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
1998-10-19
2000-12-26
Davis, Robert
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
425116, 4254515, 425592, B29C 4502, B29C 4566
Patent
active
061654051
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a device for encapsulating electronic components, mounted on so-called lead frames, in a mould assembled from two mould halves movable relative to each other and closable onto each other, comprising: in cavities of the mould.
The invention also relates to methods for operating such a device.
Existing presses of the type mentioned in the preamble operate at limited speeds and are susceptible to malfunction and require frequent maintenance.
The present invention has for its object to provide an improved device and improved methods for operating such a device with which electronic components can be encapsulated at higher speed and with less chance of breakdown.
The invention provides for this purpose a device of the type stated in the preamble wherein the means for causing the mould halves to move and to close are formed by a rotatable eccentric which can be coupled to one of the mould halves with interposing of at least one connecting rod. The dimensions of the eccentric are preferably such that the position of the eccentric in a fully opened position of the mould halves is rotated less than 180.degree. relative to the position of the eccentric in which the mould halves close onto each other. A first advantage of a rotatable eccentric for causing the mould halves to move and close is that the movement can take place relatively rapidly. A rotation of the eccentric of a maximum of 180.degree. can take place very rapidly, while an alternative such as for instance driving of a mould half with a screw spindle is less rapid. A second important advantage of the rotatable eccentric is the very favourable movement characteristic which can be derived therefrom. When reaching the two extreme positions of the mould half to be driven, the position of the eccentric will, at a turn of 180.degree. of the eccentric as seen from the driven-out mould half, be situated almost completely behind respectively almost completely in front of the rotation axis of the eccentric. The speed of movement of the driven mould half will, at constant rotation speed of the eccentric, correspond with semi-sinusoids, wherein the speeds close to the end positions approach 0 metres per second. While this ideal situation is only achieved at a rotation of the eccentric through 180.degree., in practice this will have to be slightly less than 180.degree.. A very significant portion of the semi-sinusoids will however be recognizable in the movement characteristic of the driven mould half. This movement characteristic increases the drive speed of the eccentric still further since in the critical positions, i.e. when approaching the end positions of the driven mould half, the speed of the driven mould half will be lower than the speed of the driven mould half when it is situated between the two end positions. Another advantage of this movement characteristic is that the load of the machine parts as well as the energy consumption will be limited compared to existing encapsulating devices. Yet another advantage is that an encapsulating device with a rotatable eccentric requires relatively little maintenance.
In a preferred embodiment the device is provided with a force sensor for measuring the force with which the mould halves close, which force sensor is connected to the drive of the eccentric in order to supply a signal to the drive of the eccentric when a desired closing force has been reached. Due to this step the eccentric not only functions to cause displacement of the driven mould half but the desired closing force can also be provided using the eccentric.
The connecting rod for coupling the rotatable eccentric to one of the mould halves is preferably curved respectively angular. This shape makes it possible to apply a continuous rotation shaft for the eccentric. The curved respectively angular connecting rod in fact enables rotation of the eccentric to a position in which it lies on the side of the rotation axis remote from the mould half. Since the eccentric does not run through a fu
REFERENCES:
patent: 3418692 (1968-12-01), Valyi
patent: 4589830 (1986-05-01), Clawson
patent: 4915608 (1990-04-01), Tsutsumi et al.
patent: 5330347 (1994-07-01), Ten Vaarwerk
patent: 5350291 (1994-09-01), Kitajima
Harmsen Wilhelmus Hendrikus Johannes
Van Haren Lambertus Franciscus Wilhelmus
Venrooij Johannes Lambertus Gerardus Maria
Davis Robert
Fico B.V.
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