Why Solder Paste with the Same Melting Point Cannot Be Used for Both Dispensing and Printing

As a result, solder paste for these two processes must differ in several critical physical parameters.

2. Key Performance Parameters That Must Be Optimized

2.2 Thixotropy (TI)

Process	Thixotropic Index	Functional Role
Dispensing	TI > 4.0	Easy extrusion under shear, rapid shape recovery after deposition
Printing	TI 2.5–4.0	Balance between filling efficiency and pattern stability

Thixotropy defines how solder paste behaves during shear–release cycles. It is one of the most important yet often overlooked differences between dispensing and printing pastes.

2.3 Alloy Powder Particle Size

Process	Typical Size Range	Practical Reason
Dispensing	20–45 μm (Type 4–5)	Prevents needle clogging and ensures dot consistency
Printing	45–75 μm (Type 3)	Reduces agglomeration, stencil smearing, and solder voiding

 

• Dispensing needles typically range from 0.1–0.3 mm; larger particles dramatically increase clogging risk.
• For printing, slightly coarser particles improve gas release during reflow, lowering void rates.

2.4 Flux Content

Process	Typical Flux Content	Engineering Logic
Dispensing	12–15 wt%	Ensures reliable wetting with very small paste volumes
Printing	8–12 wt%	Controls residue, reduces bridging, improves insulation reliability

Dispensing involves very small paste deposits, so higher flux content is necessary to maintain solderability. In contrast, printing prioritizes cleanliness and dimensional control.

3. Process Compatibility and Application Scenarios
 

Aspect	Dispensing	Printing
Primary Goal	Precise control of single-dot volume	High-efficiency replication of solder patterns
Typical Applications	Irregular pads, rework, selective soldering, power devices	QFP, BGA, 01005/0201, mass-production PCBs
Production Efficiency	Low (point-by-point)	High (hundreds or thousands of pads per cycle)
Main Process Risks	Insufficient volume, tailing, overflow	Bridging, incomplete print, misalignment

This is why dispensing is commonly used for prototyping, automotive electronics, and low-volume/high-mix production, while stencil printing dominates consumer electronics and high-volume manufacturing.

4. Common Misconception: “Same Melting Point = Interchangeable”

4.1 Using Printing Paste for Dispensing

• Low viscosity causes paste to flow and lose dot definition Insufficient thixotropy leads to collapse and bridging
• Larger particles increase needle clogging and interrupted dispensing

Result: unstable dispensing, solder bridging, and poor repeatability

4.2 Using Dispensing Paste for Printing

• Excessive viscosity prevents complete stencil aperture filling
• Poor stencil release and heavy surface residue
• Fine particles tend to agglomerate, causing rough edges and missing deposits

Result: low printing yield and inconsistent mass production quality

5. Final Conclusion

Same alloy and melting point do not guarantee process compatibility.

• Melting point is a metallurgical property.
• Process suitability is a rheological and mechanical property.

Dispensing solder paste is engineered for: - Anti-slump stability - Needle flow consistency - Reliable soldering with minimal volume.
Printing solder paste is engineered for: - Fast stencil filling - Clean release and repeatability - Stable, defect-free mass production.
Using the wrong solder paste may appear to work in small trials, but it almost always introduces hidden risks that compromise yield, reliability, and long-term process stability.
For reliable PCBA manufacturing, solder paste must be selected not only by alloy and melting point, but by process-specific design and application requirements.
With 16 years of expertise in PCBA design, manufacturing, and service, KingshengPCBA is ready to help turn your ideas into reality. Feel free to contact us anytime to discuss your requirements and get a professional quotation.