Overview

General comment

Production covered

Wafer-level package whose redistribution wiring is dual-damascene copper in a deposited silicon-oxide dielectric, planarized by polishing instead of plated over a polymer. Functional unit is one package STARTED: the reference flow is a single package entering assembly, and the activities listed run through completed assembly and final test of that package.

Modelling choices

By the count-once yield-ownership convention, the gross-up from packages started to good packages is carried by the consuming IC or component dataset, not here.

Technology: WLP DAMASCENE
Geography: Global average data from equipment vendor specifications and industry literature

System boundary

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 1.8 Very good

Reliability

2.5

Completeness

2.2

Temporal

1.3

Geographic

2.0

Technological

1.2

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

Sampling procedure: Equipment vendor specifications, academic papers, industry literature
Coverage status: Partial
Pedigree-scored source files: 10 — the source records behind this dataset's manufacturing operations. Each carries the five pedigree axes above; the composite DQI aggregates them.

Technosphere inputs

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

CF₄ production Process gasg · -38.5% / +61.5%

Derivation basis: Scaled from front-end etch parameters

No source is attached to this row.
Source citations: Not stated
Upstream REEL dataset: Carbon tetrafluoride (CF4)
Background dataset: Modelled by REEL; see the upstream dataset above.
Uncertainty: -38.5% / +61.5% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

ArF Photoresist Process chemicalg · ±25%

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: ArF Photoresist (193nm)
Background dataset: Modelled by REEL; see the upstream dataset above.
Uncertainty: ±25% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

TMAH Developer (2.38% solution) Process chemicalg · ±32.5%

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: TMAH Developer (2.38% solution) (N(CH3)4OH (aq))
Background dataset: Modelled by REEL; see the upstream dataset above.
Uncertainty: ±32.5% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

CMP Slurry (Copper) Process chemicalg · ±22.2%

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: Copper CMP Slurry
Background dataset: Modelled by REEL; see the upstream dataset above.
Uncertainty: ±22.2% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

Water supply (municipal) Waterm3 · -27.6% / +30.6%

Derivation basis: Calculated from process-water and ultrapure-water demand across all manufacturing operations, plus facility water allocated to each finished unit. 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
Upstream REEL dataset: Water Supply (Municipal)
Background dataset: Modelled by REEL; see the upstream dataset above.
Notes: Net fresh-water intake, supplied as municipal water
Uncertainty: -27.6% / +30.6% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: m3

Electricity, Taiwan (TW) ElectricitykWh · -50.6% / +84.9%

Derivation basis: Calculated from equipment energy across all manufacturing operations. It also includes the assembly site's facility overhead: air handling and cleanroom conditioning, chilled water, compressed dry air, exhaust and dust collection, wastewater treatment and uninterruptible power.
REEL derivation: engineering estimate of per-package laser-marking energy from the marker system power rating and line throughput; no single published document reports this per-package value

The sources below come from the manufacturing operations behind this row.
Sources (inherited): Inherited, rolled up from the contributing process steps:

CAE Online: Teradyne Catalyst Specifications

EE Journal: "Advantest Unveils New Ultra-High-Current Power Supply" (2024)

4Semi: TEL Precio Wafer Prober Specifications

FormFactor Summit 11000/12000 Facility Planning Guide

3D InCites: "ERS Electronic Introduces High Power Dissipation Thermal Chuck" (2023)

Abachy: "How Much Energy and Water Are Required for Wafer Fabrication" (2025)

Heller Industries. MK7 Reflow Oven Brochure
Background data: ecoinvent 3.12
Background dataset: electricity, medium voltage
Uncertainty: -50.6% / +84.9% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: kWh

O₂ Process gasg · ±50%

Derivation basis: RIE etch parameters

No source is attached to this row.
Source citations: Not stated
Background data: ecoinvent 3.12
Background dataset: oxygen, liquid
Uncertainty: ±50% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

Ar Process gasg · -41.3% / +60%

Derivation basis: No retrievable public document identified

No source is attached to this row.
Source citations: Not stated
Background data: ecoinvent 3.12
Background dataset: argon, liquid
Uncertainty: -41.3% / +60% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

SiH₄ Process gasg · -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: silicon tetrahydride
Uncertainty: -40% / +60% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

N₂O Process gasg · ±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: nitrous oxide
Uncertainty: ±40% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

N₂ Process gasg · -31.9% / +35.1%

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: ecoinvent 3.12
Background dataset: nitrogen, liquid
Uncertainty: -31.9% / +35.1% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

Compressed air Process gasg · -30% / +40%

Source citations: CAE Online: Teradyne Catalyst Specifications
EE Journal: "Advantest Unveils New Ultra-High-Current Power Supply" (2024)
4Semi: TEL Precio Wafer Prober Specifications
FormFactor Summit 11000/12000 Facility Planning Guide
3D InCites: "ERS Electronic Introduces High Power Dissipation Thermal Chuck" (2023)
Abachy: "How Much Energy and Water Are Required for Wafer Fabrication" (2025)
Background data: ecoinvent 3.12
Background dataset: compressed air, 700 kPa gauge
Uncertainty: -30% / +40% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

Cu Plating Solution Process chemicalg · -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: proxy-mapped
Background dataset: copper sulfate
Uncertainty: -40% / +60% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

Flux paste Process chemicalg · -60% / +100%

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: flux, for wave soldering
Uncertainty: -60% / +100% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

Stencil cleaner (IPA) Process chemicalg · -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: ecoinvent 3.12
Background dataset: isopropanol
Uncertainty: -50% / +100.1% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

RDL Cu Materialkg

Derivation basis: Calculated from per-operation consumption, operation counts, and manufacturing yield.

The sources for this row are listed below.
Source citations (dataset-level): Analog Devices. "Wafer Level Chip Scale Package (WLCSP)." AN-617
Yole Group. "Amkor's Advanced Packaging: A Closer Look." 2017
Keser, B., et al. "Board level reliability and surface mount assembly of 0.35mm and 0.3mm pitch wafer level packages." IEEE ECTC
Sharma, G., et al. "Solutions Strategies for Die Shift Problem in Wafer Level Compression Molding."
Medium. "Why is Fan-Out Wafer-Level Packaging (FOWLP) the Future." 2025
Strategic Market Research. "Semiconductor Packaging Industry Statistics."
Background data: ecoinvent 3.12
Background dataset: copper, cathode
Uncertainty: No range defined.
Unit: kg

Under-bump metallization Materialkg

Derivation basis: Calculated from per-operation consumption, operation counts, and manufacturing yield.

The sources for this row are listed below.
Source citations (dataset-level): Analog Devices. "Wafer Level Chip Scale Package (WLCSP)." AN-617
Yole Group. "Amkor's Advanced Packaging: A Closer Look." 2017
Keser, B., et al. "Board level reliability and surface mount assembly of 0.35mm and 0.3mm pitch wafer level packages." IEEE ECTC
Sharma, G., et al. "Solutions Strategies for Die Shift Problem in Wafer Level Compression Molding."
Medium. "Why is Fan-Out Wafer-Level Packaging (FOWLP) the Future." 2025
Strategic Market Research. "Semiconductor Packaging Industry Statistics."
Background data: ecoinvent 3.12
Background dataset: copper, cathode
Uncertainty: No range defined.
Unit: kg

Solder Balls Materialkg · -34.9% / +45.6%

Source citations: thor.inemi.org (date not recorded). IPC/EIA J-STD-032, Performance Standard for Ball Grid Array Balls, Table 1, October 2000. Industry standard.
Background data: composite
Background dataset: Modelled as a composite of its constituent materials.
Uncertainty: -34.9% / +45.6% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: kg

Outputs and waste

Wastewater Wastewaterm3 · -27.6% / +30.6%

Derivation basis: Calculated from the water balance: fresh-water input minus evaporation.

No source is attached to this row.
Source citations: Not stated
Background data: carried, no background dataset
Background dataset: No treatment route recorded for this output.
Uncertainty: -27.6% / +30.6% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: m3

Spent photoresist (liquid spin-off) Solid wasteg · -25% / +45.6%

Source citations: patents.google.com (date not recorded). US9720325B2, "Photoresist coating scheme". Patent.
patents.google.com (date not recorded). US7405033B2, "Method for manufacturing resist pattern and method for manufacturing semiconductor device". Patent.
microchemicals.com (date not recorded). MicroChemicals GmbH, "Spin-Coating", chapter of Basics of Microstructuring / Fundamentals of Microstructuring. PDF document.
cdn.vanderbilt.edu (date not recorded). MICROPOSIT S1805 POSITIVE PHOTORESIST, Material Safety Data Sheet, revision date 04/08/2011, version 3.2. PDF document.
nanofab.utah.edu (date not recorded). JSR ARF AM 2073J-19 Material Safety Data Sheet, date prepared April 15, 2009 (Revision 5). PDF document.
epa.gov (date not recorded). US EPA, Emission Inventory Improvement Program (EIIP) Volume II, Chapter 6: Preferred and Alternative Methods for Estimating Air Emissions from Semiconductor Manufacturing, 2/24/99. PDF document.
rcrapublic.epa.gov (date not recorded). US EPA RCRA Online RO 11249, memorandum 9444.1987(18), letter to Mr. Frank Czigler, S & W Waste Inc., dated MAY 20 1987. PDF document.
patents.google.com (date not recorded). US9421567B2, "Recycle photochemical to reduce cost of material and environmental impact". Patent.
pmc.ncbi.nlm.nih.gov (date not recorded). Ni, J., Zhang, Q., Zhang, X., Sun, Z., Bao, D., "Detection Method and Common Characteristics of Waste Solvent from Semiconductor Industry", Molecules 28(16):5992, 2023. Journal article.
epa.gov (date not recorded). US EPA, "Defining Hazardous Waste: Listed, Characteristic and Mixed Radiological Wastes".
semiengineering.com (date not recorded). SemiEngineering, "Improving EUV Process Efficiency".
dspace.mit.edu (date not recorded). Modeling and analysis of extrusion-spin coating: an efficient and deterministic photoresist coating method in microlithography (MIT Mechanical Engineering thesis). Thesis.
Background data: ecoinvent 3.12 treatment route
Background dataset: treatment of hazardous waste, hazardous waste incineration, with energy recovery
Uncertainty: -25% / +45.6% around the published quantity. The bounds themselves ship with the dataset on Circa.
Unit: g

Copper in CMP sludge/recovery Solid wasteg

Source citations (dataset-level): epa.gov (date not recorded). U.S. EPA Office of Water, "Preliminary Study of the Electrical and Electronic Components Point Source Category", EPA-821-R-22-005, DCN 11197 (2022) - Table 12 indirect Cu median 0.05 / mean 0.213 / max 5.64 / min 0.00015 mg/L (67 facilities, 1,309 results, 996 detects); Table 13 direct; Table 6 named-facility treatment trains; sec. 1.2.3.1 post-1983 process additions. Government report.
Source citations (dataset-level): Inherited from this dataset's own bibliography, not tied to this row:

epa.gov (date not recorded). U.S. EPA Office of Water, "Preliminary Study of the Electrical and Electronic Components Point Source Category", EPA-821-R-22-005, DCN 11197 (2022) - Table 12 indirect Cu median 0.05 / mean 0.213 / max 5.64 / min 0.00015 mg/L (67 facilities, 1,309 results, 996 detects); Table 13 direct; Table 6 named-facility treatment trains; sec. 1.2.3.1 post-1983 process additions. Government report.
Background data: ecoinvent 3.12 treatment route
Background dataset: market for copper scrap, sorted, pressed
Uncertainty: No range defined.
Unit: g

CMP slurry treatment 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, underground deposit
Uncertainty: No range defined.
Unit: g

Flux residue on stencil 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

Dicing slurry (Si/EMC/Cu particles) Solid wasteg

Derivation basis: No retrievable public document identified

No source is attached to this row.
Source citations: Not stated
Background data: ecoinvent 3.12 treatment route
Background dataset: treatment of hazardous waste, underground deposit
Uncertainty: No range defined.
Unit: g

Emissions to air

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

CF₄ Emission to airg

Source citations: AZoM. (2011). "RIE-Etching Using A HBr/Cl2 Mixture."
Bogart et al. (2002). "Spatially averaged global model of HBr/Cl2..." J. Vac. Sci. Technol. A
das-ee.com (date not recorded). Resource- & Emission Efficiency in Semiconductors | DAS EE. Web page.
das-ee.com (date not recorded). STYRAX Abatement-System for Waste Gas Treatment | DAS EE. Web page.
(2023). "Effect of SF6 and C4F8 Flow Rate on Etched Surface Profile..."
Atlas - Edwards Vacuum abatement technology (Atlas Etch for semiconductor etch processes)
Compartment: Air (non-urban air or from high stacks)
CAS number: 75-73-0
ecoinvent 3.12 elementary flow: Tetrafluoromethane
Uncertainty: A minimum-maximum range is defined for this flow. Bounds ship with the dataset on Circa.
Unit: g

CO₂ Emission to airg

Derivation basis: Calculated from CF4 fate parameters

No source is attached to this row.
Source citations: Not stated
Compartment: Air (non-urban air or from high stacks)
CAS number: 124-38-9
ecoinvent 3.12 elementary flow: Carbon dioxide, fossil
Uncertainty: No range defined.
Unit: g

VOCs (from photoresist) Emission to airg

Source citations: microchemicals.com (date not recorded). MicroChemicals GmbH, "Spin-Coating", chapter of Basics of Microstructuring / Fundamentals of Microstructuring. PDF document.
epa.gov (date not recorded). US EPA, Emission Inventory Improvement Program (EIIP) Volume II, Chapter 6: Preferred and Alternative Methods for Estimating Air Emissions from Semiconductor Manufacturing, 2/24/99. PDF document.
escholarship.org (date not recorded). Boyd, S.B., "Life-cycle Assessment of Semiconductors" (UC Berkeley dissertation, 2009). PDF document.
semiengineering.com (date not recorded). SemiEngineering, "Improving EUV Process Efficiency".
Compartment: Air (non-urban air or from high stacks)
ecoinvent 3.12 elementary flow: NMVOC, non-methane volatile organic compounds
Uncertainty: A minimum-maximum range is defined for this flow. Bounds ship with the dataset on Circa.
Unit: g

Flux volatiles 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

Particulates (marking fume) Emission to airg

Derivation basis: Estimated from mold compound ablation

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: Particulate Matter, < 2.5 um
Uncertainty: A minimum-maximum range is defined for this flow. Bounds ship with the dataset on Circa.
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.

Cu2+ Emission to waterg

Source citations: epa.gov (date not recorded). U.S. EPA Office of Water, "Preliminary Study of the Electrical and Electronic Components Point Source Category", EPA-821-R-22-005, DCN 11197 (2022) - Table 12 indirect Cu median 0.05 / mean 0.213 / max 5.64 / min 0.00015 mg/L (67 facilities, 1,309 results, 996 detects); Table 13 direct; Table 6 named-facility treatment trains; sec. 1.2.3.1 post-1983 process additions. Government report.
Compartment: Water (surface water)
Formula: Cu
CAS number: 7440-50-8
ecoinvent 3.12 elementary flow: Copper ion
Uncertainty: A minimum-maximum range is defined for this flow. Bounds ship with the dataset on Circa.
Unit: g

Flows not quantified

1 flow is recorded for this dataset but carries no quantity — cut off below the significance threshold, or with no background dataset available. It remains inside the declared system boundary; each is listed with its reason.

Not quantified - no background dataset available (1)

Silica Dielectric Materialkg

Derivation basis: Calculated from per-operation consumption, operation counts, and manufacturing yield.

The sources for this row are listed below.
Source citations (dataset-level): Analog Devices. "Wafer Level Chip Scale Package (WLCSP)." AN-617
Yole Group. "Amkor's Advanced Packaging: A Closer Look." 2017
Keser, B., et al. "Board level reliability and surface mount assembly of 0.35mm and 0.3mm pitch wafer level packages." IEEE ECTC
Sharma, G., et al. "Solutions Strategies for Die Shift Problem in Wafer Level Compression Molding."
Medium. "Why is Fan-Out Wafer-Level Packaging (FOWLP) the Future." 2025
Strategic Market Research. "Semiconductor Packaging Industry Statistics."
Background data: no background dataset
Background dataset: Not applicable: this flow is not quantified in the inventory.
Reason: The inter-metal dielectric of a damascene redistribution layer is a silicon dioxide film grown in the deposition chamber from silane and nitrous oxide. No suitable deposited-oxide production activity is registered for linkage here, so the film is recorded as a retained mass with no separate material purchase linked to it. The recorded film sits inside the oxide that the silane this dataset buys could build if all of it converted, so the two are consistent as an upper bound. What is not established is how much of that silane actually reaches the film rather than leaving as chamber deposit or as exhaust: no measured conversion is available for this chamber, so the film and its purchased precursor are still not reconciled, and that reconciliation is an open item on this dataset. An organic dielectric film is not substituted, because it would misstate the material.
Uncertainty: No range defined.
Unit: kg

Limitations and unquantified flows (3)

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.

The uncertainty range on this dataset's abated fluorinated-gas emissions to air is the range of the incoming gas, carried through in proportion. It does not widen for how much of the gas is consumed in the reaction, or for how completely the abatement destroys what is left; both of those are held at their central values on this dataset. Wafer datasets do carry those two through into the range, so the range published here is narrower than the one a wafer dataset publishes for the same kind of emission.
These materials are used at a step of the modelled flow and are also carried by this dataset's own material list. Each is counted once, on that list, and the step does not book it again: Damascene RDL Layer 1 uses Ti sputtering target, Cu sputtering target and Cu electroplating anode; Damascene RDL Layer 2 uses Ti sputtering target, Cu sputtering target and Cu electroplating anode; Ball attach reflow uses SAC305 solder balls.
Some consumable pulls referenced by the modelled process steps did not resolve to an inventory row and are absent from this dataset. They are itemised in the dataset's own export audit.

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