Cu Bump on Ti/Al Wiring for Reliable MicroLED Connections
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Solution Overview
Problem
The formation of copper bump electrodes on titanium-aluminum (TAT) laminated films for electronic devices, particularly in large-scale LED display apparatuses, faces challenges in terms of shape and manufacturing complexity, leading to low connection reliability between the bump electrodes and the underlying wiring.
Innovation Solution
A laminated film structure is used, comprising a titanium or titanium alloy conductor layer and an aluminum or aluminum alloy conductor layer, with a copper or copper alloy conductor portion bonded to the first wiring, and a solder containing tin formed on top, along with methods like electroplating and zincate treatment to enhance bonding strength and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If copper bump electrodes are formed on TAT laminated film wiring, then electrical resistance is reduced, but connection reliability deteriorates due to precipitous side surfaces that can be damaged by stress
Solution Approach 1:
The patent applies preliminary action by forming a flat-sided copper bump structure before final bonding. The electroplating process is controlled to create precipitous side surfaces initially, then a flattening process is performed to create flat sides before bonding. This preliminary flattening prevents stress damage during bonding while maintaining the low electrical resistance of the copper material.
Solution Approach 2:
The patent changes the physical parameters of the copper bump by controlling the electroplating conditions to create specific side surface angles. By adjusting plating parameters such as current density, plating time, and electrolyte composition, the side surfaces are formed with controlled precipitous angles that are then flattened to optimal bonding surfaces, resolving the contradiction between maintaining copper's low resistance and ensuring reliable connections.
2Loss of energy
If copper bump electrodes are formed on TAT laminated film wiring, then electrical resistance is reduced, but manufacturing process complexity increases
Solution Approach 1:
The patent merges the copper bump formation process with the existing electroplating infrastructure. By using electroplating instead of traditional methods like eutectic bonding or wire bonding, the process integrates with standard PCB manufacturing workflows. The flat-sided bump structure is achieved through controlled electroplating parameters, combining material deposition with shape formation in a single process step, thereby reducing overall manufacturing complexity while maintaining low electrical resistance.
3Ease of manufacture
If precipitous side surfaces are formed on bump electrodes, then manufacturing is simplified, but bonding interface reliability deteriorates due to stress damage
Solution Approach 1:
The patent performs preliminary flattening of the bump electrode side surfaces before the bonding step. This preliminary action creates flat bonding surfaces that prevent stress concentration and interface damage during bonding, while the bumps retain their elevated structure for proper electrical connection. The flattening is achieved through controlled electroplating or mechanical processes that create flat tops and sides suitable for reliable bonding.
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
Improves the electrical characteristics and connection reliability of the bump electrodes by enhancing the bonding strength between the copper and aluminum layers, reducing manufacturing complexity and the risk of interface destruction under stress.
Implementation Method 1
a step of selectively forming, at a position of overlapping the first opening and around the first opening, a first conductor portion made of copper or a copper alloy by an electroplating method while the first wiring is energized
Implementation Method 2
a step of selectively forming, on the first conductor portion, a second conductor portion made of solder containing tin while the first wiring is energized
Data Source
AI summary
An electronic device has: a substrate; a wiring formed on the substrate; an inorganic insulating layer covering the wiring; and a bump electrode that is connected to the wiring at a position of overlapping a first opening formed in the inorganic insulating layer and protrudes form the inorganic insulating layer. The wiring is a laminated film of: a first conductor layer made of titanium or a titanium alloy and formed on the substrate; and a second conductor layer made of aluminum or an aluminum alloy and laminated on the first conductor layer. The bump electrode includes: a first conductor portion made of copper or a copper alloy and bonded to the wiring; and a second conductor portion made of solder containing tin and formed on the first conductor portion.