Prepreg Melt Viscosity Dynamic Range during Thin Core Lamination Profiles
Matching prepreg melt viscosity minima to press pressure ramps prevents thin-core distortion and resin starvation in high-density multilayer lamination.
Dynamic Rheology
Viscoelastic Measurement
Analysis of the flow and deformation characteristics of resin systems under oscillating stress provides a profile of the material behavior during thermal processing. Employing dynamic rheology allows engineers to identify the exact temperature where a prepreg becomes fluid and the point where it begins to harden. This technique distinguishes between the viscous response and the elastic storage of energy within the polymer.
Lamination Application
Heating the resin causes a drop in viscosity that allows it to encapsulate the copper traces. Through the use of dynamic rheology, the lamination window is defined by the duration and depth of this fluid state. If the resin flows too early or stays liquid for too long, the board may suffer from uneven thickness or resin starvation.
The instrument measures the complex modulus throughout the heating cycle.
Testing Equipment
Rotating plates or parallel discs apply a known frequency of movement to a small sample of the resin. Sensors within the equipment used for dynamic rheology detect the phase shift between the applied strain and the resulting stress. This data is converted into viscosity curves that guide the development of press profiles for complex multilayer assemblies.
A typical test includes a temperature ramp and a steady hold period. Sophisticated models use these curves to calculate the degree of cure at any point in the cycle.