Coating processes – Electrical product produced – Integrated circuit – printed circuit – or circuit board
Patent
1986-07-16
1988-11-15
Beck, Shrive
Coating processes
Electrical product produced
Integrated circuit, printed circuit, or circuit board
437225, 437245, B05D 512
Patent
active
047848723
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for encapsulating microelectronic hybrid semi-conductor circuits, or microelectronic semi-conductor components.
DESCRIPTION OF THE PRIOR ART
Highly reliable microelectronic circuits for professional, medical, and military use require a long-term protection against the effects of moisture traces or corrosive agents. For this purpose, mostly metallic or ceramic housings are used which are hermetically sealed by welding or soldering. Such housings, for example Kovar housings, as well as the associated encapsulation technologies, for example rolled seam-, ring hump-, electron-, or laser beam welding, or glass soldering as well as glazing techniques, are very involved or costly and are not thermally uncritical for micro-circuits.
Therefore, it has been attempted for years to improve inexpensive as well as expedient plastic packaging for professional microelectronic circuits of proven use in commercial electronics and especially in consumer electronics.
For this purpose, numerous special plastic compounds and sealing techniques were developed, which are described, for example, in the following German Patent Publications Nos. DBP 2,347,049, DE-AS 2,538,119, DE-AS 2,628,823, DE-AS 2,545,471, DE-OS 2,748,523, DE-OS 2,656,139, DE-OS 3,137,480, and DE-OS 3,151,902.
It has been shown, however, that the proposed solutions did not achieve completely gas-and water-tight seals. The higher expansion coefficient of the plastic encapsulation namely leads to tensions and thereby to detachments and cracks at the ceramic boundary surfaces due to high temperature changes. Under high reliability requirements and strong thermomechanical shock loading (-65.degree. to +125.degree. C.), plastic capsules are therefore not used. Also according to MIL-M-38510 specifications until now only hermetically welded or soldered metal and ceramic housings have been acceptable.
It is further known, for example from German Patent Publication DE-PS No. 2,347,049, that bonded semi-conductor circuits may be protected by elastic cover-layers made of plastic foam. Under large temperature change loads, high thermomechanical tensions must be expected in the capsule, especially with foam cushioning, so that the boundary surfaces separate from each other and moisture or corrosive agents may penetrate along the seams. If one avoids the capsule and directly pour-seals the cover-layer with a synthetic resin which approximately matches the expansion coefficient as disclosed in German Patent Publication DE-OS No. 2,922,005, then the water-steam impermeability, or the lack of cracks as well as pores, is not assured. Also with epoxy resin-silicone elastomer combinations (DE-OS No. 2,922,005), a separation is to be expected under loads caused by large temperature change due to the low adhesion, so that, due to hair-line cracks, moisture may be distributed along the entire separation seam.
It is further known from German Patent Publications DE-OS Nos. 2,551,778, DE-PS 1,514,478 to encapsulate condensers in a moisture-tight manner with two-sided plastic laminated metal foils. However, this technique requires a geometrically simple stuctural element shape and an adhesive shrink-on plastic lamination. Hybrids which are covered by closely spaced bonded IC's or small discrete components are not adhesively laminatable in a pressureless manner without seams or hollow spaces, so that under temperature change requirements between -65.degree. and +125.degree. C. separations or wire deformations occur, which have an adverse on the electrical functional characteristics.
All of the known processes are therefore not suitable to ensure the necessary security of the encapsulation against environmental effects.
OBJECTS OF THE INVENTION
It is the aim of the invention to provide a process which substantially combines the advantages of plastic encapsulation, such as among others, the simple economical configurations, good electrical insulation, and low material costs, with the advantages of the metal and ceramic housing,
REFERENCES:
patent: 3608029 (1971-09-01), Hough
patent: 3876461 (1975-04-01), Flowers
patent: 4001863 (1977-01-01), Kobayashi
patent: 4327369 (1982-04-01), Kaplan
patent: 4388132 (1983-06-01), Hoge et al.
Moeller Werner
von Luettichau Harald
Beck Shrive
Dang Vi Duong
Fasse W. G.
Kane, Jr. D. H.
Messerschmitt-Boelkow-Blohm GmbH
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