Plastic article or earthenware shaping or treating: apparatus – Distinct means to feed – support or manipulate preform stock... – Opposed registering coacting female molds
Patent
1984-12-17
1986-07-08
Lowe, James
Plastic article or earthenware shaping or treating: apparatus
Distinct means to feed, support or manipulate preform stock...
Opposed registering coacting female molds
26427217, 2643288, 425125, 425544, B29C 4502, B29C 4514
Patent
active
045990620
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention generally relates to encapsulation by transfer molding and more particularly, to an encapsulation molding apparatus or transfer molding press for use in encapsulation by transfer molding of miniature or small-sized electrical elements with employment of a synthetic resin.
TECHNICAL BACKGROUND
Conventionally, it has been a common practice that miniature or small-sized electrical elements are preliminarily attached, at a predetermined pitch or interval, to a lead frame of a thin sheet blanked to form a large number of terminals as shown in FIG. 1. Subsequently, the electrical elements thus prepared are formed into a package by a thermosetting resin material such as phenolic resin, epoxy resin and the like so as to be made into product main body resin portions (2) as shown in a side elevational view of FIG. 2, and thereafter, formed into finished products through processes for cutting off the terminal portions along one-dotted chain lines, trimming at opposite selvadge or edge portions, and finally folding the respective terminals along side faces of said resin portion (2). In connection with the above, the packaging work by the synthetic resin material as described above is normally effected on a large scale through mass production by the employment of a transfer molding press in which metal molds for packaging are set.
FIG. 3 shows such packages formed by a conventional apparatus in a state as they are withdrawn from metal molds, with a portion at the upper right equivalent to slightly over 1/4 of the entire drawing being represented in a top plan view for convenience of illustration. In FIG. 3, there is provided a cull portion (3) formed at a sprue located at the central portion of the metal molds, and connected to respective encapsulation molded resin portions (2) through portions each formed by gates (4) and runners (5) of the metal molds.
Incidentally, in the metal molds, shallow recesses into-which the sprue (3), runners (5), gates (4) and lead frames (1) are fitted, are mainly formed in a lower mold, while cavities into which the resin material is injected under pressure to form the product main body resin portions (2), are formed in an upper mold and the lower mold. The upper mold is further formed with a through-opening in a position immediately above the sprue (3) of the lower mold, to which opening, a lower half portion of a pot for charging the resin material thereinto is fixedly connected. The resin material as described above heated in the pot so as to be in a semi-molten state is injected into the cavities referred to above by an extruding plunger connected to a rod of a pressing cylinder of a molding press through the sprue (3), runners (5) and gates (4) so as to form the respective encapsulation molded resin portions (2) through pressurization. In the above case, since the upper and lower molds of the metal molds are respectively clamped in contact with an upper plate and a lower plate in which heaters are embedded, these upper and lower molds are heated up to a predetermined temperature through heat conduction, but, between one resin portion (2) at a position A which is molded at the cavity closest to the pot i.e. the sprue (3) and another resin portion (2) at a position B to be molded at the cavity farthest from the sprue (3) on the contrary, there is a difference in the time required for the resin material to reach there. Accordingly, owing to the necessity for the resin material which has flowed into the cavity at the position B to retain a fluidity required for the pressure molding, it is so arranged that a filler which delays the hardening time i.e. which increases the fluidity index is mixed into the whole resin material. With the use of the molten resin material as described above, the resin material is poured under pressure from the pot into the respective cavities through the plunger referred to earlier so as to be subjected to a pressure molding, with a subsequent curing to achieve sufficient hardening, and thus, in the conventional practi
REFERENCES:
patent: 2382200 (1945-08-01), Brunner
patent: 3013308 (1961-12-01), Armour
patent: 4347211 (1982-08-01), Bandoh
patent: 4368168 (1983-01-01), Slepcenic
Dai-Ichi Seiko Co., Ltd.
Lowe James
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