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The persistence of Tin/Lead plating

One of the biggest projects in my time at Harwin was the introduction of RoHS. The first iteration of this legislation took effect on 1st July 2006 – which meant changes to product and all new stock had to be in place well before this deadline.

For Harwin, the main concern was the restriction of Lead. Back then, tin/lead was the most popular plating finish for solderable contacts. The technology for tin/lead soldering was well understood and well-researched, and there were no surprises using these solders and components. Then we had to drop Lead from the mix. We also had to make sure that the plastics used could withstand higher soldering temperatures. These changes probably affected more than two-thirds of our existing product mix.

Over time, we assumed we’d see a fairly quick disappearance of Non-RoHS parts. But here we are 14-plus years later, and we still have regular sales for connectors with tin/lead plated terminations – why?

 

Europe, not Global

First, we should address the fact that (at first) RoHS was a European legislation. For a global company like Harwin selling into multiple continents, naturally we had customers requiring components that were compatible for their RoHS-compliant assemblies. But we also had (and still have) customers that do not sell into Europe, and do not need to meet this EU requirement.

Admittedly, this pool of customers is steadily shrinking – both as companies drive to expand and sell globally via the internet, and also as other countries and regions adopt their own version of RoHS. It’s not difficult to see a time when RoHS requirements are practically world-wide.

 

Exempt Markets – Military and Medical

The biggest factor in supporting tin/lead plated connectors are the exempt markets/applications – Medical and Military. These sectors got a ‘pass’ due to their safety and mission critical requirements. Tin/lead soldering had history. Pure tin-plated components and other tin-based solders were still relatively new, did not have years of field-testing or even many laboratory results. And then there was tin whiskers.

 

What’s a Tin Whisker?

There are a lot of research papers out there that will cover this in depth. In brief, a pure tin plating layer on a copper alloy base material will, over time, grow a thin whisker-like crystal. These tiny microscopic ‘hairs’ can get long enough to short across to another track or joint. By adding lead to the tin plating, this property was prevented – as well has lowering the solder temperature to an acceptable level.

 

Avoiding Tin Whiskers in the RoHS Era

There are 3 choices, each of which has pros and cons:

  • Switch to gold – Gold plating on contacts also has its own set of issues, called gold embrittlement. This can be reduced by smart choices on the thicknesses of gold used, but you are still using a solder joint with dissimilar metals (gold plating against tin-based solders). At least it’s a well-known and researched effect, and this plating option is worth serious consideration in exempt markets.
  • Make sure your 100% tin plating has a ‘mitigation’ feature to prevent tin whiskers. There are multiple methods with varying degrees of success, but we recommend a nickel undercoat. We use this method on all our tin-plated connectors and have not had a single confirmed case of tin whiskers in the field.
    NOTE: Be wary of matte v bright tin arguments – testing on this in the early 2000s was done with these two options plated directly onto the copper alloy base metal. This showed matte as being less prone to whiskers than bright tin – but still not truly effective at stopping this problem. Nickel undercoat under either finish is vastly more effective and makes it irrelevant whether the tin is bright or matte.
  • Stick with Tin/Lead – which is where we return to why we still have this plating option for our exempt customers.

 

Will there always be Tin/Lead?

Time for a crystal ball… The Medical and Military sectors are slowly being forced into RoHS, as less and less components are continued in tin/lead formats. Some manufacturers may now only offer these products as made-to-order or customer specials only, increasing the price, MOQ (Minimum Order Quantity) and lead-times. It’s unlikely this trend will reverse.

In addition, as more research is done into RoHS compliant soldering, the confidence will increase in the safety and reliability of these products. There may come a time when EU legislation no longer allows for any exempt markets, and all electrical & electronic products sold within the EU will have to be RoHS compliant.

 

Harwin and Tin/Lead finishes

Our Hi-Rel range of Datamate (2mm pitch) is the only standard product now available with tin/lead options. While we have a demand for tin/lead finishes within our Datamate range, we will continue to supply them. Our other Hi-Rel ranges of Gecko and M300 were introduced post-RoHS, and have always been full gold plating to provide the simplest solution for our military and medical customers to avoid tin whisker concerns.

Many of our products are aimed at more commercial markets and have required compliant products since 2006, so are available in RoHS compliant plating finishes only.

Although the demand for non-compliant product is in a slow steady decline, we are not at the end of the road yet. However, it would not surprise me to see the end of tin/lead in the next 10 years – and surely that can only be good for the environment.

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