I had 5 two-layer boards fabricated by a popular assembly house in China and I'm curious what folks thoughts are based on what I received. Here is a photo of the 5 boards which has a red square around all 5.
Essentially each board has a MCP23017 GPIO extender and the base control board at the bottom controls these MCP's via the I2C bus. The firmware I'm running just turns on all the LEDs as part of my test.
Interestingly 2 of the 5 boards has one or more issues with an LED not lighting up when it should. After investigation of these two faulty boards I have confirmed that the LED's are not burned out and light up properly when ground is applied to them. The LED's are controlled via a MOSFET and the GPIO extender actually controls the gate of the MOSFET. I'm using a SOT-23 2N7000 MOSFET for each LED.
I've determined that in the cases where the LED does not light up, there is 3.3V at the proper pin on the MCP23017 but there is no voltage on the gate of the corresponding MOSFET.
The boards have been very carefully handled (although I hope to use these in a high school classroom electronics course so I'm hoping they are not super fragile).
Here is a video of proper operation for 3 of the 5 boards.
Here is a video showing the top boards being replace by the other 2 faulty ones.
I'm curious what folks think about this? Is this a production issue that I should hit up the manufacturer about or might something else be going on?
I would think this failure rate of SOT-23 to LED (80 pairs across all 5 boards) with 5 failures out of 80 that rate seems way too high to me.