Patent Application
20060046527
This invention relates generally to sockets for electronic device packages.
Electronic devices are operating at faster and faster speeds. With this increase in performance, a designer should take into consideration the possibility of increased noise, cross-talk, ringing, etc. that may occur on the signal lines of the electronic device.
Electronic devices may reside in any of a number of package technologies, for examples, flat pack, dual in-line package (DIP), pin grid array (PGA), and land grid array (LGA). Electronic devices such as microprocessors generally reside on packages with multiple pins such as an LGA.
Current LGA socket technology has inherent I/O performance limitations. Manufacturing capability limitations of LGA socket technology limit minimum socket height, socket self inductance, socket loop inductance, and socket capacitance. These aspects of the socket design impose impedance discontinuities that limit the performance (i.e., speed) of I/O signaling in electronic device products that use present LGA socket technology.
Currently, these problems have been addressed by reducing socket height, controlling pitch, optimizing mold material, and optimizing the land configuration. However, these solutions have limitations. For example, regarding socket height, the height of the socket can only go so small to control inductance. Similarly, land pitch can only control inductance to a certain degree. Moreover, to reduce impedance discontinuities with land configuration, one may have to completely surround a signal land with ground lands. This requires too many lands to practically use a socket for a microprocessor application.
At high frequencies, impedance (Zo) is equal to the square root of inductance divided by capacitance (Zo=(SQRT L)/C). Current solutions attempt to control the impedance by controlling the inductance (L). In current solutions however, the inductance is generally too high, or the inductance to capacitance ratio is not controlled to the degree desired. Therefore, when an electronic device in a LGA package, for example, is plugged into a socket, signals on the lands of the LGA package see impedance discontinuities causing signal integrity problems.
Thus, there is a need for better LGA packages.
A grounded metal plate may be embedded within a land grid array (LGA) electronic socket. The plate may provide a balancing capacitance that compensates for the inductance of the socket, reducing the discontinuity presented by the socket interconnect elements in some embodiments.
Referring to
The conductive plate 18 provides capacitive coupling to each contact 22, which may reduce the impedance discontinuity at the socket 16. Morover, coupling between adjacent contact 22 pairs may be improved, enabling use of the socket 16 for differential signaling in some embodiments.
Initially, the electrical properties of the electronic package 12 are identified. The electrical properties of the contacts 22 in the socket 16 are determined. An inductance is determined. A desired impedance between each contact 22 and the conductive plate 18 is determined. The inductance may be fixed for a particular socket. Therefore, by identifying a desired impedance, the capacitance C can be varied to get the desired performance.
The diameter of each hole 20 in the conductive plate 18 is determined to achieve the desired impedance. The diameter of the hole 20 can be varied to vary the capacitance C between the conductive plate 18 and the contact 22. Therefore, knowing a desired impedance, the hole 20 diameter may be set to achieve a particular capacitance C that produces the desired impedance.
For a particular electronic package assembly 10, the desired impedance may be the same for every contact 22 on the socket 16. In this case, the diameter of each hole 20 in the grounded conductive plate 18 may be the same. However, it is possible that different impedances are desired for different contacts 22 on a socket 16 based, for instance, on the size of the contact 22 or the signal evolving from the contact. In this case, the grounded conductive plate 18 may have holes 20 of varying diameters.
A land grid array package 12, which may carry an integrated circuit, may be contacted from below by the deformed end 26. The deformed end 26 may have a curved upper contact portion. The contact 22 may have a generally horizontally deformed portion 24, and a bent section 21 that couples to a vertical section 23. The vertical section 23 may be the portion of the contact 22 that extends through the embedded conductive plate 18. In one embodiment, stamped metal contact land grid array technology may be utilized.
Referring to
As a result, when the package 12 is pressed onto the socket 16, the deformed ends 26 of the contacts 22 are deformed to make tight spring biased electrical connections to the package 12. However, the contacts 30 deform so that their lands 33 make electrical connection to the embedded conductive plate 18. This connection grounds the embedded conductive plate 18 via solder balls 32 to the grounded motherboard 28.
Referring to
In accordance with still another embodiment, shown in
Sockets with conductive plates, according to some embodiments of the present invention, may reduce the impedance discontinuity of LGA contacts. Moreover, some embodiments allow extension of present LGA sockets to differential signaling applications. Further, electrical parasitics (inductance and capacitance) may be distributed to avoid potential resonance issues at high frequencies in some cases.
Referring to
While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.
