Printed Circuit Board (PCB) Measurement from Thermal Loading
The image above shows how the VIC-3D digital image correlation system is set up with 5 MP cameras and 35 mm lenses to view the PCB and it’s attached components. Thermal load was applied by a heat gun to the opposite side of the board. The DIC data below shows the dimensions of the area of interest to be roughly equal to 58 mm x 39 mm x 6 mm. The test lasted nearly one hour and temperatures exceeded 350 degrees Fahrenheit (177 °C). Full-field color contour data shows the area of interest in extremely high detail on the surface of the PCB and its various components.
Printed circuit boards (PCBs) have two primary functions: to provide electrical connections between terminals on the board, and to affix electronic components such as resistors, capacitors, and microchips via soldering. PCBs are used in many devices around the world on a day-to-day basis. Their small and lightweight design allows them to be found in nearly every electronic device, such as smart watches, phones & computers, and even digital cameras.
In this application example, the effects of thermally loading a PCB and its attached components are measured and analyzed. Thermal loading tests are commonly performed in the PCB industry to ensure products meet expectations when operating under normal conditions.
It becomes obvious that thermal warpage is occurring in the top right of the PCB when deformation is viewed. Out-of-plane displacement (W) and displacement in the Y direction (V) show a movement of the board up and away from its original position,
Average principal Lagrangian strains fall between 700 microstrain and 4000 microstrain. If extractions are performed on each of the components, it becomes clear how thermal loading of the PCB affects both the board and the soldered components.
DIC can be utilized to characterize material properties such as Young’s Modulus, Poisson's Ratio, glass transition temperature (Tg), and Coefficient of Thermal Expansion (CTE). This is valuable when trying to evaluate candidate materials such as PCB laminates. Solder fatigue is often driven by thermomechanical damage due to CTE mismatches between the package and PCB. Measuring the CTE of the PCB or components can help identify solder fatigue risks due to thermal cycling.
PCB and component warpage is often a concern during reflow soldering. Excessive warpage can lead to poor interconnect formation, solder joint bridging, or component cracking. Warpage measurements made via DIC can help identify warpage as an issue during reflow or compare candidate components and board laminates.
DIC testing can be used to both characterize FEA inputs such as material properties, as well as validate simulation results. Strain gauging provides localized strain values and may potentially miss problematic strain regions that occur in complex assemblies or loading conditions. Full-field displacement and strain maps allow for more comprehensive comparisons to FEA results.
For more information, please see “The Value Of Digital Image Correlation In Electronic Design And Root Cause Analysis” .