Flip Chip Solder Bridge Prevention via Flux and Two-Stage Pressing
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Solution Overview
Problem
In fluxless flip chip bonding, the non-uniform oxide film on solder bumps leads to solder bridges between adjacent bumps due to uneven deformation during the bonding process, resulting in reduced joint reliability.
Innovation Solution
Applying flux to the solder bumps before reflow and cleaning, ensuring a thin and uniform oxide film, and using a two-stage pressing method during bonding to minimize local solder protrusions and promote even deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fluxless flip chip bonding is used, then cleaning complexity is reduced, but solder bridges form between adjacent bumps due to non-uniform oxide film
Solution Approach 1:
The patent applies flux to the solder bumps before reflow and cleaning processes are performed. This preliminary application of flux ensures that the oxide film becomes thin and uniform across the solder bump surfaces, preventing solder bridge formation during subsequent fluxless bonding while maintaining the simplicity of the overall process
2Reliability
If uniform oxide film is achieved through flux application, then solder bridge formation is reduced, but process complexity increases
Solution Approach 1:
The patent combines multiple functions into a single integrated process flow: flux application, reflow, and cleaning are performed together in sequence. This merging ensures uniform oxide film formation for reliable bonding while avoiding the need for separate, complex process steps, thus maintaining process simplicity
3Manufacturing precision
If two-stage pressing method is used, then local solder protrusions are minimized, but bonding process time increases
Solution Approach 1:
The bonding process is divided into two distinct pressing stages: a first pressing stage that applies initial contact pressure, and a second pressing stage that applies increased pressure to minimize local solder protrusions. This segmentation of the pressing operation achieves high bonding precision while keeping each stage relatively quick, minimizing total process time
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 reduces the formation of solder bridges and enhances the joint reliability by ensuring a uniform oxide film and controlled deformation, leading to improved bonding quality.
Implementation Method 1
the bonding head 18 is heated to the predetermined preheat temperature higher than the solder melting point
Implementation Method 2
the solder bumps 5(5b) formed over the semiconductor chip 4 are melted
Implementation Method 3
the melted and integrated solder bumps 5 are periodically rhythmically vibrated (scrubbed) either in the horizontal direction X or in the vertical direction Y
Implementation Method 4
the oxide film covering the surfaces of the solder bumps 5 is broken and taken into the solder bumps 5
Implementation Method 5
the semiconductor chip 4 is held over the wiring board 2 for a predetermined time with a predetermined gap maintained between them
Implementation Method 6
the solder bumps 5(5b) on the chip side are pressed into the solder bumps 5a on the substrate side
Implementation Method 7
The bonding stage 19 is provided with an exhaust system 19a and is exhausted to vacuum through this exhaust system 19a and is caused to suck and hold the wiring board 2
Data Source
AI summary
The joint reliability in flip chip bonding of a semiconductor device is enhanced. Prior to flip chip bonding, flux 9 is applied to the solder bumps 5a for flip chip bonding over a substrate and reflow/cleaning is carried out and then flip chip bonding is carried out. This makes is possible to thin the oxide film over the surfaces of the solder bumps 5a and make the oxide film uniform. As a result, it is possible to suppress the production of local solder protrusions to reduce the production of solder bridges during flip chip bonding and enhance the joint reliability in the flip chip bonding of the semiconductor device.