5.4 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 defense is a disciplined system of clocks, cabinets, and controlled bakes. By tracking floor life from the moment an MBB is opened, pausing it only in true dry storage, and resetting it correctly after qualified baking, factories keep moisture a managed variable instead of a silent saboteur. With proper labeling and traceability, every reel, tray, and PCB carries its own moisture history, ensuring no surprises at the oven.

5.4.1 Terms you’ll see

MSL: Moisture Sensitivity Level per J-STD-033/020.
Floor life: Allowed time at ≤30 °C / 60 % RH after an MBB is opened.
MBB / HIC / Desiccant: Moisture barrier bag, humidity indicator card, and drying agent.
DRY-CAB: Dry cabinet (≤10 % RH, ≤5 % preferred) that pauses floor life.

5.4.2 MSL levels (1–6) — quick reference

(Floor life at ≤30 °C / 60 % RH; always defer to the device label/datasheet.)

MSL	Floor life	Typical parts	Handling notes (what changes for you)
1	Unlimited	Most resistors/caps, robust logic	Dry-pack not required by J-STD; still use ESD controls. Treat like non-MSD unless customer dictates otherwise.
2	1 year	Many SOIC/QFP, robust QFNs	Dry-pack for shipping; start timer at first open. Normal feeder/shift rules apply (5.4.6).
2a	4 weeks	Finer-pitch QFN/LGA, some small BGAs	Keep cabinets close to kitting to minimize ambient time. Label remaining hours clearly.
3	168 h (7 days)	BGAs, QFNs, CSPs, modules	Most common “real” MSD on the floor. Plan changeovers; avoid leaving reels mounted overnight. Pre-bake before hot-air rework (5.4.7/5.4.9).
4	72 h	Moisture-sensitive analog/PMICs	Treat like MSL3 but with tighter buffers. Prefer cabinet-parked feeders for any pause.
5	48 h	Very moisture-sensitive packages	Kitting issues only what you’ll place today. Expect more frequent reseal events.
5a	24 h	Ultra-sensitive fine-pitch/CSPs	Avoid night holds at ambient; cabinet-park between runs. Reseal promptly.
6	Bake + mount-within (per label)	Extreme cases	Mandatory bake before use; must be mounted within the labelled time after bake. No exceptions—plan takt accordingly.

Good to know

Floor-life pauses only in a sealed MBB or ≤10 % RH dry cabinet (5.4.5).
After a qualified bake (5.4.9), the device returns to full floor life for its MSL when resealed (DRY-PACK (RESET)).
MSL ≠ shelf life. MSL is moisture exposure after opening; chemical shelf life lives in 5.5.
Read the MSL triangle label and HIC on every open (5.4.4); if the HIC low-% spot is wet, treat as expired and follow 5.4.8.
For PCBs, apply the same logic when moisture-loaded (OSP especially); see PCB bake notes in 5.4.9.

5.4.3 Where things happen (area roles)

REC-STAGE / BULK-PARTS: Transit only; do not open MBBs here (5.2).
CMP-STORE (EPA): Open/inspect MBBs, read HICs, apply UID/line labels, DRY-CAB storage (5.1/5.2).
LINE-SMKT (EPA): Kitting/feeding; manage exposure; cabinet-park feeders for pauses (5.2).

5.4.4 Opening an MSD pack (start the clock right)

Prep in CMP-STORE: ESD on (5.3), UID ready (5.1).
Open MBB cleanly; immediately read HIC.
- OK: low-% spot still “dry” color → proceed.
- Caution: mid/high spots turned → proceed but note.
- Wet: low-% spot shows “wet” → treat as expired → go to Bake decision (5.4.8).
Start the floor-life timer in MES at the moment of opening; apply visible line label with remaining hours.
Unused remainder back to DRY-CAB or reseal (5.4.10).

5.4.5 What pauses vs runs the timer

Timer RUNS whenever parts are at ambient (benchtop, kitting table, mounted on feeders, carts).
Timer PAUSES only when either:
- The pack is sealed in an MBB, or
- The parts are fully inside a DRY-CAB ≤10 % RH.
  Zip bags and “covered boxes” don’t count unless your site has qualified them—assume no.

5.4.6 On-feeder exposure, shift hand-off, and changeovers

Mounted on a machine = timer runs.
Pausing across breaks or shifts: either cabinet-park the feeder+reel in a DRY-CAB with feeder slots, or reseal the reel and remove it.
Night holds: never leave MSDs mounted at ambient overnight.
Kitting discipline: issue shift demand + buffer; keep the rest sealed/dry.
Visual control: every reel/feeder shows remaining hours; supervisors verify at hand-off.

5.4.7 Rework & re-exposure (don’t popcorn at hot-air)

Assemblies before hot-air/BGA/QFN work: if they’ve seen ≥1 day ambient or suspect humidity, pre-bake the assembled PCB (5.4.9) to avoid popcorning/pad lift.
Salvaged MSDs: unless kept dry from first opening, treat as expired; default is scrap or tray-rebake if device and tracking allow.
Cumulative exposure: add rework exposure to the device’s timer; if it exceeds floor life, bake then reseal/reset before reuse.

5.4.8 Bake decision (simple rule)

Bake if any of these are true:

Floor life expired or will expire before next use.
HIC low spot wet on opening.
Evidence of compromised storage (torn MBB, humidity excursion, unknown history).
Pre-rework bake required as above.

Otherwise, continue with timer rules.

5.4.9 Bake profiles (ICs vs PCBs; pick the safest that works)

Always check the device/packaging ratings. Some carrier tapes, labels, or elastomers can’t take heat.

ICs / components

Preferred (in trays/tubes): 125 °C dry bake; duration per site table (typ. 24 h for MSL3+; longer for higher MSL).
If still in tape-and-reel:
- Many tapes soften at 60–90 °C. Choose low-temp/long-time (40–60 °C, ≤5 % RH, extended hours), or re-tray parts suitable for 125 °C and bake.
MSL6: follow label exactly (mandatory bake and mount-within time).

PCBs (bare or assembled)

General FR-4: 105–125 °C, 2–8 h based on thickness/storage history.
OSP finish: prefer lower temp, longer time (e.g., 105 °C) to protect finish.
Assembled boards for rework: ~105 °C for 4–8 h; mask or remove heat-sensitive labels, elastomers, bezels.
Heavy copper/thick boards: choose longer times.

After bake

Cool to ≤30 °C in dry conditions before reseal or immediate use; don’t open-air cool in humid rooms.

5.4.10 Reseal & reset (MBB done right)

Bag: Use qualified MBB sized for minimal free volume; no pinholes.
Desiccant: Fresh, in-date; mass matched to free volume per site table; distribute evenly.
HIC: New card placed on top, visible at next open.
Purge (optional): Short dry N₂ purge; don’t crush sharp edges.
Seal: Straight, 10–12 mm heat seal; wrinkle-free; quick squeeze test for leaks.
Label (outside): PN, lot/date, MSL, state (DRY-PACK (RESET) or REMAINING x h), open time, reseal time, remaining time if not baked, operator/workstation.
Reset logic:
- After a qualified bake → timer resets to full floor life.
  Reseal without bake → timer stays at remaining hours.

5.4.11 Data & traceability links

Every reel/tray/tube has a UID (5.1) bound to MSL, timer state, bake/ reseal events, and feeder IDs while mounted.
Rework tickets carry added exposure and any pre-bake performed.
Pack labels mirror the MES state—so operators don’t guess.

5.4.12 Acceptance cues (fast table)

Area	Accept	Reject
HIC at open	Low-% spot dry	Low-% spot wet → Bake
Timer control	MES timer matches label; pauses only in MBB/DRY-CAB	Handwritten guesses; timer “paused” in zip bag
Feeder pauses	Feeder+reel cabinet-parked or reel resealed	Mounted overnight at ambient
Bake profile	Matches device/medium; safe temps	125 °C with tape; OSP baked too hot
Reseal	Fresh HIC + desiccant; straight seal; full label	Missing HIC; no desiccant; unlabeled
Reset	“RESET” only after qualified bake	Timer reset without bake

5.4.13 Common traps → smallest reliable fix

Trap	Symptom	First move
“We’ll finish tomorrow” on feeder	Popcorning, HiP, delam	Cabinet-park or reseal; add shift hand-off check
Baking tape at 125 °C	Warped tape, loose pockets	Low-temp/long-time or re-tray
Zip bags used as dry pack	HIC wet on next open	Only MBB or DRY-CAB pauses the clock
Rework without pre-bake	Cracked packages at hot-air	Pre-bake assemblies before rework
OSP boards baked hot	Poor wetting in next run	Bake lower/longer for OSP
No reseal label	Timers reset by rumor	Label state + times + remaining h; update MES

5.4.14 Pocket checklists

Open & stage (CMP-STORE)

ESD on; open MBB; read HIC
Start MES timer; apply remaining-hours label
Remainders to DRY-CAB or reseal

On the line

Issue shift demand + buffer; cover reels
Pauses: cabinet-park feeder or reseal
Supervisor verifies remaining hours at hand-off

Bake & reseal

Profile matches device & medium
Cool dry; fresh desiccant + HIC; straight seal
Label with state/times; reset only if baked; MES updated

Rework

Pre-bake assemblies if ambient-exposed
Salvaged MSDs handled per policy (rebake/scrap)
Added exposure logged on ticket

Following these handling, baking, and resealing rules transforms moisture from a lurking failure mode into a predictable parameter. The payoff is smooth reflow, higher yields, and products that endure long after they leave the line.