Spin Semiconductor

Hi all! I'm experiencing a strange issue with a couple of FV-1 builds having unresponsive S0 or S1 pins.

I have a circuit that's been in production for a while and it uses the FV-1 in a pretty conventional way. An SPDT on-on-on with 10K resistors connects 3.3V to S0, S1, or neither, to select from 3 programs on an EEPROM.

On a recent build batch a few units have had either S0 or S1 not respond to the switch so only 2 out of 3 programs load. All the voltages and continuity are correct, the switches are sending the 3.3V to the pins when engaged. This is a tried and tested circuit, the other 47 builds in this batch are fine.

Is there anything else common I should be looking for to diagnose what's happening here or is it possible these FV-1s have just been damaged at that pin? I couldn't find anything similar in this forum or elsewhere but I may have missed it.

Thank you!

That is very strange, all the S pins are tested in production so would expect to catch it there. While there will always be a few parts that pass test but fail quickly in the field (often called "infant mortality")it is strange to get 3 out of 50.

In most cases like this the issue is something like a solder bridge under the chip or the board was not cleaned well after assembly. Water soluble flux is very nasty as it is corrosive and conductive, if you are using an assembly house that uses this then make sure they really washed the boards well after assembly. Just the slightest amount can cause a short or eat a trace.

Ah I see. Super helpful, thank you. Maybe just bad luck on the "infant mortality". No visible bridges and all the continuity and voltages are when and where they should be. It was done with liquid flux (not the water soluble acid kind) but I can't find evidence of issues from it. Still, could be. A good clean and a reflow didn't change anything.

Sounds like it's likely one of these but I think the only thing left is to just swap out the chip!

Something just hit me, you state:

jbwires wrote: ↑Thu Jan 16, 2025 7:49 am An SPDT on-on-on with 10K resistors connects 3.3V to S0, S1, or neither, to select from 3 programs on an EEPROM.

Do you mean that S0 and S1 are tied to 3V3 through 10K and you use the switch to ground one of them to select the program? Just want to be sure I have a clear understanding of the circuit.

The switch is used to connect 3.3V to either S0, S1, or neither, with the resistors pulling down to ground. It's an on-off-on switch, not on-on-on (I mistyped previously).

Schematic screengrab: https://drive.google.com/file/d/1OyPFaO ... sp=sharing

First off to clarify: the assembly house is me carefully hand soldering these onto otherwise pre-assembled boards.

I ran into a fourth FV-1 with an unresponsive S1, it was the next one after the other 3. It almost seems like they were grouped together. After more testing and troubleshooting I still couldn't find any evidence of bridges or damaged traces, all voltages and continuity as it should be, so I replaced the FV-1. Works perfectly. So I replaced the other 3 and they all work perfectly now too.

I suppose this is something of a resolution in that the builds are working now, but I'm still not 100% sure what the issue was. The fact that it seemed like a group of them in the tube does have me wondering whether they passed QA but then failed later.