Structure with a plurality of substrates, its manufacturing method and crystal oscillator with the structure

The structure provided with a plurality of substrates of the present invention is provided with a plurality of substrates each provided with chip-shaped circuit devices connected by poles also used as electrical wiring. At least one pole connecting the plurality of substrates is also used as one of the circuit devices. Simultaneously, the circuit devices also used as poles are mounted on each substrate in a standing posture.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a structure provided with a plurality of substrates, a manufacturing method thereof and a crystal oscillator using the structure, and more particularly, it relates to a structure provided with a plurality of substrates capable of effectively utilizing its surface area, a manufacturing method thereof and a crystal oscillator using the structure.

2. Description of the Related Art

There is sometimes a case where a circuit for performing necessary operations must be provided within a predetermined area for design reasons. If the area needed when all devices constituting such a circuit on one substrate exceeds the predetermined area, usually the substrate is divided into a plurality of substrates so that all the devices can be accommodated in the divided substrates within the predetermined area.

For example, a structure provided with a plurality of substrates is installed in an apparatus for the above-mentioned purpose. The explanation below is given by using a crystal oscillator as one example of an apparatus including a structure provided with a plurality of substrates.

A crystal oscillator is built into radio equipment, for example, as the reference source of a communication frequency. With the recent use of higher frequencies as communication frequencies, sometimes the number of components increases due to the use of multiplier circuits and the like, and there miniaturization is required.

FIG. 1is the basic section view of a conventional crystal oscillator disclosed by the following Patent reference1and the like. The crystal oscillator comprises a first substrate1aand a second substrate1b, which are vertically disposed. On the first substrate1aand second substrate1b, circuit devices2, such as a crystal oscillator, an IC, a capacitor, a resistor and the like, are installed.

The first substrate1ahas a surface-mounted external terminal3at each of its four corners of its base surface (back surface). A metal pin4is connected to the surface of each of the four corners by solder5as a pole and is installed on the first substrate1a. The second substrate1bis connected to the first substrate1athrough the metal pin4by solder5and is held above the first substrate1a. The metal pin4electrically connects the respective circuit patterns of the first and second substrates1aand1b. Then, a metal cover, which is not shown inFIG. 1, is jointed to the first substrate1ato cover the second substrate1b.

SUMMARY OF THE INVENTION

It is an object of the Present invention to provide a structure provided with a plurality of substrates, capable of facilitating its miniaturization with low cost by effectively utilizing the surface area of each substrate and a manufacturing method thereof.

It is another object of the present invention to provide a surface-mounted oscillator adopting a structure provided with a plurality of substrates, capable of promoting its miniaturization with low cost by effectively utilizing the surface area of each substrate.

The structure provided with a plurality of substrates in the first aspect of the present invention is provided with a plurality of substrates each provided with chip-shaped circuit devices which are connected by poles also used as electrical wiring. At least one of the poles connecting the plurality of substrates is also used as one of the circuit devices. Simultaneously, the circuit device also used as a pole is mounted on each substrate in a standing posture.

Since the circuit device mounted on the substrate in a lying posture conventionally is mounted on the substrate in a standing posture, its required space on the substrate can be reduced by the difference between the area occupied by the circuit device when it is mounted on the substrate in a lying posture and the area occupied by the circuit device when it is mounted on the substrate in a standing posture, thereby realizing the miniaturization of a structure provided with a plurality of substrates with low cost.

In the crystal oscillator in the second aspect of the present invention, the first and second substrates each provided with chip-shaped circuit devices constituting an oscillation circuit are connected by a pole which is also used as electrical wiring, and are vertically disposed. At least one of the poles is also used as one of the circuit devices.

The manufacturing method of a structure provided with a plurality of substrates in the third aspect of the present invention manufactures a structure provided with a plurality of substrates each provided with chip-shaped circuit devices which are connected by poles also used as electrical wiring. The manufacturing method comprises the steps of coating solder on a pattern formed on each substrate, mounting circuit devices on the substrate coated with solder and melting the solder of the circuit device. When manufacturing at least one of the poles connecting the plurality of substrates also used as one of the circuit devices, the manufacturing method further comprises as a part of each of the steps the steps of mounting circuit devices also used as poles on the front or beneath the back surface in a standing posture, fixing the circuit devices also used as its poles on the substrate by melting the solder, coating solder on a position corresponding to the electrode(s) of the circuit devices, on the front or beneath the back surface of the substrate and also fixing the circuit devices also used as its poles on or beneath the joined substrate by melting the solder in a combined state of the coated solder and electrode(s) of the circuit devices.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2is a cross section view of the surface-mounted oscillator in one preferred embodiment of the present invention. The same reference numerals are attached to the components the same as those of the conventional oscillator, and their descriptions are simplified or omitted here.

As described earlier, the surface-mounted oscillator comprises circuit devices2constituting an oscillation circuit, the first substrate1awith a mounting terminal3and the second substrate1bsupported by poles at the corners of its boundary.FIGS. 6A and 6B, which are described later, are enlarged cross section views of the pole shown inFIG. 2. In each ofFIGS. 6A and 6B, at least one pole, for example, the two front ones of the four poles installed at the corners of its rectangle are also used as circuit devices, such as chip resistors2a. All the poles can also be used as circuit devices.

Specifically, the first and second substrates1aand1bare mechanically connected by connecting each end (terminal6) of the chip resistor2ato the respective circuit patterns7of the first and second substrates1aand1b. Simultaneously the respective circuit patterns7of the first and second substrates1aand1bare also electrically connected.

If circuit devices, such as the chip resistor2aand the like, are also used as poles in this way, the area of each substrate can be effectively utilized, for example, without miniaturizing the circuit devices. Accordingly, the effective use of its surface area can be realized at low cost. Since in this preferred embodiment, a circuit device, such as the chip resistor2ais mounted on the substrate in a standing posture in the direction normal to the substrate, the maximum space between the first and second substrates1aand1bcan be secured and also the support by poles connecting the substrates can be stabilized. Even if a large size of a structure is anticipated in its initial design, it can be avoided. Simultaneously, the required space on each substrate can be reduced by the difference between an area occupied by the circuit device when it is mounted on the substrate in a lying posture, that is, a rectangular surface of a circuit device (a rectangular parallelepiped) which touches the substrate contains two edges excluding the shortest edge of the rectangular parallelepiped and, an area occupied by the circuit device when it is mounted on the substrate in a standing posture, that is, a rectangular surface of a circuit device (a rectangular parallelepiped) which touches the substrate contains the shortest edge of the rectangular parallelepiped, thereby realizing the miniaturization of a structure provided with a plurality of substrates with low cost.

As shown inFIG. 3, many circuit devices11, such as a chip resistor and the like, basically take the shape of a rectangular parallelepiped. More specifically, in this rectangular parallelepiped, the length corresponding to one edge, “Z” is less than the length corresponding to the remaining two edges, “X” and “Y”. And the rectangular parallelepiped usually has a terminal (electrode)12at each longitudinal end.

If in this preferred embodiment, such a circuit device taking the shape of a rectangular parallelepiped is also used as a pole, as shown inFIG. 4, the circuit device11is mounted on a substrate using solder5in a standing posture in such a way that the direction connecting the respective terminals12at each end of the circuit device coincide with the direction normal to a substrate. Alternatively, as shown inFIG. 5, the circuit device11can be mounted on the substrate using solder5in a standing posture in such a way that the direction connecting the respective terminals12at each end of the circuit device is perpendicular to the direction normal to the substrate.

FIGS. 6A and 6Bare cross section views of a pole joined beneath a substrate in the states shown inFIGS. 4 and 5, respectively. If its mass production is not intended, the soldering of poles and the like can also be manually performed.

InFIG. 6A, the direction connecting the electrodes at each end of a circuit device coincides with the direction normal to a substrate. In this case, a circuit device, such as the chip resistor2aor the like, is electrically connected to the circuit pattern7on the front surface of the first substrate1aor beneath the back surface of the second substrate1bvia the terminal6and solder5.

However, inFIG. 6B, the direction connecting the electrodes at each end of a circuit device is perpendicular to the direction normal to a substrate. In this case, the chip resistor2ais connected to the circuit pattern7and a dummy pattern7aof the first substrate1avia the terminal6and solder5on the one side of each end of the circuit device, and is connected to the circuit pattern7and dummy pattern7aof the second substrate1bvia the terminal6and solder5on the other side of each end. Since the dummy pattern is provided on the substrate in accordance with a position in which solder is coated, it is isolated and is not included in patterns constituting the circuit pattern. Thus, the chip resistor2ashown inFIG. 6Bis electrically connected to the first or second substrates only via the circuit pattern7.

FIGS. 7A,7B, and7C show the summary of the manufacturing process of the surface-mounted oscillator shown inFIG. 2.

As shown inFIG. 7A, firstly, in order use to a circuit device2aas a pole, the circuit device2amounted on the substrate1ain a standing posture and a circuit device2mounted normal to the substrate1ain a lying structure are fixed on the substrate1aby a re-flowing process. As to the substrate1b, as shown inFIG. 7B, a circuit device2mounted normally to the substrate1bin a lying posture is fixed on the substrate1bby a re-flowing process. After these processes, as shown inFIG. 7C, a circuit device2ain a standing posture which is mounted on the substrate1aand, the back surface of the substrate1bis fixed by the re-flowing process.

FIG. 8is a flowchart showing the manufacturing process of a structure provided with a plurality of substrates, such as a crystal oscillator or the like. In this example, it is assumed that a plurality of substrates each provided with chip-shaped circuit devices are connected by poles which are also used as electrical wiring.

As shown inFIG. 8, firstly, in step S101, solder is coated on a pattern generated on the substrate. In step S102, a circuit device is mounted on the coated substrate. In step S103, the coated solder is melted by a re-flowing process. However, during these processes, poles connecting the plurality of substrates which are also used as the above-mentioned circuit devices are simultaneously generated.

Specifically, as shown inFIG. 9, in step S201as a part of the mounting process, a circuit device is mounted in a standing posture so that either of its terminals touches the substrate or both of its terminals touch the substrate as shown inFIG. 4or5. In step S202as a part of the re-flowing process subsequent to the mounting process, the circuit device is fixed to the substrate by melting solder. In step S203as a part of the later process of combining the substrates, solder is coated in a position corresponding to an electrode(s) of the circuit device beneath the back surface of a covering substrate, and the solder is melted in the combined state of the coated solder and electrode(s) of the circuit device.

InFIG. 9, a circuit device which is also used as a pole is mounted on the lower substrate in a standing posture. And the circuit device which is also used as a pole is joined to the upper substrate. However, it is also possible to mount a circuit device which is also used as a pole on the upper side substrate from beneath, and then, join the circuit device which is also used as a pole to the lower substrate.

FIG. 10shows an example of a design plan of the substrate1aor1bshown inFIG. 2.

InFIG. 10, resistors on the substrate1benclosed by a broken line are designed to also be used as poles beforehand. In this case, as shown inFIG. 11, their required space on the substrate can be reduced by the difference (shown by broken lines in the second or third row ofFIG. 11) between an area occupied by the circuit device when it is mounted on the substrate in a lying posture and an area occupied by the circuit device when it is mounted on the substrate in a standing posture, that is, in such a way that the direction connecting the respective electrodes at each end of the circuit device coincides with the direction normal to the substrate or in such a way that the direction connecting the respective electrodes at each end of the circuit device is perpendicular to the direction normal to the substrate, thereby realizing the miniaturization of a structure provided with a plurality of substrates with low cost.

The circuit device2to be used as a pole can be a chip capacitor or another circuit device constituting an oscillator circuit instead of the chip resistor2a. For example, if the oscillator circuit is of a constant temperature oven type, the circuit device to be used as a pole can be a thermal control device.

In the above description, a pole is also used as a circuit device. However, since usually a plurality of circuit devices with the same dimensions are used as a plurality of circuit devices to be mounted on a substrate, the height of each pole connecting substrates can be kept constant by using a plurality of circuit devices with the same dimensions as circuit devices which are also used as poles even if a plurality of circuit devices are used as a plurality of poles.

If a circuit device which is also used as a pole is mounted in a standing posture in such a way that the direction of the respective terminals at each end of the circuit device can be in parallel with the direction normal to each substrate, its mounting process can also be as follows. Specifically, either of the terminals (electrodes) of a circuit device11which is also used as a pole can also be mounted on a pattern coated with solder5as shown inFIG. 12, and in the re-flowing process subsequent to the mounting process, the circuit device11which is also used as a pole can also be mounted in a standing posture by rotating it around the axis A using the tombstone phenomenon by melting the solder5.

Although in a part of the above description, a crystal oscillator (a surface-mounted oscillator) is used, the present invention is also applicable to a structure provided with a plurality of substrates constituting a circuit other than a crystal oscillator.