Humidity control / component storage - Page 1
Forum section: electronics / general

author: pastaclub
author_rank: Regular Contributor
timestamp: June 01, 2023, 11:49:00 am
content: Any suggestions on my approach, or maybe best-practice recommendations with regards to humidity control?I own these pieces of equipment:1. fruit dryer2. vacuum bag sealer3. dry cabinetThe fruit dryer is my attempt at "baking". It basically blows warm air through a cylindrical container thus drying what's inside. I set it to 60C and put reels, trays and desiccant inside for 12-18 hours. I originally bought this machine to dry 3D printing filament. Though it was not intended for any of these purposes, I assume it works pretty well. It can really pull all the liquid out of fruits, so I assume it will do the same for components. One concern is that it might affect the plastic tape (SMD tape on reels) or the strip that covers it, therefore I don't set the temperature any higher.The vaccum bag sealer does its job (pull the air out and seal bags) but the bags never seem to be completely air-tight. Although the sealing looks good, I find the vacuum gone after a week.The dry cabinet is a thing I got used cheap and it's marketed as a dry storage for camera gear. It's small (65L) and draws less than 2A at 5V, which seems underpowered. Its digital hygrometer typically shows 19% RH (outside air is typically >50%) but it will never go lower. I use it to store unsealed components as well the sealed trays with the most expensive chips (FPGAs).My storage time for components is >2 years. Most reels I have are resistors and capacitors - I just store them open without any special care. There's always the fruit dryer for baking before they go to PCBA.

author: David Hess
author_rank: Super Contributor
timestamp: June 01, 2023, 03:13:56 pm
content: Quote from: pastaclub on June 01, 2023, 11:49:00 amCheck that the plastic in the bags you are using is not permeable to atmospheric gases, including water vapor. Common polyethylene and polypropylene bags will leak through the plastic. Metalized Mylar (polyester) bags will not.

author: PCBprototyping
author_rank: Contributor
timestamp: June 02, 2023, 07:23:05 pm
content: Fruit dryer is not good as it accelerates the oxidation of pins.Dry cabinet is good, but it needs to be at 5% RH to stop the floor life, anything above the 5% will just slow down the process of sucking moisture.RH below 5% will reset the floor life, in production process, best RH is around 1% to reset the floor life quick enough.After drying is done, vacuum seal the components together with silica gel to store them for long periods of time.Standard vacuum sealers are typically not powerful enough for aluminum bags, you need a good vacuum sealer.To get the best results for long term storage, nitrogen is supplied into the vacuum bag and then resealled, so it pushes out the oxygen and keeps the the inside of the bag safe from oxidation.In your case, since you don't have dry cabinet with 5% RH, best would be to reseal the bags immediately after you open them and take out some components, so the exposure to humid air would be as short as possible.

author: pastaclub
author_rank: Regular Contributor
timestamp: June 03, 2023, 05:40:51 pm
content: Can I modify my existing dry cabinet to make it more suitable?I know nothing about dehumidifiers. If I get a more powerful one and add it to the cabinet, will that lower the achievable RH%?

author: PCBprototyping
author_rank: Contributor
timestamp: June 03, 2023, 10:25:27 pm
content: Zeolite dessicant is used in dry cabinets to achieve RH below 5%:https://superdry-totech.com/super-dry-desiccant-technology/I'm not sure how low can you go with fridge compressor and power consumption would be higher.

author: jayx
author_rank: Regular Contributor
timestamp: June 16, 2023, 09:52:32 pm
content: Only non-transparent bags are proper moisture barrier, but you can't see through them to check humidity inside.Normal digital hygrometers, not to mention cheap ones, are usually not suitable for measuring very low humidity. Anything below 10-15% is out of range.I think the best DIY approach would be some sort of air tight metal cabinet with a glass in the door / wall and chemical humidity indicator so you can see the humidity level inside. Plus dessicant "cartridge" inside (say a dessicant granules in a tube), with a fan for blowing the air through it. Periodically you'd have to swap the cartridge and bake dessicant to dry it, depending how often you open the door and how airtight the cabinet is.

author: TimFox
author_rank: Super Contributor
timestamp: June 16, 2023, 10:22:07 pm
content: The traditional approach for dry storage in laboratories is "desiccators", as seen inhttps://www.coleparmer.com/c/desiccatorsThe plastic ones (not suitable for vacuum) cost $89 to $134, for ID between 138 and 248 mmhttps://www.coleparmer.com/p/cole-parmer-essentials-desiccators-pp-pc/59151At university, we used "indicating DrieriteTM" as the desiccant material, which changes color from blue (dry) to pink (moist), then requiring heating to reconstitute.https://www.coleparmer.com/p/drierite-desiccants/48253These are professional lab supply prices, probably cheaper stuff available elsewhere.