Advanced Solder Technology: solder flux vs solder paste
Innovations in low-temperature, halogen-free solder paste solutions for heat-sensitive electronic components
The Evolving Landscape of Electronic Soldering
With the rapid development of the electronics industry, the demand for low-temperature soldering applications in heat-sensitive areas such applications in heat-sensitive areas such as smart hardware radiators, LED lighting component mounting, and solar photovoltaics has grown significantly. As a connecting material between electronic components and circuit boards, lead-free solder paste has been widely used. When examining solder flux vs solder paste, it's important to understand their unique properties and applications in these evolving technologies.
Currently, solder pastes prepared with lead-free alloy solders such as SnAgCu and SnAg have a reflow soldering temperature of generally above 230°C, which cannot meet the requirements of low-temperature soldering. These materials are unsuitable for the soldering process of heat-sensitive electronic components. Therefore, tin-bismuth based lead-free solder pastes with lower melting points have become the preferred material in the field of low-temperature soldering.
However, existing tin-bismuth based lead-free solder pastes have low activity, which prevents the pads from removing surface oxide layers, leading to soldering defects such as cold solder joints, tombstoning, solder balls, and non-wetting. In the ongoing debate of solder flux vs solder paste, these performance characteristics play a crucial role in determining the right material for specific applications.
To address these issues, existing technologies mainly use halides with strong corrosiveness (such as ammonium fluoride, tetrahydroxypropyl ethylenediamine hydrofluoride, etc.) as activators to remove black oxides formed during the soldering process. This not only corrodes solder joints and substrates, reduces surface insulation resistance, and affects the electrical performance of solder joints, but also fails to solve the problem of solder paste storage stability.
Challenges in Current Solder Technology
High Temperature Requirements
Traditional solder pastes require reflow temperatures above 230°C, damaging heat-sensitive components.
Oxidation Issues
Formation of black oxides during soldering leads to poor joint quality and reliability concerns.
Corrosive Materials
Halide-based activators cause corrosion, reducing electrical performance and longevity.
Storage Stability
Many formulations suffer from poor shelf life and consistency over time.
Precision Soldering in Modern Electronics Manufacturing
The choice between solder flux vs solder paste depends on application requirements, component sensitivity, and performance needs.
Limitations of Existing Solutions
Chinese Patent Application Publication No. CN104625483A discloses a low-residue, low-corrosion aluminum soft solder paste and its preparation method, using tetrahydroxypropyl ethylenediamine hydrofluoride obtained from the reaction of hydrofluoric acid and hydroxylamine as an activator. While this improves the storage stability of the solder paste to some extent, the hydrofluoric acid produced by high-temperature decomposition causes severe corrosion to the solder alloy powder and substrate (pad), affecting the mechanical and electrical properties of the solder joint.
This highlights a critical aspect in the solder flux vs solder paste discussion: balancing activation performance with material compatibility. Many existing solutions sacrifice long-term reliability for short-term soldering performance, creating challenges in high-reliability electronic applications.
Key Limitations of Current Formulations
Corrosion Issues
Halide-based activators cause significant corrosion to both the solder alloy and substrate materials, reducing component lifespan and reliability.
Oxide Formation
Inadequate oxide removal during the soldering process leads to poor wetting and weak joints, particularly problematic in tin-bismuth systems.
Solder Joint Quality
Common issues include post-soldering peripheral blackening, excessive solder balls, and excessive residues that affect both appearance and performance.
Storage Instability
Many formulations suffer from poor shelf life, with changes in viscosity and performance over time affecting manufacturing consistency.
Invention: High-Performance Halogen-Free Lead-Free Solder Paste
The objective of this invention is to provide a high-performance halogen-free lead-free solder paste and its preparation method. The solder paste has high activity, low corrosiveness, and minimal residue, effectively solving common problems in current low-temperature lead-free solder pastes such as post-welding peripheral blackening, excessive solder balls, and excessive residues. This significantly reduces printing defects and improves soldering reliability, marking an important advancement in the ongoing solder flux vs solder paste technology evolution.
This invention achieves these objectives through a carefully engineered formulation that balances activation capability with material compatibility, addressing long-standing challenges in the field of low-temperature soldering for heat-sensitive components.
Core Advantages
- High activity for effective oxide removal
- Low corrosion and minimal residue
- Superior wetting and printing performance
- Enhanced storage stability
- Improved solder joint reliability
- Suitable for heat-sensitive components
Composition of High-Performance Halogen-Free Lead-Free Solder Paste
The high-performance halogen-free lead-free solder paste comprises the following components in percentage by mass, representing a significant advancement in the solder flux vs solder paste technology:
| Component | Mass Percentage | Function |
|---|---|---|
| Tin-based alloy powder | 85-92% | Provides the metallic bonding structure |
| Film-forming agent | 3-8% | Forms protective layer and aids in oxide removal |
| Rheological additive | 0.5-2% | Enhances paste viscosity and printing performance |
| Polyaniline | 0.1-1% | Improves oxidation resistance |
| Hydroxy acid metal salt | 1-3% | Acts as activator for oxide removal |
| Acidic alkyl phosphate | 0.5-2% | Enhances wetting and activation |
| Amine antioxidant | 0.2-1% | Prevents re-oxidation and discoloration |
| Hydroxyethylidene diphosphonic acid | 0.3-1.5% | Aids in oxide removal and corrosion inhibition |
| Cosolvent | 2-6% | Enhances solubility and viscosity control |
Tin-based Alloy Powder
Selected from one of the following alloys:
- Sn64.5Bi35Cu0.5
- Sn64.6Bi35Ag0.4
- Sn58Bi42
- Sn58Bi0.3Ag41.7
- Sn42Bi58
Hydroxy Acid Metal Salts
Tin or zinc salts of:
- Tartaric acid
- Lactic acid
- Malic acid
- Glycolic acid
- Citric acid
Acidic Alkyl Phosphates
Acidic phosphate monoesters selected from:
- Monooctanoic acid phosphate
- Monodecanoic acid phosphate
- Monoisodecanoic acid phosphate
- Monolauric acid phosphate
Acidic phosphate diesters selected from:
- Dioctanoic acid phosphate
- Didecanoic acid phosphate
- Diisodecanoic acid phosphate
- Dilauric acid phosphate
Other Key Components
Amine antioxidants:
Diisooctyl diphenylamine, dialkyl diphenylamine, dinonyl diphenylamine, butyloctyl diphenylamine (at least one)
Film-forming agents:
Hydrogenated rosin resin, polymerized rosin, disproportionated rosin resin, acid-modified rosin, acrylic resin, phenolic resin (at least one)
Rheological additives:
Hydrogenated castor oil, polyamide-modified hydrogenated castor oil, polyamide, octadecyl stearamide, ethylene bis-stearamide, ethylene bis-lauramide (at least one)
Cosolvents:
Ethyl borate, N,N-dimethylacetamide, diethylene glycol butyl ether in a mass ratio of (2-4):(1.5-3):(3-5)
Preparation Method
The method for preparing the high-performance halogen-free lead-free solder paste involves the following steps, representing a refined process in the solder flux vs solder paste manufacturing realm:
Flux Preparation
Add the film-forming agent, rheological additive, polyaniline, acidic alkyl phosphate, and cosolvent to a reaction kettle. Stir thoroughly to dissolve at 100-120°C. When the solution cools to 70-80°C, add the amine antioxidant and hydroxyethylidene diphosphonic acid, stir evenly, continue cooling to room temperature, and add the hydroxy acid metal salt, stirring evenly to obtain the flux.
Flux Processing
Refrigerate the flux at 2-10°C for 12-24 hours, then return to room temperature. Grind using a three-roll mill until the flux particle size is 10-20μm.
Paste Formation
Mix the tin-based alloy powder and flux in proportion in a vacuum mixer until uniform, resulting in the halogen-free lead-free solder paste.
Precision Manufacturing Process
Careful control of temperature and mixing parameters ensures consistent quality in advanced solder paste formulations.
Working Mechanism & Innovation
This invention selects hydroxy acid metal salts, acidic alkyl phosphates, and hydroxyethylidene diphosphonic acid as activators, which play a highly active role in removing black metal oxides during the solder paste soldering process. This prevents solder joint blackening and results in full, bright solder joints, representing a significant innovation in the solder flux vs solder paste technology landscape.
Activation Mechanism
The hydroxy acid metal salts can decompose into hydroxy acids, tin ions, or zinc ions. The electron-withdrawing effect of the hydroxyl groups in hydroxy acids makes them more acidic than carboxylic acids, effectively removing metal oxides without causing strong corrosion to the solder alloy powder like halogen-containing inorganic salts or organic halides.
The tin ions or zinc ions form good metallurgical bonds with the pads, promoting solder wetting. Acidic alkyl phosphates have good corrosion inhibition, wetting, and lubricating capabilities, which can promote the ionization of H+ ions from hydroxy acids and hydroxyethylidene diphosphonic acid, enhancing the ability to break through metal oxide films, promoting oxide removal, and facilitating smooth solder spreading.
Hydroxyethylidene diphosphonic acid has good corrosion inhibition and antioxidant effects, can dissolve oxides on metal surfaces, promote the peeling of black oxides from solder joints, and can form chelate structures with solder alloys and pad metals, adsorbing on the metal surface, isolating oxygen contact, and alleviating metal oxidation reactions.
Protective Mechanisms
The polyaniline has the function of reducing the electrode potential of the metal substrate, making it difficult for the metal to lose electrons, thereby greatly improving the oxidation resistance of the solder and the metal of the welded parts and reducing the oxidation degree.
The selected amine antioxidants can effectively prevent bismuth re-oxidation and solder joint blackening. Additionally, the amine antioxidants are somewhat alkaline and form unstable phosphate amine salts or phosphoric acid amine salts with acidic alkyl phosphates and hydroxyethylidene diphosphonic acid, improving the storage stability of the solder paste.
The rheological additives can enhance the toughness of the solder paste, increase the softness and smoothness during dispensing and printing, prevent the solder paste from coarsening, maintain the uniformity of the solder paste, and endow the solder paste with good printing performance.
The film-forming agent has good electrical properties, can increase the光洁度 of the metal surface, shows no activity in its protective film at room temperature, but exhibits certain activity at soldering temperatures, promoting metal oxide removal.
Solvent System Innovation
The cosolvent system, a critical differentiator in the solder flux vs solder paste comparison, uses a combination of ethyl borate, N,N-dimethylacetamide, and diethylene glycol butyl ether. This innovative blend not only effectively dissolves and wets the flux materials, providing an excellent ionization environment for active substances, but also offers a broad boiling point range to accommodate temperature changes throughout the soldering process.
Enhances solubility and provides thermal stability during soldering
Improves wetting properties and activates flux components
Controls viscosity and ensures proper flow during soldering
This carefully balanced solvent system ensures the solder paste remains in a liquid state throughout the soldering process, maintaining good fluidity and spreadability, and ensuring soldering reliability across varying temperature profiles.
Advantages Over Prior Art
In the ongoing analysis of solder flux vs solder paste technologies, this invention offers numerous significant advantages over existing solutions, addressing key limitations in low-temperature soldering applications:
Superior Solder Joint Quality
The halogen-free lead-free solder paste of the present invention has high activity, effectively removing black oxides formed during soldering, resulting in bright, full solder joints. It improves the surface insulation resistance of solder joints and enhances both mechanical and electrical properties.
Excellent Processing Properties
The formulation exhibits excellent wettability and printability with low corrosion and minimal residue. It effectively inhibits soldering defects such as solder balls, dewetting, and slump, significantly reducing printing defects and improving soldering reliability.
Enhanced Storage Stability
The solder paste offers excellent storage stability with minimal corrosion to the solder alloy at room temperature. It resists drying out, coarsening, and skinning, making it particularly suitable for soldering heat-sensitive electronic components.
solder flux vs solder paste: Application Advantages
| Application Area | Traditional Materials | This Invention |
|---|---|---|
| Smart Hardware Radiators | High temperature causes component damage | Low-temperature process protects heat-sensitive components |
| LED Lighting Components | Oxidation issues affect light output and longevity | Superior oxide removal ensures consistent performance |
| Solar Photovoltaics | Corrosion reduces long-term reliability | Low corrosion formulation improves durability in harsh environments |
| Consumer Electronics | Excessive residues cause reliability issues | Minimal residue improves long-term performance |
| Automotive Electronics | Poor vibration resistance in solder joints | Stronger metallurgical bonds improve durability |
Revolutionizing Low-Temperature Soldering
This high-performance halogen-free lead-free solder paste represents a significant advancement in the solder flux vs solder paste technology landscape, addressing critical limitations in low-temperature soldering applications for heat-sensitive electronic components.
By balancing high activity with low corrosion and excellent storage stability, this innovative formulation sets new standards for reliability and performance in modern electronics manufacturing.
Learn more