Selective Copper Etching on PCBs Without Tin Dissolution
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for treating copper or copper alloys fail to selectively etch surfaces without affecting tin, leading to surface roughness, contamination, and impaired solderability, with limited reliable long-term operating times and unsuitable conditions for subsequent metal deposition.
Innovation Solution
A method involving an alkaline treatment solution with copper (II) ions, halide ions, and ammonia, followed by an acidic treatment solution to remove metal oxides, ensuring selective etching of copper or copper alloys without affecting tin, and enhancing solderability and adhesion for subsequent metal layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional etching methods are used to remove copper, then copper can be completely removed to generate circuit patterns, but the etching rate is difficult to control and surface roughness increases
Solution Approach 1:
The patent changes the chemical parameters of the etching solution by specifying precise concentrations of copper chloride (2-10 g/L), ammonium chloride (10-50 g/L), and ammonia (0.5-5 g/L), along with controlling pH (8-10) and temperature (20-40°C). These parameter changes enable controlled etching that removes copper without creating excessive surface roughness, resolving the contradiction between etching productivity and surface precision.
2Productivity
If conventional etchants are used to etch copper, then copper can be removed, but copper chloride hydroxide and oxides form on the surface interfering with subsequent metal deposition
Solution Approach 1:
The patent extracts and removes the harmful copper chloride hydroxide and oxide formations from the etched surface by controlling the etching chemistry to prevent their formation in the first place. The specific composition of the etchant and post-etching rinsing with water removes these contaminants, leaving a clean copper surface suitable for subsequent metal deposition without interference from oxides or hydroxides.
3Productivity
If phenolsulfonic acid is used in the etchant, then copper can be etched, but cords and brown residues form on the surface impairing later deposition and soldering
Solution Approach 1:
The patent replaces phenolsulfonic acid with a different chemical system based on copper chloride, ammonium chloride, and ammonia that achieves the same etching capability without producing persistent harmful residues. The new etchant system is designed to be consumed and rinsed away completely, leaving no cords or brown residues on the surface, thus eliminating the harmful effects while maintaining etching productivity.
4Productivity
If conventional etchants are used, then copper can be etched, but the method does not selectively affect tin, leading to tin dissolution
Solution Approach 1:
The patent applies local quality by creating an etching environment that is specifically tailored to affect copper while leaving tin untouched. The etchant composition (copper chloride, ammonium chloride, ammonia with pH 8-10) and controlled conditions (temperature 20-40°C, specific concentrations) create a selective chemical environment that targets copper atoms on the surface while being inert toward tin, achieving both etching efficiency and selectivity.
5Productivity
If the etched copper surface is coated with metal layers, then circuit patterns can be formed, but the metal deposition bath is contaminated by surface oxides and alkaline etchant
Solution Approach 1:
The patent performs preliminary actions by thoroughly rinsing the etched copper surface with water immediately after etching and before metal deposition. This preliminary cleaning step removes residual etchant and prevents oxide formation, ensuring that the copper surface is clean and ready for metal deposition. This prevents contamination of the metal deposition bath while maintaining deposition efficiency.
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 method provides a controlled etching process that maintains the integrity of tin layers, achieves smooth surfaces, and ensures good solderability and adhesion for deposited metal layers, with a reliable long operating time.
Implementation Method 1
contacting the surface with an alkaline treatment solution... an etchant comprising a source of copper (II) ions, a source of halide ions and ammonia
Implementation Method 2
contacting the surface obtained by step (i) with an acidic treatment solution, wherein in step (ii) metal oxides are removed from the surface
Implementation Method 3
an etchant comprising a source of copper (II) ions, a source of halide ions and ammonia
Data Source
AI summary
The present invention relates to a method of selectively treating the surface of copper or copper alloys without affecting other metals, particularly tin. The methods are suited for treating surfaces of copper or copper alloys in order to facilitate subsequent deposition of metal layers and enhance solderability of the surfaces of copper, copper alloys and said subsequently deposited metal layers. The methods are applied to printed circuit boards (PCBs) and lead frames or integrated circuit substrates (IC substrates).