Amada UNIFLOW 4 REMOTE, Руководство по эксплуатации, Страница: 164 / 176

APPENDIX E: GUIDELINES FOR REFLOW SOLDERING
UNIFLOW
®
4 PULSED HEAT CONTROL
E-2 990-908
There are three common types of termination designs used on flex circuits for the pulse heated reflow
process:
1. The “exposed lead” design has both sides of the polyimide
material removed, leaving the traces free of insulation. This
allows the thermode to contact the traces directly, and conduct
heat to the parts. If the PCB pads and thermode footprint are
sized correctly, this design will tolerate some excess solder on the
pads, as there will be open areas into which the solder may flow.
During the process, solder will also wet to the top of the trace.
Caution must be exercised for part handling as the traces can be
easily bent or damaged.
2. The “single-sided” flex design has the polyimide removed on one
side only. Heat is conducted from the thermode through the solid
polyimide surface to the exposed traces underneath. The
polyimide conducts heat through the insulation to the exposed
traces and pads on the PCB. The polyimide thickness in the joint
area is limited to 0.002” enabling conduction. If the polyimide
has to be heated much past 260

C, burning of the surface and
thermode contamination can result. This design is not tolerant of
excess solder on the PCB pads, as there is little room for excess
to flow.
3. The “open windowed” flex design has both sides of the
polyimide material removed from the joint area, but has support
from the remaining polyimide material on the sides and also
along the end of the traces. This design gives some strength to
the assembly and is resilient to harsher handling. As the traces
are exposed, the thermal transfer to the parts is good and excess
solder has extra space to flow. Thermode sizing is critical as it
must fit into the window and allow space for the molten solder to
flow.