You know the drill.
Five hand-built prototypes. All passed. You placed the order.
Then the problems started.
That gap between “prototype works” and “production works” is what pilot runs are supposed to catch. Sometimes they get skipped. Sometimes they don’t catch enough. Here are three real examples of what happens when something falls through that gap—and what we learned from each.
Each of these projects taught us something about what the prototype to pilot run transition requires. None of the issues were design failures in the traditional sense. They were all process failures—things that only show up when you move from “we can make one” to “we can make a hundred.”
A client’s product required ultrasonic welding to seal the enclosure. The prototypes were hand-assembled and everything fit. No pilot run—straight to production.
30% failure rate.
The design hadn’t accounted for tolerance stack-up across different components. The enclosure, the PCBA, the internal brackets—each had its own manufacturing tolerance. When they came together on the line, the cumulative variation exceeded what the ultrasonic welding could compensate for.
The fix: We cut EVA pads to shim the PCBA inside the enclosure, stabilizing it against the housing. We also extended every wire harness by 5mm to give more room for positional variation.
The takeaway: Your bench prototypes are assembled with care, patience, and individual attention. Production is not. If you skip the prototype to pilot run step, you don’t find out about tolerance stack-up until you’re looking at 30% scrap. That’s not a design failure—it’s a process failure. And it’s entirely avoidable.
Another client sent us physical samples, test procedures, and assembly instructions before the prototype to pilot run phase. They asked ahead of time about ESP32 programming—whether we preferred USB or the official programming pad method.
We recommended USB. It’s faster.
What we didn’t anticipate: the ESP32’s official programming cable has a connector that requires you to press a latch clip every time you plug it in. Works fine for a few boards. But on day three of a production run, your operators’ fingers are sore, their speed is dropping, and your throughput is tanking.
The fix: We switched to a different programming method with a more ergonomic connector.
The takeaway: This client did everything right—they provided samples, documentation, and asked the right questions early. But even then, something that seemed trivial in the lab became a production bottleneck. A proper prototype to pilot run transition isn’t just about testing the board. It’s about testing the process. If you don’t run the actual production process on a small batch first, you don’t find out that your operators’ hands are going to hurt until they actually hurt.
Related: Box Build Assembly Service — Final Product Integration & Functional Testing
Some clients treat the prototype to pilot run phase like a game of 20 questions—piece by piece, one requirement at a time.
One client approached us with a project. They didn’t give us all the information upfront. They gave us enough to get started, then added more requirements later—cost targets, delivery deadlines, per-order quantities. Each new piece of information required a new assessment, a new adjustment to the quote, a new round of internal coordination.
From their side: “Why are they so slow? They keep changing their answers.”
From our side: “Why didn’t they just tell us all this at the beginning?”
The fix: We eventually got everything on the table and delivered a comprehensive solution. But it took three rounds of quoting instead of one.
The takeaway: The prototype to pilot run phase isn’t just about testing the hardware—it’s about testing the working relationship. If information comes in pieces, the solution comes in pieces. If you want a system-level answer, give a system-level question. The earlier you share your complete requirements—cost redlines, delivery hard deadlines, per-order volumes—the more coherent the solution your manufacturing partner can design for you.
Related: Turnkey PCB Assembly & EMS Services
Three different problems. One common cause.
All three came from the same place: not validating the full production process before scaling.
IPC-A-610D, the industry standard for electronic assembly acceptability, defines what a good solder joint looks like. But it doesn’t tell you whether your ultrasonic welding fixture will hold up at volume, or whether your programming jig will give your operators repetitive strain injuries. That’s what the prototype to pilot run step is for.
A well-executed prototype to pilot run phase is not a formality. It’s your last chance to find problems before they find your customers.
Ready to run a pilot that actually tells you something? Send us your design files. We’ll do a DFM review and a process walkthrough—and tell you what we think might break before it does.
