Thermal Profiling of Pre-heater Configurations with Added Convection to Determine Heating Effectiveness for Selective Soldering

The quality of through-hole soldering joints is determined by the percentage of solder fill within a printed circuit board (PCB) hole. Good wetting is required to achieve this via heating and optimal flux selection. The applied heat activates the flux chemistry facilitating its surface cleaning action.

Traditionally, either infra-red (IR) heaters or convection ovens are used for this purpose. While IR is fast, it is surface-sensitive, can be reflected, and its penetration depth is dependent on wavelength. Convection can homogenously heat larger assemblies but is comparatively slow. Combining these methods will allow a pre-heat station to quickly heat a variety of board configurations.

Printed circuit boards with varying levels of copper traces have been profiled. Thermal profilers with thermocouples were used to measure the top and bottomside temperature profiles.

Varying arrangements of fast response shortwave IR topside and bottomside pre-heat in both open and closed loop configurations have been used. Varying power levels and target temperatures were used for each method, respectively. An air blower system was then fitted to allow for added convection heating for each of the above configurations.

This parametric study will provide key insights into the most efficient methods to heat printed circuit boards for selective soldering. IR heating provides the most immediate surface heating effect, via radiative transfer, and the addition of air blowing has been explored in conjunction. Machine configuration must be explored to enhance efficiency. The goal is to replicate the uniform surface and through-thickness heating typically achieved with convection.