CORDIS provides links to public deliverables and publications of HORIZON projects.
Links to deliverables and publications from FP7 projects, as well as links to some specific result types such as dataset and software, are dynamically retrieved from OpenAIRE .
Exploitable results
The objectives of the project were: -To develop both reflow and wave soldering processes using lead-free solders, board and component metallisations (i.e. totally lead-free systems) with fluxes that are substantially free of volatile organic compounds (VOCs).
-To devise repair and rework procedures with novel lead-free flux-cored wire.
-To establish the properties of the lead-free solders compared with the tin-lead eutectic in respect of their mechanical and thermo-mechanical performance. In the three years of the project, the candidate solders and their matched fluxing systems, board finishes and component metallisations were selected and tested in extensive assembly trials.
Conclusions:
- A lead-free soldering technology based on Sn(Ag,Cu,Bi,Sb) alloys, possibly with minor additions to enhance aspects of soldering performance, is technically and industrially viable.
- A SnAgBiSb alloy has been shown to be suitable for single-side wave soldering.
- Bi additions to solder for both reflow and wave applications reduced the joint formation temperature, but caused other problems.
- The process window for lead-free wave soldering is within the established region for tin-lead soldering, albeit at the top end in terms of soldering time and temperature.
- A VOC-free flux for lead-free wave soldering has been developed.
- The process window for lead-free reflow soldering is compatible with the majority of current component demands, but the minimum soldering temperature of 225-230°C is a cause for concern for some IC packages, capacitors and connectors. This is clearly an impediment to the rapid adoption of lead-free solders unless the reflow temperature can be reduced.
- The reliability of lead-free assemblies is seen to be equivalent to tin-lead equivalents in terms of cycles to failure in thermo-mechanical fatigue tests. Specific conclusions from the reliability work were:
- An Sb addition resulted in increased reliability in wave soldering, but additions to the reflow solder of 0.25% or 0.5% had no effect on joint lifetime (the equivalent grain-refining effect of the Sb addition to wave soldered joints was not seen).
- Bi additions had contradictory effects on joint lifetimes. In the absence of lead, the joint lifetimes were extended by up to 80%, but the combination of Bi from the solder and Pb from a metallisation can cause severe life shortening, probably due to the formation of SnPbBi eutectic liquid (96 °C). This is thought not to be inevitable, but this combination would have to be verified for each application.
- Nitrogen inerting did not affect joint lifetime for reflow soldering
- SnCu0.7 solder showed poorly in early screening trials and was rejected
- There was no evidence to suggest that SnAg3.8Cu0.7 will allow increased operating temperatures
- Tolerance to a wide range of standard board and component finishes has been demonstrated.
In summary, lead-free soldering technology has been demonstrated to be viable. In addition to being attractive from an environmental point of view, it is demonstrating other benefits including an extended service life under some conditions. In fulfilment of the targets of IDEALS, the first lead-free products will be available during 1999.
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