Investigating the effect of large SMD components on heating during vapour phase soldering

The paper presents fundamental investigations into the field of vapour phase soldering, specially focusing on the effect of large surface mounted components (e.g. shadowing and possible consequent tombstoning). During the vapour phase reflow the heat transfer processes are based on condensation and the temperature distributions are affected by the geometry and thermal masses of the heated assemblies. The paper investigates the problem from the aspect of components with high thermal mass, which may affect the process of condensation, due to their increased thermal requirements. The experimental is based on FR4 type printed circuit boards, where large packages (SMD capacitors) are attached with SMD adhesives on the top surface of the board at specified locations. The thermocouples are fixed in bores inside the PCB at given locations to highlight any possibility of shadowing (caused by condensate flow blocking effect or vapour consumption) and inside the components where any significant transient effects serve information about the process itself. The measurements are logged with a custom data logger device, which was developed specifically for the investigations. The initial results show that shadowing might not be a problem even near large components, however the overall heating characteristics of the board and the components are affected by the relatively large thermal masses of the applied packages.