6.6 MSD Handling & Baking

Moisture Sensitive Devices (MSDs) are ticking time bombs in the manufacturing process. The danger is not "wetness" in the traditional sense; it is hygroscopic accumulation within the plastic package. During reflow soldering, this trapped moisture turns to superheated steam, expanding rapidly to crack the package ("popcorning") or delaminate the die. This failure is often internal and invisible to Optical Inspection (AOI), passing electrical test only to fail in the field.

Treat MSD control as a strict Time-Based Ledger. Every minute a part is exposed to ambient air is a debit against its Floor Life. Once the balance hits zero, the part is dead until reset (baked) or scrapped.

The MSL Hierarchy (Know Your Limits)

Adhere strictly to IPC/JEDEC J-STD-033. Do not guess based on package size.

• MSL 1: Unlimited Floor Life. (Safe).
• MSL 2 – 2a: 1 year to 4 weeks exposure.
• MSL 3: 168 Hours (7 Days). Standard for many ICs. High risk.
• MSL 4 – 5a: 72 to 24 Hours. Extremely critical.
• MSL 6: Mandatory Bake before use. No floor life.

The Exposure Clock: Start, Stop, Reset

The warehouse system must track the exact "Open Time" for every reel.

• Opening the Barrier Bag (Start Clock):
  • Inspect the Humidity Indicator Card (HIC) immediately.
  • If HIC passes (Blue/Brown) → Then Start the Floor Life Clock in ERP.
  • If HIC fails (Pink > 10%) → Then STOP. The part is already compromised. Move to Baking.
• Dry Storage (Pause Clock):
  • Storing parts in a Dry Cabinet (< 5% RH) pauses the exposure clock. It does not reset it to zero unless stored for 5X the exposure time (refer to J-STD-033 for exact calculations).
• Re-Sealing (Stop Clock):
  • Vacuum sealing in a Moisture Barrier Bag (MBB) with fresh desiccant and a new HIC stops the clock.
  • Pro-Tip: Never re-use the old desiccant. It is saturated. Throw it away.

Baking Logic: The "One-Time" Reset

Baking is not a harmless administrative fix. It imposes thermal stress and accelerates lead oxidation, which ruins solderability. Baking is a last resort.

• When to Bake:
  • If Floor Life exceeded (e.g., MSL 3 part exposed for > 168 hours).
  • If HIC indicates moisture (> 10% spot is Pink).
  • If traceability is lost (unknown exposure time).
• Baking Constraints:
  • Tape & Reel: Low temp bake only (40°C). High temp (125°C) will melt the carrier tape.
  • Tray / Bulk: High temp bake (125°C) is permitted if tray is rated for it (check the "MAX TEMP" stamp on the tray).
  • Cycle Limit: Do not bake a component more than once. If it expires again → Scrap.

Handling Opened Reels & Trays

A partially used reel returned to stock is the most common failure point.

• The 15-Minute Rule: A reel should not sit on a kitting table for hours waiting to be sealed. Define a maximum window (e.g., 15 mins) from "Line Return" to "Vacuum Seal."
• Labeling: The bag must carry a label stating:
  • MSL Level
  • Remaining Floor Life (e.g., "Remaining: 45 Hours").
• Vacuum Quality: A "soft" bag is a leaking bag. The package must be tight ("brick-hard").
  • If a bag loses vacuum in storage → Then treat as fully exposed.

Pro-Tip: Treat an MSD violation as a "Process Escape." If an expired part reaches the Pick & Place machine, it requires an Incident Report, not just a casual bake.

Final Checklist: The Release Gate