LEADFRAME FOR SEMICONDUCTOR PACKAGES
A leadframe for semiconductor packages. The leadframe includes a die pad, a side rail, a tie bar, and a plurality of leads. The side rail is around the die pad. The tie bar connects the die pad and the side rail. The leads extend from the side rail to close proximity to the die pad. Each lead has a corresponding lead relative to a predetermined center line. A predetermined pair of corresponding leads are substantial asymmetrical with each other in appearance relative to the predetermined center line.
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1. Field of the Invention
The invention relates to leadframes for semiconductor packages and in particular to leadframes for high frequency applications.
2. Description of the Related Art
Semiconductor dies are enclosed in plastic packages that provide protection from hostile environments and enable electrical interconnection between the semiconductor die and a printed circuit board via a metal leadframe. The conventional leadframe type semiconductor package has a central supported die pad for supporting semiconductor die, a plurality of leads peripherally located therein, a plurality of bonding wires for electrically connecting the semiconductor die to the leads, and a mold compound, such as plastic, for encapsulating these components in a package structure.
In most semiconductor package configurations, a portion of the leadframe is internal to the package, (i.e., completely surrounded by the mold compound). Portions of the leads of the leadframe typically extend externally from the package body for electrically connecting the package to the printed circuit board.
In the electronics industry, there is continued demand for developing semiconductor dies which have increasing processing speeds and higher degrees of integration. For a semiconductor package to accommodate these enhanced semiconductor dies, the number of leads included in the semiconductor package must be significantly increased. To avoid an undesirable increase in the size of the semiconductor package attributable to the increased number of leads, a common practice is to reduce or narrow the spacing between the leads. However, a decreased spacing between the leads increases the capacitance between the leads, and increases the level of self inductance and mutual inductance. This inductance adversely affects the quality of signals transmitted on the leads of the leadframe by increasing signal reflections; causing greater impedance mismatches.
Especially, in high frequency applications the semiconductor package has the greatest influence on total performance of the circuit, and one of the main causes of performance degradation is inductance of the interconnections between chip and printed circuit board. Therefore, as the operating frequency of these circuits increases, there is a need for even lower impedance mismatches packages. As shown in
The invention provides leadframe for semiconductor packages and a method utilizing the same, providing flexible impedance match design, improving the electrical performance of the resulting electronic products.
The invention provides leadframe for semiconductor packages comprising a die pad, a side rail, a tie bar, and a plurality of leads. The side rail is around the die pad. The tie bar connects the die pad and the side rail. The leads extend from the side rail to close proximity to the die pad. Every lead has a corresponding lead relative to a predetermined center line. A predetermined pair of corresponding leads is substantially asymmetrical with each other relative to the predetermined center line.
Further scope of the applicability of the invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
A detailed description is given in the following embodiments with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGSThe invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
The invention provides the capability to vary the impedance of an electrical device. As examples, impedance can be controllably varied by changing: the length of the leads; the pitch of the leads; the spacing between the leads; and/or the width of the leads. In consequence, in order to respectively adjust the impedance of the leads, the invention provides an asymmetrical leadframe structure.
In
In some cases, the corresponding lead of a specific lead depends on the selected center line, such as the center line 50 of this embodiment. In
Referring to
In
In
In
In
In
Next, a conventional symmetrical leadframe is shown in
In
In
In
A magnified drawing of the shortened leads 1145, 1146, 1148, and 1149 is shown in
In
A magnified drawing of the leads 1145, 1146, 1148, and 1149 of
The efficacy of the inventive leadframes at developing asymmetrical lead route or lead distribution provides effective impedance match for the resulting products.
While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
Claims
1. A leadframe for semiconductor packages, comprising:
- a die pad;
- a side rail around the die pad;
- a tie bar connecting the die pad and the side rail; and
- a plurality of leads extending from the side rail to close proximity to the die pad; wherein
- every lead has a corresponding lead relative to a predetermined center line; and
- a predetermined pair of corresponding leads are substantial asymmetrical with each other relative to the predetermined center line.
2. The leadframe as claimed in claim 1, wherein the leads of the predetermined pair comprise substantially different lead lengths.
3. The leadframe as claimed in claim 1, wherein the leads of the predetermined pair comprise substantially different lead widths.
4. The leadframe as claimed in claim 1, wherein the leads of the predetermined pair comprise substantially asymmetrical extending traces.
5. The leadframe as claimed in claim 1, wherein the leads of the predetermined asymmetrical pair are for impedance matching.
Type: Application
Filed: Oct 6, 2006
Publication Date: May 3, 2007
Applicant: MEDIATEK INC. (Hsin-Chu)
Inventor: Tao Cheng (Hsinchu City)
Application Number: 11/539,239
International Classification: H01L 23/495 (20060101);