QFN fail

QFN packages and I could not get on the same page. I made one prototype of the V1 design with TMC2209 drivers and only 3 out of 5 worked. I had to re-solder them 3 times just to get them to talk to the CPU. I was just thinking these are just hard on my aging hands and eyes.

I found countless YouTube videos of people soldering chips with QFN packages and it all seems so effortless. I thought I just suck at this.

Yesterday I made some driver board for the V2 design with the 2209 drivers and again had to re-solder the chips, followed the YouTube guides and no luck. Two would move the motors in very strange way and consume quite a bit of power and one plain would not move.

Here is one of the dreaded beasts

I was ready to give up, when I decided to check the driver datasheet for the recommended PCB land pattern. I thought maybe I’m missing something.

For background I downloaded a KiCAD footprint from somewhere and foolishly assumed since it was for Trinamic drivers, it should be correct. Oh well, lesson learned.

Turns out this chip has oversized exposure pad. It is so big that it would touch the pads for the pins on the PCB. It is very likely some of the pins on my board are just shorted to the ground via the die pad underneath.

This is the chip footprint I downloaded:

Looks pretty normal, except the center pad (29) is 3x3mm size. According to the TMC2209 datasheet, the pad on their chip is 3.7×3.7 mm size. Look what happens when I update the center pad size to match the datasheet:

The pin pads are almost connected to the center pad. I resized the pins to match the spec and this is the result

GRRR, All I have to say is “^@%$@^%$!”

I ordered a new set of driver boards with the fixed footprint.

V2 Board in all its glory

I managed to assemble a few driver boards. Here is the V2 board loaded with 3 TMC2660 drivers and 3 TMC2209 drivers:

I also got marlin to load and communicate with the drivers. More testing tomorrow.

V2 prototype assembled – sort of

Here is my first assembled prototype of the V2 board. I only had patience to solder 3 PCIe connectors and skipped on the Thermocouple and servo connectors for now.

Sorry about the “no clean” solder paste gunk around the fuses. I noticed it after I took the picture.

Here is a picture with the driver boards in the slots

And slightly different angle

Here I added a 40x10mm fan for scale comparison

I’m not set on the 40mm fans for cooling, I ordered some 60mm and some 50mm and will do some experimentation what would be the best combination.

Next, I’ll make some driver boards and start porting Marlin to test the contraption.

V2 prototype boards have arrived

Many thanks to the awesome team at JLCPCB. I’m really impressed by the speed and the exceptionally low prices. I ordered a set of prototype boards for the V2 design on Oct 28th and they arrived today at my door. Total 8 days including shipping from China.

Here it is 150x105mm 2 layer board:

I ordered the 2660 drivers also from JLC, but I don’t like the red mask color:

The 2660 driver is 4 layer board with “gold fingers” – this is code for the board edge PCIe connector.

The purple board is the 2209 driver. That board is from ohspark. No much difference between the two, except the ENIG finish is standard on oshpark and the purple color is dope. The JLC board comes with a little chamfer around the connector, which is nice.

This is what the driver board looks like plugged in a PCIe slot.