via module#

Via definitions#

This module provides classes for defining vias, including via types, backdrill specifications, and via properties.

Bases: Positionable

Via definition that can be instantiated in the board. Layer indexes referenced in this definition are absolute in the board: 0 is always the top layer. They are not relative to any component / circuit. Flipping via instances in the UI will not flip those layers, contrary to landpattern pads.

>>> class StandardVia(Via):
...     start = Side.Top
...     stop = Side.Bottom
...     diameter = 0.6
...     diameters = {0: 0.5, 1: ViaDiameter(0.5, nfp=0.2)}
...     hole_diameter = 0.3
...     type = ViaType.MechanicalDrill

type: ClassVar[ViaType]#

MechanicalDrill or LaserDrill.

Type:: Type of via drilling method

start_layer: ClassVar[int]#: Starting layer for the via. Setting this to a layer index other than the top layer allows for creating buried or blind vias.

stop_layer: ClassVar[int]#: Ending layer for the via.

diameter: ClassVar[float | ViaDiameter]#: Pad diameter of the via, in mm. Can be overridden on a per-layer basis by diameters.

diameters: dict[int | tuple[int, ...], float | ViaDiameter] = {}#: Pad diameters of the via for specific layers. Overrides diameter for the given layers.

hole_diameter: ClassVar[float]#: Drilled or laser-cut hole diameter for the via, in mm.

filled: ClassVar[bool] = False#: Whether the via is filled.

tented: ClassVar[set[Side] | Side | None | bool] = True#: Whether the via is tented on Top, Bottom, or both sides. Untented sides will have a solder mask opening.

via_in_pad: ClassVar[bool] = False#: Whether the via is allowed to be placed inside a component’s pads.

backdrill: ClassVar[BackdrillSet | Backdrill | None] = None#: Backdrill specifications. If a Backdrill is used, it will be assumed to be drilled from bottom.

models: ClassVar[dict[tuple[int, int], PinModel]] = {}#

Specifies delay and loss models for the via, used by signal integrity constraints.

Each entry defines a model for a pair of layers. Layers are specified as layer indices. Models are assumed to be symmetric, so the order of layer indices is arbitrary. It is an error to specify multiple models for the same pair of layers.

It is recommended to not specify models with the same start and end layer. They will currently be ignored by the constraint solver (since path does not travel through the via) but this behavior may change in a future version of JITX. The models are given in terms of the same jitx.si.PinModel object used by components.

>>> class MyVia(Via):
>>>     # Other via parameters...
>>>     models = {
>>>         # Top to bottom layer (through-hole via)
>>>         (0, -1): PinModel(5e-12, 0.05),
>>>         # Top to inner layer 1 (blind via)
>>>         (0, 1): PinModel(2e-12, 0.02),
>>>         # Inner layer 1 to inner layer 2 (buried via)
>>>         (1, 2): PinModel(2e-12, 0.02),
>>>     }

Not all layer pairs need to be specified. If you know that, for example, all usages of a via will go between the top and bottom of the board, then only that model needs to be provided.

Via models can also be generated programmatically using loops. For example, to define models for all layer pairs in a multi-layer board where delay and loss scale linearly with the number of layers traversed:

>>> class MultiModelVia(Via):
>>>     # Other via parameters...
>>>
>>>     # Generate models for all layer pairs
>>>     total_layers = 4
>>>     models = {}
>>>     for i in range(total_layers):
>>>         for j in range(i + 1, total_layers):
>>>             # Model that scales with number of layers
>>>             n_layers = j - i
>>>             models[(i, j)] = PinModel(
>>>                 2e-12 * n_layers,
>>>                 0.05 * n_layers
>>>             )

When models are not provided for a via, placeholder models are automatically inserted. When using placeholder models (models with ideal delay and loss), any timing or loss constraints involving signals through these vias will be flagged as unsatisfied. This is because the placeholder model assumes some arbitrary transmission delay and loss values, which are not set by the user. For accurate signal integrity analysis, provide calculated, measured, or simulated via models for all layer pairs used in your design.

For maximum accuracy, it is recommended to simulate or measure each specific pair of layers rather than using a simplified linear model. The loop approach is most useful for initial designs or when detailed measurements are not yet available.

class ViaDiameter(pad, *, nfp=None)[source]#

Bases: object

Diameters of various features of a via.

Parameters:

pad (float)
nfp (float | None)

pad: float#: Pad diameter for the via, in mm.

nfp: float | None = None#: Pad diameter for the via when non-functional pads are removed, in mm. When provided, it overrides the pad diameter except on the start layer if there is no top backdrill, stop layer if there is no bottom backdrill and intermediate copper layers that have traces or pours connected to the via.

class ViaType(*values)[source]#

Bases: Enum

Type of via drilling method.

MechanicalDrill = 1#

LaserDrill = 2#

class Backdrill(diameter, startpad_diameter, solder_mask_opening, copper_clearance)[source]#

Bases: object

Backdrill specification for a via.

Parameters:

diameter (float)
startpad_diameter (float)
solder_mask_opening (float)
copper_clearance (float)

diameter: float#: Diameter of the backdrill in mm.

startpad_diameter: float#: Diameter of the starting pad in mm.

solder_mask_opening: float#: Solder mask opening size in mm.

copper_clearance: float#: Copper clearance diameter in mm.

class BackdrillSet(top=None, bottom=None)[source]#

Bases: object

Set of backdrill specifications for top and bottom sides.

Parameters:

top (Backdrill | None)
bottom (Backdrill | None)

top: Backdrill | None = None#: Backdrill specification for the top side.

bottom: Backdrill | None = None#: Backdrill specification for the bottom side.