PCB Trace Galvanic Etching Reduction via Homogeneous Plating

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Solution Overview

Problem

The galvanic effect between metallic materials in printed circuit boards, particularly in data storage devices, leads to voltage differentials that cause over-etching and weakening of internal connection points, resulting in increased resistance and potential failure of traces and connections.

Innovation Solution

The solution involves plating the contact finger and exposed portions of the contact trace with a common material to reduce galvanic etching, and electrically connecting them through a component or bond wire, allowing for precise control of trace impedances by separating the contact trace into a contact trace portion and an impedance trace, ensuring they are electrically isolated and plated with the same material.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the contact finger and contact trace are made of different metallic materials to provide good electrical connection and solderability, then electrical performance is improved, but galvanic etching occurs causing trace over-etching and increased resistance

Engineering Contradiction:

Improveelectrical connection reliabilityVSAvoidgalvanic etching

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies homogeneity by plating the contact finger and exposed contact trace with the same material (e.g., OSP or other protective coatings). This eliminates the galvanic effect between dissimilar metals at the interface, preventing trace over-etching while maintaining electrical connectivity and solderability through the unified material composition.

Inventive Principle:

Principle #33Homogeneity

Solution Approach 2:

The patent introduces an intermediary protective plating layer between the contact finger and the contact trace. This intermediate layer acts as a barrier that prevents direct galvanic interaction between dissimilar metals, thereby protecting the trace from etching while still allowing electrical connection to be established.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Strength

If the contact trace is oversized to account for potential etching, then trace strength is improved, but trace impedance control precision deteriorates

Engineering Contradiction:

Improvetrace strengthVSAvoidimpedance control precision

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The patent applies preliminary anti-action by pre-plating the contact trace with the same material as the contact finger before the galvanic etching process occurs. This preventive measure counteracts the potential etching effect in advance, allowing the trace to maintain its designed dimensions and impedance characteristics without requiring oversizing for compensation.

Inventive Principle:

Principle #9Preliminary anti-action

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 effectively reduces etching due to the galvanic effect, maintaining precise trace design and reducing impedance variations, thereby enhancing the reliability and performance of data storage devices.

Implementation Method 1

The cleaning chemical, combined with the metallic finger having a much larger surface area of metal as opposed to the internal connection points that are electrically connected to the metallic finger results in a voltage differential between the metallic finger and the associated internal connection point due to the galvanic effect.

Methodology Applied

Scientific EffectGalvanic effect:

Implementation Method 2

The contact finger and the exposed portion of the contact trace are plated with a common material to reduce galvanic etching of the contact trace

Methodology Applied

Scientific EffectPlating: Electroplating

Data Source

PatentUS11234327B1Printed circuit board trace for galvanic effect reduction

Publication Date: 2022.01.25 SANDISK TECHNOLOGIES LLC

AI summary

Devices and methods are described for reducing etching due to galvanic effect within a printed circuit board that may be used, for example, in a data storage device, such as a card-type data storage device. Specifically, a contact trace is coupled to a contact finger that has a substantially larger surface area than the contact trance, and that is configured to couple the data storage device to a host device. The contact trace is electrically isolated from the rest of the circuitry during a fabrication process. The contact finger and an exposed portion of the contact trace are plated with a common material to reduce galvanic etching of the contact trace during fabrication. The contact trace is then connected to an impedance trace though at least one of a component and a bond wire.