Plastic and nonmetallic article shaping or treating: processes – Vacuum treatment of work – To degas or prevent gas entrapment
Patent
1996-08-12
1999-03-09
Ortiz, Angela
Plastic and nonmetallic article shaping or treating: processes
Vacuum treatment of work
To degas or prevent gas entrapment
2642711, 26427211, 264311, 425120, 425434, 425435, 425546, B29C 3908, B29C 3910, B29C 3942
Patent
active
058795987
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of encapsulating electronic components and also to an apparatus by which such components can be encapsulated. The invention extends to filling, casting, embedding, encapsulation, impregnation and potting applications. In such applications, typically a relatively high viscosity liquid resin is to be introduced into a small cavity, and a particular use for which the invention is envisaged is the introduction of encapsulating resins into housings for electronic components.
It is known to make use of centrifugal force to assist the filling of mould cavities with fluid materials, for example molten metals or plastics. Such processes are known as "spin casting" or "centrifugal casting".
It is also known from British Patent Specification 2 241 465 to use centrifugal force to assist the filling of components with encapsulating resin. However in this specification an overfilling technique is described, and the top face of the components is closed during filling. This has the disadvantage that it is necessary to snap off an injection nozzle from the filled and cured component.
In prior art processes, a certain quantity of resin or other liquid remains in and hardens in a feed channel and is waste which is discarded.
According to the present invention there is provided a method of encapsulating components in an encapsulating liquid, the method comprising the steps of defining a cavity, and an opening, encapsulate the components in the associated chamber, the opening of each chamber, when the centrifuge is operating, lies radially outside of a dispensing opening of the dispensing vessel, with the chamber walls surrounding each cavity opening being out of contact with the dispensing vessel, the liquid is introduced, and dispensing opening, into the cavity and around the component through centrifugal force.
By charging the dispensing vessel with the exact quantity of liquid to be introduced into the cavity, the advantage is achieved that no liquid is wasted. This is of particular benefit when the liquid is a resin which cures, because once curing has taken place, recycling of the resin is no longer possible. Furthermore by suitably designing the dispensing vessel and its opening, it is possible to ensure that after operation the dispensing vessel needs no cleaning before being refilled with the next charge of resin.
In the encapsulation of electronic components by a settable resin, it is important to ensure that no air is trapped in the resin and/or in the cavity. Preferably therefore the resin to be introduced into the cavity is degassed before being placed in the dispensing vessel.
According to a second aspect of the invention there is provided apparatus for encapsulating components in an encapsulating liquid, the apparatus comprising a plurality of dispensing vessels each having a dispensing opening, the dimensions of the dispensing openings being such that encapsulating liquid will not flow therethrough under normal gravitational conditions but will flow therethrough when centrifugal force is applied, a vacuum centrifuge, chambers defining cavities within which the components will be encapsulated, and means for locating the dispensing vessels and the chambers in the vacuum centrifuge so that when the centrifuge is operating the cavities are evacuated and are located radially outward of, and out of contact with, the dispensing openings of the dispensing vessels such that when the liquid is drawn out of the dispensing openings on application of centrifugal force through centrifuge operation, the liquid will flow into the cavities and around the components in the cavities to encapsulate the components.
Conveniently the dispensing vessel comprises a cup with an open top and a narrow bore in its base to form the dispensing opening. A measured quantity of liquid resin can be placed in the cup through the open top, and will be prevented from flowing out through the opening under normal gravitational conditions by surface tension or suitable rheology.
In a preferred embodiment the dispensi
REFERENCES:
patent: 2413401 (1946-12-01), Youngblood et al.
patent: 4374080 (1983-02-01), Schroeder
patent: 4443175 (1984-04-01), Rose et al.
patent: 5200125 (1993-04-01), Osada
patent: 5665281 (1997-09-01), Drummond
Electronic Techniques (Anglia) Limited
Ortiz Angela
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