surface (an upper face in FIG. 2-2 ) 11 a and the other surface (a lower face in the figure) 11 b , on the portion as enclosed with two-dot chain lines in FIG. 2-1 , on which an optical module A is to be placed.

A predetermined wiring patterns 12 a and wiring terminals 12 b are formed adjacent the mounting portion of the optical module A on the upper face 11 a of the wiring board 11 A.

The heat-conducting portions 14 comprise a plurality of through holes 11 c piercing the wiring board 11 A from its upper face 11 a to lower face 11 b , and a plurality of heat-conducting members 14 A each held within each of the through holes 11 c . Both ends 14 a , 14 b of the heat-conducting member 14 A are appearing on the upper surface 11 a and lower surface 11 b.

Placing the optical module A onto the mounting portion, the upper end 14 a of the heat-conducting member 14 A and a bottom face of the optical module A come in contact with each other. In this configuration, the heat transferred from the optical module A is conducted from the upper end 14 a to the lower end 11 b of the heat conducting member 14 A, and thereafter dissipated into the air.

For the purpose of enhancing heat conducting performance, the mounting board 11 A may be formed with a first heat-conducting layer in contact with the upper ends 14 a of the heat-conducting members 14 A exposed on the upper face 11 a of the mounting portion on which the optical module A is placed, and a second heat-conducting layer in contact with lower ends 14 b of the heat-conducting members 14 A exposed on the lower face 11 b.

Such heat-conducting layers enable efficient heat transfer from a wider area of the upper surface 11 a to the lower surface 11 b , and efficient heat dissipation from the lower surface 11 b , since the first heat-conducting layer collects heat to the upper ends 14 a of the heat-conducting members 14 A and the second heat-conducting layer spreads heat transferred to the lower ends 14 b over the second heat-conducting layer, wherefrom the heat is dissipated.

In the present example of the heat-conducting mounting board 11 A, the plating layers 13 formed both on the upper surface 11 a and the lower surface 11 b of the wiring board 11 A serve as the first and the second heat-conducting layers. In this case, the plating layer 13 may be formed simultaneously with the wiring patterns 12 a during a manufacturing process of the wiring board 11 A.

Alternatively, a metal layer deposited by PVD (physical vapor deposition) or the like method, or a sheet of metal adhered to the board may be used as the heat-conducting layers.

In the above example, the upper ends 14 a of the heat-conducting member 14 A may preferably be formed flat so as to come in planar contact performance is enhanced.

A formation process of the heat-conducting portions 14 will be explained below.

First, a plurality of through holes 11 c are formed in a portion on a board 11 A on which the optical module A is to be placed, as shown in FIG. 2-3A .

Then, as shown in FIG. 2-3B , plating layers 13 are formed on internal surfaces of all the through holes 11 c , an upper surface in the mounting portion and a lower surface of the wiring board 11 A.

Thereafter, melt of a low-melting point metal is poured inside the through holes 11 c and cooled there to form heat-conducting members 14 A within the through holes 11 c , as shown in FIG. 2-3C . Preferably, the melt are poured until at least upper ends 14 a of the resulting heat-conducting members 14 A are flush with or slightly project above the upper face (mounting surface) 11 a of the wiring board 11 A, in order to ensure the contact between the heat-conducting member 14 A and the optical module A.

The upper ends 14 a of the heat-conducting members 14 A may be polished to be flush with the plating layer 13 , such that the bottom face of the optical module A are in contact with both the heat-conducting members 14 A and the plating layer 13 .

Note that the number, positions, size or shape, etc. of the heat-conducting members 14 A are determined in relation to the heat dissipating performance required.

FIGS. 2-4 to 2 - 7 shows other examples of the heat-conducting portions in the wiring board.

The heat-conducting portion 15 shown in FIG. 2-4 comprises a plating layer 13 formed on an internal surface of a through hole 11 c piercing the board 11 A from its upper face 11 a to a lower face 11 b , and a heat-conducting member 15 A held within the through hole 11 c.

The heat-conducting portion 15 comprises a core body 15 a , a plating layer 13 formed on the internal surface of the through hole 11 c and a binder 15 b interposed at least in their gap.

The core body 15 a may be formed of a metal such as aluminum or copper, or a non-metal of high thermal conductivity such as AlN (aluminum nitride) or a composite material such as resin dispersed with fibrous carbon.

The binder 15 b may be formed of low melting point metal.

As shown in FIG. 2-4 , the binder 15 b may cover the upper and lower ends of the core body 15 a and may be exposed in the aperture of the through hole 11 c , with their upper and lower surfaces being almost coplanarly disposed respectively with the upper and lower surfaces 11 a , 11 b of the board 11 A.

The heat-conducting portions 15 may be formed in the following way. First, like in the case of forming the heat-conducting portions 14 , a plurality of through holes 11 c are formed on a wiring board 11 A, and then the upper and lower surfaces 11 a , 11 b of the board 11 A and internal surfaces of the through holes 11 c are plated with a plating layer 13 . Thereafter, a plurality of core bodies 15 a , each having a smaller diameter than the diameter of the through hole 11 c , are fitted within the plurality of through holes 11 c . Melt of a low-melting point metal (solder) is poured in each gap between the core body 15 a and the plating layer 13 in the through hole 11 c , and is cooled there. In the heat-conducting portions 15 thus formed, piercing the board 11 A from its upper and lower face, the core body 15 a and the surrounding metal are combined to serve as the heat-conducting member 15 A.

Note that the core bodies 15 a may preferably be plated with Au or Ni in advance in order to ensure wettability of the low melting point metal.

Another example of the heat-conducting portions is shown in FIG. 2-5 . In this heat-conducting portion 16 , the upper face 11 a and lower face 11 b of the wiring board 11 A and the internal surfaces of the through holes 11 c are plated, and then, the heat-conducting member 16 A formed of metal of relatively small hardness, such as aluminum or copper, is fitted into each of the holes 11 c . The upper end 16 a and the lower end 16 b of the heat-conducting member 16 A are exposed respectively on the upper surface 11 a and lower surface 11 b of the wiring board 11 A.

In the above example of the heat-conducting portions, the plating layer 13 may be omitted.

FIG. 2-6 shows still another example of the heat-conducting portions. In this example, the heat conducting portions 17 is formed by fitting heat-conducting members 17 A into the through holes 11 c such that the upper ends 17 a and lower ends 17 b thereof are coplanar respectively with the upper and lower surface 11 a , 11 b of the board 11 A. Then, the plating layers 13 are formed on both surfaces of the board.

Further, the heat-conducting portions may have s different structure, of which the forming process is shown in FIG. 2-7 . In the first step of this forming process, the heat-conducting members 18 A are fitted into the through holes 11 c such that the upper ends 18 a and the lower ends 18 b project respectively beyond the upper surface 11 a and lower surface 11 b of the board 11 A by an amount equivalent to or larger than a thickness of a plating layer 13 to be formed in subsequent step (see FIG. 2 - 7 A). Then, the plating layer 13 is formed on both surfaces of the board 11 A, including both ends and exposed side surface of the heat-conducting members 18 A (see FIG. 2 - 7 B). Finally, the projected portions of the heat-conducting members 18 A are trimmed and polished until the heat-conducting members 18 A are flush with the plating layer 13 (see FIG. 2 - 7 C).

(Second Example of Heat-Conducting Mounting Board)

The more complicated the electric circuits for driving an optical module on a mounting board, the more difficult it will become to make such electric wiring in a single wiring board, and so does it with the wiring board according to the first example. Using multi-layer wiring boards according to a second example described below can be a solution in such cases. Therefore, the second example of the heat-conducting board relates to the multi-layer wiring boards.

As shown in FIG. 2-8 , the mounting board 21 B of the second example is a multi-layer wiring board which comprises three layers 21 C, 21 D, 21 E sequentially stacked in this order. Like in the wiring board 11 A of the first example, on a portion on which an optical module A is to be placed, a plurality of heat conducting members 27 A are fitted into a plurality of through holes 21 d to form heat-conducting portions 24 . In addition, a first heat-conducting layer 23 a and a second heat-conducting layer 23 b are formed, being in contact with upper ends 27 a and lower ends 27 b of the heat-conducting members 27 A exposed respectively on an upper and lower surface of the multi-layer wiring board.

In the multi-layer wiring board 21 B, heat transferred from the optical module A is transmitted from the upper ends 27 a of the heat-conducting members 27 A to the lower ends 27 b thereof, to be eventually dissipated into the air.

Note that the multi-layer wiring board may comprise a greater number of layers. However, since efficiency of heat transfer is nearly inversely proportional to the length L (see FIG. 2-8 ) of the heat-conducting member 27 A, it is preferable that the multi-layer wiring board is thin. Preferably, the thickness of the multi-layer wiring board is in the range of 1 to 5 mm.

The wiring boards 11 A and 21 B of the above examples can be used to dissipate heat generated by optical modules more efficiently if used with one of the securing members 3 A, 3 B, 3 C, 3 D in the manner depicted in FIG. 1-14 . However, the wiring boards of the above examples are so efficient in heat dissipation that heat dissipating efficiency may be practically sufficient, if dispensing with the securing member.

The optical module mounted body of such configuration is shown in FIG. 2-9 . As shown in FIG. 2-9 , an optical module A is placed on a mounting portion of a mounting board 11 A(or 21 B) formed with the heat-conducting portions 14 . The heat transferred from the optical module A is transmitted in a practically efficient manner through the heat-conducting portions 14 to a lower face 11 b of the wiring board 11 A to be eventually dissipated into the air, whereby the performance of the optical module can be maintained irrespective of its own heat generation.

The optical module mounted body, having an optical module A and a wiring board 11 A(or 21 B) as described above, may be used in optical equipments in the state that the lower face 11 b of the wiring board 11 A is fixed directly to an internal surface of a housing of optical equipments (see FIG. 2 - 9 ). In this configuration, the mounting board 11 A( 21 B) serves both as a wiring board and an efficient heat sink that dissipates heat to the housing. Therefore the wiring board described herein can be advantageously used to downsize the equipments that utilize optical module mounted body therein.

In another application, as shown in FIG. 2-10 , the optical module mounted body may be equipped with fins or other heat sink attached to the lower face 11 b of the wiring board 11 A.

In the configurations as depicted in FIGS. 2-9 and 2 - 10 , heat-conducting grease, heat-dissipating sheet formed of aluminum, indium alloy or graphite, or heat-spreader may be disposed, if necessary, between the optical module A and the wiring board or between the fins and the wiring board.

Advantages derived from the present invention may include one or more of the following.

According to one or more embodiments of the present invention, an optical module can be fixed in proper contact with the mounting board. Because of this, in the optical module mounted body, heat transferred from the optical module can be efficiently dissipated to outside.

According to one or more embodiments of the present invention, the optical module is not screwed to the mounting board to be fixed. Therefore, the optical module mounted body is immune from undesirable deformation of a securing member, a mounting board or the optical module.

According to one or more embodiments of the present invention, the optical module is fixed with a force worked along a wide range where the engagement portions of the securing member and the lower corner of the through holes are in contact. Hence, in the present invention, the optical module is immune from concentration of strain on any particular portion thereof. Therefore, the optical coupling between the optical semiconductor chip and the optical fiber is not changed.

According to one or more embodiments of the present invention, the optical module is fixed to the mounting board by using a compact and easily attachable/detachable securing member. Therefore, the optical module can be attached to or detached from the mounting board very easily, and it is possible to secure the optical module in a shortened tact time.

According to one or more embodiments of the present invention, the securing member or the optical module does not need a flange for being screwed to the mounting board. Because of this, the optical module mounted body of the present invention occupies less space, and is advantageous in downsizing the equipment using the optical module mounted body.

According to one or more embodiments of the present invention, a mounting board has heat-conducting portions that pierce the board, connecting a surface on which the optical module is placed and the opposite surface from which heat is dissipated. Hence, the heat transferred from the optical module can be efficiently dissipated.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.