Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package
Reexamination Certificate
2000-01-31
2002-04-23
Clark, Jhihan B (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
C257S099000, C257S100000, C257S081000, C257S082000, C257S432000, C257S433000
Reexamination Certificate
active
06376902
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to an optoelectronic structural surface-mountable structural element (SMD) in which an optoelectronic chip is attached to a chip carrier part of a lead frame via a heat-conducting connection. The lead frame has a connecting part disposed at a distance from the chip carrier part which is connected with an electrically conducting electrical contact of the optoelectronic chip. The optoelectronic chip and a part of the lead frame are encased by a casing forming a foundation, whereby the foundation has a first main surface and a second main surface opposite the first main surface. The external connections of the chip carrier part and the connection part provided in the lead frame project outside the casing, whereby the external connections are either bent outside the foundation at first to the second main surface of the foundation opposite the first main surface and in the further course either below the foundation to its center or are bent away to form rocker-shaped connection stumps. It particularly relates to an optoelectronic structural element with an optoelectronic semiconductor chip, especially with a light-diode chip (LED) operated at a high output.
Such a structural element is known, for example from Published, European Patent Application EP 0 400 176 A. A so-called TOPLED is described here, in which a light-emitting semiconductor chip (LED chip) is attached to a flat chip carrier part of a lead frame. The lead frame consists of a chip carrier part with external connections and a connection part disposed at a distance from the latter, thus electrically insulated from it. The chip carrier part with the semiconductor chip, the connection part, and partial areas of the external connections are encased by a casing consisting of an emission-impermeable foundation with a recess and an emission-permeable window part filling this recess. The chip carrier part and the connection part are encased by the foundation or are embedded in it so that partial areas of upper sides of the chip carrier part and the connection part with the remaining floor surface tightly close the recess. The semiconductor chip is completely encased by the emission-permeable window part except for its lower side, with which it lies on the chip carrier part. The recess and its inner surfaces are formed and disposed so that they form an essentially truncated cone-shaped reflector for the radiation emitted by the semiconductor chip.
An optoelectronic structural element is described in Published, Non-Prosecuted German Patent Application DE 195 36 454 A1 in which, to improve the heat conduction of the semiconductor chip, two external connections of the chip carrier part of the lead frame are widened opposite the external connections of the connection part.
In the case of the known optoelectronic structural elements described above, the semiconductor chip operates at high currents and thereby high output, as for example is the case with so-called power-LEDs, leading to high heating because of insufficient heat conduction from the semiconductor chip. This heating frequently leads to impairments of the functional ability of the semiconductor chip, such as accelerated aging, breaking off of the semiconductor chip from the lead frame, breakage of the semiconductor chip away from the lead frame, breaking away of bond wires, or destruction of the chip. The known widened external connections of the chip carrier part favor delamination of plastic from the lead frame that, for example, can cause penetration of moisture to the semiconductor chip.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an optoelectronic structural element that overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which improved heat conduction from the chip is assured, without at the same time substantially altering the housing dimensions and without at the same time substantially increasing delamination danger.
With the foregoing and other objects in view there is provided, in accordance with the invention, an optoelectronic surface-mountable structural element (SMD), including:
a lead frame having a chip carrier part, external connections, and a connection part disposed at a distance from the chip carrier part, at least three of the external connections being heat-conducting connections thermally conductively connected to the chip carrier part;
an optoelectronic chip heat-conductively connected to the chip carrier part of the lead frame, the optoelectronic chip having an electrical contact electrically conductively connected to the connection part; and
a casing having a foundation encasing the optoelectronic chip and a part of the lead frame, the foundation having a first main surface and an outward facing second main surface disposed opposite the first main surface, the external connections and the connection part project outside of the casing, the external connections and the connection part being bent outside of the foundation toward the outward-facing second main surface of the foundation and in a further course being further bent one of below the foundation toward a center of the outward-facing second main surface and away from the foundation for forming rocker-shaped connection stumps, the at least three of the external connections projecting from the casing on at least two sides of the casing at different places at a distance from each other, the heat-conducting connections as seen in a top view of the lead frame projecting from the casing on at least two sides and starting from the chip carrier part run toward the outside in a stellate form within the casing and separately from each other.
In the structural element according to the invention, it is provided for the chip carrier part to have at least three separate thermally conducting external connections connected with the chip carrier part which project from the casing at different places at a distance from each other and are configured so that they all simultaneously lie on the connection or lead plate in the assembled state of the structural element provided for mounting the structural element. The heat resulting in the chip in the operation of the structural elements is consequently fed into the lead plate at three different points and is distributed on a broad surface of the latter. A distinctly improved heat conduction from the optoelectronic chip is thereby obtained.
In a particularly preferred form of the structural element according to the invention, the external connections of the chip carrier part, in a top view of the lead frame, run separately from each other in an essentially stellate form, starting from the chip carrier part. The heat conduction points from the structural element to the lead plate thereby present large distances from each other, whereby a very large-surface distribution of the thermal energy derived from the chip in the operation of the structural element is conducted away by way of the chip carrier part and its external connections.
The external connections in the area in which they run outward in a star shape advantageously present longitudinal central axes, wherein two adjacent connections always present an angle of about 90° to each other. In this configuration, the plastic area between the connections is maximum, whereby the delamination danger is reduced, for example in the case of temperature fluctuations.
If the structural element is provided with at least a first and a second optoelectronic chip, the chip carrier part according to the invention presents at least two external connections which project from the casing at various places on it with a distance between them. The lead frame here presents at least two connection parts with an external connection in each case, which also project sideways from the casing. It is also preferable here for the external connections of the chip carrier part and the connection parts, viewed from the top of the lead frame, to essentially be disposed in the stellate form, wh
Clark Jhihan B
Osram Opto Semiconductors GmbH & Co. oHG
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