PCB assembly, from first demo boards to production

Rigid FR-4 boards, HDI boards with microvias, flexible circuits, rigid-flex boards and metal-core boards. Each needs its own handling: flex and rigid-flex boards ride on carriers that hold them flat during printing and placement, and metal-core boards need a reflow profile that allows for the heat the aluminum pulls away from each joint.

The board type is declared on the fabrication side of the same order, so the assembly plan knows which board it is soldering before the parts arrive. For the constructions themselves, see HDI PCB, rigid-flex PCB and metal-core PCB.

Placement count and unique part count, more than anything else. Placements are machine time. Unique part numbers are setup: each distinct part needs its own feeder, its own incoming check and its own BOM line. Four hundred placements from thirty part numbers is a different job from four hundred placements from a hundred and eighty.

After those two come the technology mix (surface-mount only, through-hole only, or both), the number of sides populated, and whether parts are sourced by us, consigned by you, or split. Programming, functional test and the depth of inspection are declared as extras. Boards larger than 600 mm per side, up to 610 mm × 914 mm, are priced by an engineer in the official quote rather than online.

Consign when you already hold the stock, when your allocation on a scarce part beats the open market, or when a part is specific to you. Have them sourced when you want one accountable party for the build, or when chasing stock for a long BOM is the real cost. A mixed model is a declared option.

Whichever you choose, no part is substituted silently. A proposed alternate is an itemized change you approve, question or decline before it is fitted. On an engineering project, availability and alternates are checked before the schematic is drawn, so these questions are settled before a board exists.

It depends on what is on the board and what a bad joint would cost. Optical inspection checks presence, polarity, alignment and the visible solder joints, and suits any populated board. X-ray, on the advanced route, is what you add when the joints you need to see sit under the part, because no optical method reaches them.

Electrical and functional test answer a different question. They do not ask whether the board was built as drawn; they ask whether it works. Both are declared per order, because a functional test needs a fixture and a definition of pass, and both come from you. Our engineers can write that definition with you when the board is ours to design.

A definition of pass. Tell us what the board must do when powered: which rails to measure, which interfaces to exercise, which firmware to load, and the limits for each result. From that, our engineers design the fixture and the test program. Without a definition, a functional test only proves the board powers up.

When we design the board, we write the test definition with you during EVT and build the fixture before PVT. The ICT and FCT stations then run the production test firmware, and each unit's results are stored against its serial number, so a field return can be traced to the test it passed.

On the same lines, with different controls. A demo build is assembled from reviewed files for a date that cannot move, and small changes between units are allowed. A production run is held to the golden sample you signed: fixed alternates policy, fixed inspection level, fixtures built before PVT, and each batch compared with the reference.

The boards in your investor demo come off the same SMT lines as the boards in your first production batch, built from the same files. The SMT program, the stencil and the reflow profile from the demo build carry into production. When the design moves through EVT, DVT and PVT, nothing moves to a new supplier, and the engineers who drew the schematic stay on the project. The portal also takes 72-hour prototype builds for teams with a fixed demo date.

The Shenzhen factory holds ISO 9001, ISO 13485, IATF 16949, AS9100 and ISO 14001, so medical, automotive and EV, and aerospace and drone assemblies run under the matching system. Board marking is declared on the order, so a shipped board can be identified after it leaves. In production, each batch is compared with the golden sample, and an engineer reviews any drift before the next batch runs.

IPC-A-610 Class 2 and Class 3 differ in how much a joint may deviate before it is rejected: fill in a plated hole, wetting at a fillet, the position of a part on its pads. Class 3 is for products that must keep working where a failure is not acceptable, and it takes more inspection time. State it on the order when your product needs it, and the free engineering review scopes the inspection to match.