RoHS (Restriction of Hazardous Substances)
RoHS (Restriction of Hazardous Substances) is the EU directive restricting ten substances in electrical and electronic equipment: lead, mercury, cadmium, hexavalent chromium, two brominated flame retardants (PBB and PBDE), and four phthalates. Limits apply at the homogeneous material level, 0.1 percent by weight for most substances and 0.01 percent for cadmium. Products in scope must comply to carry the CE mark in the EU.
Examples
Failed plating screen: An XRF check on a batch of 25,000 zinc-plated brackets shows hexavalent chromium in the passivation layer. The lot is quarantined, the plater switches to a trivalent process, and the buyer adds a Cr(VI)-free callout to the drawing.
Exemption expiry watch: A motor controller uses a high-lead solder under a RoHS exemption. The compliance team tracks the renewal cycle; when renewal looks uncertain, engineering qualifies an alternative alloy 14 months ahead of the expiry date instead of scrambling after it.
Per-part declarations: An OEM requires a RoHS certificate for each of the 340 part numbers on a new control box. Its EMS partner supplies 310 from its database within a week; the remaining 30, mostly custom mechanical parts, need fresh supplier statements.
Definition
The phrase that does the work in RoHS is "homogeneous material". Limits are assessed not on the finished product or even the component, but on each material that could be mechanically separated: the solder joint, the wire insulation, the plating layer. A 500 g power supply is non-compliant if a single 2 mg solder joint exceeds the lead limit, which is why declarations from an EMS partner have to roll up from the full bill of materials, not just the board level.
Exemptions keep the directive workable. Lead is still permitted in specific applications, such as high-melting-temperature solders and as an alloying element in some brass alloys, and every exemption carries an expiry date subject to renewal. Designing against an expiring exemption is a quiet risk: a part can be compliant today and non-compliant in two years without any change to the drawing.
Where REACH mostly requires article makers to disclose an evolving substance list, RoHS is a hard restriction on a fixed set of ten. Practical management means RoHS clauses in every specification for in-scope parts, a certificate of compliance on file per part number, and verification of high-risk commodities (platings, solders, cables) with periodic XRF screening or lab testing rather than paperwork alone.
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