Effect of high humidity in storage on assembled PCBs - Page 1
Forum section: electronics / general

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 13, 2015, 01:47:24 pm
content: A question has come up about the project I'm currently installing in Hong Kong, regarding storage conditions after it gets taken down after Christmas.The hardware consists of LED strip PCBs, fixed together with plastic rivets, with spring contacts (SIM connectors) for electrical contact onto ENIG pads. Finish is white solder resist.What long term (say 1 year) effects might there be if PCBs are stored in an indoor but non-climate controlled environment in a very humid country?This is different to the known issues of moisture absorbtion prior to soldering, where PCBs and LEDs can be damaged by 'popcorning' when any moisture boils during reflow.I would imagine there may be some change in the mechanical properties of the PCB - would these be reversible by baking ?Would there be issues of surface degredation of ENIG pads - I know ENIG isn't really meant to provide physical surface protection beyond soldering.How about effect on nylon snap rivets?Sneak preview :

author: Tomorokoshi
author_rank: Super Contributor
timestamp: November 13, 2015, 03:42:16 pm
content: Perhaps some of the problem could be mitigated by using a sealant like Humiseal 1B73:http://www.humiseal.com/products/acrylics/1b73/I just use this for my little projects:http://www.rustoleum.com/product-catalog/consumer-brands/stops-rust/clear-enamel

author: coppice
author_rank: Super Contributor
timestamp: November 13, 2015, 04:35:17 pm
content: When you say indoors and uncontrolled I assume you mean warehouse conditions. In Hong Kong silver plated RF parts in a warehouse will go black in a couple of weeks, if they are not dessicated. I've never had much trouble with ENIG boards, though. I think pollutant build up on the surface is more likely to give you poor contact than actual corrosion. I've had some bare boards stored for years without much care, and they were still very solderable. Tinned surfaces certainly tarnish quite a bit. I've never seen FR4 noticeably degrade. There are lot of problems with modern plastics degrading rapidly, but I don't know of any that specifically relate to Hong Kong's climate. This is the dryer time of year. If things are pulled out of storage now they should be fairly dry. If they were pulled out in July they might actually be dripping.

author: SeanB
author_rank: Super Contributor
timestamp: November 13, 2015, 05:21:16 pm
content: You will probably have a few bad contacts after a year of storage in an uncontrolled atmosphere. Any non wiping contacts will degrade with the inactivity, and the ENIG will have some corrosion under the thin gold plate. You will find the rivets will have changed dimension slightly, and if they got warm ( over 50C ) then there is a good chance they will be brittle as well as swollen and warped.Best is to arrange some sealed packaging for the individual boards, a thick non permeable PET bag, and wrap the boards before insertion in some static dissipative bubble wrap, with a large desiccant pack per bag, the whole lot being stored in another big bag with more bubble wrap and desiccant blocks. then put in cardboard boxes with a double wall, with an inner double wall box and sheets of that foamed plastic that they love there for packing stuff as wrapping for the bags of boards, and then store. Should keep the boards looking like new, though you will probably want to store the nylon rivets separate and put a few packs extra to replace the ones that will break.

author: all_repair
author_rank: Frequent Contributor
timestamp: November 13, 2015, 06:15:59 pm
content: Though humidity is not desirable, I would be more concerned about the nearby VOC unintentionally introduce throughout the storage period from neaby storage, painting or emission from other objects. Strink-wrap them, throw in a bag or 2 of drying agent, shall buy a long time.

author: Ian.M
author_rank: Super Contributor
timestamp: November 13, 2015, 07:38:56 pm
content: Was that meant to be "Stink-wrap them,"? If so as the concern was VOCs, I don't thing it would be very helpful. I've had some of that 'stink'-wrapping in a shipment and it nearly made the product too foul to use! <LOL>