Dehydrating moisture sensitive chips at home - Page 1
Forum section: electronics / general

author: clearchris
author_rank: Newbie
timestamp: April 22, 2021, 04:28:44 pm
content: So I bought some stm32 chips to repair a 3d printer board. They were on the shelf in the bag with dessicant for 6 months, but the moisture detector strip shows under 60% moisture, but over 10% moisture. I need to bake them.QuoteI can bake the chip at 125C for 24 hours, but "under ntirogen atmosphere" is a bit of a problem. I have read that the nitrogen is required because even at 125C the air could have as much as 20% humidity. That seems a bit high to me, but I don't have a hygrometer, so that's hard to verify.What do you recommend for drying these chips? I was going to reflow them, but I think that's out at this point, I just need them OK for hand soldering or soldering with hot air (recommendations?). There's no pad underneath the chip, it's not bga, just smt.Here's are some items that could be relevant in making a solutionI have a reflow oven (https://hackaday.io/project/171619-not-just-a-reflow-oven)dessicantvacuum pump3d printers with heated beds that could be used as a hot plate up to 120C or so40cf nitrogenMy oven isn't airtight enough to run a nitrogen purge, but I could do something like find a small jar, put the dessicant in with a the chip, drill a small hole in the lid and bake in the oven. Or I could build a small vacuum chamber and run the vacuum pump. Anyone have thoughts or ideas?Thanks!

author: David Hess
author_rank: Super Contributor
timestamp: April 22, 2021, 07:05:16 pm
content: For hand soldering nothing needs to be done.I would place them under a vacuum for hours to days to remove the moisture. Under a vacuum and heated would be even better.

author: KE5FX
author_rank: Super Contributor
timestamp: April 22, 2021, 08:12:52 pm
content: This is the kind of thing you need to worry about in commercial production, but unless you plan on assembling thousands of units at home you will almost certainly never have a problem. Don't sweat it.

author: jogri
author_rank: Frequent Contributor
timestamp: April 22, 2021, 08:40:33 pm
content: Quote from: David Hess on April 22, 2021, 07:05:16 pmYou need a rather good vacuum to remove water... Should be well below 10 mbar. I've used that method to dry stuff, but it takes quite some time (or a vacuum pump that can reach 0.01-0.1 mbar). You add a bunch of fresh desiccant to the chamber, evacuate it and let it sit for a few days.

author: clearchris
author_rank: Newbie
timestamp: April 22, 2021, 09:14:31 pm
content: Quote from: David Hess on April 22, 2021, 07:05:16 pmQuote from: KE5FX on April 22, 2021, 08:12:52 pmHmm. In the past, I had attempted to tranplant an stm32 chip from a blue pill to the printer board, and failed each time. IIRC I tried 2 or 3 times, and it was by hand with hot air. Maybe I destroyed the chips removing them with the hot air. I have always hated using chipquik on chips that I'm going to re-use, it's near impossible to get that stuff off.Quote from: jogri on April 22, 2021, 08:40:33 pmI have used my pump to reach 25 micron, though usually I wouldn't take it that low. Large diameter evacuation hosesreallyspeed the process. (https://appiontools.com/mh120006eak/) Would be easier to raise the temperature of the chamber to boil off the water faster, though I might be concerned about popcorning at that point.Ok, thanks everyone, I think I'll bake it for 24 hours, maybe with dessicant, but no nitrogen, and hand solder with an iron. I want to be extra sure of success this time. Wish me luck, fourth time is the charm?

author: Agent24
author_rank: Regular Contributor
timestamp: April 22, 2021, 10:58:32 pm
content: This might be completely irrelevant but if you've replaced the chip 3 times and it still doesn't work, are you sure it's the chip? Or only the chip?Do you know why the original died? You sure you don't have a shorted regulator or something that's killing every new chip you put on?

author: clearchris
author_rank: Newbie
timestamp: April 22, 2021, 11:09:00 pm
content: Quote from: Agent24 on April 22, 2021, 10:58:32 pmAs I was typing that last post out, that thought had occurred to me. The original died due to a flaky barrel jack. I inserted the power, saw the big blue arc, stm32 chip was melted. So yeah, I should probably check the regulators now that you mention it. Anything else you think I should check?

author: clearchris
author_rank: Newbie
timestamp: April 23, 2021, 12:32:56 am
content: Quote from: Agent24 on April 22, 2021, 10:58:32 pmI just pulled the datasheet, it's an XL1509-3.3. The datasheet and name sounds familiar, it's possible I checked this two years ago when I fried it. 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. I also checked the stepper drivers and mosfets, I don't detect any shorts. Nothing else gets VIN. I do remember attempting to transplant the stm32 chip back to the blue pill, and was also unsuccessful. So for certain something fried those chips, either removing with hot air, or something on the 3d printer board.This time, I'll bring the voltages up slowly, and see what I get then. I'll either feed in 4.5v which is the minimum the buck converter needs, or maybe I'll feed in 3v3 past the buck converter. I don't know if the second option is wise, my power supply is of my own making, I don't know how much I trust the cheap buck converter that in it.

author: jmelson
author_rank: Super Contributor
timestamp: April 23, 2021, 02:08:44 am
content: The vacuum chamber + heat will CERTAINLY pull the moisture out. I have not had the issue with ICs, but have had boards blister in the past. My system, now, is to bake all boards that have been in house more than a few months. I spread them out like a deck of cards and bake for 1/2 to an hour at 50 C, then up to 70 C and bake for 2 hours. Never had a problem after this process. Chips might take a bit longer baking.Jon

author: Bud
author_rank: Super Contributor
timestamp: April 23, 2021, 05:27:43 am
content: When hand soldering with hot air and where i feel baking may be needed, i leave the ICs overnight on a tabletop coffee mug warmer. The warmer runs at about 100 C.

author: james_s
author_rank: Super Contributor
timestamp: April 23, 2021, 05:32:11 am
content: 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.

author: clearchris
author_rank: Newbie
timestamp: April 23, 2021, 02:20:57 pm
content: Quote from: james_s on April 23, 2021, 05:32:11 amI 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.

author: wraper
author_rank: Unknown
timestamp: April 23, 2021, 02:27:40 pm
content: Quote24 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.

author: wraper
author_rank: Unknown
timestamp: April 23, 2021, 02:36:13 pm
content: 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. 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.

author: wraper
author_rank: Unknown
timestamp: April 23, 2021, 03:02:19 pm
content: More sensible document from SThttps://www.st.com/resource/en/technical_note/dm00238092-mounting-instructions-for-smd-surface-mounting-device-packages-stmicroelectronics.pdfPage 6:Quote

author: clearchris
author_rank: Newbie
timestamp: April 23, 2021, 03:25:04 pm
content: Quote from: wraper on April 23, 2021, 02:27:40 pmYeah, it's level 3.