The Challenges of LGA Server Socket Trends

Jackson Chang, Michael Hung, Bono Liao, and Nick Lin
Foxconn Electronics, Inc.
Tu-Cheng, Taipei Hsien, Taipei R.O.C.

Andrew Gattuso
Foxconn Electronics, Inc.
Chandler, AZ, USA

Bob McHugh
Foxconn Electronics, Inc.
Evergreen, CO, USA

The high end server market trends present several manufacturing and technical challenges to socket manufacturers. There are five notable trends that present challenges:

1. There is a trend towards lower contact resistance. Contact resistance has a negative impact on current carrying capability and leads to higher socket operating temperatures. Given space constraints, the best approach to lowering contact resistance is by selecting materials with higher electrical conductivity. However, the tradeoff to higher conductivity materials is reduced mechanical performance.

2. There is a trend towards increasing pin-counts coupled with a need to maintain or lower the socket's overall loading force. Larger loading forces can impact the socket's mechanical integrity and create ergonomic challenges. One way to achieve this is by reducing contact normal force.

3. There is a trend towards contacts having shorter electrical paths. As server frequencies increase, signal becomes more sensitive to noise. Reducing the seating plane height forces a shorter contact signal path and reduces the potential for noise in the circuit.

4. There is a trend towards higher contact density. The need for maintaining legacy real estate requirements along with the need for higher pin-counts results in the need for contact pitch reduction.

5. Due to the higher pin counts and smaller contacts, the trend in manufacturing is towards robotic assembly lines to make the production process more stable and increase yield rates.

This presentation aims to discuss the challenges and some potential solutions for each of these trends.

As can be understood from the preceding discussion, there is much work in many areas that needs to be done to continue to meet the difficult requirements of future high end LGA sockets. Not only does the manufacturing technology need to continue to be optimized and improved, but also the raw materials used to make the sockets needs to also be developed. In particular, contact materials with high strength and better conductivity are needed to meet the increased current requirements on tighter pitches, and thermoplastics that have good flow characteristics, while maintaining high strength with thinner walls.