The present invention generally relates to a separable interface connector, and more particularly relates to a separable interface connector that joins a printed circuit board through reflow soldering to an electrical component, such as a motherboard.
Various electronic systems, such as computers, comprise a wide array of components mounted on printed circuit boards, such as daughterboards and motherboards, which are interconnected to transfer signals and power throughout the system. The transfer of signals and power between the circuit boards requires electrical interconnection between the circuit boards.
Certain interconnections include a socket assembly and a plug assembly, or integrated circuit (IC) chip. Some socket assemblies include spring contacts, which are configured to mate with conductive pads on the plug assembly. As the socket assembly and plug assembly mate, the spring contacts exert a normal force on the contact pads, thus ensuring proper electrical contact between the spring contacts and the conductive pads.
In order to establish adequate contact, the spring contacts wipe across the conductive pads, cleaning both surfaces, as the plug assembly is mated into the socket assembly. Typically, during mating, the spring contacts are deflected. During deflection, the spring contacts exert a resistive force on the plug assembly. The resistive force typically has normal and tangential components. The normal force is usually referred to as the contact force and the tangential force is usually caused by the frictional behavior of the wiping motion.
Typical socket assemblies, whether pin grid array (PGA), land grid array (LGA), or ball grid array (BGA) assemblies, are soldered to an electrical component, such as a motherboard. Typically, solder balls are attached to the bottom of the socket assembly. The socket assembly is positioned on a motherboard, and both components are passed through an oven, or other heating device, to begin the solder reflow process. During the solder reflow process, the solder balls melt and form a cohesive layer between the socket assembly and the motherboard. The solder layer cools after the heating and forms an electrically conductive bond between the socket assembly and the motherboard.
Some socket assemblies are soldered to motherboards such that the solder layer is the only intervening material that supports and extends between the socket assembly and the motherboard. That is, the socket assembly does not contact the motherboard at any other point during or after the solder reflow process. When the plug assembly is mated into the socket assembly, however, the mating or clamping force exerted into the socket assembly is fully translated to, and absorbed by, the solder layer. The solder layer may be further collapsed, disrupted or otherwise compressed due to the forces absorbed. Consequently, the electrical connection between the socket assembly and the motherboard may be adversely affected.
In order to counter the effects of mating or clamping forces being exerted into the solder layer, some socket assemblies include standoffs that support and stabilize the socket assembly onto the motherboard. Typically, the standoffs extend a distance that is less than that of the solder balls, but more than that of the natural reflow height of the solder balls. That is, before the solder reflow process, the standoffs do not touch the motherboard. When the socket assembly is soldered to the motherboard, the height of the socket assembly from the motherboard is dictated by the standoffs. U.S. Pat. No. 6,155,848, issued to Lin (xe2x80x9cthe ""848 patentxe2x80x9d), describes an auxiliary device for a ZIF electrical connector that uses standoffs. The ""848 patent discloses that the height of the stand-off portion is less than the height of the solder balls before soldering, and equal to the height of the solder balls after soldering. Thus, after the solder reflow process, the resulting solder layer is dictated by the height of the standoffs. U.S. Pat. No. 6,220,884, issued to Lin (xe2x80x9cthe ""884 patentxe2x80x9d) discloses a BGA socket that comprises an insulative cover supported by standoffs on a base. The standoffs of the cover extend beyond a bottom surface of the base. After the solder reflow process, the resulting solder layer is dictated by the height of the standoffs.
Additionally, in both the ""848 and ""884 patents, the components (such as IC chips) that mate with each socket include pins. That is, the IC chips include pins that are mated into the socket. The existence of pins on the IC chips mandates that the height of the sockets is adequate to receive and retain the pins.
However, conventional socket assemblies, including those of the ""848 and ""884 patents, do not allow the solder balls to reflow to the height they naturally would if there were no components that interfered. That is, the solder balls do not melt to a natural reflow height. Rather, the height of the resulting solder layer is dictated by the height of the standoffs. Because the solder layer is not necessarily at its natural height, electrical transmission through the solder layer may be adversely affected. For example, the solder layer may be too dense or too sparse due to the fact that the standoffs dictate the height of the solder layer.
Thus, a need exists for a socket assembly that may be reflow soldered to an electrical component more efficiently, and in a manner that ensures a better conductive path through the resulting solder layer.
Certain embodiments of the present invention provide a socket assembly configured to be reflow soldered to a circuit board. The socket assembly comprises a socket frame, or perimeter frame, having a central open area surrounded by perimeter walls. The socket assembly may be configured to be surface mounted on a circuit board, wherein at least one of the perimeter walls includes a post extending downward therefrom. The socket assembly also comprises a socket board, or base, fit into the open area of the socket frame. The socket board is separate and distinct from the socket frame. Optionally, the socket frame may be integrally formed with the socket board as a single unit during manufacture. During assembly, the socket frame may then separate, or break away, from the socket board by way of a separation zone, such as a perforated area between the socket frame and the socket board.
The socket board has a post hole therein positioned to mate with the post. Additionally, the socket assembly comprises contacts held by the socket board, and solder balls provided on a bottom surface of the socket board. The solder balls engage the contacts and, prior to, and after, soldering, extend beyond a bottom of the socket frame.
The post is held partially seated in the post hole when the socket board and frame are positioned in a pre-soldered state. The post becomes fully seated in the post hole when the socket board and frame move during a plug assembly mating state, that is, when a plug assembly is mated into the socket assembly. The assembly process is controlled in that, after the reflow process, the post is able to move through the post hole in a mating direction defined by the direction of the plug assembly moving into the socket assembly.