Capillary Sidewall Design for Flip Chip Stud Bump Stand-Off Height
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Solution Overview
Problem
Existing flip chip assembly methods face challenges in achieving stronger, more reliable joints due to limited stand-off height of stud bumps, which restricts underfill adhesive flow and increases manufacturing time and stress on the die when using stacked bumps or removing protective overcoats.
Innovation Solution
A capillary design with an internal sidewall that raises the chamfer, allowing for increased stand-off height of stud bumps in a single process, enabling larger bumps without the need for stacked bumps or removal of protective overcoats, facilitating better underfill flow and stronger joints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the stand-off height of stud bumps is increased to allow better underfill flow, then underfill adhesive flow is improved, but manufacturing time increases and stress on the die increases when using stacked bumps
Solution Approach 1:
The patent introduces a sidewall feature within the capillary that extends vertically to raise the chamfer, creating additional vertical space within the same lateral footprint. This dimensional change allows the stud bump to achieve greater stand-off height without requiring multiple stacked bumps, thereby improving underfill flow while avoiding the time penalty of additional bonding cycles.
Solution Approach 2:
The sidewall and raised chamfer are pre-formed as integral features of the capillary tooling before the bumping process begins. This preliminary preparation of the capillary geometry ensures that the increased stand-off height is achieved automatically during the normal single-pass bumping operation, without requiring subsequent stacking operations or removal of protective overcoats.
2Ease of operation
If stacked stud bumps are used to increase stand-off height, then underfill flow is improved, but manufacturing time and stress on the die increase
Solution Approach 1:
Instead of increasing stand-off height by stacking multiple bumps vertically through separate bonding operations, the patent uses a sidewall feature within the capillary to raise the chamfer during a single bumping operation. This achieves the same underfill flow benefit in one pass, maintaining productivity.
Solution Approach 2:
The patent extracts the need for multiple stacking operations by incorporating the height-increasing feature directly into the capillary tooling. The sidewall and raised chamfer are built into the capillary structure, allowing the stand-off height to be achieved during the initial single-pass bumping process rather than requiring subsequent stacking steps.
3Ease of operation
If protective overcoats are removed to increase stand-off height, then underfill flow is improved, but die protection is lost
Solution Approach 1:
The patent achieves increased stand-off height through a sidewall feature that raises the chamfer vertically within the capillary, providing the necessary space for underfill flow while preserving the protective overcoat on the die surface. This dimensional solution allows both underfill access and die protection to coexist.
Solution Approach 2:
The raised chamfer created by the sidewall acts as an intermediary structure that provides the necessary clearance for underfill flow without requiring removal of the protective overcoat. This intermediate geometric feature mediates between the need for underfill access and the need to maintain die protection.
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 capillary design enables the production of stronger, more reliable joints with increased stand-off height, allowing for improved underfill flow and reduced manufacturing time, while maintaining die protection, resulting in enhanced mechanical and electrical connections.
Implementation Method 1
A capillary design with an internal sidewall that raises the chamfer, allowing for increased stand-off height of stud bumps in a single process
Implementation Method 2
A gold wire passes through a capillary tool and is melted to form a ball or sphere on a chip bond pad
Implementation Method 3
The underfill may be dispensed along the edges of the assembly and then drawn into the area under the chip by capillary action
Data Source
AI summary
System and method for creating single stud bumps having an increased stand-off height. A preferred embodiment includes a method of using a capillary for creating stud bumps in a flip chip assembly, the capillary includes a hole section adapted to pass a wire, a chamfer section providing a transition from the hole section to a stud bump section, and a sidewall within the stud bump section, the sidewall having a sidewall height, wherein the side wall height is equal to, or greater than, the a diameter of the stud bump section.