Silver-Coated Copper Powder Solder Paste
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Solution Overview
Problem
Reflow soldering processes face challenges in achieving high wettability and preventing void generation in solder layers due to the rapid reaction between tin and copper, leading to oxidation and poor solderability, especially with existing barrier coatings like nickel which oxidize at low temperatures.
Innovation Solution
A solder paste comprising a mixture of tin, silver, and copper powders, where the copper powder is coated with a silver barrier film, controlling the weight percentage and thickness of the silver coating to delay the reaction and maintain oxidation above the reflow temperature, thereby enhancing wettability and reducing void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If tin and copper are mixed directly without barrier coating, then soldering speed and reaction efficiency are improved, but oxidation occurs and wettability deteriorates
Solution Approach 1:
A silver barrier coating is applied on the copper powder surface to act as an intermediary layer. This silver layer prevents direct oxidation of copper while controlling the reaction between tin and copper during soldering. The silver coating serves as a mediator that enables both fast soldering reaction and good wettability by regulating the interaction between tin and copper.
Solution Approach 2:
The invention uses a composite structure of silver-coated copper powder combined with tin powder. This composite material approach allows the silver coating to provide oxidation protection while the copper core maintains soldering reactivity. The composite structure resolves the contradiction by combining materials with complementary properties.
2Reliability
If a thick silver barrier coating is applied on copper powder, then oxidation prevention is improved, but reaction delay becomes excessive and solderability decreases
Solution Approach 1:
The silver coating thickness is precisely controlled within the range of 0.1-5 μm, and the silver content is adjusted to 1-50 wt% of the total solder paste. By optimizing these parameters, the silver coating provides sufficient oxidation protection while maintaining adequate reaction speed for soldering. This parameter optimization resolves the contradiction between protection and reactivity.
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 silver-coated copper powder solder paste achieves improved wettability and reduced void generation in solder layers, maintaining solderability and preventing oxidation during reflow soldering, thus enhancing the reliability and efficiency of the soldering process.
Implementation Method 1
maintain oxidation above the reflow soldering temperature
Implementation Method 2
copper powder is coated with a silver barrier film
Implementation Method 3
enhancing wettability
Data Source
AI summary
A solder paste includes a flux and powder mixed with the flux, where the powder includes first powder and second powder mixed with each other. The first powder may be a tin (Sn) and at least one metal dissolved in the tin (Sn), and the second powder may be a copper (Cu) powder, the surface of which is coated with silver (Ag).