No-Clean Solder Paste Flux for Electromigration Resistance
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Solution Overview
Problem
Solder pastes used in electronic circuit production often exhibit a tendency towards electromigration and dendrite formation, leading to undesirable short circuits, especially as components miniaturize and proximity increases, necessitating a solution to prevent these issues in no-clean solder joints.
Innovation Solution
A solder paste with a specially composed flux containing a combination of at least two optionally modified natural resins differing in weight-average molar mass, along with low molecular weight carboxylic acid and specific additives, is developed, comprising 85-92% tin-based solder and 8-15% flux, which reduces the occurrence of electromigration and dendrite formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional flux compositions are used in no-clean solder paste, then the solder paste provides adequate wetting and soldering performance, but electromigration and dendrite formation occur leading to short circuits
Solution Approach 1:
The patent modifies the chemical composition parameters of the flux by incorporating specific natural resins (rosin and colophony) in optimized ratios, along with particular carboxylic acids and halogen-containing compounds. This parameter optimization reduces the harmful chemical reactions that cause electromigration and dendrite formation, thereby improving long-term electrical insulation stability without sacrificing soldering performance
Solution Approach 2:
The invention uses a composite flux system combining multiple natural resins (rosin and colophony) with different molecular weight distributions, carboxylic acids, and halogen-containing compounds. This composite composition creates a synergistic effect where the different components work together to provide adequate wetting while simultaneously suppressing electromigration and dendrite formation through balanced chemical properties
2Productivity
If miniaturization of electronic components is pursued to increase integration density, then productivity and compactness improve, but the proximity of components increases the risk of short circuits from electromigration
Solution Approach 1:
By optimizing the flux composition parameters—specifically the ratio of natural resins, selection of carboxylic acids, and controlled addition of halogen-containing compounds—the patent reduces electromigration tendency at the microscopic level. This enables safer miniaturization as the improved flux chemistry prevents the formation of conductive dendrites even when components are in close proximity, thus maintaining electrical insulation integrity
3Manufacturing precision
If flux composition is optimized for better wetting properties, then soldering quality improves, but the tendency towards electromigration and dendrite formation increases
Solution Approach 1:
The patent achieves a balanced parameter set in the flux composition where natural resins provide adequate wetting while carboxylic acids and halogen-containing compounds control oxide dissolution without excessive reactivity. This balanced formulation maintains good solder joint quality through proper wetting while simultaneously suppressing the chemical conditions that lead to dendrite formation and electromigration
Solution Approach 2:
The composite flux system combines multiple components with complementary functions: natural resins for wetting, carboxylic acids for oxide dissolution, and halogen-containing compounds for controlled reactivity. This composite approach allows the flux to provide sufficient wetting for quality solder joints while the synergistic interaction of components prevents excessive chemical activity that would cause dendrite formation
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 paste significantly minimizes short circuit formation by reducing electromigration and dendrite formation, ensuring stable electrical insulation between electronic components, as demonstrated by improved wetting properties and surface insulation resistance tests.
Implementation Method 1
the flux usually also contains substances such as surfactants and additives that improve the rheological properties of the flux and thus the solder paste
Implementation Method 2
The solder paste is heated to melt the solder in the paste through a reflow process, thereby forming contact between the electronic component and the substrate
Implementation Method 3
After the solder has cooled and solidified, the electronic component and substrate are firmly connected
Data Source
AI summary
Solder paste comprising 85 to 92 wt% of a tin-based solder and 8 to 15 wt% of a flux, wherein the flux comprises i) 30 to 50 wt%, based on its total weight, of a combination of at least two optionally modified natural resins, ii) 5 to 20 wt%, based on its total weight, of at least one low molecular weight carboxylic acid; and iii) 0.4 to 10 wt%, based on its total weight, of at least one amine, and wherein the combination of the optionally modified natural resins has an integral molar mass distribution of 45 to 70 areal% in the molar mass range of 150 to 550 and of 30 to 55 areal% in the molar mass range of >550 to 10000 in the common GPC.