Residues Can Cause Low Voltage Electronics to Ignite

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Analyzing electronics failures due to residues leads us in many directions. Foresite recently worked with a fire investigation client to determine whether low voltage/low power consumer electronic devices can start fires. Traditionally, fire investigators have naturally looked for obvious damage such as arcing on heavier gauge conductors and have focused on higher wattage devices such as large household appliances. Devices such as remote controls were thought to have insufficient energy to be a source of ignition.

What we found

Even though we were looking in a new direction, we found a familiar failure mode: ionic and organic contaminants from manufacturing processes and the environment on electronics, causing electrochemical dendritic growth and short-circuiting.

The leakage current, even in low voltage/low power applications, was demonstrated to be sufficient to eventually ignite proximate fuel and lead to sustained fire. In one failure analysis case circuitry powered by only a 3.3V button cell battery sustained ignition – surfaces on the PCBA were found to have flux residue levels (weak organic acid) seven times the maximum considered safe.

What is causing this?

Several factors are exacerbating this fire risk, not to mention the risk to electronics performance:

• Elimination of flame retardants in boards due to RoHS requirements
• Process changes due to the elimination of lead (Pb) from solders, again due to RoHS
• Use of fluxes that are more difficult to completely complex (make benign), plus, no longer contain rosin which acted as a protectant
• Miniaturization of electronics (greatly reduced circuit spacing)
• Reduced and ineffective cleaning (no relevant industry specifications for cleanliness)
• Outsourced manufacturing

Going forward

This is an area of concern that is going to heat up. The average home now has over 26 consumer electronic appliances or portable electronic devices – a number that is only likely to grow. In one investigation, it was shown that an internal electronics failure in one device caused a fire in a remote device, due to electrical overstressing. Another disconcerting case involved a very low power automotive remote key fob that burned through the user’s pants pocket.

This research confirms another market driver for the need to address cleanliness in the manufacturing of reliable electronics.

Steve Ring is Foresite’s Director of Business Development. He manages funded research programs and formerly managed the development of the C3.