Next generation environment-friendly soldering technology

The result consists of a global assessment of the current and scenarios for future metal use for conventional and lead-free soldering in the electronics industry and an evaluation of the impacts on sustainable development. The term "sustainable development" was specified to toxic releases into the environment, energy consumption, metal resources, cost and a future resource consumption scenario for soldering. For the assessment of these impacts, new methodologies were created taking into account the particular requirements of sustainable development. The results show that lead-free soldering reduces the toxic potential of WEEE and PWBs at the end of life stage. The increased energy consumption over the life cycle will require around one additional nuclear plant globally. The technological progress, in particular miniaturization and integration, which are reducing the soldering material consumption on the component level, cannot compensate the increasing demand of soldering materials due to the market growth in the electronics industry. A new efficiency approach shows that the use of bismuth increases the efficiency of mining, but decreases the eco-efficiency of soldering. An in-depth study yielded detailed data about the performance of the recycling and smelting infrastructure in Europe. This knowledge facilitated calculating the additional consumption of metals in lead-free solders compared to conventional soldering. Besides for bismuthe, the fears that there might not be enough metal resources and supplies for lead-free soldering could be disproved. However, the trend to increasing use of soldering materials due to market growth remains an issue of concern in particular with respect to the currently increasing prices due to the economical uprise of Asian countries, especially China. This situation needs further increases of the global collection and recycling rates of WEEE and further improvements in the recycling performance in particular for tin and other metals besides noble metals and platinum group metals, which already have very high recycling rates.

This result comprises a new innovative solder paste as well as its characteristics and functional tests. It corresponds to deliverables 1D8 and 1D11. Based on SnAgCu alloys, it has been especially developed for very fine pitch soldering and for use in a wide range of applications, from consumer markets to critical automotive electronics. It exhibits safe residue in no clean process and good wettability with large reflow process window on different lead free finishes. This product is widely available in Europe, Asia and North America.

To allow a systematic and precise evaluation of new EFSOT solder paste, a test board was developed, it is used to validate all kinds of very fine pitch printing and soldering as well as more specific needs such as: cleaning feasibility, insulation properties, power components soldering, compatibility of various PCB finishing (Imm Tin, Imm Silver, Gold, OSP, thickfilm Ag/Cu) with LF solder etc... The design did contain the different standard pattern of TTA, Philips and AB for comparison and has been used intensively by TTA, Philips and AB to manufacture boards and validate the soldering processes (Screen printing parameters and cleaning, paste deposite, demolding and abandon time, Oven profiles) This test is a major support for implementing high yield lead-free processes. The window framing design of AB was found to give best results in high volume production using AOI.

This result consists of a proposal for a standard whisker test that was worked out in co-operation with standardization committees. The proposal is based on the results of the root cause research for whiskering. The risk of whiskers (growth of tin needles on package leads and on solder joints) are increased with transition to lead-free soldering because of the high tin content in solders and finishes. Techniques to prevent or reduce the formation of whiskers are important for the transition to lead-free electronic products. Understanding of whisker formation is essential to develop a globally accepted test. Mechanisms that influence whisker formation for different substrates and lead-free product finishes have been studied and a model has been developed that explains observed phenomena quite well. The proposals are currently under discussion in standardization committees. It is expected that the final version in IEC will be available in the second half of 2006. Discussions on the JEDEC standard are still going, but JEDEC shifts more and more into the direction of IEC. Accelerated tests are not yet available and will be a target for further research.

This result comprises 3 sub-results: - LCA comparison of alternatives to lead-free soldering (deliverable 3D5) - Methodology for LC impact assessment (deliverable 3D3) to input SIMAPRO database - Assessment of the differences in the Japanese, Korean and European results (deliverable 3D7) In the first sub-result, environmental impact of alternative soldering has been studied. The LCA is dominated by the impact of mining and refining of metals. Energy consumption during solder application is relevant for reflow techniques. Regarding the importance of finish application, this impact is irrelevant for immersion techniques. The damage methodology results also from a cooperation outside EFSOT: the RECIPE project. Resource depletion and toxicity of less known metals (as bismuth or silver) are being evaluated. Exchanges with our Asian colleagues concern the impact assessment models as well as the LCA results. The comparison is not yet fully completed but minor differences might appear as climate, geology, energy data show differences. Additionally, the project contemplates the compilation of the methodology and the data used for the study into a database that will be delivered to the EFSOT consortium.

This result consists of a new reliability testing method for lead-free solder joints and a model for the reliable assembly of PWBs. The reliability test can assess the reliability impacts of different solder/finish combinations and solder joint gap geometries. This is a clear progress compared to the bulk tests that have been widely used so far. The new test is an adaptation to the requirements of lead-free soldering with its variety of solder/finish combinations on one hand. On the other hand it allows reliability assessments of fine pitch solder joints and thus enters new dimensions for reliability testing following the permanent trend of miniaturization and ever smaller solder joints. Additionally to testing, the proper assembly especially of complex and miniaturized PWBs requires a deeper knowledge on how to design and assemble such boards. A model was therefore developed and tested to achieve highly reliable PWBs in production and later use. Reliability at 0 h (quality of solder joints and ppm level of failures after board assembly) was modelled. Modelling results show that simultaneous reduction of tomb-stoning and bridging, and an increase in self-alignment, are incompatible. A theoretical model was also developed for each of the three phenomena. Therefore, intermediate settings are recommended, until the occurrence of a particular defect in the reflow process requires shifting the settings to correct for this phenomenon to optimize the ppm reject level. The combination of the model outcomes and the experimental results led to new insights for each phenomenon. The most important of these is that dynamic processes, such as the formation of an oxide layer on fillet surfaces, during reflow, play a major role.

This result consists of newly developed recycling and re-use processes providing small and medium recycling companies with a cost effective and environmental friendly end-of-life treatment for lead-free solder printed wire boards (PWBs) from medium or big sized post-consume equipment. The main differences between the proposed process and the current recycling scheme lie in the inclusion of the new stages of: - Lead-containing and lead-free solder PWBs sorting. - Valuable components recovery for reuse purpose. - Recovery of lead-free solders concentrates. The expected coexistence between both traditional and new lead-free solder PWBs in WEEE for several years requires a previous sorting step to avoid a mixture of metals more complicated to separate and recover in metallurgic processes. The consequences of lead-free solders in recycling market and the theoretical behaviour of lead-free solder PWBs in copper smelters have been also considered. An LCA ensured the environmental benefit of the developed processes. This result is based on Deliverables 4D1 (New lead-free solders PCBs from reuse and recycling point of view), 4D2 (Specific recycling schemes for the lead-free solder PWBs), 4D3 (System for the discrimination of lead-containing from lead-free solder PWBs) and 4D4 (Comparison of lead-containing and lead-free PWBs reuse and recycling by LCA).

The result shows different possibilities for labelling and marking of lead-free soldering materials and components and introduces international labelling standards under discussion. It highlights the differing requirements for such labels of the various actors in the supply chain and along the life cycle and discusses the economic conditions of labelling.

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