Hot Air Levelling Technology Lead-free(SnCuNi und SnAgCu)!

The nearer the deadline draws to the compulsory implementation of lead-free regulations(ROHS), the greater the attempts to achieve lead-free solutions that are comparable to the “all purpose answer” SnPb in terms of technology and cost. Two systems are particularly predominant: tin/silver/copper (SnAgCu) and, more recently, stabilised tin/copper (SnCuNi). Although the level of efficiency of both systems is not yet completely clear, the following presents the latest information:

SnAgCu

There is more experience in the field of silver systems. Here, differentiation is made between the Sn-3.5Ag-0.7Cu, Sn-4Ag-0.5Cu and Sn-3Ag-0.5Cu systems which vary in use from continent to continent.

However, the agreed expert opinion(IPC/Soldertech-Conference Brussels 2003) is that the technological differences between the three systems are negligible. Sn-3.5Ag-0.7Cu is the most common alloy in Europe.

SnCuNi

Although there are even fewer field results for he stabilised tin/copper system Sn-0.7Cu-0.1Ni, it shows a lot of potential. It is called“stabilised” because the addition of nickel is said to show an improved hardening reaction in soldering.

The creation of needle-structured crystals is said to alter to rounder structures, achieving an improved soldering flow for wave soldering of PCBs (reduction in torn soldering, less electrical bridging).

This alloy was developed in Japan and is supplied in Germany by the license holder, Balver Zinn.

The Printed Circuit Board Manufacturer

The SnCuNi system is particularly interesting for the PCB manufacturer as the investment needed to convert from conventional lead-tin techniques to tin/copper is far lower than for facilities providing the processing technology for chemically produced surfaces.

Because, this is also a melting pot procedure And only the solder’s tolerance with the dippingcontainer needs to be further researched.

Soldering Trials

As already mentioned, there has been insufficient field research. Therefore direct comparison of soldering characteristics has been undertaken in diverse trial campaigns by expert and work groups (BDF Germany, Boeing USA).

Both systems enable smooth, shining surfaces and reliable soldering joins, using wave soldering as well as reflow.

The tin-copper system promises advantages in terms of the copper’s peeling reactions(leaching) on the circuit boards. The effect on the copper surface is halved.