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General advice for assembly

Warning

This a VERY COMPLEX project (especially the computer board, now with over 1000 pads to be soldered). This is NOT an ideal project to learn soldering techniques! You've been warned... In any case, take your time, read throughfully all the directions FIRST, then start building step-by-step as indicated -- and be patient!.

Danger

Soldering is a risky activity! From severe burns to toxic fumes inhalation and MANY other hazards! Make sure you follow ALL of the Safety Advice stated on this document BEFORE attempting any soldering!

Tools and materials

  • Obviously, you'll need a soldering iron. Doesn't need to be a fancy one, but you'll definitely need a very fine tip -- some people prefer the chisel-shaped ones. Temperature regulation is not essential, but might be helpful -- some pads are connected to broad ground planes, which do "stole" quite a bit of heat from the iron. In case a fixed power iron is used, anything between 11 and 30 Watts seems suitable.
  • About solder (tin) itself, since these are very dense boards, fine (~0.5 mm) solder wire is recommended; however, thicker wire (~1 mm) may be useful for bigger joints (connectors etc). Depending on your local regulations and health concerns, you might use leaded or lead-free solder; the latter will need somewhat higher temperatures and may require some extra experience (this is NOT a project for newbies, anyway). Most solder wire nowadays include a flux core for easier soldering.
    • If leaded solder is to be used, make certain proper safety procedures are used: the use of gloves is recommended and, of course, do wash your hands throughly after a soldering session.
  • In any case, avoid inhaling fumes (actually from the flux core inside most soldering wires) by working in a well ventilated area or using a suitable fume extractor! This is a MUCH bigger concern than the use of leaded solder, by the way.
  • Flux is not essential, but sometimes helpful as it cleans the soldering surfaces. Fumes are harmful, thus check the ventilation advice above.
  • On projects of such complexity, errors are to be expected... Some way to desolder components is really helpful:
    • A desoldering pump is a cheap and relatively efficient way for casual desoldering.
    • A desoldering iron combines a regular iron with a (usually bulb-operated) pump, for convenience.
    • Solder wick is somewhat slower, but usually gives the best finish. Adding liquid flux to the braid may improve performance, especially when using lower-priced wicks.
    • For higher volume and utmost convenience, a desoldering station is best -- at a price.

Soldering advice

Besides following all of the safety advice, it is assumed that you already have some experience with soldering, as this is NOT a project for newbies... In any case, here are some general advice:

  • Place one or more components on the board (component side, where the outlines and values are silkscreened). Since soldering is done on the opposite side (where the component designators are the only silkscreen) you need some way to preclude components from falling off the board: adhesive tape, blue tack or even a suitable rag are helpful. Do NOT bend component leads as tempting as it may look, since that will make future repairs WAY more difficult.
  • Take your time on each solder joint! The usual procedure is: 1. Put the soldering iron heating both the pad and the component lead for a couple of seconds. 1. Apply the solder wire to the heated pad -- never on the iron tip! It should melt and flow easily around the pad, perhaps a tiny movement of the soldering iron might help. - Some pads are connected thru Vcc or GND to broad ground planes. Depending on your soldering iron and the particular tip, these pads might need a few seconds more to heat up properly. - If solder does not "embrace" the pad, but forms a "ball" besides the component lead, you probably need some cleaning on the surfaces. A previous wipe with Iso-Propyl Alcohol is useful in these cases, as is the use of flux before soldering. 1. After removing the solder wire, keep the iron for a couple of seconds to let the solder flow completely. Power and ground pins may need a longer time here; as a rule of thumb, keep the iron after soldering as long as it was preheating the pad before. 1. Check (at least from time to time) the quality of your solder joint: it should look shiny, not matte. Reflowing the solder joint (repeating the step above) will usually fix a rushed soldering work and may avoid future malfunction. Beware of short circuits between nearby pads!
  • For components with several pins (e.g. integrated circuits, sockets, resistor packs etc) it's best to solder two opposite corners first, check alignment and then continue with the remaining pins. If you are doing several similar components in a row, it's advisable to do one pin on each component, then the next pin etc, in order not to build excessive heat on the same component in a short amount of time.

Warning

Some components (especially semiconductors, like diodes, transistors and non-socketed integrated circuits are sensitive to heat! Solder them in a diligent, timely fashion. If you're having trouble with a pin, try another component and get back to that pin later -- or wait at least 10 seconds or so before resoldering it.

Build procedure

  1. First of all, get the desired PCB(s). Take note of the version number on the silkscreen, as well as the desired build option (if available), since both the BOM and required fixes may change between revisions! Don't forget to read the appropriate Hacks & Fixes document linked on each step-by-step page.
  2. Get the components as stated on the BOM, having into account the selected option and revision number, if available!
  3. Proceed with soldering, following each and every safety advice as stated above! For best results, fit the components in reverse height order -- that is, place shallower components first, and let the tallest ones for the end. Generally speaking this order results in:
    1. Horizontally mounted axial components, like resistors and diodes (e.g. on the Keyboard PCB)
    2. IC sockets and resistor packs. Very small capacitors are likely to be fitted now as well.
    3. Pin sockets and small connectors. Note that the expansion connector on the Durango PCB must be mounted absolutely flush!!!
    4. Vertically mounted components: resistors, diodes, transistors and small electrolytic capacitors.
      • Beware of polarity! Most resistor packs have a dot on the common pin, diodes and electrolytic caps have a band near the negative pin; for transistors, check the outline on the silkscreen. On LEDs, the negative side is the shorter lead; usually they have a flatter capusule near that lead.
    5. Pin headers are usually fitted now, depending on height.
    6. Power resistors (like R27 on the Durango·X PCB, if fitted) are somewhat taller and thus mounted afterwards. Ditto for taller capacitors -- just sort everything by height.
    7. Big connectors usually go last.

Danger

Once again, beware of polarity. A transistor fitted backwards will work weakly, a backwards diode won't work at all; but an electrolytic capacitor mounted the other way round will actually EXPLODE!!!.