Recommendation on PCB assembly USBULC6-2M6
8/10
5.3 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.
5.4 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. The
symmetrical layout is recommended, in case any tilt phenomena caused by
asymmetrical solder paste amount due to the solder flow away.
5.5 Reflow profile
Figure 17. ST ECOPACK
®
recommended soldering reflow profile for PCB mounting
Note: Minimize air convection currents in the reflow oven to avoid component movement.
0
01234567
Time (min)
Temperature (°C)
2°C/s recommended
6°C/s max
220°C
125 °C
260°C max
255°C
180°C
90 sec max
10-30 sec
90 to 150 sec
3°C/s max
0
01234567
Time (min)
Temperature (°C)
2°C/s recommended
6°C/s max
220°C
125 °C
260°C max
255°C
180°C
90 sec max
10-30 sec
90 to 150 sec
3°C/s max
