Low-Temperature Solder Paste Composition for PET and PCB Joining
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Solution Overview
Problem
Conventional solder alloys have high melting points, making them unsuitable for use with low-cost, heat-sensitive substrates like PET films, and their fluxes are not effective at lower temperatures, leading to reliability issues.
Innovation Solution
A solder alloy comprising 40-65 wt.% bismuth, 1-10 wt.% indium, and optional additives such as gallium, zinc, copper, and silver, which has a lower melting point and improved mechanical properties, allowing for reliable soldering on PET substrates with a suitable flux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional solder alloys with high melting points are used, then reliable soldering can be achieved on traditional substrates, but heat-sensitive substrates like PET films cannot be used due to thermal breakdown and distortion
Solution Approach 1:
The patent changes the compositional parameters of the solder alloy by incorporating bismuth (40-65 wt.%), indium (1-10 wt.%), and optional additives (gallium, zinc, copper, silver) to achieve a lower melting point while maintaining reliable soldering performance on heat-sensitive substrates like PET films
Solution Approach 2:
The patent creates a composite solder alloy system combining multiple elements (bismuth, indium, and optional additives) to achieve properties that individual elements cannot provide alone, specifically lowering the melting point while maintaining mechanical and thermal properties suitable for PET substrate soldering
2Temperature
If conventional solder fluxes with aggressive activators are used to achieve low temperature soldering, then lower melting point alloys can be soldered, but paste homogeneity is disturbed by reactions with solder alloys in storage and electrical reliability is adversely affected by unreacted activators in residue
Solution Approach 1:
The patent changes the chemical parameters of the flux by using mild activators instead of aggressive ones, and carefully controlling the activator package composition to enable effective low-temperature soldering without compromising paste stability or electrical reliability
Solution Approach 2:
The patent employs a flux formulation where the activator is designed to be fully consumed during the soldering process, leaving minimal residue that could affect electrical reliability, effectively making the activator a single-use component
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 solder alloy achieves reliable soldering on PET substrates at lower temperatures, reducing reflow-induced warpage and maintaining favorable mechanical and thermal properties, thus enhancing the reliability of electronic components.
Implementation Method 1
The solder alloy comprises: from 40 to 65 wt. % bismuth; from 1 to 10 wt. % indium; at least one of: from 0.1 to 5 wt. % gallium, from 0.1 to 5 wt. % zinc, from 0.1 to 2 w. % copper, from 0.01 to 0.1 wt. % cobalt, from 0.1 to 2 wt. % silver, from 0.005 to 0.05 wt. % titanium, and from 0.01 to 1 wt. % nickel
Implementation Method 2
the solder melts and wets the soldering surfaces on the boards as well as the components
Data Source
AI summary
A solder paste comprising: a solder alloy, and a solder flux comprising an activator, wherein the activator comprises an organic acid activator and an organic amine activator, and wherein the molar ratio of organic acid activator to organic amine activator is from 0.8 to 2.5. A method of forming a solder joint comprising: (i) providing two or more work pieces to be joined; (ii) providing the solder paste of claim 1; and (iii) heating the solder paste in the vicinity of the work pieces to be joined.