In accordance with the previous discussion, typical process parameters for Würth Elektronik connector WR-TBL 691701510004B are defined as follows:
PCB thickness (Tb ) = 1.6 mm
Pin diagonal (dp) = 1.2 mm
Pin length = 2.6 mm
Pin width (Wp) = 1 mm
PTH hole diameter (Dh) = dp + 0.3 = 1.5 mm
Pin volume (Vp ) = Wp x Wp x Tb = 1 x 1 x 1.6 = 1.6 mm³
PCB PTH volume (Vh ) = π x (Dh/2)² x Tb = π x (1.5/2)² x 1.6 = 2.8 mm³
In consequence, the needed solder paste volume (Vsp) is:
Considering that the solder paste will fill about 80% of the PTH at the time of the printing, the aperture of the stencil has to be accordingly smaller.
Typically, with a stencil thickness (Ts ) of 150 µm (namely 0.15 mm) the stencil aperture volume (Vsa) should be calculated as follows:
By experience, we recommend to apply a coefficient of 1.5 to Vsa in order to have a proper soldering joint that matches the standard in soldering quality, the IPC-A-610D. After adding this coefficient, Vsa becomes 0.24 mm³.
Therefore the theoretical diameter (Ds) of the stencil aperture in case of a round aperture should be:
In this particular example Ds is smaller than Dsp, the solder pad diameter, that we advise at 2.3 mm (Dh + 0.8). Therefore, we recommend using the theoretical formula mentioned previously (Pad diameter – 0.1), i.e. 2.2 mm.
According to the previous extract from IPC/JEDEC J-STD 020D, Würth Elektronik recommends the following profile, shown in figure 2.89, for both WR-TBL THR connectors series 7013 and 7015.