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Method for electrical connector underfill with embedded solder balls

IP.com Disclosure Number: IPCOM000029207D
Publication Date: 2004-Jun-17
Document File: 4 page(s) / 146K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for electrical connector underfill with embedded solder balls. Benefits include improved functionality, improved reliability, and improved ease of manufacturing

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Method for electrical connector underfill with embedded solder balls

Disclosed is a method for electrical connector underfill with embedded solder balls. Benefits include improved functionality, improved reliability, and improved ease of manufacturing

Background

              As sockets become larger warpage of the socket and PCB become more important. Thermal solutions require higher loads on the CPU to make better thermal contact. Sockets must withstand greater mechanical loads. The use of land-grid arrays (LGAs) across different segments increases the importance of the rigidity of the printed circuit board (PCB) in maintaining a consistent load level. Distributing the load across the full socket helps to make the system reliable.

              Solder balls can crack and fail at the PCB contact/attach point (see Figure 1) if loads are not evenly distributed. Uneven loads cause stress on the central processor unit (CPU) substrate which can crack the die and is transferred to the flip-chip attach interface.

              These problems are conventionally solved by adding external PCB stiffeners and a bottom-side backing plate with a thermal solution (see Figures 2 and 3). Socket standoffs are required to bear the load, which is more effective than not using standoffs. However, in many cases, standoffs are insufficient (see Figure 4).

General description

              The disclosed method is an underfill process for electrical connectors and CPU sockets. The process creates an underfill layer beneath a socket to reduce stress on the solder ball and compensate for changes in the flatness of the socket. The underfill reduces CPU substrate flexibility and die stress.

Advantages

              The disclosed method provides advantages, including:

•             Improved functionality due to providing PCB reinforcement (stiffening)

•             Improved reliability due to decreasing sensitivity to shock and vibration

•             Improved reliability due to preventing die cracking on the CPU and solder ball cracking on the socket

•             Improved ease of manufacturing due to eliminating the socket reflow process to attach solder balls and a board-mount reflow step during board assembly

Detailed description

              The disclosed method equalizes the load generated by the thermal solution (heatsink and clip solution) over the whole socket base via the underfill. The method reduces the requirement for a backing plate or external board stiffener. The underfill adds little to the mass of the CPU stack while reducing solder ball failure. Stress on the CPU substrate and die is reduced (see Figure 5).

 

              The disclosed method enables greater mechanical loads to be put on the thermal system, making cooling more efficient without breaking the die, substrate, or solder balls. Actuating the socket with an improved reliability and thermal solu...