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In the SMT manufacturing process, the solder paste printing result has a significant impact on the SMT manufacturing quality. There are many factors that affect the quality of solder paste printing, such as the manufacturing process of the stencil, the stencil aperture design, the flatness of the PCB, the setting of printing parameters, and the characteristics of the solder paste itself. So, how to choose the right solder paste for your application? What factors need to be evaluated? KINGSHENG, as a PCBA processing factory with 15 years of experience, has a zero-defect pursuit of PCBA quality, so how does KINGSHENG do it?
Quality Inspection Procedures
I. Define Welding Requirements
1. Welding Process
- Reflow Soldering: Suitable for SMT placement process, requiring solder paste with appropriate viscosity, good wettability, low residue, and good thermal stability; Alloy composition: Sn63/Ph37, SAC305; Particle size: Type 3 (25-45µm), Type 4 (20-38µm), Type 5 (10-25µm), for example: Kester EP256, Indium 8.9HF；
- Wave Soldering: Suitable for DIP plug-in process, requiring the selection of solder paste with good wettability, oxidation resistance, fluidity, and thermal stability. Alloy composition: Sn63/Ph37, SAC305; Solder resist: Rosin-based, No-clean, Water-soluble; Particle size: Type 3 (25-45µm), Type 4 (20-38µm), for example: Kester 2331-ZX, Indium 8.9HF
Quality Inspection Procedures
2.Component Types
- Common components: such as resistors and capacitors. Due to their simple structure, low soldering requirements, and cost sensitivity, general-purpose solder paste can be selected, such as SAC305 (Sn-3.0Ag-0.5Cu) and SAC0307 (Sn-0.3Ag-0.7Cu).
- Precision components: such as BGA, QFN, require high-precision, low-residue solder paste. For example: Kester EP256, Indium 8.9HF, AIM NC259, Senju M705-GRN360-K2 High-temperature components: such as C0G/NP0 ceramic capacitors, and components in power devices, automotive electronics, and industrial control equipment, require solder paste with good high-temperature resistance. Kester EP256, Indium 8.9HF
3. PCB Types
- Ordinary PCBs: Such as FR-4 substrates, general-purpose solder paste can be selected.
- Special PCBs: Such as high-frequency boards require lead-free, low-residue, high-purity solder paste, and flexible boards require dedicated solder paste.
Quality Inspection Procedures
II. Key Parameters of Solder Paste
1. Alloy Composition
- Sn63/Pb37: Eutectic tin-lead alloy with a low melting point (183°C) and good soldering performance, but does not meet RoHS requirements.
- SAC305 (Sn96.5/Ag3.0/Cu0.5): Lead-free alloy, compliant with RoHS requirements, with a higher melting point (217°C) and high soldering strength.
- Other lead-free alloys: Such as Sn99.3/Cu0.7, low cost, but slightly inferior soldering performance.
2. Particle Size
- Type 3 (25-45µm): Most commonly used, suitable for most SMT processes.
- Type 4 (20-38µm): Suitable for precision components (such as 0201, BGA).
- Type 5 (10-25µm): Suitable for ultra-precision components (such as 01005, micro BGA).
3. Flux Types
- No-Clean: Leaves minimal residue after soldering, suitable for most scenarios.
- Water-Soluble: Requires water cleaning after soldering, suitable for high-reliability applications.
- Rosin-Based: Offers good soldering performance, but leaves more residue and requires cleaning.
4. Viscosity
- Low Viscosity: Suitable for high-speed printing and fine-pitch components.
- High Viscosity: Suitable for large pads and high-thickness printing.
5. Storage and Usage Conditions
- Storage Temperature: Typically 0-10°C, avoid high temperatures and humidity.
- Shelf Life: Must be used within 24-48 hours after opening.
III. Summary
When processing PCBA, KINGSHENG selects suitable solder paste by comprehensively considering key parameters such as soldering process, component type, PCB type, alloy composition, particle size, and flux type. Through a scientific selection process and professional support, we can ensure the advantages of soldering quality and zero-defect manufacturing, provide customers with high-quality PCBA processing services, and help customers successfully launch their products.
Please send Email to kspcba@c-alley.com or call us through +86 13828766801 Or submit your inquiry by online form. Please fill out below form and attach your manufacturing files( PCB Gerber files and BOM List) if need quotation. We will contact you shortly.
+86 13828766801
kspcba@c-alley.com
https://www.kingshengpcba.com/
2/F, Building 6, Tangtou 3rd Industrial Zone, Tangtou Community, Shiyan Town, Baoan District, Shenzhen, China, 518108
We would also like to thank our customers for their trust and support. The company's outstanding achievements are mainly due to the loyalty of our customers, which also encourages and spurs our company to forge ahead.
