Reliability Metal Traces Photoimageable Passivation
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Solution Overview
Problem
Conductive traces in touch sensor panels are prone to failures due to environmental effects, such as corrosion and chemical penetration, despite the use of passivation layers, which can lead to reliability issues and catastrophic failures.
Innovation Solution
A photoimageable passivation layer of organic polymer is applied over a stackup of metal layers, including Aluminum Neodymium (Al/Nd) and Molybdenum Niobium (Mo/Nb), providing enhanced protection against moisture, temperature, and foreign materials, with finer tolerances than conventional inorganic compositions, and the option to use a single thicker Mo/Nb layer for improved conductivity and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inorganic passivation layers (e.g., SiO2, SiNx) are used to protect conductive traces, then corrosion protection is provided, but reliability issues persist due to chemical penetration and environmental effects
Solution Approach 1:
The patent applies a composite passivation structure consisting of an inorganic layer (SiO2 or SiNx) combined with an organic polymer layer. This composite approach leverages the advantages of both materials: the inorganic layer provides base protection and conformal coverage, while the organic polymer layer adds enhanced chemical resistance and blocks penetration pathways that the inorganic layer alone cannot prevent, thereby resolving the reliability issue caused by chemical penetration.
Solution Approach 2:
The organic polymer passivation layer acts as a flexible protective film that conforms to the underlying conductive trace structure. This thin film provides continuous coverage and seals potential defects or pores in the inorganic layer, creating an effective barrier against moisture and chemical agents while maintaining the structural integrity of the trace protection system.
2Reliability
If conventional inorganic passivation layers are used, then protection is provided, but product dimensions increase due to larger tolerance requirements
Solution Approach 1:
The patent changes the material parameter from purely inorganic to a combination of inorganic and organic polymer materials. This parameter change allows for thinner overall passivation structure while maintaining or improving protection effectiveness, as the organic polymer layer can be applied more precisely and with better conformality, reducing the tolerance stack-up and minimizing the increase in product dimensions.
3Reliability
If Al/Nd layer is used for conductive traces, then conductivity is achieved, but adhesion to substrate is poor
Solution Approach 1:
The conductive trace structure uses a composite material system of Al/Nd combined with Mo/Nb layers. The Mo/Nb layer serves as an adhesion promoter that bonds well to the substrate, while the Al/Nd layer provides the required conductivity. This composite trace structure resolves the adhesion problem by separating the adhesion function (Mo/Nb) from the conductivity function (Al/Nd), allowing each material to optimize its primary role.
Data Source
AI summary
The formation of improved reliability conductive traces in touch sensor panels that are less prone to failures due to environmental effects is disclosed. Conductive traces, which can be formed from a stackup of metal layers or a single metal layer, can be protected with an additional photoimageable passivation layer of a material such as an organic polymer. This photoimageable coating can be patterned so that it does not appear in the visible area of the touch sensor panel, with much finer tolerances than conventional passivation layers to help keep product dimensions to a minimum.