Tin Alloy Etching for Planarized PCB Recessed Structures
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Solution Overview
Problem
Existing methods for etching tin and tin alloys in recessed structures on printed circuit boards and IC substrates result in dimples due to non-homogeneous etching, leading to unstable and unreliable solder joints, and require multiple process steps or etch resist usage.
Innovation Solution
An aqueous etching solution comprising hydroxide ions and a nitro-substituted aromatic sulfonic acid with a pH greater than 7 is used to uniformly remove excess tin or tin alloy deposits, preventing dimple formation by ensuring a smooth planarization of recessed structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If aqueous etching solutions known in the art are used to remove excess tin or tin alloy, then the excess layer is removed, but dimples are formed in the recessed structures due to non-homogeneous etching
Solution Approach 1:
The patent changes the chemical parameters of the etching solution by using an alkaline aqueous solution with specific pH range (8-14) and controlled concentration (0.1-10 g/L of tin etching agents), along with temperature control (20-80°C), to achieve homogeneous etching that removes excess tin without forming dimples, thus maintaining surface planarity and solder joint reliability
Solution Approach 2:
The etching solution is designed to provide different etching rates for different locations: faster etching for the excess tin layer on the surface and controlled etching for the tin within recessed structures, achieving uniform surface planarity while preserving the integrity of the filled recessed structures
2Manufacturing precision
If etch resist is deposited and used to remove excess tin or tin alloy, then the excess layer is removed, but the process requires several additional process steps and increases device complexity
Solution Approach 1:
The patent extracts and eliminates the etch resist step from the conventional process by using a specially formulated alkaline aqueous etching solution that can selectively remove excess tin without requiring protective resist layers, thereby simplifying the process flow while maintaining surface planarity
Solution Approach 2:
By changing the chemical composition and pH parameters of the etching solution to alkaline conditions with specific additives, the patent achieves selective etching that eliminates the need for etch resist, reducing the number of process steps while maintaining manufacturing precision
3Manufacturing precision
If complete filling of recessed structures is achieved by electroplating, then the recessed structures are fully filled with tin or tin alloy, but an excess layer is deposited on the surrounding conductive seed layer
Solution Approach 1:
The alkaline aqueous etching solution provides spatially selective etching action that targets only the excess tin layer on the surface while preserving the tin within the recessed structures, achieving local material removal without affecting the filled structures
Solution Approach 2:
By controlling the pH, concentration, and temperature parameters of the alkaline etching solution, the patent achieves precise control over etching rate and selectivity, removing the necessary excess material while maintaining complete filling of recessed structures
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 solution achieves stable and reliable solder joints by eliminating dimples and reducing the number of process steps, ensuring uniform etching independent of grain size, thereby enhancing the manufacturing process for printed circuit boards and IC substrates.
Implementation Method 1
contacting said substrate with said aqueous etching solution for removing said excess tin or tin alloy layer
Data Source
AI summary
A process for etching excess tin or tin alloy deposits including the steps of providing a substrate having recessed structures filled with tin or a tin alloy and an excess layer of tin or tin alloy, providing an aqueous etching solution consisting of a source of hydroxide ions and a nitro-substituted aromatic sulfonic acid and having a pH value greater than 7, and contacting said substrate with said aqueous etching solution for removing said excess tin or tin alloy layer on top of the recessed structures filled with tin or a tin alloy.