General > General Technical Chat
Dehydrating moisture sensitive chips at home
james_s:
I would pull the IC and then power up the board and check the voltages, I bet you fried the regulator. I've swapped dozens of large ICs, many that sat exposed to room air for years and I never baked them or took any special precautions.
clearchris:
--- Quote from: james_s on April 23, 2021, 05:32:11 am ---I would pull the IC and then power up the board and check the voltages, I bet you fried the regulator. I've swapped dozens of large ICs, many that sat exposed to room air for years and I never baked them or took any special precautions.
--- End quote ---
I applied power to the board with the stm32 chip removed. The buck converter checks fine, I started feeding the board 5v and went up to 11.5 and VIN was as expected, output was 3v3 at all input values and feedback was 3v3 or 3v2 (discrepancy probably due to my meter). I haven't hooked a scope up to it, but that seems pretty good to me. It's possible that the buck converter reacts differently under more load, but seems pretty unlikely. I'll for sure keep some hooks on the buck converter / regulator it when I power it up after adding the stm32 chip.
wraper:
--- Quote ---STM32 AN2639 Application Note:
The stm32 After opening a dry pack, soldering should be done within 24 hours.
--- End quote ---
24 hours is basically impossible. It's for MSL 5a which is almost impossible to find for IC. You normally see MSL 1 or 2, MSL 3-4 at worst.
wraper:
That AN2639 appnote contradicts itself. First they say you can store it according to MSL level. Then say it must be soldered within 24 hours after opening :palm:. Also what "YES" on that diagram. Some shitty low quality document.
If 10% indicator became pink but 60% indicator did not turn pink, you can check packing date and MSL level. If time passed since packing date does not exceed floor time for MSL level, you can safely use the part.
wraper:
More sensible document from ST https://www.st.com/resource/en/technical_note/dm00238092-mounting-instructions-for-smd-surface-mounting-device-packages-stmicroelectronics.pdf
Page 6:
--- Quote ---The permissible time (from opening the moisture-barrier bag until the final soldering process), during which a component can remain outside
the moisture barrier bag, is a measure of the sensitivity of the component to ambient humidity (moisture-sensitivity
level, MSL). The most commonly applied standard, IPC/JEDEC J-STD-033*, defines eight different MSLs. Please
refer to the “Moisture Sensitivity Caution Label” on the packing material, which contains information about the
MSLs of our products.
--- End quote ---
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