Stacked Die Support Structures for Robust Solder Interconnects
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Solution Overview
Problem
Traditional solder joints in semiconductor device assemblies are susceptible to breakage during assembly, leading to open-circuit or short-circuit issues due to mechanical stress, necessitating more robust mechanical and electrical interconnects between stacked dies.
Innovation Solution
The implementation of die support structures with stand-off pillars and pads, featuring a smaller solder joint thickness than the interconnects, which provide mechanical support and can optionally serve as electrical interconnections or thermal pathways, using a thermo-compressive bonding process to secure the dies in parallel alignment and reduce solder joint thickness variability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional solder joints are used to connect stacked semiconductor dies, then electrical interconnection is achieved, but the joints are susceptible to breakage during assembly due to mechanical stress
Solution Approach 1:
The patent introduces underfill material that is applied beforehand to the substrate before mounting the semiconductor die. This underfill material acts as a cushioning layer that distributes mechanical stress and protects the solder joints from breakage during assembly and operation, directly addressing the vulnerability of traditional solder joints to mechanical stress
Solution Approach 2:
The patent employs composite material structures including the combination of underfill material with the substrate and solder joints. This composite structure provides both mechanical support and stress distribution, enhancing the overall reliability and mechanical strength of the interconnect system
2Strength
If excessive force is applied during bonding of adjacent dies to ensure mechanical support, then bonding strength is improved, but solder joints can be damaged leading to open-circuit or short-circuit
Solution Approach 1:
The underfill material is applied in advance to provide a compliant layer that allows bonding forces to be distributed evenly across the substrate-die interface. This cushioning effect enables achieving bonding strength without concentrating excessive force on individual solder joints, thus preventing damage to electrical connections
Solution Approach 2:
The underfill material serves as an intermediary layer between the substrate and the semiconductor die. This intermediary provides mechanical compliance and stress distribution, mediating the bonding process to achieve strong adhesion while protecting the delicate solder joints from excessive bonding forces
3Strength
If larger solder joints are used to improve mechanical robustness, then resistance to breakage is increased, but the risk of mechanical contact between adjacent joints increases creating short circuits
Solution Approach 1:
The underfill material provides a cushioning effect that allows the use of adequately sized solder joints for mechanical robustness while preventing them from deforming into each other during assembly. The compliant underfill layer absorbs excess mechanical stress and maintains proper spacing between adjacent joints
4Reliability
If mechanical support structures are added to protect interconnects, then interconnect damage is reduced, but device complexity increases
Solution Approach 1:
The underfill material serves multiple functions simultaneously: it provides mechanical support, distributes stress, protects solder joints, and enhances bonding strength. This multi-functionality achieves interconnect protection without adding separate structural elements, thus avoiding increased device complexity
Solution Approach 2:
The underfill material creates a homogeneous protective layer that integrates with the existing substrate and die structure. This homogeneous approach provides protection without introducing heterogeneous complex structures, maintaining manufacturing simplicity while improving reliability
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
This solution enhances the mechanical robustness of semiconductor device assemblies, reduces the risk of interconnect damage, and simplifies the bonding process by using force feedback as a control mechanism, improving yield and preventing warpage-related defects during manufacturing.
Implementation Method 1
The bond material can include a solder material and the solder material can be reflowed to form the first solder joint and the second solder joint
Implementation Method 2
using a thermo-compressive bonding process to secure the dies in parallel alignment and reduce solder joint thickness variability
Data Source
AI summary
A semiconductor device assembly is provided. The assembly includes a first semiconductor die and a second semiconductor die disposed over the first semiconductor die. The assembly further includes a plurality of die support structures between the first and second semiconductor dies and a plurality of interconnects between the first and second semiconductor dies. Each of the plurality of die support structures includes a stand-off pillar and a stand-off pad having a first bond material with a first solder joint thickness between them. Each of the plurality of interconnects includes a conductive pillar and a conductive pad having a second bond material with a second solder joint thickness between them. The first solder joint thickness is less than the second solder joint thickness.