Finishing

In its 13 February 2003 issue, the Official Journal of the European Union officially published the new provisions concerning old electrical and electronic equipment (WEEE*) and the reduction of the use of hazardous substances in electrical and electronic equipment (RoHS*).

* WEEE = Waste from Electrical and Electronical Equipment
* RoHS = Reduction of Hazardous Substances

The following restrictions on hazardous substances result from that:

Heavy metals:
- Lead (Pb)
- Mercury (Hg)
- Cadmium (Cd)
- Hexavalent chromium (Cr VI)

Flame retardant:
- Polybrominated biphenyl (PBB)
- Polybrominated diphenyl ether (PBDE)

This applies to electrical and electronic equipment that is put into circulation from 1 June 2006.

For the electronic industry, this means that all electronic products have to be manufactured with lead-free connection techniques in time, with the usual or a better quality and reliability and (preferably!) with no higher costs.
Furthermore, the insulation material, including in particular the base material for printed circuit boards, must be PBB and PBDE-free.
The RoHS significantly affects the soldering processes, the components, the soldering equipment and the printed circuit boards. The RoHS allows specific, technically justified exceptions from the ban on lead, e.g. for medical radiation protection, lead-containing solder in medical equipment and in monitoring and control devices.

The contacts of the printed circuit board have to be coated with a surface finish. The coating provides support for the different doldering and contact processes, but also protects exposed copper from oxidation. There is no good or not so good surface finish. The choice of the right surface primarily depend on the technical requirements (e.g. bonding), the design (pitch spacing) and the field of application (e.g. temperature change).

Surface

Typical thickness

Application

electroless Ni/Au

0.05 - 0.07 µm Au, 4 - 7 µm Ni

Soldering, bonding, fine-pitch

electroless Sn

0.8 - 1.0 µm Sn*

Soldering, fine-pitch

HAL (lead-free)

1 - 8 µm Sn

Soldering, multiple soldering

HAL (leaded)

1 - 8 µm Pb/Sn

Soldering, multiple soldering

Pb/Sn refounded

8 µm Pb/Sn

Soldering, multiple soldering

plated Ni/Au

1.5 µm Au, 3 - 6 µm Ni

Gold connectors, switch contacts

plated Ni

3 - 6 µm Ni

Casing contacting

electroless Ni/Pd/Au

electroless Ni 4-8 µm
electroless PD 0,1-0,3 µm
electroless Au 0,02-0,08 µm

Wire bonding

Wire bonding Ag

0,15-0,45 µm

Soldering, fine-pitch


Applications on inner layers (buried vias):
- closed, metallized buried vias serve as capture pad
- higher packing density
- little sinking

Disadvantages:
- thicker copper layers
- not fully applicable for laser drilled micro vias
- higher production complexity

Buried Via

Applications on outer layers (via in pad):
- closed, metallized blind vias serve as solder surface
- planar via surfaces, no carryover or air pockets
- higher packing density
- little sinking

Disadvantages:
- thicker copper layers
- hhigher production complexity
- not applicable for fine line printed circuits (undercut)

Via