JP2004259977A - Electronic circuit module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic circuit module without causing unnecessary stress and capable of securely radiating heat. <P>SOLUTION: The electronic circuit module includes a metal hermetically sealed housing 4 for storing a board 3 on which an integrated circuit 2 is packaged, and a thermal conductive member 6 inserted in a gap 5 formed between the integrated circuit 2 and the housing 4. The thermal conductive member 6 is deformed to absorb the stress by forming convexities 7, 13 on either one or the both of the place of an inner wall of the housing 4 opposed to the integrated circuit 2 or the integrated circuit 2, or by forming convexities on the thermal conductive member 6. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electronic circuit module in which an integrated circuit is housed in a closed casing, and more particularly to an electronic circuit module capable of reliably releasing heat without causing unnecessary stress.
[0002]
[Prior art]
2. Description of the Related Art An optical transceiver used for optical communication is a type of electronic circuit module in which an optical element for photoelectric conversion and light-to-light conversion and an electronic circuit for processing an electric signal are combined. An electronic circuit is realized by mounting a semiconductor integrated circuit package (hereinafter, simply referred to as an integrated circuit) and a resistor on a substrate. The electronic circuit module to which the present invention is applied is one in which this substrate is housed in a sealed metal case. The reason why the casing is made of metal and hermetically sealed is mainly to shield high-frequency radiation due to high-speed operation of the integrated circuit.
[0003]
In order to reliably shield high frequencies, the housing is made such that the gap is as small as possible. For example, when an optical fiber for optical communication is attached to an optical element in a state where the optical fiber is optically coupled, a hole for guiding the optical fiber out of the housing can allow a positional shift for optical axis alignment. It is made as small as possible, leaving some clearance. As described above, the enclosure of the electronic circuit module accommodating the substrate generating the high frequency has a high degree of sealing in order to shield high-frequency radiation.
[0004]
On the other hand, integrated circuits generate heat due to charge / discharge currents and the like due to the logical inversion operation of individual logic elements that process logic signals, and integrated circuits that operate at high speed naturally generate significant heat. In particular, in an IC or LSI in which a large number of logic elements are integrated, a large number of heat sources are densely packed in a small area, so that the heat is likely to be high. Therefore, in order to protect the integrated circuit from deterioration due to heat, it is necessary to improve heat dissipation. However, in the above-described electronic circuit module, since the substrate is confined in a housing with a high degree of sealing, heat radiation is not good.
[0005]
Conventionally, in order to solve this problem, heat is released from the upper surface of the integrated circuit to the ceiling of the housing by heat conduction. Since the case is made of metal, it is optimal for heat dissipation. However, it is not preferable to directly contact a hard integrated circuit (in which a semiconductor chip is embedded in an exterior package generally made of ceramic or resin) and a hard housing (generally made of aluminum die-cast). Therefore, a heat conductive sheet made of an elastomer (elastic body) having heat conductivity is placed on the upper surface of the integrated circuit, and the ceiling of the housing is brought into contact with the heat conductive sheet. This requires a gap between the top surface of the integrated circuit and the ceiling to accommodate the heat conducting sheet.
[0006]
As shown in FIG. 3, the various integrated circuits 2 (2a, 2b, 2c) mounted on the substrate 3 have different heights. That is, the integrated circuit 2 is of a type in which the solder connection terminals are arranged on the bottom surface of the exterior package and soldered to the substrate 3 with solder balls, and the solder connection terminals are arranged on the outer periphery of the exterior package and soldered to the substrate 3 from the component side. There are a type and a type in which a lead protruding from an exterior package is inserted into a through hole of the substrate 3 and soldered from the solder surface side, and the height varies depending on the type. The height of the compatible integrated circuit 2 differs depending on the manufacturer. The height of the ceiling of the housing 4 is determined for each location so that the gaps 5 are uniform according to the height of the integrated circuit 2. The heat conductive sheet 6 is sandwiched between these gaps 5. The heat conductive sheet 6 is slightly pressed down by the ceiling 12 of the housing 5.
[0007]
[Patent Document 1]
JP-A-10-308484
[Problems to be solved by the invention]
The height of the integrated circuits 2 varies depending on the individual. For example, the heights of the integrated circuits 2 of the same type manufactured by the same manufacturer slightly differ from each other. Further, when the integrated circuit 2 is mounted on the substrate 3, the height of the integrated circuit 2 with respect to the substrate 3 also varies due to the finish of the soldering. In addition, the height of the housing 4 from the mounting position of the substrate 3 to the ceiling 12, the thickness of the substrate 3, and the thickness of the heat conductive sheet 6 also vary among individuals. Therefore, the gap 5 between the upper surface of the integrated circuit 2 and the ceiling 12 of the housing 4 is not constant depending on the individual when the substrate 3 is mounted on the housing 4.
[0009]
If the height of the upper surface of the integrated circuit 2 is higher than the height intended in the design due to the variation, the gap 5 becomes relatively narrow, and the heat conductive sheet 6 must be compressed more than expected. Then, extra stress is applied to the integrated circuit 2. However, if the gap 5 is designed to be wider, on the contrary, when the height of the integrated circuit 2 is less than the design, the gap 5 becomes too wide and the heat conductive sheet 6 does not contact the housing 4. If the heat conductive sheet 6 does not contact the housing 4, the expected heat radiation effect cannot be obtained.
[0010]
Since the designer must design the housing 4 so that none of the gaps 5 at a plurality of locations is too narrow or too wide, a large work load is imposed.
[0011]
Therefore, an object of the present invention is to solve the above-mentioned problems and to provide an electronic circuit module that can reliably release heat without causing unnecessary stress.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method in which a substrate on which an integrated circuit is mounted is housed in a metal hermetic housing, and a gap is formed between the integrated circuit and an inner wall of the housing. In an electronic circuit module having a heat conductive member sandwiched in a gap, irregularities are formed in a portion of the inner wall of the housing facing the integrated circuit.
[0013]
Further, according to the present invention, a substrate on which an integrated circuit is mounted is housed in a metal hermetic housing, a gap is formed between the integrated circuit and an inner wall of the housing, and a heat conducting member is formed in the gap. In an electronic circuit module sandwiching the above, an unevenness is formed on the integrated circuit.
[0014]
Further, according to the present invention, a substrate on which an integrated circuit is mounted is housed in a metal hermetic housing, a gap is formed between the integrated circuit and an inner wall of the housing, and a heat conducting member is formed in the gap. In the electronic circuit module sandwiching the above, unevenness is formed on the heat conductive member.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
[0016]
As shown in FIG. 1, in an optical transceiver as an electronic circuit module according to the present invention, a printed circuit board (hereinafter, referred to as a board) 3 on which an optical element 1 and an integrated circuit 2 are mounted is sealed by a metal enclosure. 4, a gap 5 is formed between the integrated circuit 2 and the inner wall of the housing 4, and a sheet-like heat conductive member (hereinafter referred to as a heat conductive sheet) 6 is sandwiched in the gap 5. In the inner wall of the housing 4, irregularities 7 are formed at locations facing the integrated circuit 2. Although the illustrated heat conductive sheet 6 has irregularities on one side, it is deformed by irregularities 7 of the housing 4 as described later, and is flat in a natural state where no stress is applied.
[0017]
The housing 4 having a flat rectangular parallelepiped shape is formed vertically into two parts with the surface parallel to the component surface of the board 3 facing upward. The board 3 is attached to the lower housing 4a, and the upper housing is 4b so as to cover the inside of the housing 4 for sealing.
[0018]
Representative components among components mounted on the substrate 3 are illustrated. That is, 2a is an IC having a high height and a long upper side, 2b is an LSI having a low height and a long upper side, and 2c is an IC having a low height and a short upper side. The optical element 1 is housed in a substantially cylindrical or prismatic outer package, and receives and emits an optical signal from one end in the longitudinal direction. An optical fiber 8 for optical communication is attached to the optical element 1 in a state where it is optically coupled, and a boot 9 for protecting the optical fiber 8 from bending or the like is attached. The connector 11 exposed to the outside of the housing 4 from the window 10 formed in the lower housing 4 b is mounted on the back surface of the board 3. Via this connector 11, it is possible to electrically communicate with other electronic devices.
[0019]
The hole of the housing 4 and the window 10 through which the boot 9 passes are formed such that the gap between the boot 9 and the connector 11 is as small as possible.
[0020]
An upper inner wall (hereinafter referred to as a ceiling) 12 of the upper housing 4a has a different height (a leveled unevenness or a height at a convex portion) for each arrangement position of the integrated circuit 2 on the substrate 3. The gap 5 at each location is set to be approximately the same distance. It is not necessary to design the gap 5 more strictly and uniformly than in the past for the reasons described below. The ceiling 12 is provided with irregularities 7 having a plurality of concave portions and convex portions over a range opposed to the integrated circuit 2 for each arrangement position of the integrated circuit 2. The unevenness 7 is provided for each of the integrated circuits 2 (2a, 2b, 2c) that need to radiate heat to the housing 4 via the heat conductive sheet 6. For example, the unevenness 7 for the integrated circuit 2a extends over a range opposed to the upper surface of the integrated circuit 2a and a plurality of protrusions close to the integrated circuit 2a and far from the integrated circuit 2a (that is, higher than the protrusions). ) A plurality of concave portions are alternately arranged. The width of each convex portion and concave portion is set so that the heat conductive sheet 6 pressed by the convex portion can be deformed into a concave portion. As a result, the heat conductive sheet 6 is scattered and pressed by the plurality of protrusions.
[0021]
In the illustrated example, the concavities and convexities 7 are formed in a parallel line shape by extending a plurality of grooves serving as concave portions in the longitudinal direction of the housing 4 (the depth direction in the drawing). The grooves may be formed in a lattice shape by running in the horizontal direction (the left-right direction on the paper). The shape of the concave portion or the convex portion is not limited to a square shape, and may be an arbitrary shape such as a cylindrical shape, a dome shape, and a tapered shape. Further, a large number of depressions serving as concave portions may be provided, and a large number of protrusions serving as convex portions may be provided. Further, the density of the unevenness 7 may be constant regardless of the location, or as shown in the figure, the integrated circuit 2a, 2b having a long upper surface may have a roughened unevenness 7 and an integrated circuit having a short upper surface. For 2c, the roughness of the unevenness 7 may be fine.
[0022]
The design value of the height of the ceiling 12 at each location of the integrated circuit 2 is set so that the heat conductive sheet 6 can sufficiently contact the housing regardless of the variation in the height of the upper surface of the integrated circuit 2. The gap 5 is determined to be narrower than the thickness in the state.
[0023]
The operation and effect of the present invention in the optical transceiver of FIG. 1 will be described.
[0024]
Since the unevenness 7 is provided on the ceiling 12 of the housing 4, when the heat conductive sheet 6 is sandwiched in the gap 5, the convex portion of the unevenness 7 applies pressure by pressing the heat conductive sheet 6. On the other hand, no pressure is applied to the heat conductive sheet 6 from the concave portions of the concave and convex portions 7. Since the heat conductive sheet 6 pressed by the convex portion is deformed into the concave portion, the portion of the thermal conductive sheet 6 in contact with the convex portion of the concave and convex 7 is concave, and the portion of the thermal conductive sheet 6 facing the concave portion rises and bites. As described above, since the heat conductive sheet 6 deforms so as to cut into the unevenness 7 and absorbs the stress, the stress transmitted to the integrated circuit 2 can be reduced.
[0025]
Conventionally, since the ceiling 12 of the housing 4 was a flat surface without irregularities, when the gap 5 was narrow, the stress applied to the heat conductive sheet directly applied to the integrated circuit 2, but according to the present invention, The unevenness 7 on the ceiling 12 deforms the heat conductive sheet 6 to absorb the stress and protect the integrated circuit 2 from the stress. As a result, the gap 5 can be designed to be narrower than before. Therefore, a situation where the integrated circuit 2 cannot be brought into contact with the housing 4 even if the height of the integrated circuit 2 is less than the design is avoided. As a result, it is not necessary to design the gap 5 as strictly as before, and the design becomes easy. Further, since the heat conductive sheet 6 bites into the unevenness 7, the contact area between the heat conductive sheet 6 and the housing 4 increases, and there is also an effect that the heat transfer efficiency is improved.
[0026]
When heat is a problem in electrical components such as resistors other than the integrated circuit 2, the unevenness 7 is provided on the ceiling 12 at the location of the electrical component, and the heat conductive sheet 6 is sandwiched between the casings 12. A heat radiation effect is obtained.
[0027]
Next, another embodiment will be described.
[0028]
The optical transceiver shown in FIG. 2 has an unevenness 13 on the upper surface of the integrated circuit 2. The configuration of the other parts is exactly the same as the configuration of FIG. The operation and effect are almost the same as those of the optical transceiver of FIG. In the case of FIG. 2, since the unevenness 13 is provided on the upper surface of the integrated circuit 2 in addition to the unevenness 7 on the ceiling 12 of the housing 4, the contact area between the heat conductive sheet 6 and the integrated circuit 2 is increased, Efficiency is improved. It should be noted that the above-described operation and effect can be obtained even if the unevenness 13 is provided only on the integrated circuit 2 without providing the unevenness on the ceiling 12 as in the related art.
[0029]
Conventionally, there has been no integrated circuit 2 provided with irregularities 13 on the upper surface of the outer package for the purpose of pressing and deforming the heat conductive sheet 6, but changing the internal structure of the integrated circuit 2 only by changing the mold for molding the outer package. Manufacturing without is feasible.
[0030]
Next, another embodiment will be described.
[0031]
In the embodiment of FIGS. 1 and 2, the unevenness 7 and the unevenness 13 are formed on the ceiling 12 of the housing 4, the upper surface of the integrated circuit 2, or both using the heat conductive sheet 6 which is flat in a natural state. In this embodiment (not shown), both the housing 4 and the integrated circuit 2 have a flat surface as before, and the heat conductive sheet 6 is provided with irregularities instead. The irregularities may be provided on only one side of the heat conductive sheet 6 or on both sides. Even when the thermal conductive sheet 6 is provided with irregularities, when the thermal conductive sheet 6 is sandwiched in the gap 5 between the integrated circuit 2 and the inner wall of the housing 4, the convex portion is deformed so as to be crushed and stress is reduced. Because of the absorption, the stress transmitted to the integrated circuit 2 can be reduced.
[0032]
Conventionally, there is no heat conductive sheet 6 provided with unevenness for the purpose of pressing and deforming the heat conductive sheet 6, but it is possible to manufacture the heat conductive sheet 6 provided with unevenness by changing the mold for manufacturing the sheet. .
[0033]
In the method of assembling the optical transceiver according to the embodiment shown in FIGS. 1 and 2, first, the integrated circuit 2 is mounted on the substrate 3, and the heat conductive sheet 6 is placed on each integrated circuit 2. Since the heat conductive sheet 6 has tackiness (property of sticking and not falling down), the heat conductive sheet 6 does not fall off even if the substrate 3 is inclined or slightly vibrated. The substrate 3 is mounted on the lower housing 4a, and is mounted so as to cover the upper housing 4b from above.
[0034]
In the above embodiments, an optical transceiver is taken as an example of an electronic circuit module. However, the present invention can be applied to various electronic circuit modules in which high-speed operating electronic circuits are housed in a highly sealed housing.
[0035]
【The invention's effect】
The present invention exhibits the following excellent effects.
[0036]
(1) Since the unevenness is formed on the inner wall of the housing, the integrated circuit, or the heat conductive member, the heat conductive member is not deformed and absorbs the stress, so that unnecessary stress is not given to the integrated circuit. The conductive member and the integrated circuit are brought into close contact with each other to reliably release heat.
[Brief description of the drawings]
FIG. 1 is a sectional view of an optical transceiver showing one embodiment of the present invention.
FIG. 2 is a sectional view of an optical transceiver showing one embodiment of the present invention.
FIG. 3 is a sectional view of a conventional optical transceiver.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Optical element 2, 2a, 2b, 2c Integrated circuit 3 Substrate 4 Housing 5 Gap 6 Heat conduction member (heat conduction sheet)
7 Concavity and convexity of housing 12 Upper inner wall (ceiling) of housing
13 Unevenness of integrated circuit

Claims (3)

An electronic circuit module in which a substrate on which an integrated circuit is mounted is housed in a metal hermetic housing, a gap is formed between the integrated circuit and an inner wall of the housing, and a heat conducting member is sandwiched in the gap. 3. The electronic circuit module according to claim 1, wherein irregularities are formed on a portion of the inner wall of the housing facing the integrated circuit. An electronic circuit module in which a substrate on which an integrated circuit is mounted is housed in a metal hermetic housing, a gap is formed between the integrated circuit and an inner wall of the housing, and a heat conducting member is sandwiched in the gap. 3. The electronic circuit module according to claim 1, wherein the unevenness is formed on the integrated circuit. An electronic circuit module in which a substrate on which an integrated circuit is mounted is housed in a metal hermetic housing, a gap is formed between the integrated circuit and an inner wall of the housing, and a heat conducting member is sandwiched in the gap. 3. The electronic circuit module according to claim 1, wherein the heat conducting member has irregularities.

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