Air Gap Corrections in Clamped Stripline in Plane Permittivity Extraction
Air gap corrections eliminate systematic two to six percent dielectric underestimation in clamped stripline tests, preventing finished board impedance failures.
Resin Compliance
Mechanical Flexibility
Ability of a polymer matrix to deform under stress without fracturing is a fundamental property of the cured laminate system. High resin compliance allows the board to absorb the mechanical energy generated by the different expansion rates of the copper and the glass fibers. This characteristic is measured by the modulus of elasticity, where a lower value indicates a more flexible material.
Flexible resins are used in applications where the board will undergo vibration or thermal shocks.
Stress Management
Internal forces that build up during the soldering process are mitigated by the movement of the polymer chains. In assemblies with large components, resin compliance prevents the solder joints from cracking by allowing the substrate to yield slightly under the load. This property is particularly valuable for lead free soldering where the temperatures are higher and the materials are more brittle.
Thermal cycling tests confirm that compliant materials maintain their bond strength over time.
Reliability Threshold
Limits on the amount of deformation a material can handle before permanent damage occurs define the operational window for the assembly. Excessive resin compliance can lead to issues with the registration of fine features if the board moves too much during processing. Designers must balance the need for flexibility with the requirement for dimensional stability during the etching and drilling stages.
The choice of resin affects the long term survival of the interconnects in harsh environments.