Matlab Model ViaSAFE

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The instruction file, verbatim from the audited commit — this is the text the model reads, and the surface the audit's instruction layer examines. Quoted here so you can judge it without cloning anything.

---
name: matlab-model-via
description: "Via modeling: pads, antipads, ground return vias, GRV placement, and signal integrity for high-speed layer transitions. TRIGGER: user asks to model a via, design a via transition, place ground return vias, analyze via performance, or check signal integrity through layer transitions. Invoke BEFORE writing code — only viaSingleEnded exists (no viaDifferential), and the location format is non-obvious. SKIP: general signal integrity without vias (use matlab-analyze-em), transmission line design (use matlab-design-pcb-transmission-line), PDN analysis (use matlab-analyze-pcb-pdn), material/stackup setup only (use matlab-manage-pcb-material)."
license: https://www.mathworks.com/content/dam/mathworks/license/pmrl/license.md
metadata:
  author: MathWorks
  version: "1.0"
---

# Modeling Vias

## When to Use

- Modeling signal vias through multi-layer PCB stackups (viaSingleEnded)
- Configuring pad and antipad geometry per layer
- Placing ground return vias for signal integrity
- Analyzing via S-parameters and identifying barrel resonances
- Evaluating GRV placement with criticalwavelength and gapratedistance

## When NOT to Use

- Designing transmission lines or impedance control — use `matlab-design-pcb-transmission-line`
- Building custom PCB structures from shapes — use `matlab-assemble-pcb-layout`
- Setting up substrate or conductor materials — use `matlab-manage-pcb-material`
- Running full-wave EM analysis on non-via structures — use `matlab-analyze-em`
- PDN analysis on imported boards — use `matlab-analyze-pcb-pdn`

## Typical Workflow

1. **Before:** `matlab-manage-pcb-material` — set up substrate and conductor for the stackup
2. **This skill:** Model the via, place GRVs, check signal integrity
3. **After:** `matlab-integrate-pcb-circuit` — cascade via model with trace/connector models → `matlab-optimize-pcb-design` — optimize GRV placement or pad geometry

## Quick Reference

| Task | Code |
|------|------|
| Create via | `via = viaSingleEnded` |
| Set signal layers | `via.SignalLayer = [1 5]` |
| Set ground layers | `via.GroundLayer = [3 7 9]` |
| Set substrate | `via.Substrate = dielectric(...)` |
| Place signal via | `via.SignalViaLocations = [x y startLayer stopLayer]` |
| Place ground return vias | `via.GroundReturnViaLocations = [x y start stop; ...]` |
| Define ports | `via.SignalTable = {viaNum layer traceWidth direction; ...}` |
| View pads | `padsTable(via)` |
| View antipads | `antipadsTable(via)` |
| Customize pads | `pads = getpads(via); pads{k}.Radius = r; via.SignalViaPad = pads` |
| Customize antipads | `ap = getantipads(via); ap{k}.Radius = r; via.SignalViaAntipad = ap` |
| Visualize | `show(via)` |
| S-parameters | `sp = sparameters(via, freq)` |
| Resonance risk check | `cw = criticalwavelength(via, freq)` |
| Max GRV distance | `gapratedistance(via, freq)` |

## viaSingleEnded Object

The `viaSingleEnded` object models signal vias through multi-layer PCB stackups with configurable pads, antipads, and ground return vias.

### Basic Setup

```matlab
via = viaSingleEnded;
via.SignalLayer = [1 5];
via.GroundLayer = [3 7 9];
via.Substrate = dielectric("Name","FR4","EpsilonR",4.8,...
    "LossTangent",0.026,"Thickness",1.27e-4,"Frequency",1e8);
via.Conductor = metal("Copper");
show(via);
```

### Key Properties

| Property | Format | Description |
|----------|--------|-------------|
| `SignalLayer` | Vector | Layer indices where signal traces connect (odd numbers) |
| `GroundLayer` | Vector | Layer indices for ground/return planes |
| `Substrate` | dielectric | Dielectric between layers |
| `Conductor` | metal | Via barrel and pad conductor |
| `SignalViaLocations` | N×4 matrix | `[x, y, startLayer, stopLayer]` per via |
| `SignalViaDiameter` | Scalar (m) | Via barrel diameter |
| `SignalViaFinishedDiameter` | Scalar (m) | Finished hole diameter (after plating) |
| `SignalViaPad` | Shape or cell | Pad shape(s) on signal via |
| `SignalViaAntipad` | Shape or cell | Antipad (clearance) shape(s) |
| `RemoveUnusedPads` | Logical | Remove pads on non-signal layers (default: true) |
| `GroundReturnViaLocations` | M×4 matrix | `[x, y, startLayer, stopLayer]` per GRV |
| `GroundReturnViaDiameter` | Scalar or vector | GRV barrel diameter |
| `GroundReturnViaFinishedDiameter` | Scalar or vector | GRV finished hole diameter |
| `SignalTable` | Cell array | Port definitions: `{viaNum, layer, traceWidth, direction}` |

## Signal Via Configuration

### Placing a Signal Via

```matlab
via = viaSingleEnded;
via.SignalLayer = [1 5];
via.GroundLayer = [3 7 9];

X = 0; Y = 0;
startLayer = 1;
stopLayer = 7;
via.SignalViaLocations = [X Y startLayer stopLayer];
```

The via barrel spans from `startLayer` to `stopLayer`. Signal connections occur on layers listed in `SignalLayer` that fall within this range.

### Via Diameter

```matlab
via.SignalViaDiameter = 0.25e-3;          % Drill diameter
via.SignalViaFinishedDiameter = 0.20e-3;  % After copper plating
```

### Unit Conversion Helper

The object provides a built-in mils-to-meters conversion:

```matlab
via.SignalViaDiameter = 10 * via.mils2meters;   % 10 mils
```

## Port Definition (SignalTable)

The `SignalTable` property defines which layers become ports for S-parameter extraction.

### Format

Each row: `{signalViaNumber, layerIndex, traceWidth, direction}`

- `signalViaNumber`: Which signal via (1-based index into `SignalViaLocations`)
- `layerIndex`: The layer where the port is placed
- `traceWidth`: Width of the connecting trace (meters)
- `direction`: Angle in degrees (0 = +x direction, 90 = +y, etc.)

### Example: Two-Port Via

```matlab
via.SignalTable = {1, 1, 3e-4, 45;   % Port 1: via 1, layer 1, 0.3mm trace, 45 deg
                   1, 5, 3e-4, 0};    % Port 2: via 1, layer 5, 0.3mm trace, 0 deg
```

### Using Table Syntax for Clarity

```matlab
vPorts = table('Size', [2 4], ...
    'VariableTypes', ["cell","cell","cell","cell"], ...
    'VariableNames', ["Signal Via Num","Layer","Trace

SAFEgrade B · trust 89/100 Nothing in the source contradicts what it says it does. Grade A is reserved for packages that have also passed the behavioural sandbox.

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