Reading PCB and Package Layouts

Scope: pcbFileRead handles both PCB boards and IC/SiP packages. ODB++ and Allegro files may contain package-level designs (BGA substrates, interposers, embedded passives). The workflow is identical — the format determines what's inside, not the function name.

When to Use

• Importing Gerber files (.gtl, .gbl, .gbr, etc.) into MATLAB for visualization or EM analysis
• Reading ODB++ archives (zipped or unzipped) to inspect board or package layouts
• Importing Cadence Allegro .brd files
• Inspecting cadnets, components, layers, pins, or shapes from imported layouts
• Extracting metal layer polygons from Gerber files for use in custom designs
• Building a pcbComponent from externally designed layouts for S-parameter analysis

When NOT to Use

• Exporting designs to Gerber files — use matlab-write-pcb-layout
• Building PCB structures from scratch with shape primitives — use matlab-assemble-pcb-layout
• Running EM analysis after import — use matlab-analyze-em
• Defining substrates or stackup materials — use matlab-manage-pcb-material

Typical Workflow

1. This skill: Import the PCB layout from Gerber, ODB++, or Allegro
2. After: matlab-analyze-pcb-pdn — PDN DC analysis on imported board; or matlab-analyze-em — S-parameter extraction from imported geometry; or matlab-model-via — via analysis on imported stackup

Quick Reference

gerberRead — Simple Import

The gerberRead function imports Gerber files and returns a PCBReader object. Use shapes() to extract the metal layers as polygon shapes.

Basic Usage

P = gerberRead('interdigital_Capacitor.gtl');
shp = shapes(P);      % Extract metal layer shapes
show(shp(1));          % Show top layer polygon

Centering Imported Geometry

Imported shapes often have non-zero offsets from CAD origin. Extract shapes, then center:

P = gerberRead('myDesign.gtl');
shp = shapes(P);
layer1 = shp(1);

% Get bounding box to compute center offset
verts = layer1.Vertices;
cx = (max(verts(:,1)) + min(verts(:,1))) / 2;
cy = (max(verts(:,2)) + min(verts(:,2))) / 2;

% Center using translate
layer1 = translate(layer1, [-cx -cy 0]);
show(layer1);

Supported Gerber File Extensions

stackUp — Multi-Layer Definition

The stackUp object defines the full PCB layer structure for importing multi-layer boards.

Default stackUp

S = stackUp;

A default stackup has numbered layers. Odd layers are conductors (metal or Gerber files), even layers are dielectrics.

Assigning Gerber Files to Layers

S = stackUp;
S.Layer1.Thickness = 0.1e-3;           % Air layer above board
S.Layer2 = 'interdigital_Capacitor.gtl'; % Top copper from Gerber

Multi-Layer Stackup

S = stackUp;
S.Layer1.Thickness = 0.1e-3;       % Air
S.Layer2 = 'top_copper.gtl';       % Top copper
S.Layer3.Thickness = 0.2e-3;       % Dielectric
S.Layer3.EpsilonR = 4.4;
S.Layer4 = 'inner_layer.g2';       % Inner copper
S.Layer5.Thickness = 1.0e-3;       % Core dielectric
S.Layer5.EpsilonR = 4.4;
S.Layer6 = 'bottom_copper.gbl';    % Bottom copper

PCBReader — Full Board Import

PCBReader wraps the stackup with Gerber files into a reader object that can be converted to pcbComponent.

Basic Workflow

S = stackUp;
S.Layer1.Thickness = 0.1e-3;
S.Layer2 = 'interdigital_Capacitor.gtl';

p = PCBReader('StackUp', S);
pcb = pcbComponent(p);
pcb.FeedDiameter = 0.001;
show(pcb);

Adding Feeds After Import

After converting to pcbComponent, add feed locations for EM analysis:

pcb = pcbComponent(p);
pcb.FeedDiameter = 1e-3;
pcb.FeedLocations = [-5e-3 0 1 3;    % Port 1
                      5e-3 0 1 3];    % Port 2
sp = sparameters(pcb, linspace(1e9, 10e9, 51), 'SweepOption', 'interp');
rfplot(sp);

Determining Feed Locations from Imported Geometry

Feed locations must fall on metal traces. After converting a Gerber import to pcbComponent, inspect the geometry to find valid feed points:

pcb = pcbComponent(p);
show(pcb);                      % Visual inspection — identify trace endpoints
layout(pcb);                    % Top-down layout view with dimensions

For programmatic placement, extract the imported layer's mesh vertices and compute edge midpoints:

m = mesh(pcb);                  % Get mesh structure for coordinate reference

When feed locations are uncertain, place feeds at the visual endpoints of the main transmission line trace, inset by at least FeedDiameter/2 from the trace edge.

FeedLocations Column Semantics

FeedLocations = [x, y, col3, col4] — Column 3 is the signal layer (where the feed probe/sphere appears). Column 4 is the ground reference layer. The probe connects from col3 to col4. If you swap them, the feed sphere renders on the wrong layer.

Edge Feeds (Strip Model)

For structures fed at the board edge (e.g., microstrip lines terminating at the PCB boundary), use the strip feed model:

pcb.FeedViaModel = 'strip';
pcb.FeedDiameter = traceWidth / 2;  % Must be half the trace width for edge feeds

The 'strip' model creates a planar feed at the board edge rather than a vertical via probe. Place feeds at the exact edge of the BoardShape where the trace terminates.

PCBReader Layer Structure

After pcbComponent(PCBReader), the Layers cell array follows the standard alternating pattern: {metal, dielectric, metal, ...}. The metal layers contain the imported Gerber shapes. Layer indices for FeedLocations follow the same odd-numbered convention (1, 3, 5, ...) as manually assembled pcbComponent objects.

Converting PCBReader to pcbComponent

The pcbComponent constructor accepts a PCBReader object directly.

Cadence Allegro .brd Import

When the user references a `.brd` file for import or analysis, always ask for their Cadence `extracta.exe` path before attempting the import. The extracta utility is required and must be configured first. Do not assume it is already set up.

% Step 1: Check if extracta is already configured
extractaSetup()                % Displays current path, or [] if not set

% Step 2: If [], ask user for path and configure (persists across sessions)
extractaSetup('C:/Cadence/SPB_17.4/tools/bin/extracta.exe')

% Step 3: Import
pcb = pcbFileRead('design.brd');

extractaSetup(path) accepts the full path to the Cadence extracta.exe executable. The path persists across MATLAB sessions — it only needs to be run once. Without this, .brd imports fail with an extracta error.

Calling extractaSetup() with no arguments displays the currently configured path (or [] if not yet set). Use this to check whether setup has already been done.

ODB++ Import

pcb = pcbFileRead('design.zip');       % Zipped ODB++
pcb = pcbFileRead('odb_directory');    % Unzipped ODB++

Board and Package Inspection

pcbFileRead opens ODB++, Allegro, or native PCB files for hierarchical inspection — layers, cadnets, components, parts, pins, and shapes. This works identically for PCB boards and IC/SiP packages.

Opening a File

pfile = pcbFileRead('ExampleBoard.odb');

The returned object exposes: NumLayers, NumCadnets, NumPadStacks, NumComponents, NumParts, LayerHeight.

Querying Layer Stackup

stackUp(pfile) returns a table of material details for every layer in the imported board:

su = stackUp(pfile);                   % Full stackup table
su = stackUp(pfile, [2 3 4]);         % Specific layers only

The table has columns: LayerNumber, LayerName, LayerType, Material, Thickness(inch), EpsilonR, LossTangent, Conductivity(S/m).

Note: This is an object function on pcbFileRead that returns a table — it is unrelated to the stackUp constructor used with Gerber import (see the Pitfalls section).

Navigating the Hierarchy

% List cadnets (electrical nets)
tbl = cadnetList(pfile);               % Returns table with net names

% Open a specific cadnet and get its shapes
cnet = cadnet(pfile, "VDD_CORE");
data = cadnetData(cnet);               % Struct with .Surfaces, .Pins, .Vias, .Traces
s = shapes(cnet);                      % Same struct as cadnetData (equivalent call)

% List and inspect components
tbl = componentList(pfile);
comp = component(pfile, "U1");
pins = componentPinData(comp);         % Returns pinsData array (see below)

% List and inspect parts (component types)
tbl = partList(pfile);
p = part(pfile, "IC6ANT");
cdata = componentData(p);             % Components that use this part type

% List padstacks
tbl = padStackList(pfile);

% Layer-level inspection (metal layers only — use pfile.MetalLayer for valid indices)
lyr = layer(pfile, pfile.MetalLayer(1));
ldata = layerData(lyr);

% Search for components in a cadnet
results = findComponents(cnet);
results = findComponents(cnet, 'ComponentType', 'IC');

Shape Data Structure

shapes(cnet) and cadnetData(cnet) are equivalent — both return a struct with fields:

s = shapes(cnet);
s.Traces(1).Vertices   % Vertices of first trace segment
numel(s.Surfaces)      % Number of copper pours

layerData(lyr) returns the same struct format. Each antenna.Polygon has a .Vertices property (Nx3 double).

componentPinData — Pin Positions and Properties

componentPinData(comp) returns a pinsData array. Each element has:

comp = component(pfile, "U1");
pins = componentPinData(comp);
pins(1).Center       % [x, y] in board units (inches for ODB++)
pins(1).CadnetName   % Which net this pin connects to
pins(1).PinNumber    % Pin identifier

Coordinate units: For ODB++ imports, pin positions (.Center) and shape vertices are in the board's native units — typically inches. Convert to meters for use in pcbComponent: multiply by 25.4e-3.

Tracing a Circuit Path Across Nets

Use findComponents + componentPinData to hop across nets via shared components:

pwr_net = cadnet(pfile, "+PWR");
pwr_comps = findComponents(pwr_net);   % Table: ComponentIndex, Refdes, PinList, ComponentType, Part

% Open a component and discover its other nets
q4 = component(pfile, string(pwr_comps.Refdes(9)));
q4_pins = componentPinData(q4);
for i = 1:numel(q4_pins)
    fprintf('%s.%s -> %s at [%.3f, %.3f]\n', "Q4", ...
        string(q4_pins(i).PinNumber), string(q4_pins(i).CadnetName), ...
        q4_pins(i).Center(1), q4_pins(i).Center(2));
end

% Follow Q4's output net to find the next component
next_net = cadnet(pfile, string(q4_pins(1).CadnetName));
next_comps = findComponents(next_net);

Using Imported Shapes in Custom Designs

Import Gerber geometry and combine with other shapes using Boolean operations:

% Import a CSRR pattern from Gerber
reader = gerberRead('csrr_pattern.gbr');
shp = shapes(reader);
csrr = shp(1);
verts = csrr.Vertices;
cx = (max(verts(:,1)) + min(verts(:,1))) / 2;
cy = (max(verts(:,2)) + min(verts(:,2))) / 2;
csrr = translate(csrr, [-cx -cy 0]);

% Use as DGS or combine with other geometry
ground = traceRectangular(Length=30e-3, Width=20e-3);
groundWithSlots = ground - csrr;

pcb = pcbComponent;
signal = traceRectangular(Length=25e-3, Width=3e-3);
sub = dielectric("FR4");
sub.Thickness = 1.6e-3;
pcb.Layers = {signal, sub, groundWithSlots};
pcb.BoardShape = ground;
pcb.BoardThickness = sub.Thickness;
show(pcb);

Import-to-Analysis Workflow

%% Import
S = stackUp;
S.Layer1.Thickness = 0.1e-3;
S.Layer2 = 'myFilter.gtl';

p = PCBReader('StackUp', S);
pcb = pcbComponent(p);

%% Configure for analysis
pcb.FeedDiameter = 0.5e-3;
pcb.FeedLocations = [-10e-3 0 1 3; 10e-3 0 1 3];
pcb.Conductor = metal("Copper");
show(pcb);

%% Analyze
freq = linspace(1e9, 10e9, 51);
sp = sparameters(pcb, freq, 'SweepOption', 'interp');
rfplot(sp);

Common Error Diagnostics

Pitfalls

1. Coordinate alignment: Gerber files from different CAD tools may use different origins. Always check and translate to center before combining layers or adding feeds.

1. Units mismatch: Gerber files can be in mils or mm. RF PCB Toolbox uses meters internally. If imported geometry looks too large or too small, check the source file's unit setting.

1. gerberRead returns PCBReader, not shapes: gerberRead returns a PCBReader object. Call shapes(P) to extract the metal layer polygons. Don't try to use P.Vertices or show(P) directly on the reader.

1. Layer ordering in stackUp constructor: Layer numbering in the stackUp constructor starts from the top. Layer1 is typically air above the board, Layer2 is the top copper. Odd-numbered physical metal layers map to even stackUp layers (since Layer1 is air).

1. `layer()` only accepts metal layer indices. layer(pfile, idx) requires idx to be a metal layer number. Use pfile.MetalLayer to get valid indices. Passing a dielectric layer index (e.g., layer(pfile, 1) when layer 1 is dielectric) errors with "Value must be a member of this set: ..."

1. `componentData` is on `part`, not `component`. To get the list of components that use a part type, call componentData(p) where p = part(pfile, partName). The component object has componentPinData and shapes, but not componentData.

1. `stackUp` name collision. S = stackUp (no arguments) creates a constructor object for defining Gerber import layer structures. su = stackUp(pfile) is an object function on pcbFileRead that returns a table of material details. These are completely different types with different purposes. Do not confuse them.

1. Large imported geometries: Full-board Gerber imports can be very large. For EM analysis, extract only the region of interest rather than analyzing the entire board.

1. Always ask for extracta path before .brd import. When the user points to a .brd file, first run extractaSetup() (no args) to check if it's already configured. If it returns [], ask the user for the path to their Cadence extracta.exe and run extractaSetup(path). Typical path: C:/Cadence/SPB_<version>/tools/bin/extracta.exe. Without this, .brd imports fail.

1. Package vs board — same workflow. ODB++ and Allegro files may contain IC packages, not just PCBs. pcbFileRead handles both identically. The format determines the content, not the function name.

Related Skills

• matlab-write-pcb-layout — Export designs to Gerber manufacturing files
• matlab-assemble-pcb-layout — Building custom PCB structures from shapes
• matlab-analyze-em — Running EM analysis on imported boards
• matlab-manage-pcb-material — Substrate setup for imported stackups
• matlab-analyze-pcb-pdn — PDN analysis on imported boards

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