Elastic Behavior
Mechanical stiffness of a polymer matrix below its transition temperature characterizes the ability of a material to store elastic energy. The glassy storage modulus represents this rigid state where the resin molecules are locked in a tightly bound configuration. This value is expressed in gigapascals and determines the structural stability of the substrate.
Substrate Measurement
Dynamic mechanical analysis measures the displacement of a sample under a sinusoidal force to extract this property. The specimen is subjected to a temperature sweep while a mechanical probe oscillates at a fixed frequency of one hertz. During this sweep, the glassy storage modulus remains high until the material approaches its glass transition region, at which point the value drops by up to three orders of magnitude.
Thermal Transition
Substrate selection for high reliability multilayers depends on maintaining sufficient stiffness through both assembly and operating temperature ranges. If the glassy storage modulus is too low, the laminate can deform during drilling or component placement, leading to misaligned microvias and cracked copper barrels. The property dictates the level of thermal stress transferred to copper traces when the board experiences reflow temperatures.
When the resin remains below its transition threshold, this rigidity protects delicate copper structures from excessive mechanical stress, preventing early fatigue failures in harsh thermal environments.
