Patent Application
20100283135
The present invention relates to the packaging of integrated circuits (ICs) and more particularly to lead frames for semiconductor packages.
Delamination of a molding compound from a lead frame of a semiconductor package is undesirable as it can cause package failure. Failure mechanisms that can result from lead frame delamination include bond lifting, heel cracking, and broken wires. Lead frame delamination can also lead to package cracking. Thus, it would be desirable to have a lead frame that can reduce the incidence of lead frame delamination.
The following detailed description of preferred embodiments of the invention will be better understood when read in conjunction with the appended drawings. The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. It is to be understood that the drawings are not to scale and have been simplified for ease of understanding the invention.
The detailed description set forth below in connection with the appended drawings is intended as a description of the presently preferred embodiments of the invention, and is not intended to represent the only form in which the present invention may be practiced. It is to be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the invention. In the drawings, like numerals are used to indicate like elements throughout.
The present invention provides a lead frame including a lead frame structure having a die support area and a plurality of electrical contact areas. In one embodiment, a shallow recess is formed on a surface of the lead frame structure. In another embodiment, a plurality of shallow recesses is formed on a surface of the lead frame structure at least partially around respective ones of a plurality of critical portions of the lead frame structure. In yet another embodiment, a shallow recess is formed on a surface of the lead frame structure. An integrated circuit (IC) die is attached to the die support area and electrically connected to the electrical contact areas. The IC die and a portion of the lead frame structure are encapsulated with a molding compound.
Referring now to
The lead frame 10 may be formed from a copper or metal alloy sheet or strip via etching or stamping, as is known in the art. The lead frame 10 may have a thickness of between about 120 microns (μm) and about 770 μm, and may be plated with a metal or metal alloy. The die support area 14 is sized and shaped to receive an integrated circuit (IC) die. The die, and consequently the die support area 14, size may vary depending on the function of the circuitry therein. As will be understood by those of skill in the art, the invention is not limited by the size and shape of the die support area 14. The electrical contact areas 16, also sometimes referred to as lead fingers, are generally situated around the perimeter of the lead frame 10, or along one or more sides of the lead frame 10. As can be seen in
Referring now to
The provision of shallow recesses 18 on a surface of the lead frame structure 12 increases the contact area between the lead frame 10 and encapsulation material that is subsequently deposited thereon. The increase in contact area helps to improve adhesion between the lead frame 10 and the encapsulation material. Additionally, the shallow recesses 18 help to contain any initial delamination between the lead frame 10 and the encapsulation material.
The shallow recesses 18 may be formed to a depth of between about 15 percent (%) and about 30% of a thickness of the lead frame structure 12, and more preferably to a depth of between about 20% and about 25% of the thickness of the lead frame structure 12. For example, the shallow recesses 18 may be formed to a depth of between about 100 microns (μm) and about 130 μm in a lead frame structure 12 having a thickness of about 510 μm.
The shallow recesses 18 may have a width of between about 0.1 millimeter (mm) and about 0.25 mm. Advantageously, the narrowness of the widths of the shallow recesses 18 relative to the surface area of particular portions 20 of the lead frame 10 in which the shallow recesses 18 are formed allows flexibility in the layout of the shallow recesses 18. For example, the shallow recesses 18 are not limited to a straight trench design, but may be formed of different shapes. The narrowness of the widths of the shallow recesses 18 also allows the shallow recesses 18 to be positioned in small critical areas of the lead frame 10.
In one embodiment, the shallow recesses 18 may be formed by etching using an etch mask. The depth of the shallow recesses 18 may be controlled by varying the aperture width of the etch mask. The aperture width of the etch mask is reduced to achieve a shallower etching depth. The shallow recesses 18 also may be formed by laser cutting, punching or other known lead frame manufacturing processes in alternative embodiments.
As shown in
Although
Referring again to
Referring now to
The semiconductor package 50 may be a power quad flat no-lead (PQFN) package or any other package type that requires a lead frame.
The lead frame structure 52 is similar to the lead frame structure 12 of
Referring now to
Referring again to
The wires 64 may be made of gold (Au), copper (Cu), aluminum (Al) or other electrically conductive materials as are known in the art and commercially available. A known wire bonding process may be used to form the electrical connections.
A well known encapsulation process such as, for example, injection molding, may be performed to encapsulate the IC die 62 and the wires 64. The molding compound 66 may comprise a well known commercially available molding material such as plastic or epoxy.
As can be seen from
As is evident from the foregoing discussion, the present invention provides a lead frame and a semiconductor package with improved mold compound locking and delamination stopping features in the form of shallow recesses on a surface of the lead frame structure. Because of their small dimensions, the shallow recesses may be formed in critical areas of the lead frame where space is a constraint. Accordingly, the present invention is able to provide improved delamination protection to critical areas of a lead frame.
The description of the preferred embodiments of the present invention have been presented for purposes of illustration and description, but are not intended to be exhaustive or to limit the invention to the forms disclosed. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but covers modifications within the spirit and scope of the present invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200910140565.9 | May 2009 | CN | national |
