At 8:49 AM -0700 7/16/03, Tim May wrote:(By the way, the USB flashdrive (a 256 MB FlashHopper) I have on my
keychain--my physical keychain!--is probably waterproof. The USB port
has a little plastic cover which slides on snugly. Until I eventually
misplace it, I am using it. I expect the thing is showerproof, though I
don't intend to test it. Water resistance can be tested
nondestructively with things like Fluorinert, of course. Also, surfers
and kayakers often have O-ring sealed gizmos they wear under their wet
suits, coming in different sizes. It would be trivial to find one to
hold either a USB flashdrive or a Compact Flash card.)
Ever since I heard that manufacturers were cleaning assembled boards with
soap and water I have wondered just how much you need to protect electronic
circuits from water. You obviously don't want to allow them to stay damp
so they corrode, but immersion for a time (up to weeks) followed by a fresh
water rinse and drying might not be so bad. Do any hardware experts have
an opinion?
DI water (deionized water) is used at various stages to rinse boards, wafers, plated devices, etc.
Soap and water is often used for cleaning bare PCBs, but this is long before the chips go in.
After wave soldering (PCBs fed on conveyer belt above hot solder bath, soldering the devices to the board in one continuous process) the flux and dross and gunk is washed off with special soaps (e.g., high acid content soaps) and water. But the water is certainly not left on the boards, not left to dry and cause spotting, etc.
Alcohol and other rinses are used.
We used to use vapor degreasers a lot, and TCE, before it got restricted.
As for the effects of water on packaged chips, they vary. Moisture intrusion usually comes when a "driving force" exists for some long amount of time, e.g., '85/85" (85 per cent relative humidity, 85 C, for some number of hours or days). External corrosion is also possible.
(One of the first things I devised for Intel was dubbed the "water drop test." Still in use, 28 years later.)
My point about not wanting to immerse my flash drive is related to why I would no immerse any other piece of electronics unless I had a compelling reason to do so.
--Tim May, Occupied America
"They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -- Benjamin Franklin, 1759.
