Moisture Sensitive Device Handling: Who Owns It in a PCBA Contract

The obligation both parties assume the other is carrying

You place a turnkey PCBA order. The BOM is approved, the CPL is clean, the first article passes, the electrical test report comes back good, and the boards ship. Four months later your customer reports field failures on a BGA that passed everything on its way out. The cross-section shows internal package delamination — damage that was done during reflow, by moisture that was inside the package before it ever reached the oven.

Now the contract conversation starts, and it goes badly for a specific reason. You believe the assembler owns process control, so moisture handling is theirs. The assembler believes they soldered exactly what you approved and that the parts arrived in whatever condition you or your distributor sent them in. Both positions are defensible, because the document you both signed named a component, a quantity and a process, and never named who held the moisture obligation.

This is not an edge case in sloppy supply chains. It is the normal outcome when a purchase order treats moisture sensitivity as a property of the part rather than as a set of actions someone has to perform, log and hand over. The part has a rating. The rating is not an instruction, and nobody is assigned to it by default.

What the MSL label states, and three things it does not

Component manufacturers classify plastic-encapsulated parts by moisture sensitivity level and mark the dry-pack with that classification, a seal date, and a humidity indicator. That marking is real, standardised and useful. Treat it as the input to your contract language, not as the contract language itself.

Here is what the label settles: this package absorbs atmospheric moisture, and once the barrier bag is open there is a bounded period during which the part may be reflowed safely. Beyond that period the part needs reconditioning before it goes through a thermal cycle.

Here is what the label does not settle, and what therefore has to come from your paperwork:

It does not say who starts the clock. The bounded period begins when the barrier is opened. Your document has to establish which event in your actual supply chain counts as that opening — and in a contract arrangement there can be several candidate events separated by weeks.

It does not say who is authorised to recondition. Reconditioning a part is a thermal operation on material that may belong to you, may already be committed to a build, and may be affected by a tape-and-reel carrier that cannot take the heat. Someone has to be allowed to make that call without asking, or required to ask. The label is silent.

It does not say who keeps the evidence. If no one is contractually required to log open-time, humidity indicator state at opening, and any reconditioning performed, then after the fact there is no record on either side. The failure analysis will tell you moisture did it. It will not tell you whose shift it happened on.

Those three gaps are why the obligation needs four explicit boundaries in your order, not one clause saying "supplier shall observe MSD requirements."

Boundary one: when the exposure clock starts

In a single-site operation this is trivial — someone cuts the bag open at the line and writes the time on it. In contract manufacturing the same physical event has at least four plausible locations, and they can be months apart.

• The distributor opened a sealed master bag to pick your quantity, then resealed into a smaller bag. Did that reset or continue?
• Your own warehouse opened the bag to count and verify incoming parts before shipping them to the assembler.
• The assembler opened it at goods-in for inspection and kitting.
• The assembler opened it at the feeder, minutes before placement.

Each of these is a legitimate reading of "the bag was opened." Only one of them can be the contractual start, and if your PO does not nominate it, each party will assume whichever reading leaves them with the most margin.

What to write instead: name the event, name who records it, and name what gets recorded. A workable formulation is that the controlled period starts at the first opening of the barrier bag downstream of the component manufacturer, that every opening event is logged with date, time and humidity indicator condition, and that the log travels with the material to the next holder. Then add the case your supply chain actually has: if parts are transferred between your warehouse and the assembler in an opened state, the accumulated time transfers with them and the assembler is entitled to treat the remaining window as reduced.

That last sentence is the one that prevents the argument. Without it, an assembler receiving opened parts has no basis to refuse them, and also no basis to accept responsibility for them.

Boundary two: who decides to bake, and who keeps the record

Reconditioning sounds like a purely technical decision, which is exactly why it gets left out of commercial documents. It is not purely technical, for three reasons that all land on the buyer.

It is a thermal operation on your material. If the parts are consigned, they belong to you. An assembler who reconditions them is subjecting your property to a process you did not specify. An assembler who does not recondition them is placing parts of unknown moisture state into reflow. Neither is obviously correct without instruction.

It can be blocked by the carrier. Many parts arrive on tape-and-reel or in trays that are not rated for the temperatures reconditioning uses. The physical consequence is that reconditioning may require removing parts from their carrier, which affects placement feasibility, handling damage risk, and in some cases whether the parts can still be machine-placed at all. That is a cost and schedule event, not a process footnote.

It consumes part of the component's thermal budget. Parts have a finite tolerance for high-temperature exposure across their life. Reconditioning draws on the same budget that reflow, rework and any future repair draw on. Doing it silently and repeatedly is not free.

So the clause has to answer: may the assembler recondition without approval, must they notify first, or must they quarantine and wait? Any of the three can be right for your programme. Leaving it unanswered is the only option that is always wrong.

Then require the record. Specify that any reconditioning performed on your material is reported with the lot identification, the quantity affected, the reason it was triggered, and the fact that it occurred — and that this report is part of the delivery documentation rather than an internal note. You are not asking for process parameters you have no standing to dictate. You are asking for a traceable statement that an operation happened to your parts, so that a future failure analysis has something to read.

If you already require a first article evidence package, the moisture handling statement belongs in it. PCB168 covers what that package has to contain and what releases against it in PCBA first article inspection report and release terms.

Boundary three: consignment material that arrives with the barrier already compromised

This is the boundary that generates the most disputes, because it is the one where the material is unambiguously yours and the problem is unambiguously visible on arrival.

A kit arrives at the assembler. One reel's barrier bag has a split seam. Another bag is intact but the humidity indicator has changed colour. A third bag was opened by your own incoming inspection and taped shut with no log. The assembler now has three different problems and, in most contracts, no instruction covering any of them.

What assemblers do in the absence of instruction is predictable and reasonable: they build. Stopping a line to escalate a bag seam is expensive, the schedule is yours, and raising it looks like manufactured delay. So the parts go in, and the event is not recorded anywhere that will be read later.

Write the path rather than the judgement. Four elements make it workable:

A defined inspection scope at goods-in. State that incoming kit verification includes barrier integrity and humidity indicator condition for moisture sensitive items, and that findings are recorded whether or not they are adverse. Recording a clean result matters as much as recording a bad one, because a clean record at goods-in moves the boundary cleanly to the assembler.

A named decision owner for adverse findings. Someone on your side has to be reachable and empowered, with a stated response window. Without that, escalation is a worse option than silence for the assembler.

Three pre-agreed dispositions. Recondition and proceed, quarantine pending your decision, or proceed as-is with a documented exception that you accept in writing. Agreeing the menu in advance means the on-the-day conversation is a selection, not a negotiation.

An explicit statement about who absorbs the cost of each. Reconditioning costs time. Quarantine costs schedule. Proceeding as-is costs risk. These are three different bills and they do not all go to the same place.

The related question of who owns the material and who absorbs its loss is a separate commercial frame, and it is worth settling first because this clause sits on top of it. PCB168 covers that in PCB assembly contract manufacturing material ownership.

Boundary four: rework, second reflow, and restarting the clock

Everything above concerns the path from goods-in to first placement. The obligation does not end there, and the second half is where documentation is thinnest.

Three situations restart the question after the board is already built:

Boards held between reflow passes. A double-sided assembly goes through reflow twice. If there is a gap between passes — a scheduling break, a queue, an awaiting-parts hold — the partly built assembly has been through one thermal cycle and is now sitting in ambient air with components already on it. Whether that gap is bounded, and by whom, is usually in nobody's document.

Rework after test. A failed joint gets reworked. That is a third thermal exposure on the part and, depending on what was done, possibly on neighbouring parts too. If a reworked part was already near its exposure limit before the first reflow, the rework can be the event that causes damage even though the rework itself was performed correctly.

Line stoppages with material already staged. Parts are out of their bags, loaded in feeders, and the line stops for a shift. On restart, some of those parts have been exposed for substantially longer than the production plan assumed.

You cannot write process rules for these; they belong to the assembler's control system. What you can write is a requirement that the control system exists and that its outcomes are reportable: that holds between thermal cycles are bounded by a documented internal limit, that reworked assemblies are identified in the delivery record as having received additional thermal exposure, and that any lot affected by an extended staging interruption is identifiable after the fact.

The value of that last requirement is narrow and real. It does not prevent anything. It means that when a field failure arrives eight months later, you can ask one question — was this serial in an affected lot — and get an answer instead of a shrug.

Where these four land by default in turnkey versus consignment

The two supply models push the default answers in opposite directions, and understanding the push is what tells you which boundaries to write hardest.

In turnkey, the assembler procures. They choose the distributor, receive the dry-pack, and control the material from first opening to placement. The whole chain sits inside one party's control, and the obligation naturally lands with them. Your work here is not to assign the obligation — it is already theirs — but to require that it is visible. Ask for the handling statement and the exception reporting. If you ask for nothing, you get a correctly handled build with no evidence that it was, which is fine until it is not.

In consignment, you procure and the chain is broken. The parts pass through your distributor, possibly your warehouse, possibly a freight forwarder, and then into the assembler's goods-in. Every handoff is a potential undocumented opening. The assembler can only be responsible from the moment they take custody, and they can only prove the state at that moment if your contract required them to inspect and record it. Here all four boundaries need writing, and boundary three needs it most.

Hybrid kits are the hardest case and the most common. Most real programmes are turnkey with a handful of customer-supplied long-lead or allocated parts. The result is one build with two responsibility regimes running through it, and the consigned items are exactly the ones most likely to have been sitting in someone's stock for a long time. State the split by BOM line, not by order. A PO that says "customer supplied items as marked" without a corresponding handling split has created an ambiguity that will be resolved in whoever's favour has the better record — which is to say, not yours.

Why this defect surfaces at your customer's site, and what that does to your claim

The commercial weight of this clause comes from one property of moisture-induced damage: it is largely invisible to the inspections you are paying for.

Automated optical inspection sees joint geometry and presence. X-ray sees voiding and internal joint structure. Electrical test sees function. Moisture damage in a plastic package — internal delamination, bond wire stress, microcracking that has not yet opened — can pass all three. The board works. It ships. It passes your own incoming inspection too, because your incoming inspection is looking at the same observable properties.

What exposes it is time, thermal cycling, and field stress. Which means the failure typically appears after delivery, after acceptance, after payment, and often after your own customer has taken possession.

Three consequences follow, and they are the reason this is a procurement document issue rather than a quality department issue:

Acceptance has already happened. Your incoming inspection plan passed the lot. Arguing afterwards that the lot was defective on arrival requires evidence you did not collect, because nothing observable was wrong on arrival. If you want to preserve any position here, the acceptance plan has to call out documentation review as part of acceptance, not just physical inspection. PCB168 covers building that plan in incoming inspection and acceptance plan for PCB delivery.

Causation is provable but attribution is not. Failure analysis will identify moisture-induced damage with reasonable confidence. It will not identify which custody period the moisture was absorbed in. Without open-time records from each holder, attribution is a negotiation between two parties with equally thin evidence, and it usually settles on whoever has more commercial leverage.

The cost is not the board. A moisture failure that reaches the field costs field service, your customer's downtime, possibly a recall decision — amounts unrelated to the assembly price. Standard rework and RMA terms written around the assembly value do not reach that exposure. If your programme carries this risk, the handling clause and the test requirement have to be read together rather than written by different people, because what you ask to be tested defines what you can later claim was missed. PCB168 covers that side in defining PCBA test and inspection requirements in an RFQ.

The declaration list for your PO and BOM handover

Nine lines. They are short because each one closes a specific gap identified above, and none of them require you to specify a process you have no standing to specify.

1. Identify moisture sensitive lines on the BOM. Not a blanket clause — a marked set of BOM lines. A blanket clause covering everything gets applied to nothing because it is obviously not meant literally.

2. Nominate the clock start event. Name the specific opening event in your chain that begins the controlled period, and state that accumulated time transfers with transferred material.

3. Require open-event logging. Date, time, humidity indicator condition, by whom, travelling with the material.

4. Set the reconditioning authority. Permitted without approval, permitted after notification, or prohibited pending your decision. One of the three, named.

5. Require reconditioning to be reported. Lot, quantity, trigger, occurrence. In the delivery documentation, not an internal note.

6. Define goods-in inspection scope for consigned items. Barrier integrity and indicator condition recorded whether adverse or not.

7. Pre-agree the three dispositions for adverse findings and state who absorbs the cost of each.

8. Require bounded holds and identifiable rework. A documented internal limit between thermal cycles; reworked assemblies identified in the delivery record.

9. Split the obligation by BOM line for hybrid kits, not by order.

Add one more thing that is not a clause: ask the assembler to tell you how they currently handle these without you specifying. A supplier who answers all four boundaries from their existing system is telling you something more useful than a supplier who agrees to every clause you send. The second answer costs nothing to give.

Where this sits in your document set: these lines belong in the PO and the BOM handover, not in a quality manual appendix, because they allocate responsibility and cost. If you are still comparing quotes, note that two assemblers can price the same BOM differently on exactly this basis — one assuming they will recondition questionable material and one assuming they will not — and the quote comparison will not show you which. PCB168 covers reading those boundaries in PCBA quote comparison and scope boundaries. When you are ready to put a specific BOM in front of us, the PCB assembly service page describes our assembly scope, and the quote request page is where the BOM, CPL and handling split go in together.

FAQ

Does a short-form clause saying "supplier shall comply with applicable MSD requirements" cover this?

It establishes that a standard applies. It does not allocate any of the four boundaries, because the standard defines handling practice rather than contractual custody in a multi-party chain. Standards tell you what correct handling looks like. Only your order can say which party performs it, at which handoff, and who records it.

We run consignment and the assembler never raises moisture issues. Is that good news?

It is not information either way. Silence is the expected outcome when no inspection scope and no escalation path have been defined, because raising an issue without a pre-agreed disposition menu looks like manufactured delay. Define the scope and require clean findings to be recorded too. Then silence becomes evidence instead of absence.

Can I just require that all moisture sensitive parts be reconditioned before placement?

You can require it, but understand what you are buying. Reconditioning is a thermal exposure that draws on the same budget as reflow and any future rework, some carriers cannot survive it, and applied indiscriminately it adds cost and handling risk to parts that did not need it. A triggered requirement tied to indicator condition and accumulated open time is more defensible than a blanket one.

Who pays when consigned parts arrive with a compromised barrier?

Whoever your contract says, which is why item seven exists. In the absence of a clause the practical outcome is that the assembler proceeds, the cost lands on you later as a field failure, and attribution is unprovable. Pre-agreeing the three dispositions and their cost owners converts an unprovable dispute into a priced decision made on the day.

If the boards passed AOI, X-ray and electrical test, doesn't that mean handling was adequate?

No, and this is the single most important point in this article. Those inspections observe joint geometry, internal joint structure and function. Moisture-induced package damage can be present and pass all three, then surface under field thermal cycling months later. Passing test tells you the assembly works today. It does not tell you the package was dry when it entered reflow.

Does this apply to the bare boards as well as the components?

Bare laminate does absorb moisture and reputable fabricators manage it, but it is a different obligation with a different owner and a different document. This article is about components in a PCBA contract. The bare board side belongs with your fabrication specification, and PCB168 covers how to make that specification binding in PCB fabrication specifications that bind the quote.

Sources: Component moisture sensitivity classification and dry-pack marking conventions are defined by the publicly available industry standards for moisture-sensitive device handling and by individual component manufacturer datasheets; assembly acceptance criteria are defined by the published assembly acceptance standards. This article deliberately cites no numeric exposure limits, bake schedules or humidity thresholds — those belong to the component manufacturer's documentation and the standards themselves, and should be referenced in your contract rather than restated from a third party. PCB168 makes no claim here regarding its own equipment, dry storage capacity, personnel qualifications, certifications, lead times or yields. The only PCB168 information referenced is the published service scope on the PCB assembly page.

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