Box build takes a populated circuit board and turns it into a finished, tested product: board, enclosure, cabling, connectors, displays and mechanical hardware, assembled and ready to ship. A supplier can be excellent at board assembly and still be a different proposition for box build, because the skills, suppliers and test equipment involved are not the same. This guide sets out what to ask before you commit a build to anyone, with figures from the 243 UK box build suppliers listed on EMS Directory.
Agree the scope in writing
"Box build" means different things on different quotes. For some suppliers it is a board dropped into an enclosure. For others it includes cable harnesses, panel and cabinet work, labelling, software loading, final test and packaging for shipment. Among UK box build suppliers on EMS Directory, 74% also list turnkey PCB assembly, 53% cable assembly and 33% repair and rework, so the work often spans several disciplines. Ask for a written scope that lists each stage, so you can compare quotes like for like and see who is responsible for what.
Check the mechanical assembly capability
Mechanical assembly is a separate skill from soldering. Ask how fastening is controlled (torque-controlled tools, with calibration records), how enclosures are sourced (customer-supplied, off-the-shelf or custom fabricated) and who manages that lead time. Enclosures and mechanical parts are often the longest lead items on a box build, so it helps to know early who owns them.
Ask about environmental protection
If your product faces moisture, vibration, dust or chemical exposure, ask which protection methods the supplier runs in-house: gluing and bonding, potting, encapsulation or conformal coating. On EMS Directory, 45% of box build suppliers list conformal coating and 16% list environmental testing. Potting and encapsulation are not tracked as a separate field, so ask each supplier directly. Some subcontract these steps, which adds a handover and a supplier to your chain. If you have an ingress protection target, the IP rating defined in IEC 60529, ask how it is verified.
Look at final product testing
Board-level test confirms the electronics were built correctly. Final product testing confirms the assembled product does its job. On EMS Directory, 55% of box build suppliers list functional testing, 51% AOI, 29% X-ray inspection, 21% in-circuit testing and 9% burn-in testing. Listings do not say whether functional testing is done at board level or system level, so ask what happens at system level: functional test under realistic conditions, any run-in or burn-in your product needs, who designs and owns the test fixtures, and what test records you receive with each batch.
Decide the sourcing and shipping model
Turnkey, consigned and hybrid sourcing each suit different projects, and our guide to turnkey, consigned and hybrid component sourcing covers the trade-offs. Of the box build suppliers listed, 65% list turnkey (full supply), 18% free issue or customer supplied, 10% kitted, 8% hybrid or partial kitting and 5% consignment, and many list more than one. Packaging and shipping matter more on box build than on bare boards, particularly for export or drop-ship orders where the supplier becomes part of your logistics chain. Ask how finished units are packed, labelled and dispatched.
Match the supplier to your volume
Of the UK box build suppliers listed, 83% list low-volume work, 77% medium volume, 74% prototype orders and 40% high volume, and 28% list fast turn. If you plan to move from a prototype run to production, filter on both ends of your range and ask how the same team and line handle that step.
Ask for examples in your sector
A listing shows the sectors a supplier serves: 62% list industrial customers, 61% medical, 58% aerospace and defence and 53% automotive. Ask for recent examples in your sector and the certification that goes with it. On EMS Directory, 79% of box build suppliers list ISO 9001, 16% ISO 13485 and 16% AS9100.
Quick-reference checklist
- Get a written scope covering enclosure, cabling, software, test, labelling and packaging
- Ask how fastening is controlled and how tooling calibration is recorded
- Confirm who sources enclosures and who owns their lead time
- Ask which environmental protection steps run in-house and which are subcontracted
- Ask what final product testing covers and which test records you receive
- Agree the component sourcing model and how finished units are packed and shipped
- Ask for examples in your sector and the matching certification
Figures come from EMS Directory listings as of October 2026 and reflect what each company states in its public information. They are not independently audited.
Where to go for more
IPC publishes the workmanship standards that apply across box build, including IPC-A-610 for electronic assemblies and IPC/WHMA-A-620 for cable and wire harness assemblies. The IEC publishes IEC 60529, which defines IP ingress protection ratings. UKAS is the UK's national accreditation body, and a useful check on who issued a supplier's certificates.
Find box build suppliers on EMS Directory
Browse UK box build assembly suppliers and narrow them with the Certifications, Testing, Industries Supported, Order Type / Volume and Component Sourcing / Procurement Model filters. Save the suppliers that fit to your shortlist, open the Compare view to see their certifications and capabilities side by side, and send one enquiry to your whole shortlist at once. Our certification and capability checklist covers the wider questions to ask any UK electronics manufacturer.