Recommendation on PCB assembly
3.3 Placement
1. Manual positioning is not recommended.
2. It is recommended to use the lead recognition capabilities of the placement system,
not the outline centering
3. Standard tolerance of ±0.05 mm is recommended.
4. 3.5 N placement force is recommended. Too much placement force can lead to
squeezed out solder paste and cause solder joints to short. Too low placement force
can lead to insufficient contact between package and solder paste that could cause
open solder joints or badly centered packages.
5. To improve the package placement accuracy, a bottom side optical control should be
performed with a high resolution tool.
6. For assembly, a perfect supporting of the PCB (all the more on flexible PCB) is
recommended during solder paste printing, pick and place and reflow soldering by
using optimized tools.
3.4 PCB design preference
1. To control the solder paste amount, the closed via is recommended instead of open
vias.
2. The position of tracks and open vias in the solder area should be well balanced. A
symmetrical layout is recommended, to avoid any tilt phenomena caused by
asymmetrical solder paste due to solder flow away.
3.5 Reflow profile
Figure 15: ST ECOPACK® recommended soldering reflow profile for PCB mounting
Minimize air convection currents in the reflow oven to avoid component
movement. Maximum soldering profile corresponds to the latest IPC/JEDEC J-
STD-020.
