That Day, the FAI Report Couldn't Be Signed Off, and the Production Line Supervisor Was Livid
"Damn it, this batch of new material is stuck again!" Xiao Chen wailed from the other end of the production line. I walked over to see what was happening. It turned out a new batch of wafer carriers had arrived from the outsourced factory and should have gone straight to machine testing. However, Ah Xiong from QA was shaking his head like a rattle drum, clutching his measuring tools. "Old Su, look at these dimensions, almost 0.2mm off. How am I supposed to sign this FAI?" Ah Xiong pointed to the data on the report; the Cpk value was only 0.85, which was a disaster. Hearing this, the production line supervisor was livid. If this batch got stuck, the machines at the next station would have to shut down. In essence, this was the daily routine of a failed First Article Inspection bringing the entire line to a halt.
What's the Problem?
What exactly is First Article Inspection (FAI) for? To be honest, it's simply a "confirmation" step. Confirmation of what? Confirmation that the batch of items you have in hand is indeed the "same thing" you initially designed and what the supplier promised. Imagine ordering fried chicken from a street vendor, and the owner gives you fried squid instead – you'd definitely complain. In a semiconductor factory, the opportunity cost of such a complaint is far too high.
The purpose of FAI is to ensure that the "samples" supplied by the vendor for the first time, or the "first batch of products" produced by a new process or new equipment, all meet the specified requirements. This is like buying a new car: before delivery, the salesperson checks all functions with you – whether any warning lights are on the dashboard, if the paint is scratched, or if the navigation works. This inspection is crucial because if there's a problem at the source, all subsequent efforts will merely be spent dealing with a pile of defective products, a sheer waste of time and cost.
Conversely, "Last Piece Confirmation" (LPC) or "Last Piece Inspection" (LPI) is conducted at the end of a production run to verify the condition of the final product. This is akin to how well you can maintain your condition at the finish line after running a marathon. It ensures that throughout the entire production batch, the process has not drifted due to equipment wear, jig fatigue, or other gradual changes.
Therefore, the key point is that FAI inspects the "starting point," and LPI inspects the "end point." The combination of both ensures the quality stability of your entire production process.
How Is It Actually Done?
In our factory, FAI is typically performed for new parts, new material suppliers, or when there are significant process changes.
- Specification Confirmation: First, we lay out all of the supplier's product drawings, specification sheets, and our own internally defined design documents.
- Measurement Comparison: The QA department uses various precision measuring instruments, such as CMM (Coordinate Measuring Machine) and vision measuring systems, to measure Critical Dimensions (CD). For example, if a wafer carrier's aperture requires 10.00 ± 0.05 mm, and it measures 10.15 mm, that's unacceptable. If the tolerance range is very tight, like our common requirement of ± 0.01 mm, then a Cpk value of 1.33 is already excellent; if it's only 1.08 and the DPMO skyrockets to 6210, that's definitely a disaster.
- Functional Testing: In addition to dimensions, functional tests are also conducted. For instance, whether the new carrier can be smoothly transported on the machine without getting stuck or scratching the wafer.
- Report Sign-off: All data and test results are recorded, forming an FAI report that requires joint sign-off from managers of relevant departments such as design, manufacturing, and quality assurance. If any aspect is non-compliant, it must be sent back for rework.
Last Piece Confirmation is relatively straightforward; it typically involves sampling and inspecting the critical dimensions or functions of the final product to confirm no significant difference from products in the middle of the batch, thereby demonstrating process stability. For example, checking if the film thickness of the last wafer is still within tolerance, or if there are any chipped corners on the diced dies.
The Most Common Pitfall
I remember one instance when we ordered a batch of critical precision parts from a new Japanese supplier. The first samples they sent were exceptionally good in terms of dimensions and surface roughness; the Cpk value even soared to 1.67. After we signed off on the FAI, we began mass procurement. However, by the time the third batch arrived, frequent issues started to appear, and machines would intermittently report errors.
Later investigation revealed that when the Japanese supplier first submitted samples, they deliberately used a top-tier processing machine and assigned their most experienced master craftsman to operate it, all just to pass the FAI. After we approved the sign-off and began mass production, they transferred the orders to their regular production line. Although the quality of these products was still within specifications, the Cpk value dropped to around 1.08. When encountered with our factory's more stringent environment, the yield went south.
Therefore, in essence, FAI isn't just about current data; it's also about assessing the supplier's "process capability." During FAI, you must require suppliers to provide their "mass production" process plan to confirm their ability to consistently produce products that meet specifications, rather than just fielding a "special forces team" to pass the inspection.
One Thing You Can Do Today
Next time you receive new material, don't rush to put it into production; first, confirm the FAI report with QA.