An Analytical Approach to Thermal Design for Manufacturing in Mini Wave Soldering

Two-side mixed assembly of THT and SMT components on printed circuit boards is widely applied in electronics production. To avoid thermal damage of surrounding components and the circuit board, as well as warpage, selective wave soldering is employed. Especially in power electronics applications, THT components are used for thermal, electrical properties of components and the mechanical properties of the solder joints. Generally, good solderability and good thermal management properties on circuit boards cause conflicting design objectives. Thermal management requires heat dissipation and high current carrying capacity lead to elevated copper layer thicknesses. As a consequence, the solder joints during the THT soldering process are hardly solderable for the high heat spread. In this paper, an analytical approach to the estimation of the temperature development in the solder joint during soldering is suggested. Therefore, the solder joint is analyzed layerwise. Each layer is treated as a cooling rib that dissipates its energy to the surrounding epoxy matrix, similarly to a heat exchanger. Further on, the layerwise calculated transient thermal profile allows the estimation of the hole fill. With this estimation circuit board designer can carefully judge the design to identify thermally critical solder joints and adjust the design in the sense of design for manufacturing in the early design stage. As a consequence, less time to market can be realized through fewer design reviews and avoided manufacturing problems.