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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.risks (The Popcorn Effect). The defense is a disciplined system of clocks, cabinets, and controlled bakes. By rigorously tracking floor life fromand managing the momentprocess, an MBBmoisture is opened, pausing it only in true dry storage, and resetting it correctly after qualified baking, factories keep moisturekept 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 TermsThe you’llMSL seeStandard and Floor Life Clock


  • Every MSL:Moisture Sensitive Device (MSD) is assigned a Moisture Sensitivity Level per J-STD-033/020.

  • Floor life:(MSL) Allowedwhich dictates the allowed time it can be exposed to ambient factory air (at ≤30 °˚C /and 60 %60% RH) afterbefore an MBBit is opened.
  • MBBconsidered / HIC / Desiccant: Moisture barrier bag, humidity indicator card,expired and dryingunsafe agent.
  • DRY-CAB:to Dry cabinet (≤10 % RH, ≤5 % preferred) that pauses floor life.
reflow.


MSL Levels and Floor Life Limits


5.4.2 MSL levels (1–6) — quick reference

(Floor life atstarts ≤30the °Cmoment /the 60Moisture %Barrier RH;Bag always(MBB) is opened. Always defer to the device label/datasheet.)datasheet first.

MSL

Floor lifeLife (≤30˚C/60%RH)

Typical parts

Handling notes (what changes for you)Notes

1

Unlimited

Most resistors/caps, robust logic

Dry-pack not required by J-STD; still use ESD controls.required. Treat like non-MSD unless customer dictates otherwise.MSD.

2

1 yearYear

Many SOIC/QFP, robust QFNs

Dry-pack for shipping; startStart timer at first open. Normal feeder/shift rules apply (5.4.6).

2a

4 weeksWeeks

Finer-pitchUse QFN/LGA, some small BGAs

Keep cabinets close totight kitting to minimize ambient time. Label remaining hours clearly.controls.

3

168 h (7 days)Days)

BGAs, QFNs, CSPs, modules

Most common “real” MSD on the floor. PlanRequires changeovers;careful avoid leaving reels mounted overnight. Pre-bake before hot-air rework (5.4.7/5.4.9).planning.

4

72 h

Moisture-sensitive analog/PMICs

Treat like MSL3 but with tighter buffers. Prefer cabinet-parked feeders for any pause.

55/5a

48 h / 24 h

Very moisture-sensitive packages

Kitting issues only what you’llwill placebe placed today. ExpectPrompt morereseal frequentis reseal events.

5a

24 h

Ultra-sensitive fine-pitch/CSPs

Avoid night holds at ambient; cabinet-park between runs. Reseal promptly.critical.

6

Bake + mount-withinMount-Within (perPer label)

Extreme casesLabel)

Mandatory bake required before use; mustno be mounted within the labelled time after bake. No exceptions—plan takt accordingly.exceptions.

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),

    Starting the deviceClock 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.
Right



The
action


taken

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 (startat the clockkitting right)

bench dictates the entire history of the part:

  1. PrepHIC in CMP-STORE:Check: ESD on (5.3), UID ready (5.1).
  2. Open the MBB cleanly;and immediately read HICthe Humidity Indicator Card (HIC). If the low-percentage spot is
    • OK:WET low-% spot still “dry” (color →changed), proceed.
    • Caution:the mid/highclock spotsis turnedconsidered →expired; proceedskip buttracking note.
    • Wet: low-% spot shows “wet” → treat as expired →and go straight to Bake decisionDecision (5.4.8)3).
  4. 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.
  5. Start the floor-life timer in MESLabel: atApply the moment of opening; applya visible line label withshowing the remaining hours.
  6. Unused remainder back to ensure operator awareness.DRY-CAB
or reseal (

5.4.10).
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

5.4.5 What pauses vs runs the timerArea

Timer RUNS

 whenever partsParts are atexposed to ambient factory air (benchtop, kitting table,carts, mounted on feeders, carts)).

    • Anywhere outside controlled storage.

    Timer PAUSES

     only when either:

    • The pack is sealed in an MBB, or
    • The partsParts are fully inside a DRY-CAB (≤1010% %RH) RHor. sealed in an
      MBB.

    • Only these two conditions pause the clock. Zip bags andor “"covered boxes”boxes" don’t count unless your site has qualified them—assumedo nonot. count.


    Line-Side and Transit Discipline


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

    • Mounted Status: Parts mounted on a machine =feeder means the timer runs.RUNS.
    • PausingNight Holds/Pauses: Never leave MSDs mounted at ambient overnight. For pauses across breaksshifts or shifts:breaks, you must either cabinet-park the feeder+reel in a DRY-CABdry withcabinet feeder slots,or or reseal the reel and remove it.
    • NightRework holds:Exposure: neverIf leavean MSDsassembled mountedPCB 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’vehas seen ≥ 1 day ambient exposure, or suspect humidity,a pre-bake is mandatory before hot-air or BGA rework to prevent popcorning failure on the assembledassembly PCBitself.
    (

    5.4.9)3 The Reset Button: Bake Decision and Reseal

    Baking is the only way to avoidfully popcorning/padreset lift.

  • Salvagedthe MSDs:floor unlesslife keptclock.

    dry from first opening, treat as     expired; default is scrap or tray-rebake if device and tracking allow.
  • Cumulative exposure: add rework exposure

    When to the device’s timer; if it exceeds floor life, bake then reseal/reset before reuse.



    • 5.4.8 Bake decision(Simple (simpleDecision rule)

    Tree)

    Bake if any of these are true:

    • Floor life has expired or will expire before the next usereflow step.
    • The HIC lowlow-percentage spot wetwas WET onupon opening.
    • EvidenceThe ofmaterial suffered a compromised storage event (e.g., torn MBB, humiditydry excursion,cabinet failure, unknown history).
    • Pre-rework bake is required asfor above.an assembled PCB.

       Otherwise, continue with timer rules.

    Bake Profiles: ICs vs. PCBs


    Baking


    must

    5.4.9be Bakequalified profiles (ICs vs PCBs; pickto the safestdevice that works)

    Always checkand the device/packagingmedium ratings.it Someis contained in, as carrier tapes, labels,tapes or elastomerscomponent can’tfinishes takemay degrade with 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)

    1. Bag: Use qualified MBB sized for minimal free volume; no pinholes.
    2. Desiccant: Fresh, in-date; mass matched to free volume per site table; distribute evenly.
    3. HIC: New card placed on top, visible at next open.
    4. Purge (optional): Short dry N₂ purge; don’t crush sharp edges.
    5. Seal: Straight, 10–12 mm heat seal; wrinkle-free; quick squeeze test for leaks.
    6. 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.
    7. 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)

    AreaMaterial

    AcceptPreferred Temperature/Time

    RejectHandling Note

    ICs (in Trays/Tubes)

    125 ˚CHIC atdry openbake (typically 24 hours for MSL 3+).

    Low-%Preferred spot dry

    Low-% spot wetmethod →for Bake

    Timermaximum control

    MESeffect timerand matches label; pauses only in MBB/DRY-CAB

    Handwritten guesses; timer “paused” in zip bagefficiency.

    FeederICs pauses(in Tape-and-Reel)

    40 ˚C to 60 ˚CFeeder+reel (≤5% RH) for cabinet-parkedextended or reel resealedhours.

    MountedUse overnightlow attemperature; ambient125 ˚C will melt most tapes. Re-tray if 125˚C is mandatory.

    PCBs (Bare FR-4)

    105 ˚CBake profilefor 2 to 8 hours (based on thickness/history).

    MatchesUse device/medium;105 safe temps

    125 °˚C withto tape;protect surface finishes like OSP baked(Organic tooSolderability hot

    Reseal

    Fresh HIC + desiccant; straight seal; full label

    Missing HIC; no desiccant; unlabeled

    Reset

    “RESET” only after qualified bake

    Timer reset without bakePreservative).


    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.

    1. Contents: Use a qualified MBB, a fresh HIC, and fresh desiccant (mass-matched to the volume).
    2. Seal: Heat-seal the bag cleanly (10–12 mm straight seal) and verify no wrinkles or leaks.
    3. 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.

    5.4.134 Compliance and Common trapsTraps

    →

    Following smallestthese reliablerules fixensures the components survive the thermal shock of reflow, safeguarding quality.

    Trap

    Symptom

    First moveMove (The Reliable Fix)

    “We’llThe finish"Finish tomorrow”Tomorrow" on feederTrap

    Popcorning,Components HiP,left delammounted on a feeder overnight.

    Cabinet-park the feeder or reseal; the reel; add a supervisor check at shift hand-off checkoff.

    Baking tapeTape at 125 °125˚C

    Warped tape, melted pockets, loose pocketsparts.

    Use Low-low-temp/long-time bake profile or re-tray parts before baking at 125 ˚C .

    Using Zip bags used as dry packBags

    HIC is wet on the next openopen. Timer was running silently.

    Ban unauthorized containers. Only MBB or DRY-CAB pauses the clockclock.

    Rework without pre-Pre-bake

    Cracked packages or pad lift at the hot-air station.

    Pre-Mandate pre-bake assemblies before rework

    OSP boards baked hot

    Poor wetting in next run

    Bake lower/longer for OSP

    Noany resealambient-exposed label

    Timersassembly resetbefore byhot-air/BGA rumor

    Label state + times + remaining h; update MESrework.



    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.


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