Bond Dissociation
Chemical scission of macromolecular bonds by water molecules breaks down polymeric materials used in dielectric substrates and protective coatings. In printed circuit board fabrication and assembly, hydrolytic cleavage attacks susceptible functional groups such as ester or imide linkages when moisture penetrates the packaging under thermal stress. The reaction reduces polymer chain length and degrades mechanical strength.
Accelerated environmental testing, including highly accelerated stress testing, forces this reaction to verify long-term packaging reliability. Dielectric breakdown and structural delamination indicate severe chain scission within the insulating material.
Substrate Degradation
Moisture ingress under high temperature and electrical bias activates nucleophilic bond cleavage across the resin matrix. When printed boards endure harsh operating conditions, hydrolytic cleavage causes micro-cracking and loss of flexural strength. Polyamide flexible circuits and bismaleimide triazine laminates exhibit loss of copper adhesion when interfacial polymer bonds cleave.
The accumulation of small polar fragments increases the material dielectric dissipation factor. Ion chromatography and surface insulation resistance testing reveal mobile ions released during bond cleavage.
Prevention Method
Selecting hydrophobic resin systems with high crosslink density limits water absorption and suppresses bond cleavage. Hydrophobic silane coupling agents applied to glass fiber reinforcements prevent interfacial debonding along the fiber matrix boundary. Proper bake-out cycles prior to reflow soldering eliminate absorbed moisture before high temperatures accelerate chemical scission.
