The FPGA for these boards is in a QFN32 package which is possible, but very difficult to solder with an iron. It is much easier to use the solder paste reflow method to assemble these boards.

The following tools and supplies will be necessary to reflow a TinyFPGA A-Series board:

• Lead-Free Solder Paste
• Solder paste squeegee. A credit card works but I really like this Stainless Steel Solder Paste Squeegee.
• Precision Tweezers for placing parts on the board
• Reflow Oven or a simple electric griddle (if you use an electric griddle, try using low-temp solder paste).
• A flat surface to use for applying the solder paste. I picked up a one foot squared piece of wood for this and it works well.

Order parts and supplies needed specifically for the TinyFPGA A-Series board:

• TinyFPGA A-Series Solder Paste Stencil
  • You'll need to generate the gerber files and upload the solder paste layer. Either stainless steel or polymide stencils should work.
• TinyFPGA A-Series PCBs
• Parts for the TinyFPGA A1 or A2
  • Mouser is a great place to get the parts from. Might as well make the A2 board if you are going through all this trouble :)

Once you have all the tools, parts, and supplies you can assemble board(s). First step of assembly is applying the solder paste. Solder paste tends to only last a couple hours before you reflow it, so you should plan on being able to assemble and reflow the board(s) in one sitting.

Before you can apply the solder paste you will need to securely mount the empty PCB onto a flat surface. Placing scrap PCBs of the same thickness around the TinyFPGA Ax PCB works well. The reason we do this is because the solder paste stencil is larger than the PCB and we want it to lay down flat while we apply the paste.

Align the solder paste stencil with the pads on the TinyFPGA Ax board and tape it down. Make sure it's flat against the surface of the board and is well aligned.

Apply solder paste to the top of the stencil and use your squeegee to wipe the paste across all of the holes in the stencil. This is a lot like silk-screen printing. Holding the squeegee at a 45-degree angle helps push the paste into the holes and maintain a flat profile against the stencil.

Hopefully one pass will fill all the holes with a uniform amount of paste. if some holes do not have enough paste you will need to make additional passes until they are even.

Remove the stencil from the board. You should see neat squares and rectangles of solder paste on all the pads. Referencing the component placement layer of the PCB design, use your tweezers to place all of the components in the correct locations. Pay close attention to the orientation of the FPGA and its alignment with the pads. It may be useful to use magnifying glasses to ensure alignment is correct.

I find it is easier to place all the components of each type before moving on to the next component type. This makes it very easy to assemble multiple boards at once.

If you have a reflow oven like the Controleo2, you can simply place your board(s) in and press start.

If you have an electric griddle or hot-plate you'll need to keep a close eye on the solder paste. Start on a low temperature for the griddle and let the boards soak for a minute. Then increase the temperature to max and watch for the solder paste to reflow and become shiny. Once all of the solder paste is shiny and has reflowed onto the components you can turn off the griddle. Let the board(s) sit until they have cooled down.

Reflow for 0603 parts and the QFN32 FPGA should be pretty reliable, but issues can arise. The 0603 parts may tombstone or become otherwise unaligned and need to be fixed by hand. A soldering iron and wick will work well for this.

If the FPGA IC is not aligned it will be more difficult to fix. A hot-air rework station and plenty of flux is recommended to fix issues there.

The pins are through-hole parts and must be soldered by hand.