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What is inside a circuit board?

A printed circuit board is layers of copper tracks in a rigid laminate, covered with chips, capacitors and connectors and joined with tin solder. It is the part of most electronics that holds the precious metals, in platings and components too small to pick out by hand, so boards are gathered in bulk and recovered together.1

Drawing of a representative pulled computer motherboard, not a specific product, lying on a bench with other pulled boards beside it: the multilayer board with its near corner cut and stepped back to show copper layers between glass-fiber laminate; a processor socket with rows of gold-plated contacts inside its steel retention frame; four memory slots, the near one cut open to show its gold-plated contacts; three expansion slots; a large ball-grid chip lifted off its pads on a grid of solder balls; a voltage regulator of copper-wound inductors, aluminum electrolytic capacitors and transistors under a small finned aluminum heat sink; yellow tantalum capacitors and fields of tiny ceramic capacitors and resistors; a coin cell in its holder; power connectors and pin headers; and rear connectors in steel shells; and beside it a memory module and an expansion card with gold-plated edge fingers, a phone-size board and a loose ball-grid chip lying belly-up.
A representative computer motherboard with one corner cut and stepped back to show the layers inside the laminate. A memory module and an expansion card lie beside it, and one large chip is lifted off its pads.

Materials in circuit boards

Main materials
MaterialWhere it sits
CopperTracks, inner layers and connector pins
TinSolder on every joint
AluminumHeat sinks and capacitor cans
SteelShields, brackets and component leads
Trace materials
MaterialWhere it sits
GoldEdge fingers, connector pins and chip contacts
SilverLead-free solder and switch contacts
PalladiumMultilayer ceramic capacitors
TantalumSmall high-capacity capacitors
LeadTin-lead solder on older boards

What a circuit board of this kind most likely holds. Amounts are given in words, not weights, because content depends on the design.

How circuit boards are recycled

Boards are pulled from equipment as it is dismantled and sorted by grade, because the value is not spread evenly: high-grade boards, low-grade boards and loose chips are kept as separate lots.2 How they are prepared matters. Purely mechanical processing loses precious metal into dust and into the steel fraction, and careful manual dismantling loses less.2 Sorted boards are commonly fed to a copper smelter. The copper of the tracks joins the molten copper and the gold, silver and palladium follow it; after the copper is refined by electrolysis, the precious metals are extracted from what is left behind.23 Tin from the solder is recovered fairly well compared with most minor metals, while the tantalum in small capacitors rarely is.45 Chemical routes that dissolve the metals directly are also studied, but they have to cope with the complexity of a board and with strong reagents.6 Worldwide, most of the precious metal in discarded electronics is still not recovered.1

More on each stream: precious metals, copper.

Find them in the games and recycle them

Sources

  1. Global E-waste Monitor 2024ITU and UNITAR
  2. Metal Recycling: Opportunities, Limits, InfrastructureUnited Nations Environment Programme, International Resource Panel (2013)
  3. AP-42, Compilation of Air Pollutant Emission Factors, Section 12.9: Secondary Copper SmeltingU.S. Environmental Protection Agency, Section 12.9.2.2 'Smelting', pages 12.9-1 and 12.9-3
  4. Tin, Chapter S of Critical Mineral Resources of the United States: Economic and Environmental Geology and Prospects for Future Supply (Professional Paper 1802-S)U.S. Geological Survey (2017), Abstract, p. S1 (uses and recycling); Figure S1 (end uses); Environmental Considerations, p. S18 (reasons recycling is feasible). Solder use: USGS, Tin Statistics and Information, overview paragraph, https://www.usgs.gov/centers/national-minerals-information-center/tin-statistics-and-information
  5. Recycling Rates of Metals: A Status ReportUnited Nations Environment Programme, International Resource Panel (2011), Appendix F, Table F1 and accompanying text, pp. 35-37 (gallium, indium, tantalum, tungsten); Appendix D, Table D1, p. 31 (tin); main text, p. 18
  6. Challenges and opportunities in the recovery of gold from electronic wasteRSC Advances, Royal Society of Chemistry (2020), peer-reviewed open-access review, full text in PubMed Central, Sections 'Hydrometallurgy' and 'Leaching'

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