At 10:18 PM -0600 11/22/02, Jeremy Derr wrote: >also, you suggested that someone might use a blow dryer to dry off a >wet circuit board. this is incorrect, and horribly bad advice. the >added heat of the blow dryer can damage chips in the same way that >lingering with a solder iron while soldering might --
I suggested using a hair dryer. The air doesn't get hot enough to cause any harm. Circuit boards are soldered in ovens that get hot enough to melt solder, and semiconductor die safely withstand these temperatures, provided they are of short duration. Can you imagine what those temperatures would do to your hair? Semiconductors are rated for continuous operation at die temperatures over 100 C, the boiling point of water. You won't be able to get these temperatures out of a hair dryer. Be careful with industrial hot air guns, some of them get hot enough to melt solder, indeed they are useful for removing surface mount chips. If you want to dry the board quickly, bring to just over 100C (212F) with an industrial hot air gun. For the cognoscenti only! You will be guaranteed to have no liquid water on it. If you get it too hot you can start melting solder, which you don't want to do. > and there's an >added risk, too. the air flowing out of many blow dryers may have a >slight electric charge. some chips are not tolerant of static >electricity. strike that. MOST chips are not tolerant of static electricity. Static damage only occurs when a static charge sparks to a component lead and causes a breakdown of an insulator, say an oxide gate on a CMOS transistor. Blowing hot air on a board is simply not going to this, unless you are using a hair dryer connected to a telsa coil that throws out sparks to your board. The typical cause of static damage is a human walking across a carpet and drawing a spark from a component lead to their finger. If you are holding the board in your hand with skin contact to the circuitry as you dry it with a hair dryer there is no possibility that a charge can build up in the board relative to your body. > why do you think most service techs ground themselves thoroughly before handling electronics components? A good practice indeed, unless of course the board is charged and the tech is not. Remember, it is the relative difference in charge that causes the spark, not the absolute charge. When transferring boards from person to person, touch the other person skin to skin before touching the board. If two people walked across the carpet in a heated room on a dry winter day and are charged to the max, they can still safely pass a board to each other provided they are both at the same charge, which is first established by skin to skin contact. Paul -- G-Books is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Refurbished Drives | -- Check our web site for refurbished PowerBooks | & CDRWs on Sale! | Support Low End Mac <http://lowendmac.com/lists/support.html> G-Books list info: <http://lowendmac.com/lists/g-books.html> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/g-books%40mail.maclaunch.com/> --------------------------------------------------------------- >The Think Different Store http://www.ThinkDifferentStore.com ---------------------------------------------------------------
