PCB arcing at low voltage, why?

[Teleno]

I've designed a 2-layer PCB using DipTrace. It was manufactured by OSH Park (shared as Pinpointer_2.zip ).

I soldered all the components and the circuit worls as expected... but ... occasionally I get arcing between the ouput of the LM78L05 and its ground terminal. It happens at random, the LM78L05 heats up with no catastrophic failure, then the circuit returns to normal. The input voltage is a mere 7.5V.



Are the default pads in DipTrace so damn close that arcing can occur at low voltages?

[eclipse]

Yup I've been there with DipTrace. Ended up making own footprint library for most commonly used components.
I recommend PCBWAY (fastest) and Smart Prototyping (slower but cheapest).

[homefire]

With voltages that low I'm thinking Contamination on the board.

[Teleno]

With voltages that low I'm thinking Contamination on the board.

It looks as if the mask was conducting. There's even smoke, yet all goes back to normal. Then it starts again. Pretty weird.

Could it be the flux paste?

---
I found this explanation:

https://www.johansondielectrics.com/arc-season-and-board-design-observations

Unfortunately organic acids used in water soluble solder paste are very active and if the assembly is not adequatelycleaned those flux residues start their damage and are difficult to remove. Now we arefaced with high leakage currents, low arc voltages and assembly failures. Add humidityand we have a new ARC season.

[kt315]

yes, flux is seems not so neitral. rare thing but thats chinese and you must be ready to a surprize.
so lowest voltage and arcing... LOL!
step between pins is very low. do 2,54 mm, 5,08 between edge pins.
i do not never same step for transistors, but see that often on chinese boards.

[kt315]

[homefire]

Is there a Voltage Pump or Converter before the Regulator ?

[Nupi]

Gerber viewer indicates that there is too little space and especially if it is not clean and/or too much solder and/or bad resin.
Maybe you can do something with this toolkit.

Saturn PCB Design Toolkit Version 7.02

https://www.saturnpcb.com/pcb_toolkit.htm

Greetings from cheeseheads country.