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 has fine alloy powder in flux. It is 85-92% metal by weight. This enables precise SMT deposition on PCBs. Flux removes oxides during reflow. Powder melts into strong joints. Use stencil printing or jet printing. Tackiness holds components pre-reflow.
Types of Solder Paste
- Lead-based vs. Lead-Free: Lead-free SAC305 or SN100CV meets RoHS rules. They suit eco-friendly production. Sn63Pb37 processes easier at low temps.
- Flux Types (IPC J-STD-004): Rosin often require specific solvent clean-up. Water-soluble requires rinsing. No-clean leaves safe traces.
- Particle Sizes (IPC J-STD-005): Type 3 (25-45µm) fits standard pitches. Type 4 (20-38µm) works for fine-pitch.
- Alloy Compositions: SAC305 melts at 217-221°C. while, SN100CV P608 D4 melts at 221-225°C and it beats SAC305 in long-term mechanical strength and thermal fatigue resistance.
Step-by-Step Solder Paste Guide
1. Prepping Solder Paste and surface
- Ensure the metal surface is properly clean and free of any dust or oils.
- Warm paste to room temperature slowly. Avoid rapid heating.
- Stir gently for even consistency. Check for optimal flow.
2. Applying Solder Paste
- Use stencil printer for high volume. Or syringe for prototypes.
- Apply precise deposits on PCB pads. Check stencil alignment.
- Place components on tacky paste. Press lightly to secure.
- Inspect with SPI for volume and bridging issues.
3. Heating (Reflow Soldering)
- Load into reflow oven. Follow datasheet temperature profile.
- Ramp slowly to liquidus point. Hold time above liquidus.
- Cool controlled to avoid thermal shock. Forms strong joints.
4. Post-Process Clean-up
- Inspect for defects like bridging or balling.
- Clean water-soluble flux with DI water and drying.
- No-clean flux usually needs no cleaning step.
- Test electrical connections and functionality.
Solder Paste Tips
- Wear gloves and use ventilation. Follow SDS safety rules.
- Type 4 paste best for fine-pitch components under 0.5mm.
- SN100CV P608 D4 beats SAC305 in long-term strength and reliability.
- Match reflow profile exactly to paste datasheet specs.
- Seal paste jars immediately after use to prevent drying.
- Store at 0-10°C in sealed containers. Shelf life is 6-12 months cold.
- Prevent slump with good rheology.
Solder Paste guide FAQs
What is the melting point of solder paste?
SAC305: 217-221°C. SN100CV P608 D4: 221-225°C. SnPb: ~183°C.
What are the benefits of lead-free solder paste?
RoHS compliant. Less toxic. Stable for consumer electronics.
How long is solder paste shelf life?
6-12 months at 0-10°C. Seal tightly always.
How do I choose solder paste flux type?
No-clean saves cost. Water-soluble for heavy residues. Rosin balances activation.
Can solder paste dry out?
Yes from air exposure. Store sealed and cold.
What causes solder paste defects?
Slump, bad profiles, rheology mismatch. SPI catches early.
Is solder paste compatible with all reflow ovens?
Match datasheet profile. Test pause response.
How do I handle solder paste safely?
Wear gloves. Use ventilation. Follow SDS rules.
Where can I buy high-quality solder paste?
DKL Metals stocks a wide variety of high quality solder pastes, including SN100CV P608 D4. Full technical support.
Learn More!