Flex PCB Manufacturer

Flexible Circuits

Solder Choices for Assembly of Flexible Circuits

 Solder Choices for Assembly of Flexible Circuits
Before the year 2000, most circuit assem-
blies used solder that consisted of tin and lead.
A popular ratio of the alloy was 63% tin and
37% lead. However, the European Union passed
a directive named Restriction of Hazardous
Substances, commonly known as RoHS, or Di-
rective 2002/95/EC. It restricted the use of lead,
mercury, cadmium and other substances in
products sold there. Electronic industries world-
wide were affected and had to come up with a
substitute for the tin/lead alloys that had been
used for decades.
Today, both RoHS and non-RoHS solders ex-
ist and are used. A typical RoHS compliant sol-
der will contain no lead and be made instead of
tin, silver and copper. This new solder requires
higher temperatures to melt than the tin/lead
versions and looks differently as well.
Both RoHS and non-RoHS solders come
mixed with flux that must be cleaned or flux
that does not require to be cleaned. The flux in
the version that requires cleaning is very cor-
rosive and can be conductive if left on the cir-
cuit, but is easily cleaned with water. The flux
in no-clean solder leaves an inert clear residue
that may remain on the circuit forever without
adverse effects. The use of these solder options
on flexible circuits is common and generally re-
quires no special considerations, aside from the
melting temperature.
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