Subject:
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Re: Soldering (fwd)
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sun, 18 May 1997 22:45:19 GMT
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Original-From:
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Tom Collins <tcollins@calsun.gtri!stopspammers!.gatech.edu>
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Viewed:
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1411 times
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Often novices miss the single most fundamental point about soldering:
you don't use the iron to melt the solder (99% of the time) -- you heat
the component leads and let them melt the solder.
To initially transfer heat effectively to the leads, a small amount of
solder melted directly on the tip is helpful, providing a "wetted"
surface, but after that, you should flow solder directly into the joint,
preferably off of the heated component leads. If you flow solder directly
off the iron into a joint with cold leads, there will be poor bonding at
the leads. This is why it's called a cold solder joint, not because it
looks "frosty."
For some components with thick leads or other large thermal mass, you
really need the higher wattage. It's easy enough to drip hot solder off
the tip onto these components, but the joint will be cold, even though it
may appear OK on the surface. Often, the best indicator is the shape of
the joint -- good joints usually have smooth concave fillets from the
board surface to the lead tip, and solder flows through at least flush to
the other side of the board. Cold joints usually look more like balls of
solder, and often little flows through.
To avoid delamination and burnt circuit boards, the key is to transfer a
lot of heat fast, finish the joint, and get on to the next joint. Small
irons can't provide the heat, and novices compensate by leaving them on
the joint for a long time or cranking up the temperature (if it is
variable). Both of these techniques are likely to damage the board. (Heat
is not equivalent to temperature.)
King, Terry writes:
> Shane is right, you'll find using very thin solder works much better.
> Along with a fine tip, you'll want to use a low wattage iron. More is
> not better here. I've used an 18 watt "Princess" soldering iron for
> years. It is excellent for this kind of work. Occasionally check the tip
> to make sure it's tight. If your having problems getting it hot enough,
> a loose tip can be the culprit.
>
> Another important key to good soldering is cleanliness. I use a damp
> sponge to occasionally wipe the tip off. (also, keep the tip well
> "tinned" with solder) All parts and surfaces need to be clean as
> possible. This is not usually a problem if your working with new parts.
> But keep handling to minimum, especially bare copper areas on the board.
> Even the natural oils from your hands and fingers will deteriorate the
> clean copper surface.
>
> A good soldered joint will look "shiny". A bad joint has a dull "frosty"
> look about it. In fact, it is referred to as a cold joint. Cold joints
> may work at first, but their a time bomb waiting to cause trouble (
> intermittent connections that will drive ya crazy). They often result
> from movement while the solder is solidifying.
>
> Cleaning the rosin away after a job can make the difference between a
> professional or an amateurish looking hack job. (That single point once
> landed me a job) You can use alcohol or other rosin cleaner.
>
> One other thing, heat is an enemy to small components. Stay on it only
> as long as necessary. If a soldering joint is going rough, fall back and
> figure out why. Let it cool, and get it shiny clean before attempting
> again. Also watch out for the copper "runs" on the board. The copper is
> glued to the board and too much heat too long will cause them to come
> loose.
>
> Don't be intimidated by it, it can actually be enjoyable. Just be
> careful. When you burn yourself (sorry, but it usually happens sooner or
> later), run your hand or finger under very cold water for several
> minutes. The recovery from the pain is shortened.
>
> Hope this helps!
> Terry King.
> Terry.King@fmr.com
--
Thomas R. Collins tom.collins@gtri.gatech.edu
Senior Research Engineer (404) 894-2509
Georgia Tech Research Institute
Electronic Systems Laboratory
400 Tenth St. NW, CRB 553
Atlanta, GA 30332-0840
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