The effects of design and environmental factors on the reliability of electronic products

Lawson, W

Abstract

The reliability of electronic products is fast becoming of major importance with the
demand for increased safety, especially in the automotive industry. Tracks, pads and vias
on printed circuit boards can suffer a variety of problems if circuits are contaminated with
electrical-conducting substances.
Electrochemical migration, especially dendrite growth, has long been a concern in safety
critical and durable systems, and current preventative methods tend to focus on various
styles of printed circuit board protective coatings. These measures have a number of
disadvantages, mainly process and material costs with extreme scepticism on their overall
efficacy. Any design related developments that can minimise the impact of dendrite
growth on reliability can lead to a more economic, durable and safer product.
The work in this thesis provides a thorough literature search of the field of electrochemical
migration on printed circuit boards. This study then develops a novel circuit-designorientated
model, based on a multilevel full-factorial design, to study the effects of
temperature, voltage and electrode gap on dendritic growth under saturated conditions.
Preparation of several DC-biased copper-comb patterned printed circuit boards placed in
temperature-controlled water-filled cuvettes enables the specific monitoring of dendrite
activity, and detects a sharp current increase that accompanies a dendritic short circuit
condition.
A high R2 polynomial correlation-model is derived and it is noted that increased voltage
and temperature and reduced track spacing increases the impact of dendritic growth on
reliability. At voltages between 3 and 4V, gas bubble formation at the electrodes has the
effect of increasing reliability by destroying the dendrite fuses. It is shown that dendrites
may not grow below 1.25V, which coincides with the theoretical onset voltage for the
decomposition of water. It was also demonstrated that electrically biased, watercontaminated
printed circuit boards form extreme acid and alkaline regions close to the
anode and cathode terminations, respectively, which can cause corrosion.
The thesis proposes a novel approach, termed ‘design contingency’, for preventing
dendritic growth through design optimisation.

Citation

Lawson, W. The effects of design and environmental factors on the reliability of electronic products. (Thesis). University of Salford, UK

• Thesis Type: Thesis
• Deposit Date: Jun 8, 2009
• Publicly Available Date: Jun 8, 2009
• Additional Information: Additional Information : PhD supervisor: Dr Richard Pilkington
• Award Date: Dec 1, 2007