Extract Per-Net Electrical Measurements via Cadence `extracta`

[vzegnameta]

Summary

Cadence Allegro computes per-net electrical characteristics (impedance, capacitance, inductance, resistance, propagation delay) from the routed layout combined with the stackup dielectric/conductor properties. These values are stored in the .brd database and can be exported programmatically using the extracta batch utility and predefined view files.

This data is distinct from design constraints (.tcfx) — it represents as-routed physical measurements, not design intent. It is valuable for post-route signal integrity analysis, impedance verification, and electrical sign-off.

This document covers everything needed to implement a tool that extracts this data: the CLI commands, the view file format, and the output file structure — all verified against a production Allegro 23.1 board.

Highest-value view file: net_bv.txt — Of the ~120 view files shipped with Cadence, net_bv.txt is the single most important for PCB Lens. It is the only view that produces data completely unavailable in either IPC-2581 exports or .tcfx constraint files: per-net post-route capacitance, inductance, resistance, impedance (min/avg/max), and propagation delay. All other view files (layer, stackup, component, etc.) produce data that is redundant with IPC-2581 or .tcfx. If only one extracta view is ever supported, it should be net_bv.txt.

---

Part 1: The extracta Utility

Location

<CADENCE_INSTALL>\tools\bin\extracta.exe

Example: C:\Cadence\SPB_23.1\tools\bin\extracta.exe

This is in the same tools\bin\ directory as a2ipc2581.exe and techfile.exe.

A companion tool extracta_compiler.exe also exists at the same path (used internally for view file compilation — not needed for basic extraction).

Environment Setup

Before calling extracta.exe, initialize the Cadence environment:

call <CADENCE_INSTALL>\tools\bin\allegro_cmd.bat

This is the same setup used for a2ipc2581.exe and techfile.exe.

Command Syntax

extracta <flags> <input.brd> <view_file.txt> <output.txt>

Verified flags:

Flag	Purpose
-q	Quiet mode — suppresses interactive prompts
-s	Suppress summary popup window

Both flags should always be used together for headless/automated operation.

All valid flag characters: [aPlcdgkmnpqrstwzAX+]

There is no -h or --help flag — passing -h produces: Switch 'h' is invalid.

Full Example

call C:\Cadence\SPB_23.1\tools\bin\allegro_cmd.bat
extracta -q -s "C:\designs\my_project\PCB\my_design.brd" "C:\Cadence\SPB_23.1\share\pcb\text\views\net_bv.txt" "C:\designs\my_project\PCB\net_electrical_data.txt"

Expected Console Output

ERROR (LMF-10025): License call failed for feature Allegro_performance ...

This license warning is non-fatal — the export completes successfully despite it. It is the same warning seen with a2ipc2581.exe and techfile.exe. There is no other console output on success — the tool writes silently to the output file.

Execution Time

3–10 seconds depending on design complexity and net count. Slower than techfile because extracta loads the full Allegro database engine to compute/read electrical values.

License Requirements

Same Allegro license as the IPC-2581 exporter. Same serialization / queuing strategy should be applied.

---

Part 2: View Files

What They Are

View files are plain-text configuration files that tell extracta which database fields to export and in what order. They are the "schema" for the output.

Location

Cadence ships ~120 predefined view files in:

<CADENCE_INSTALL>\share\pcb\text\views\

View File Syntax

#
# Comment lines start with #
#
DATABASE_VIEW_NAME

  FIELD_NAME_1
  FIELD_NAME_2
  # COMMENTED_OUT_FIELD    <-- not exported
  FIELD_NAME_3
END

• The first non-comment, non-blank line is the database view selector (e.g., LAYER, NET)
• Each uncommented line between the view name and END is a field name to export
• Fields are exported in the order listed
• Commenting out a field (#) excludes it from output
• Custom view files can be created by copying and editing these templates

Relevant View Files for Electrical Data

🔑 net_bv.txt is the #1 priority. It is the only extracta view that produces data not available from any other export path (IPC-2581 or .tcfx). The layer/stackup views below are included for completeness but their data overlaps heavily with the .tcfx stackup section.

net_bv.txt — Per-Net Electrical Measurements ⭐ HIGHEST VALUE

#
# net_baseview - basic fields for the NET view minus many of the properties
#
NET
  NET_NAME_SORT

  NET_NAME
  NET_STATUS
  NET_CAPACITANCE
  NET_ETCH_LENGTH
  NET_ETCH_WIDTH_AVERAGE
  NET_IMPEDANCE_AVERAGE
  NET_IMPEDANCE_MAXIMUM
  NET_IMPEDANCE_MINIMUM
  NET_INDUCTANCE
  NET_MANHATTEN_LENGTH
  NET_PATH_LENGTH
  NET_PROPAGATION_DELAY_ACTUAL
  NET_RESISTANCE
  NET_VIA_COUNT

  NET_ECL
  NET_ELECTRICAL_CONSTRAINT_SET
  NET_FIXED
  NET_LOGICAL_PATH
  NET_NO_RAT
  NET_NO_RIPUP
  NET_NO_ROUTE
  NET_NO_TEST
  NET_PHYSICAL_TYPE
  NET_PROBE_NUMBER
  NET_RATSNEST_SCHEDULE
  NET_ROUTE_PRIORITY
  NET_ROUTE_TO_SHAPE
  NET_SAME_NET
  NET_SCHEDULE
  NET_SPACING_TYPE
  NET_WEIGHT
END

layer_bv.txt — Layer Stackup Properties (Primary Stackup Only)

#
# layer_baseview - basic fields for the LAYER view
#
LAYER

  LAYER_SORT
  LAYER_SUBCLASS
  LAYER_ARTWORK
  LAYER_USE

  LAYER_CONDUCTOR
  LAYER_DIELECTRIC_CONSTANT
  LAYER_ELECTRICAL_CONDUCTIVITY
  LAYER_MATERIAL
  LAYER_FILLIN_MATERIAL
  LAYER_SHIELD_LAYER
  LAYER_THERMAL_CONDUCTIVITY
  LAYER_THICKNESS
  LAYER_TYPE
  LAYER_FUNCTION_TYPE
  LAYER_LOSS_TANGENT
  LAYER_FREQUENCY_DEPENDENT_FILE
  LAYER_EMBEDDED_STATUS
  LAYER_ETCH_FACTOR

  # LAYER_STACKUP_NAME       <-- uncomment for multi-region designs
  # LAYER_STACKUP_TYPE
END

Important: With LAYER_STACKUP_NAME commented out, only the PRIMARY stackup layers are exported. To get all stackup regions, use multi_stackup_bv.txt instead (see below).

multi_stackup_bv.txt — Multi-Region Layer Stackup

#
# multi-layer_stackup_baseview - basic fields for the LAYER view for multi-zone designs
#
LAYER

  LAYER_SORT
  LAYER_STACKUP_NAME
  LAYER_STACKUP_TYPE
  LAYER_SUBCLASS
  LAYER_CONDUCTOR
  LAYER_MATERIAL
  LAYER_FILLIN_MATERIAL
  LAYER_THICKNESS
  LAYER_FUNCTION_TYPE
END

When LAYER_STACKUP_NAME is included, extracta outputs one record per layer per stackup region. This is essential for multi-region flex/rigid-flex designs where different areas have different layer counts.

stackups_bv.txt — Stackup Region Summary

#
# stackups_baseview - basic fields for the LAYER view to give layer stackup info only
#
LAYER

    LAYER_STACKUP_NAME
    LAYER_STACKUP_POSITION
    LAYER_STACKUP_TYPE
    LAYER_SORT
END

Outputs one record per stackup region (not per layer) — just the region names, types, and positions.

---

Part 3: Output File Format

General Characteristics

• Encoding: Plain text, no BOM
• Delimiter: Space-separated positional fields (NOT CSV, NOT TSV)
• Header row: None — field order must be inferred from the view file
• Quoting: None — no quoting of any fields, ever
• Empty fields: Appear as consecutive spaces
• Line terminator: CRLF on Windows
• One record per line

Parsing Challenges

Material names contain spaces. This is the biggest parsing issue. Examples from verified output:

TAIFLEX FHB0525L311BT4(BLACK)
FLEX BASE(PI)
TAIYOINK-PSR-9000 FLX81EM
PLATED_COPPER_FOIL
ADHESIVE_EPOXY

Since the output has no quoting and uses spaces as delimiters, naive split(" ") parsing will break on multi-word material names. A positional/column-width parser or field-count-aware parser is needed.

Units are inline. Numeric values include their unit as a separate space-delimited token:

0.393701 mil
596000 mho/cm
0.27 pF
111.54 ohms
3.15 nH
0.00843 ns
39.61 mohms

Verified Output: net_bv.txt

One row per net. Fields in order (matching the view file):

Position	Field	Example	Unit
1	Net name (sort key)	SHORT_70_	—
2	Net name sort index	00000030	—
3	Net name	SHORT_70_30	—
4	Net status	REGULAR	—
5–6	Capacitance	0.27 pF	picofarads
7	Etch length	1.0600	mm (design units)
8	Average etch width	0.1346	mm
9–10	Average impedance	111.54 ohms	ohms
11–12	Maximum impedance	161.35 ohms	ohms
13–14	Minimum impedance	96.69 ohms	ohms
15–16	Inductance	3.15 nH	nanohenries
17	Manhattan length	1.0715	mm
18	Path length	1.0600	mm
19–20	Propagation delay	0.00843 ns	nanoseconds
21–22	Resistance	39.61 mohms	milliohms
23	Via count	8	—
24+	Schematic logical path	@\design_name\.\schematic\(sch_1):net_name	—

Full example row:

SHORT_70_ 00000030 SHORT_70_30 REGULAR 0.27 pF 1.0600 0.1346 111.54 ohms 161.35 ohms 96.69 ohms 3.15 nH 1.0715 1.0600 0.00843 ns 39.61 mohms 8    @\sc-XXXXXXX-01.a_design_name\.\sc-XXXXXXX-01.a\(sch_1):short_70_30

Observed record count: One row per routed net. Unrouted nets may not appear or may show zero-valued fields. A test design with 155 nets produced 31 rows — only nets with routed copper had records.

Verified Output: multi_stackup_bv.txt

One row per layer per stackup region. Fields in order:

Position	Field	Example
1	Sort key	000003
2	Stackup region name	PRIMARY
3	Stackup type	RIGID
4	Layer subclass name	TOP (blank for dielectrics)
5	Conductor?	YES / NO
6	Material	PLATED_COPPER_FOIL
7	Thickness + unit	0.393701 mil
8	Function type	CONDUCTOR / DIELECTRIC / DIELECTRIC_COVERLAY / SOLDER_MASK / SURFACE / CONDUCTIVE_FOIL / DIELECTRIC_BASE / DIELECTRIC_PREPREG

Sort key encoding: The thousands digit groups records by stackup region (000xxx = region 0, 003xxx = region 1, 005xxx = region 2, etc.). Within each group, the ones digits give the layer order from top to bottom in the cross-section.

Full example rows:

000000 PRIMARY RIGID  NO AIR  0 mil SURFACE
000001 PRIMARY RIGID COVERLAY_TOP NO TAIFLEX FHB0525L311BT4(BLACK)  0.984252 mil DIELECTRIC_COVERLAY
000003 PRIMARY RIGID TOP YES PLATED_COPPER_FOIL  0.393701 mil CONDUCTOR
000004 PRIMARY RIGID  NO POLYIMIDE  0.511811 mil DIELECTRIC
000006 PRIMARY RIGID L2 YES COPPER  0.393701 mil CONDUCTOR
...
009000 3L RIGID  NO AIR  0 mil SURFACE
009003 3L RIGID L2 YES COPPER  0.393701 mil CONDUCTOR
009005 3L RIGID L3 YES COPPER  0.393701 mil CONDUCTOR
009008 3L RIGID L4 YES COPPER  0.393701 mil CONDUCTOR

Observed record count: A design with 5 stackup regions and 18 layers in the primary stackup produced 87 rows total.

Verified Output: layer_bv.txt

One row per layer in the PRIMARY stackup only. Fields in order:

Position	Field	Example
1	Sort key	000003
2	Layer subclass name	TOP (blank for dielectrics)
3	Artwork type	POSITIVE (blank for non-conductor)
4	Conductor?	YES / NO
5	Dielectric constant (Dk)	4.500000
6–7	Electrical conductivity	343000 mho/cm
8	Material	PLATED_COPPER_FOIL
9	Fill-in material	(blank or material name)
10	Shield layer?	NO
11–12	Thickness	0.393701 mil
13	Layer type	CONDUCTOR / DIELECTRIC / MASK / SURFACE
14	Function type	CONDUCTOR / DIELECTRIC / DIELECTRIC_COVERLAY / SURFACE / etc.
15	Loss tangent	0.035
16	Embedded status	NOT_EMBEDDED (blank for non-conductors)
17	Etch factor	90.000 (blank for non-conductors)

Full example rows:

000000    NO 1.000000 0 mho/cm AIR  NO  0 mil SURFACE SURFACE 0   0.000
000001 COVERLAY_TOP   NO 4.300000 0 mho/cm TAIFLEX FHB0525L311BT4(BLACK)  NO  0.984252 mil MASK DIELECTRIC_COVERLAY 0.035   0.000
000003 TOP POSITIVE  YES 4.500000 343000 mho/cm PLATED_COPPER_FOIL  NO  0.393701 mil CONDUCTOR CONDUCTOR 0  NOT_EMBEDDED 90.000
000006 L2 POSITIVE  YES 1.000000 596000 mho/cm COPPER  NO  0.393701 mil CONDUCTOR CONDUCTOR 0  NOT_EMBEDDED 90.000

Observed record count: 18 rows for a 5-layer flex (5 conductors + dielectrics + coverlays + surfaces).

---

Part 4: How the Electrical Values Are Computed

The values in the net_bv.txt output are not raw measurements — they are computed by Allegro's built-in analysis engine from the routed layout geometry combined with stackup properties. Understanding this is important for interpreting the data correctly.

Field	How Allegro Computes It
Capacitance	2D/2.5D field-solver model. Uses routed trace geometry (width, length, spacing to adjacent copper) combined with stackup dielectric properties (Dk, thickness) from the cross-section. Sums distributed capacitance of each trace segment to its reference plane(s), including fringing field corrections.
Inductance	Same field-solver approach. Models the magnetic loop formed by the trace and its return path (reference plane). Computes partial inductance per segment from trace geometry and spacing to the return plane, then sums across the net.
Resistance	DC resistance: R = ρ · L / (W · t) where ρ is resistivity (from CDS_LAYER_ELECTRICAL_CONDUCTIVITY in the stackup), L is etch length, W is trace width, t is copper thickness. Via barrel resistance is added per via.
Impedance (min/avg/max)	Characteristic impedance Z₀ = √(L/C) per unit length. The min/max/avg reflects variation along the net as trace width and reference plane spacing change (e.g., a trace crossing from a 5L region to a 3L region, or necking down near a via).
Propagation delay	t_pd = √(LC) per unit length × total etch length. Depends directly on the stackup Dk values — higher Dk means slower propagation.

These values are post-route — they are stored/updated in the .brd database after routing and DRC. They reflect the as-routed physical reality, not design intent (constraints).

---

Part 5: Real-World Data Characteristics

Based on testing with a production Allegro 23.1 flex design:

Metric	Observed Value
extracta execution time	3–10 seconds
net_bv.txt output size	~7 KB for 31 nets
multi_stackup_bv.txt output size	~6 KB for 87 rows (5 stackup regions)
layer_bv.txt output size	~1.5 KB for 18 rows
Nets with electrical data	Only routed nets appear (31 of 155 total)
Output file encoding	Plain text, CRLF, no BOM

---

Part 6: Available View Files

Cadence ships ~120 view files. The full list (filename and size) from a verified SPB 23.1 installation:

Filename	Size	Description
net_bv.txt	682 B	⭐ Per-net electrical data — HIGHEST VALUE. Only view with data unavailable elsewhere (post-route C/L/R/Z/tpd). If only one view is supported, it must be this one.
layer_bv.txt	1,510 B	Layer stackup (primary region only)
multi_stackup_bv.txt	1,318 B	Multi-region layer stackup
stackups_bv.txt	1,132 B	Stackup region summary
comp_bv.txt	712 B	Component data
net_rep.txt	457 B	Net report
pad_rep.txt	760 B	Padstack report
pad_rep2.txt	3,374 B	Extended padstack report
via_structure.txt	255 B	Via structure data
drc_rep.txt	124 B	DRC report
bom_rep.txt	649 B	BOM report
ncdrill.txt	1,991 B	NC drill data
fabmaster.txt	3,572 B	Fabmaster export
analysis.txt	1,193 B	Analysis data

(~106 additional view files exist for manufacturing, placement, pin, symbol, and other data — omitted for brevity.)

Custom view files can be created by copying any of these and adding/removing/commenting field names.