Electrical connectors – Preformed panel circuit arrangement – e.g. – pcb – icm – dip,... – With provision to conduct electricity from panel circuit to...
Reexamination Certificate
2000-07-26
2001-07-10
Abrams, Neil (Department: 2839)
Electrical connectors
Preformed panel circuit arrangement, e.g., pcb, icm, dip,...
With provision to conduct electricity from panel circuit to...
C439S083000, C439S515000
Reexamination Certificate
active
06257899
ABSTRACT:
SPECIFICATION
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an internal touch contact for an integrated circuit (IC) socket, and particularly to a soft internal touch contact for a land grid array (LGA) socket for facilitating signal transmission between an IC package and a printed circuit board (PCB).
2. Description of Prior Art
IC packages having leads arranged in a land grid array (LGA) are well known as LGA packages. The LGA packages have a relatively low height, which is desirable for saving space in electronic assemblies.
Connectors for removably mounting an LGA package on a PCB are known as LGA sockets. An LGA socket typically comprises a substantially flat dielectric housing which is positioned between the LGA package and the PCB. The housing defines an array of passageways with electrical contacts received therein in correspondence with the array of leads of the LGA package. Each contact has a pair of oppositely extending free ends spaced apart a predetermined distance in an original position. The two free ends project beyond external surfaces of the socket housing for respectively engaging with corresponding contact pads on a bottom surface of the LGA package and on a top surface of the PCB. When the LGA package is sandwiched between the socket and the PCB, the two free ends of each contact are compressed to contact each other thereby shortening the signal transmission path. Typically, the compressive force may be applied by pressure plates which are fastened together to sandwich the package, the socket and the PCB therebetween. Even if the two free ends of the contact fail to contact each other, the signal can still be transmitted through the contact but along a relatively longer path. This kind of contact is called an internal touch contact.
Various internal touch contacts for LGA sockets are disclosed in the prior art. One problem encountered with the conventional internal touch contacts, such as those disclosed in U.S. Pat. Nos. 4,262,986; 4,268,102 and 5,092,783, is that one of the two free ends of the contact is constructed as a flat, non-yielding part whereby the normal force required to establish the contact interface is increased so sharply that it has proven difficult to control it within desired limits. The increased normal force generally has a negative effect on connector performance. Therefore, it is desired to have a soft internal touch contact that operates using a small normal force.
U.S. Pat. Nos. 4,354,729; 4,511,197 and 4,969,826 disclose internal touch contacts having free ends thereof engaged with each other via side edges thereof. As such contacts become increasingly miniaturized, and as the thickness of the contacts is decreased, it becomes increasingly difficult to mate the side edges of the two free ends of the contact. Hence, a contact having free ends thereof engaged with each other via major surfaces thereof is also required to ensure reliable internal contact performance.
Furthermore, the conventional LGA sockets do not provide solutions to CTE (Coefficient of Thermal Expansion) problems. During cooling after the contacts are soldered to corresponding contact pads of the PCB, stresses resulting from a difference between the CTEs of the socket housing and the PCB will develop in the soldered connections between the contact and the PCB, possibly causing failure of soldered connections. Additionally, when there is a large change in environmental temperature, larger stresses can develop in the soldered connections. Accordingly, an improved LGA socket is required to overcome the above disadvantages of conventional LGA sockets.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a soft internal touch contact for an LGA socket that has free ends deflectable under load which engage with one another using only a small normal force.
Another object of the present invention is to provide a soft internal touch contact for an LGA socket that has free ends engagable with each other via major surfaces thereof for ensuring a reliable engagement therebetween.
A further object of the present invention is to provide an LGA socket having contacts loosely received therein for relieving stresses resulting from a difference between CTEs of a housing thereof and a mating printed circuit board.
In order to achieve the objects set forth, a soft internal touch contact for an LGA socket in accordance with the present invention comprises first and second spring arms formed on opposite ends thereof and a solder portion between the first and second spring arms for being soldered to a contact pad of a PCB. The first spring arm has a curved engaging section for engaging with a contact pad of an LGA package and a first free end section having a downwardly facing inclined surface. The second spring arm has a second free end section having an upwardly facing inclined surface facing the downwardly facing inclined surface of the first spring arm.
Upon downward deflection of the first spring arm to engage with the second spring arm, the second spring arm correspondingly yields downward whereby a wiping action is generated between the downwardly and upwardly facing inclined surfaces of the respective first and second spring arms along a direction substantially tangential to the inclined surfaces and also between the curved engaging section of the first spring arm and the contact pad of the LGA package along a horizontal direction. Accordingly, the normal force is significantly reduced during the mutual engagement between the first and second spring arms, and a shortened electrical path is thus established between the LGA package and the PCB.
To relieve stresses resulting from a difference between CTEs of an insulative housing of the LGA socket and the PCB under a wide range of environmental temperatures, a pair of wings is formed on the solder portion of the contact for being loosely received in upwardly exposed slots of the insulative housing of the LGA socket.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
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Abrams Neil
Chung Wei Te
Hon Hai - Precision Ind. Co., Ltd.
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