What Is Solder Paste?
In this solder paste guide we help you understand types of solder paste, how to use it, and cover some of the frequently asked questions.
Solder paste is a critical material in modern electronics manufacturing, composed of tiny solder alloy particles suspended in a flux medium. It facilitates the soldering process by providing both the metal to form solder joints and flux to clean and prepare surfaces for optimal bonding. Manufacturers widely use solder paste in surface mount technology (SMT), wave soldering, and reflow soldering processes.
Types of Solder Paste
- Lead-based vs. Lead-Free Solder Paste: Lead-free pastes comply with RoHS regulations and are common in environmentally sensitive applications. Lead-based solder paste, typically SnPb alloys, offers lower melting points and easier wetting but is less eco-friendly.
- Flux Types in Solder Paste: No-clean flux paste leaves minimal residue and requires no cleaning after soldering. Water-soluble flux offers superior cleaning power but requires post-solder cleaning. Rosin-based flux is traditional, balancing cleaning and ease of use.
- Alloy Compositions: Typical alloys include SAC305 (tin-silver-copper), SnPb (tin-lead), and specialty low-temperature alloys. Choice depends on melting point requirements and application specifics.
- Nihon Superiors brand new SN100CV P608 D4: A direct replacement for SAC305 with higher mechanical strength and thermal fatigue resistance making it a better and more economical choice.
How to Use Solder Paste
- Proper storage is vital—solder paste should be refrigerated and brought to room temperature before use.
- Dispense solder paste using stencil printing or syringe dispensing for precise application.
- After application, components are placed on the paste, followed by reflow soldering using controlled oven profiles matching the paste’s melting characteristics.
- Handle solder paste with care to avoid contamination or drying out.
Solder Paste Guide: Frequently Asked Questions (FAQs)
What is the melting point of solder paste?
The melting point depends on the alloy composition. For example, SAC305 and SN100CV typically melts around 217–221°C. Leaded solders melt lower, around 183°C.
What are the benefits of lead-free solder paste?
Lead-free solder paste meets environmental standards like RoHS, reduces health hazards, and suits consumer electronics applications.
How long can solder paste be stored?
Most solder pastes have a refrigerated shelf life of 6 months to 1 year, so always follow manufacturer guidelines and store under recommended conditions.
How do I know which flux type to choose?
Choose no-clean fluxes for minimal post-solder cleaning, water-soluble fluxes for applications needing thorough residue removal, and rosin fluxes when a traditional approach suffices.
Can solder paste dry out?
Yes, exposure to air or improper storage can cause solder paste to dry and become unusable, so always seal containers properly and maintain cold storage.
What causes solder paste defects?
Common defects include insufficient wetting, bridging, solder balling, and head-in-pillow defects, often caused by improper stencil design, paste application, or reflow profiles.
Is all solder paste compatible with all reflow ovens?
Reflow compatibility depends on the recommended temperature profile matching the paste’s melting characteristics. Always consult datasheets.
How do I handle solder paste safely?
Use gloves to avoid skin contact, work in well-ventilated areas, and follow safety data sheet (SDS) precautions.
Where can I buy high-quality solder paste?
DKL Metals offers a selection of industry-grade solder pastes, with detailed technical support, testing, and reliable supply chains.
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