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ERA is a UK based consultancy organisation, and has helped many manufacturers with lead free soldering issues. RoHS compliance requires a lot of work and there are many technical challenges. This is because there are no drop-in replacements for tin/lead as all of the lead free solder alloys are different.
There are several issues that need to be resolved. First,
which solder alloy should be used? The table below lists the
main choices that are available.
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Alloy Composition
|
M.pt. oC
|
Comments
|
| Sn0.2Cu |
227
|
Widely used for wave soldering applications |
| Sn3.5Ag |
221
|
Wetting inferior
to SnAgCu |
Sn3.5Ag0.7Cu
(& variations on this) |
217
|
Most widely used
lead free alloy. Various percentages of silver
and copper are used |
| Sn1Ag0.5Cu and Sn0.3Ag0.7Cu |
~220 |
Relatively new lower cost alloys. Not suitable for all applications |
SnAgBi alloys
(some with Cu) |
Ca. 210 - 215
|
Better wetting
properties than SnAgCu but must not be used with
lead. Mainly used in Japan |
| Sn97n |
198
|
Zinc-containing
alloys are difficult to use, need special fluxes
and are susceptible to corrosion |
| 58B142Sn |
138
|
Low melting point,
hard, brittle alloy |
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All of the most useful solders have higher melting temperature than tin/lead and this creates a variety of reliability issues. One of the more common failures of components found by the Reliability and Failure Analysis Group at ERA is cracking of chip capacitors. Figure 1 shows a typical example.
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Figure 1. Crack in chip capacitor
Higher temperature also puts more strain into PCBs and faults in plated through holes such as shown in Figure 2 are likely to become more frequent.
Figure 2. Plated through hole
Most components now have lead-free termination coatings with few available that have tin/lead solder. The most common coating is electroplated tin but this can be susceptible to tin whiskers if a suitable mitigation strategy is not adoped. PCB protective coatings are less of a problem as alternatives to tin/lead HASL (hot air solder levelling) have been available for many years.
Bond reliability is also an issue. The thermal fatigue properties of lead-free solders are not yet well understood and bond reliability depends on many variables.
All of these issues take time to resolve and research into lead-free processes is continuing. Choosing the most appropriate solder products, finding suitable components, developing and optimising production processes and then testing products for reliability all take time and effort.
How can ERA help?
ERA has been supporting industry worldwide, UK government, RoHS enforcement bodies and the European Commission for several years on practical approaches to RoHS compliance and is internationally recognised as being leading experts in this area. ERA can help in the following ways:-
- Investigation of failures
- Assessment of new product quality
- Guidance on reliability issues and new product testing
- Assistance with lead-free design and process development
- Tin whisker mitigation strategies
All of these can be carried out on an individual or call off contract basis or through our subscriber scheme, AccessERA.
Further Information
ERA is supporting industry by keeping them abreast of these developments and how to respond, developing and presenting technical evidence to support exemptions, and choosing substitute materials. ERA runs courses on RoHS compliance and publishes a comprehensive RoHS guide for the electrical products sector. To find out more call us on +44 (0)1372 367444 or email. |
Lead
Free Soldering
