Guidelines for the Management of Moisture-Sensitive Devices in SMT

Moisture-sensitive devices (MSDs) are prone to cracking and delamination during reflow soldering after absorbing moisture, posing a risk no less serious than that of electrostatic discharge (ESD). This article systematically outlines the storage management, baking processes and carrier replacement specifications for MSDs, to assist SMT manufacturers in establishing standardised control procedures and reducing product defect rates.

I. Understanding the Risks of Moisture-Sensitive Devices

MSDs, or moisture-sensitive devices, are electronic components that are highly sensitive to ambient temperature, humidity and electrostatic discharge (ESD). In SMT assembly, the management of moisture-sensitive components is as challenging as ESD protection. When moisture-sensitive components absorb moisture and are subsequently exposed to the high-temperature environment of the reflow oven, the internal moisture rapidly vaporises and expands, causing the package to crack, delaminate or exhibit the ‘popcorn effect’, resulting in irreversible damage. Strengthening the storage and usage management of MSDs is a critical step in enhancing product reliability.

II. Objectives of Standardised Control

To establish a comprehensive control methodology for MSDs, preventing moisture-absorbed components from entering the reflow soldering stage and eliminating the risk of moisture-related damage at source. Through systematic control, reduce product defect rates and enhance the long-term reliability of end products.

III. Reheating Treatment for Moisture-Affected Components

For moisture-affected MSDs, the reheating conditions specified on the manufacturer’s original packaging warning labels should be followed as a priority. Where the manufacturer has not provided explicit instructions, a high-temperature reheating scheme is recommended. Low-temperature baking is not recommended to ensure that moisture is fully expelled from the deeper layers. When replacing carriers, strict ESD protection measures must be implemented to prevent secondary damage.

IV. Oven Equipment Requirements

Baking equipment must be equipped with forced ventilation to ensure uniform heat distribution and the timely removal of moisture. The equipment should be capable of maintaining the set temperature stably under environmental conditions where humidity is less than 5%, thereby preventing secondary moisture absorption during the baking process.

V. Baking Specifications for High-Temperature Carrier Components

Unless otherwise specified by the manufacturer, surface-mount components transported in high-temperature carriers may be baked at 125°C. This temperature is suitable for most plastic-encapsulated devices; baking time should be determined based on the moisture sensitivity class and exposure history.

VI. Baking Restrictions for Low-Temperature Carrier Components

Components transported in low-temperature carriers must not be baked at temperatures exceeding 40°C. If high-temperature treatment is required, the low-temperature carrier must first be removed and replaced with a high-temperature-resistant carrier before heating can commence. Forcing high-temperature baking on a low-temperature carrier will cause the carrier to deform and melt, damaging the internal components.

VII. Carrier Material Removal Requirements

Paper or plastic carriers must be completely removed prior to baking. Rubber straps or plastic trays must also be removed when baking at 125°C. Retain only high-temperature-resistant metal trays or dedicated baking fixtures to ensure uniform heat conduction and the absence of contaminant residues.

VIII. Supplementary Storage Management Points

Strictly enforce exposure time controls for moisture-sensitive components after opening; complete mounting before the moisture-sensitive indicator card changes colour. Maintain humidity below 10% RH and a temperature of approximately 25°C in the drying cabinet. Seal any unused components promptly and record the exposure time; components exceeding the exposure limit must undergo mandatory baking to reset them.

IX. Conclusion

MSD control represents a quality blind spot in small-batch SMT processing; standardised procedures must be established across multiple dimensions, including storage environment, exposure time, baking processes and carrier management. Strict adherence to the operating specifications corresponding to each humidity sensitivity level can effectively mitigate the risk of damage during reflow soldering and ensure the manufacturing quality of high-reliability electronic products.