Part 1. Solder Paste, Stencils & Printing (with in-line SPI)
Printing is not just "applying glue"; it is the foundation of quality in SMT assembly. Studies consistently show that 60-70% of all soldering defects originate here. This chapter breaks down the science of getting the right amount of paste in the right place, every single time.
We dissect the variables that control transfer efficiency:
- Paste Science: Choosing the right alloy (SAC305, low-temp) and powder size (Type 4 vs. 5) to match your component pitch.
- Process Discipline: Why strict storage, thawing, and handling rules are non-negotiable for preserving rheology.
- Stencil Engineering: Using area ratios and aperture modifications to prevent bridging and tombstoning.
- SPI (Solder Paste Inspection): Closing the loop with 3D volumetric measurement to catch drift before it becomes a defect.
Master the printer, and the rest of the line becomes easy. fail here, and reflow won't save you.
2.1 Paste Chemistry & Alloy Choice
Solder paste is the nervous system of Surface Mount Technology (SMT). Its chemical mix dictates e...
2.2 Storage, Thawing & Handling
Solder paste is not a simple commodity; it is a fragile chemical system with an expiration date, ...
2.3 Stencil Types & Thickness
The stencil is where the two critical elements of SMT — the paste and the PCB — first meet. Its g...
2.4 Aperture Design Tactics
Aperture design is where physics meets geometry to determine printing stability and final joint q...
2.5 Printer Setup & Cleaning
The screen printer is where perfect design meets physical reality. Its setup is a high-impact, lo...
2.6 SPI Metrics and Closed Loop
SPI (Solder Paste Inspection) is your 3D radar for printing quality. It doesn't just catch defect...