Flip Chip Inner Lead Layout for Thermal Bonding Shift
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Solution Overview
Problem
The conventional flip chip structure experiences bonding shift between bumps on a chip and inner leads on a circuit board due to mismatched coefficients of thermal expansion, leading to potential unbonding or insufficient bonding areas.
Innovation Solution
The solution involves arranging first and second bonding portions of inner leads on a circuit board in different directions, with corresponding bumps on the chip aligned and bonded to these portions, thereby enhancing the circuit board's resistance to thermal expansion and contraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional inner leads are arranged in a single direction on the chip-mounting area, then the circuit board structure is simple, but bonding shift occurs between bumps and inner leads due to thermal expansion and contraction
Solution Approach 1:
The inner leads are segmented into multiple groups (first inner leads and second inner leads) with different orientations. Each group is arranged in a specific direction (first direction and second direction respectively) to independently compensate for thermal expansion in different axes, thereby resolving the bonding shift issue without requiring complete redesign of the entire lead structure
Solution Approach 2:
The patent introduces asymmetric arrangement of inner leads by creating two distinct groups with different directional orientations. The first inner leads extend in a first direction while the second inner leads extend in a second direction, creating an asymmetric pattern that balances thermal stress distribution and prevents uniform bonding shift across all bumps
2Manufacturing precision
If inner leads are arranged to compensate for thermal expansion, then bonding shift is reduced, but the arrangement complexity of inner leads increases
Solution Approach 1:
Different regions of the chip-mounting area are assigned different lead orientations based on local bonding requirements. The first inner leads are positioned and oriented for bumps requiring compensation in one direction, while the second inner leads serve bumps requiring compensation in another direction, optimizing each local bonding interface independently
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 arrangement effectively reduces or avoids bonding shift between inner leads and bumps, ensuring reliable bonding even under temperature variations, thus preventing unbonding and ensuring sufficient bonding areas.
Implementation Method 1
Due to coefficients of thermal expansion (CTE) mismatch of the substrate 11a, the circuit layer 11b and the protective layer, expansion and contraction may occur in the circuit board 11 in response to temperature variation to cause bonding shift between the bumps 12a and the inner leads 11b1
Data Source
AI summary
A flip chip structure includes a circuit board and a chip. The circuit board includes first inner leads and second inner leads, each of the first inner leads has a first bonding portion, each of the second inner leads has a second bonding portion and a connecting segment. An included angle exists between the second bonding portion and the connecting segment, and an included angle exists between center lines of the first and second bonding portions. The chip includes first bumps and second bumps, and an included angle exists between center lines of the first and second bumps. Each of the first bumps is bonded to the first bonding portion, and each of the second bumps is bonded to the second bonding portion and the connecting segment to avoid bonding shift between the inner leads and the bumps or lessen bonding shift.