Circuit Building 101

Step 6 Soldering

You've probably heard that solder should melted on the parts and not the iron tip. The catch is that a dry tip will not transfer heat very well. You need to have a little solder, called a heat bridge, between the iron tip and parts. Do this by either melting a small amount of solder on the tip before soldering ("tinning" the tip) or adding some solder at the junction between tip and work. Then melt solder on the opposite. It should spread out towards the iron tip and heat. A video is available with many more details.

Usually people say that joints should come out looking shiny, but this is only true for lead-based solder. Lead-free joints will have a duller surface finish, but still be perfectly fine joints. With either type, the solder should cling to or wet the surfaces, and not just sit on top of them. It should form a smooth ramp and feather out across the pad. The above link also has some galleries of good and bad joints.

It's a good idea to check the part for correct alignment after soldering one pin. Adjustments can easily be made at this point by reheating that one pin, but once multiple pins have been soldering, the part may need to be completely removed to adjust it.

Comments

[theprofessor]

no lead solder should also look shiny, the myth that it wont is perpetuated by the fact that you need a hotter tip to melt it and most hobby irons are not hot enough to cause it to wick properly.

[CuriousInventor.com]

So you do in fact get shinny joints with lead-free solder? Could I ask what brand you're using and what the chemistry is? kester seems to claim their K100LD solder comes off looking shiny, but my experience with most flavors is that the joints do in fact look duller. I am also basing this assessment from the IPC-610 Inspection criteria, which you can fortunately see a preview for. Check out page 5.

There are several sites like http://www.wiringharnessnews.com/Articles/1999/SOLDER/solder.HTM that have similar comments about lead-free:
"We will need to re-train our inspectors because the solder joints will look different. They will have a little more white in them; they will not be as bright and shiny, and we will not like what we see. The wet-ability and shape of the termination will look the same but the brilliance will be different."

In my testing, even cheap RadioShack 25W irons get hot enough, although you'll have to wait for a while in between joints for the tip to recover. Here's [http://www.kester.com/en-us/documentation/Alloy%20Temperature%20Chart%20(17Nov04).pdf Kester's alloy temperature chart] that shows a bunch of melting points for a variety of lead-free solders.

Please don't take this to be stubborn or argumentative, I'm just trying to provide references for my claims. It sounds like you've experienced / heard things differently, so I'd be interested in hearing the rationale / experience.

[ac-dc]

Lead free solder can certainly look shiney, it's shiney all over a computer motherboard I'm looking at. However, not all forumulations are shiney even if heated hot enough, they tend to have a whiter hazy sort of look to them. With these, no amount of heating will make a difference.

[ac-dc]

One mistake I often see people make is removing the soldering iron tip the moment it looks like the solder had wicked into the joint. Granted, some parts are especially heat sensitive but cooking the joint just a slight bit longer than the moment of wicking action will be far less likely to result in only partial or cold joints.