First Article Inspection For PCB Assembly

The first board that comes off a line after a setup is the only one that can be examined without any assumption about the process having worked. Everything after it is a copy, and if the setup was wrong, the copies carry the same error. That is the reason for a first article inspection: a deliberate, documented check of the first unit against the drawing and the bill of materials before the rest of the lot is built.

This article describes what a first article covers, who performs it, what it cannot establish, and how the records are used.

What The First Article Is For

The check exists to confirm that the process is set up for this product. It verifies that the correct stencil is loaded, that the placement program matches the revision of the board, that the correct components are in the correct feeders, that the profile is the one qualified for the assembly, and that the fixtures and the supports are arranged for the panel in front of the machine.

It also protects the customer and the shop at the same time. A lot that is built without a first article and found to be wrong afterwards has to be reworked or scrapped, and the cost is multiplied by the number of boards in the lot. The check is usually a condition of the contract for a new product and a requirement of the quality system for every subsequent build. Related process steps are described under PCBA development process.

What Is Checked

The verification begins with the physical check, which covers the placement of every component against the assembly drawing or the placement file: position, rotation and the presence of the correct part. In practice the check is focused on the parts that can be wrong in a way that is invisible: a polarized component placed the wrong way round, a part with the same footprint as another but a different value, a connector of the right family but the wrong pin count, and a package with a thermal pad that must be soldered.

The process check covers the paste deposit, the profile and the soldering. The deposit is measured, the profile is measured with a thermocouple on the board, and the joints are inspected at the magnification the product requires. Where the product has a specific requirement, such as a void limit under a ball grid array or a fill requirement in a through hole, that measurement is part of the first article rather than a later audit. The standards that the joints are judged against depend on the alloy, and the differences are described under lead free versus leaded solder.

Who Performs It And When

The inspection is performed by the quality function rather than by the operator who set up the line, because the person who made the setup is the least likely to notice that it is wrong. It is performed at the start of every production run, after any change of stencil, paste, feeder, program or profile, and after any interruption long enough for the line to have changed state.

The timing matters as much as the content. A first article that is checked after the whole lot has been built is a post mortem. The check is performed on the first board, and the line waits, or at least the remainder of the lot is held, until the result is known. On a long run the same logic applies to the first board after a shift change, since a feeder that has been reloaded is a new risk.

Documentation And Records

The record should show what was checked, by whom, on which board, with which equipment, and what the result was. Where a measurement is made, the figure belongs in the record rather than a tick: a profile with its peak temperature and time above liquidus, a paste volume, a void percentage. A record of ticks with no figures cannot support a later investigation.

Where a result is outside the requirement, the record should show what was done about it. A first article that found a problem and was corrected before the lot is a success, and the record of the correction is what turns the event into an improvement. A record that shows only passes is a record that has stopped providing information.

What It Does Not Cover

A first article does not prove that the whole lot will be good. It proves that the setup was correct at the moment it was checked, and the process can still drift. That is why the first article is paired with in process inspection and with a defined sampling plan for the rest of the run.

It also does not cover design defects. A board that is correctly assembled to a drawing that contains an error will pass every check, and the error will appear at the functional test or at the customer. The design side is covered by the design rules, which are described under manufacturable design guidelines, and by the review that happens before the board is released rather than after it is built.

Improving The Check

The most valuable improvement is to make the check specific to the product rather than generic. A list that names the components that are at risk on this board, the measurements that matter for this assembly and the tolerances that apply is far more useful than a general checklist, and it takes less time to complete because it does not ask questions that have no consequence.

The second improvement is to use the data. Recording the paste volume, the profile and the void figures over many lots builds a picture of the process, and a drift that is visible in that picture can be corrected before it produces a defect. The first article becomes the anchor point of a trend rather than a single event, and the effort spent on it is repaid by the defects that never happen.

Tools That Make The Check Faster

An automated optical inspection system can compare the placed board with a reference image and report every difference, which turns a manual search into a review of a list. The system is not a substitute for the check, because it does not know which differences matter, but it removes the mechanical part of the work and it makes the result reproducible. The same applies to a solder paste inspection system, which measures every deposit and reports the ones outside the window.

Where such equipment is not available, a photograph of the reference board taken once and compared with the first article is a cheap substitute. The photograph is taken under the same lighting from the same angle, and the two images are compared side by side. It finds the missing part and the rotated part quickly, which are the two errors that a visual check is most likely to miss on a dense board.

FAQ

Is a first article needed for every lot? It is needed at the start of a production run and after any change to the setup. For a continuous run of the same product the check is performed once at the start, with in process inspection during the run.

Can the operator check their own setup? They can check the parts they loaded, and they should. The independent first article by the quality function is a separate step that exists because self checking has a blind spot.

What happens if the first article fails? The setup is corrected and the check is repeated on a new board, and the boards built before the correction are quarantined and assessed. The record of the failure and the correction is part of the quality history.