Wednesday, December 27, 2017

More PCB manufacture gremlins

I was talking to a friend last night about how I'm using a reflow tool that another friend kindly lent me. He asked me what temperature I was using. "400" I replied. 400 ... what? Celsius? Fahrenheit? That led to some hilarity where it became clear I was frying my chips with 400 Celsius hot air then expecting them to work.

Today I set myself the task of creating  new board from scratch. I tried the recommended 235 Celsius or thereabouts but I was having trouble getting the solder to reflow, so I went back to soldering with the iron. I got to this point:


I then plugged in a Fio V3 and verified that the I2C mux was working, and that the temperature sensor chip was showing up correctly on bus 0x04 at address 0x48. All seemed great.

I then went back and installed the IC headers for my pressure sensors. Same workflow as yesterday. After that step, I had the following:


I then plugged in the Fio V3 and ... silence. Nada. Nothing.

Could it be that I fried the I2C mux? I de-soldered it and installed a new one. Nope. Didn't help.

Could it be that I needed to wash off the flux? (Grasping at straws here.) No, didn't help either.

Could the Fio V3 be busted? No, when removed from my board, it works just fine.

Could the Fio V3 be busted in some way that removing it from my board does not detect? No, when I plugged it into my working-but-slightly-flakey board that is populated with pressure sensors and that I used for my road test yesterday, it worked fine and sent back pressure signals.

My only conclusion is that I have no ability at this point to reliably manufacture the simple circuit I have designed.

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