Micro LED Bonding Pad Structure for Stable Eutectic Joining
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Solution Overview
Problem
The challenge in micro LED display manufacturing is the limited flexibility in selecting bonding materials for the solderless layer and bonding pads, leading to issues such as overflow and poor bonding, which affects the stability and efficiency of the bonding process.
Innovation Solution
The display panel design incorporates bonding pads with a lamination structure of two different metal layers, where the first metal layer has an opening exposing the second metal layer, allowing the solder pattern to form a eutectic bonding, thereby stabilizing the bonding process and preventing overflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solderless layer is used to stabilize bonding between micro LED and bonding pads, then bonding stability is improved, but material selection flexibility is reduced due to overflow or poor bonding issues
Solution Approach 1:
The bonding pad structure is segmented into multiple functional layers: a first metal layer (e.g., tungsten nickel) for preventing solderless overflow, a second metal layer (e.g., copper or nickel gold) for providing good solderability and eutectic bonding, and an optional third metal layer for additional protection. This segmentation allows each layer to perform its specific function independently, resolving the contradiction between bonding stability and material selection flexibility.
Solution Approach 2:
The bonding pad uses a composite structure combining different metal materials with complementary properties. The first metal layer (tungsten nickel) provides overflow prevention, while the second metal layer (copper or nickel gold) provides excellent solderability. This composite material approach enables both bonding stability and material selection flexibility to coexist.
2Ease of manufacture
If the bonding pad uses a single material structure, then manufacturing is simpler, but bonding reliability is reduced due to overflow or poor bonding
Solution Approach 1:
The bonding pad is divided into multiple layers with distinct functions. The first metal layer prevents solderless overflow, the second metal layer ensures good solderability and eutectic bonding. This segmentation improves bonding reliability while maintaining reasonable manufacturing complexity through standardized multi-layer fabrication processes.
3Strength
If the first metal layer is made completely solid, then structural strength is improved, but solder pattern overflow increases and eutectic bonding is compromised
Solution Approach 1:
The first metal layer is designed with a local opening at its center, creating different local qualities: the surrounding solid metal provides structural strength and prevents overflow, while the central opening exposes the second metal layer for eutectic bonding. This local quality variation resolves the contradiction between structural strength and bonding quality.
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 design enhances the bonding yield by stabilizing the eutectic bonding between the solder pattern and the bonding pads, reducing solder pattern overflow and ensuring electrical continuity between the light emitting devices and the circuit board.
Implementation Method 1
The solder patterns each contact the second metal layer through the opening of the first metal layer of the one of the bonding pads, thereby forming a eutectic bonding
Data Source
AI summary
A display panel including a circuit board, a plurality of bonding pads, a plurality of light emitting devices, and a plurality of solder patterns is provided. The bonding pads are disposed on the circuit board, and each includes a first metal layer and a second metal layer. The second metal layer is located between the first metal layer and the circuit board. The first metal layer includes an opening overlapping the second metal layer. A material of the first metal layer is different from a material of the second metal layer. The light emitting devices are electrically bonded to the bonding pads. Each of the solder patterns electrically connects one of the light emitting devices and one of the bonding pads. The solder patterns each contact the second metal layer through the opening of the first metal layer of one of the bonding pads to form a eutectic bonding.