Electricity: conductors and insulators – Boxes and housings – Hermetic sealed envelope type
Patent
1995-09-05
1997-06-03
Tolin, Gerald P.
Electricity: conductors and insulators
Boxes and housings
Hermetic sealed envelope type
310344, 361809, 257704, H05K 506
Patent
active
056356722
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a hermetically sealed package fop an electronic device (hereinafter sometimes simply referred to as a device) in which the sealing is carried out under milder conditions than have conventionally been used. The package of the present invention is applicable to packaging of a wide range of devices.
BACKGROUND ART
Electronic devices include a variety of kinds, and most of them ape not resistant against the environment as they are. That is, if exposed as such in the air, a device undergoes deterioration by moisture, oxygen or other corrosive substances in the air and reduces its functions.
Among such delicate devices are included semiconductor devices such as IC, LSI, transistors, And diodes; piezoelectric devices; oscillators; condensers; and resistors.
These devices do not withstand long-term use stably unless some protection against the environment is afforded. Protection is, in principle, to prevent a device from being exposed directly to air and includes various means, from simple coating to packaging, i.e., perfect hermetic sealing, selected according to the type of the device, the purpose of protection or the degree of desired protection.
Of these protecting means, a "package" is important. While "package" in general covers a considerably broad concept, the term "package" as used herein means a hollow container, comprising a body in which a device is to be put and a cap or lid for covering the body, the body and the cap or lid being hermetically sealed.
The above-mentioned package has a sealing part at which the body and the cap or lid are adhered to each other, and this part has great influences on the airtightness of the whole package.
A widely used method for hermetically sealing the body and the cap or lid is "adhesion" in its broad sense. The term "adhesion" in its broad sense embraces not only mere adhesion with an adhesive but welding and fusing.
Where sealed areas are made of metal, they may be subjected to welding or silver soldering. Sealed areas made of ceramic or glass may be fused together with a glassy adhesive. Resin adhesives may be used irrespective of the material to be adhered.
However, the former two methods mentioned above require heating to such a high temperature that the device might be damaged, and are therefore unsuitable to those devices which are easily deteriorated at high temperatures. Besides, these methods incur high cost.
Adhesion with a resin adhesive is preferred for the low sealing temperature and the low sealing cost but has a disadvantage of low retention of airtightness, in particular, low impermeability to moisture. Therefore, resin adhesives have not yet been widespread in those packages requiring long-term reliability.
DISCLOSURE OF THE INVENTION
An object of the present invention is to eliminate the disadvantages associated with use of a resin adhesive in package sealing and to provide a widely applicable resin-sealed package.
In the present invention, use of a metal foil as a covering member of a package for an electronic device provides sufficient hermetic seal even with a resin adhesive, thereby accomplishing the above object.
The inventors of the present invention first of all evaluated airtightness of conventional resin-sealed packages in terms of moisture impermeability. Since it is not easy to measure change of humidity inside a package, a package for a quartz oscillator, which suffers appreciable deterioration of characteristics by humidity, was tested under accelerated conditions in a pressure cooker.
The accelerated test was conducted as follows. A quartz oscillator, the oscillation frequency of which had previously been measured, was sealed into a package. The frequencies were measured before and after sealing, and the difference between them was taken as an initial change. The sealed test piece was kept in saturated steam at 121.degree. C. under 2 atm in a pressure cooker and taken out occasionally to measure the oscillation frequency to obtain changes with time. The measurement continued for 48 hours
REFERENCES:
patent: 4472652 (1984-09-01), Brice et al.
patent: 4480262 (1984-10-01), Butt
patent: 4542259 (1985-09-01), Butt
patent: 4814943 (1989-03-01), Okuaki
patent: 4930345 (1990-06-01), Bausch
patent: 5473216 (1995-12-01), Brosig
Nippon Carbide Kogyo Kabushiki Kaisha
Tolin Gerald P.
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