Flip Chip Solder Bump Transfer for Stress-Tolerant Bonding
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Solution Overview
Problem
Existing flip chip mounting methods using thermocompression are prone to bond failure due to temperature cycling, necessitating an improved attachment method for electronic components that is more tolerant of stress and provides controlled separation between components.
Innovation Solution
The use of solder bumps with a bump core, where the solder layer is transferred from an intermediate structure onto the bump core, forming a reliable bond between the flip chip and external device, allowing for controlled separation and increased thickness uniformity, reducing costs and complexities associated with material screening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermocompression bonding is used to attach gold bumps to contact pads, then electrical connection is achieved, but the bond fails under temperature cycling stress
Solution Approach 1:
The patent changes the material parameters of the bonding structure by replacing gold bumps with solder bumps that have a eutectic composition. This allows the bonding process to occur at lower temperatures (melting point of solder) rather than requiring thermocompression at high temperatures, fundamentally changing the bonding mechanism and improving reliability under thermal stress
Solution Approach 2:
The patent employs a composite structure consisting of a bump core (providing mechanical strength and structural integrity) combined with a solder layer (providing reliable bonding and electrical connection). This composite approach allows the bump core to maintain structural stability while the solder layer provides stress-tolerant bonding that withstands temperature cycling
2Ease of manufacture
If solder bumps are formed directly on the die, then material screening is required, but this increases costs and complexities
Solution Approach 1:
The patent segments the bump formation process into two independent stages: first forming the bump core on the die, then separately applying the solder layer in a subsequent reflow process. This segmentation eliminates the need for material screening during bump formation, as the solder is applied separately from the die fabrication process, thereby reducing costs and process complexity
Solution Approach 2:
The bump core is formed on the die in advance during the semiconductor fabrication process, before the final assembly. This preliminary action allows the die to be prepared with the structural component (bump core) while the bonding material (solder) is applied later in a separate reflow process, eliminating the need for complex material screening and integration
3Reliability
If gold bumps are used for bonding, then electrical connection is established, but the attachment is not tolerant of stress
Solution Approach 1:
The patent changes the material properties by using solder with a lower melting point and different mechanical properties compared to gold. The solder material exhibits greater ductility and stress tolerance, allowing the bonding interface to accommodate thermal expansion and mechanical stress without failing, thereby improving reliability under stress conditions
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 solder bump attachment method provides a more reliable and stress-tolerant bond between flip chips and external devices, enabling controlled separation and uniform solder layer thickness, enhancing the durability and efficiency of electronic component connections.
Implementation Method 1
The transfer pad is transferred from the substrate to the bump core such that the transfer pad becomes the solder layer on the bump core
Implementation Method 2
The solder layer can be refold to attach the flip chip to the external device
Data Source
AI summary
Forming the chip attachment system includes obtaining a chip having a bump core on a die. The method also includes obtaining an intermediate structure having a transfer pad on a substrate. The method further includes transferring the transfer pad from the substrate to the bump core such that the transfer pad becomes a solder layer on the bump core.