Resin Fracture
Microscopic fissures occurring within the dielectric substrate of a printed circuit board define glass crazing. This condition arises when mechanical stress exceeds the tensile strength of the reinforcement fibres or the surrounding polymer matrix. Internal fractures develop along the weave pattern of the laminate, appearing as white halos or lines beneath the surface of the solder mask.
Such degradation compromises the electrical insulation properties of the base material. The phenomenon reduces the long-term reliability of interconnections under thermal cycling.
Substrate Degradation
Excessive localized heating during drilling or assembly operations triggers the separation of resin from glass bundles. High-aspect-ratio holes generate thermal shock that accelerates these separations if the coefficient of thermal expansion mismatch between components reaches extreme levels. Repeated mechanical pressure from test probes also propagates existing microcracks into wider areas of delamination.
Laminate suppliers quantify this susceptibility through the measurement of glass transition temperatures and moisture absorption rates. Operators identify these features by utilizing high-magnification optical inspection equipment under bright field illumination.
Compliance Limit
Standards for acceptance require the absence of evidence showing path connectivity between conductive features resulting from these substrate fissures. Boards failing to maintain a minimum distance between copper tracks due to the presence of cracks face automatic rejection from high-voltage applications. Strict controls over the moisture content of prepreg materials before lamination prevent the formation of vapor pockets that encourage internal splitting.
Controlled cooling rates during reflow cycles minimize the residual stress trapped within the dielectric layer. Final inspection protocols prioritize the detection of sub-surface fractures to ensure consistent dielectric performance.
