Testing Standard
An industry test protocol established by the IPC defines the experimental procedure for determining the curing state and thermal stability of printed board resins through differential scanning calorimetry. Under the requirements of IPC-TM-650 Method 2.4.53, laboratory technicians heat a small laminate specimen at a controlled rate to measure how much energy the material absorbs or releases during its transition from a glassy state to a rubbery state. This test validates that the base laminate has been cured during the lamination process and will not delaminate during subsequent soldering operations.
Measurement Protocol
The procedure begins with preparing a thin slice of the laminate material weighing between ten and twenty milligrams. Technicians place the sample in a sealed aluminum pan and insert it into the calorimeter alongside an empty reference pan. As the temperature rises, sensors record the difference in heat flow, which reveals the glass transition temperature of the polymer.
A second heating cycle is immediately executed to ensure that no further chemical curing occurs. If the second run shows an upward shift in the transition temperature, it indicates that the board was under-cured during its primary fabrication.
Structural Limitation
The method remains unreliable for polymers with high concentrations of mineral fillers, as these additives suppress the thermal signal. In such cases, alternative methods like dynamic mechanical analysis must be used instead. This limitation restricts the test to unfilled or lightly filled epoxy and polyimide systems.
