In the fast-paced world of electronics manufacturing, Surface Mount Technology (SMT) relies heavily on the quality of solder paste to ensure reliable and durable connections.
Whether assembling consumer electronics or industrial-grade PCBs, choosing the right solder paste leaded or lead-free is critical. This article explores the major types of solder paste, their classifications, and the top global manufacturers trusted in the SMT industry.
What is Solder Paste?
Solder paste is a homogeneous mixture of powdered solder alloy and flux, formulated to temporarily adhere components onto PCB pads during placement and to form strong electrical/mechanical connections during reflow soldering.
Types of Solder Paste Used in SMT
Solder pastes are classified based on their alloy composition, flux type, and particle size. Here’s a detailed breakdown:
1. Based on Alloy Composition
✅ Leaded Solder Paste
- Sn63/Pb37 (63% Tin, 37% Lead)
- Eutectic alloy with a sharp melting point at 183°C
- Provides excellent wetting and reliable joints
- Common in industrial and non-RoHS applications
✅ Lead-Free Solder Paste
- SAC305 (Sn96.5/Ag3.0/Cu0.5)
- Most widely used RoHS-compliant alloy
- Melting range: ~217–219°C
- Balances cost, performance, and availability
- Sn99.3/Cu0.7
- Tin-copper alloy for low-cost lead-free soldering
- Suitable for wave and selective soldering
- Sn/Ag or other specialty compositions
- Used in high-reliability sectors like aerospace and automotive
2. Based on Flux Type
- No-Clean Flux
- Leaves minimal, non-corrosive residues
- Cleaning not required in most cases
- Ideal for consumer electronics and compact boards
- Water-Soluble Flux
- Requires post-soldering cleaning with deionized water
- Preferred in industries with stringent reliability requirements
- Rosin-Based Flux (RMA/RA)
- Derived from natural resins
- Requires solvent cleaning
- Used in military, aerospace, or legacy applications
3. Based on Powder Particle Size (Per IPC J-STD-005)
| Type | Particle Size (µm) | Application |
|---|---|---|
| Type 3 | 25–45 µm | General SMT components (≥0.5mm pitch) |
| Type 4 | 20–38 µm | Fine-pitch components (0.4mm pitch) |
| Type 5–7 | 15–25 µm or smaller | Microelectronics, 01005 components |
Leading Global Manufacturers of Solder Paste
Numerous manufacturers supply high-performance solder pastes suited for a variety of SMT applications. Here are the most recognized global players:
1. Indium Corporation (USA)
- Flagship pastes: Indium8.9, TACFlux®
- Strength: Ultra-low residue, high-reliability, and fine-pitch soldering
2. Alpha Assembly Solutions (MacDermid Alpha, USA)
- Popular products: OM-338, CVP-390
- Strength: Lead-free, low voiding, and high-speed printing applications
3. Kester (ITW, USA)
- Products: EP256, NP560
- Known for: No-clean, high-reliability formulations
4. Henkel (Loctite, Germany/USA)
- Notable lines: Loctite GC 10, Loctite XP Series
- Unique feature: Stable at room temperature, long stencil life
5. Senju Metal Industry (Japan)
- Known for: M705 series
- Applications: Automotive, consumer, and industrial electronics
6. AIM Solder (USA)
- Bestsellers: RX18, NC259
- Advantage: Excellent solderability with a wide process window
7. Tamura Corporation (Japan)
- Products: EcoSol series
- Focus: Environment-friendly and halogen-free pastes
8. Shenmao Technology (Taiwan)
- Offers both leaded and lead-free pastes
- Serves: EMS, telecom, and computing industries
9. Heraeus (Germany)
- Products: F640 series
- Target: High-end and fine-pitch electronics
10. KOKI Company Ltd. (Japan/China)
- Series: S3X series
- Focus: Low residue, RoHS-compliant, high-reliability solder pastes
Conclusion :
Solder paste is more than just a bonding agent—it’s a key element in ensuring performance, durability, and reliability in electronic assemblies. Understanding the difference between leaded and lead-free types, as well as the offerings from top global manufacturers, helps engineers and EMS providers make informed decisions for quality production.
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