Barrier Layer Protects Semiconductor Electrodes From Acidic Flux
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Solution Overview
Problem
The existing configurations of passivation layers and solderable contacts in semiconductor devices lead to device reliability issues due to silver ion migration and dendrite formation, and the use of lead-free solders causes acidic fluxes to react with aluminum electrodes, forming holes and affecting semiconductor junctions.
Innovation Solution
A semiconductor device with barrier layers made of conductive materials like titanium, extending between solderable contacts and passivation layers, and along gaps to protect electrodes from acidic fluxes in lead-free solders, preventing reaction and ensuring reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If passivation layer and solderable contacts are formed in an abutting/overlapping configuration, then device structure is simplified, but silver ions migrate and form dendrites reducing reliability
Solution Approach 1:
A barrier layer is introduced as an intermediary between the solderable contact and the passivation layer. This barrier layer prevents silver ions from the solderable contact from migrating through the passivation layer to form dendrites, while still allowing the simplified abutting/overlapping configuration to be used. The barrier layer acts as a mediator that blocks the harmful ion migration path.
Solution Approach 2:
The structure is segmented into distinct functional layers: the solderable contact layer, the barrier layer, and the passivation layer. This segmentation allows each layer to perform its specific function - the barrier layer specifically addresses the silver migration issue while the passivation layer provides overall protection, resolving the reliability problem without increasing overall structural complexity.
2Object-affected harmful factors
If lead-free solders are used to eliminate environmental hazards, then environmental safety is improved, but acidic fluxes react with aluminum electrodes forming holes and affecting semiconductor junctions
Solution Approach 1:
The barrier layer serves as an intermediary protective layer between the aluminum electrode and the acidic flux in lead-free solders. It prevents the acidic flux from directly contacting and reacting with the aluminum electrode, thereby preventing hole formation and protecting the semiconductor junctions while allowing the use of environmentally safer lead-free solder.
Solution Approach 2:
The barrier layer is applied in advance before the soldering process to preemptively protect the aluminum electrode from the acidic flux. This preliminary protective action prevents the harmful chemical reaction from occurring in the first place, allowing the use of lead-free solder without compromising device reliability.
3Reliability
If solderable contacts are exposed to allow complete solder coverage, then silver dissolution is maximized preventing dendrites, but acidic fluxes can contact and react with aluminum electrodes
Solution Approach 1:
The barrier layer is positioned between the aluminum electrode and the flux environment. It allows the solderable contact to remain exposed for complete solder coverage and silver dissolution to prevent dendrites, while simultaneously blocking the acidic flux from reaching and reacting with the aluminum electrode.
Solution Approach 2:
The barrier layer provides localized protection specifically at the interface between the electrode and flux, while allowing the solderable contact surfaces to remain exposed for their protective function. This local application of protection resolves the contradiction by allowing exposure where needed (at solder surfaces) while blocking where harmful (at electrode-flux interface).
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 barrier layers effectively prevent acidic fluxes from contacting the electrodes, reducing the formation of holes and enhancing device reliability by protecting the active semiconductor junctions from lead-free solder fluxes.
Implementation Method 1
barrier layers that cover at least a portion of the top surfaces of the source and gate electrodes... protect the electrodes from acidic fluxes in lead-free solders, preventing reaction
Data Source
AI summary
A semiconductor device includes a die with at least one electrode on a surface thereof, at least one solderable contact formed on the electrode, and a passivation layer formed over the electrode and including an opening that exposes the solderable contact. The passivation layer opening may be wider than the solderable contact such that a gap extends between the contact and the passivation layer. The device also includes a barrier layer disposed on the top surface of the electrode, and along the underside of the solderable contact and across the gap. The barrier layer may also extend under the passivation layer and may cover the entire top surface of the electrode. The barrier layer may also extend along the sidewalls of the electrode. The barrier layer may include a titanium layer or a titanium layer and nickel layer. The barrier layer protects the electrode and underlying die from acidic fluxes found in lead-free solders.