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Survey on Lead Free Solder Systems
 | Test boards have been realised by lead free reflow soldering at a peak temperature of
240°C and soldering time of 60 s at >217°C. |
| Lead free hand soldering requires much heat (pre-heat may be required) and full wetting
of the plated-through-holes is problematic. Special solder iron set-up is required
compared to traditional tin-lead soldering. |
| Integrity of realised lead free reflow soldered joints is found to be acceptable, even
if some tendency of solder void formation is observed most pronounced for the OSP board
finish test variants. |
| OSP board finish is found to result in incomplete wetting of solder lands in the case of
both of the lead free solders tested due to somehow poorer wetting properties compared to
tin-lead soldering. |
| Resistance to solder heat was found to be critical in the case of the metallised
polyester film capacitor due to a specification/performance mismatch by lead free
soldering condition. Robustness to solder heat is a key issue in component
selection/specification in lead free soldering. |
| Damp heat testing confirmed the flux from both of the lead free solder pastes to be
acceptably low activated, no corrosion observed. |
| Component shear testing vs. high temperature ageing testing did not indicate any
critical solder joint degradation up to 2000 h at 125°C. |
| Similar component shear testing vs. temperature cycling is found to result in gradual
degradation in the solder joints, but still typical lead free solder joints are expected
to pass 1000x, -40°C; +85°C without open circuit failures. |
| Results from component shear testing indicate OSP board finish to offer a somehow lower
performance relative to gold-nickel board finish, probably due to the difference in
wetting properties. |
| Destructive physical analysis of reliability tested parts confirmed the performance of
the tested lead free solders to be very similar. In all cases of solder joint degradation
the degradation is found to be in the "bulk" solder material of the joints. |
| In general, the results indicate the reliability of tin-silver-copper and tin-silver
lead free reflow soldered joints to be somehow comparable/similar to the reliability of
traditional tin-lead reflow soldered joints. |
| Lead is very toxic to humans and may cause serious deleterious chronic effects. The
other metals (tin, silver and copper) have significantly weaker toxicological effects on
humans than lead. |
| From a human toxicological point of view it may seem justified to avoid lead in solders,
as there is a risk of exposure. The use of modern technology, where the solder process
takes place in full containment will reduce or eliminate the exposure of workers to solder
vapors and fumes to nothing, regardless of the solders used (lead-containing or
lead-free). |
| There will though always be a risk of occupational exposure in connection with
maintenance, repair, etc., which from a human toxicological point of view may still
justify avoidance of lead in solders. |
| There is a risk of human exposure from residues from incineration of waste containg lead
solder. |
| From an ecotoxicological point of view substitution to lead-free solders is more
uncertain as emission and environmental fate are uncertain; exposure is therefore
uncertain. In a life cycle perspective, the main environmental load will not be during the
production/solder process, provided the production is optimized (e.g. with minimal losses
during manufacturing), but after end of use. The future general-purpose lead-free solder
implies the use of silver, which is much more toxic to aquatic organisms than lead. |
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