Moisture Sensitive Devices: MSL, Floor Life & Turnkey PCBA Handoff

ORINEWPCB · COMPONENT HANDLING & TURNKEY PCB ASSEMBLY

A component can be the correct part number, electrically suitable and available for placement, yet still need a handling decision. This guide focuses on the handoff between purchasing, stores and PCB assembly: what to check, what to record and what to ask when moisture exposure is known, uncertain or already over the stated allowance.

It is intended for hardware engineers releasing a board, product managers planning a batch and buyers comparing assembly quotations. The examples are illustrative planning tools, not customer case studies or a substitute for a component manufacturer’s process instructions.

What are moisture sensitive devices, and what does MSL mean?

Moisture sensitive devices are components whose packages require precautions against absorbed moisture when exposed to soldering heat. A package may take in moisture during ambient storage. During reflow, internal stresses associated with moisture and heating can contribute to cracking or delamination. Moisture sensitivity is therefore a material-handling issue as well as an assembly issue.

MSL describes a package’s moisture/reflow classification. It is not a universal shelf-life rating for every electronic component, and a higher number does not mean that the device has better electrical quality. The rating must be read together with the applicable environmental conditions and the component’s peak reflow limit.

Check the exact orderable part and shipment label. Do not assign one MSL to all QFNs, BGAs or parts from the same manufacturer. Microchip’s July 2020 MSL communication explains that even a package type can have different classifications when the package materials used at different assembly sites differ.

IPC/JEDEC J-STD-020 covers moisture/reflow classification; J-STD-033 covers handling, packing, shipping and use. The reviewed J-STD-033D document is dated April 2018. Use the revision specified for the project together with current product-specific guidance; a summary table alone does not define an approved factory process.

MSL floor-life reference table

Floor life is the permitted exposure interval outside a compliant dry environment before reflow, subject to the stated conditions. This quick reference matches the common classifications documented in TI’s SLVA840 and NXP’s AN1902. A shipment’s caution label and product requirements take precedence when they impose a specific restriction.

On a phone, swipe within the table or focus the table region and use the arrow keys.

These values are not a blanket permission to leave parts on a bench. Conditions above the reference temperature or humidity may reduce the usable exposure interval. If the actual environment differs, ask for a handling assessment rather than applying a guessed multiplier.

What to check when a reel or tray arrives

For a practical incoming review, ask for a traceable connection between the physical material and the BOM line. One photograph of a reel is rarely enough if it does not show the relevant label or bag condition.

1. Match identity: manufacturer, full ordering code, package, quantity and lot/date-code identifiers where available. Keep substituted or mixed lots separate in the record.
2. Inspect the packaging: note whether the moisture barrier bag (MBB) is sealed, damaged, opened or resealed. Retain the bag’s caution label and seal date.
3. Record the handling evidence: when opened under the procedure, check the humidity indicator card (HIC) as instructed and keep the result with the material record. An HIC is not a complete timeline of earlier exposure.
4. Clarify prior use: for a partial reel, ask who opened it, when, for how long and in what environment. “Stored carefully” is not a measurable exposure history.
5. Set a disposition: accepted for the planned process, held for clarification, assigned an approved drying step, or replaced. Identify the person responsible for releasing it.

Keep moisture control and ESD control separate in the checklist. Do not assume an antistatic bag is a compliant moisture barrier bag. Ask the supplier to identify the packaging and handling requirements for the exact device.

How to track cumulative floor life: an MSL 3 example

The useful question is how much permitted exposure has already been used before the next relevant reflow operation. Preparation, placement delays and interruptions need to be considered in the agreed process. Records should follow the lot, not just the purchase-order number.

A useful lot record can contain: part number; lot identifier; label MSL and reflow limit; bag seal/open times; exposure intervals; temperature/RH evidence; storage or drying history; remaining allowance; planned process; and release authorization. There is no need to hide uncertainty: write “unknown” and resolve it.

For double-sided assembly or later rework, ask how the handling plan accounts for all relevant heating steps. Record the release assumptions before parts are issued to the line. A spreadsheet that covers only the first placement step can miss a later scheduling gap.

When should parts be held instead of sent to assembly?

Make the decision visible to purchasing and production. This suggested review matrix helps teams ask the right question without pretending that every device has the same recovery process.

For a purchasing team, the commercial consequence is usually a decision dependency: extra review, drying, repacking or replacement may affect when material can be released. Request that dependency in the quotation. Do not convert it into a promised delay or a standard surcharge before the actual lot has been reviewed.

Why there is no universal baking recipe

Baking time and temperature depend on the device, package thickness, exposure history and approved drying method. Shipping carriers have their own temperature limits. Microchip specifically notes that its MSL 1 products can ship in non-bakeable trays; a tray should not be treated as heat-compatible merely because the component is.

Before authorizing a drying step, ask:

• Which component instruction and standard revision define the procedure?
• Is the reel, tape, tray or tube rated for that temperature, or must parts be transferred to an appropriate carrier?
• What records will show the completed drying step and subsequent storage?
• How will the lot remain identifiable during any transfer, splitting or repacking?
• Who will confirm that the material can re-enter the assembly process?

Likewise, placing material into a dry cabinet does not automatically establish a new 168-hour allowance. The storage conditions, duration and applicable procedure must support any pause or recovery claim. Record the transition instead of deleting the earlier exposure history.

Bare PCBs need their own assessment. This component MSL table is not a universal PCB baking specification. Discuss board material, finish and fabrication guidance separately; a component-handling instruction should not be copied onto a bare-board work order without review.

Full turnkey versus supplied parts: assign the handling owner

A turnkey PCB assembly project can connect PCB fabrication, component procurement and assembly through one project review. It still needs explicit decisions about material evidence and any parts supplied by the customer. Use the following responsibility checklist when comparing scopes.

Engineers should resolve the component and process limits. Product managers should make material release a prerequisite for the planned build date. Buyers and business owners should compare responsibility and scope exclusions alongside price. These are recommended project controls, not claims that a particular supplier includes every activity by default.

For a broader scope comparison, see the partial turnkey PCBA sourcing checklist and the brand’s OrinewPCB turnkey assembly overview.

MSL handoff checklist for a turnkey PCBA quote

You can start a discussion while some documents are pending. Mark those gaps clearly so the preliminary scope is not mistaken for production release. Include these inputs:

• Build identity: board name, revision, assembly variant and requested prototype/production quantities.
• Fabrication and assembly data: Gerber or agreed fabrication files, BOM, placement file and assembly drawing.
• BOM detail: full manufacturer part numbers, approved alternatives, DNP positions and which parts are customer-supplied.
• Moisture-sensitive material: label photos, lot quantities, MSL/reflow requirements, bag status and known exposure/storage history.
• Process requirements: double-sided assembly, secondary soldering, programming, testing or rework restrictions that need review.
• Planning information: target date, delivery destination and the contact authorized to approve material questions or substitutions.

Keep the moisture record alongside the other release documents. The prototype-to-production checklist covers the wider release decisions; this article provides the specific component-exposure handoff.

Related OrinewPCB video: production release risks

This companion video discusses component variables, manufacturability and checks before a production batch. It provides broader release-planning context; it is not an MSL baking tutorial or a device-specific process instruction.

Watch on the official OrinewPCB YouTube channel · Browse OrinewPCB videos

Frequently asked questions

Technical basis and application limits

The floor-life reference was cross-checked against Texas Instruments SLVA840 (January 2017) and NXP AN1902 Rev. 9 (28 April 2021). Shipment-label considerations were checked against Microchip’s MSL communication (July 2020). The handling/classification distinction was checked against the IPC publication for J-STD-033D (April 2018). These are reference documents; they do not establish a universal baking cycle. Confirm the current device documentation and the standard revision agreed for your project.

Review the material handoff before your next build