AVR XMegaA4 breakout

Here at last is the breakout board I designed for the Atmel XMegaA4 a while back. It’s a simple thing, just headers, a crystal, a ISP programming connector, and various power supply and analog voltage reference filters. The board is sized to fit within Seeed Studio’s lowest cost bracket for their PCB service. The board:

Mostly surface mount parts…don’t let that scare you away, they’re not that hard to deal with…easier than through hole parts, in some ways. You don’t need to go buy solder paste, you do need some flux. The procedure:

  1. Apply flux to the surface mount pads with toothpick.
  2. Bead solder on the pads. If it gets sticky and forms peaks, use more flux. Get too much solder on, wipe it off with the soldering iron. You don’t need much, just enough to form a solder joint, and too much will make things difficult.
  3. Apply more flux…it will not only help solder flow, it’ll hold your parts in place (like solder paste does, but cheaper). Don’t apply too much…it’ll liquefy and pull your parts off their pads before the solder melts. You want the solder beads sticky, you don’t want your parts swimming in flux. Use toothpicks to remove excess flux.
  4. Tack the parts down on the fluxed solder-beaded pads, nudging them into place with toothpicks. Too large/round of a solder bead will make this difficult. Some troublesome parts are the inductor and the crystal load capacitors, which have a tendency to get pulled off their pads.
  5. Reflow the board. You want to heat the whole thing up so the solder melts. You’ll see parts shift into place when this happens. Electric skillets and toaster ovens are popular approaches to this, I’ve used a cheap hot air gun for my first two and a skillet for the third, and recommend the skillet (with a bent piece of aluminum sheet metal under the board to help spread heat and help with placement and removal). This board’s small enough to easily heat evenly with this approach. If using the hot air gun, approach the board slowly with the airstream to get the flux melted…this will help hold the parts in place better, and keep them from blowing away.

You’ll want to omit or remove the capacitors on PA0 (C10 and C11) and PB0 (C9 and C12) if you need to use those pins for digital signals of any significant speed, they are filters for external analog references. L1 can be replaced with a short wire if you don’t need the extra filtering on the analog supply.

The parts list:

Part Value Device Package
C1 100nF 0805
C2 15pF 0805
C3 15pF 0805
C4 100nF 0805
C5 100nF 0805
C6 10uF 0805
C7 100nF 0805
C8 10uF 0805
C9 100nF 0805
C10 100nF 0805
C11 4.7uF 0805
C12 4.7uF 0805
IC1 XMEGA32A4A TQFP44
JP1 PINHD-1X19 1X19
JP2 PINHD-1X19 1X19
JP3 PINHD-2X3 2X03
L1 27nH IMC0805ER27NJ01 L2012C
Q1 4MHz ABL-4.000MHZ-B2 HC49/S
R1 10k 0805

Most of the parts were available from Mouser, though I went to Avnet for the XMega32A4. The board should work fine for others of that series, of course.

And finally, the Gerber files:
xmegagerbs.zip

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