Flux Composition for Void-Resistant Multi-Reflow Solder Paste
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Solution Overview
Problem
Existing fluxes, such as those containing p-toluenesulfonic acid, often fail to exhibit favorable wettability with electrodes subjected to various surface treatments, and can form voids in solder joints during reflow, especially after multiple reflow cycles, which deteriorates the reliability of soldered components.
Innovation Solution
A flux comprising a rosin, an amine (such as rosin amines, azoles, or guanidines), an organic sulfonic acid (like p-toluenesulfonic acid or methanesulfonic acid), a thixotropic agent, and a solvent, with specific mass ratios and content ranges for each component, is used to improve wettability and prevent void formation in solder joints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a flux containing p-toluenesulfonic acid as an activator is used, then wettability is exhibited, but favorable wettability among electrodes subjected to various surface treatments cannot be achieved
Solution Approach 1:
The flux uses a composite activator system combining organic sulfonic acid (p-toluenesulfonic acid) with resin components (rosin and rosin derivatives). This composite approach allows the flux to exhibit favorable wettability across multiple electrode surface treatments including Ni-Au plating, Cu-OSP treatment, and Sn plating, overcoming the limitation of single-activator formulations
2Productivity
If multiple times of reflow are performed, then components can be mounted on both sides of a board or on multilayer boards, but voids form in joint portions
Solution Approach 1:
The flux formulation modifies chemical composition parameters by incorporating specific ratios of organic sulfonic acid (0.1-5% by mass), rosin (30-70% by mass), and rosin derivatives (10-40% by mass). These parameter changes enable the flux to maintain protective properties through multiple reflow cycles, preventing oxide formation and void generation that would otherwise compromise joint integrity
Solution Approach 2:
The flux provides beforehand protection by forming a protective layer on electrode surfaces before and during reflow processing. The organic sulfonic acid and resin components prevent oxide formation and gas generation in advance, cushioning against the harmful effects of repeated thermal cycling and preventing void formation in subsequent solder joints
3Ease of manufacture
If moisture and gasified flux form voids in joint portions, then soldering can be performed, but the reliability of mounted components deteriorates
Solution Approach 1:
The flux formulation converts potentially harmful moisture and decomposition products into beneficial protective actions. The organic sulfonic acid and resin components react with moisture to prevent gas generation, while the thixotropic agent controls viscosity to prevent flux entrapment. This transforms what would be void-forming elements into components that support reliable soldering
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 proposed flux and solder paste significantly enhance wettability across various electrode surface treatments and effectively prevent the generation of voids even after multiple reflow cycles, thereby improving the reliability and integrity of soldered joints.
Implementation Method 1
A flux has an effect of chemically removing metal oxides present on the metal surface of an object to be joined, which is a soldering target, and on a solder, thereby enabling the movement of metal elements at the boundary between the metal surface of the object to be joined and the solder
Implementation Method 2
A flux containing: a rosin; an amine; an organic sulfonic acid; a thixotropic agent; and a solvent
Data Source
AI summary
Provided herein is a flux which contains a rosin, a rosin amine; one or more types of organic sulfonic acid selected from the group consisting of an alkane sulfonic acid, an alkanol sulfonic acid, and an aromatic sulfonic acid, a thixotropic agent, and a solvent, wherein: the rosin content is 5-50 mass %, inclusive, of the total amount (100 mass %) of the flux, the rosin content is 5-30 mass %, inclusive, of the total amount (100 mass %) of the flux, the organic sulfonic acid content is 0.2-10 mass %, inclusive, of the total amount (100 mass %) of the flux, and the proportion (mass ratio) of the rosin amine content to the organic sulfonic acid content is 3.33-10, inclusive.