Recommendation on PCB assembly ESDAxxSCxY
12/15 DocID028400 Rev 1
4 Recommendation on PCB assembly
4.1 Solder paste
1. Use halide-free flux, qualification ROL0 according to ANSI/J-STD-004.
2. “No clean” solder paste recommended.
3. Offers a high tack force to resist component displacement during PCB movement.
4. Use solder paste with fine particles: powder particle size 20-45 µm.
4.2 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.
4.3 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.
