Moisture-Sensitive Parts Waiting on an Indian SMT Floor: The Floor-Life Bill

Once a moisture-barrier bag is opened, an MSL-3 part has 168 hours at 30 °C/60 % RH before it must be soldered, baked or dried. An MSL-4 part has 72. On most Indian EMS floors that clock is consumed by waiting, not by placement: the kit is opened and staged, and then the line runs late. The bill comes as bake hours, reels written off and a line that sits idle while QA decides what is still usable.

By the Mama Editorial Team. Mama scopes camera projects for Indian factories. Last verified: 13 October 2026, against the manufacturer notes cited inline. Get the current standard from JEDEC/IPC before you write a process spec.

Key takeaways

• Floor life is cumulative from the moment the bag is opened. A shelf does not stop it; only qualifying dry storage pauses it.
• Most of the loss is a scheduling problem. A kit opened for a line that frees up three days later has used most of its MSL-4 window before the first board is placed.
• Reels are the expensive case. TI says tape and reel should not be baked above 40 °C, where a thicker MSL-4 part needs weeks. Lapsed reels usually get replaced.
• Indian humidity makes the textbook numbers optimistic. The floor-life table assumes 30 °C/60 % RH. A floor that runs wetter has less time than the label says.
• A camera sees the waiting that burns floor life (parked kits, reels beside an idle line, open cabinet doors), not the exposure clock or the humidity.

The clock nobody owns

The rules come from IPC/JEDEC J-STD-033, the joint standard for handling, packing, shipping and use of moisture/reflow-sensitive surface-mount devices (JEDEC listing; revision D, April 2018, per Infineon's storage note). Plastic packages absorb moisture; in reflow it turns to vapour and can crack or delaminate the package, often invisibly. Texas Instruments reproduces the J-STD-033 floor-life table in its handling note (TI SPRABY1A):

TI adds that "most semiconductor products are rated MSL3 or higher" (TI SPRABY1A): your passives are mostly MSL 1, your ICs, BGAs and modules mostly not. Where a label gives no MSL period, Renesas tells customers to solder within 168 hours of opening (Renesas handling guide).

Three details catch Indian plants out.

It is cumulative. Two days at line side, back to the shelf, two more next week: four days spent. Resealing does not give hours back.

Dry storage pauses the clock only in a real dry cabinet. J-STD-033C clauses 4.1.2.1–4.1.2.2, as quoted by a dry-cabinet maker, say a cabinet holding not more than 10 % RH pauses floor life for parts within their limits. After a short exposure the clock can also be reset by drying. For MSL 2, 2a and 3, exposure of no more than 12 hours needs at least 5× that time in desiccation. For MSL 4, 5 and 5a, exposure of no more than 8 hours needs at least 10× that time in a cabinet at not more than 5 % RH (J-STD-033C as quoted by Eureka Dry Tech). Some component makers are stricter: Broadcom tells users to keep part-used reels below 5 % RH and says the clock is paused there, not reset (Broadcom AV02-1298EN). A reel that sat out over a weekend is well past both limits. Drying in a cabinet will not rescue it, so it has to be baked.

The 30 °C/60 % RH assumption is generous for India. TI notes that higher humidity or temperature "potentially shortens the floor life". J-STD-033 has a separate equivalent floor-life table for 20–35 °C and 5–95 % RH (TI SPRABY1A). Outdoor air near Chennai's electronics corridor shows why this matters. At Meenambakkam, morning (08:30) relative humidity averaged 87 % in November 2022 and 89 % in December 2022, and did not fall below 67 % in any month from June 2022 to May 2023 (Statistical Hand Book of Tamil Nadu 2022–23, Climate and Rainfall). That is outdoor air, not your shop floor, but any stores or staging area outside the controlled zone is running parts above the label's assumption.

Bake hours: what a lapse actually costs in time

A lapsed part is not automatically scrap, but drying takes time. The table below is the J-STD-033 user bake table as reproduced in Monolithic Power Systems' Moisture Sensitivity Technical Note (April 2024), for parts that have exceeded their floor life by less than 72 hours:

Parts more than 72 hours past their floor life take longer: for example, 27 hours at 125 °C for a 1.4–2.0 mm MSL-3 part. BGAs larger than 17 × 17 mm and stacked-die packages get 96 hours at 125 °C (MPS). Some suppliers give their own, more conservative numbers. Murata lists "125°C for 48 hours or 40°C with an RH of 5% for 67 days" for its MSL-managed products and allows baking at most twice (Murata FAQ). A TI BGA reference guide asks for at least 48 hours at 125 °C for an MSL-3 device past 168 hours (TI SLDA021B).

What the table does not tell you is that 125 °C is only available for parts in high-temperature trays or loose parts. TI states that "Tape and Reel material should not be baked above 40°C" (TI SPRABY1A). Renesas says "As tape and reel are not heatproof, do not bake those packing" (Renesas). For a reel, the choice is between a 40 °C bake measured in days or weeks, de-taping and baking loose parts (with handling risks of its own), or replacing the reel.

How it happens: the kit that waits

The typical sequence:

1. Planning releases a job for Monday. Stores kit it on Monday morning, open the bags to count and verify, and move the trolley to the line.
2. The line is still running Friday's job, which overran. Then a changeover goes long, or a stencil or feeder problem appears (the pattern described in Where a Mid-Size Indian EMS Line Loses Hours).
3. The kit sits in the staging lane or beside the loader, bags open, for one shift, then two, then a weekend.
4. On Thursday someone checks the MSD log, if there is one, and finds the MSL-4 parts are out of time.

Nobody did anything wrong in isolation; the parts were opened before the line was actually free. That makes it a scheduling and capacity problem, the constraint covered in PLI-Scale Volume: Can Your SMT Line Actually Take It?, not housekeeping.

The dry cabinet adds a second, quieter leak. A cabinet is only as dry as its door discipline. Each opening lets in humid air. One storage-equipment vendor's guide puts recovery at 15–30 minutes after a prolonged opening, and warns that a cabinet opened dozens of times per shift may never reach its target (Neotel guide via SMTnet). That matters most for MSL 4–5a parts, which need ≤5 % RH, not just ≤10 %, for the short-exposure reset.

A worked example in ₹

Every figure below is an assumption for illustration. Replace the part costs, line rate and frequency with your own. For the line-hour figure, the downtime cost calculator helps.

Assume a 4,000-board job for a consumer-electronics customer. The kit includes 6 reels of MSL-3 QFNs (≤1.4 mm), 2 reels of an MSL-4 module (1.4–2.0 mm) at ₹70,000 a reel, and 1 high-temperature JEDEC tray of MSL-4 BGAs (1.4–2.0 mm thick, body under 17 mm square). Bags are opened at kitting on Monday at 08:00. Because of an overrun and a long changeover, the line starts the job on Thursday at 08:00, 72 hours later. Assume the floor held at 30 °C/60 % RH throughout, which is the best case.

If this happens twice a month (an assumption), the plant loses about ₹53 lakh a year (₹2,22,600 × 24). Almost all of it comes from one decision: opening the bags three days before the line was ready.

Two caveats push it up: a floor wetter than 60 % RH ate more than 72 hours of the MSL-3 life, and a part that should have been baked but went through reflow moves the cost to field returns.

What fixes it without new capex

• Open at the line's real start time, not the plan's. Kit and verify against sealed bags. Open them only when the previous job is within one changeover of finishing.
• Return rule. If the line stops for more than a set number of hours, opened MSL 3+ parts go back into the cabinet. A 12-hour limit for MSL 3 and 8 hours for MSL 4 matches the short-exposure reset limits.
• First-expiring-first-out. Issue the partly used reel with the least floor life left first.
• Door discipline. Pick list ready before the cabinet opens; door shut between picks; hygrometer reading logged per shift.
• Plan the oven like a machine. A 20-hour bake blocks a shared oven for most of a day.

What a camera can and cannot tell you here

What a camera can see (with timestamps):

• Kits waiting in staging. A trolley parked on Monday and still there on Wednesday shows up as dwell time, with no scanning.
• Material at line side on an idle line. Reels or trays on the bench or feeder cart while the line has been stopped for hours. That combination is the expensive one.
• Dry-cabinet doors left open. How long, and how often per shift.
• Bake oven occupancy. A rough count of bake events you may have in no register.

What a camera cannot see:

• A specific reel's exposure clock. Reels look alike and labels are small. Per-lot exposure comes from scans at bag-open and cabinet in/out (MSD log or MES).
• Humidity and temperature, in the room or the cabinet. Use a data logger; a camera cannot reliably read a humidity indicator card either.
• MSL level, seal quality or package damage. Cracks and delamination need X-ray or acoustic microscopy.

The useful combination is the MSD log for the "which reel, how many hours" question and cameras for "how long did material sit, and why". Cameras on stores and line side record people walking past. Report aggregates (dwell, door-open minutes), not individuals, and put up the worker notice described in The Worker CCTV Notice Your Factory Needs Under DPDP. For the wider camera layout of an EMS plant, including ESD and changeovers, see Cameras in Electronics/EMS Plants.

Where Mama fits

Mama reads the cameras a plant already has, or ones added where none exist. Each morning it tells the owner where material and machines waited the previous day: which kits sat in staging longest, how many hours material sat at an idle line, how long the dry-cabinet doors stood open. It watches material and machines and reports aggregates, never named operators. It will not tell you a reel's floor life. It will show you the waiting that uses it up. Leave an email or phone in the form below and Mama will get back to you with a camera plan for your stores and SMT line side.

FAQ

Does putting an opened reel back on the shelf stop the floor-life clock? No. Floor life is cumulative at ambient conditions. Only a qualifying dry cabinet pauses it (≤10 % RH per summaries of J-STD-033C, ≤5 % RH for the MSL 4–5a short-exposure reset). A reseal in a moisture-barrier bag needs fresh desiccant and a proper heat seal. Hours already spent are not returned.

Can we bake a full reel at 125 °C to save time? No. TI and Renesas both say tape-and-reel packing must not be baked at high temperature (TI gives 40 °C as the ceiling). At 40 °C and ≤5 % RH, a thicker MSL-4 part can need weeks. That is why lapsed reels are so often replaced.

Our floor is air-conditioned. Is the 168-hour figure safe? Only if every place the parts sit, stores and staging included, stays at or below 30 °C/60 % RH. Log line-side humidity through a monsoon month before relying on it.

Can a camera track MSL exposure automatically? No. It times how long kits and reels sit in view and how long cabinet doors stay open. Per-reel exposure needs barcode scans.