Retro Challenge update #4

Today I finished the PCB layout of the HD6309 computer! As expected, it took longer than expected to route all the signals of the board. To make life a little easier, I did the pin swapping dance in KiCAD more than a few times, especially on the ATF16V8 GALs. This is the final design:


The board is a mix of through-hole and surface mount (SMD) parts. Many hobbyists shy away, almost religiously, from using SMD. After practicing a few times, I can solder 0805 resistors and capacitors, and QFP packages down to 0.5mm (I haven’t tried smaller yet) pin pitch with ease! Full disclosure: I have had cataract surgery on both eyes and have trembling hands; if I can do it, you can too. All that is needed is a cheap hot air station, such as the Atten 858D, some tweezers and flux. Having solder paste in a syringe makes solder 0805 resistors and capacitors easier. I don’t use a microscope — I only have small monocular that I use for final inspection.

To solder the LQFPs and TSSOPs, I use the following steps:

  1. apply flux to the PCB.
  2. using a regular iron, apply solder to all the pads.
  3. align the part with the pads and use a regular soldering iron to tack one or two pins to keep the part in place.
  4. if needed, check the part alignment with a magnifying glass and repeat step 3 if alignment is not to your liking.
  5. apply flux to pins of IC.
  6. heat the part and PCB with the hot air station until all pins have been soldered.
  7. if needed, check pins using a magnifying glass.
  8. touch pins that haven’t been soldered properly with a regular iron (rarely needed).

I don’t use the drag soldering technique or an SMD stencil with solder paste because I find it bends the pins or produces solder bridges.

This static RAM expansion board was done using the technique outlined above:sram_example

Up next

The board is on its way to and will be returned to me on the 27th of April, which leaves very little time to populate the board and test everything :-/

For the time being, I’ll concentrate on programming the ATF16V8B GALs, write an emulator and create a UART bootloader for the HD6309 computer.

Hmm, I should really think of a name for this project.. Any suggestions?


4 thoughts on “Retro Challenge update #4

    • Hi Remco,

      Thanks for the tip! I didn’t know that. Luckily, my entire workbench is on a master switch that I turn always turn off.
      To make sure I do, I have a radio on the same circuit that is always on.

  1. Hope it works! Looks good, but I’ve be nervous without breadboarding / veroboarding it. Using GALs is a good move, because it pushes more stuff to the realm of ‘software.’ Using 74xx glue logic instead would have been quite a commitment.

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