Raspberry Pi A, User Manual, Page: 232 / 314

P A R T I V
H A R D W A R E H A C K I N G
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This process of tinning the tip protects it against damage and ensures that it will efficiently trans-
fer heat onto the surfaces to be soldered. Failure to properly tin the iron’s tip is one of the most
common causes of bad solder joints. You may need to repeat this process more than once if you’re
soldering a lot of connections, and you’ll need to do it again at the end of the soldering session. In
general, if the tip of the soldering iron loses its shiny coating, repeat the tinning process.
With the iron prepared, it’s time to start soldering. Place the items to be soldered—such as a
printed circuit board and the legs of a component—into the work stand, and ensure that
you’ve got a good view. Extend a length of solder from the container or reel, and begin to
solder the components using these basic steps:
1. If you’re soldering through-hole components into a printed circuit board, stripboard or
similar through-hole board, place the legs of the component through the holes and
bend them outwards so the component doesn’t fall out when the board is flipped over.
2. With the board secured in the work stand, push the tip of the iron against both the
component and the copper contact on the board. It’s important that the iron touches
both items: if the iron is only in contact with one, the finished joint will be bad.
3. It takes only a few seconds for the area to heat up. Count to three, and then push the
solder against the component and copper contact (see Figure 13-6). If the solder
doesn’t melt, withdraw it, count a couple of seconds more, and then try again. If it still
doesn’t melt, try repositioning the soldering iron.
4. As the solder flows, you’ll see it drawn down into the hole in the board. This is an indi-
cation that the area is hot enough for a good solder join. If the solder floats, it indicates
that the area is not yet hot enough.
5. Remove the solder from the join first, followed by the iron. (If you remove the iron
first, the solder will harden and leave your spool of solder stuck to the contact!)
If all went well, you’ll be left with a solid solder join that will last for many years. If not, don’t
be disheartened—just press the iron against the join to reflow the solder, and use the desol-
dering wick if you need to clean up a spill or any excess. A perfect solder joint should have a
shape somewhat like a volcano, rising up from the surface of the board to meet the leg of the
component.
Never leave the iron in contact with the parts for more than a few seconds. This is especially
important when soldering heat-sensitive components like integrated circuits, which can
be damaged by prolonged contact with a hot soldering iron. If you’re using a temperature-
controlled solder station, make sure the temperature is set to an appropriate level for the
solder being used (check the solder’s packaging or data sheet for details).