1.26 MSD Handling & Baking
Moisture damage is one of the most deceptive threats in electronics assembly—parts look fine until reflow, when trapped vapor explodes into cracks, pad lifts, or hidden reliability risks (The Popcorn Effect). The defense is a disciplined system of clocks, cabinets, and controlled bakes. By rigorously tracking floor life and managing the process, moisture is kept a managed variable instead of a silent saboteur.
5.4.1.26.1 The MSL Standard and Floor Life Clock
Every Moisture Sensitive Device (MSD) is assigned a Moisture Sensitivity Level (MSL) which dictates the allowed time it can be exposed to ambient factory air (≤30 ˚C and 60% RH) before it is considered expired and unsafe to reflow.
MSL Levels and Floor Life Limits
Floor life starts the moment the Moisture Barrier Bag (MBB) is opened. Always defer to the device label/datasheet first.
MSL | Floor Life (≤30˚C/60%RH) | Typical Handling Notes |
1 | Unlimited | Dry-pack not required. Treat like non-MSD. |
2 | 1 Year | Start timer at first open. |
2a | 4 Weeks | Use tight kitting controls. |
3 | 168 h (7 Days) | Most common MSD on the floor. Requires careful planning. |
4 | 72 h | Prefer cabinet-parked feeders for any pause. |
5/5a | 48 h / 24 h | Kitting issues only what will be placed today. Prompt reseal is critical. |
6 | Bake + Mount-Within (Per Label) | Mandatory bake required before use; no exceptions. |
Starting the Clock Right
The action taken at the kitting bench dictates the entire history of the part:
- HIC Check: Open the MBB and immediately read the Humidity Indicator Card (HIC). If the low-percentage spot is WET (color changed), the clock is considered expired; skip tracking and go straight to Bake Decision
(5.4.3). - MES Start: If the HIC is DRY, start the MES timer the instant the bag is opened. This is the official start of the floor life clock.
- Label: Apply a visible line label showing the remaining hours to ensure operator awareness.
5.4.1.26.2 Managing the Clock: Run, Pause, and Transit
The goal is to minimize run time and utilize dry storage to pause the timer whenever possible.
Run vs. Pause Rules
Timer Status | Condition | Control Area |
Timer RUNS | Parts are exposed to ambient factory air (benchtop, carts, mounted on feeders). | Anywhere outside controlled storage. |
Timer PAUSES | Parts are fully inside a DRY-CAB (≤10% RH) or sealed in an MBB. | Only these two conditions pause the clock. Zip bags or "covered boxes" do not count. |
Line-Side and Transit Discipline
- Mounted Status: Parts mounted on a machine feeder means the timer RUNS.
- Night Holds/Pauses: Never leave MSDs mounted at ambient overnight. For pauses across shifts or breaks, you must either cabinet-park the feeder+reel in a dry cabinet or reseal the reel and remove it.
- Rework Exposure: If an assembled PCB has seen ≥ 1 day ambient exposure, a pre-bake is mandatory before hot-air or BGA rework to prevent popcorning failure on the assembly itself.
5.4.1.26.3 The Reset Button: Bake Decision and Reseal
Baking is the only way to fully reset the floor life clock.
When to Bake (Simple Decision Tree)
Bake if any of these are true:
- Floor life has expired or will expire before the next reflow step.
- The HIC low-percentage spot was WET upon opening.
- The material suffered a compromised storage event (e.g., torn MBB, dry cabinet failure, unknown history).
- Pre-rework bake is required for an assembled PCB.
Bake Profiles: ICs vs. PCBs
Baking must be qualified to the device and the medium it is contained in, as carrier tapes or component finishes may degrade with heat.
Material | Preferred Temperature/Time | Handling Note |
ICs (in Trays/Tubes) | 125 ˚C dry bake (typically 24 hours for MSL 3+). | Preferred method for maximum effect and efficiency. |
ICs (in Tape-and-Reel) | 40 ˚C to 60 ˚C (≤5% RH) for extended hours. | Use low temperature; 125 ˚C will melt most tapes. Re-tray if 125˚C is mandatory. |
PCBs (Bare FR-4) | 105 ˚C for 2 to 8 hours (based on thickness/history). | Use 105 ˚C to protect surface finishes like OSP (Organic Solderability Preservative). |
Post-Bake Rule: Always cool the materials to ≤ 30 ˚C in dry conditions before resealing or immediate use. Do not cool in humid ambient air.
Reseal Protocol and Clock Reset
Resealing is critical to lock in the material's current state.
- Contents: Use a qualified MBB, a fresh HIC, and fresh desiccant (mass-matched to the volume).
- Seal: Heat-seal the bag cleanly (10–12 mm straight seal) and verify no wrinkles or leaks.
- Label: Apply a final label that mirrors the MES record: PN, MSL, Open Time, Reseal Time, and State.
- Reset Logic: Only packages sealed after a qualified bake are labelled DRY-PACK (RESET), and the clock is reset to full floor life. All others retain the REMAINING x H state.
5.4.1.26.4 Compliance and Common Traps
Following these rules ensures the components survive the thermal shock of reflow, safeguarding quality.
Trap | Symptom | First Move (The Reliable Fix) |
The "Finish Tomorrow" Trap | Components left mounted on a feeder overnight. | Cabinet-park the feeder or reseal the reel; add a supervisor check at shift hand-off. |
Baking Tape at 125˚C | Warped tape, melted pockets, loose parts. | Use low-temp/long-time bake profile or re-tray parts before baking at 125 ˚C . |
Using Zip Bags | HIC is wet on the next open. Timer was running silently. | Ban unauthorized containers. Only MBB or DRY-CAB pauses the clock. |
Rework without Pre-bake | Cracked packages or pad lift at the hot-air station. | Mandate pre-bake for any ambient-exposed assembly before hot-air/BGA rework. |