Agitating – Stirrer within stationary mixing chamber – Rotatable stirrer
Reexamination Certificate
2000-01-27
2001-10-30
Soohoo, Tony G. (Department: 1723)
Agitating
Stirrer within stationary mixing chamber
Rotatable stirrer
C366S325400, C366S348000
Reexamination Certificate
active
06309097
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to encapsulants for microelectronic devices, and more particularly to a device for mixing multi-part encapsulants to ensure a homogeneous mixture.
DESCRIPTION OF THE RELATED ART
Encapsulants such as silicone encapsulants used for sealing, protecting and preserving microelectronic devices are well known. Typically, encapsulants are formed by thoroughly mixing two component parts (i.e., a base and a curing agent) followed by a vacuum de-airing to release entrained air bubbles entrained in the mixture. Following the de-airing process the encapsulant is dispensed on a device and finally cured.
Encapsulants prepared by manual stirring are subject to excessive air entrapment. Before these encapsulants can be used for coating dies and other devices, they must be de-aired to remove unwanted air bubbles. A typical de-airing procedure is a two-step process in which a mixture is first vacuum de-aired for up to 30 minutes, followed by a standing period of 5 to 10 minutes to allow any remaining small surface bubbles to dissipate. Thus, the total time required for de-airing may average about 40 minutes.
In addition, when encapsulant components are combined manually, it is difficult to consistently obtain homogeneous mixtures. Variations in mixing times, stirring speeds and stirring techniques are known to produce non-homogeneous materials. When a nonconforming material is used to coat a device such as an integrated circuit, the coating may not completely cure. If the coating fails to completely cure, the entire integrated circuit must be scrapped.
Accordingly, it is desirable to provide improved apparatus and methods for mixing encapsulants for microelectronic devices. The preferred device and method would provide a homogeneous encapsulant with minimal entrainment of air bubbles.
SUMMARY OF THE INVENTION
The invention provides a stirring machine and method for mixing encapsulants. The stirring machine includes a variable speed motor; a stirring rod coupled to an output shaft of the motor; a lead screw for vertical adjustment of the stirring rod; a stirring head secured to the stirring rod, the stirring head including at least two spaced apart arms, each of the arms being radially equidistant form the axis of rotation; and a control system for varying the rotational rate and height of the stirring head and the duration of stirring.
REFERENCES:
patent: 468844 (1892-02-01), Sullins
patent: 4175875 (1979-11-01), Van Horbek
patent: 4923908 (1990-05-01), Lostumo et al.
patent: 5549384 (1996-08-01), Reynolds
patent: 5739582 (1998-04-01), ElHatem et al.
Pengkuson Somchai
Petkra Jom
Wongsarakham Nipon
Agere Systems Guardian Corp.
Duane Morris & Heckscher LLP
Soohoo Tony G.
Sorkin David
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