JPS584821B2 - Substrate for microwave integrated circuits - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microwave IC board that has a ground point at an arbitrary position and can be easily hermetically sealed.

Conventionally, a microwave IC circuit consisting of a microstrip line and a semiconductor element is constructed on a dielectric substrate such as alumina, but it is often necessary to provide grounding due to the construction of the circuit.

In the microwave range, the location of the ground is determined by the circuit, so it is often not possible to bring the ground wire to the side of the board.

In these various cases, a hole is made in the board and grounded between it and the ground plane on the back side.

However, in this case, it is difficult to maintain airtightness between both surfaces of the substrate, and even if the upper surface of the substrate is sealed, the semiconductor element cannot be used as a chip from the viewpoint of reliability.

For this reason, the electrical characteristics of the element have been sacrificed to some extent to use a cased element, or the semiconductor chip has been covered with a resin such as epoxy.

Due to its characteristics, when it is necessary to use a semiconductor element as a chip, the entire case containing the substrate is hermetically sealed.

In addition, high input/output semiconductor devices must have good heat dissipation, so they cannot be used on the same board as other circuits, so it is necessary to install the device in a case with good heat dissipation, or to use beryllia for that part. A substrate with good thermal conductivity was brazed to a metal plate, and a semiconductor chip was placed on top of it.

The present invention is characterized in that holes are made in the board at ground points necessary for the circuit pattern, and electrical continuity is established between the holes and a thin metal plate brazed to the back of the board. By sealing the upper surface of the substrate, complete hermetic sealing can be achieved and the semiconductor elements, including high input/output elements, can be used as chips.

This will be explained in detail below. 1 and 2 are views showing one embodiment of the present invention, in which FIG. 1 is a plan view and FIG. 2 is an enlarged cross-sectional view taken along the line A--A in FIG. 1.

In Figures 1 and 2, 1 is a dielectric substrate, 2.2'
3 is a metal layer constituting a circuit pattern, 3 is a thin metal plate, 4 is a metal layer that constitutes a circuit pattern,
5 is a hole for grounding, 5 is a cap for airtight sealing, 6 is a semiconductor chip, and 7 is a bonding wire.

The metal plate 3 is, for example, the substrate 1 which has been metalized and then brazed, and is electrically connected to the circuit patterns 2, 2' by metalizing or plating the side surface of the ground hole 4.

When the substrate 1 is made of ceramic, there is no problem even if the metal plate 3 is thin as long as the size is about 10 mm square or less, but if the substrate 1 becomes large, the difference in coefficient of thermal expansion between the substrate 1 and the metal plate 3 will cause problems. Stress is applied to the substrate 1, causing a crack in the substrate 1.

However, if the thickness of the metal plate 3 is set to about 0.05 mm, cracks can be avoided and the metal plate 3 has sufficient strength for hermetically sealed handling.

If the substrate 1 is made of ceramic such as alumina, if you use Kovar, a metal with a similar coefficient of thermal expansion, you can braze it to a larger substrate 1 even if the metal plate 3 is thicker, but Kovar has a lower electrical resistance than copper etc. It is large and leads to deterioration of electrical characteristics.

However, if a thin metal plate 3 is used as in this embodiment, a copper plate can be used.

In addition, since copal has poor thermal conductivity, as substrate 1,
Although it is not possible to use a high input/output semiconductor element even if a material with good thermal conductivity such as Beryllia is used, in this example, a copper plate with good thermal conductivity can be used, so this can be used as a heat sink. By attaching the chip to the chip, it becomes possible to use a high input/output semiconductor element as a chip on a single substrate, which was almost impossible in the past.

Also, by embedding metal in the ground hole, it is possible to ground the back side and make it airtight, but in this case too, cracks may occur in the board due to the difference in thermal expansion coefficient between the board and the metal. It is easy to achieve this, and it cannot be achieved with anything other than a sufficiently small hole.

It is also difficult to maintain complete airtightness.

In the case of this example, it is only necessary to attach metal to the side of the hole, so there is no need to worry about cracks in the board, and the shape and size of the hole can be arbitrary to a certain extent, and it is possible to ground over a wide area using slits, etc. is also possible.

Furthermore, since this embodiment maintains airtightness between both surfaces of the substrate, the entire circuit pattern can be easily hermetically sealed by sealing the top surface of the substrate with a cap.

Therefore, the semiconductor element can be used as a chip as shown in FIGS. 1 and 2.

As explained above, the present invention is a microwave IC circuit using a large-area substrate, which can be grounded to the back surface at necessary positions on the circuit, and can be easily and completely hermetically sealed. can be used as a chip, and by using a substrate with good thermal conductivity, high input/output elements can be used as chips on a single substrate.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing one embodiment of the present invention.
The figure is a plan view thereof, and FIG. 2 is an enlarged view of the AA cross section in FIG. 1. DESCRIPTION OF SYMBOLS 1... Dielectric substrate, 2, 2... Metal layer constituting a circuit pattern, 3... Thin metal plate, 4... Hole for grounding, 5... Cap for airtight sealing, 6 ... Semiconductor chip, 7... Bonding wire.

Claims (1)

[Claims] 1. Glue a thin metal plate to the entire back surface of a substrate with holes or slits made at necessary positions on the circuit pattern of the microwave integrated circuit to seal the openings on the back side of the holes or slits and form a ground electrode. A substrate for a microwave integrated circuit, characterized in that a grounding point that is electrically connected to the ground electrode through the hole or slit is formed on the surface of the substrate.