Live-Entry Gold Plating to Eliminate Microvoids
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Solution Overview
Problem
Electroplated copper solder joints in printed circuit boards (PCBs) fail due to the presence of microvoids at the plated metal-substrate interface, which are caused by corrosion and improper nucleation during the plating process, leading to outgassing, corrosion, physical collapse, and compromised strength in solder joints.
Innovation Solution
A vertical type plating process, known as 'live-entry,' where the substrate is lowered into an acid-containing bath with an initial current applied to prevent corrosion and formation of microvoids, combined with increasing the current density to near the mass-transfer-limit for gold deposition to ensure proper nucleation and prevent the creation of voids, ensuring that plating begins as soon as the substrate enters the bath.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electroplating process is used, then plating can be applied to copper substrates, but microvoids form at the plated metal-substrate interface causing solder joint failure
Solution Approach 1:
The patent applies preliminary action by initiating the plating process immediately upon substrate immersion into the electrolyte bath. The substrate is conveyed through the bath with continuous plating current applied from the moment of contact, preventing the formation of microvoids at the interface by eliminating the delay that would otherwise allow corrosion and improper nucleation to occur.
Solution Approach 2:
The patent changes the timing parameter of the plating process by eliminating the traditional sequence where substrates are fully immersed before current application. Instead, current is applied immediately upon partial immersion, and the plating continues throughout the substrate's passage through the bath. This parameter change ensures proper nucleation and prevents microvoid formation at the interface.
2Ease of manufacture
If substrate is lowered into plating bath without immediate current application, then immersion plating can occur, but corrosion and microvoid formation are caused
Solution Approach 1:
The patent applies continuity of useful action by maintaining continuous plating current application throughout the entire process of substrate immersion and conveyance through the electrolyte bath. This continuous action ensures that plating occurs uniformly from the moment of substrate contact with the electrolyte, preventing corrosion and microvoid formation while maintaining process simplicity.
3Manufacturing precision
If current density is increased to near mass-transfer-limit, then proper nucleation and uniform grain growth are achieved, but energy consumption increases
Solution Approach 1:
The patent changes the current density parameter by operating near the mass-transfer limit throughout the plating process. This high current density ensures proper nucleation and uniform grain growth, preventing microvoid formation. The energy increase is justified by the elimination of solder joint failures and the need for high interface quality.
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 significantly reduces the formation of microvoids at the gold/copper interface, enhancing the reliability of solder joints by preventing corrosion, outgassing, and ensuring uniform grain growth, thereby improving the durability and integrity of solder bonds.
Implementation Method 1
electroplating a metal on a substrate avoids the creation of microvoids at the plated metal/substrate interface
Implementation Method 2
initial current is applied between the substrate, acting as a cathode, and an anode in the bath
Implementation Method 3
increasing the current density to near the mass-transfer-limit for gold deposition to ensure proper nucleation
Data Source
AI summary
A method of plating a copper substrate with gold that reduces or eliminates the presence of microvoids at the interface of the gold/copper substrate is described. Suitably, live entry of the substrate into the plating bath is performed with application of external current to the bath such that no portion of the substrate is exposed to the bath for more than one second without the application of the external current. Increase of the applied current for gold strike to the mass-transfer-limit for gold reduction accomplishes the full measure of improvement in eliminating microvoids.