White residue on SMD resistor used in LED driver

[14_powerelectronics]

There was a led light output blinking problem. While i was examining the board I saw a white residue on the SMD resistors which was place next to the bridge rectifier.The resistors was used as ACDC and it is going to the µC. This device was used in Sydney. Preliminary examination lead to the conclusion that, this might be a salt or flux residue. Has any one ever seen such phenomenon?

 

[BradtheRad]

It's quite common and there's a variety of possible sources.

It looks as though the deposits seeped out of the resistors. But they don't contain flowing substances, and the package is supposed to be sealed.

Cleaning away flux is proper technique. Conceivably flux remained beneath the component and crept over time.

Is a battery close by? Seepage is a common problem.

Capacitors (especially electrolytic type) sometimes break a seal due to age, heat, or over-voltage. Fluid might travel or fly anywhere.

 

[14_powerelectronics]

It's quite common and there's a variety of possible sources.

It looks as though the deposits seeped out of the resistors. But they don't contain flowing substances, and the package is supposed to be sealed.

Cleaning away flux is proper technique. Conceivably flux remained beneath the component and crept over time.

Is a battery close by? Seepage is a common problem.

Capacitors (especially electrolytic type) sometimes break a seal due to age, heat, or over-voltage. Fluid might travel or fly anywhere.

Thank you for your response.

There is no battery close by. The device was supposed to working in an air conditioned room. But not sure if the AC was on through out the day. Is there any chance humidity in combination with salts in air could be the reason behind this?

I did a flux test. But it came out negative. Tiny amount of flux was present. suppose there was a chemical reaction due to humidity , flux, temperature difference and salt content in the air and if it happened will the flux test give positive result? or due to the reaction the flux is no longer retain it property and cant be detected . Application area for this device is in a costal area.

 

[14_powerelectronics]

I have found Silver deposits in a resistor used for AC-DC detection. Does anyone know how can there be silver deposits in resistors?

 

[betwixt]

Possibly migration from the solder joints if there is a moisture path across the top of the resistor. In situations like that I add a conformal coating to the board after construction to keep moisture out.

Brian.