Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!olivea!mintaka!bloom-beacon!eru!hagbard!sunic!fuug!news.funet.fi!funic!nntp.hut.fi!nntp!iisakkil From: iisakkil@vipunen.hut.fi (Mika R Iisakkila) Newsgroups: sci.electronics Subject: Re: Surface mount advice wanted Message-ID: Date: 28 May 91 17:02:49 GMT References: Sender: usenet@nntp.hut.fi (Usenet pseudouser id) Organization: Otaniemi Underground Broadcasting System Lines: 58 In-Reply-To: eric@zen.maths.uts.edu.au's message of 28 May 91 15:12:00 GMT Nntp-Posting-Host: vipunen.hut.fi eric@zen.maths.uts.edu.au (Eric Lindsay) writes: > Does anyone have any hints and tips on > hand soldering stuff that small? (I made up a couple of ...little... > boards this weekend, and holding down chip resistors with a toothpick > while you solder them with a 40 watt iron didn't impress me one little > bit.) After spending 4 months building prototypes and repairing existing gadgets that were almost entirely SMD, I think I can give some advice on hand soldering :-) First of all, you'll need the thinnest solder wire you can find (you have probably noticed that already...). I found 0.5mm wire to be thin enough for soldering 44-pin PLCC-cased microprocessors and similar beasts. A small soldering iron with a needle-like tip is a must too. When you try to solder in a SMD resistor, transistor or some other small component, melt some solder on one pad on the PCB first (without the component). Then, hold the component at place with pincers and just warm the solder bubble until the component drops at place. After this, it is easy to solder the other contacts on the component. Try not to roast the component itself, SMD resistors easily crack and start malfunctioning in normal thermal stress during use. Larger components, like ICs, are a bit harder but they can be soldered with the same technique. Solder two pins at the opposite corners of the IC first to hold it at place while working on the other pins. It is very easy to make almost invisible short circuits while hand soldering (the machines make even more of them...). PLCC cases (with pins that bend underneath the case) can suck the offending solder bridge so far that it's impossible to find it without an ohmmeter. A clocksmith lupe (or better yet, a stereo microscope) is invaluable while debugging. Then, after you have found the short circuit, you'll notice that it's difficult to fix it while the component is in place (although solder removing wick or-whatever-it-is-in-English may help). Small components (less than 4 pins) can be removed by heating them directly with a soldering iron and _carefully_ pushing them with a small screwdriver. Excessive force will break the PCB because the board and the miniscule copper traces don't expand evenly with the heat. If you break the PCB, you're in big trouble. The components are also easily destroyed by the heat, so it's better not to reuse them unless you're short of cash. Larger components are impossible to remove with a soldering iron without ruining the PCB. The only way (that I know of) is to turn the board upside down and heat the pins of the bloody chip with a hot air blower until the chip falls off (don't push it, just shake the board gently). It's much easier than it sounds. The chips will survive the handling too, if you have an accurate blower and torch just the pins of the chip. Most of the SMD components are actually amazingly tough (they must be, to live through the IR oven in automatic soldering). I could tell you something on the availability of components in Finland too, but I guess that wouldn't be very useful to you... Have a steady hand - regards, Mika Iisakkila