RoHS compliant tin/lead plating

A. I'm working very hard on understanding this. I'm still not there. I see your letter has gone unanswered for a while, so I'll run this up the flagpole...and see who shoots it full of holes. Take what I say with a grain of salt.

The rule is, as far as I can understand, that not more than 0.1% of any "homogenous" part can consist of lead. A plated coating is not considered "homogenous" in that it's not something you can unscrew - it's part of the metal.

So, I suppose you would determine the thickness of the coating, the density of the alloy, then, the surface area of the part. Now, you have the weight of the coating...multiply by 0.03, now, you have the weight of the lead.

Now, weigh the whole component, and divide the weight of the lead by that weight. If the number is less than 0.001, it's compliant. If it's greater, it's not. That is what I think it all means, anyway.

There are numerous exemptions. They are also still arguing about what's "homogenous."

A. Dave, that seems a long way of saying 3% lead exceeds 0.1% lead so non-RoHS.

Jim, there are exemptions to the 0.1% lead limit, but probably none applies. See the Global Automotive Declarable Substance List (GADSL), which includes both RoHS & ELV, at http://www.gadsl.org
Exemptions include free-machining alloys and critical electronics applications in aerospace and computers. Some exemptions are being phased out as replacements are developed. Intel uses a 5% Pb solder on present CPU chips but has announced next generation, 0.45 nm chips will use a new, Pb-free solder.

A. Not only was it long, Ken, it was wrong.

Apparently plated coatings are considered to be a "homogenous" part, because they can be physically separated from the substrate. So, the answer to the original posters question is pretty definitely 'no', unless it falls under one of those exemptions.

A. Hello Ji. The reason most contact materials may be noble metals today is that electronics continue to grow smaller, lower power, and more critical. The thing is: tin-lead plating, tin plating, nickel plating, and all the non-noble metals tarnish -- they grow non-conductive or marginally conductive oxide layers which interfere with conductivity. The amount of resistance wasn't an issue in many of the circuits of 50 years ago, but is today. Noble metals don't tarnish and are more appropriate for low power digital signals.

 Hi, Dave. No one can possibly fault you for your difficulty in accepting the European Parliament's ridiculous definition of the word "homogeneous" :-)

The goals of RoHS and related restrictions are obvious and probably admirable, but getting there has involved really weird definitions of words, to wit, a chromate conversion coating that can be easily rubbed off the plating by a child with a pencil eraser is considered "homogeneous" with the plating (inseparable from it), but the plating layer which can't be removed by a trained machinist with a factory full of machine tools is considered to be "not homogeneous" with the substrate :-)

Basically, they want people to stop using lead and hexavalent chromium, and it may be best if we just ask Ji and Jim to simply accept that -- because they will probably continue to twist words as necessary to achieve that end :-)

Regards,

A. Hi Lisa. I am not understanding the word 'depot' in this context. Was it perhaps a spell-check replacement for "deposit" or "the part"?

"Alodine" is a Henkel trade name for chromate conversion coatings and non-chromate post treatments on (to my understanding) aluminum, and on cadmium and zinc plating. Post treatments of similar sorts have been used on tin-lead plating as a tarnish inhibitor, so I would say there will be no negative interaction.

But I have to admit that I don't understand the question -- I don't know the substrate material, whether "Alodine" enhances that surface or not, or whether it is even remotely satisfactory to call tin-lead plating and Alodine conversion coating 'equivalent' or 'satisfactory' for your application.

Regards,