Water Soluble Flux Viscosity Control for BGA Residue Staining
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Solution Overview
Problem
The existing two-step flux process for ball grid array (BGA) packages results in residue staining from no-clean flux, leading to cosmetic defects and visual inspection rejections due to the spreading of flux residue over bond pads, which is not effectively cleaned by the initial water-soluble flux stage.
Innovation Solution
A one-step water-soluble flux process with increased bonding polymer and reduced amine content is used, increasing viscosity to eliminate the need for a second flux stage, allowing the flux to both clean the substrate and provide stable solder ball support during reflow, thereby reducing residue staining and improving yields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a two-step flux process is used (water-soluble flux followed by no-clean flux), then solder ball support and wetting are improved, but residue staining occurs leading to cosmetic defects and visual inspection rejections
Solution Approach 1:
The patent combines the functions of water-soluble flux (cleaning and initial solder ball support) and no-clean flux (solder ball retention and wetting) into a single no-clean flux formulation. This eliminates the need for a second flux application and subsequent residue cleaning, while maintaining both solder ball support and wetting performance through optimized flux chemistry and viscosity parameters.
Solution Approach 2:
The patent extracts and removes the harmful residue-generating components from the flux process by using a water-soluble flux formulation that can be completely removed by water rinsing, while still providing adequate solder ball support and wetting through controlled viscosity and chemical composition.
2Ease of manufacture
If water-soluble flux is used in the first step, then OSP cleaning is achieved, but the flux residue is not effectively removed leading to staining when no-clean flux is applied
Solution Approach 1:
The patent modifies the viscosity parameters of the water-soluble flux by adjusting bonding polymer content and amine reduction, creating a flux with optimized flow characteristics that provides adequate solder ball support without excessive spreading. This parameter optimization ensures complete water solubility and effective residue removal, preventing staining issues.
3Reliability
If no-clean flux is applied in a second step, then solder ball retention and wetting are improved, but flux spreads over bond pads creating cosmetic defects
Solution Approach 1:
The patent optimizes the viscosity of the no-clean flux through bonding polymer concentration and amine content adjustment, ensuring the flux has sufficient thickness to retain solder balls during reflow but limited spreading capability to prevent residue from extending beyond bond pad boundaries onto the second level interconnect interface.
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 one-step flux process effectively reduces residue staining, increases yields, and minimizes visual inspection rejections by maintaining stable solder ball support and controlled flux spread, enhancing the overall quality of BGA packages.
Implementation Method 1
A one-step water-soluble flux process with increased bonding polymer and reduced amine content is used, increasing viscosity
Data Source
AI summary
A one-step water soluble (WS) flux process may reduce residue staining and increase yields for bond grid array (BGA) packages. In one example, the WS flux may use increased amounts of bonding polymer (BP) and reduced amounts of amine to increase viscosity. The increased viscosity may eliminate using a second no-clean flux and enable a single WS flux to both clean the associated substrate and provide stable solder ball support during reflow.