Technical Information

In the course of the new legislation for reduction of environmental pollution

• Restriction of Hazardous Substances ( RoHS) in electrical and electronic devices,
• Waste Electrical and Electronic Equipment (WEEE)

the preferred choice for the coating material is pure tin rather than tin-lead alloys which have been widely used in the past.

For wires with pure tin coatings our company offers exclusively fully RoHS-compliant products.

Users of pure tin coated wires face problems arising from the Tin Whisker Formation.

Whisker

Whiskers are monocrystals which may grow out from the coating surface and cause short circuits on Printed Circuit Boards or in Connectors.

For pure tin coatings applied on to a copper base material by electroplating the risk of Whisker Formation occurs. If the combination of copper and tin is mechanically stressed - for example by bending - the tendency for Whisker Formation increases.

Whiskers on a Electroplated Coated Wire 1)		Typical whisker at an electroplated tin layer 2)

Consequently, for production of coated surfaces as well as for the further processing of the coated elements, wires or other piece parts appropriate countermeasures need to be considered.

Coatings for reduced Whisker Formation

Following latest research results whisker formation can be reduced more or less by applying either of the following methods:

1. Coating by hot-tin-dipping.
   The coating from molten tin offers the highest level of whisker mitigation.
2. By introducing a barrier layer of at least 2µ nickel between copper and tin.
3. By subsequent reflowing of the pure tin coating applied by electroplating.
4. The addition of (at least 2%) lead to the tin as alloying element when using the electroplating process - Note: not RoHS compliant.

Edelhoff's Offer for Whisker-reduced Pure Tin Coatings

Our company is capable for offering all four of the afore mentioned coating versions. In close dialog with our customer we evaluate and specify the most appropriate version of whisker mitigation with regard to his requirements.

Upon request further methods of processing can also be offered.

The oldest coating technology, which our customers have awarded the accolade "whisker reduced" is the hot-tin-dipping technology. Especially Edelhoff's FOV-type quality has been and still is groundbreaking.

With electroplating, the application of a nickel barrier layer is nowadays a common choice.

Sometimes a multiple tinning type structure might be required. Wires from our DC-type process have been developed from such an approach. As an electroplating process, a DC-type wire provides a well developed Intermetallic Phase between copper and tin.

For other special applications Reflowing may be the appropriate method for whisker mitigation.