Stock material or miscellaneous articles – Structurally defined web or sheet – Including variation in thickness
Patent
1982-08-02
1985-04-23
Lesmes, George F.
Stock material or miscellaneous articles
Structurally defined web or sheet
Including variation in thickness
428163, 428167, 248633, B25H 306, B25H 110
Patent
active
045130469
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an antistatic support for work places serving for the manipulation of electronic components and composed of a rubber layer having a specific volume resistance (according to DIN 53482) of at least 10.sup.2 .OMEGA.cm.
The damage to electronic components by the effects of electrostatic charges constitutes a problem which increases with the sensitivity of such components. Of particular significance is the high capacitance constituted by a human being. Values up to 4,000 pF have already been measured and the mean value is in the order of about 200 pF. Due to rubbing against articles of clothing, the floor, seating surfaces and the like the body is electrostatically charged up to peak voltages of 6,000 volts. The discharge of such voltages across an electronic component can lead to its destruction, and the damage need not be immediately noticeable, rather can be present in terms of appreciably impairing the service life.
Particularly endangered electronic components are, for instance, so-called CMOS switching circuits, because their insulated control electrode (gate) possesses a high impedance and capacitively influences the flow of current. Such type of switching circuits possess an extremely thin dielectric film which is suitable for taking-up an undesired charging state, whereby then, if there is exceeded a critical threshhold, there occurs a breakdown through the dielectric to ground potential. Also a great many other electronic components are highly sensitive to antistatic charges.
In order to counteract such problem there are used simultaneously at the present time three measures: can be accomplished a neutralization of electrical charges, a protective resistance, and finally there is ensured removal of electrostatic charges.
As an additional safety factor there are also used floor covering mats which cause grounding of all persons who come into the vicinity of the work place.
The known antistatic supports possess a multi-layer construction, and the top layer consists of a mass of ground conductive plastic material. Located therebelow is a highly conductive intermediate layer, for instance in the form of a mesh composed of carbon fibers. Below such there is finally located a foamed plastic layer for increased comfort and an underside composed of a material resistent to sliding.
This known support can attain the desired effect of removing antistatic charges, but it is however relatively uneconomical by virtue of its complicated construction. Additionally, the temperature resistance of the plastic material used in the top layer is not sufficient in order to avoid damage to such layer, for instance during unintentional contact with a soldering iron. In fact, there exists the danger that upon burning through the top layer the highly conductive intermediate layer will be exposed, which can lead not only to undesired short-circuits of the manipulated components, but even constitutes a certain danger in the event there come into contact therewith bare conductor parts.
There have also already become known supports formed of antistatic rubber material. These supports likewise possess, just as was the case for the above-mentioned multi-layer supports, an essentially smooth, if desired, slightly structured top surface. During the course of the work which is performed at such type of support, for instance the fabrication of electronic circuits, such support becomes contaminated by wire pieces, solder material and waste, and hence, hinders a rapid and clean work.
Therefore, the present invention has for its object the provision of an antistatic support which from the standpoint of electrical safety is 100% satisfactory, affords a positive withdrawal of electrical charges from antistatically charged bodies, is resistant against sliding, and always presents a clean work surface even over longer periods of use.
This is achieved according to the invention with an antistatic support of the previously mentioned type in that, at least a part of the top surface of the support possesses preferab
REFERENCES:
patent: Re20924 (1938-11-01), Nickle
patent: D85859 (1931-12-01), Capouch
patent: 2032935 (1936-03-01), Hurt
patent: 2449465 (1948-09-01), Flaker
patent: 3922409 (1975-11-01), Stark
patent: 4139138 (1979-02-01), Besselman, Jr.
patent: 4281038 (1981-07-01), Ambros et al.
Advertisement published in the Journal "Elektronik", vol. 3, 1978, p. 7.
Tichy Heinz
Waniek Kurt
Kleeman Werner W.
Lesmes George F.
Semperit Aktiengesellschaft
Swisher Nancy A. B.
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