In the course of the manufacturing of printed circuit assemblies the insertion and soldering steps are mostly defined by the packaging type and the geometrical size of the components. In the progress towards miniaturization, at growing function and component density, for better reliability etc., surface mounted (SM) components are assembled onto single or double sided or multilayer boards. For connectors and for other big size components, like electrolytic capacitors and coils, high holding force is necessary, so through hole (TH) components cannot be replaced.
Conventionally the TH components are mounted by wave soldering, while the SM components by reflow soldering. When both technologies have to be used, the manufacturing cost increases; therefore the solution for the problem is searched worldwide. The Alternative Assembly and Reflow Technology (AART) is a process for simultaneous reflow soldering of surface mount and through hole components. My present diploma work is about Through Hole Reflow Soldering (THRS), other name the Pin-in-Paste (PiP) technology.
In case of THRS, the application of the larger amount of solder paste for hole filling causes most of the problems. To apply the necessary solder paste for miniaturized small pitch TH components is critical, because there is not enough space for overprinting the paste. I tested the two side soldering technique for using sufficient amount of paste.
In order to avoid filling the holes I used special stencil aperture geometries to apply different amounts of paste onto the first side of the self designed testboard. Then I reflowed the paste, printed paste onto the other side, mounted the components, and reflowed again. I evaluated the results by defining one of the most important parameters of the joints, the filling degree of the holes, with the help of X-ray and micro section tests.
Because of some manufacturing inaccuracies of the testboards I recommend further tests. However, the results of the small deviation samples let me conclude that in case of 0,9 mm nominal hole diameter with using 0,63*0,63 mm component pin, the double bridge aperture is suitable for overprinting.