GLOSSARY

RoHS

Restriction of Hazardous Substances

What it is

RoHS (Restriction of Hazardous Substances) is a set of regulations that cap the amount of certain hazardous materials in electrical and electronic equipment placed on the market. The original directive was Directive 2002/95/EC, which was recast by Directive 2011/65/EU (usually called RoHS 2) and then amended by Directive (EU) 2015/863, which added four phthalates to the list of restricted substances (that amendment is often informally referred to as “RoHS 3”, though it is not a separate directive).

The UK has its own domestic RoHS regime based on the RoHS Regulations 2012, as amended. It is broadly aligned with the EU regime, but Great Britain and Northern Ireland now differ in some respects — most notably in how RoHS exemptions are administered.

For anyone buying, selling, or making electronics in the UK or EU, RoHS was a major reason mainstream electronics assembly moved from tin/lead solder to lead-free alloys such as tin/silver/copper — and the reason a lot of components got redesigned in the mid-2000s.

What it restricts

RoHS caps ten substances by weight in any homogeneous material within an in-scope product:

  • Lead (Pb) — 0.1 %
  • Mercury (Hg) — 0.1 %
  • Cadmium (Cd) — 0.01 %
  • Hexavalent chromium (Cr VI) — 0.1 %
  • Polybrominated biphenyls (PBB) — 0.1 %
  • Polybrominated diphenyl ethers (PBDE) — 0.1 %
  • Bis(2-ethylhexyl) phthalate (DEHP) — 0.1 %
  • Butyl benzyl phthalate (BBP) — 0.1 %
  • Dibutyl phthalate (DBP) — 0.1 %
  • Diisobutyl phthalate (DIBP) — 0.1 %

The percentages are per homogeneous material, not per assembly — a leaded solder joint can exceed the limit even though the lead as a fraction of the whole board's weight is well under it. Both regimes also provide specific exemptions that permit higher concentrations of restricted substances in defined applications. GB and EU/NI maintain separate exemption arrangements, and exemptions are application-specific and time-limited.

Why solder went lead-free

Tin/lead (Sn63Pb37) solder was the electronics standard for decades — a low melting point (~183 °C), easy to work with, extremely reliable joints. RoHS put lead over the cap for in-scope products, so mainstream assembly moved to lead-free alloys. The three you'll encounter in practice:

  • SAC305 (Sn96.5/Ag3/Cu0.5) — the default reflow alloy for RoHS-compliant assembly. Melts around 217 °C. This is what our boards are reflow-assembled with.
  • Sn/Cu (Sn99.3/Cu0.7) — cheaper, melts a little higher (around 227 °C). Common as a wave-solder bath alloy and in some HASL finishes.
  • Sn/Bi (Sn42/Bi58) — a low-temperature alloy melting around 138 °C. Used to reduce peak process temperature; joints can be more brittle than SAC solder joints, so it's not a drop-in for mechanically-stressed assemblies.

RoHS is primarily a product-regulation regime rather than a general ban on possessing or using leaded solder. Whether repair, modification or reuse is covered depends on the circumstances and the applicable jurisdiction; other rules on hazardous substances and occupational exposure may also apply.

What “RoHS compliant” on a datasheet promises

A manufacturer's RoHS declaration states that the part complies with the applicable RoHS requirements — the maximum concentration limits for each homogeneous material, together with any applicable exemptions. For a typical IC that covers the die attach, bond wires, mould compound, lead-frame plating, and any external finish. For a passive it covers the termination plating and the body material.

A RoHS-compliant marking does not necessarily tell you the exact composition or plating system used on the terminals. Two components can both be RoHS-compliant with different finishes (matte tin, nickel/palladium/ gold, tin/silver, etc.) that may not be interchangeable for a given assembly process. For that, look for specifications such as “terminal finish”, “lead finish” or “plating” in the manufacturer's datasheet.

And a RoHS-compliant component is not the same thing as a RoHS-compliant finished product. In the UK and EU, it is the manufacturer placing the finished equipment on the market who is responsible for determining and demonstrating compliance of the whole product, even when component suppliers provide their own RoHS declarations.

REACH, WEEE, and friends

RoHS is often mentioned alongside two other regimes it gets confused with. Worth naming so the marks on a product don't look mysterious:

  • REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) — a much broader chemicals regime covering substances and their use in products. The EU and UK have separate REACH regimes, though the UK regime is closely based on the EU framework. Both work through several mechanisms — including restrictions (Annex XVII under EU REACH, the equivalent UK REACH list) and authorisation for Substances of Very High Concern — that can impose obligations quite separate from RoHS. A product can comply with RoHS while still having obligations under REACH.
  • WEEE (Waste Electrical and Electronic Equipment) — governs the collection, treatment, recovery, and environmentally responsible disposal of electrical and electronic equipment at end of life. Unlike RoHS, which restricts substances in products, WEEE is primarily concerned with what happens to those products when they become waste. It's the reason electronics carry the crossed-out wheelie-bin symbol.