Electroless Nickel / Electroless Palladium (ENEP) with pure Pd for Copper Wire Bonding

In electronics packaging copper is getting more and more employed as interconnection material due to its various advantages over gold. Cost reduction and superior electrical and thermal conductivity are the main benefits among others. Copper wire is the bonding wire material of choice for high current or high power applications. Presently the established pad surface for copper wire bonding on IC-substrates and PCBs is electrolytically plated nickel and gold. The gold thickness deposited can be up to 0.5 µm. If the gold could be replaced by cheaper metals the cost saving would be tremendous.

: The Cu-wire bonding performance of ENEP in terms of pull strength is similar to electrolytic nickel gold.

A surface finish, which is considered to be a candidate for electrolytic NiAu replacement is ENEP as it already proofed to be well suitable for copper wire bonding on the Semiconductor side.

Atotech started together with K&S the transfer of Cu-wire bonding on ENEP from the semiconductor to the substrate level. It can be stated that the results look very promising (sample 4). Cu-wire bonding on flexible PCBs showed also impressive results as can be seen with sample 5.

Pull Test Parameters

Dage 4000
WP 100 pull cartridge (100 g max)
2.5 mil (63 µm) hook diameter
500 µm/sec pull speed
50 g range
1.7 mm wire length
pulled ~ 350 µm from the end (from the stitch pull)