Oxidative Decay
Chemical degradation processes in polymer substrates involve the reaction of the epoxy resin with oxygen at elevated temperatures. Thermo-oxidative aging leads to the gradual hardening and eventual cracking of the dielectric material, which reduces the mechanical reliability of the board. This process is most active on the surface of the board where oxygen is most available to react with the polymer.
Material Brittleness
As the chemical bonds in the resin break down, the material loses its flexibility and becomes more likely to fracture under vibration or shock. Thermo-oxidative aging also changes the color of the board, often turning it from a light green to a dark brown. These changes indicate a loss of the original mechanical properties and a reduction in the electrical insulation resistance of the substrate.
Environment Life
Designing for long-term reliability requires understanding how the specific resin system will react to its operating environment over many years. Engineers use the data from thermo-oxidative aging tests to set the maximum safe operating temperature for the electronics. Protective coatings or encasements can be used to limit the amount of oxygen that reaches the board surface and slow down the decay.
Regular inspection of older equipment often focuses on finding the signs of this aging to prevent unexpected failures in the field.
