Segmented Underfill for Semiconductor Solder Ball Reliability
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Solution Overview
Problem
The excessive contraction and expansion of underfill during thermal cycling can damage the junction of solder balls in semiconductor devices, reducing the binding force between the semiconductor package and the circuit board, and also between packages in stacked configurations, leading to reliability issues.
Innovation Solution
A semiconductor package assembly where a first underfill is disposed only on the interfaces between the solder balls and the semiconductor package and the circuit board, with the underfill removed from the area between adjacent solder balls, thereby maintaining a stable bonding and reducing the risk of damage from thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If underfill is dispensed from the junction of the solder ball to supplement thermal and mechanical characteristics, then the reliability of the semiconductor device is improved, but the underfill causes excessive contraction and expansion during thermal cycling that damages the solder ball junction and reduces binding force
Solution Approach 1:
The underfill application is segmented into two distinct regions: (1) a first underfill region disposed on the interface between the solder ball and the substrate, and (2) a second underfill region disposed on the interface between the solder ball and the circuit board. This segmentation allows the underfill to provide mechanical and thermal support at critical interfaces while avoiding excessive material in the area between adjacent solder balls, thereby preventing harmful contraction and expansion during thermal cycling.
Solution Approach 2:
The patent applies different quantities and distributions of underfill to different locations. The underfill is concentrated at the solder ball junctions where it is needed for mechanical strength and thermal management, while the area between adjacent solder balls has reduced or removed underfill to prevent excessive contraction and expansion. This local quality approach optimizes the balance between improving reliability and maintaining solder ball strength.
2Strength
If underfill is used to supplement thermal and mechanical characteristics, then the binding force between semiconductor device and circuit board is improved, but the underfill damages the junction of solder balls between semiconductor devices in stacked configurations
Solution Approach 1:
The underfill is segmented into specific functional zones: the first underfill region at the substrate-solder ball interface provides mechanical anchoring and thermal management without interfering with solder ball junction integrity, while the second underfill region at the circuit board interface provides structural support. This segmentation prevents the underfill from causing excessive contraction and expansion that would damage solder ball junctions in stacked configurations.
Solution Approach 2:
The patent implements local quality by applying underfill selectively at critical interfaces (substrate-solder ball and solder ball-circuit board) while avoiding or minimizing underfill in the region between adjacent solder balls. This localized application maintains the binding force between the semiconductor device and circuit board while preserving the integrity of solder ball junctions, thereby resolving the contradiction between strength and 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 reliability of the semiconductor package assembly by maintaining a stable bonding force between the semiconductor package and the circuit board, and between packages, while preventing excessive underfill contraction and expansion, thus improving the overall reliability and durability.
Implementation Method 1
excessive contraction and expansion by heat during a thermal cycling (TC) test
Data Source
AI summary
A semiconductor package assembly has a first semiconductor package. A plurality of first solder balls is attached to the first semiconductor package. A circuit board is provided having a plurality of mounting pads that is electrically connected to the plurality of first solder balls. A first underfill is disposed on each of the plurality of first solder balls. The first underfill is disposed on interfaces between each of the plurality of first solder balls and the first semiconductor package and each of the plurality of first solder balls and the circuit board. The first underfill is removed from an area between adjacent first solder balls.