Moisture Sensitive Device (MSD) Control and Baking Specifications

During PCBA processing, improper handling of Moisture Sensitive Devices (MSD) is a common cause of soldering quality failures. MSDs absorbing ambient moisture will rapidly expand internally during reflow soldering due to high temperatures. This can lead to internal cracking (popcorn effect), solder joint fractures, or electrical performance failures. This article outlines the core operating procedures for MSD control and baking from incoming inspection to pre-placement.

1. MSD Identification and Classification
1.1 Classification Levels
Per IPC/JEDEC J-STD-033, MSDs are divided into six levels (MSL 1 to MSL 6). MSL 1 is not sensitive to ambient humidity. MSL 6 must be placed within 8 hours after baking. Common sensitivity levels are MSL 2, 2a, 3, and 4. Most SoC, BGA, LGA, and QFN packages fall into MSL 3-4.
1.2 Identification Method

• Check the moisture sensitivity label on the device packaging (Moisture Barrier Bag, MBB label)
• Read the Floor Life and seal date on the label
• Confirm the specified MSL level and recommended baking conditions

2. MSD Receiving and Storage Control
2.1 Incoming Receiving

• Inspect the vacuum packaging for damage. Treat devices from damaged packages as exposed.
• Record the status of the Humidity Indicator Card (HIC) inside the bag. The 5%-10% humidity dot must be blue for direct use; >10% requires baking.
• Verify the seal date and expiration date. MBB packaging exceeding one year from manufacture requires re-baking.

2.2 Storage Requirements

• Unopened MSD: Keep in the original moisture barrier bag. Store at temperature <30°C and humidity <60%RH.
• Opened but unused MSD: Must be stored in a desiccator cabinet (humidity ≤10%RH, ≤5%RH recommended).
• Desiccator cabinets require daily temperature and humidity checks with records.

2.3 Floor Life Control

• MSL 3: 168 hours
• MSL 4: 72 hours
• MSL 5: 48 hours
• MSL 6: Must be baked before placement

Floor life starts counting from the moment the moisture barrier bag is opened or the device is removed from the desiccator cabinet. If the floor life is exceeded before reflow, mandatory baking is required.

3. MSD Baking Specifications
3.1 When to Bake
Baking is mandatory under any of the following conditions:

• Vacuum packaging is damaged, or HIC indicates humidity exceeds the limit
• Floor life exposure exceeds the specified limit for the MSL level
• Desiccator cabinet humidity control fails for more than 5 minutes during storage
• Devices come from bulk materials of unknown status

3.2 Baking Parameters (Based on J-STD-033)
Device Package Type & Temperature & Time (min) & Note

• Thickness ≤1.4mm, MSL 2-4 -> 125°C -> 5-7 -> Trays must be heat-resistant
• Thickness ≥1.4mm, MSL 2-4 -> 125°C -> 7-9 -> Prevents core moisture
• BGA/CSP (diameter ≤17mm) -> 125°C -> 5-7 -> Avoid over-baking
• Moisture-sensitive plastic packages -> 90±5°C -> 720-960 -> Low-temperature long bake

Standard 125°C baking is preferred. However, devices containing connectors, LEDs (non-high-temperature tolerant), or polycarbonate encapsulation must use 40-65°C extended baking, always following the device datasheet.
3.3 Baking Operation Points
Bake devices of the same package type, same MSL level from the same batch together
Place devices flat in a single layer or staggered arrangement to ensure hot air circulation
After baking, cool devices to room temperature (approx. 30-45 minutes) inside a desiccator cabinet before placement
Record for each baking batch: temperature, duration, quantity, and expiry date


4. Key Documentation and Process Checks

• Incoming inspection checklist: MBB seal time, HIC value, MSL level
• Desiccator cabinet log: Daily physical recording of temperature and humidity
• Baking log: Oven ID, start/end time, temperature profile, operator name
• Pre-placement double-check: Confirm remaining floor life has not been exceeded

Strict implementation of MSL identification, moisture-proof storage, and standard baking can reduce moisture-related soldering failures by approximately 85%. The shop floor must establish an MSD control work instruction and incorporate the above procedures into daily audits.

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