2.2 MSD Handling & Storage (J-STD-033)

Moisture Sensitivity Devices (MSD) fail not due to corrosion, but due to internal vapor pressure. During the rapid thermal ramp of reflow soldering (ambient to 240˚C+ in minutes), trapped moisture at the die-to-plastic interface vaporizes. This expansion generates delamination, internal cratering, and wire bond fractures known as the "Popcorn Effect." These defects are often internal and undetectable by Visual Inspection or AOI. Control of the Floor Life—the cumulative time a component is exposed to ambient humidity—is the only effective mitigation strategy.

Classification & Exposure Limits (MSL)

The Moisture Sensitivity Level (MSL) dictates the allowable exposure window (Floor Life) before baking is required. Adherence to the manufacturer’s label is mandatory; assumptions based on package size are statistically dangerous.

Standard J-STD-020 Classifications:

• MSL 1: Unlimited Floor Life (at ≤ 30˚C / 85% RH).
• MSL 2: 1 Year.
• MSL 3: 168 Hours (7 Days). Most common failure point in production.
• MSL 4: 72 Hours.
• MSL 5 / 5a: 48 / 24 Hours.
• MSL 6: Mandatory Bake before use (Time on Label).

Pro-Tip: MSL ratings are non-linear and package-dependent. A thin TQFP is typically more sensitive (MSL 3) than a thick BGA because the moisture path to the die interface is shorter.

Operational Logic: Managing the Clock

The "Floor Life Clock" is a cumulative metric. It does not reset to zero simply by returning parts to storage unless a bake cycle is performed.

Process Decision Logic:

• IF Moisture Barrier Bag (MBB) is Sealed:
  • THEN Floor Life Clock is PAUSED. Shelf life is typically 12 months.
• IF Bag is Opened:
  • THEN Floor Life Clock STARTS. The exact time and date must be recorded on the component label or ERP system.
  • Requirement: Verify the Humidity Indicator Card (HIC). If the 10% spot is Pink, the parts are already compromised.
• IF Parts are stored in Dry Cabinet (< 5% RH):
  • THEN Clock is PAUSED (Stopped), but not RESET.
  • Calculation: Exposure time = (Time on Line) + (Previous Exposure).
• IF Cumulative Exposure > MSL Limit:
  • THEN Floor Life = 0. Bake Required.

Recovery: Baking Protocols

Baking resets the floor life by driving moisture out of the package. However, it introduces thermal stress and promotes oxidation on the leads, which degrades solderability.

Critical Baking Rules:

1. Low Temperature Bake: 40˚C (+5/-0). Preferred for components in standard tape and reel. Very slow (can take 9 to 68 days depending on MSL/Thickness).
2. High Temperature Bake: 125˚C. Fast (typically 4 – 24 hours).
   • Constraint: Requires transfer from standard polystyrene reels to High-Temp Trays or Aluminum Reels. Standard reels will melt/warp at 125˚C.
3. Cumulative Stress: Components should not be baked more than 3 times. Excessive baking creates intermetallic growth that causes wetting failures during reflow.

Dry Packing Verification

To maintain the "Paused" state, the packaging system must be robust. A compliant Dry Pack consists of:

1. MBB: Moisture Barrier Bag (ESD Shielding + Moisture prevention). Mechanical integrity (no punctures) is critical.
2. Desiccant: Amount calculated based on bag surface area and transit duration.
3. HIC: The Humidity Indicator Card is the primary audit tool.
   • Audit Point: The 10% dot. If Pink, the environment is wet (>10% RH). If Blue, it is dry.

Note: Older standards used 20% Audit Point. J-STD-033 current revision requires the 10% spot.

Final Checklist