Copper Intermediary Layer for Silver Soldering
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Solution Overview
Problem
Soldering to thin silver-containing layers in electronic circuits is challenging due to poor wetting and silver dissolution, leading to reduced mechanical strength and reliability of interconnection joints, especially in next-generation electronics and printed circuit boards.
Innovation Solution
A method using a copper-containing layer as a bonding layer between a traditional solder and a silver-containing layer, deposited via printing or electrochemical techniques, and sintered at low temperatures, forming a solder joint with a copper-silver interface to prevent silver dissolution and enhance solderability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If standard solders are used on printed silver-containing layers, then soldering process is simple, but wetting is poor and solder beads form on the surface
Solution Approach 1:
A copper-containing layer is introduced as an intermediary between the silver-containing layer and the solder. This copper layer acts as a mediator that improves wetting behavior and prevents solder bead formation, while also preventing silver dissolution into the solder. The copper layer enables reliable interconnection joints without requiring complex process changes.
2Reliability
If high temperature brazing is used to solder silver, then silver dissolution is prevented, but mechanical strength is reduced
Solution Approach 1:
The invention changes the temperature parameter from high temperature brazing (618-899°C) to low temperature soldering (at or below 300°C). By introducing the copper-containing layer, the process enables reliable silver soldering at lower temperatures, thereby improving mechanical strength while maintaining silver-substrate adhesion through the copper intermediary layer.
3Reliability
If specialty low melting point high silver content solder is used, then silver dissolution is reduced, but mechanical strength is still poor
Solution Approach 1:
Instead of relying on specialty solders with high silver content, the invention uses a copper-containing layer as an intermediary. This approach prevents silver dissolution into the solder while allowing the use of traditional solders that provide superior mechanical strength, thereby resolving the strength limitation of specialty solders.
4Adaptability or versatility
If copper-containing layer is deposited via printing technique, then manufacturing flexibility is improved, but additional sintering step is required
Solution Approach 1:
The invention uses printing techniques to deposit the copper-containing layer, which can be performed at low temperatures. The subsequent sintering step consolidates the printed copper particles into a continuous, conductive layer. This approach provides manufacturing flexibility through printing while the sintering parameter (temperature and atmosphere) is optimized to achieve proper layer consolidation without excessive complexity.
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 method creates reliable interconnection joints with improved mechanical strength and electrical conductivity by preventing silver dissolution and ensuring proper wetting, suitable for next-generation electronics and flexible substrates.
Implementation Method 1
forming a solder joint having a solder-copper interface between the electronic assembly material and the at least a portion of the copper-containing layer, and a copper-silver interface between the copper-containing layer and the at least a portion of the silver-containing layer
Implementation Method 2
sintering the copper-containing layer at or below a temperature of 300° C. via at least one of: thermalsintering, photosintering, lasersintering, or local resistive heating
Implementation Method 3
depositing the copper-containing layer occurs via at least one of: a printing technique, or electrochemical deposition
Implementation Method 4
forming a solder joint at or below a temperature of 300° C.
Data Source
AI summary
The present disclosure describes methods of soldering on printed circuits, and, more specifically, to methods of using a copper-containing layer or copper “ink” in low-temperature soldering using established solder processes on silver-containing layers in circuit boards. The present disclosure is also directed, in part, to a solder joint having a copper-containing layer acting as a bonding layer between a traditional solder and a silver-containing layer “ink” on a printed circuit board. The low-temperature forming of the solder joint occurs at or below a temperature of 300° C. and occurs via at least one of sintering, photosintering, lasersintering, local resistive heating, or electrochemical deposition. The methods disclosed can satisfy the growing demand for creating reliable interconnection joints that can be used in next generation electronics and printed electrical circuit boards.