JP7364516B2 - Circuit board and imaging module - Google Patents

Description

The present disclosure relates to a circuit board and an imaging module.

Patent Document 1 discloses an image sensor unit that includes a mounting board, an image sensor mounted on the mounting board, and a shield plate located between the image sensor on the back side or the front side of the mounting board. The shield plate can reduce the propagation of electromagnetic noise to the image sensor even if a source of electromagnetic noise such as a stepping motor is placed near the image sensor unit.

Japanese Patent Application Publication No. 2005-039691

Image sensors require high precision in mounting angle. When mounting such an image sensor on a circuit board with a shield plate in between, high precision is also required in the mounting angle of the shield plate. Bonding the shield plate to the circuit board using an adhesive or the like with high mounting accuracy requires a complicated process, which increases manufacturing costs.

The present disclosure aims to provide a circuit board that has a shielding function and can be manufactured at low cost, and an imaging module that includes such a circuit board.

The circuit board according to the present disclosure includes:
a ceramic substrate including a film-like wiring conductor;
a thick conductor film located on the ceramic substrate;
having a mounting area on the conductor film in which an image sensor is mounted;
The conductor film has higher conductivity than the wiring conductor and is thicker than the wiring conductor.

The imaging module according to the present disclosure includes:
The above circuit board,
an image sensor mounted on the mounting section;
Equipped with

According to the present disclosure, it is possible to provide a circuit board that has a shielding function and can be manufactured at low cost, and an imaging module that includes such a circuit board.

FIG. 2 is a plan view (A) and a cross-sectional view (B) taken along line BB of an imaging module according to an embodiment of the present disclosure. 7 is a cross-sectional view showing a circuit board of Modification 1. FIG. 7 is a cross-sectional view showing a circuit board of Modification 2. FIG. 7 is a cross-sectional view showing a circuit board of Modification 3. FIG. FIG. 7 is a cross-sectional view showing a circuit board of Modification 4.

Embodiments of the present disclosure will be described in detail below with reference to the drawings.

FIG. 1 is a plan view (A) and a cross-sectional view (B) taken along the line BB, showing an imaging module according to an embodiment of the present disclosure. The imaging module 1 of this embodiment includes a circuit board 100 and an imaging element 200 mounted on the circuit board 100. The type of image sensor 200 is not limited, and may be, for example, a CCD (Charge Coupled Device) image sensor, a CMOS (Complementary Metal Oxide Semiconductor) image sensor, or the like.

Circuit board 100 includes a ceramic substrate 110, a conductor film 150 on ceramic substrate 110, and a resin film 160 interposed between conductor film 150 and image sensor 200. It is assumed that the circuit board 100 is placed near a source of high frequency electromagnetic noise such as a motor module. The motor module generates electromagnetic noise at a PWM (Pulse Width Modulation) frequency (for example, 200 kHz or higher) from a power conversion circuit. The conductive film 150 suppresses electromagnetic noise from being transmitted to the image sensor 200 when it propagates from a motor module or the like. Hereinafter, the area on the conductive film 150 that overlaps with the image sensor 200 when viewed from the direction perpendicular to the first surface 111 will be referred to as a mounting area R1. The mounting area R1 has the same size as the image sensor 200 when viewed from a direction perpendicular to the first surface 111.

The ceramic substrate 110 is a laminate in which a plurality of insulating ceramic layers 110a are stacked. The ceramic substrate 110 has a first surface 111 on which the conductor film 150 is located, and a second surface 112 opposite to the first surface 111.

The ceramic substrate 110 further includes wiring conductors (via conductor 121, wiring conductor 122, wiring electrode 131, and external electrode 132). The wiring conductor includes a plurality of wiring electrodes 131 located on the first surface 111 and electrically connected to the terminals of the image sensor 200, and an external electrode located on the second surface 112 and electrically connected to external components. 132, a via conductor 121 located within the ceramic substrate 110, and a film-like wiring conductor 122. The wiring electrode 131 is located in a region of the first surface 111 that is outside a region in which the mounting region R1 of the image sensor 200 is projected (a region projected in a direction perpendicular to the first surface 111). The wiring electrode 131 is electrically connected to an electrode of the image sensor 200 via, for example, a bonding wire w. The via conductor 121 extends in a direction perpendicular to the first surface 111, and the wiring conductor 122 extends in a direction along the first surface 111. The via conductor 121 and the wiring conductor 122 electrically connect the wiring electrode 131 on the first surface 111 and the external electrode 132 located on the second surface 112.

The via conductor 121 and the wiring conductor 122 contain a metal material such as tungsten or molybdenum, or an alloy material of these metals as a conductor component, and are fired integrally with the plurality of ceramic layers 110a. The wiring electrode 131 and the external electrode 132 contain a metal material such as tungsten or molybdenum, or an alloy material of these metals as a conductor component, and may be fired integrally with the plurality of ceramic layers 110a, or may be fired integrally with the plurality of ceramic layers 110a. After the layer 110a is fired, it may be constructed of a post-attached metallized conductor formed by screen printing and firing a metal paste.

The conductor film 150 is located on the first surface 111 of the ceramic substrate 110 and shields high frequency electromagnetic noise. The conductive film 150 is located on the first surface 111. A mounting region R1 is located on the conductor film 150. The conductor film 150 may be located over the entire mounting region R1, or may be located in an area excluding a part of the mounting region R1. When viewed from the direction perpendicular to the first surface 111, the conductive film 150 is larger than the mounting region R1 and may include the mounting region R1. It is possible to further suppress electromagnetic noise that propagates from the side (obliquely to the ground). Furthermore, it is easy to disperse electromagnetic noise propagating from the front side to the surroundings. Here, the front and back sides of the conductor film 150 are shown with the mounting area R1 side of the image sensor 200 (the side opposite to the ceramic substrate 110) as the front side.

The conductor film 150 is thicker than the film-like wiring conductor 122 and has higher conductivity than the film-like wiring conductor 122. The conductor film 150 may be thicker than the wiring electrode 131 and the external electrode 132 and have higher conductivity than the wiring electrode 131 and the external electrode 132. As an example, the thickness of the wiring conductor 122 is 5 to 10 μm, while the thickness of the conductor film 150 is 100 μm or more. The thickness of the conductor film 150 may be 300 μm or less. The electrical conductivity (room temperature) of the wiring conductor 122 almost matches that of tungsten or molybdenum, 17.5 to 18.5 [×10 ⁶ S/m], and the electrical conductivity (room temperature) of the conductor film 150 matches that of copper or silver. The conductivity is approximately equal to 59 to 61.4 [×10 ⁶ S/m]. The conductive film 150 having such a thickness and dielectric constant can shield electromagnetic noise having a frequency of, for example, 100 kHz or more.

The conductor film 150 is a thick film conductor made of fired metal paste. The conductor film 150 may also be called a metallized conductor or fired metal obtained by firing a metal paste. The metal paste that is the material of the conductor film 150 contains copper, silver, or both as conductor components, and the conductor film 150 after firing contains copper, silver, or both as main components. The fact that the conductor film 150 is a thick film conductor, a metallized conductor, or a fired metal can be confirmed by the fact that the cross section contains many grain boundaries.

The conductor film 150 is formed after firing the ceramic substrate 110. The conductor film 150 is formed by printing a metal paste multiple times using screen printing to form a predetermined shape, and then firing the metal paste while maintaining its shape. The conductor film 150 may be formed by applying a metal paste using a mold.

In order to adopt the above-mentioned high value as the electrical conductivity of the conductor film 150, it is necessary to use a low melting point metal such as copper or silver, which makes co-firing with the ceramic substrate 110, which has a high firing temperature, difficult. However, by firing the ceramic substrate 110 after firing, the conductor film 150 can be formed on the ceramic substrate 110 at a lower cost and with higher accuracy than when joining metal plates with an adhesive or a brazing material. Furthermore, higher strength and higher durability (heat resistance) can be obtained at the joint of the conductor film 150 than when metal plates are joined with an adhesive.

The conductor film 150 may have a structure including a plurality of layers, such as a base layer in contact with the ceramic substrate 110 and a main layer located on the base layer. The base layer may contain a component (glass or active metal) that provides high bonding strength to the ceramic substrate 110, and the main layer may contain a larger amount of metal component. The entire conductor film 150 may be made of the same component including a component (glass or active metal) that provides bonding strength to the ceramic substrate 110.

The resin film 160 is located on the conductor film 150. The resin film 160 may be located over the entire area of the projected area of the mounting area R1 (the area projected in the direction perpendicular to the first surface 111), or may be located in an area excluding a part of the projected area. good. The resin film 160 compensates for errors occurring in the parallelism and flatness of the surface of the conductor film 150, and further improves the parallelism and flatness of the mounting surface on which the image sensor 200 is mounted. As a material for the resin film 160, an epoxy-based thermosetting resin can be used. The material of the resin film 160 may include a magnetic material (particles of Fe (iron), Fe-Si (ferrosilicon), etc.). The resin film 160 can be formed by screen printing and curing an uncured resin material after firing the conductor film 150. The resin material before hardening may have a lower viscosity than the metal paste before hardening that constitutes the conductor film 150. As the resin film 160, various other curable resins and resins made of various materials may be employed.

As shown in FIG. 1, the resin film 160 may cover the entire outer surface of the conductor film 150 (the upper surface and side surface on the side where the image sensor 200 is located). With such a configuration, the corrosion resistance of the conductor film 150 can be improved. The image sensor 200 is mounted on the resin film 160.

<Manufacturing method>
Next, an example of a method for manufacturing the circuit board 100 will be described. The ceramic substrate 110 is made of a ceramic sintered body, such as an aluminum oxide sintered body or an aluminum nitride sintered body. As the ceramic material, a silicon carbide sintered body, a mullite sintered body, or the like may be used. If the ceramic substrate 110 is made of an aluminum oxide sintered body, it can be manufactured as follows. First, raw material powder mainly composed of aluminum oxide powder and powder of silicon oxide, which is a sintering aid component, is kneaded with an organic solvent and a binder to form a slurry, and this slurry is processed using a doctor blade method or a lip coater method. A ceramic green sheet (hereinafter also referred to as a green sheet) that is molded into a sheet shape and becomes the ceramic layer 110a by the molding method described above is produced. Next, a laminate is produced by laminating a plurality of green sheets. Thereafter, the ceramic substrate 110 can be manufactured by firing this laminate at a temperature of approximately 1300° C. to 1600° C.

The wiring conductors (via conductor 121, wiring conductor 122, wiring electrode 131, external electrode 132) of the ceramic substrate 110 are made of a metal material such as tungsten or molybdenum, or an alloy material of these metal materials, and a ceramic green sheet. A metallized conductor is formed on the surface and inside of the ceramic substrate 110 by sintering at the same time as firing. For example, it may contain an inorganic component such as glass or ceramics in order to improve sinterability or bond strength with ceramics. As the above metal material or alloy material, a metal material such as manganese, a composite material further containing manganese or copper, or an alloy material of these metals may be applied.

For example, when the film-like wiring conductor 122, wiring electrode 131, and external electrode 132 are metalized layers of tungsten, they can be formed as follows. For example, it is formed by printing a metal paste prepared by mixing tungsten powder with an organic solvent and an organic binder on a predetermined position of the green sheet that will become the ceramic layer 110a using a method such as screen printing, and firing it together with the green sheet. can do. In addition, the via conductor 121 is formed by providing a through hole at a predetermined position of the green sheet prior to printing the metal paste described above, filling the through hole with the same metal paste as described above, and firing it together with the green sheet. can be formed with.

A nickel film of approximately 1 to 10 μm and a gold film of approximately 0.1 to 3 μm are sequentially formed on the surfaces of exposed conductor layers such as the wiring electrodes 131 and external electrodes 132 to protect the surfaces and to prevent soldering. It is possible to improve the bondability of materials, solders, etc. The nickel film and the gold film can be formed as a plated film or a thin film by electrolytic plating.

The conductor film 150 is a metallized conductor obtained by sintering a metal material such as copper or an alloy material of such a metal material after firing the ceramic green sheet. The conductor film 150 is formed by, for example, printing a metal paste prepared by mixing metal powder such as copper with an organic solvent and an organic binder at a predetermined position on the first surface 111 of the ceramic substrate 110 multiple times using a method such as screen printing. The ceramic substrate 110 can be formed by molding it into a predetermined thickness and shape and firing it at a temperature lower than the firing temperature of the ceramic substrate 110.

The resin film 160 can be formed by printing, for example, an epoxy-based thermosetting resin at a predetermined position by a method such as screen printing and curing the resin film 160 after firing the conductor film 150. The resin before curing has a lower viscosity than the metal paste that is the material of the conductor film 150, and by providing a sufficient thickness and curing it while maintaining horizontality, the surface of the conductor film 150 has a high degree of parallelism. Parallelism with respect to one surface 111) and high flatness can be achieved. For example, the thickness of the resin film 160 in the range overlapping with the mounting region R1 may be 100 μm to 250 μm, and the lowest surface of the conductor film 150 in the range overlapping with the mounting region R1 when the first surface 111 is made horizontal. Flatness with a difference of 30 μm or less between a point and a high point can be achieved. The range that overlaps with the mounting area R1 above means the range that overlaps in the direction perpendicular to the first surface 111, and is synonymous with the area in which the mounting area R1 is projected (the area projected in the direction perpendicular to the first surface 111). be.

As described above, the circuit board 100 and the imaging module 1 of this embodiment include the ceramic substrate 110 having the film-like wiring conductor 122 and the conductor film 150 located on the ceramic substrate 110. Then, a mounting region R1 for the image sensor 200 is located on the conductor film 150. Further, the conductive film 150 is thicker than the wiring conductor 122 and has higher conductivity than the wiring conductor 122. Therefore, even if electromagnetic noise propagates from the second surface 112 side of the circuit board 100, the conductor film 150 can shield the electromagnetic noise and suppress the propagation of electronic noise to the image sensor 200. When the thickness of the conductor film 150 is three times or more the thickness of the wiring conductor 122, the electromagnetic noise shielding effect can be further improved. Furthermore, since the conductor film 150 is a thick film conductor made of fired metal, it can be manufactured at a lower cost without reducing the precision of the mounting angle, compared to bonding using adhesives or brazing filler metals. Furthermore, compared to bonding using an adhesive or the like, high strength and high durability (heat resistance) can be imparted to the bonded portion between the conductive film 150 and the ceramic substrate 110.

Furthermore, the circuit board 100 of this embodiment is applied as a board on which an image sensor 200, which is an image sensor, is mounted. A source of electromagnetic noise, such as an optical component or a motor module that displaces the imaging module 1, may be placed near the imaging device, and if electromagnetic noise is added to the imaging signal, image quality may deteriorate. Therefore, by the electromagnetic noise shielding effect described above, it is possible to suppress noise from being added to the imaging signal and deterioration of the captured image due to the noise.

Furthermore, according to the circuit board 100 and the imaging module 1 of this embodiment, the resin film 160 located on the conductor film 150 is further provided. By having the resin film 160, even if an error occurs in the parallelism and flatness of the surface of the conductor film 150, the resin film 160 compensates for the error and improves the parallelism and flatness of the mounting surface on which the image sensor 200 is mounted. You can further improve your degree. When the thickness of the conductor film 150 is increased, errors tend to occur in the parallelism and flatness of the surface of the conductor film 150, but since the resin film 160 can compensate for the above errors, the parallelism and flatness of the mounting surface can be reduced. Therefore, the conductor film 150 can be designed to be thicker. Furthermore, since the resin film 160 contains a magnetic material, the resin film 160 can also have an electromagnetic noise shielding effect.

Furthermore, in this embodiment, the conductor film 150 is made of a metal material different from that of the wiring conductor 122 in the ceramic substrate 110. Therefore, the characteristics required for the wiring conductor 122 (for example, characteristics that allow co-firing with the ceramic substrate 110, etc.) and the characteristics required for the conductor film 150 (high conductivity, formability of thick films, etc.) are different. We can also meet both requests.

According to the imaging module 1 of this embodiment, the noise resistance performance can be improved by the circuit board 100 that exhibits the above-described effects.

(Modified example)
FIG. 2 is a sectional view showing a circuit board of Modification 1. In FIG. 2, the image sensor 200 is shown by a virtual line. The circuit board 100A of Modification 1 is the same as the circuit board 100 described above, including the structure, material, application, and manufacturing method, except that the region in which the resin film 160A is formed is different. In the circuit board 100A of Modification 1, the resin film 160A is placed on the conductor film 150, and does not cover the side surfaces of the conductor film 150. Such a configuration makes it easier to mold the resin film 160A.

FIG. 3 is a sectional view showing a circuit board of Modification 2. FIG. FIG. 4 is a sectional view showing a circuit board of Modification 3. In FIGS. 3 and 4, the image sensor 200 is shown by a virtual line. The circuit boards 100B and 100C of Modifications 2 and 3 are different from the circuit board 100 described above in terms of structure, material, application, and manufacturing method, except that the shapes of the conductor films 150B and 150C and the resin films 160B and 160C are different. The same is true.

As shown in FIG. 3, the conductive film 150B of Modification 2 is thinner at the center than at the edge when viewed from a direction perpendicular to the first surface 111. For example, the center portion of the conductor film 150B may be thinner by 30 μm to 70 μm than the edge portion. Such a shape can be formed by a printing pattern when a plurality of unfired metal pastes are stacked and screen printed. Further, the conductor film 150B having the above shape can also be formed by molding. On the other hand, the resin film 160B is thicker at the center than at the edge of the mounting area R1 when viewed from the direction perpendicular to the first surface 111, so as to offset the depression on the surface of the conductor film 150B, and the resin film 160B is The mounting surface is flat.

By making the thickness of the conductive film 150B different between the edge portion and the center portion, this portion of the conductive film 150B can be prevented from electromagnetic noise propagating diagonally toward the image sensor 200 via the side surface of the conductive film 150B. By increasing the thickness of the part, the shielding effect can be improved. Furthermore, by making the thickness of the conductor film 150B different between the edge and the center, the amount of copper used can be minimized. This has the effect of easily accumulating the material in the concave portion of the conductive film 150B and making it easy to flatten the surface of the resin film 160B after hardening.

As shown in FIG. 4, the conductive film 150C of Modification 3 has a plurality of irregularities D on the surface facing the image sensor 200. The unevenness D may be a linear unevenness or a dot-like unevenness. When the direction perpendicular to the first surface 111 is defined as the height direction, the height from the bottom to the top of the unevenness D may be 15 μm to 50 μm. The resin film 160C covers the unevenness D of the conductor film 150C and has a flat mounting surface for the image sensor 200. The unevenness D of the conductor film 150C can be formed by screen printing a metal paste in a mesh shape before firing.

By having a plurality of irregularities D on the surface of the conductive film 150C, it is possible to obtain a shielding effect against electromagnetic noise that cannot be shielded by a flat conductor. Furthermore, the plurality of irregularities D suppresses the resin before hardening from flowing in the lateral direction (direction along the first surface 111) when forming the resin film 160C, making it easier to mold the resin film 160C. Furthermore, the plurality of irregularities D has the effect of increasing the bonding strength between the conductor film 150C and the resin film 160C.

FIG. 5 is a cross-sectional view showing a circuit board of modification 4. In FIG. 5, the image sensor 200 and the bonding wire w are shown by virtual lines. In the circuit board 100D of modification 5, the ceramic substrate 110 has a recess F on the first surface 111, and the conductor film 150 and the resin film 160 are located within the recess F. The other structures, materials, uses, and manufacturing methods are the same as those of the circuit board 100 described above. The wiring electrode 131 may be located outside the opening of the recess F. According to such a configuration, the increase in thickness due to the conductive film 150 and the resin film 160 can be absorbed by the recessed portion F, and the thickness of the imaging module 1 can be reduced. Furthermore, the difference in height between the wiring electrode 131 and the image sensor 200 is reduced, making wire bonding work easier. Note that the aforementioned circuit boards 100, 100A to 100C without recesses F have the advantage that screen printing is easy to perform when forming the conductive film 150 and the resin film 160.

The embodiments of the present disclosure have been described above. However, the present invention is not limited to the above embodiments. For example, in the above embodiment, a circuit board having the resin film 160 is shown, but the resin film 160 may be omitted. Other details shown in the embodiments can be changed as appropriate without departing from the spirit of the invention.

1 Imaging module 100, 100A to 100D Circuit board 110 Ceramic substrate 110a Ceramic layer 111 First surface 112 Second surface 121 Via conductor 122 Wiring conductor 131 Wiring electrode 132 External electrode 150, 150B, 150C Conductor film 160, 160A, 160B, 160C Resin film 200 Image sensor D Unevenness F Recess R1 Mounting area w Bonding wire

Claims (8)

a ceramic substrate including a film-like wiring conductor;
a thick conductor film located on the ceramic substrate;
having a mounting area on the conductor film in which an image sensor is mounted;
The circuit board, wherein the conductor film has higher conductivity than the wiring conductor and is thicker than the wiring conductor. A resin film located on the mounting area of the conductor film,
Further prepare,
The circuit board according to claim 1. The resin film contains a magnetic material.
The circuit board according to claim 2. The thickness of the conductor film is three times or more the thickness of the wiring conductor,
The circuit board according to any one of claims 1 to 3. The conductor film has a thickness smaller at the center than at the edges.
The circuit board according to any one of claims 1 to 4. The conductor film has a plurality of unevenness in the thickness direction,
The circuit board according to any one of claims 1 to 5. The conductor film is made of a metal material different from the wiring conductor,
The circuit board according to any one of claims 1 to 6. The circuit board according to any one of claims 1 to 7,
an image sensor mounted in the mounting area;
An imaging module comprising:

Images