The present invention relates to the packaging of integrated circuit dies and, more particularly, to heat dissipation in lead frames.
Very similar processes are utilized to manufacture a large variety of integrated circuit packages or chips. A starting substrate, e.g., a thin wafer of silicon or gallium arsenide, is masked, etched and doped during several process steps, with the type, number and order of the steps depending on the type of integrated circuit being manufactured, to form a number of dies or separate integrated circuits thereon. The dies are singulated or separated with a wafer saw and then packaged individually to form integrated circuit packages or chips.
Each die typically has a back that is devoid of circuitry and a front having integrated circuitry formed thereon. The integrated circuitry is accessible via die wire bonding pads that may be arranged in a variety of configurations on the face or edges of the die.
During the packaging process, each die is attached to a corresponding lead frame. The lead frames are processed in groups, typically in strips or in a continuous coil form. Each strip contains multiple, e.g., six, lead frames and is several, e.g., nine, inches long. A coil contains a larger number of lead frames because it is a much longer continuous strip of material. Each lead frame strip or coil typically is a metal frame designed to support several dies for packaging and to provide the leads for the final integrated circuit package.
A typical lead frame strip or coil is produced from metal sheet stock, e.g., a copper or nickel alloy, by subjecting the sheet stock to a stamping or photochemical etch process to form lead fingers, and side rails having pilot holes therein. The side rails and pilot holes therein facilitate transport and indexing of the lead frame strip or coil by automated packaging machinery. For example, a lead frame strip, individually, or a lead frame coil, as a whole, can be removably clipped to carrier belts that move the lead frame strip or coil through the various manufacturing stages.
Each lead frame has a plurality of lead fingers for connection to the die bonding pads. The lead fingers typically are spot plated with palladium, gold or silver. The conductive leads are plated to provide a metallic surface to which wires may be bonded, as a bond wire usually will not stick directly to lead frame material, such as copper or nickel or alloys thereof.
As the demand for thinner packages increases, it becomes desirable to make the die-lead frame assembly thinner, which can be accomplished by reducing the thickness of the lead frame. However, thinner lead frames exacerbate the problems of heat dissipation both during manufacture and use. Particularly, thinner lead frames will, in the absence of other modifications, be less capable of dissipating the tremendous amount of heat that might build up either during manufacture or during operation.
Problems of heat dissipation have also been encountered in view of increased power demands in the context of integrated circuit packages or chips. Particularly, as integrated circuit packages and chips are increasingly used in operating environments that notably increase the power provided thereto, the need for efficient and effective heat dissipation becomes more and more apparent.
To attend to the task of heat dissipation, manufacturers often provide supplementary media for dissipating heat away from the lead fingers. These supplementary media have often taken the form of small metal elements that are connected to portions of a lead frame.
Conventionally, this attachment is often achieved by using small rivets or tappets to interconnect a portion of a lead frame with the heat dissipating element. However, many disadvantages have been encountered with such an arrangement. Particularly, the use of separate interconnecting members, for the purpose of attaching a heat dissipating element to the lead frame, results in extra components that require undesirable additional expenditures of materials and cost.
It is also known to impart a significant thickness to the heat dissipating element in order to increase heat dissipation capabilities. However, by imparting a significant thickness to a heat dissipating element, limitations are subsequently placed on the overall thickness of the integrated circuit package or chip being manufactured.
Generally, the ends of lead fingers, when juxtaposed adjacent to one another, form the outline of a square or other rectilinear shape which might or might not be occupied by additional material. One type of conventional heat dissipating arrangement involves the placement of a quantity of thermally conductive material within this rectilinear space, along with thermally conductive connections to the siderails or other conducting portions of the lead frame. However, since the areal extent of such a heat dissipation arrangement is limited by the dimensions of the rectilinear space, it is often the case that only a significantly small heat dissipating element is realizable, with the result that heat dissipating capabilities may not be as great as desired.
The present invention broadly contemplates, in accordance with at least one presently preferred embodiment, a lead frame apparatus comprising: a lead frame; and an arrangement for dissipating heat generated at the lead frame, the heat dissipating arrangement being uninterruptedly connected to the lead frame.
In accordance with another presently preferred embodiment, the present invention broadly contemplates lead frame heat dissipating apparatus comprising at least one element for dissipating heat generated at a lead frame, the at least one element comprising an arrangement for directly and uninterruptedly connecting with a lead frame.
In accordance with another presently preferred embodiment, the present invention broadly contemplates lead frame apparatus comprising an arrangement for directly and uninterruptedly accommodating at least one external element for dissipating heat generated at the lead frame.
In accordance with yet another presently preferred embodiment, the present invention broadly contemplates a method of making lead frame apparatus, the method comprising the steps of: providing a lead frame; providing an arrangement for dissipating heat generated at the lead frame; and uninterruptedly connecting the heat dissipating arrangement to the lead frame.
Finally, in accordance with yet another presently preferred embodiment, the present invention broadly contemplates lead frame apparatus comprising: a lead frame; an arrangement for dissipating heat generated at the lead frame; and an arrangement for mechanically connecting the lead frame with the heat dissipating arrangement; the connecting arrangement consisting essentially of constituent portions of the lead frame and the heat dissipating apparatus.