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Overview

General comment

Coherent optical transceiver module built on a silicon-photonics chip that carries the modulators, photodetectors and fiber coupling once handled by separate transmit and receive sub-assemblies.

Technology
Not stated
Geography
Global average data from equipment vendor specifications and industry literature

System boundary

System boundary - Optical Transceiver QSFP DD 400G ZrSystem boundary figure: identity, gate in, entering flows, the dashed system boundary and the unit processes inside it, the reference product, emissions and waste, and below it the flows that are recorded but not quantified. No inventory quantities.Optical Transceiver QSFP DD 400G ZrGATE INSub-component procurementENTERING FLOWSElectricityWaterMaterialsFreight transportOtherSYSTEM BOUNDARYCOMPOSED OF OTHER REEL DATASETSDigital Signal Processor7nm FinFET wafer, 300mm, moderatescenarioSiP PIC90nm Silicon Photonics wafer, 200mm,moderate scenarioLaser SourceInP Laser Wafer 1550nm wafer, 100mm,United StatesPrinted Circuit Board8-Layer HDI PCB, ENIG finishFiber ConnectorFiber LC ConnectorDecoupling capacitors(0201 size)MLCC X7R 0201Bulk decoupling capacitors(0603 size)MLCC X7R 0603Signal conditioningresistorsChip Resistor 0402Power supply filteringFerrite Bead 0402REFERENCE PRODUCTOptical Transceiver QSFP DD 400GZrFinal assemblyEMISSIONS AND WASTEEmissions to airEmissions to waterWaste routesRECORDED BUT NOT QUANTIFIEDIn scope, left out of the quantified inventoryCut off below the significance threshold, or with no background dataset available - each is listed with its reason9FLOWSsystem boundaryreference flowentering flowemission / waste

The figure groups this dataset's unit processes by class. It is not a count of manufacturing steps — each process runs over as many passes as the flow requires, and those pass counts ship with the dataset.

Download this figure (SVG)

Data quality and references

Composite DQI 2.2 Good
Reliability
3.0
Completeness
2.0
Temporal
2.0
Geographic
2.0
Technological
2.3
How the score is calculated: Constituent datasets have more influence when they contribute a larger share of the modelled cradle-to-gate energy demand.

Pedigree scores follow the ecoinvent data-quality matrix: 1 is the best attainable, 5 the weakest. The composite is their aggregate.

Sampling procedure
Component vendor specifications, academic papers, industry literature
Coverage status
Composed from linked REEL datasets
Pedigree-scored source files
75 — the source records behind this dataset's manufacturing operations. Each carries the five pedigree axes above; the composite DQI aggregates them.

Technosphere inputs

21 flows. Quantities are not published; they ship with the dataset on Circa.

Digital Signal Processor REEL datasetwafer
Derivation basis
  • Calculated by the manufacturing model. The linked REEL dataset carries the upstream life cycle sources.

No source is attached to this row.

Source citations
Not stated
Background dataset
Modelled by REEL; see the upstream dataset above.
Notes
Wafer demand calculated from die count, rectangular wafer packing, die yield and assembly yield. Wafer manufacturing yield is already included upstream.
Uncertainty
No range defined.
Unit
wafer
SiP PIC REEL datasetwafer
Derivation basis
  • Calculated by the manufacturing model. The linked REEL dataset carries the upstream life cycle sources.

No source is attached to this row.

Source citations
Not stated
Background dataset
Modelled by REEL; see the upstream dataset above.
Notes
Wafer demand calculated from die count, rectangular wafer packing, die yield and assembly yield. Wafer manufacturing yield is already included upstream. This entry states no die yield of its own, so the sizing uses the die yield this dataset declares for that die.
Uncertainty
No range defined.
Unit
wafer
Laser Source REEL datasetwafer
Derivation basis
  • Calculated by the manufacturing model. The linked REEL dataset carries the upstream life cycle sources.

No source is attached to this row.

Source citations
Not stated
Background dataset
Modelled by REEL; see the upstream dataset above.
Notes
Wafer demand calculated from die count, rectangular wafer packing, die yield and assembly yield. Wafer manufacturing yield is already included upstream.
Uncertainty
No range defined.
Unit
wafer
Printed Circuit Board REEL datasetm2
Derivation basis
  • Calculated by the manufacturing model. The linked REEL dataset carries the upstream life cycle sources.

No source is attached to this row.

Source citations
Not stated
Upstream REEL dataset
8-Layer HDI PCB, ENIG finish
Background dataset
Modelled by REEL; see the upstream dataset above.
Notes
Adjusted for assembly yield.
Uncertainty
No range defined.
Unit
m2
Fiber Connector REEL datasetunit
Derivation basis
  • Calculated by the manufacturing model. The linked REEL dataset carries the upstream life cycle sources.

No source is attached to this row.

Source citations
Not stated
Upstream REEL dataset
Fiber LC Connector
Background dataset
Modelled by REEL; see the upstream dataset above.
Notes
Quantity is in reference-component equivalents, not pieces: this entry's declared total mass divided by the referenced dataset's reference-component mass, then adjusted for assembly yield. Read it against that reference mass, not against any piece count in this row's name.
Uncertainty
No range defined.
Unit
unit
Decoupling capacitors (0201 size) REEL datasetunit
Derivation basis
  • Calculated by the manufacturing model. The linked REEL dataset carries the upstream life cycle sources.

No source is attached to this row.

Source citations
Not stated
Upstream REEL dataset
MLCC X7R 0201
Background dataset
Modelled by REEL; see the upstream dataset above.
Notes
Adjusted for assembly yield.
Uncertainty
No range defined.
Unit
unit
Bulk decoupling capacitors (0603 size) REEL datasetunit
Derivation basis
  • Calculated by the manufacturing model. The linked REEL dataset carries the upstream life cycle sources.

No source is attached to this row.

Source citations
Not stated
Upstream REEL dataset
MLCC X7R 0603
Background dataset
Modelled by REEL; see the upstream dataset above.
Notes
Adjusted for assembly yield.
Uncertainty
No range defined.
Unit
unit
Signal conditioning resistors REEL datasetunit
Derivation basis
  • Calculated by the manufacturing model. The linked REEL dataset carries the upstream life cycle sources.

No source is attached to this row.

Source citations
Not stated
Upstream REEL dataset
Chip Resistor 0402
Background dataset
Modelled by REEL; see the upstream dataset above.
Notes
Adjusted for assembly yield.
Uncertainty
No range defined.
Unit
unit
Power supply filtering REEL datasetunit
Derivation basis
  • Calculated by the manufacturing model. The linked REEL dataset carries the upstream life cycle sources.

No source is attached to this row.

Source citations
Not stated
Upstream REEL dataset
Ferrite Bead 0402
Background dataset
Modelled by REEL; see the upstream dataset above.
Notes
Adjusted for assembly yield.
Uncertainty
No range defined.
Unit
unit
Thermal Interface Material Materialkg
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12
Background dataset
silicone product
Uncertainty
No range defined.
Unit
kg
Copper Conductors Materialkg · -30% / +40%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12
Background dataset
copper, cathode
Uncertainty
-30% / +40% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
Epoxy Encapsulant Materialkg · -30% / +40%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12
Background dataset
epoxy resin, liquid
Uncertainty
-30% / +40% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
Gold Wire (bonding) Materialkg · -40% / +60%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12
Background dataset
gold
Uncertainty
-40% / +60% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
Latch Spring (Steel) Materialkg · -30% / +40%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12
Background dataset
steel, low-alloyed
Uncertainty
-30% / +40% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
Nickel Plating Materialkg · -33.3% / +46.7%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12
Background dataset
nickel, class 1
Uncertainty
-33.3% / +46.7% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
UV-Cure Adhesive Materialkg · -50% / +100.1%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
proxy-mapped
Background dataset
methyl methacrylate
Uncertainty
-50% / +100.1% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
Zinc Alloy (Zamak 3) Materialkg · ±20%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12
Background dataset
zamak ingot, 10% primary zinc input
Uncertainty
±20% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
Wafer transport, TW fab to packaging site - Air (short haul) Freight transporttkm · -47.4% / +80%
Derivation basis
  • Specified for this manufacturing operation and scaled to the dataset's functional unit.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12
Background dataset
transport, freight, aircraft, dedicated freight, short haul
Notes
Freight for the part-finished product moving between REEL-modelled sites: the wafer fraction this dataset consumes, travelling from foundry fab to packaging site, cross-border. Shipped mass is that wafer fraction times the wafer mass implied by its declared diameter, times a shipping-packaging factor covering the returnable front-opening shipping box and its secondary carton; the packaging production burden is excluded as returnable, while its mass is carried because freight scales with what is actually shipped. Air freight is allocated on chargeable weight rather than actual shipped mass. The authored band holds the fixed route distance: its lower endpoint uses actual shipped mass, its central uses chargeable-weight allocation, and its upper endpoint adds the separate reusable-carrier return service, not aircraft backhaul.
Uncertainty
-47.4% / +80% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
tkm — tonne-kilometres, a transport effort rather than a mass
Wafer transport, United States – Western Grid (WECC) fab to packaging site - Air (long haul) Freight transporttkm · -47.4% / +80%
Derivation basis
  • Specified for this manufacturing operation and scaled to the dataset's functional unit.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12
Background dataset
transport, freight, aircraft, dedicated freight, long haul
Notes
Freight for the part-finished product moving between REEL-modelled sites: the wafer fraction this dataset consumes, travelling from US compound-semiconductor fab to its Asian packaging site, intercontinental. Shipped mass is that wafer fraction times the wafer mass implied by the diameter, thickness and substrate its own model declares, times a shipping-packaging factor covering the returnable wafer shipping box and its secondary carton. No published container mass was found for a wafer of this diameter, so the factor carried here is the one derived for the largest diameter in this database rather than one derived for this one. The two diameters that do have a measured carrier show the factor rising as the wafer gets smaller, because a box's own mass does not fall in proportion to the wafer material it holds, so this leg's shipped mass is more likely to be understated than overstated; the packaging production burden is excluded as returnable, while its mass is carried because freight scales with what is actually shipped. Air freight is allocated on chargeable weight rather than actual shipped mass. The authored band holds the fixed route distance: its lower endpoint uses actual shipped mass, its central uses chargeable-weight allocation, and its upper endpoint adds the separate reusable-carrier return service, not aircraft backhaul. The route distance is a declared proxy: the route evidence records this vendor class's back-end location as not public and carries only a representative long-haul air lane from the United States to an Asian assembly hub, so that representative lane stands in for a site pair no public source states.
Uncertainty
-47.4% / +80% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
tkm — tonne-kilometres, a transport effort rather than a mass
Electricity, China (CN) ElectricitykWh · -17% / +21.5%
Derivation basis
  • Calculated from equipment energy across all manufacturing operations. This model includes no facility support, so the total is the manufacturing operations alone.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12
Background dataset
electricity, medium voltage
Uncertainty
-17% / +21.5% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kWh
Process water WaterL · -24.9% / +29.6%
Derivation basis
  • Calculated from process-water and ultrapure-water demand across all manufacturing operations. This model includes no facility support, so the demand is the manufacturing operations alone. The fresh intake shown is that demand less the share reused under the water-recycling scenario this dataset assumes, and wastewater follows the same balance.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12
Background dataset
tap water
Notes
Aggregated water demand of this dataset's production stages.
Uncertainty
-24.9% / +29.6% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
L

Outputs and waste

UV adhesive waste (cure overflow, applicator residue) Solid wasteg
Derivation basis
  • Calculated from the mass balance of spent materials and consumables, with treatment selected from the waste classification.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12 treatment route
Background dataset
treatment of hazardous waste, hazardous waste incineration, with energy recovery
Uncertainty
No range defined.
Unit
g
Failed fiber array units Solid wasteg
Derivation basis
  • Calculated from the mass balance of spent materials and consumables, with treatment selected from the waste classification.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12 treatment route
Background dataset
treatment of inert waste, sanitary landfill
Uncertainty
No range defined.
Unit
g
Dicing kerf (Bi2Te3) Solid wasteg
Derivation basis
  • Calculated from the mass balance of spent materials and consumables, with treatment selected from the waste classification.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12 treatment route
Background dataset
treatment of inert waste, sanitary landfill
Uncertainty
No range defined.
Unit
g
Failed TEC modules Solid wasteg
Derivation basis
  • Calculated from the mass balance of spent materials and consumables, with treatment selected from the waste classification.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12 treatment route
Background dataset
treatment of inert waste, sanitary landfill
Uncertainty
No range defined.
Unit
g
Die casting runners/gates Solid wasteg
Derivation basis
  • Calculated from the mass balance of spent materials and consumables, with treatment selected from the waste classification.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12 treatment route
Background dataset
market for zinc scrap, post-consumer
Uncertainty
No range defined.
Unit
g
Plating sludge Solid wasteg
Derivation basis
  • Calculated from the mass balance of spent materials and consumables, with treatment selected from the waste classification.

No source is attached to this row.

Source citations
Not stated
Background data
ecoinvent 3.12 treatment route
Background dataset
market for metalliferous hydroxide sludge
Uncertainty
No range defined.
Unit
g

Emissions to air

1 elementary flow released to air by this dataset's own operations. Quantities are not published; they ship with the dataset on Circa.

VOCs Emission to airg
Derivation basis
  • Calculated as an air release, from a mass balance on the process gases going in, with the destruction or removal efficiency of any point-of-use abatement applied.

No source is attached to this row.

Source citations
Not stated
Compartment
Air (non-urban air or from high stacks)
ecoinvent 3.12 elementary flow
NMVOC, non-methane volatile organic compounds
Uncertainty
No range defined.
Unit
g

Emissions to water

1 elementary flow released to water by this dataset's own operations. Quantities are not published; they ship with the dataset on Circa.

Nickel (dissolved) Emission to waterg
Derivation basis
  • Calculated as a release to water, from a contaminant mass balance on the process chemistry.

No source is attached to this row.

Source citations
Not stated
Compartment
Water (surface water)
Formula
Ni2+
CAS number
14701-22-5
ecoinvent 3.12 elementary flow
Nickel II
Uncertainty
No range defined.
Unit
g

Flows not quantified

9 flows are recorded for this dataset but carry no quantity — cut off below the significance threshold, or with no background dataset available. They remain inside the declared system boundary; each is listed with its reason.

Cut off - below the significance threshold (1)

Pull Tab (Plastic) Materialkg · -30% / +40%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
cut off
Background dataset
Not applicable: this flow is not quantified in the inventory.
Reason
A generic plastic housing or insulation material, recorded in this inventory. Where its mass is significant it is tracked as a named plastic at component level, so no upstream production dataset is attached to this catch-all entry.
Uncertainty
-30% / +40% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg

Not modelled (8)

Aluminum Nitride Ceramic (AlN) Materialkg · -30% / +40%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
not modelled
Background dataset
Not applicable: this flow is not quantified in the inventory.
Reason
The quantified material is retained, but its authored name does not identify a sufficiently specific background dataset or defensible proxy; background modeling remains an explicit gap.
Uncertainty
-30% / +40% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
Bismuth Telluride (Bi2Te3) n-type Materialkg · -33.3% / +46.7%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
not modelled
Background dataset
Not applicable: this flow is not quantified in the inventory.
Reason
The quantified material is retained, but its authored name does not identify a sufficiently specific background dataset or defensible proxy; background modeling remains an explicit gap.
Uncertainty
-33.3% / +46.7% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
Bismuth Telluride (Bi2Te3) p-type Materialkg · -33.3% / +46.7%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
not modelled
Background dataset
Not applicable: this flow is not quantified in the inventory.
Reason
The quantified material is retained, but its authored name does not identify a sufficiently specific background dataset or defensible proxy; background modeling remains an explicit gap.
Uncertainty
-33.3% / +46.7% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
Fiber Array Unit (FAU) Materialkg · -40% / +60%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
not modelled
Background dataset
Not applicable: this flow is not quantified in the inventory.
Reason
The quantified material is retained, but its authored name does not identify a sufficiently specific background dataset or defensible proxy; background modeling remains an explicit gap.
Uncertainty
-40% / +60% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
Index Matching Gel Materialkg · -60% / +100.1%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
not modelled
Background dataset
Not applicable: this flow is not quantified in the inventory.
Reason
The quantified material is retained, but its authored name does not identify a sufficiently specific background dataset or defensible proxy; background modeling remains an explicit gap.
Uncertainty
-60% / +100.1% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
Label/Marking Materialkg · -30% / +40%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
not modelled
Background dataset
Not applicable: this flow is not quantified in the inventory.
Reason
The quantified material is retained, but its authored name does not identify a sufficiently specific background dataset or defensible proxy; background modeling remains an explicit gap.
Uncertainty
-30% / +40% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
NTC Thermistor Materialkg · -30% / +50%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
not modelled
Background dataset
Not applicable: this flow is not quantified in the inventory.
Reason
The quantified material is retained, but its authored name does not identify a sufficiently specific background dataset or defensible proxy; background modeling remains an explicit gap.
Uncertainty
-30% / +50% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg
Solder (SnBi eutectic) Materialkg · -31.3% / +37.4%
Derivation basis
  • Calculated from per-operation consumption, operation counts, and manufacturing yield.

No source is attached to this row.

Source citations
Not stated
Background data
not modelled
Background dataset
Not applicable: this flow is not quantified in the inventory.
Reason
The quantified material is retained, but its authored name does not identify a sufficiently specific background dataset or defensible proxy; background modeling remains an explicit gap.
Uncertainty
-31.3% / +37.4% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit
kg

Limitations and unquantified flows (2)

Limits this dataset declares about itself: first any limit stated in its own description, then any limit it declares flow by flow, grouped by channel. Each entry below is the model's own disclosure.

  • Not quantifiedThe die-cast housing is quantified at the mass the shared casting process publishes. A coherent module of this class is expected to carry a heavier casting for thermal reasons, and no public source for that mass was found, so the extra metal is not quantified on this dataset.
  • Between about a third and two thirds of the declared module mass is not itemised in this bill of materials. The optical sub-assemblies, electrical die and the housing are included; the remaining shell, gasket, thermal-interface and fastener mass is not.

The flows above are this dataset's own records. What follows are the scope rules set once for the whole database in the methodology report, repeated here so every dataset page carries them.

Database-wide boundary policy — applies to every REEL dataset

These boundaries are set once for the whole database, in Chapter 2 of the methodology report, and apply to this dataset wherever they are relevant to it. The excluded flows listed above are specific to this dataset.

Use phase
Product operation is outside the cradle-to-gate scope.
End-of-life treatment
Recycling and disposal are outside the cradle-to-gate scope.
Distribution and retail
The gate is a finished component ready for integration into a higher-level assembly.
Inbound transport of raw materials
Transport of purchased raw materials to the manufacturing facility is already inside the upstream "market for" datasets that users link to a background database, so it is not modelled a second time here. This does not cover freight between REEL production stages, which is modelled where a dataset authors it.
Returnable shipping containers
Where freight between production stages is modelled, the mass moved is the product itself. The shipping container (FOSB, SEMI M31) is returnable capital equipment whose per-trip share is unsourced, so its tare is excluded from the transport effort.
Photomask fabrication
A mask set's embodied burden is amortised across a high-volume production run and is not attributed per wafer. Users assessing low-volume production should add mask fabrication separately; the methodology report gives the basis for the exclusion.
Employee transport, administration and R&D overhead
Employee transportation, facility administration and R&D/pilot-production overhead are outside scope.
Capital goods
Manufacturing equipment, cleanroom construction and facility infrastructure are excluded, on the grounds of absent public data on equipment embodied energy, uncertainty in equipment lifetime and allocation, common practice in electronics LCA, and a focus on the operational inventory. Future versions may include capital goods when sufficient public data becomes available.
Precious metal recovery credits
Scrap recovery credits for precious metals are excluded pending data availability.
Wafer reclaim
Test wafers and scrap are outside the system boundary.

Inside the boundary, linked rather than modelled

Silicon ingot growth and wafer slicing
Inside the cradle-to-gate scope, but treated as upstream material inputs linked to background databases rather than modelled as REEL processes.
Freight between production stages
Where a dataset's product moves between REEL production stages - wafer fabrication to the packaging site, for example - that leg is authored as a transport service and linked to an ecoinvent freight activity. It is measured as a transport effort in tonne-kilometres, not as a mass. Route distances are authored per route class with a stated band; a lower bound of zero is a modelling statement that the two sites can be co-located, not a missing value.

Cut-off criteria

A flow is excluded from a process inventory when it contributes less than 1 % of the total mass of inputs to that unit process, or less than 1 % of its total energy input. The denominator is total process inputs, not product mass. That distinction matters in semiconductor manufacturing, where the input mass of water, chemicals and gases greatly exceeds the product mass, so the threshold removes only genuinely minor flows.

Included regardless of the cut-off

  • Perfluorocarbons (CF4, C2F6, SF6, NF3) - high GWP, EPA regulated
  • Heavy metals (Pb, Cd, Hg, Cr(VI)) - RoHS regulated, high toxicity
  • Volatile organics (photoresist solvents, PGMEA) - air quality
  • Precious metals (Au, Ag, Pd, Pt) - high embodied impacts
  • Ozone-depleting substances (legacy CFCs, HCFCs) - Montreal Protocol