This process involves removing the components from their packaging (e.g. tape) and placing them on the board, either with solder paste or wire.

Preparing to solder

Many of the smaller surface mount components are not marked, or a static and/or moisture sensitive, so it's important not to unpackage them until you're ready to place them on the board. It's helpful to review the packages and mark off which components are on the bottom of the board, so that you only unpack the components for each side as it's assembled. The PCB indicates which components go where. Be sure to check the schematic against the packaged components as you go.

Polarised components

The diodes D1-4 and LEDs BT1,2 CAN1,2 POWER, RX,TX LED are all polarised, which means that like batteries, they only work one way around. The pads intended for the component's cathodes are marked with a line or dots closest to the pad.

Diodes

Orient the diodes such that the faint white line that runs along the edge of the diode is on the left pad (when looking at the top side with the 12P connector at the top). The PCB has lines for each of the diodes that are closer to the pads where the lines should be.

LEDs

These are also a kind of diode (Light Emitting Diode), so they're also polarised. However, the markings to indicate polarity vary on these depending on the part (different colours are different parts, in this case). Some are marked on the top with green dots or lines, or on the bottom with T shaped marks. Refer to this page and compare to your components as you place them on the board. All the diodes have the cathode on the right pad of the board, nearest their corresponding resistor (Rs 1-5, 16, 17). Refer to this site for pictures and examples showing the various markings used.

Three soldering phases

As the PCB has components on the surface of both sides as well as connectors that penetrate holes in the board, building the module proceeds in three stages:

1. Top side surface mounting
2. Bottom side surface mounting
3. Through hole component mounting

Top side assembly

"Skillet" reflow method (recommended)

If you have access to a hot plate and an old skillet or frying pan with a heavy base you don't mind never using for food again, you can quickly solder all of the top side surface mount components to the pcb without having to individually solder them. You still have to place them manually using solder paste, and then heat the board on the hot plate until the solder melts. As soon as all the solder melts, switch off the heat and allow to cool before disturbing the board. The components may move if the solder is still liquid and the board is jarred/lifted. The button and mic socket are particularly vulnerable during this cooling period. There are tutorials and videos online that explain this method, for example.

You can only use the reflow method for one side of the board since the other side can't be heated once components are attached. Since there are more components on the top side, this is more worthwhile as a time saver.

Hand soldering (alternate)

If the reflow method doesn't suit, place the components on the PCB and solder, starting in the centre and working outwards.

"Drag" soldering

This technique relies on the application of flux and the surface tension of molten solder to only adhere to PCB pads and component legs or terminals that are intended for attachment. By dragging your soldering iron across the pads/legs of an IC or module whilst it's held in place, the flux and solder work together to only adhere to the each pad, and not create bridges between them (as long as you haven't added an overwhelming amount of solder).

Bottom side assembly - hand soldering

This uses the same technique as for hand soldering the top side of the board.

Through hole components - hand soldering

This is a simple process of placing each header, socket or connector one at a time and soldering using wire solder. All through hole components are soldered to the bottom side of the PCB. Solder the 12P connector last, after attaching it with the specified screw/nut sets.

Amplifier shield (optional)

Because of the small number of components, it's probably not worth the setup effort for reflow soldering the amp shield. Simply place and solder all the top side surface mount components, followed by bottom side SM components, then lastly the header connector (through hole). The same process and advice as outlined above for the main PCB applies to the shield.

Visual inspection/hardware check

To prevent damage to your computer, Ardiuno or AVR-ISP unit and most importantly your car's electronic systems, you should carefully inspect your assembled PCB(s) on both sides for correctly placed components and solder bridges. Before plugging the module to any power source, USB cable or your car, you should also test for shorts between Vcc and Gnd pins on each of the headers and the 12P connector using an Ohmmeter/multimeter.