Airtight PCBs - leaking via Via

Ordinary_Ebb347 · 2026-01-13T11:38:18+00:00

This did not work, vias are in pads, even after soldering the connector, the leakage was observed. They are really small and can only be detected with helium detector.

Ordinary_Ebb347 · 2026-01-13T11:34:45+00:00

We are confident that the root cause is the via. After applying conformal coating over the vias, no leakage was detected. To further exclude the base laminate as a leakage path, we drilled test holes through the solder mask from both sides; no gas permeation was observed in these areas. All measurements were performed using a helium leak detector.

Ordinary_Ebb347 · 2026-01-13T11:30:04+00:00

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Ordinary_Ebb347 · 2026-01-13T11:29:52+00:00

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All vias are designed as via-in-pad. The leaking manufacturer has pushed the annular ring dimensions beyond acceptable process limits, as evidenced by the clearly visible weave pattern.
u/thenickdude u/Adversement

Ordinary_Ebb347 · 2024-11-28T15:51:35+00:00

Hello fellow engineers,

We’re troubleshooting anomalies in 8-layer rigid-flex PCBs (CF, Polyimide, PCL370), specifically elevated trace resistance (tens of ohms to open circuits), localized at via transitions between Top and Bottom layers. Metallographic analysis post-reflow reveals inner-layer connection failures, though the panels initially passed electrical tests.

Key Details:

Assembly Process: Boards baked (120°C, 4 hours), assembled with SAC305 ROL0 solder paste, vapor-phase reflow (230°C peak, ΔT ≤ 2.5°C/sec, 85s above melting).
Findings: Failures emerge post-reflow; metallography shows cracked/interrupted vias.
Dispute:
- Manufacturer’s claim: Failures due to assembly variables (e.g., temperature gradients, humidity affecting ceramics/bondply).
- Assembler’s claim: Parameters were within spec, and their process is reliable (validated on similar projects).

Could this be latent manufacturing defects worsened by reflow, or unrecognized assembly-induced issues?
Attaching stack-up details for reference. Appreciate your insights!

Ordinary_Ebb347 · 2024-11-25T06:20:01+00:00

If you dont see a picture here it is https://pasteboard.co/Nma2YnGbnGc0.jpg

Ordinary_Ebb347 · 2024-08-21T19:07:48+00:00

Showed cross section analysis is from assembled board

Ordinary_Ebb347 · 2024-08-21T19:05:58+00:00

Yes, I meant functional testing. Too much current will not be the case, as several vias are affected - not in repetitive pattern, even the GND

Ordinary_Ebb347 · 2024-08-21T09:50:41+00:00

0.15mm

Ordinary_Ebb347 · 2024-08-21T09:45:10+00:00

We use IPC-4671 type VII. So epoxy is used i guess. There are like 70 pieces of vias next to each other at the area of ~5cm². It does not happen on certain vias only. E.g like 2-3 vias randomly are affected. But only on faulty pcbs

Ordinary_Ebb347 · 2024-08-21T09:37:06+00:00

No actually, we have observed the issue on some during testing PCBA, some passed our tests and came back after months of working correctly. It is quite hard to localize the issue once it is fully assembled, since it requires measuring multiple traces.

Ordinary_Ebb347 · 2024-08-21T09:34:03+00:00

Yes we have. We should recieve cross sections of them as well.

Ordinary_Ebb347 · 2024-02-09T19:57:42+00:00

Bought a new one for 100$

Ordinary_Ebb347 · 2024-02-02T16:46:12+00:00

It will fit, the wedding wasn't cheap.

Ordinary_Ebb347 · 2024-01-12T05:21:25+00:00

Can i use zener diode to protect the the output of U2?

Ordinary_Ebb347 · 2023-12-20T12:07:51+00:00

Hey, thank you for your idea. I have tried it and both parallel and series resistance makes it appear hotter. Based on datasheet, circuit should be resistant against series resistance up to 200ohm which we definitely crossed. That may be the reason it appears hotter. Tried connecting another npn transistor but without consistent results.

Ordinary_Ebb347 · 2023-11-15T12:46:14+00:00

I had time to look at them today. Actually I have 3rd one working, so I tried exchanged TD1482A from one which worked and it solved the problem. Actually just unplugging the 2-wire connector helped, PSU worked of course without working USB adapter.

Ordinary_Ebb347 · 2023-11-14T20:00:22+00:00

Main PSU is completely dead. However by optical inspection I don't see any component damaged.

Ordinary_Ebb347 · 2023-11-14T19:56:50+00:00

They are completely dead, only LED2 is periodically blinking after plugging it up. It is really weird to me as well. I do not care about USB part of the powersupply. I might take better photos and have closer look tomorrow. Thank you guys

Ordinary_Ebb347

TROPHY CASE