Pre-applied Underfill for Flip Chip Alignment
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Solution Overview
Problem
Current flip chip technology faces challenges in achieving high throughput and minimizing filler inclusions in underfill connections due to the difficulty in aligning pre-applied underfill on substrates, which increases costs and complicates the joining process, especially for multi-chip modules and CSP applications.
Innovation Solution
The development of columnar solder bumps or metal columns on substrates or chips, combined with a pre-applied underfill that minimizes the over-bumped amount of underfill, allowing for easy automatic alignment and reducing the thickness of the underfill layer, thereby minimizing filler inclusions and enhancing assembly yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pre-applied underfill is used on substrates, then alignment between chip and substrate can be achieved, but the alignment process becomes complex and costly
Solution Approach 1:
The underfill material is pre-applied to the substrate surface before chip placement, creating a ready-to-use alignment medium that simplifies the subsequent bonding process while maintaining precise alignment capabilities through the material's optical properties
Solution Approach 2:
The pre-applied underfill acts as an intermediary layer between the chip and substrate, providing both mechanical support and optical contrast for alignment marks, thereby mediating the alignment process and reducing overall system complexity
2Ease of manufacture
If pre-applied underfill is used on substrates, then joining process can be simplified, but filler inclusions in underfill connections increase
Solution Approach 1:
The viscosity of the underfill material is carefully controlled and optimized to allow proper flow and filling of gaps during bonding while preventing excessive resin displacement that would cause filler inclusions, thereby maintaining solder joint reliability
Solution Approach 2:
The pre-applied underfill layer is applied with controlled thickness and coverage, providing sufficient material to fill gaps and accommodate thermal expansion without excessive amounts that would lead to resin entrapment and filler inclusions during the bonding process
3Quantity of substance
If taller bumps are used, then sufficient underfill can be accommodated, but resin displacement increases
Solution Approach 1:
The viscosity and flow characteristics of the underfill material are optimized to match the height and geometry of the taller bumps, allowing the material to properly fill gaps and accommodate the increased volume without excessive displacement or entrapment during bonding
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 approach broadens the processing window for flip chip assembly, enabling faster alignment and higher reliability of solder joints with reduced underfill inclusion, leading to improved assembly yields and lower costs by allowing taller bumps to accommodate sufficient underfill without excessive resin displacement.
Implementation Method 1
a pre-applied underfill that minimizes the over-bumped amount of underfill, allowing for easy automatic alignment and reducing the thickness of the underfill layer, thereby minimizing filler inclusions
Implementation Method 2
enabling faster alignment and higher reliability of solder joints with reduced underfill inclusion, leading to improved assembly yields and lower costs by allowing taller bumps to accommodate sufficient underfill without excessive resin displacement
Data Source
AI summary
A preassembly semiconductor device comprises chip soldering structures on a semiconductor chip and substrate soldering structures on a substrate corresponding to the chip soldering structures. The substrate soldering structures extend toward the chip soldering structures for forming solder connections with the chip soldering structures. The chip and the substrate are in preassembly positions relative to one another. The height of the substrate soldering structures is greater than the height of the chip soldering structures. A pre-applied underfill is contiguous with the substrate and is sufficiently thick so as to extend substantially no further than the full height of the substrate soldering structures. In another embodiment the height of the chip soldering structures is greater than the height of the substrate soldering structures and the pre-applied underfill is contiguous with the semiconductor chip and sufficiently thick so as to extend substantially no further than the full height of the chip soldering structures. A process comprises manufacturing semiconductor assemblies from these devices by soldering the chip and the substrate to one another