Solder Column Exoskeleton Sleeve Prevents Thermal Collapse
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Solution Overview
Problem
Conventional solder column designs fail to maintain structural integrity and efficiently conduct heat from the underside of high-power CGA packages, particularly due to coefficient of thermal expansion mismatches between substrates and PCBs, leading to potential collapse and electrical connection failures.
Innovation Solution
The development of solder column structures with an exoskeleton sleeve comprising multiple small-diameter copper wires, electroplated and coated with a wettable solder alloy, which provides mechanical support, electrical conductivity, and thermal conduction, allowing the columns to maintain shape and integrity during reflow and absorb thermal stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solder columns are used in high-power CGA packages, then electrical connections are provided, but structural integrity is lost due to collapse from thermal expansion mismatches
Solution Approach 1:
The solder column is constructed as a composite structure with a solder core (Sn96.5/Ag3.0/Cu0.5 alloy) surrounded by a copper wire exoskeleton sleeve. The copper sleeve has higher strength and lower thermal expansion than the solder core, providing structural support while maintaining electrical and thermal conductivity. This composite design prevents collapse under thermal stress from coefficient of thermal expansion mismatches between the CGA substrate and PCB board.
2Loss of energy
If conventional solder columns are used, then electrical connections are established, but heat conduction from the underside of CGA packages is insufficient
Solution Approach 1:
The exoskeleton sleeve is strategically positioned to surround the solder core, creating a thermal conduction pathway specifically optimized for heat removal from the underside of the CGA package. The copper material in the sleeve has superior thermal conductivity compared to the solder alloy, locally enhancing heat dissipation capability where it is most needed for high-power applications.
3Strength
If solder paste is applied to conductive pads, then intermetallic connections are formed, but the solder paste does not provide sufficient mechanical support during reflow
Solution Approach 1:
The copper wire exoskeleton sleeve acts as an intermediary structural element between the solder core and the surrounding environment. During reflow, the sleeve provides the mechanical strength and structural support needed to prevent collapse, while the solder paste still performs its function of forming intermetallic connections with the conductive pads. The sleeve essentially mediates the mechanical support function that the solder paste alone cannot provide.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The improved solder column design prevents catastrophic collapse, ensures reliable electrical connections, and effectively conducts heat away from the CGA substrate through the printed circuit board, enhancing the structural and thermal integrity of the interconnects.
Implementation Method 1
an exoskeleton sleeve structure surrounding at least a majority of an outside surface of the solder core and comprising a plurality of wires woven together to form a mesh
Implementation Method 2
electroplated and coated with a wettable solder alloy
Implementation Method 3
effectively conducts heat away from the CGA substrate through the printed circuit board
Implementation Method 4
After heating, the solder paste reflows on the conductive pads causing an intermetallic connection between the solder columns and the conductive pads on the LGA
Data Source
AI summary
An improved solder column, having a solder core comprising a solder core material, an exoskeleton sleeve structure surrounding at least a majority of an outside surface of the solder core and comprising a plurality of wires woven together to form a mesh, and a plurality of spaces formed in the exoskeleton between the plurality of wires. The exoskeleton sleeve can be configured such that the exoskeleton sleeve will support the solder core so as to prevent a collapse of the solder core at temperatures exceeding a liquidus temperature of the solder core. Optionally, each of the plurality of spaces can have a width and a height that is at least as large as a width of the wire adjacent to the space, and the spaces can be configured to provide additional flexibility to the solder column.