Copper Surface Activation Void Suppression via Phosphonate Mediator
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Solution Overview
Problem
The formation of undesired voids on copper or copper alloy surfaces during the activation process for electroless plating, which can reduce the reliability of solder joints and wire bonds, is a significant issue in the manufacturing of printed circuit boards and semiconductor devices.
Innovation Solution
A method involving the use of an aqueous solution containing palladium ions, a phosphonate compound, and halide ions, without carboxyl group-containing organic acids or salts, to activate copper or copper alloy surfaces for electroless plating, which suppresses the formation of voids and ensures a strong adhesion of the deposited metal or metal alloy layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an acidic activation solution containing palladium ions and carboxyl group-containing organic acid is used for activating copper surface, then the electroless plating can be performed, but undesired voids form in the copper surface area
Solution Approach 1:
The invention changes the chemical composition parameters of the activation solution by replacing carboxyl group-containing organic acids with phosphonate compounds. This parameter change modifies the activation mechanism to prevent void formation while maintaining the electroless plating capability, thereby improving both surface quality and joint reliability
Solution Approach 2:
Phosphonate compounds serve as intermediary substances that mediate between the palladium ions and the copper surface. They facilitate the deposition of a uniform palladium seed layer without causing the void formation that occurs with carboxyl group-containing organic acids, thus resolving the contradiction between achieving activation and maintaining surface integrity
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 method effectively prevents the formation of voids and ensures a strong adhesion of the metal or metal alloy layer on the copper or copper alloy surface, enhancing the reliability of solder joints and wire bonds by eliminating skip plating and extraneous plating, and providing sufficient adhesion during electroless plating.
Implementation Method 1
The most prominent means for activating a copper or copper alloy surface is the deposition of a palladium seed layer by immersion-type plating of palladium which is a redox reaction wherein copper is oxidized and palladium ions present in the activation solution are reduced to metallic state
Implementation Method 2
contacting said substrate with the following components a. an aqueous solution containing a source of palladium ions, b. an aqueous solution containing a phosphonate compound
Implementation Method 3
depositing a metal or metal alloy layer onto the activated copper or copper alloy surface obtained in step ii. by electroless plating
Data Source
AI summary
The present invention relates to method for activating a copper or copper alloy surface for depositing a metal or metal alloy layer by electroless (autocatalytic) plating thereon wherein the formation of undesired voids is suppressed. The copper or copper alloy surface is contacted with palladium ions, at least one phosphonate compound and halide ions followed by electroless (autocatalytic) deposition of a metal such as palladium or a metal alloy such as a Ni—P alloy.