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You are here: Home > Products > Environment  > Lead Free

Harwin and the Elimination of Lead

Prior to twenty years ago, the standard plating finish for solder terminations was 60/40 tin/lead, to match the typical mix found in solders. Since then the ratio has been changed to 90/10, reducing the amount of lead in the terminations. From the announcement of the impending legislations, Harwin has been further reducing its lead consumption. Given the wide diversity of alternative solders that the industry has been trying, 100% pure Tin was chosen as the best plating finish to match all conditions.

Some Harwin products have now been lead-free for a number of years. Many others have been recently converted to a lead-free format, view our RoHS compliance diagram for current product options.

As the legislation stands, some industry sectors (such as medical or military) are still exempt from the current version of the Directive. This is partly due to the original emphasis of the legislation being aimed at consumer electronics, and also due to the safety-critical and mission-critical status of medical and military equipment. However, these other market sectors are due for consideration at the next review of the legislation in 2008, and may be included as soon as 2010, pending further research. Harwin are continuing to offer leaded connectors for these exempt sectors wherever possible.

Impact of Soldering Temperatures

One of the primary reasons for the use of lead in solder was to reduce the temperature required to satisfactorily melt the solder mix. Although alternatives have been added to the lead-free solders, none are as effective as the Lead. Soldering temperatures have risen by typically 10° to 20°C, and as high as 270°C. This now has an impact on the plastic elements of Harwin connectors.

One of the favoured materials for the plastic moulding in connectors had been PBT (Polybutylene Terephthalate), which gives good mechanical strength and ease of moulding. However, it typically has softening temperatures of 210° to 230°C – which is not suitable in a lead-free soldering process.

For all our solder-terminating products, Harwin have committed to offering the RoHS compliant items with a plastic designed to withstand the lead-free soldering process. This has involved the moulding material being changed to a High-temperature mould material, with softening temperatures higher than those of PBT. Any instances where this has not been possible, it will be noted within the description of the product.

Tin Whiskers

The exact cause of tin whiskers is still unclear (see the Links area for further information on this phenomenon). Research is still being carried out on this subject. However, there are certain measures that can be implemented to help prevent whisker growth:

Plating specification – thin 100% tin over nickel (standard plating for Harwin tin-plated connectors).

Stress reduction – can be minimised by consideration of the component design.

Storage – Parts should be stored in dry, regulated temperatures.

Solder processing – Solder processing should avoid sudden and rapid changes of temperature where possible.

Discolouration and Dewetting

Discolouration is caused by oxide formation on the plating finish. Although of significant visual impact, it is unlikely to affect the solderability of the product. However, Dewetting (the plating finish or solder pools into clusters on the product) is more serious, and can cause poor solder joint quality. There are steps that can be taken to minimise these incidences.

Plating specification – thin 100% tin over nickel (standard plating for Harwin tin-plated connectors).

Use of additives to minimise discolouration.

Solder Preheat – Heat should be applied at a gradual rate of no more than 1°C/sec from ambient. If possible, parts should be held at Preheat Temperature for a short period to allow all components and laminates to equalise to the same temperature

Solder temperature – for ideal conditions, soldering should be carried out at 240°C ± 5°C. Regardless of oven temperature, component temperature should be checked using a “mole” probe which measures temperature at the pcb surface. Exposure time for the highest soldering temperatures should be kept to the minimum that will ensure a good solder joint.

Solder oven – Convection ovens give the greatest control of temperature gradients and steady temperatures, and even heating across the PCB surface. Infra-Red (IR) ovens are not recommended – process control is difficult, and surface temeperatures can vary by as much as 40°C.

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