Imaging device with an imaging element and an electronic component

An imaging device includes a circuit board having a wiring line formed as part of an upper surface thereof; an electronic component mounted on the circuit board; a frame body mounted on the circuit board so as to surround the electronic component, and having connection electrodes formed on or above an upper surface thereof and external terminals formed on or above at least one of a side surface and a lower surface thereof which are electrically connected to the connection electrodes; an imaging element having a light-receiving section located in a central portion of an upper surface thereof, the imaging element being mounted on the upper surface of the frame body so as to cover an opening of the frame body; and a lens barrel having a lens, which is bonded to an outer periphery of the upper surface of the frame body so as to cover the imaging element.

CROSS-REFERENCE TO THE RELATED APPLICATIONS

This application is a national stage of international application No. PCT/JP2010/073404, filed on Dec. 24, 2010, and claims the benefit of priority under 35 USC 119 to Japanese Patent Application No. 2009-292206, filed on Dec. 24, 2009, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an imaging device which employs an imaging element of CCD (Charge Coupled Device) type or CMOS (Complementary Metal Oxide Semiconductor) type for example.

BACKGROUND ART

There is a heretofore known imaging device applicable to a digital camera, an optical sensor, and so forth, which is constructed by mounting an imaging element e.g. of CCD type or CMOS type on a wiring board. In such an imaging device, for example, an imaging element is mounted on a wiring board, and a lens is disposed above the imaging element by a lens securing member, so that the imaging element and the lens can be sealed by the lens securing member. Moreover, electronic components including a capacitor and a resistor are installed around the imaging element. The imaging device is designed to convert light (image) inputted to a light-receiving section of the imaging element mounted on the wiring board into an electric signal by the imaging element, and output a converted signal to an external circuit or the like within a digital camera via a connecting member such for example as a bonding wire, a wiring conductor of the wiring board, and an external terminal.

In one of known examples of such an imaging device (refer to Patent Literature 1, for example), in the interest of area reduction in the imaging device for miniaturization, a recess is formed at an upper surface of a wiring board, and an imaging element is disposed on the upper surface of the wiring board so as to cover the recess. Moreover, a plurality of electronic components including an IC, a capacitor, a coil, and a resistor for processing electric signals from the imaging element are mounted on the bottom of the recess. In another known example of the imaging device (refer to Patent Literature 2, for example), a recess is formed at a lower surface of a wiring board, and a plurality of electronic components including an IC, a capacitor, a coil, and a resistor for processing electric signals from an imaging element are mounted inside the recess.

A wiring board such as adopted in those imaging devices is made of an insulating material such as ceramics or resin. For example, in the case of using ceramics, the wiring board can be fabricated by laminating a plurality of ceramic green sheets of predetermined configuration on top of each other and then firing the resultant stacked body. In keeping up with the recent trend toward low-profile imaging devices, the recess formed in the wiring board has a bottom thickness in a range of about 0.3 mm to 0.4 mm, and has a depth in a range of about 0.3 mm to 0.4 mm. That is, the constituent ceramic green sheets are very small in thickness.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, in recent years, further slimming-down has come to be increasingly demanded of imaging devices for use in electronic equipment such as cellular phones and digital cameras. In order to meet the demand, in an imaging device of the type that incorporates a plurality of electronic components including an IC, a capacitor, a coil, and a resistor for processing electric signals from an imaging element that are mounted in a recess formed in a wiring board, the imaging device is made lower in profile by decreasing the bottom thickness of the recess. To date, the bottom thickness of the recess has been reduced to very low values ranging from about 0.3 mm to 0.4 mm, wherefore an additional reduction in the bottom thickness could lead to further deterioration in mechanical strength of the wiring board. After all, the imaging device is subjected to breakage when a force is applied to the bottom of the recess due to the placement of the imaging element or electronic component. Furthermore, in the case where the wiring board is made of ceramics, and more specifically composed of stacked ceramic green sheets, an attempt to reduce the bottom thickness of the recess makes it difficult to form ceramic green sheets constituting the bottom of the recess. Furthermore, because of the influence of shrinkage resulting from firing process, the recess does not have a flat bottom; that is, the bottom of the recess has surface irregularities ranging in dimension from 0.05 mm to 0.1 mm. Therefore, in the case where a recess for mounting electronic components is formed on the lower surface of the wiring board, and the imaging element is mounted on the upper surface thereof, the imaging element stands in a tilted position. This makes it impossible to implement an imaging device for producing output of high-quality image signals. In addition, in the case where electronic components are mounted on the bottom of the recess formed at the upper surface of the wiring board, the electronic components cannot be mounted properly. This leads to improper mount, for example, the area of junction between an electrode of the electronic component and a wiring line on the wiring board is so narrow that the resistance at the junction is increased, or the electrode of the electronic component and the wiring line on the wiring board cannot be bonded to each other. In order to avoid such problems, the recess needs to be configured to have a bottom thickness large enough to prevent development of irregularities. This renders further slimming-down of the imaging device impossible.

Furthermore, in the imaging device, the distance between the light-receiving section of the imaging element and the lens is determined according to a focal length of the lens. It is therefore difficult to make the imaging device lower in profile for example by decreasing the height of the lens barrel for the shortening of the distance between the lens and the light-receiving section of the imaging element.

The invention has been devised in view of the problems associated with the conventional art as mentioned above, and accordingly an object thereof is to provide an imaging device including an imaging element and an electronic component, which can be made lower in profile and smaller in size, and is capable of producing output of high-quality image signals.

Solution to Problem

The invention provides an imaging device, including: a circuit board having a wiring line formed as part of an upper surface thereof; an electronic component mounted on the circuit board; a frame body mounted on the circuit board so as to surround the electronic component, the frame body having a plurality of connection electrodes formed on or above an upper surface thereof and a plurality of external terminals formed on or above at least one of a side surface and a lower surface thereof which are electrically connected to the connection electrodes; an imaging element having a light-receiving section located in a central portion of an upper surface thereof, the imaging element being mounted on the upper surface of the frame body so as to cover an opening of the frame body; and a lens barrel having a lens, the lens barrel being bonded to an outer periphery of the upper surface of the frame body so as to cover the imaging element.

Advantageous Effects of Invention

The imaging device of the invention includes a circuit board having a wiring line formed as part of an upper surface thereof; an electronic component mounted on the circuit board; a frame body mounted on the circuit board so as to surround the electronic component, the frame body having a plurality of connection electrodes formed on or above an upper surface thereof and a plurality of external terminals formed on or above at least one of a side surface and a lower surface thereof which are electrically connected to the connection electrodes; an imaging element having a light-receiving section located in a central portion of an upper surface thereof, the imaging element being mounted on the upper surface of the frame body so as to cover an opening of the frame body; and a lens barrel having a lens, the lens barrel being bonded to an outer periphery of the upper surface of the frame body so as to cover the imaging element. Accordingly, in this construction, in contrast to a conventional-type imaging device, there is no portion corresponding to the bottom of the recess of the wiring board. That is, breakage of the bottom of the recess that is associated with the conventional imaging device will not take place, wherefore the imaging device as a whole can be slimmed down to an extent that is equivalent to the bottom thickness of the recess. Moreover, since the imaging element is mounted on the upper surface of the frame body and the electronic component is mounted on the circuit board so as to be surrounded by the frame body, there is no need to increase the area of the frame body, as well as the area of the circuit board, for the sake of securing a space for mounting the electronic component on the upper surface of the frame body. This makes it possible to avoid an undesirable increase in area of the imaging device in a plan view, and thereby render the imaging device lower in profile and smaller in size than ever.

Moreover, the electronic component is mounted on the circuit board, and the imaging element is mounted on the upper surface of the frame body. Accordingly, at the time of mounting the electronic component and the imaging element, it never occurs that, as seen in the conventional imaging device, the imaging element is mounted in a tilted position under the influence of deformation of the bottom of the recess, and the electronic component is mounted improperly. In consequence, the imaging device becomes capable of producing output of high-quality image signals.

DESCRIPTION OF EMBODIMENTS

Now, an imaging device pursuant to the invention will be described with reference to the accompanying drawings. InFIGS. 1 to 10, reference numeral1represents a circuit board, reference numeral2represents a wiring line, reference numeral3represents an electronic component, reference numeral4represents a frame body, reference numeral4arepresents a wall, reference numeral5represents a connection electrode, reference numeral6represents an external terminal, reference numeral7represents a wiring conductor, reference numeral8represents an imaging element, reference numeral8arepresents a light-receiving section, reference numeral8brepresents a signal processing circuit, reference numeral8crepresents an electrode, reference numeral9represents a lens, reference numeral10represents a lens barrel, reference numeral11represents a connecting member, reference numeral12represents a bonding member, and reference numeral13represents a light-transmittable plate.

As in an example shown in the sectional view ofFIG. 2, the imaging device of the invention includes: a circuit board1having a wiring line2formed as part of an upper surface thereof; an electronic component3mounted on the circuit board1; a frame body4mounted on the circuit board1so as to surround the electronic component3, the frame body having a plurality of connection electrodes5formed on or above an upper surface thereof and a plurality of external terminals6formed on or above at least one of a side surface and a lower surface thereof which are electrically connected with the connection electrodes5; an imaging element8having a light-receiving section8alocated in a central portion of an upper surface thereof, the imaging element being mounted on the upper surface of the frame body4so as to cover an opening of the frame body4; and a lens barrel10having a lens9, is the lens barrel being bonded to an outer periphery of the upper surface of the frame body4so as to cover the imaging element8.

Here, the imaging element8is mounted on the upper surface of the frame body4so as to cover the opening of the frame body4via the bonding member12made of resin or the like, the bonding member being formed so as to extend throughout the outer periphery of the opening of the frame body4. Connection terminals of the imaging element8and the plurality of connection electrodes5formed on or above the upper surface of the frame body4are connected to each other via the connecting members11made of a bonding wire.

According to such an imaging device of the invention, in contrast to the conventional-type imaging device, there is no portion corresponding to the bottom of the recess of the wiring board. That is, the imaging device as a whole can be slimmed down to an extent that is equivalent to the thickness of the recess formed in the wiring board. Moreover, since the imaging element8is mounted on the upper surface of the frame body4and the electronic component3is mounted on the circuit board1so as to be surrounded by the frame body4, there is no need to increase the area of the frame body4, as well as the area of the circuit board1, for the sake of securing a space for the installation of the electronic component3on the upper surface of the frame body4. This makes it possible to avoid an undesirable increase in area of the imaging device in a plan view, and thereby render the imaging device lower in profile and smaller in size than ever.

Moreover, the electronic component3is mounted on the circuit board1, and the imaging element8is mounted on the upper surface of the frame body4. Accordingly, at the time of mounting the electronic component3and the imaging element8, it never occurs that, as seen in the conventional-type imaging device, the imaging element8is mounted in a tilted position under the influence of deformation of the bottom of the recess, and the electronic component3is mounted improperly. In consequence, the imaging device becomes capable of producing output of high-quality image signals.

In an example as shown in the top view ofFIG. 1(a) and in the sectional view ofFIG. 1(b), the frame body4has a rectangular-shaped opening, and the rectangular-shaped imaging element8is located so as to cover the opening of the frame body4. The frame body4and the imaging element8are bonded by the bonding member12. The imaging element8and the connection electrode5formed on or above the upper surface of the frame body4are electrically connected to each other by the connecting member11made of a bonding wire. Thereby, the imaging element8can be mounted on the frame body4. Moreover, the electronic component3is located on the circuit board1so as to lie inside the opening of the frame body4, and is electrically connected to the wiring line2on the circuit board. Thereby, the electronic component3can be mounted on the circuit board1.

InFIG. 2, there is shown an example of the imaging device in which the lens barrel10having the lens9is disposed on the upper surface of the frame body4of the example shown inFIGS. 1(a) and1(b).

Moreover, as in an example shown in the sectional view ofFIG. 3likeFIG. 2, it is advisable that the frame body4is configured to have a stepped upper surface to provide a shoulder which is 0.2 mm to 0.3 mm lower in level than the top and located toward the opening, and that the imaging element8is located on the opening side of the upper surface of the shoulder of the frame body4, so that it can be bonded to the upper surface of the frame body4via the bonding member14. In this case, by the connecting member11made of a bonding wire, electrical connection is established between the imaging element8and the plurality of connection electrodes5formed on or above that part of the upper surface of the frame body4which is higher in level than the shoulder part bonded with the imaging element8, whereby the imaging element8is mounted on the frame body4. Then, the lens barrel10having the lens9is located and bonded at the outer periphery of the upper surface of the frame body4. In this way, the imaging device is fabricated. In such an imaging device, there is a difference in level between the surface to which the imaging element8is bonded and the surface on which the connection electrodes5are located. Since the surface on which the connection electrodes5are located is higher in level, it follows that the bonding member12in a yet-to-be cured state is caused to flow onto the connection electrodes5, wherefore a failure of electrical connection between the imaging element8and the connection electrodes5can be prevented. This makes it possible to arrange the bonding member12and the connection electrode5close to each other, and thereby gain the advantage of being able to render the imaging device compact. Moreover, even if an electrically conductive material such for example as solder is used as the bonding member12, it is possible to prevent occurrence of electrical short-circuiting between the connection electrodes5attributable to the bonding member12.

Further, as in an example shown in the sectional view ofFIG. 4likeFIGS. 2 and 3, it is advisable that the frame body4is configured to have a stepped upper surface to provide a shoulder which is 0.2 mm to 0.3 mm lower in level than the top and located toward the opening, that the imaging element8is located on the opening side of the upper surface of the shoulder of the frame body4, so that it can be bonded to the upper surface of the frame body4via the bonding member14, and that the light-transmittable plate13is located on that part of the upper surface of the frame body4which is higher in level than the surface to which the imaging element8is bonded. In this case, by the connecting member11made of a bonding wire, electrical connection is established between the imaging element8and the plurality of connection electrodes5formed at the outer periphery of the upper surface of the frame body4to which the imaging element8is bonded, whereby the imaging element8is mounted on the frame body4. The light-receiving section8aof the imaging element8is sealed with the light-transmittable plate13, and the lens barrel10having the lens9is disposed so that the lens9is located above the light-transmittable plate13. In this way, there is obtained the imaging device in which the lens barrel10is bonded around the light-transmittable plate13. In such a case, a low-pass filter or IR cutoff filter as will hereafter be described may be formed on the light-transmittable plate13. Moreover, since the light-receiving section8aof the imaging element8and the light-transmittable plate13are sealed by the bonding member12, it is possible to protect the light-receiving section8aof the imaging device8. Further, even if changes in atmospheric pressure take place due to temperature variation in the external environment, since the space by the side of the imaging element8sealed with the light-transmittable plate13is smaller in volume capacity than the space sealed solely with the lens barrel10having the lens9, it follows that, in contrast to the case where the imaging element8is sealed solely with the lens barrel10having the lens9, the imaging element8can be protected against deformation even under a pressure resulting from a difference in atmospheric pressure caused between the sealed space and the exterior space.

Moreover, in the examples shown inFIGS. 1 to 10, a bonding wire is used as the connecting member11for establishing electrical connection between the imaging element8and the connection electrode5. Alternatively, the imaging element8and the connection electrode5may be electrically connected to each other by means of solder bonding, ultrasonic bonding using Au bump, or bonding using anisotropic conductive resin. In this case, the imaging element8and the connection electrode5are positioned in overlapping relation in a plan view. This makes it possible to reduce the area of the imaging device in a plan view, and thereby gain the advantage of being able to render the imaging device compact.

Moreover, as in examples shown inFIGS. 5 to 9, in the imaging device of the invention, it is advisable that there is provided a wall4aconfigured to pass over the mid-portion of the opening of the frame body4to divide the opening in a plan view. In this case, the frame body4is restrained from becoming deformed even under a thermal stress or mechanical stress. This makes it possible to protect the imaging element8mounted on the upper surface of the frame body4against deformation. Note that the “mid-portion” is part of the opening ranging from the opening center to a location spaced a distance of about a quarter of the opening length away from the opening edge, in a plan view.

Moreover, as in an example shown inFIG. 7(a), in the imaging device of the invention, it is advisable that the upper surface of the wall4acomes in contact with the lower surface of the imaging element8. In this case, the imaging element8mounted on the upper surface of the frame body4is restrained from becoming deformed so that it is curved convexly in a direction toward the opening, and also heat generated in the imaging element8is readily transmitted to the frame body4. This makes it possible to suppress heat-induced deformation of the light-receiving section8aof the imaging element8. At this time, the upper surface of the wall4aand the lower surface of the imaging element8may be brought into contact with each other with the bonding member12interposed therebetween. In this case, the imaging element8is restrained from becoming deformed so that it is curved convexly in a direction opposite to the opening. It is desirable to use resin containing a metal or the like having high thermal conductivity or a metal paste for the bonding member12, because the use of such a material makes it possible to facilitate transmission of heat generated in the imaging element8to the frame body4, and thereby suppress heat-induced deformation of the light-receiving section8aof the imaging element8.

Moreover, as in an example shown inFIG. 7(b), in the imaging device of the invention, it is advisable that the wall4ais positioned in non-overlapping relation with the electronic component3in a plan view and kept out of contact with the connecting member11which connects the side surface of the electronic component3with the wiring line2formed as part of the upper surface of the circuit board1. In this case, since the wall4ais situated above the connecting member11, it is possible to decrease the distance between the wiring lines2each bonded with the electronic component3arranged next to each other in a plan view, and thereby reduce the size of the imaging device in a plan view. In the case of locating the wall4abetween the connecting members11, to avoid contact with the connecting members11, the wall4amay be narrowed at its part facing the connecting member11, or the wall4amay have a notch formed at its part facing the connecting member11. This makes it possible to reduce the size of the imaging device in a plan view without the necessity of decreasing the area of the upper surface of the wall4a.

Moreover, as in examples shown inFIGS. 8 and 9, in the imaging device of the invention, it is advisable that a plurality of opening segments obtained by dividing the opening by the wall4aare each circularly-shaped, elliptically-shaped, or given a polygonal shape with its rounded corners, in, a plan view. In this case, since the opening segment is free of an angle which is susceptible to stress concentration, it is possible to suppress that a crack is developed at the angle and spreads therefrom with consequent breakage of the wall4aand the frame body4.

Moreover, as in an example shown inFIG. 10, in the imaging device of the invention, it is advisable that the imaging element8has a signal processing circuit8bwhich is located on the frame body4. In this case, heat generated in the signal processing circuit8bis readily transmitted to the frame body4, but is hardly transmitted toward the light-receiving section8a. This makes it possible to suppress heat-induced deformation of the light-receiving section8aof the imaging element8.

Moreover, as in an example shown inFIG. 11, it is preferable that the signal processing circuit8bas a whole is situated on the frame body4in a plan view. This makes it possible to facilitate transmission of heat generated in the signal processing circuit8bto the frame body4, and thereby suppress heat-induced deformation of the light-receiving section8amore effectively.

As the signal processing circuit8b, for example, there is provided a DSP (Digital Signal Processor) or the like capable of filtering on signals sent from the imaging element8for noise reduction and compensation of optical distortion.

Moreover, as in the examples shown inFIGS. 1 to 11, in the imaging device of the invention, it is advisable that, when the upper surface of the imaging element8is seen in a plan view, the electrode8cof the imaging element8is positioned in overlapping relation with the frame body4, and that electrical connection is established between the electrode8cof the imaging element8and the connection electrode5formed on or above the frame body4by a bonding wire. In this case, since the frame body4is situated below the electrode8cof the imaging element8, it is possible to join the bonding wire to the electrode8cof the imaging element8with ease of application of force to the junction.

Moreover, as in the example shown inFIG. 11, in the imaging device of the invention, it is advisable that the light-receiving section8aof the imaging element8is positioned in overlapping relation with the opening of the frame body4in a plan view. In this case, since the light-receiving section8adoes not overlap the bonding member12in a plan view, it is possible to suppress deformation of the light-receiving section8aunder a stress applied during solidification of the bonding member12.

The imaging device of the invention is fabricated in the following manner. To begin with, a circuit board1as described hereinabove is prepared.

The circuit board1is constructed by forming the wiring line2on an insulating substrate made of an insulating material such as ceramics or resin. In the case of adopting ceramics as the material for the insulating substrate, examples thereof include aluminum oxide sintered compact (alumina ceramics), aluminum nitride compact, mullite sintered compact, and glass ceramics sintered compact. On the other hand, in the case of adopting resin as the material for the insulating substrate, examples thereof include epoxy resin, polyimide resin, acrylic resin, phenol resin, polyester resin, and fluorine resin typified by tetrafluoroethylene. In addition, a material in which a matrix made of glass fiber is impregnated with resin, such as glass epoxy resin, can also be used.

In the case where the circuit board1is made of aluminum oxide sintered compact for example, its fabrication can be accomplished as follows. Firstly, suitable organic solvent and solution medium are admixed in powder of raw material such as alumina (Al2O3), silica (SiO2), calcia (CaO), and magnesia (MgO) to form a slurry. The slurry is shaped into a sheet-like form by a heretofore known technique such as the doctor blade method or the calender roll method to obtain ceramic green sheets. Subsequently, the plural ceramic green sheets are laminated on top of each other on an as needed basis while being subjected to appropriate punching. The resultant stacked body is fired at a high temperature (in the range of from about 1500° C. to 1800° C.).

On the other hand, in the case where the circuit board1is made of resin for example, its fabrication can be accomplished by means of transfer molding, injection molding, or otherwise with use of a mold capable of molding a material into a predetermined shape. Moreover, the fabrication of the circuit board can be accomplished by using a material in which a matrix made of glass fiber is impregnated with resin, such for example as glass epoxy resin. In this case, a glass fiber-made matrix is impregnated with a precursor of epoxy resin, and the resultant epoxy resin precursor is thermally cured at a predetermined temperature.

In the case where the insulating substrate of the circuit board1is made of ceramics, the wiring line2is made of metallized powder such as tungsten (W), molybdenum (Mo), manganese (Mn), silver (Ag), and copper (Cu). A conductor paste for forming the wiring line2is printed in a predetermined configuration onto the ceramic green sheets constituting the insulating substrate of the circuit board1by means of screen printing or otherwise. The conductor paste is fired together with the ceramic green sheets, whereby the wiring line2can be formed at a predetermined location on the circuit board1. Out of internal conductors, a through conductor passing through the ceramic green sheets in the thickness direction is formed by filling a through hole formed in the ceramic green sheets with a conductor paste by means of printing. The conductor paste is prepared by kneading powdery metal such as tungsten (W), molybdenum (Mo), manganese (Mn), silver (Ag), and copper (Cu) in addition to suitable solvent and binder, and adjusting the viscosity of the resultant kneaded product to the desired level. In the interest of enhancement in the strength of bonding with the insulating substrate of the circuit board1, the conductor paste may contain glass or ceramics.

Moreover, in the case where the circuit board1is made of resin, the wiring line2is made of a metal material such as copper, gold, aluminum, nickel, chromium, molybdenum, titanium, and alloys of those metals. For example, the wiring line2is formed by transfer-printing copper foil processed into a form of the wiring line2onto a resin sheet made of glass epoxy resin and then laminating the resin sheets bearing the transfer-printed copper foil on top of each other and bonding them with an adhesive. Out of internal conductors, a through conductor passing through the resin sheet in its thickness direction is formed by depositing a conductor paste on the inner surface of a through hole formed in the resin sheet by means of printing or plating, or formed by filling the through hole with the conductor paste. Alternatively, the wiring line2may be obtained by forming metal foil or metal column integrally with the resin-made insulating substrate, or obtained by depositing the above material on the insulating substrate of the circuit board1by means of sputtering, vapor deposition, plating, or otherwise.

Then, the electronic components3including an IC, a capacitor, a coil, a resistor, and so forth for processing electric signals are mounted in connection with the wiring line2on the circuit board1by the electrically conductive connecting member11such for example as solder. The mounting of the electronic component3on the circuit board1may be conducted after the mounting of the frame body4as will hereafter be described on the circuit board1, or conducted before the mounting of the frame body.

Next, the frame body4is prepared for use. The frame body4is, just like the insulating substrate of the circuit board1, made of an insulating material such as ceramics or resin. In the case of adopting ceramics as the material for the frame body4, examples thereof include aluminum oxide sintered compact (alumina ceramic), aluminum nitride sintered compact, mullite sintered compact, and glass ceramics sintered compact. On the other hand, in the case of adopting resin as the material for the frame body4, examples thereof include epoxy resin, polyimide resin, acrylic resin, phenol resin, polyester resin, and fluorine resin typified by tetrafluoroethylene. In addition, a material in which a matrix made of glass fiber is impregnated with resin, such as glass epoxy resin, can also be used.

In the case where the frame body4is made of aluminum oxide sintered compact for example, its fabrication can be accomplished by using the same material and method as adopted in the fabrication of the circuit board1. Note that the opening of the frame body4can be obtained by forming a through hole acting as the opening in the ceramic green sheets constituting the frame body4by means of punching using a die or punch, laser machining, or otherwise, and then performing firing operation. Moreover, as in the examples shown inFIGS. 3 and 4, in the case where the frame body4is configured to have a stepped upper surface to provide a shoulder which is lower in level than the top and located toward the opening, the plurality of ceramic green sheets are formed with through holes of different sizes, and these ceramic green sheets are laminated in an arrangement to allow for the formation of a shoulder in a desired shape to thereby form a ceramic green sheet stacked body.

On the other hand, in the case where the frame body4is made of resin for example, its fabrication can be accomplished in accordance with the same method as adopted in the fabrication of the circuit board1.

Moreover, in the example shown inFIG. 5, in the case where the frame body4is made of ceramics, the wall4acan be obtained by performing punching on ceramic green sheets with use of an appropriate die, or obtained by forming cutouts in the ceramic green sheets by means of laser or otherwise. In the case where the frame body4is composed of stacked ceramic green sheets, the punching operation may be conducted before or after sheet lamination. The advantage of conducting the punching operation after the sheet stacking is that the wall4acan be formed without any influence of layer-to-layer misregistration in the sheet lamination, and thus the likelihood of development of surface irregularities at the section of the wall4acan be minimized. Meanwhile, as the thickness of the frame body4is increased, deformation of the wall4ais likely to take place during the punching operation. It is therefore desirable to conduct the punching operation before the sheet lamination. In the case where the wall4ais made of resin, its formation can be accomplished by using a mold capable of molding a material into a predetermined shape.

Moreover, in the example shown inFIG. 7(a), in the case where the wall4ais made of ceramics, it is advisable to increase the thickness of the wall4aby applying a ceramic paste made of the same material as that used for the wall4ato the upper surface of the wall4a, or placing a ceramic green sheet having the same shape as that of the wall4ain a plan view on the upper surface of the wall4a, so that the upper surface of the wall comes in contact with the lower surface of the imaging element8. Instead of the aforementioned ceramic paste, a metal paste made of a material having high thermal conductivity may be used, such as tungsten, molybdenum, copper, or the like metal. In this case, heat generated in the imaging element8is readily transmitted, through the wall4a, to the frame body4. This makes it possible to suppress heat-induced deformation of the light-receiving section8aof the imaging element8. Further, in the case of repeating paste application several times, it is possible to use both the metal paste and the ceramic paste.

Moreover, in the example shown inFIG. 7(b), the wall4ais positioned in non-overlapping relation with the electronic component3in a plan view and kept out of contact with the connecting member11which connects the side surface of the electronic component3with the wiring line2on the circuit board1. In order to obtain such a structure, where the frame body4is composed of stacked ceramic green sheets, the lowermost ceramic green sheet of the ceramic green sheet stacked body is subjected to punching so that it corresponds only with the range of the frame body4. Further, in the case where the wall4ahas a notch formed at its part facing the connecting member11, the notch can be formed by removing part of the ceramic green sheets by means of laser or otherwise.

Moreover, in the example shown inFIGS. 8 and 9, each of a plurality of opening segments obtained by dividing the opening by the wall4ahas rounded corners. Such an opening segment can be formed by punching operation using an appropriate die, or by making a cutout by means of laser or otherwise.

In the case where the frame body4is made of ceramics, the wiring conductor7, the connection electrode5, and the external terminal6can be formed by using the same material and method as adopted in the formation of the wiring line2in the case where the circuit board1is made of ceramics. Moreover, the wiring conductor7can be formed in three-dimensional configuration within the frame body4by a combination of a through conductor and a conductor paste printed on ceramic green sheets on an as needed basis. This makes it possible to arrange the connection electrode5and the external terminal6in a desired positional relation.

On the other hand, in the case where the frame body4is made of resin, the wiring conductor7, the connection electrode5, and the external terminal6can be formed by using the same material and method as adopted in the formation of the wiring line2in the case where the circuit board1is made of resin. Also in this case, it is possible to arrange the connection electrode5and the external terminal6in a desired positional relation by the same technique as adopted in the case where the frame body4is made of ceramics.

On exposed surfaces to which the wiring line2, the connection electrode5, the external terminal6, and the wiring conductor7are exposed, a plating layer is deposited by a plating technique such as electrolytic plating and electroless plating. The plating layer is made of a metal which excels in corrosion resistance and in connectivity of the connecting member11, such as nickel and gold. For example, a nickel plating layer having a thickness in a range of about 1 μm to 10 μm and a gold plating layer having a thickness in a range of about 0.1 μm to 3 μm are deposited one after another on the exposed surfaces. This makes it possible to effectively suppress corrosion of the wiring line2, the connection electrode5, the external terminal6, and the wiring conductor7, as well as to strengthen the connection between the wiring line2of the circuit board1and the external terminal6of the frame body4, the bonding between the wiring line2of the circuit board1and the electronic component3, and the bonding between the connection terminal of the imaging element8and the connection electrode5.

Next, the imaging element8of CCD type or CMOS type is located on the upper surface of the frame body4so as to cover the opening of the frame body4, and is fixed to the frame body4by the bonding member12, and electrical connection is established between them by the connecting member11so as to electrically connect the connection terminal of the imaging element8with the connection electrode5of the frame body4. In the interest of preventing occurrence of electrical short-circuiting between the connection electrodes7caused by the flow of the bonding member12, the bonding member12is preferably made of non-conductive resin. However, as in the example shown inFIG. 3, in a case where the stepped surface configuration with a shoulder is provided to render the surface on which the connection electrode7is located higher in level than the surface mounting the imaging element8, solder or electrically conductive resin may be used for the bonding member12. Moreover, in a case where the imaging element8has the connection electrode located on a lower surface thereof, solder bonding, ultrasonic bonding using Au bump, or flip-chip bonding using anisotropic conductive resin may be carried out. In the case of performing flip-chip bonding using solder or Au bump, the bonding of the connection terminal of the imaging element8with the connection electrode5is strengthened, and the light-receiving section8ais preferably sealed by filling of an underfill material (not shown) in order to protect the light-receiving section8a.

Then, the lens barrel10having the lens9is prepared, and is bonded to the outer periphery of the upper surface of the frame body4so as to cover the imaging element8. According to such a structure, there is obtained the imaging device which is made smaller in size and lower in profile and is capable of producing output of high-quality image signals. The lens9, which is made of glass, resin such as epoxy resin, or the like, is attached to the lens securing member12so as to allow entry of light which has passed through the lens9through the opening of the lens securing member12on the light-receiving section8aof the imaging element8. The lens securing member12is made of resin or metal, and is fixed to the upper surface of the frame body4by an adhesive such as epoxy resin or solder, or fixed to the frame body4by a hook or the like (not shown) provided in the lens securing member12in advance, as in the example shown inFIGS. 2 to 4.

The light-transmittable plate13, which is made of crystal, glass, or resin such as epoxy resin, is bonded to the frame body4by an adhesive such as thermosetting- or ultraviolet curable-type epoxy resin or glass. For example, after ultraviolet curable-type epoxy resin is applied to the upper surface of the frame body4or the outer edge of the light-transmittable plate13by a dispensing technique, the light-transmittable plate13is emplaced on the upper surface of the frame body4. Upon ultraviolet irradiation, the adhesive is cured with consequent achievement of sealing. A filter may be formed on the light-transmittable plate13.

Exemplary of the filter to be formed on the light-transmittable plate13is a low-pass filter composed of a stack of two or three crystal plates of differing crystalline azimuth, which is capable of preventing a moiré phenomenon from occurring in an image taken by the imaging element8by exploiting the birefringent characteristics of the crystal plates. In the case of using a crystal plate for the light-transmittable plate13, the light-transmittable plate13serves also as one of the crystal plates constituting the low-pass filter.

Another exemplary of the filter to be formed on the light-transmittable plate13is an IR cutoff filter. In general, the imaging element8exhibits higher sensitivity to light in a red to infrared region than do human eyes. The IR cutoff filter cuts off light in a red to infrared wavelength range to adapt the imaging element8to the color-tone sensitivity of human eyes. The IR cutoff filter can be fabricated by forming several dozens of dielectric multilayer films alternately on the surface of the light-transmittable plate13. The dielectric multilayer film is customarily formed by alternately laminating several dozens of high-refractive-index dielectric layers made of a dielectric material having a refractive index of 1.7 or more and low-refractive-index dielectric layers made of a dielectric material having a refractive index of 1.6 or less by means of vapor deposition, sputtering, or otherwise. As the dielectric material having a refractive index of 1.7 or more, tantalum pentoxide, titanium oxide, niobium pentoxide, lanthanum oxide, and zirconium oxide are usable. As the dielectric material having a refractive index of 1.6 or less, silicon oxide, aluminum oxide, lanthanum fluoride, and magnesium fluoride are usable.

In the manner as above described, on the circuit board1is mounted the imaging device composed for example of the frame body4of about 10 mm per side, the electronic component3housed in the frame body4, the imaging element8of about 8 mm per side, and the lens barrel10having the lens9which is located above the imaging element8, the lens barrel having a height of about 5 to 10 mm.

It should be understood that the application of the invention is not limited to the specific embodiments described heretofore, and that many modifications and variations of the invention are possible within the spirit and scope of the invention. For example, each of the opening segments obtained by dividing the opening by the wall in the examples shown inFIGS. 5,8, and9may be designed in honeycomb configuration. By adopting the honeycomb configuration, it is possible to increase the proportion of opening part per unit area in a plan view while enhancing the strength of the wall4a, and thereby gain the advantage of being able to impart compactness and high strength to the imaging device.

REFERENCE SIGNS LIST