7.1 Temperature & Humidity Control

The manufacturing environment is a critical process variable in electronics assembly. Deviations in temperature and humidity directly correlate to defect generation in solder paste printing (viscosity changes), component reliability (moisture absorption), and electrostatic discharge (ESD) events. This chapter establishes the non-negotiable atmospheric windows required for high-reliability PCBA production.

7.1.1 The Humidity Window (40% – 60% RH) 

Relative Humidity (RH) must be actively regulated between 40% and 60%.

• Low Humidity Risk (<30%): Dielectric breakdown strength of air decreases, causing exponential increases in electrostatic charge generation. Solder paste dries out on the stencil, reducing tackiness and causing component release failures during placement.
• High Humidity Risk (>60%): Moisture Sensitive Devices (MSDs) absorb ambient moisture beyond safe limits (per J-STD-033), leading to "popcorning" (delamination/cracking) during reflow. Solder paste absorbs water (hygroscopic), causing voiding and solder balling.

7.1.2 Temperature Stability (22°C ± 3°C) 

Solder paste is a thixotropic fluid; its viscosity is highly temperature-dependent. Fluctuations >5°C during a shift alter the printing definition, leading to bridging or insufficient coverage.

• Gradient Control: HVAC systems must prevent localized "hot spots" near reflow ovens or "cold spots" near loading docks.
• Monitoring: Independent data loggers must record Temp/RH at 15-minute intervals. Alarms must trigger if limits are breached for >1 hour.

Final Checklist