RDL Structure with Self-Aligned Recess for Solder Joint Strength
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Solution Overview
Problem
Conventional wafer level packaging processes face issues with weak bonding force and peeling of solder balls due to small contact area between the under-ball metallurgy (UBM) layer and solder balls, leading to problems like intermetallic compounds (IMCs), cold joints, and solder bridges.
Innovation Solution
A redistribution layer (RDL) structure is manufactured using 3D printing technology to form a self-aligned structure with a recess, allowing a conductive layer to conformally cover the structure and a conductive connector to be embedded, increasing the contact area and structural strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional planar UBM layer is used, then the manufacturing process is simple, but the contact area with solder ball is small and bonding force is weak
Solution Approach 1:
The patent applies curvature by forming a recess (concave structure) in the UBM layer instead of using a planar surface. This recessed structure increases the contact area with the solder ball by allowing the solder ball to nestle into the depression, thereby enhancing the bonding force between the UBM layer and solder ball while maintaining manufacturing simplicity.
2Reliability
If the contact area between UBM layer and solder ball is increased, then bonding force is improved, but the manufacturing complexity increases
Solution Approach 1:
The recessed UBM layer structure is formed using standard photolithography and etching processes, which are conventional manufacturing techniques. This approach increases the contact area and bonding reliability without requiring complex or specialized manufacturing equipment, thus maintaining ease of manufacture while improving reliability.
3Reliability
If the UBM layer structure is modified to increase contact area, then peeling and IMC issues are prevented, but the process complexity increases
Solution Approach 1:
The recessed UBM layer structure prevents peeling and intermetallic compound formation by increasing the bonding interface area between the UBM layer and solder ball. The concave geometry distributes mechanical stresses more evenly and reduces the formation of brittle IMCs, thereby improving solder joint reliability without requiring complex multi-step processes.
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 enhances the structural strength and reliability of the RDL structure, preventing peeling and cracking, while simplifying the manufacturing process and reducing costs.
Implementation Method 1
A self-aligned structure is formed on the dielectric layer by using a first three-dimensional (3D) printing technology
Implementation Method 2
The conductive layer extends from the pad to conformally cover a surface of the self-aligned structure
Data Source
AI summary
Provided is a redistribution layer (RDL) structure including a substrate, a pad, a dielectric layer, a self-aligned structure, a conductive layer, and a conductive connector. The pad is disposed on the substrate. The dielectric layer is disposed on the substrate and exposes a portion of the pad. The self-aligned structure is disposed on the dielectric layer. The conductive layer extends from the pad to conformally cover a surface of the self-aligned structure. The conductive connector is disposed on the self-aligned structure. A method of manufacturing the RDL structure is also provided.