Cicuit and process of manufacturing the circuit

Details Cicuit and process of manufacturing the circuit Cicuit and process of manufacturing the circuit

1993-03-18

1995-05-16

Fiorilla, Christopher A.

Electricity: conductors and insulators

Conduits, cables or conductors

Preformed panel circuit arrangement

156 89, 419 10, B22F 702

Patent

active

054162777

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a process of manufacturing a circuit including a first circuit plane composed of a ceramic substrate which is covered with, for example, thick-film structures and imprinted with corresponding conductor paths having contact faces.
Increasing requirements for the complexity of future hybrid circuits and the demand for short circuit path lengths can be realized only with multi-layer circuits. New processes have been developed due to process specific drawbacks, particularly due to geometrical limitations as a result of uneven topography and curvatures of the substrate and due to decreasing yields as a result of the high number of process steps in multi-layer thick-film circuits equipped with printed-on dielectric materials. These processes include the so-called green tape process. In this green tape or green sheet process, unsintered ceramic sheets are imprinted with switching elements and conductor paths, generally assembled into a multi-layer element, pressed and sintered. The development of these low-temperature sintering (at approximately 850.degree. C.) glass ceramic sheets permits the realization of highly complex multi-layer circuits with high yields.
On the other hand, the thermal conductivity of these multi-layer circuits lies at only about 15% of a ceramic element composed, for example, of Al.sub.2 O.sub.3. Likewise, its mechanical strength lies below that of an Al.sub.2 O.sub.3 ceramic, namely even below half the strength. Therefore, these green tape circuits are not well suited for robust use in the electronic systems of automobiles.


SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a ceramic substrate is to be connected with a second circuit plane made of a green tape substrate. For example, the green tape substrate may constitute the signal portion of a multi-layer circuit in a thick-film hybrid circuit. For this purpose, however, it is necessary to have a reliable electrical and mechanical connection between the two substrates. This connection is the object of the process sequence described below.
The multi-layer circuit will generally cover only part of the circuit area of the ceramic substrate. The multi-layer circuit, that is, the green tape substrate, could also be provided with recesses into which the power components are inserted which are then electrically connected with the circuit, for example, by means of bonding wires.
The circuit according to the invention avoids the drawbacks of the green tape substrate, since the strength and thermal conductivity of the entire circuit is determined by the ceramic substrate.
According to the invention, vias are formed in the green tape substrate before the ceramic substrate and the green tape substrate are connected and these vias are filled with silver or a similar conductive contact material. The surfaces of this contact material then form counter-contact faces on the green tape substrate corresponding to the contact faces on the ceramic substrate. Vias are stamped and drilled holes in the green tape substrate. A typical via has a diameter of about 0.2 mm.
Before the two substrates are connected, the contact faces on the ceramic substrate are imprinted with a bonding layer. A silver paste that is low in glass or free of glass is available as a bonding layer. If copper is selected as the bonding layer a particularly reliable bond can be produced between the silver contact face on the ceramic substrate and the counter-contact face on the green tape substrate.
The diameter of the contact faces and thus of the connecting layer as well should in any case be larger, for example 1 mm, than the diameter of the counter-contact faces (0.2 mm). Thus there exists a certain tolerance for the placement of the green tape substrate onto the ceramic substrate in order to align the counter-contact face to the corresponding contact face.
Another significant aspect of the present invention is that, likewise before the connection of ceramic substrate and green tape substrate, either t

REFERENCES:
patent: 4130722 (1978-12-01), Levijoki
patent: 4645552 (1987-02-01), Vitriol et al.
patent: 4652977 (1987-03-01), Jones
patent: 4799984 (1989-01-01), Rellick
patent: 5087509 (1992-02-01), Kuromitsu et al.
patent: 5176772 (1993-01-01), Ohtaki
patent: 5176773 (1993-01-01), Thompson et al.

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