Can you guess what does this picture represent?
The picture shows a void i.e. an air bubble in a glob top material. The glob top is commonly used in electronics to protect components and interconnections from environmental stresses. Typically, they are thermoset polymer materials which are often filled with particles to improve their properties such as thermal conductivity or thermal expansion.
In this case, we used the glob top to protect isotropic electrically conductive adhesive (ICA) interconnections (the picture below shows a schematic cross-section of the structure). To study the structure of the interconnections and glob top, we manufactured a cross section of the structure. Afterwards, we studied the cross-section using both optical and scanning electron microscope (SEM).
This SEM image shows a close view of the glop top with silica fillers (the lighter particles) and the void. Voids are commonly seen in glop top materials and may cause reliability issues depending on their size or location. Have you had problems with voids in your products?