High Current Testing for Land Grid Array Sockets

Land grid array (LGA) sockets are currently used for industry standard and custom microprocessors to meet the increased performance challenges for a variety of server applications. Along with the need for increased high speed signaling capabilities comes the challenge to support lower voltages and higher currents. Typical testing that is conducted by the LGA socket suppliers does not provide an accurate assessment of the maximum current capabilities in a real product application due to the test card design and construction limitations. Typical test card designs use a daisy chain connection to wire multiple LGA socket contacts in series. The daisy chain wiring in the test card adds to the resistive heating and results in an inaccurate maximum current rating. Also, the test cards typically do not have a cross section construction that is representative of a real product application with multiple ground planes that provide improved thermal dissipation of the heat generated by the LGA socket interface. High current LGA socket testing has been conducted to better understand the performance limitations in a variety of product applications. Three different test vehicles were used in the testing to evaluate two LGA processor module configurations along with a board to board LGA socket configuration. All three test vehicles were designed to use multiple voltage and ground planes in the circuit card to provide a low impedance path for current flow and a low voltage drop through the LGA socket interface. The test variables included different types of LGA sockets contacts, the number of contacts for current supply, the number of contacts for return current, the current path in the module, and the airflow effects. The test results provide additional insights into the differences in the LGA socket contact designs and materials along with correlation between the different test vehicles and product applications.