Contract board assembly: clear-to-build, line hours and the handover pack

Clear-to-build status governs the schedule, not the machine

Scheduling in an assembly shop starts with which jobs have every part physically available and verified. A kit missing one reel is not nearly ready; it is not ready, because building partially and adding components later multiplies handling, rework and traceability problems. Shops therefore run a clear-to-build review before committing a slot, and they resist customer pressure to start regardless. Where shortages are chronic, the honest fix lies upstream: alternates approved in advance, longer buffers on constrained parts, or a design change. Starting anyway fills a floor with half-built product and destroys visibility of what is genuinely owed.

A line hour is the unit actually being sold

Behind every board price sits an assumed number of minutes on a printer, a placement line and a test station, plus setup amortised across the batch. Assemblers who price this way see immediately whether a job earns its slot; those who price by copying the previous quotation cannot. The difference shows up in scheduling behaviour, since a shop that knows its line rates will decline work consuming capacity below the return it needs, while one that does not accepts everything and then wonders why a full factory yields no margin. Customers gain by asking how a quotation was built.

The handover pack decides how the first build goes

Introduction problems are usually documentation problems: missing paste layer data, ambiguous polarity marking, an out-of-date parts list, no approved alternates, unclear criteria for cosmetic features, or a test specification assuming equipment the assembler does not own. Each generates a query, each query costs days, and queries raised mid-build cost far more than those raised beforehand. Mature assemblers run a formal data review and refuse to schedule until it closes. Customers who dismiss that review as bureaucracy learn its value the first time a batch is built to a superseded revision.

Inspection layers and the defects each one misses

Optical inspection sees only what is visible, which excludes joints hidden beneath packages. Those require radiographic inspection, which is slower and depends on interpretation skill rather than equipment alone. Electrical testing finds connection faults but will pass a marginal joint that fails later under thermal cycling. Functional testing exercises behaviour yet may not reach every circuit. No single method suffices, and stacking all of them is rarely justified. The useful discipline maps likely failure modes for the specific design against what each method detects, then chooses deliberately rather than buying reassurance by the layer.

Box build pulls the assembler into the customer's product

Moving beyond bare board work into enclosure fitting, cabling, configuration, serialisation, packing and sometimes direct shipment changes the relationship substantially. The assembler now holds mechanical parts with long lead times, loads software and configuration data, owns cosmetic quality judgements, and may become the record holder for what shipped to whom. Margins usually improve compared with boards alone, and so does exposure, since a mechanical shortage stops shipment of an otherwise finished product. Customers gain simplicity and lose the ability to switch suppliers quickly, because build knowledge now sits with the assembler.

Frequently asked questions

What does clear-to-build mean, and why does it slip?

It means every item on the parts list is physically present, inspected and reserved for the job before scheduling. It slips because component lead times move, deliveries arrive short or damaged, alternates were never approved, or a design change lands after material was ordered. Shops publishing clear-to-build status openly give customers a chance to intervene while intervention still helps. Shops reporting a schedule date without that status are usually reporting an intention rather than a plan.

When is radiographic inspection worth paying for?

Whenever joints cannot be seen: packages with connections under the body, connectors with hidden terminations, or dense assemblies where solder voiding affects thermal performance. It also earns its place during introduction, while a process is being proven, even if it is later reduced to sampling. Applying it to every board on a mature, well-controlled process rarely pays. The decision should follow from the design and the consequence of failure, not from a wish to justify the equipment.

Should a customer extend from board assembly into full box build?

It often makes sense where mechanical content is modest and the product ships in configurations the assembler can hold. It makes less sense where enclosure work needs specialist capability, where certification of the finished product rests on the customer's own approvals, or where the customer wants freedom to move assembly suppliers quickly. Either way, the transfer should include a documented build standard, so the knowledge does not live only in one supplier's memory.