Nanoscale Coating for Flow Sensor Bond Pad Corrosion
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Solution Overview
Problem
Flow sensors are prone to corrosion and short circuits due to electrochemical reactions between exposed metal layers and corrosive fluids, particularly at the edge of the refractory metal diffusion barrier layer sidewalls, leading to oxidation and flaking of the top metal layer, which can result in field failures.
Innovation Solution
A multi-layer corrosion protection coating comprising a nanoscale adhesion layer, nanoscale diffusion barrier, and a self-assembled monolayer (SAM) that is hydrophobic or hydrophilic is applied to the sensor bond pads and bond wires, encapsulating the metal diffusion barrier layer sidewalls to prevent corrosion and electrochemical reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the metal diffusion barrier layer sidewall is exposed, then the sensor bond pads can be accessed for electrical connection, but the exposed sidewall is susceptible to corrosion and electrochemical reactions with corrosive fluids
Solution Approach 1:
A multi-layer coating system comprising a first coating layer (e.g., silicon nitride or silicon oxide), a second coating layer (e.g., parylene), and a third coating layer (e.g., hydrophobic or hydrophilic self-assembled monolayer) is applied to encapsulate the metal diffusion barrier layer sidewall. These thin film layers provide flexible protection against corrosive fluids while maintaining the electrical connection functionality through bond pads and wire bonds.
Solution Approach 2:
The protection system uses a composite multi-layer coating structure where each layer provides specific functionality: the first layer provides dielectric protection, the second layer provides moisture barrier, and the third layer provides surface energy control for enhanced corrosion resistance. This composite approach addresses both electrical connection requirements and corrosion protection needs.
2Reliability
If the top metal layer is exposed at the diffusion barrier layer sidewall edge, then electrical connectivity is maintained, but oxidation and flaking occur leading to field failures
Solution Approach 1:
The multi-layer coating system encapsulates the top metal layer at the sidewall region, forming a protective shell that prevents direct exposure to corrosive environments. This eliminates oxidation and flaking while preserving electrical connectivity through the underlying bond structure.
Solution Approach 2:
The coating layers are applied in advance to prevent oxidation and electrochemical reactions before they can occur. The hydrophobic or hydrophilic third layer specifically addresses preliminary protection against moisture ingress that would lead to oxidation.
3Reliability
If a protective coating is applied to the sensor bond pads, then corrosion resistance is improved, but the coating must not interfere with electrical bonding and wire attachment
Solution Approach 1:
The coating system is designed with local quality variations where the first and second layers provide protection, while the third layer's surface properties are specifically engineered to allow wire bonding. The coating is applied selectively to protect only the diffusion barrier sidewall while maintaining bondability at the bond pad surface.
Solution Approach 2:
The third coating layer changes the surface energy parameters of the bond pad, making it either hydrophobic or hydrophilic depending on the application requirements. This parameter adjustment enables both corrosion protection and maintained bondability without interfering with the electrical bonding process.
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 multi-layer coating effectively prevents oxidation and short circuits, enhancing the reliability and longevity of flow sensors by providing comprehensive protection against corrosive environments and moisture exposure.
Implementation Method 1
a self assembled monolayer (SAM) that is hydrophobic or hydrophilic
Implementation Method 2
a self assembled monolayer (SAM) that is hydrophobic or hydrophilic
Implementation Method 3
nm scale adhesion layer
Implementation Method 4
nm scale diffusion barrier
Data Source
AI summary
A corrosion resistant flow sensor apparatus includes a flow sensor including a micromachinable substrate mounted on a package substrate that includes electrically conductive traces and substrate bond pads. The flow sensor includes a MEMS sensing structure for sensing a mass flow parameter and sensor bond pads coupled to the sensing structure. The sensor bond pads include a top metal layer on a metal diffusion barrier layer including a metal diffusion barrier layer sidewall. Bond wires couple the sensor bond pads to the substrate bond pads. A housing including sides and a top portion is around the flow sensor and includes a flow channel having an inlet and an outlet. A multi-layer corrosion protection coating includes a nm scale adhesion layer and a self assembled monolayer (SAM) is on the adhesion layer. The protection coating covers the sensor bond pads including the metal diffusion barrier layer sidewall.