My last post here asked the question, are your products toxic? Perhaps I should have said your products are toxic. What do you plan to do about that? Removing even one toxic compound from semiconductor manufacturing takes much longer than expected.

Leaded or Unleaded?

Lead in solder is an excellent example. Twenty years after the industry started weaning itself off of Pb-based solders in anticipation of the Restrictions on Hazardous Substances (RoHS) directive, we are still not done.

Françoise von Trapp interviewed Dean Payne, Indium Corporation product manager, about this topic as part of her ECTC 2022 podcast coverage. The episode aired today and can be found here. (If you’re not a subscriber, I invite you to check it out and subscribe.)

The transition is taking this long because Pb is an excellent solder material. As Dean says, “Nothing else does the job as well as lead.” Faced with restrictions, though, the industry had no choice but to find alternatives. Tin-silver-copper (SAC) alloys are now established replacements for eutectic tin-lead (Sn-Pb). It took many years of work to overcome reliability challenges.

Eutectic Sn-Pb contains 37% Pb by weight. RoHS restrictions have banned this alloy in electronics for around 15 years. Ironically, high-Pb solders containing at least 85% Pb are still allowed. This is a case where the practical aspects—lack of a suitable alternative that comes close enough to meeting performance requirements—have outweighed the goal of removing a toxic element. High reliability remains the top priority for applications like military and aerospace, where the failure of solder joints can endanger human life.

Indium Corporation will soon release a new alloy that can be a drop-in replacement for high-Pb solder. This Pb-free alloy can be reflowed at the same temperature range, avoiding some of the problems that plagued the adoption of SAC alloys. According to Dean, testing shows excellent thermal and electrical performance.

Regulations and Exemptions

Why did it take 20 years to launch a Pb-free solder for high-reliability applications? I suspect that the longstanding RoHS exemption had something to do with it. In the absence of urgency to meet regulations, solder manufacturers were not willing to invest time and money in developing such a product.

When I look at the categories of products covered and exempted from RoHS, I sometimes wonder if the regulation does any good. Global Pb production increased nearly 50% from 2006—the year RoHS first went into effect—to 2019. Most of that is for use in vehicle batteries, and transportation is one of the sectors exempted from RoHS. In 2011, solders accounted for only 2% of global Pb consumption. Although that is old data, I doubt the balance has significantly changed (Table 1).

Table 1: Global end use of lead in 2011 by category.

While it might be prudent to tackle Pb use in batteries, I congratulate Indium Corporation on launching the new alloy. (Full disclosure: I have held a bias toward Indium Corporation since the company gave me free indium-based alloys for my Ph.D. research in the 1990s.)

Regulations like RoHS have value. They can force manufacturers to become more environmentally responsible. I also believe it is critical to include scientists and engineers in decision-making and for those professionals to disclose their affiliations to avoid conflicts of interest. Technical experts with the knowledge to understand and explain the technology plus a genuine interest in protecting public health can step up and guide future regulation. With this input, we can regulate hazardous materials in a way that best protects people and the environment.

Julia Goldstein

Julia Goldstein is an author and business owner on a mission to make manufacturing more…

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