A US electronics company had a problem that most sourcing agents cannot solve. Their first PCB samples failed functionally, and the deadline had not moved.
They did not need another supplier who could quote boards. They needed someone who would open the failed units, find out why, take the cost of being wrong, and still hit the ship date.
This is what that project looked like from the inside.
The Problem: Failed Boards and a Deadline That Would Not Move
The client’s initial samples failed in the field test. That is the worst moment in a hardware project, because it is also the moment when everyone in the chain starts explaining why it is not their fault: the design house points at the fab, the fab points at the assembly house, the assembly house points at the components.
We took the failed units and started from the board itself. What we found was not a design flaw and not a component problem. It was a soldering problem at one position: U4, a QFN IC, with insufficient solder coverage.
That matters because a QFN is one of the hardest packages to inspect. The lead is under the body, the thermal pad is under the part, and a joint that looks fine from the side can be open underneath. On a functional test it shows up as an intermittent fault — which is exactly the kind of fault that gets misdiagnosed as firmware.
Step 1 — QFN Soldering Failure Analysis
Our engineers received the failed samples and worked the failure backwards rather than reflowing and hoping.
The fault was isolated to U4: the QFN was not fully soldered, so the device failed intermittently under load. Once you know the position, the rest of the question is narrow — is it paste volume, reflow profile, pad design, or part placement? 【可选：如果你们能说清是其中哪一项，这里补一句会极大提升专业可信度】
This is the part most sourcing agents skip. A trading agent ships boards; it cannot tell you why a board failed, and it cannot rework one. The difference shows up precisely on the project that goes wrong — and every project goes wrong once.
Step 2 — Re-soldering and Re-verification
We re-soldered the QFN at U4 to full coverage and restored normal operation, then re-verified the units before anything shipped.
That sequence — diagnose, repair, verify — is what turns a failure into a data point instead of a delay.
Step 3 — 20 Free Replacement Samples, and What the One Failure Proved
We supplied twenty free replacement boards so the client could re-run their own validation without waiting on a commercial negotiation. We also added thirty extra boards free of charge on the first mass order, so the client was not paying for our learning curve. 【确认：30 片赠送是按原文口径写的】
During re-verification, one of those twenty boards failed. We caught it in our own test, before the batch reached the client’s line, and resolved it immediately.
We are leaving that sentence in the article on purpose. A supplier who tells you twenty samples passed is telling you nothing — every supplier says that. A supplier who tells you nineteen passed and one did not, and what happened next, is showing you the part of the process that decides whether your production line stops. 【这段的写法假设那片是你们自己复验时发现的，如果不是这个情形，告诉我，我改口径】
Step 4 — Firmware Programming: Delivering Units, Not Bare Boards
The boards were not shipped as bare PCBs. We programmed the firmware to the client’s specification and delivered functional units — flashed, verified and ready to install.
For a client, the difference between a bare board and a programmed unit is a programming station, a fixture, a test procedure and the labour to run them. For a small hardware team, that difference is often the whole schedule.
Step 5 — Split-Batch Delivery: 100 + 900
We produced 1,000 units and split the shipment into 100 and 900 to match the client’s inventory position rather than our convenience. The first batch let them start; the second let them scale without holding stock they could not yet sell.
The Result: One Root Cause, One Supplier, One Ship Date
- Root cause identified and fixed — U4 QFN soldering, found and repaired on the failed samples
- 20 free replacement boards supplied for the client’s own re-verification
- 30 additional boards free on the first mass order
- 1,000 units produced and functionally tested before packing
- Firmware programmed to spec — delivered as ready-to-use units
- Split delivery 100 + 900 to match the client’s inventory plan
- All of it inside one supplier — assembly and integration on one site, with no handoff between a trading agent and a factory
What the Client Said
“Your team identified the QFN soldering issue quickly and provided a clear solution. The firmware programming service saved us a significant amount of work.”
Looking for PCBA Sourcing That Includes the Hard Part?
Most PCBA sourcing quotes cover the easy part: buy the components, place them, ship the boards.
The hard part is what happens when a board fails. That is when you find out whether your supplier can read a failure, rework a joint, re-verify a batch and still hold a date.
We are a custom injection molding factory that took on the assembly end — not a trading company that added a board supplier to its list.
Send us your boards, BOM or failure report →
What to send
- Gerber files and BOM
- Quantity, and whether you expect split delivery
- Firmware or test procedure, if the units need to ship programmed
- The failed samples or the failure report, if the project is already in trouble
What comes back
A manufacturability and sourcing review on the BOM, a failure analysis note if you sent failed boards, and a quote that separates component cost, assembly, programming and test — so you can see what you are actually paying for.
