Printed Circuit Boards Are Core to the Future of the Digital World Our expertise

Delamination or separation of the layers in printed circuit boards during the manufacturing process, particularly wave soldering, is a leading cause of product failure. Hence, there is a need for a quick test that can predict failure before production. Manufacturers measure printed circuit boards’ thermal stability to determine their performance under different temperatures and develop PCBs that resist breaking down due to heat and stress.

Thermal stability is affected by thermal conductivity, glass transitions, and coefficient of thermal expansion, all of which are measured by thermal analysis instruments. Mechanical stability and durability are affected by the material stiffness and fatigue resistance of electronic assemblies.

The thermomechanical analysis (TMA) technique which measures the dimensional change in materials with temperature is an ideally suited technique for evaluating the onset of delamination in these materials. The PC board is subjected to the following temperature regimen; heating at a constant heating rate for a period followed by an isothermal hold at the typical temperature of a wave soldering bath. The matrix material becomes glassy and expands at the beginning of heating but when the glass transition occurs, the matrix becomes more "rubbery" and expands faster.

At a certain time while the temperature is held constant, a slight creep occurs due to the force on the TMA probe followed by delamination, as indicated by a sudden upward dimensional change of the PC board. The duration from creep to delamination is called delamination time, which indicates the heat resistance of the material. The longer time, the higher the heat resistance. In normal processing, the TMA delamination test is currently being reviewed as an IPC standard test method (IPC-TM650). This provides additional information valuable to the proper processing and handling of the material.

In addition to measuring whole PCB qualities, manufacturers also perform more detailed testing on PCB materials, such as the cured laminate and adhesive that hold wires in place and strengthen PCB structure. Since their cure is essential for end-use performance and reliability, manufacturers use thermal analysis to rapidly evaluate the degree of cure and adjust their formulations.

The degree of cure in thermosets can be determined by measuring the glass transition temperature (Tg) or a residual cure exotherm using differential scanning calorimetry (DSC). From small components to finished products, PCBs are improved at all stages by superior material characterization.

Characterization of the resin glass transition temperature can sometimes be difficult by DSC because of its high fiber content. PCB materials are comprised of fiberglass braid impregnated with a thermosetting resin. DMA, because of its inherent sensitivity to the glass transition, is an ideal technique for identifying the Tg of these highly filled systems.