Microchip Cap Layer Adhesion for Redistribution Metal Migration
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Solution Overview
Problem
Microchips face reliability issues due to metal migration and short circuits in the redistribution layer, especially when exposed to extreme temperatures and humidity, caused by poor adhesion between passivation and solder mask layers.
Innovation Solution
A microchip design with a substantially-uniform passivation layer and a cap layer formed from the same material, such as inorganic oxide using PECVD, to enhance adhesion and prevent metal migration, along with a protective layer from a different material to isolate the redistribution conductors and prevent bridging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a spin-on or spray-coating method is used to form the solder mask layer, then the manufacturing process is simple and fast, but the step coverage becomes non-uniform leading to key-hole formation and poor adhesion
Solution Approach 1:
The patent replaces the mechanical spin-on or spray-coating method with a chemical vapor deposition (CVD) process. This substitution eliminates the key-hole formation and non-uniform step coverage issues while maintaining manufacturing efficiency through a more controlled deposition mechanism that ensures uniform material distribution across complex topographies.
Solution Approach 2:
The patent changes the deposition parameters by using CVD instead of spin-on coating. This parameter change transforms the process from a mechanical application method to a chemical deposition method, which provides better control over film thickness and uniformity, eliminating key-hole formation while maintaining production throughput.
2Ease of manufacture
If the solder mask layer is applied over trench regions with poor step coverage, then the manufacturing process remains simple, but metal migration and short circuits occur in the redistribution layer
Solution Approach 1:
The patent replaces the mechanical spin-on coating process with chemical vapor deposition to form the solder mask layer. This substitution ensures uniform and complete coverage over trench regions and via structures, providing reliable electrical isolation and preventing metal migration while maintaining process simplicity through a single-step deposition method.
Solution Approach 2:
The patent introduces an intermediate layer or modified deposition process that acts as a mediator between the trench structures and the solder mask layer. This ensures complete coverage and adhesion in difficult-to-reach areas, preventing metal migration while maintaining the overall simplicity of the manufacturing process.
3Device complexity
If a non-uniform solder mask layer is formed, then the manufacturing process is straightforward, but adhesion between passivation and solder mask layers deteriorates causing metal migration
Solution Approach 1:
The patent replaces the mechanical spin-on coating method with chemical vapor deposition to form the solder mask layer. This substitution ensures uniform thickness and complete coverage, providing strong adhesion to the passivation layer and preventing metal migration, while maintaining the simplicity of the overall layer structure through a single deposition process.
Solution Approach 2:
The patent changes the deposition parameters from spin-on coating to CVD, which provides better control over film uniformity and adhesion properties. This parameter change ensures consistent layer strength and prevents metal migration while keeping the device structure simple and the manufacturing process straightforward.
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 design provides a robust redistribution layer resistant to metal migration and short-circuit failures, ensuring reliability even in harsh environments.
Implementation Method 1
the passivation layer and the cap layer have at least one compatibility that facilitates an amount of adhesion therebetween sufficient to prevent migration of the conductive material between the interfaces of the passivation and cap layers
Implementation Method 2
A microchip design with a substantially-uniform passivation layer and a cap layer formed from the same material, such as inorganic oxide using PECVD
Implementation Method 3
a protective layer from a different material to isolate the redistribution conductors and prevent bridging
Data Source
AI summary
A microchip includes a passivation layer formed over underlying circuitry, a redistribution layer formed over the passivation layer, and a cap layer formed over the redistribution conductors of the redistribution layer and in contact with the passivation layer. The passivation layer and the cap layer have one or more compatibilities that provide sufficient adhesion between those two layers to prevent metal migration from the conductors of the redistribution layer between the interfaces of the passivation and cap layers. In one embodiment, the passivation and cap layers are each formed from an inorganic oxide (e.g., SiO2) using a process (e.g., PECVD) that provides substantially-uniform step coverage by the cap layer in trench and via regions of underlying circuitry. The invention increases the reliability of the microchip, because it eliminates metal migration, and the electrical shorting caused therefrom, in the redistribution layer.