Today’s electronic packages have high clock speeds (multi-gigahertz range), fine pin densities (below 0.4-mm pitch), and high pin counts (over 2000). When assembled onto a printed-circuit board (PCB), these packages perform certain functions at certain speed. Attaching these packages through an IC socket is one way to test the functionality of IC packages without damaging it.
Connecting these high-speed and high-density IC packages requires an innovative solution to overcome the challenges of designing a shorter signal path (less resistance), good electrical insulation (prevents signal loss), and proper thermal management. Socket design is dictated not only by the aforementioned functions, but also by the other parameters such as durability, power consumption, assembly methods, and the operating environment. An IC socket using elastomer interconnect provides a solution that is fast, dense, and durable(Fig. 1).
A socket can be defined as an electromechanical device that provides a removable interface between the IC package and system circuit board with minimal effect on signal integrity. A removable interface—the primary reason for using a socket—is required for a variety of reasons, including ease of assembly, reworking, upgrading, and cost savings. The cost advantage comes from not having to attach the IC permanently to PCB. The socket is semi-permanently (solderless) attached to the PCB, while the IC device can be inserted into, or removed from, the socket without disturbing the connections to the PCB.
A socket helps to test, evaluate and inspect the complete system. It also allows for in-the-field maintenance, testing, replacement, or upgrades. This has become ever-more critical as technology evolves. The PCB surface to which the socket is attached needs to meet certain constraints (pad size, location, plating finish, etc.) to function properly. In this article, we examine the impact of different plating finishes on the PCB pads, and how it affects testing IC devices using an elastomer interconnect socket.