Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Patent
1996-10-22
1999-03-23
Ortiz, Angela
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
26427217, 2643284, 2643285, B29C 3108, B29C 4502
Patent
active
058855076
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for encasing various `lead frames` which are provided with integrated circuits.
BACKGROUND OF THE INVENTION
A method of this type is disclosed in the `Patent Abstracts of Japan`, vol. 13, no. 44 (E-710), 31 Jan. 1989. In this publication the use of an elongated plunger which has to be moved in a corresponding distribution cavity is described. An elongated tablet is placed in this distribution cavity. The plastic tablet is of a particular size and it is therefore also necessary to produce this tablet as a special product. The production of such elongated tablets is relatively complex and differs from the production of standard tablets. In this context reference is made to European Patent Application 0 370 564. The tablet is fed from above, i.e. in a direction parallel to the direction of movement of the plunger, in a manner which is not indicated in more detail. With this procedure, the problem arises that it is necessary to accurately determine the amount of plastic for each injection. After all, the amount of plastic must be metered depending on the size of the injected casing.
If a large number of different sizes of casing are used in a factory, this implies that a large diversity of tablets is required.
In order to solve this problem, the largest possible casing is often taken as the starting point. This means that if smaller casings are used a large amount of waste is produced. Frequently, the amount of waste will be greater than the amount of material used for the casing. Because these materials are frequently thermosetting plastics, there is no simple way of re-using them. If the tablets are to be fed through an opening in the plunger sleeve when said opening is exposed by the plunger, a relatively long stroke of the plunger is required. This leads to complications because, at least in the final phase of this so-called transfer movement, the plunger has to transmit a very high force in order to inject the plastic.
Because of the presence of the opening or the movement of the plunger completely outside the plunger sleeve, an appreciable temperature difference arises between the plunger and the plunger sleeve. Because the plunger is colder, problems arise in liquefying the tablets.
A further disadvantage is that if a machine is operated with various molds where, for example, a larger or smaller number of injections is necessary, the plunger block together with the mold must be interchanged.
U.S. Pat. No. 4,983,110 discloses a mold which has an elongated distribution cavity and rows of mold cavities located on either side. There is at least one further row of mold cavities behind each row of mold cavities. Fluid plastic originating from the distribution cavity must be transported from the first row to the second row in order to encase the articles located therein. A construction of this type is found to be inadequate in practice and leads to metering difficulties and/or errors in encasing.
It is stated in this patent that one or more tablets can be placed in the elongated mold cavity.
In the `Patent Abstracts of Japan`, vol. 16, no. 57, March 1990, a method and installation are disclosed for injecting into rows of mold cavities located opposite one another from an elongated distribution cavity. A single rectangular plunger is used for this purpose.
In the `Patent Abstracts of Japan`, vol. 9, no. 226, a distribution cavity located between two rows of mold cavities is described, the plastic tablets being fed into the distribution cavity in a direction perpendicular to the plunger and perpendicular to the distribution cavity. It can immediately be seen from the drawing that the tablets are present in the mold assembly for a relatively long period, which leads to warming of said tablets and the onset of the hardening reaction. This leads to substantial problems if a malfunction occurs in the installation. The tablets will then be exposed to this heat for a prolonged period while the installation is stationary, and it is necessary to clean the enti
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Boschman Holding B.V.
Ortiz Angela
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