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PICAXE PRIMER

It may seem odd that both boards in the photo only have two four-pin headers for insertion into a breadboard, but for some reason eight of the DS3231’s 16 pins do not connect to anything.

After you have finished this article and practiced a little SMD soldering on your own, you may also want to try your hand at soldering SOIC devices. If so, there are literally hundreds of SOIC to DIP adapters available on eBay. Also, I intend to discuss the DS3231 in detail in a future installment of the Primer, and I’ll add a custom PCB to my site for use with that particular article.

If you’re familiar with SOIC chips, you know that the pin spacing is 0.05 inches, which is exactly half that of the DIP chips we’re used to using. Of course, there are many sizes of SMDs with pins spaced much more closely than 0.05”, but soldering those devices generally requires special techniques and/or fairly expensive equipment. We won’t be discussing those devices, but there’s a wealth of information online; just search for “surface-mount soldering tutorial.” If you do some online searching, you will quickly learn that many people use fairly expensive equipment, including hot air rework stations and even surface-mount reflow soldering ovens that can cost hundreds of dollars. However, if we limit ourselves to SOIC devices and the larger sizes of passive devices (resistors, capacitors, LEDs, etc.), we really don’t need to spend much at all to get started with SMDs. The equipment listed here is all that’s required.

■ FIGURE 2. Tweezers for SMD soldering.

• A soldering iron with a long, thin tip. I use a Weller WESD- 51 temperature-controlled soldering station with an ETS long conical tip, but any soldering iron will work; it’s the long thin tip that’s important.

• A spool of very thin solder.

Radio.Shack sells a small spool of 0.015 inch diameter solder (catalog #64-035) that’s perfect for soldering SMDs by hand. Larger spools of the same diameter solder are also available online.

• Desoldering braid. In the event of an accidental solder bridge between two pins, it’s helpful to have a roll of desoldering braid (solder wick) to remove that bridge. Again, RadioShack sells a small spool (catalog #64-2090), and solder wick is also readily available online.

• Tweezers. Most SMDs are too small to manipulate by hand or even with needle-nose pliers, so tweezers are a necessity. To get started, I would suggest a pair of regular straight tweezers and a pair of locking straight tweezers. (Locking tweezers must be squeezed to open their points, so they are useful as temporary clamps to hold a component in place as it’s being soldered.)

Figure 3 shows the size comparisons of the SMDs that we’ll be discussing in this article. The decimal rule in the photo is graduated in tenths of an inch (with 0.02” subdivisions). In order