Page 191 - Make Your Own PCBs with EAGLE from Schematic Designs to Finished Boards

Soldering IC Packages

Soldering ICs is very similar to the process just described. The only real difference is that you may
well want to clean up the connections using soldering braid, as shown in Figure 7-15.

Packages with Hidden Connections

Some IC packages have inaccessible components on their underside. To solder these, put paste on the
pads as normal, and then while you hold the IC in place with the tip of your tweezers, play the hot-air
gun over the whole IC socket until you feel like the solder has melted. If you do this for too long, you
may damage the chip.

Using a Reflow Oven

By far the quickest way to solder a SMT board of any complexity is to use a reflow oven. It has the
advantage that you only have to place the components on top of the solder-pasted pads. Once this is
done, the whole board is cooked in the reflow oven, soldering all the components in one go. What is
more, once you gain confidence, you can cook a whole batch of PCBs in one go. In any case, the
cooking process only takes a couple of minutes.

If you have a board that contains both surface-mount and through-hole components, then solder the
surface-mount components first.

Get Everything Together

Solder paste will dry out after maybe half an hour, so before you do anything, make sure that you have
all the components that you need and that you know exactly how they will fit onto the PCB (which
way around LEDs and so on are to be placed). I find it useful to actually put the components onto the
board without any paste just to make sure that I have everything I need. I have the board on a plain

sheet of paper, so when I am sure that I have everything in place, I can move everything off to one
side, keeping the same relative positions of the components.
Another approach is to use labeled bottle caps or even just circles on a sheet of paper labeled
with the component part and/or value.

Applying Solder Paste

The low-tech way of applying solder paste is the same as I described earlier when I looked at using a

hot-air gun. Simply go round the board adding a little blob of solder paste onto every pad on the PCB
using the syringe dispenser. This is the time-consuming bit.
The alternative to using a syringe is to use a stencil. Many PCB manufacturing services will also
(for a small extra fee) supply you with a stencil. This can be made of thin steel, Mylar, or other