[sdiy] Moving to Surface Mount - lots of questions
Matthias.Herrmann at jeppesen.com
Tue Dec 6 12:10:11 CET 2011
> On 06/12/11 07:45, Mike Beauchamp wrote:
> > Hey all,
> > after assembling a few PCB's with a few hundred resistors, I've been
> > thinking about moving to Surface Mount for my next project. Please
> > convince me, or talk me out of it :)
> I haven't got the patience, dexterity or enthusiasm to sit and fiddle
> with awkward through-hole components any more. They're just plain
> horrible to work with.
Well put. I use SMT for one-offs as well. I find hand soldering SMT much more comfortable than TH, and replacing a resistor is done much easier and faster than when using TH... however, I used 1206 only so far. Will have to try 0805.
> > Reliability: I know that repairing a through-hole board is easier for
> > most people, but is the reliability of SMT stuff on par with TH?
> Typically reliability is about the same. Many of my real genuine
> repairs (ie. a hardware fault, not "finger trouble" or misprogrammed
> equipment) come from replacing ceramic caps that have gone leaky - SMD
> and through-hole fail at about the same rate but SMD is far easier to
> Getting SMT chips off isn't as easy but if you're certain the chip has
> failed you just cut its legs away and wick them off with braid leaving
> the pads nice and clean. You can get special hot air rework tools with
> nozzles that fit over the chip shielding it from the heat and directing
> hot air onto the legs - this allows you to lift a chip off and solder
> back down in seconds.
> > Storage: Those SMD resistors are tiny! What are some good ways to
> > store 30-40 different values so they can easily be grabbed for
> > populating?
> They come in strips or reels of tape with little pockets containing
> individual parts. Write what the part is on the end of the reel in
> marker pen.
> > Toxicity: Soldering irritates my asthma, although my fume extractor
> > helps heaps. Does sticking solder paste into an oven cause similar
> > fumes?
> Again, I don't use solder paste and don't see the point outside
> production work. As with all soldering you should do it in a
> well-ventilated area. If your fan is a bit brutal it might blow some
> the very tiny components around, so be careful ;-)
> It's not synthesizer-related, but the Kanga Finningley software defined
> radio kit is all SMT except the sockets. It's an excellent first
> project, with everything laid out really clearly in the instructions.
> It's worth even just grabbing the PDF of the assembly instructions off
> the site for a read.
> Gordon JC Pearce MM0YEQ
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