Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame – With structure for mounting semiconductor chip to lead frame
Reexamination Certificate
1999-08-06
2001-12-04
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
With structure for mounting semiconductor chip to lead frame
C257S081000, C257S099000, C257S787000, C361S723000, C361S772000, C361S773000, C361S813000
Reexamination Certificate
active
06326680
ABSTRACT:
This application comprises an invention which is partly also described in the simultaneously filed applications “Optocomponent capsule having an optical interface” and “Leadframe for an encapsulated optocomponent”.
The present invention relates to devices and a method for retaining and positioning optocomponents in a mould cavity during encapsulation of optocomponents by means of transfer moulding.
BACKGROUND
In the earlier Swedish patent application SE-A 9400907-3, filed Mar. 18, 1994, a method is described for encapsulating optocomponents by means of transfer moulding and for achieving at the same time an optical interface in the wall of the capsule. This method was developed based on a conventional encapsulating method for microelectronic circuits, where an electrically conducting leadframe is used for establishing an electric connection to microelectronic circuit chips. The leadframe is usually a punched or etched metal piece, e.g. a thin copper or aluminium sheet. The leadframe comprises a special, suitably adapted portion termed “flag”, onto which a microelectronic circuit is mounted before it is moulded into the encapsulating material. Before the moulding embedment, the microcircuit chip is also electrically connected to contact pins of the leadframe by friction welding (ultrasonic welding), “bonding” by means of “bonding” wires.
Moreover, when encapsulating optocomponents an optical interface is to be formed in the wall of the capsule. This, of course, puts additional conditions on the method. The required mechanical accuracy is achieved by mounting the optocomponents on a common carrier or substrate such as a plate, which thereafter is attached to the flag. Finally the carrier is positioned in relation to the external geometry. This is achieved by means of V-grooves on the carrier plate, in which guide pins extending through the mould cavity fit.
However, it can in many cases be difficult to keep, during the moulding embedment, the carrier plate with its guide grooves well engaged with the guide pins, due to the fact that a high pressure is normally required in injection moulding. This pressure can typically be of the magnitude of order of 10-15 bars. Furthermore, the injected material can have a high viscosity, which can also prevent or deteriorate the good alignment of the guide grooves with the guide pins.
Optical fiber connectors having alignment means such as guide pins are disclosed e.g. in U.S. Pat. No. 5,199,093.
In the published European patent applications EP-A2 0 361 283 and EP-A1 0 600 501 typical encapsulated semiconductor devices are disclosed comprising a lead frame.
In the published International patent application WO-A1 93/18456 an integrated circuit package is disclosed having a moulded ring at the edges of the circuit chip enclosing a lead frame. The lead frame has a centrally located flag, having a window and attached to the marginal portions of the bottom side of the chip, the ring and the window allowing access to the bottom side of the chip.
In U.S. Pat. No. 5,233,222 an encapsulated semiconductor device is disclosed having a lead frame comprising a flag, a hole being provided in the flag.
In the published Swedish patent application SE-B 461 456 a mould is disclosed for forming through-holes in a moulded body. The mould has pins engaging at their ends the lower side of a diaphragm, the top side of the diaphragm being subjected to a pressurized fluid.
SUMMARY
It is an object of the invention to provide a method and suitable moulds for manufacturing an encapsulated optocomponent having accurately arranged guide holes for providing an optical interface.
It is an additional object of the invention to provide means for positioning positively and securely an optocomponent at guide pins in the moulding process for producing an encapsulated optocomponent.
It is a further object of the invention to provide means, in the production of an encapsulated optocomponent and when using guide pins for positioning the optocomponent in a mould, so that the guide pins during the encapsulation can be supported as close to the optocomponent or a carrier thereof as possible, for avoiding the risk that the guide pins will be deflected during injection of an encapsulating material, for providing a high accuracy to the positioning of the optocomponent or carrier comprising guide grooves in relation to the guide pins and the guide holes made by them in a moulding process.
It is a further object of the invention to provide an encapsulated optocomponent having provisions of improved thermal dissipation from the component and a leadframe for achieving it.
These and other advantageous objects are achieved by the invention and appear from description hereinafter, the scope of the invention being defined in and the characteristics thereof being set out in the appended claims.
Thus, an encapsulation method is used which is based on the conventional encapsulation process of microelectronic circuits and comprises essentially that a leadframe is used for providing electronic contact between optocomponents and electronic components. Further, in the encapsulating process an optical interface is simultaneously produced at an exterior side of the capsule.
In the encapsulating process it is required, as has been mentioned above, that the carrier or substrate, i.e. the part on which the optocomponents are mounted and which can then be attached to the flag of a leadframe, is adequately positioned during the moulding stage. By providing then, in one embodiment the mould tool with a spring-loaded plunger moving in a cylindrical bore, the plunger is pressed against the bottom side the flag and thereby against the carrier, so that the carrier will remain in a correct position in relation to guide pins during the moulding stage.
The positioning method also implies that the hole, which the plunger after the moulding stage leaves behind next to the bottom side of the flag, can be efficiently used for dissipation of thermal heat generated by the optocomponent. A cooling flange of a heat conducting material can then be mounted directly against the embedded optocomponent or flag and provide a good thermal dissipation.
Generally a method for production of an encapsulated optocomponent, in which the optocomponent is moulded into an encapsulating material, in particular a plastics material, comprises that first an optocomponent is manufactured or provided. The component shall comprise guide grooves or positioning grooves on a first, top surface and further it has a second, bottom surface, which is located opposite to the first one, and is generally essentially flat. The guide grooves are highly parallel to each other and are advantageously located next to edges of the optocomponent. The optocomponent can comprise a substrate plate having the guide grooves and carrying an optochip.
In a first case, the optocomponent is positioned by placing guide pins are placed in an opened mould cavity in a suitably designed mould and then placing the optocomponent in the open mould cavity of the mould, so that the guide pins engage the guide grooves. In a second case, the opposite sequential order of these steps can be used, i.e. the optocomponent can first be placed in an opened mould cavity of the mould and then the guide pins are placed in the opened mould cavity, so that the guide pins engage in the guide grooves.
After this, the mould cavity of the mould is closed and a resilient force is applied to the second surface of the optocomponent, so that it is pressed with a force against the guide pins for a correct positioning of the optocomponents having its guide grooves in hard engagement with the guide pins, this force being chosen to be sufficient for maintaining this mutual position. An elastic force can also be applied before the closing of the mould cavity. Thereupon, a normal encapsulating process is performed by introducing, e.g. injecting, the encapsulating material into the closed mould cavity and by making it solidify, by a hardening procedure and/or by cooling. Then the procedure is finished and the mo
Engstrand Jan-Åke
Eriksen Paul
Moll Hans-Christer
Steijer Odd
Burns Doane Swecker & Mathis L.L.P
Chambliss Alonzo
Chaudhuri Olik
Telefonaktiebolaget LM Ericsson (publ)
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