Prototyping with matrix board

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Super Juno being prototyped with single sided FR4 tinned matrix board by Craig Barnes, Feb 2023.

Prototyping with matrix board is quicker than designing a PCB, having it fabricated inexpensively, assembling it, testing it, and then repeating those steps if changes are needed. Equipment made this way is adequate for testing and evaluation but is not intended for production. This method is suitable for audio applications, while circuits operating above 100 kHz should be prototyped using the ground plane method.

Tools

  • A typical 25 Watt soldering iron and stand
    A typical 25 Watt soldering iron and stand
  • Economical Plato 170 Flush Cutters.
    Economical Plato 170 Flush Cutters.
  • The recommended type of wire stripper.
    The recommended type of wire stripper.
  • An awl.
    An awl.
  • Wire stripper: For stripping 30 gauge wire with marked measurements for consistent stripping lengths, e.g. CK 330013.
  • Snips: pack of cheap ones to have replacements when they break.
  • Needle nose pliers: useful for bending and straightening leads.
  • Awl or hole punch tool: useful for pushing wires into shape, with tip fine enough it can be inserted into a hole to keep wires out of the way from the soldering.
  • Soldering iron: 25 Watt e.g. Antex XS25 (420 °C nominal tip temperature). A chisel tip transfers heat the fastest.
  • Soldering iron stand: with damp sponge for tip cleaning, e.g. Antex ST4.
  • Solder sucker: For removing solder.
  • Desk fan: To blow the flux smoke away.
  • Magnifying glass: for inspecting components and solder joints.
  • Desktop magnifier: for detailed work, particularly useful for more precise soldering such as SMD parts.
  • Multimeter: To test continuity.
  • A transistor tester is useful to confirm component values.
  • Box cutter and flat file: to score along a line of perforations, snap off the excess material, and smooth the edge.

Materials

  • Typical 9 x15 cm single-sided FR4 matrix board, with 0.1-inch spaced holes and isolated copper pads.
    Typical 9 x15 cm single-sided FR4 matrix board, with 0.1-inch spaced holes and isolated copper pads.
  • 30 AWG PVC insulated tinned copper wire.
    30 AWG PVC insulated tinned copper wire.
  • Good quality Sn60Pb40 rosin cored, 0.8 mm solder.
    Good quality Sn60Pb40 rosin cored, 0.8 mm solder.
  • Wire: B-30-100. It's called 'Wire wrapping Wire' but it isn't really that, it's PVC insulated 30 AWG solid core tinned copper wire, (maximum 0.86 amps).
  • Tinned copper wire: 22 or 24 AWG for wiring the ground plane.
  • Short wires trimmed from component leads are also useful for making smaller connections.
  • 0.8 mm solder: 60/40 tin/lead rosin core.
  • Single sided tinned or plated FR4 matrix board. FR2 (SRBP) is weaker than FR4 and bare copper oxidises and makes good soldering difficult.

Method

Matrix board here refers to FR4 or FR2 with (approximately) 0.8 mm holes and isolated solder pads at 0.1 inch (2.54 mm) spacing.

Good practices for assembly and wiring

Following accepted good practice will make it easier if you need to troubleshoot later:

  • Cut the board to size and drill any holes and so one before soldering anything into place. Do not inhale the dust from FR4, as it can be harmful to your health.
  • Use a large enough board unless you need something small, so you don't waste time making components fit. This will make it easier to replace or add components later if needed.
  • Fix components in the PCB from the smallest and lowest profile components such as wire links, diodes and resistors.
  • Inspect your soldering for proper wetting of pads, leads and pins. Ensure there are no cold solder joints or unwanted solder bridges.
  • Trim the excess leads from after soldering, don't cut into the solder.
  • Verify the placement and connections of each component against the schematic.
  • Use a heavier gauge wire for higher currents. For example, 22 or 24 gauge instead of the 30 used for for control and signal voltages.
  • Without a ground plane (a large copper area on a PCB that provides a common ground), you should connect ground connections directly to the power supply’s ground to ensure good electrical performance and reduce noise.
  • As much as possible place components so that all pin 1s, colour codes, text and polarities face the same direction, e.g. reads left to right and top to bottom.
  • Fitting the wires flush to the board and running them only vertically and horizontally makes the wiring neater. Keep it tidy as you go along.
  • As much as possible avoid wires on the component side and components on the solder side.
  • Don't place any wires on the component side or components on the solder side.

Layout

This is important to get the layout correct because once you've committed to the build it's difficult to make any changes. Arrange the components on the board to determine the layout.

  • Initial placing of components to work out the controller board layout.
    Initial placing of components to work out the controller board layout.
  • The committed controller board layout.
    The committed controller board layout.

Bear in mind the space that the finished board will have to fit into, connections to power, other boards, input/output, to or from the front panel and where access might be required. Place connectors and chips to facilitate wiring. Grouping components neatly will make wiring easier to follow. Try to follow a layout similar to the schematic although the physical layout doesn't need to exactly match the circuit layout, and sometimes moving components can simplify the wiring. Take a photo of the layout, it might be useful later.

The arrangement and connections of electronic components on a matrix board can be exactly replicated in PCB design software.[1]

Component soldering

Sandwich components in place with an empty board before turning the board over to hold the components in place. First, tack solder the components and make sure they're properly seated before soldering fully in place. Soldering components in order from the lowest to the highest reduces the risk of obstructing access to the smaller parts with the larger ones and makes it easier to place and solder each component. When you need to bend component leads to make a connection, do so before tack soldering them in place.

For easier orientation when working on the solder side use permanent marker to highlight significant points, e.g. IC pin 1 with blue, red for VCC and black for ground.

Connection soldering

  • Example wiring: Three 4051s, on one a decoupling capacitor, with VCC, GND, and C wired in sequence with continuous wire.
    Example wiring: Three 4051s, on one a decoupling capacitor, with VCC, GND, and C wired in sequence with continuous wire.
  • Detail of the partially wired controller board.
    Detail of the partially wired controller board.

First, connect the tinned copper wire ground lines and any directly attached components (e.g., decoupling capacitors). Next, connect the other power wires, followed by the remaining wires, typically from the shortest to the longest, to manage wire routing and minimise interference.

With connections from discrete components bend the leads over so they meet the connection and solder together. For example with a 100 nF decoupling capacitor on a DIP logic IC, insert the capacitor in the hole above pin 16 (VCC) of the IC or IC socket, bend the other lead over towards pin 8 (GND) and tack solder the capacitor in place, bend the first lead over to touch pin 16, off the excess length of lead and solder the one capacitor lead to the pin 16 and connect the other to pin 8 with a slight solder bridge.

Cut the insulated wire wrap wire to the total length. Measure the lengths between component pins/leads add a small amount of length for routing. Part the insulation from the conductor at those lengths. Tin the conductor and solder tack it onto the component pin or lead. Soldering from one exposed conductor to another, first tinning each. Flex the wire as little as possible to avoid breaking the conductor.

It's easier to follow connections with different coloured wires. At a minimum use different colours for different voltages, e.g. orange for +12 volt, blue for -12 volts, red for +5 volts, yellow for +3.3 volts and white for everything else. Use the heavier gauge uninsulated tinned copper wire for ground connections.

Mark off the connections on a schematic to ensure every connection has been made.

  • A selection of SMT to 0.1" DIP breakout boards, these interface with standard 0.1" headers.
    A selection of SMT to 0.1" DIP breakout boards, these interface with standard 0.1" headers.
  • Offcut decoupling capacitor leads used as loops to route wires.
    Offcut decoupling capacitor leads used as loops to route wires.

Off board wiring

Wiring between the board and elsewhere, such as front panel components, should be flexible. Use regular stranded hookup wire as required or 1.27mm pitch ribbon cable.

Cleaning flux residue

With 60/40 lead/tin, rosin cored solder, shortly after soldering because the residues quickly harden, clean flux residue off with isopropyl alcohol and stiff brush through lint-free cleaning tissue (e.g. Kimwipes).[2][3]

Check connections

Visually inspect each solder joint for a secure connection. Ensure there are no cold joints or solder bridges. If you're uncertain use a multimeter to test for continuity.

See also

References

  1. ^ Matrix Boards, Talking Electronics
  2. ^ Cleaning Up Your PCB by Dave-T, Instructables, 2012
  3. ^ Clean Up, CuriousInventor

External links

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