Vacuum Deposition
Physical vapor deposition deposits thin dielectric layers during multilayer circuit board fabrication, where physical vapor deposition relies on cathodic target bombardment under high vacuum. Sputtered polyimide forms thin base films or interlayer dielectrics through energetic particle ejection from a solid source directly onto a moving copper substrate. Target power density controls deposition rate while chamber pressure dictates residual gas incorporation within the resulting molecular chains.
Automated optical inspection verifies thickness uniformity across large panels before subsequent metallization etching steps.
Dielectric Integrity
Insulating performance depends entirely on chemical structure retention during energetic particle transfer from cathode to substrate. Molecular bond scission occurs when bombardment energy exceeds polymer thresholds, generating trapped charges that degrade breakdown voltage during high voltage testing. Thermal gravimetric analysis measures residual solvent content and moisture outgassing propensity prior to vacuum chamber entry.
High frequency signal propagation suffers when film density varies across the panel area because relative permittivity fluctuates with local packing fraction. Surface roughness measurements confirm whether the deposited layer maintains sufficient smoothness for fine line lithography without pinhole formation.
Adhesion Mechanics
Interlayer bonding relies on atomic scale interlocking achieved through substrate surface cleaning prior to film growth. Ion bombardment removes native oxides and organic contaminants to expose active metal sites for polymer chain anchoring. Peel strength testing quantifies mechanical retention under tensile load, identifying interfacial failure modes caused by thermal mismatch stress during soldering operations.
Residual stress accumulates as the panel cools from deposition temperature to ambient conditions due to differences in thermal expansion coefficients between the metal foil and the dielectric layer. Thermal shock cycling reveals delamination risks before populated boards undergo final functional test.
