Printed circuit board and electronic device

A printed circuit board includes an electronic component including a first land, a printed wiring board including a resist portion and a second land, and a connecting portion interconnecting the first land and the second land. An opening larger than the first land in plan view from the electronic component side is defined in the resist portion. In plan view from the electronic component side, the first land is disposed inside the opening, the second land including a body portion disposed inside the opening and a protruding portion protruding from the body portion, the body portion being disposed further on an inside than an outer edge of the first land, and at least part of the protruding portion protruding further to an outside than the first land.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a technique of interconnecting an electronic component and a printed wiring board.

Description of the Related Art

An electronic device such as a digital camera serving as an example of an image pickup apparatus or a smartphone including a camera serving as an image pickup apparatus includes a printed circuit board including an electronic component such as an image sensor and a printed wiring board on which the electronic component is mounted.

Accompanied by miniaturization of electronic device, the electronic component has been also miniaturized. A land of the electronic component and a land of the printed wiring board are interconnected by a bump containing solder and serving as an example of a connecting portion, and the bump is also miniaturized in accordance with the miniaturization of electronic component. Accompanied by the miniaturization of bump, a problem of connection failure of the bump has arisen. Japanese Patent Laid-Open No. 9-219583 discloses forming a shape of a pad, that is, a land of a printed wiring board in a concavo-convex shape and determining that an open failure has occurred when an X-ray transmission image of the bump has a circular shape.

However, even in the case where the land is formed in a concavo-convex shape as disclosed in Japanese Patent Laid-Open No. 9-219583, in some cases, the bump protrudes from the land of the printed wiring board, thus the X-ray transmission image of the bump has the same shape as the shape of an open failure, and therefore it is difficult to determine whether or not an open failure has occurred.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a printed circuit board includes an electronic component including a first land, a printed wiring board including a resist portion and a second land, and a connecting portion interconnecting the first land and the second land. An opening larger than the first land in plan view from the electronic component side is defined in the resist portion. In plan view from the electronic component side, the first land is disposed inside the opening, the second land including a body portion disposed inside the opening and a protruding portion protruding from the body portion, the body portion being disposed further on an inside than an outer edge of the first land, and at least part of the protruding portion protruding further to an outside than the first land.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described in detail below with reference to drawings.

First Exemplary Embodiment

FIG.1is a section view of a printed circuit board300according to the first exemplary embodiment. The printed circuit board300includes an electronic component100and a printed wiring board200on which the electronic component100is mounted. The electronic component100is a package of a land grid array: LGA. To be noted, the electronic component100may alternatively be a package of a ball grid array: BGA. The electronic component100includes a semiconductor element101and a package substrate102on which the semiconductor element101is mounted. The package substrate102includes an insulating substrate103and lands130serving as a plurality of first lands disposed on a main surface111of the insulating substrate103. The semiconductor element101is disposed on a surface112of the insulating substrate103opposite to the main surface111. The lands130are electrodes formed from conductive metal such as copper, and, for example, are each a signal electrode, a power source electrode, a ground electrode, or a dummy electrode. The main surface111is parallel to an X-Y plane defined by an X direction and a Y direction. In addition, an out-of-plane direction perpendicular to the main surface111is defined as a Z direction. For example, the insulating substrate103is a ceramic substrate formed from a ceramic such as alumina.

The printed wiring board200includes an insulating substrate202and lands230serving as a plurality of second lands disposed on a main surface211of the insulating substrate202. The lands230are electrodes formed from conductive metal such as copper, and, for example, are each a signal electrode, a power source electrode, a ground electrode, or a dummy electrode. The insulating substrate202is formed from an insulating material such as epoxy resin.

A solder resist film240serving as an example of a resist portion is provided on the main surface211. In the solder resist film240, openings550are defined at positions corresponding to the lands230.

The lands130and the lands230are electrically and mechanically connected to each other by connecting portions400containing solder. The lands230are connected to the lands130by the connecting portions400through the openings550of the solder resist film240. In plan view from the Z direction, the connecting portions400are surrounded by resin portions450serving as underfill. The resin portions450is mainly formed from a cured product of a curable resin. For example, the curable resin is a thermosetting resin. In the present exemplary embodiment, the plurality of connecting portions400are surrounded by one integrated resin portion450. To be noted, although it is preferable that the plurality of connecting portions400are surrounded by the one integrated resin portion450, the configuration is not limited to this, and the plurality of connecting portions400may be surrounded by a plurality of separate resin portions.

FIG.2Ais a plan view of the electronic component100as viewed from the main surface111side.FIG.2Bis a plan view of the printed wiring board200as viewed from the main surface211side. To be noted, a section view of the printed circuit board300illustrated inFIG.1is a section view taken along a line I-I ofFIG.2B. As illustrated inFIG.2A, the plurality of lands130are arranged with intervals therebetween in a grid shape, that is, a square lattice shape. As illustrated inFIG.2B, the plurality of lands230are arranged with intervals therebetween in a grid shape, that is, a square lattice shape. The lands230each include a body portion231serving as a main body of the land230, and a protruding portion232protruding from the body portion231. Although most part of the main surface211of the insulating substrate202is covered by the solder resist film240, the solder resist film240is provided with the openings550, and the lands230are disposed in the openings550.

A method for manufacturing the printed circuit board300and a method for inspecting the manufactured printed circuit board300will be described.FIGS.3A to3CandFIGS.4A to4Care each an explanatory diagram of each step of the method for manufacturing the printed circuit board300illustrated inFIG.1, andFIG.5is an explanatory diagram of a step of the method for inspecting the printed circuit board300.

In step S1, the printed wiring board200is prepared as illustrated inFIG.3A. To be noted, although illustration is omitted herein, the electronic component100is also prepared on an unillustrated mounter.

Next, in step S2, a paste P is disposed on one or both of the lands130illustrated inFIG.2Aand the lands230illustrated inFIG.2B. In the present exemplary embodiment, the paste P is disposed on the lands230as illustrated inFIG.3B.

The paste P is a solder paste containing solder powder. In the present exemplary embodiment, the paste P further contains an uncured thermosetting resin. The thermosetting resin is preferably a thermosetting epoxy resin, and particularly preferably bisphenol-A epoxy resin. The paste P may further contain a flux component required for soldering.

In step S2, the paste P is supplied to the printed wiring board200by screen printing or using a dispenser. To be noted, the solder paste P may be supplied to cover the entirety of the body portions231of the lands230illustrated inFIG.2Bor supplied to cover parts of the body portions231. In the present exemplary embodiment, the paste P is supplied to the printed wiring board200such that the entirety of the openings550is filled with the paste P.

Next, in step S3, the electronic component100is placed on the printed wiring board200such that each paste P interposed between the land130and the land230as illustrated inFIG.3C. In the present exemplary embodiment, in step S3, the electronic component100is placed on the printed wiring board200by using the unillustrated mounter. At this time, the electronic component100is aligned with and placed on the printed wiring board200such that the lands130are opposed to the lands230.

Next, in step S4, the printed wiring board200and the electronic component100are conveyed to a reflow furnace1000in a state in which the electronic component100is placed on the printed wiring board200as illustrated inFIG.4A. Then, in step S5-1illustrated inFIG.4Band step S5-2illustrated inFIG.4C, the paste P is heated while adjusting the temperature inside the reflow furnace1000, that is, the heating temperature, and thus the electronic component100and the printed wiring board200are bonded to each other.

First, step S5-1illustrated inFIG.4Bwill be described. In step S5-1, the temperature inside the reflow furnace1000is adjusted to a first temperature T1equal to or higher than the melting point of the solder powder contained in the paste P. As a result of this, the solder powder of the pastes P is melted, and the paste P is separated into a molten solder401and an uncured thermosetting resin451. Specifically, the molten solder401aggregates, and thus the thermosetting resin451moves to the vicinity of the molten solder401. Although the first temperature T1is preferably constant over time, the first temperature T1may change over time.

In step S5-1, the paste P is separated into the aggregated molten solder401and the uncured thermosetting resin451having flowed to the vicinity of the molten solder401. At this time, the surface area of the uncured thermosetting resin451is smaller than in the paste state, and thus the viscosity thereof apparently decreases and the fluidity thereof increases. The thermosetting resin451whose fluidity has increased flows to narrow gaps by a capillary phenomenon.

Then, in step S5-2illustrated inFIG.4C, the temperature inside the reflow furnace1000is adjusted to a second temperature T2lower than the melting point of the solder powder, and thus the molten solder401is solidified. That is, T2<T1holds. As a result of this, the connecting portions400interconnecting the lands130and the lands230are formed.

The second temperature T2is also a temperature at which the thermosetting resin451is cured, and the temperature inside the reflow furnace1000is kept at the second temperature T2for a period equal to or longer than a predetermined time required for the thermosetting resin451to be cured. As a result of this, the thermosetting resin451is gradually cured, and thus the resin portions450illustrated inFIG.1are formed. Although the second temperature T2is preferably constant over time, the second temperature T2may change over time.

The connecting portions400, more specifically contact portions between the connecting portions400and the lands130and contact portions between the connecting portions400and the lands230are reinforced by the resin portions450illustrated inFIG.1, and thus the reliability of connection by the connecting portions400is improved. In addition, the resin portions450connect the electronic component100to the solder resist film240of the printed wiring board200.

To be noted, although a case where step S5-1illustrated inFIG.4Band step S5-2illustrated inFIG.4Care continuously performed in the same reflow furnace1000has been described, the configuration is not limited to this. In the case where the size of the reflow furnace1000is small and sufficient time for step S5-2cannot be secured, an intermediate product may be moved to an unillustrated heating furnace after the heating in the reflow furnace1000of step S5-1, and then the thermosetting resin451may be heated to the second temperature T2to cure.

By manufacturing the printed circuit board300by using the paste P containing a thermosetting resin, solder bonding and formation of underfill can be simultaneously performed by only performing the heating steps S5-1and S5-2. That is, although the paste P may be a paste that contains solder powder but does not contain a thermosetting resin, a step for injecting an underfill material can be omitted by using the paste P containing a thermosetting resin in the present exemplary embodiment. Therefore, the printed circuit board300can be easily manufactured.

Next, in an image capturing step S6, an image of the manufactured printed circuit board300is captured from the Z direction by an X-ray image pickup apparatus900as illustrated inFIG.5. Whether the quality of the connecting portions400is good or not is determined by visually observing an X-ray transmission image obtained by this image capturing by human eyes or subjecting the X-ray transmission image to image analysis by a computer. This serves as an inspection step. In the X-ray transmission image, the connecting portions400containing solder have different contrast from an insulating material, and therefore a person visually observing the X-ray transmission image displayed on a monitor or the like can easily recognize the connecting portions400.

FIG.6Ais an enlarged plan view of a land230and the vicinity of the land230, which is a part of the printed wiring board200according to the first exemplary embodiment. To be noted, inFIG.6A, a land130of the electronic component100is indicated by a broken line for the sake of convenience of description.

The land230includes a body portion231, and protruding portions232protruding from the body portion231. Although the number of protruding portions232included in the land230may be one or two, the number of protruding portions232included in the land230is preferably 3 or more, and is 4 in the present exemplary embodiment. The protruding portions232are formed to extend radially from the outer periphery of the body portion231in plan view from the Z direction. The four protruding portions232are arranged at approximately even intervals, that is, at intervals of 90°, in the peripheral direction of the body portion231. In plan view from the Z direction, the entirety of the body portion231is formed in an opening550of the solder resist film240, and part or entirety of each protruding portion232is formed in the opening550of the solder resist film240. In the present exemplary embodiment, part of each protruding portion232is formed in the opening550. The area of the body portion231in the opening550is preferably larger than the total area of the plurality of protruding portions232, and the body portion231serves as a main part of solder bonding.

The lands130of the electronic component100are formed in circular shapes in plan view from the Z direction. The body portions231of the lands230are formed in circular shapes in plan view from the Z direction. The openings550of the solder resist film240are formed in circular shapes in plan view from the Z direction. The openings550of the solder resist film240are defined to be larger than the lands130in plan view from the Z direction.

The body portions231are formed to be smaller than the lands130in plan view from the Z direction. Therefore, the molten solder401illustrated inFIG.4Balso wet-spreads toward the outside of the body portions231. In addition, side walls of the openings550of the solder resist film240also have a role of holding back the molten solder401. Excessive wet-spreading of the molten solder401is suppressed by the side walls of the openings550.

By adjusting the areas of the body portions231, a contracting force of reducing the distance between the electronic component100and the printed wiring board200and a resistive force caused by surface tension of a portion of the molten solder401in contact with the insulating material of the insulating substrate202and the solder resist film240are generated in the molten solder401. The height of the molten solder401in the Z direction is controlled by the balance between these forces. In the case where the electronic component100is an LGA package, particularly in the case where the printed circuit board300is manufactured by using the solder paste P containing a thermosetting resin, the amount of solder is smaller than in the case of a BGA package, and therefore controlling the height of the molten solder401in the Z direction is important. Therefore, in the present exemplary embodiment, the body portions231of the lands230are formed to be smaller than the lands130. However, in a situation in which the molten solder protrudes from the lands of the printed wiring board, merely forming the lands of the printed wiring board in concavo-convex shapes does not prevent almost all the connecting portions from appearing as circular shapes in the X-ray transmission image.

Therefore, in the present exemplary embodiment, the protruding portions232are formed to protrude further to the outside than the lands130in plan view from the Z direction. The shapes of the connecting portions400are controlled by the protruding portions232. In the case where an open failure has not occurred, that is, in the case where the connecting state of the connecting portions400is good, the connecting portions400wet-spread along the protruding portions232having high wettability. That is, in the openings550, the connecting portions400are formed to wet-spread on the body portions231, on the plurality of protruding portions232, and on portions between adjacent protruding portions among the plurality of protruding portions232. Solder more easily wet-spreads on the protruding portions232than on the portions of the main surface211of the insulating substrate202between the adjacent protruding portions232. Therefore, if the amount of solder is optimum, the connecting portions400have shapes corresponding to the protruding portions232that are different from circular shapes in plan view.

The lands130also appear as shades in the X-ray transmission image. Therefore, in the case where the protruding portions232protrude further to the outside than the lands130, the connecting portions400appear as images larger than and having different shapes from the lands130in the X-ray transmission image unless an open failure has occurred in the connecting portions400. From the viewpoint of controlling the shapes of the connecting portions400, the number of protruding portions232of each land230is preferably 3 or more such that a user can easily identify the shapes of the connecting portions400in the X-ray transmission image. By setting the number of protruding portions232of each land230to 3 or more, the connecting portions400becomes more likely to appear as approximately polygonal shapes, which can be easily identified by the user, in the X-ray transmission image. Particularly, the number of protruding portions232of each land230is preferably 4 to 6. By setting the number of protruding portions232of each land230to 4 to 6, the connecting portions400becomes more likely to appear as approximately quadrangular shapes, approximately pentagonal shapes, or approximately hexagonal shapes, which can be particularly easily identified by the user among the approximately polygonal shapes, in the X-ray transmission image. The number of the protruding portions232of each land230is particularly preferably 4 among 4 to 6 because the connecting portions400are likely to appear as approximately quadrangular shapes, which can be particularly easily identified by the user, in the X-ray transmission image.

The maximum width W1of each protruding portion232in a width direction D12of the protruding portion232perpendicular to a protruding direction D11thereof may be constant in the protruding direction D11, or may be gradually smaller at a position closer to a distal end233thereof in the protruding direction D11. The minimum width of each protruding portion232depends on the type and supply amount of the paste, and surface roughness of, material of the lands of, and manufacturing process of the printed wiring board and of the electronic component, and may be of any value as long as the molten solder401illustrated inFIG.4Bcan wet-spread along the protruding portions232. Specifically, from the viewpoint of controlling the shapes of the connecting portions400, the maximum width W1of each protruding portion232is preferably 10 μM or more such that the molten solder easily wet-spreads in the protruding direction D11. This is because it is difficult for the molten solder401to wet-spread along the protruding portions232in the case where the maximum width W1is smaller than 10 μm. In the case where the number of protruding portions232of each land230is 4 to 6, the maximum width W1is preferably 50 μm to 300 μm from the viewpoint of controlling the shapes of the connecting portions400.

The distal end233of each protruding portion232is preferably covered by the solder resist film240. This prevents the protruding portions232, that is, the lands230from peeling off from the main surface211of the insulating substrate202, and thus improves the reliability of connection by the connecting portions400.

FIG.6Bis an explanatory diagram in which part of the electronic component100is omitted in the printed circuit board300.FIG.7is an explanatory diagram of the inspection step using the X-ray transmission image according to the first exemplary embodiment.FIG.7illustrates patterns (1) to (7) of X-ray transmission images, sections taken along lines VIIA-VIIA and VIIB-VIIB ofFIG.6B, and results of evaluation of the patterns (1) to (7). An evaluation result “A” corresponds to “Very good”, an evaluation result “B” corresponds to “Good”, and neither of these indicates an open failure. An evaluation result “C” indicates that “there is a possibility of open failure”, and indicates that a conduction test to determine whether an open failure has occurred is needed.

In step S5-1illustrated inFIG.4B, the molten solder401is interposed between the lands130of the electronic component100and the lands230of the printed wiring board200, and spreads in a direction parallel to the main surface211. Since the lands130and230are formed from metal, the lands130and230have higher wettability with solder than the surface of the solder resist film240formed from resin, the surface of the insulating substrate of the printed wiring board200, and the surface of the insulating substrate of the electronic component100. The aggregated molten solder401first wet-spreads on the lands130and the body portions231of the lands230, which have high wettability. In the case where the molten solder401is solidified in this state, since the lands130are larger than the body portions231of the lands230, the connecting portions400appear as circular shapes having the same sizes as the lands130in the X-ray transmission image, and an X-ray transmission image like the pattern (2) ofFIG.7is obtained. To be noted, also in the case where an open failure has occurred in the connecting portions400, the connecting portions400appear as circular shapes having the same sizes as the lands130in the X-ray transmission image, and an X-ray transmission image like the pattern (1) ofFIG.7is obtained. In both cases of the patterns (1) and (2), the part of the protruding portions232protruding further to the outside than the lands130in the openings550of the solder resist film240appear in a different contrast from the insulating material therearound in the X-ray transmission image. That is, the protruding portions232have a different contrast from the insulating material therearound, and therefore can be distinguished from the insulating material in the X-ray transmission image. To be noted, the part of the protruding portions232covered by the solder resist film240has an unclear contrast, and therefore can be distinguished from a part positioned in the openings550in the X-ray transmission image. In a case corresponding to either one of the patterns (1) and (2), the evaluation result is “C”.

In the case where the molten solder401is not cooled enough and is not solidified in the state of the pattern (2), the molten solder401further wet-spreads toward the edges of the openings550of the solder resist film240along the protruding portions232of the lands230. The side walls of the solder resist film240at the edges of the openings550having a height corresponding to the thickness of the solder resist film240serve as dams, and the low wettability of the solder resist film240with solder and the surface tension of solder suppress wet-spreading of the molten solder401. At the same time, since the body portions231are smaller than the lands130, the molten solder401also wet-spreads on the portions between the adjacent protruding portions232. As a result of this, the connecting portions400each appear as an approximately quadrangular shape like the pattern (3) ofFIG.7different from the patterns (1) and (2) in the X-ray transmission image. Since this shape is the most identifiable, the connecting state of the connecting portions400is good in this shape, and the height of the connecting portions400is appropriate in this shape, the evaluation result is “A” in this case.

In the case where the molten solder401is not cooled enough and is not solidified in the state of the pattern (3), the molten solder401further wet-spreads, the distance between the electronic component100and the printed wiring board200in the Z direction is reduced, and the molten solder401is squished. In the case where the molten solder401wet-spreads to the edges of the openings550of the solder resist film240and is cooled to solidify, the connecting portions400each appear as a shape like the pattern (4) or (5) in the X-ray transmission image. The connecting state of the connecting portions400is also good in this case, and the evaluation result is “A”.

In the case where the molten solder401is not cooled enough and is not solidified in the state of the pattern (5), the molten solder401further wet-spreads, and the distance between the electronic component100and the printed wiring board200in the Z direction is further reduced. The connecting portions400each appear as circular shapes having the same size as the openings550of the solder resist film240like the pattern (6) in the X-ray transmission image. In this case, the evaluation result is “B”.

In the case where the paste P is supplied too much, the molten solder401goes over the solder resist film240, and the connecting portions400each appear as an abnormal shape like the pattern (7). To be noted, in the case of the pattern (7), no short circuit failure with adjacent connecting portion has occurred. In this case, the evaluation result is “B”. Whether or not a short circuit failure has occurred can be easily determined from the X-ray transmission image.

In the case of the pattern (3), (4), or (5), it can be determined that the solder has wet-spread on the lands130and230, and therefore it can be easily determined that the bonding state of the solder is good. In addition, in the case where the solder protrudes out of the openings550to have an abnormal shape as in the pattern (7), the printed circuit board300can be determined as a good product as long as a short circuit with an adjacent connecting portion400has not occurred. However, it can be determined that there is a higher risk for a short circuit, and therefore taking measures such as reconsidering the process conditions in consideration of whether the pattern (7) continuously occurs at the same position in a different lot or the occurrence of the pattern (7) is just temporary also becomes possible. As a cause of the shape of a connecting portion400becoming like the pattern (7), excessive supply of the solder paste P, warpage of the electronic component100or the printed wiring board200, and the like can be considered, and optimum measures may be taken appropriately depending on the phenomenon.

In addition, there is also a case where the materials of the lands130and the lands230are different and the lands130have higher wettability with solder, and a case where the lands130and the lands230are formed from the same material but the wettability of the lands230with solder is degraded by some kind of contaminating matter attaching to the lands230. In these cases, the molten solder401is attracted to the lands130, and an open failure in which the distance between the electronic component100and the printed wiring board200is large and the solder is separated from the lands230occurs. In the case of the pattern (1) or (2), whether or not an open failure has occurred may be determined by an electrical conduction test. To be noted, even if conduction is confirmed as a result of the electrical conduction test, there is still a possibility that disconnection occurs due to deterioration over time. In both cases of the patterns (1) and (2), measures such as reconsidering the process conditions can be taken by checking the state of the lands.

As described above, according to the present exemplary embodiment, which of the patterns (1) to (7) the connecting portions400correspond to can be determined from the X-ray transmission image, and therefore the connecting state of the connecting portions400, that is, whether or not an open failure has occurred can be easily determined. Therefore, the printed circuit board300having high reliability of connection by the connecting portions400can be obtained.

Modification Examples

FIGS.8A to8Fare each an enlarged plan view of a land and the vicinity thereof, which are a part of a printed wiring board of a modification example. Although the shape of the body portion231of each land230in plan view is preferably a circular shape, the shape is not limited to this, and may be, for example, a quadrangular shape as illustrated inFIGS.8A and8B. In addition, although the shape of each opening550of the solder resist film240in plan view is preferably a circular shape, the shape is not limited to this, and may be, for example, a quadrangular shape as illustrated inFIG.8C. In addition, although the number of protruding portions232protruding from each body portion231is preferably 4, the number is not limited to this, and may be, for example, 3 as illustrated inFIG.8D, or5as illustrated inFIG.8E. In addition, although it is preferable that the distal end233of each protruding portion232is covered by the solder resist film240, the configuration is not limited to this, and the distal end233does not have to be covered by the solder resist film240as illustrated inFIG.8F. In the case where the distal end233is not covered by the solder resist film240, the protruding portion232preferably extends to the edge of the opening550of the solder resist film240. To be noted, the shape of the body portion231of each land230and the shape of each opening550of the solder resist film240are not limited to the shapes exemplified above. In addition, although illustration is omitted herein, the shape of each land130in plan view is neither limited to a circular shape, and may be a quadrangular shape or a different shape.

In any of these cases, the body portion of a second land is disposed inside an opening provided in a resist portion and further on the inside than an outer edge of a first land in plan view from the Z direction. Further, at least part of the protruding portion protrudes further to the outside than the outer edge of the first land in plan view from the Z direction.

Second Exemplary Embodiment

FIG.9is an explanatory diagram of a digital camera1500that is an image pickup apparatus serving as an example of an electronic device according to a second exemplary embodiment. The digital camera1500that is an image pickup apparatus is a digital camera of a lens-replacing type, and includes a camera body2000. A lens barrel3000is attachable to and detachable from the camera body2000. The camera body2000includes a casing2001, an image pickup unit300A that is a printed circuit board, and an image processing device2240. The image pickup unit300A and the image processing device2240are disposed inside the casing2001. The camera body2000includes a liquid crystal display2250that is fixed to the casing2001in a state of being exposed to the outside of the casing2001. The image pickup unit300A includes an image sensor100A serving as an example of an electronic component, and a printed wiring board200A on which the image sensor100A is mounted.

The lens barrel3000includes a casing3001and an imaging optical system3100that is disposed inside the casing3001and focuses an optical image on the image sensor100A when the casing3001, that is, the lens barrel3000is attached to the casing2001. The imaging optical system3100includes a plurality of lens.

The casing3001includes a lens side mount3010in which an opening is defined, and the casing2001includes a camera side mount2010in which an opening is defined. The lens barrel3000, that is, the casing3001, is attached to the camera body2000, that is, the casing2001, by engaging the lens side mount3010with the camera side mount2010. Light traveling in an optical axis direction L of the imaging optical system3100is guided to the inside of the casing2001through the opening of the lens side mount3010of the casing3001and the opening of the camera side mount2010of the casing2001. In the casing2001, a mirror2220, a shutter2230, and so forth are provided along the optical axis direction L in front of the image sensor100A in the optical axis direction L.

The image sensor100A is, for example, a complementary metal oxide semiconductor: CMOS image sensor or a charge coupled device: CCD image sensor. The image sensor100A has a function of converting incident light into an electric signal. The image processing device2240is, for example, a digital signal processor. The image processing device2240has a function of obtaining an electric signal from the image sensor100A, correcting the obtained electric signal, and generating image data.

FIG.10is a section view of the image pickup unit300A according to the second exemplary embodiment. The image sensor100A serving as an electronic component is an LGA package. To be noted, the image sensor100A may alternatively be a BGA package. The image sensor100A includes a sensor element101A serving as a semiconductor element and a package substrate102A on which the sensor element101A is mounted. The package substrate102A includes an insulating substrate103A and lands130A and130B serving as a plurality of first lands disposed on a main surface111A of the insulating substrate103A. The sensor element101A is disposed on a surface112A of the insulating substrate103A opposite to the main surface111A. A glass104A is disposed on the surface112A side of the insulating substrate103A such that the glass104A is not in contact with the sensor element101A, and the sensor element101A is disposed in a hollow portion surrounded by the glass104A and the insulating substrate103A. The lands130A and130B are electrodes formed from conductive metal such as copper, and, for example, are each a signal electrode, a power source electrode, a ground electrode, or a dummy electrode. The main surface111A is parallel to the X-Y plane defined by the X direction and the Y direction. In addition, an out-of-plane direction perpendicular to the main surface111A is defined as the Z direction. For example, the insulating substrate103A is a ceramic substrate formed from a ceramic such as alumina.

The printed wiring board200A includes an insulating substrate202A and lands230A and230B serving as a plurality of second lands disposed on a main surface211A of the insulating substrate202A. The lands230A and230B are electrodes formed from conductive metal such as copper, and, for example, are each a signal electrode, a power source electrode, a ground electrode, or a dummy electrode. The insulating substrate202A is formed from an insulating material such as epoxy resin.

A solder resist film240A serving as an example of a resist portion is provided on the main surface211A. In the solder resist film240A, openings550A are defined at positions corresponding to the lands230A, and openings550B are defined at positions corresponding to the lands230B.

The lands130A and lands230A are electrically and mechanically connected to each other by connecting portions400A containing solder. The lands230A are connected to the lands130A by the connecting portions400A through the openings550A of the solder resist film240A. The lands130B and lands230B are electrically and mechanically connected to each other by connecting portions400B containing solder. The lands230B are connected to the lands130B by the connecting portions400B through the openings550B of the solder resist film240A. In plan view from the Z direction, the connecting portions400A and400B are surrounded by resin portion450A serving as underfill. The resin portions450A is mainly formed from a cured product of a curable resin. For example, the curable resin is a thermosetting resin. In the present exemplary embodiment, the plurality of connecting portions400A and400B are surrounded by one integrated resin portion450A. To be noted, although it is preferable that the plurality of connecting portions400A and400B are surrounded by the one integrated resin portion450A in plan view from the Z direction, the configuration is not limited to this, and the plurality of connecting portions400A and400B may be surrounded by a plurality of separate resin portions.

FIG.11Ais a plan view of the image sensor100A as viewed from the main surface111A side.FIG.11Bis a plan view of the printed wiring board200A as viewed from the main surface211A side. To be noted, a section view of the image pickup unit300A illustrated inFIG.10is a section view taken along a line XA-XA ofFIG.11B. As illustrated inFIG.11A, the plurality of lands130A and130B are arranged with intervals therebetween in a grid shape, that is, a square lattice shape. Among the plurality of lands130A and130B arranged in a lattice shape, the lands130B are positioned at corner portions of the insulating substrate103A. The lands130B are formed to be larger than the lands130A to enhance the strength of the connecting portions400B where stress is concentrated.

As illustrated inFIG.11B, the plurality of lands230A and230B are arranged with intervals therebetween in a grid shape, that is, a square lattice shape. Among the plurality of lands230A and230B arranged in a lattice shape, the lands230B are positioned at corner portions of the insulating substrate202A. The lands230B are formed to be larger than the lands230A to enhance the strength of the connecting portions400B where stress is concentrated. Whereas most part of the main surface211A of the insulating substrate202A is covered by the solder resist film240A, some part of the main surface211A is present in the openings550A and550B provided in the solder resist film240A.

The method for manufacturing the image pickup unit300A serving as a printed circuit board and the inspection method for the image pickup unit300A are similar to the methods for manufacturing and inspecting the printed circuit board according to the first exemplary embodiment, and therefore the description thereof will be omitted.

FIG.12Ais an enlarged plan view of a land230A and the vicinity of the land230A, which are a part of the printed wiring board200A according to the second exemplary embodiment. To be noted, inFIG.12A, a land130A of the image sensor100A is indicated by a broken line for the sake of convenience of description.

The land230A includes a body portion231A, and protruding portions232A protruding from the body portion231A. Although the number of protruding portions232A included in the land230A may be one or two, the number of protruding portions232included in the land230A is preferably 3 or more, and is 4 in the present exemplary embodiment. The protruding portions232A are formed to extend radially from the outer periphery of the body portion231A in plan view from the Z direction. The four protruding portions232A are arranged at approximately even intervals, that is, at intervals of 90°, in the peripheral direction of the body portion231A. The entirety of the body portion231A is formed in an opening550A of the solder resist film240A, and part or entirety of each protruding portion232A is formed in the opening550A of the solder resist film240A. In the present exemplary embodiment, part of each protruding portion232A is formed in the opening550A. The area of the body portion231A in the opening550A is preferably larger than the total area of the plurality of protruding portions232A, and the body portion231A serves as a main part of solder bonding.

The lands130A are formed in circular shapes in plan view from the Z direction. The body portions231A of the lands230A are formed in circular shapes in plan view from the Z direction. The openings550A of the solder resist film240A are formed in circular shapes in plan view from the Z direction. The openings550A of the solder resist film240A are defined to be larger than the lands130A in plan view from the Z direction.

The body portions231A are formed to be smaller than the lands130A in plan view from the Z direction. Therefore, the molten solder401illustrated inFIG.4Aalso wet-spreads toward the outside of the body portions231A. In addition, side walls of the openings550A of the solder resist film240A also have a role of holding back the molten solder401. Excessive wet-spreading of the molten solder401is suppressed by the side walls of the openings550A.

The protruding portions232A are formed to protrude further to the outside than the lands130A in plan view from the Z direction. The shapes of the connecting portions400A are controlled by the protruding portions232A. In the case where an open failure has not occurred, that is, in the case where the connecting state of the connecting portions400A is good, the connecting portions400A wet-spread along the protruding portions232A having high wettability. That is, in the openings550A, the connecting portions400A are formed to wet-spread on the body portions231A, on the plurality of protruding portions232A, and on portions between adjacent protruding portions among the plurality of protruding portions232A. Solder more easily wet-spreads on the protruding portions232A than on the portions of the main surface211A of the insulating substrate202A between the pairs of two adjacent protruding portions232A. Therefore, if the amount of solder is optimum, the connecting portions400A have shapes corresponding to the protruding portions232A that are different from circular shapes in plan view.

The lands130A also appear as shades in the X-ray transmission image. Therefore, in the case where the protruding portions232A protrude further to the outside than the lands130A, the connecting portions400A appear as images larger than and having different shapes from the lands130A unless an open failure has occurred in the connecting portions400A. From the viewpoint of controlling the shapes of the connecting portions400A, the number of protruding portions232A of each land230A is preferably 3 or more such that a user can easily identify the shape of each connecting portion400A in the X-ray transmission image. By setting the number of protruding portions232A of each land230A to 3 or more, the connecting portions400A is more likely to appear as approximately polygonal shapes, which can be easily identified by the user, in the X-ray transmission image. Particularly, the number of protruding portions232A of each land230A is preferably 4 to 6. By setting the number of protruding portions232A of each land230A to 4 to 6, the connecting portions400A becomes more likely to appear as approximately quadrangular shapes, approximately pentagonal shapes, or approximately hexagonal shapes, which can be particularly easily identified by the user among the approximately polygonal shapes, in the X-ray transmission image. The number of the protruding portions232A of each land230A is particularly preferably 4 among 4 to 6 because the connecting portions400A are likely to appear as approximately quadrangular shapes, which can be particularly easily identified by the user, in the X-ray transmission image.

The maximum width W2of each protruding portion232A in a width direction D22of the protruding portion232A perpendicular to a protruding direction D21thereof may be constant in the protruding direction D21, or may be gradually smaller at a position closer to a distal end233A thereof in the protruding direction D21. The minimum width of each protruding portion232A depends on the type and supply amount of the paste, and surface roughness of, material of the lands of, and manufacturing process of the printed wiring board and of the electronic component, and may be of any value as long as the molten solder401illustrated inFIG.4Bcan wet-spread along the protruding portions232A. Specifically, from the viewpoint of controlling the shapes of the connecting portions400A, the maximum width W2of each protruding portion232A is preferably 10 μm or more such that the molten solder401easily wet-spreads in the protruding direction D21. This is because it is difficult for the molten solder401to wet-spread along the protruding portions232A in the case where the maximum width W2is smaller than 10 μm. In the case where the number of protruding portions232A of each land230A is 4 to 6, the maximum width W2is preferably 50 μm to 300 μm from the viewpoint of controlling the shapes of the connecting portions400A.

The distal end233A of each protruding portion232A is preferably covered by the solder resist film240A. This prevents the protruding portions232A, that is, the lands230A from peeling off from the main surface211A of the insulating substrate202A, and thus improves the reliability of connection by the connecting portions400A.

FIG.12Bis an enlarged plan view of a land230B and the vicinity of the land230B of the printed wiring board200A according to the second exemplary embodiment. To be noted, inFIG.12B, a land130B of the image sensor100A is indicated by a broken line for the sake of convenience of description. The land230B includes a body portion231B and protruding portions232B, and has approximately the same structure as the land230A except for the size thereof. The body portion231B and the land130B each have a circular shape in plan view. The openings550B of the solder resist film240A each have an approximately quadrangular shape in plan view.

FIG.13is an explanatory diagram of an inspection step using an X-ray transmission image according to the second exemplary embodiment.FIG.13illustrates patterns of X-ray transmission images of the connecting portions400A and400B. The method for evaluation is the same as in the first exemplary embodiment. Also in the second exemplary embodiment, the connection state of the connecting portions400A and400B can be easily determined from the shape in the X-ray transmission image similarly to the first exemplary embodiment. As a result of this, the image pickup unit300A having high reliability of connection by the connecting portions400A and400B can be manufactured. To be noted, various modifications such as ones described above with reference toFIGS.8A to8Fcan be made on the lands230A and230B and the openings550A and550B of the second exemplary embodiment. Various modifications can be made also on the lands130A and130B.

Although a case where the lens barrel3000is attachable to and detachable from the camera body2000has been described in the second exemplary embodiment, the configuration is not limited to this, and the lens and the camera body may be integrated in the camera. In addition, although a case where a camera serves as an example of an electronic device has been described, the configuration is not limited to this, and the electronic device may be a mobile device including an image pickup unit such as a smartphone.

In addition, although a case where the electronic component is an image sensor has been described, the configuration is not limited to this, and the electronic component may be a memory, a memory controller, or any other semiconductor package. In this case, the electronic device including the printed circuit board is not limited to an image pickup apparatus, and the printed circuit board may be incorporated in any kind of electronic device.

In Example 1, the printed circuit board300was manufactured by the manufacturing method described in the first exemplary embodiment, and the manufactured printed circuit board300was inspected. The diameter of each of the lands130of the electronic component100was set to φ1.0 mm, and the pitch between the lands130was set to 1.6 mm. The lands130were formed as electrodes plated with Au, Ni, or the like. The thickness of the solder resist film240was set to about 0.02 mm. The diameter of each of the openings550of the solder resist film240was set to φ1.25 mm. The diameter of the body portion231of each land230was set to φ0.75 mm, which was smaller than that of the land130. The four protruding portions232were formed to extend radially with even intervals therebetween, and the width of each protruding portion232was set to 0.2 mm. The insulating substrate202of the printed wiring board200was formed from an FR-4 base material, and the size thereof was set to about 50.0 mm×about 50.0 mm Cu was used as the material of the lands230. The number of valid terminals formed from solder was set to 100.

In step S2illustrated inFIG.3B, the paste P was supplied onto the printed wiring board200by screen printing. A printing plate having a thickness of 0.02 mm was used for the screen printing. The paste P containing a flux component was used. The alloy composition of the solder powder was a eutectic composition of tin-58 bismuth having a melting point of 139° C. The average particle diameter of the solder powder was 40 μm. In step S5-1illustrated inFIG.4Band step S5-2illustrated inFIG.4C, reflow heating was performed in accordance with a temperature-time profile shown inFIG.14.

X-ray transmission observation of the printed circuit board300manufactured by the conditions described above was performed on the upper surface side. As a result of this, the plurality of connecting portions400each corresponded to one of the patterns (3), (4), (5), and (6) among the patterns (1) to (7) shown inFIG.7. As described above, the connection state of the connecting portions was easily determined in Example 1.

In Example 2, the printed circuit board300A of the second exemplary embodiment was manufactured, and the manufactured printed circuit board300A was inspected. The size of the insulating substrate103A of the image sensor100A was set to 34.0 mm×28.4 mm. The diameter of each of the lands130A of the image sensor100A was set to φ1.0 mm, and the pitch between the lands130A was set to 1.5 mm. The diameter of each of the lands130B was set to φ1.5 mm. The lands130A and130B were formed as electrodes plated with Au, Ni, or the like. The thickness of the solder resist film240A was set to about 25 μm. The diameter of each of the openings550A of the solder resist film240A was set to φ1.25 mm. The size of each of the opening portions550B having an approximately quadrangular shape was set to 1.75 mm×1.75 mm. The diameter of the body portion231A of each land230A was set to φ0.75 mm, which was smaller than that of the land130A. The four protruding portions232A were formed to extend radially with even intervals therebetween, and the width of each protruding portion232A was set to 0.2 mm. The diameter of the body portion231B of each land230B was set to φ1.2 mm, which was smaller than that of the land130B. The four protruding portions232B were formed to extend radially with even intervals therebetween, and the width of each protruding portion232B was set to 0.3 mm. The insulating substrate202A of the printed wiring board200A was formed from an FR-4 base material, and the size thereof was set to about 50.0 mm×about 50.0 mm Cu was used as the material of the lands230A and230B. The number of valid terminals formed from solder was set to 300.

X-ray transmission observation of the image pickup unit300A manufactured by the conditions described above was performed on the upper surface side. As a result of this, the plurality of connecting portions400A and400B each corresponded to one of the patterns illustrated inFIG.13. As described above, the connection state of the connecting portions was easily determined in Example 2.

Comparative Examples

As printed circuit boards of Comparative Examples, a first sample in which the lands of the printed circuit board did not include the protruding portions232and a second sample in which the length of the protruding portions was small were manufactured.

In the first sample of the printed circuit board, the diameter of each opening of the solder resist film was set to φ0.75 mm, and the diameter of each land of the printed wiring board was set to φ0.75 mm, that is, this was configured as a so-called surface mount device: SMD. Other than this, the same conditions as Example 1 were used. In the second sample, the protruding portions were formed to be inside the lands of the electronic component in plan view. X-ray transmission image inspection and electrical conduction test were performed on the first sample and second sample described above.

In X-ray transmission observation of the first sample, the solder shapes of most of the connecting portions were circular shapes of almost the same diameters as the lands of the electronic component or abnormal shapes larger than and deformed from the circular shapes like the pattern (7) shown inFIG.7. Particularly, even in the case where the solder shapes were the circular shapes of almost the same diameters as the lands of the electronic component, conduction failure was detected in some connecting portions in the electrical conduction test. That is, whether or not the connection state of the connecting portions was good could not be determined by the X-ray transmission image inspection.

In the X-ray transmission image of the second sample, the solder shapes were not the quadrangular shapes like the pattern (3) shown inFIG.7, and were circular shapes of almost the same diameters as the lands of the electronic component, or the change in the solder shapes in the openings of the solder resist film was unclear. In the second sample, there were not as many connecting portions having abnormal shapes like the pattern (7) shown inFIG.7as in the first sample. Since the change in the solder shapes was unclear, whether or not the quality of the product was good could not be determined from the X-ray transmission image, and conditions such as the structure and the process could not be reconsidered.

To be noted, the present invention is not limited to the exemplary embodiments described above, and various modifications can be made within the technical concept of the present invention. In addition, the effects described in the exemplary embodiments are merely enumeration of the most preferable effects that can be realized by the present invention, and the effects of the present invention are not limited to those described in the exemplary embodiments.

Although a case where the insulating substrate of the package substrate is a ceramic substrate has been described, the configuration is not limited to this, and the insulating substrate may be formed from, for example, a glass epoxy material similarly to the printed wiring board. Similarly, although a case where the insulating substrate of the printed wiring board is formed from a glass epoxy material has been described, the insulating substrate of the printed wiring board may be formed from, for example, a ceramic substrate similarly to the package substrate.

Other Embodiments

This application claims the benefit of Japanese Patent Application No. 2018-188696, filed Oct. 3, 2018, which is hereby incorporated by reference herein in its entirety.