First article inspection is not a perfunctory signature process, but the most critical practical verification checkpoint before the production line switches from a stopped state to stable mass production. If inspection is missed or items are simplified, hundreds of boards produced in the subsequent continuous run may all need rework. We encountered three cases in the Jia Jinyuan workshop where skipping the stencil tension test caused the tombstoning rate of 0201 resistors in the entire batch to exceed 12%. Therefore, Solder Paste thickness, volume, offset, and bridging tendency must all be included in the scope of first article inspection, rather than only checking whether the AOI alarms.

For first article inspection after startup and board changeover, the first step is to confirm the recognition and matching degree of the stencil and PCB MARK points, while verifying whether the current station program calls the correct version. Because the Jia Jinyuan production line once missed the judgment of 37 IC pin short circuits due to not switching the AOI inspection template, and this problem could have been found by magnifying glass visual inspection during first article inspection. The nozzle vacuum value of the placement machine, the vibration frequency of the feeder, and the track transmission gap also need to be recorded synchronously. Although these parameters do not directly appear on the report form, they jointly determine the stability of placement accuracy, and any abnormal item will be exposed on the first board in the form of offset, side standing, reverse placement, etc.

The reflow oven temperature profile must be compared zone by zone with the specified profile for this PCB model. In particular, the peak temperature deviation must not exceed ±2℃, and the time above liquidus must be controlled within 60±10 seconds; otherwise, it will lead to poor wetting of lead-free solder joints or excessive void rate at the bottom of the BGA. We once found that the BGA X-ray inspection void rate of the first board reached 38% after a customer switched to a new batch of solder paste, and the investigation found that the heating rate of the preheating section was 0.5℃/s faster than the standard. This difference can only be captured by actual measurement with a profiler during first article inspection.

First article inspection must also include an initial functional test step, such as loading a minimum system program on a motherboard with an MCU to run UART communication, or applying power to a power module to verify whether the output voltage ripple of each channel is lower than 15mV. This kind of test cannot wait until the final inspection, otherwise, if the dozens of boards that have flowed out earlier have design compatibility problems, they can only be scrapped. Jia Jinyuan handled an incident last year where replacing a capacitor from a new supplier with high ESR caused LDO startup failure, and the root cause of the problem was that no power-on aging test was done during first article inspection.

All first article inspection data must be handwritten into a paper form and signed on the spot by the operator, technician, and team leader. Electronic system backup is only for archiving purposes, because electrostatic interference, touch failure, or network delay in the on-site environment may cause data loss, and a signature means the responsibility is traceable. We insist on using a red pen to circle out-of-tolerance items and note the disposal method next to them, such as 'SPI solder paste thickness average 4.8μm (standard 5.2±0.8), retest passed after adjusting squeegee pressure +0.2N'. This kind of first article inspection with action feedback is truly closed-loop process control.