How GOB Coating Changes Your LED Module Lead Time

1. The four blocks that make up GOB lead time

A bare LED module becomes a shippable GOB-coated module in four stages, and each stage has its own owner, its own waiting, and its own way to go wrong.

The first block is the only one the coating machine controls. The other three are planning blocks. A delivery promise that counts only the first block is wrong by the sum of the other three.

JH-D900 precision dispensing machine — a dispensing reference, not a GOB coating machine. The coating step is only the first block of GOB lead time; curing, inspection and rework follow.

2. Why curing is the block most plans get wrong

Curing is the easiest block to underestimate, because nothing visible happens while it runs. The module sits still, the glue hardens, and the line looks idle. Three facts from the glue's own material data explain why this block cannot be compressed by wishing:

The practical rule is simple: treat curing as its own dated block in the plan, with a named start (when the last module of the batch is coated) and a named release condition (the glue's datasheet condition is met and the module passes its handling check). Until that condition is met, the batch is not shippable, however good it looks. The handling rules for this waiting period — what a module may and may not do while it cures — are covered in our companion piece on curing, handling, and storage after GOB coating.

3. Sequencing batches so the line never waits for curing

Curing time is only dead time if one batch occupies the whole line. The coating machine finishes a batch and moves on; the curing area holds the finished batch while the machine starts the next one. That overlap is where realistic planning recovers most of the lost day, but it only works if three conditions hold:

1. The next batch is ready to coat. Its program is loaded and proven, its fixture is seated, and its glue batch is verified. If any of those checks is still open when the machine finishes the first batch, the machine waits — and the overlap is lost.

2. The curing area is separate from the coating station. Coated modules must leave the machine's work area to a labelled curing space. If they stay on the machine table "just until they set," they block the next batch and the plan collapses into a single file.

3. One variable changes at a time. If the next batch uses a different module size, a different program, or a new glue batch, that change is verified on its own — a first article, a program check, a glue identity check — before the batch runs. Stacking two changes on the first batch of the day is how a planning gain turns into a rework day.

A useful way to lay this out is a simple two-row plan for each production day: which batch is on the machine, and which batch is curing. If the curing row is empty, the machine is the only thing working. If the machine row is empty, the curing row is the only thing working. The day is planned well when neither row is empty for long.

4. Two moments that always extend the plan: the first article and a new glue batch

Two moments in every GOB run deserve their own time in the plan, because both are decision points, not formalities.

The first article. Before a batch runs, one module is coated first and checked — coverage, edges, uniformity, and visible bubbles — to decide whether to follow, adjust one thing and repeat, or stop the batch. That check is the cheapest inspection in the whole job: it costs one module and a few minutes, and it can save a full batch. A plan that skips it to save time has not saved time; it has moved the risk to the end of the batch, where it is most expensive. The same discipline applies before coating starts at all: inspect the bare module first, so coating does not lock in a defect that was already there.

A new glue batch. When a batch of modules changes to a new glue batch midway, the new batch must be verified before it is used, and the traceability record must split at that point so modules coated before and after the change can be told apart. That verification and the record split are small jobs, but they are jobs — they belong in the plan as their own lines, not as interruptions discovered halfway through a shift.

Both moments are also the points where a good record pays for itself. If a customer later asks why a batch was late, or why a module was held, the record shows the decision and the reason. If there is no record, the conversation starts from zero.

5. The rework buffer: plan for it, do not hide it

Some modules will fail inspection. That is not a planning failure; it is the reason inspection exists. What turns it into a delivery failure is a plan with no room for it.

When a coated module fails, the decision is repair or scrap, and that decision needs evidence: what the defect is, where it is, which glue batch and program coated it, and whether the same defect appears on neighbouring modules. Our companion piece on reworking a GOB-coated module works through that decision. For planning purposes, the point is narrower: the decision takes time, the rework takes time, and the re-inspection after rework takes time. None of that time exists in a plan that assumes every module passes first time.

A workable approach is to promise the customer a release date that already contains a rework allowance, and to keep that allowance visible inside the factory as "held for decision" rather than quietly absorbing it by skipping inspection. Skipping inspection to protect a date does not protect the date — it moves the failure to the customer's site, where it costs a return, a replacement batch, and the next order.

6. What to tell the customer

A delivery promise for GOB-coated modules should name the release date, not the coating date. Three sentences cover most situations:

None of this requires quoting a price or a speed the factory has not demonstrated. It requires only that the date you give is the date the batch is genuinely ready to leave.

7. Planning checklist: before you promise a date

8. Common mistakes

Promising same-day shipment of a coated batch. Coating is one block. Curing and inspection are separate blocks, and they do not finish on the same day just because the coating did.

Counting curing as overlapping coating on the same machine. Curing overlaps the next batch's coating, not the same batch's. The batch being coated now still has to wait.

Assuming the first batch of a new size runs at full speed. The first article, the fixture check, and the program check are part of the first batch's time, not overhead to be ignored.

Skipping inspection to save a day. The day is not saved; the defect is shipped, and the cost returns as a complaint, a return, or a lost order.

Heating the cure to recover a lost day. The material data advises against it, and a bubbled coating fails inspection — the recovery costs more than the delay. Stable air pressure matters for the same reason: a pressure dip during coating creates defects that inspection then has to catch, and that costs the day twice.

Letting the curing area become the packing area. A module that is moved, stacked, or packed before it is released is a module whose curing and inspection records no longer match what was shipped.

FAQ

Q1: How much extra time does GOB coating add to a module order?
There is no single number. It depends on the glue's curing condition, the layer thickness, the workshop temperature, the inspection scope your customer requires, and whether the first article or a glue-batch change falls inside the run. Plan it as four blocks — coat, cure, inspect, release — and date each one from the glue's datasheet and your customer's acceptance standard, not from a rule of thumb.

Q2: Can we coat the next batch while the first one cures?
Yes — that is the normal way to keep the line busy — provided the curing area is separate from the machine, the next batch's program, fixture, and glue batch are already verified, and only one change is introduced at a time. If any of those is not ready, the machine waits and the overlap is lost.

Q3: The customer wants the modules the day after coating. Is that possible?
Only if curing, inspection, and packing can genuinely finish by then for that glue, that thickness, and that acceptance standard. If they cannot, the honest answer is the release date, given before the order is confirmed — not a coating date presented as a delivery date.

Q4: What should we do when inspection holds part of a batch?
Hold the affected modules, record the defect, the glue batch, and the program, and decide repair or scrap on evidence — not on the delivery date. Tell the customer how many modules are held and what happens next before the promised release date passes.

Q5: Does a faster coating machine shorten lead time?
It shortens the coating block only. Curing, inspection, and rework do not get faster because the machine does. A faster machine helps most when the plan already overlaps curing with the next batch's coating — then the machine is never the bottleneck.

Bottom line

GOB coating does not add one delay to a module order; it adds a sequence — coating, curing, inspection, and release — and each step has its own clock. Plan all four, overlap curing with the next batch's coating, protect time for the first article and for rework, and promise the release date. The factory that does that delivers late less often than the factory that promises the coating date and hopes the rest takes care of itself.