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Documentation / Altium Designer / ... / High Speed PCB Design /
PCB Layer Stack Management Search this space
CONTENTS
PCB Layer StackupTechnology andTerminology
A Single Design withMultiple Layer Stacks
Defining the Layer Stackin the Layer StackManager
Adding, Removing andConfiguring the LayerStacks
Adding and RemovingLayers from a Stack
Configuring the LayerProperties
Layer Types, Propertiesand Function
PCB Layer Stack ManagementModified by on 6-Nov-2013
A printed circuit board, or PCB, is used to mechanically support
and electrically connect electronic components. An
Austrianscientist, Dr Paul Eisler, is credited with making the
first operational printed wiring board in 1943, where the printed
circuitsreplaced the bulky wiring in a vacuum tube radio.
The PCB is designed and formed as a stack of layers. In the
early days of printed circuit board (PCB) manufacturing, theboard
was simply an insulating core layer, clad with a thin layer of
copper on one or both sides. Wiring was formed in thecopper
layer(s) as conductive traces, by etching away (removing) unwanted
copper.
A simple, single-sided PCB. Note how the circuit tracks that are
on the bottom layer are visible through the board.
Fast forward to today, where almost all PCB designs have
multiple copper layers. Two to ten copper layers are common, butit
is possible to fabricate a board with over thirty copper layers.
These copper layers are defined in the design environment
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and Function
Assigning a Net to a PlaneLayer
Defining the OverallBoard Shape
Defining a Board Regionand Assigning a Sub-Stack
Managed Stacks andEmbedded Components
Documenting the LayerStack
Configuring the Drill Pairs
Including a Drill Table
RELATED VIDEOS
Define New LayerStacks
Layer Stack Regions
as part of the layer stack, along with the insulation material
that separates them.
To design a single printed circuit board it is only necessary to
define a single layer stack, which defines the entire boardarea in
the vertical direction, or Z plane. However, technological
innovation and refinements in the processing technologyhas led to a
number of revolutionary concepts in PCB fabrication, including the
ability to design and manufacture flexiblePCBs. By joining rigid
sections of PCB together via flexible sections, complex, hybrid
PCBs can be designed, that can befolded to fit into unusually
shaped enclosures.
Rigid sections of PCB connected via flexible sections of PCB, an
innovative concept that supports the design of creative and compact
electronic
products.
Since it is fabricated as a single entity, a rigid-flex PCB must
be designed as a single entity. To do this, the designer must
beable to define multiple PCB layer stacks, and assign different
layer stacks to different parts of the rigid-flex design.
PCB LAYER STACKUP TECHNOLOGY AND TERMINOLOGY
Main article: PCB Layer Stackup Technology and Terminology
PCB technology has been driven not only by the quest for smaller
electronic products, a leading driver of PCB technology has also
been the quest for morecompact components to use in those products.
PGA and BGA components, with their array of interconnects are often
fabricated using an internal PCB. It's thetechnology developed for
this PCB, often referred to as High Density Interconnect (HDI)
technology, that is now making its way into mainstream PCB
fabrication.
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An example of the internal structure of a Ball Grid Array
package.
An excellent reference for building a good understanding of the
materials and techniques of both the design and the fabrication
of
printed circuits is Right First Time - a Practical Handbook on
High Speed PCB and System Design, by Lee Ritchley. A free PDF
version can be
downloaded from http://www.thehighspeeddesignbook.com/.
A SINGLE DESIGN WITH MULTIPLE LAYER STACKS
Like a simple, rigid PCB, a rigid-flex PCB is fabricated as a
single entity. To be able to do this, the designer must be able
to:
Define the overall shape of the rigid-flex PCB.Define a master
set of layers that includes all layers needed in the rigid-flex
design.Define multiple layer stacks, where each stack includes only
the layers needed for each of the rigid and flexible zones of the
PCB.Define the different rigid and flexible zones where each
sub-stack is applied.Generate detailed output fabrication and
documentation files needed to fabricate the rigid-flex PCB.
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This board has had 3 layer stacks defined, 2 Rigid stacks and 1
Flex stack.
DEFINING THE LAYER STACK IN THE LAYER STACK MANAGER
All layer stacks are defined in the Layer Stack Manager. To open
the Layer Stack Manager select Design Layer Stack Manager from the
menus. For a new board,its single default stack comprises: a
dielectric core, 2 copper layers, as well as the top and bottom
solder/coverlay and overlay layers, as shown in the imagebelow.
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Layer stack management is performed in the Layer Stack Manager
dialog. The default single stack for a new board is shown.
The dialog has two modes. In its Simple mode, the dialog
provides the features and functionality needed to manage the layers
in the stack for a traditional rigidPCB. For rigid-flex PCBs, you
need to be able to create and manage multiple stacks. This is
performed by entering the dialog's Advanced mode - by clicking
theAdvanced button at the bottom-left of the dialog.
Controls for adding and managing stacks are made available by
entering the dialog's Advanced mode, which displays the lower Stack
region of the dialog.
In this mode, the dialog is visually and functionally divided
into two key regions:
Stack region (the lower region) providing controls to add,
delete and re-order layer stacks.Layer region (the upper region)
providing controls to manage the layers available to the defined
stacks (add, remove, enable/disable, and re-order layers,as well as
defining layer properties).
The stack currently selected in the lower region of the dialog
has its name highlighted with a grey background, and this stack is
displayed
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in the upper layer region of the dialog.
Adding, Removing and Configuring the Layer Stacks
Stacks are added, removed and their order is configured in the
lower half of the Layer Stack Manager. Note that this section is
only displayed if the
button has been clicked.
Notes about adding, removing and configuring stacks:
1. A single, default Board layer stack is defined when a new
board is created. Note that this stack cannot be deleted, but it
can be renamed.2. When the Add Stack button is clicked, the
currently selected stack is duplicated and added to the right of
the selected stack.3. Layer properties apply to the entire layer,
across all stacks that the layer is a member of. Note that separate
Solder Mask/Coverlay and Overlay layers can
be added for each stack, if required.4. The order of the stacks,
from left to right, can be changed using the Move Left and Move
Right buttons at the bottom-right of the stack region. Note
that
the order that the stacks are shown in the Layer Stack Manager
does not dictate how they are used in the board design.5. Each
stack should be named to uniquely identify it, this helps ensure
the correct stack is applied to each user-defined board region.6.
Each stack that is flexible must have its Flex option enabled, so
that required flex bending properties can be applied. Note that
flex bending is defined by
placing a Bending Line across the flex region (Design Board
Shape menu), and then editing its properties in the PCB panel when
the panel is set to LayerStack Regions mode.
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A board with a total of 3 stacks defined, 2 rigid stacks and 1
flex stack.
As you click on the cell associated with a particular layer in
the layer region of the Layer Stack Manager, that layer will be
highlighted in
the graphical display of the currently selected stack (to the
left), and also across all defined stacks that use that layer, in
the stack region of
the dialog.
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Adding and Removing Layers from a Stack
Layers are added, removed and re-ordered in the upper half of
the Layer Stack Manager using either the Add Layer button (for
adding) or the right-click menu(for all types of changes).
Notes about adding, removing and moving layers:
1. To add a new layer, click the Add Layer button and choose the
type of layer to add (signal layer, internal plane, dielectric, or
overlay).2. New layers are added into the set of layers listed in
the upper part of the Layer Stack Manager. By default a newly added
layer is enabled for use across all
existing stacks. Simply select each stack in turn and disable
the layer if it is not required in that stack, using the checkbox
to the left of a layer's name.3. Note that this behavior, to
automatically add a layer to all stacks, does not occur if Solder
Mask/Coverlay and Overlay layers are added. These layer types
can be added/removed to each stack.4. Initially, when a copper
layer (signal or plane) is added, a dielectric layer is
automatically added too, maintaining the symmetry of the stack
(copper-
dielectric-copper-dielectric, and so on). The location and type
of dielectric that is added is controlled by the technology style
setting, located at the top-right of the dialog. This is not the
case if the style option is set to Custom, in this case only the
chosen layer type is added (more details on the style
settingbelow).
5. To move a layer up or down in the stack, right-click on the
layer and select the Move Layer Up or Move Layer Down command, or
use Move Up or MoveDown buttons. Note that when a copper or
dielectric layer is moved the adjacent dielectric/copper layer will
also move unless the style option is set toCustom, then only the
selected layer will move.
6. Layer Properties apply to the entire layer, across all stacks
that the layer is a member of. This does not apply to Solder
Mask/Coverlay and Overlay layersthat have been selectively added to
a stack.
7. One or more layers can be selected and deleted. A deleted
layer is removed from the set of available layers, and therefore
removed from all stackscurrently using it.
8. Use the Undo and Redo buttons to roll layer stack changes
backward or forward.
The Layer Stack Manager includes an option at the top right of
the dialog for selecting the Style of layer technology to be used
on this
board. The available options include: Layer Pairs, Internal
Layer Pairs, Build-up or Custom. Note that this option does not
affect the final
design of the layer stackup, it is simply used to help select
the appropriate type of dielectric layer to add and the location in
the stack
where it is added, when you run an Add Layer command. In all
modes other than Custom, whenever a signal layer is added, a
dielectric
layer will also be added. The type and location of dielectric
added depends on: the current number of layers used, and the
current Style
setting. Note that once a second layer Stack has been added, the
Style is automatically set to Custom. In Custom mode, new layers
are
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added one-by-one.
CONFIGURING THE LAYER PROPERTIES
The properties of each layer must be completely defined, which
should be done in consultation with the PCB fabricator. This
information is included in theLayer Stack Table, the properties of
each layer are edited directly in the layers region of the dialog.
To edit a cell double-click on it, if that cell supports editing
itwill become available for editing.
Multi-cell editing is supported, to do this:
Use the Windows standard Shift+Click (for a range) or Ctrl+Click
(for individual cells) to select multiple cells.Press F2 to enter
editing mode (do not use the mouse, or you will loose your
selection).Use the keyboard to type the required string, or use the
mouse to select the required option from a dropdown.For checkboxes,
Shift+Click or Ctrl+Click in the cell around the checkbox, then
press the Spacebar to toggle the setting of the selected
checkboxes.
Layer Types, Properties and Function
In Altium Designer there is a single set of layers defined, and
any layer can then be used in any layer stack. This set of layers
includes all of the layers that areused in the overall PCB design,
regardless of whether the design is a single PCB, or a rigid-flex
design incorporating numerous rigid and flex sections. A varietyof
types of layers can be included in the layer stack: including
copper, dielectric, surface finish and mask layers. Each layer must
be completely specified interms of its material and mechanical
requirements, including: the material used, the thickness, the
dielectric constant, and so on. The selection of materials andtheir
properties should always be done in consultation with the board
fabricator.
The layer types and their properties are detailed in the table
below, the process of defining the required layers and assigning
them to the various stacks,follows that.
Layer Type Material Thickness Properties toDefine
Comments
Signal Coppermm ormils
ThicknessCopper layer used to define signal routing, carriesthe
electrical signals and circuit supply current.Typically annealed
foil and electro-deposited.
Internal Plane Coppermm ormils
Thickness
Solid copper layer used to distribute power andground, can be
split into regions. Also must specifythe distance from the plane
edge to the board edge(pullback). Typically annealed foil.
TypeInsulating layer, can be rigid or flexible. Used todefine
core, prepreg and flexible layers.
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DielectricVaries, including: FR4, polyimide, and a variety
ofmanufacturer-specific materials offering differentdesign
parameters
mm ormils
(function),Material,ThicknessandDielectricConstant(Dk).
define core, prepreg and flexible layers.
Important mechanical properties include; includingdimensional
stability over moisture and tempranges, tear resistance,
flexibility.
Important electrical properties include; insulationresistance,
dielectric constant (Dk), dissipation factor(loss tangent, Df or
Dj)
Overlay Screen printed epoxy, LPI (liquid photoimageable)
Present text/artwork, such as componentdesignators.
SolderMask/Coverlay
1) Liquid photoimageable solder mask (LPI or LPSM) ,Dry Film
photoimageable Solder Mask (DFSM), or
2) Adhesive coated flexible film, typically polyimide
orpolyester.
mm ormils
Type(function),Material,ThicknessandDielectricConstant(Dk).
1) Protective layer that restricts where solder can beapplied to
the circuit. A cost effective and proventechnology, suitable for
rigid and flex use class A(flex-to-install) applications. Suitable
for finerfeatures than flexible film coverlay.
2) Suitable for flex use classes A and B (dynamicflex). Requires
rounded holes/corners, which aretypically drilled or punched.
Paste Mask
Layer from which a paste mask stencil is fabricated.Stencil is
typically stainless steel. Openings in thestencil define locations
where solder paste is to beapplied to the component pads, prior to
componentplacement.
Mask layer used to fabricate solder mask screen,which defines
locations where solder paste is to beapplied.
Assigning a Net to a Plane Layer
Main Article: Internal Power and Split Planes
In earlier versions of Altium Designer, a net could be assigned
to a plane either through the Layer Stack Manager, or by
double-clicking on the plane layer in theworkspace. With the
introduction of multiple layer stacks, the net is always assigned
to the plane by double-clicking on the plane layer in the workspace
(theplane layer must be the active layer). When you double-click
the Split Plane dialog will open, select the required net, as shown
in the image below. This processis the same if you are assigning a
single net to the entire plane, or are assigning a net to a split
region of the plane.
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To assign a net to a plane layer, make the plane layer the
active layer then double-click to open the Split Plane dialog,
where the net is assigned.
DEFINING THE OVERALL BOARD SHAPE
Main Article: Creating and Modifying the Board Shape
Regardless of the final make up of the board (single rigid area
or multiple rigid-flex sections), the overall outer shape is
defined as the Board Shape. The BoardShape can be:
Defined manually - by redefining the shape, or moving the
existing board vertices (corners). Switch to Board Planning Mode
(View Board Planning Mode)then use the commands in the Design
menu.
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Defined from selected objects - typically done from an outline
on a mechanical layer. Use this option if an outline has been
imported from another designtool. Switch to 2D Layout Mode (View 2D
Layout Mode) then use the command in the Design Board Shape
sub-menu.Defined from a 3D body - use this option if the blank
board has been imported as a STEP model from an MCAD tool into an
Altium Designer 3D Body Object(Place 3D Body). Switch to 3D Layout
Mode (View 3D Layout Mode) then use the command in the Design Board
Shape sub-menu to select the boardshape.
The main View menu has a cluster of PCB editor working modes
with easy to remember shortcuts, allowing you to quickly switch
between
Board Planning Mode (1), 2D Layout Mode (2), and 3D Layout Mode
(3). The editor menus will populate with relevant commands for each
of
the respective modes. So if you're used to finding your favorite
board shape command on the Design menu and can't see it
anymore,
make sure you're in the right mode!
DEFINING A BOARD REGION AND ASSIGNING A SUB-STACK
Main Article: Defining Board Regions and Bending Lines
When a new board is created, the overall board shape is
automatically assigned the board region called Default Layer Stack
Region. Double-click anywherewithin the board shape to open the
Board Region dialog and change the default name. This default board
region is automatically assigned the default Boardlayer stack. Note
that the default Board layer stack is named in the Layer Stack
Manager.
The board can be divided into regions by switching to the Board
Planning Mode (View Board Planning Mode, shortcut: 1) and defining
Split Lines (Designmenu). To learn more, refer to the article
Defining Board Regions and Bending Lines.
MANAGED STACKS AND EMBEDDED COMPONENTS
Related article: Designing with Embedded Components
When you embedded a component, Altium Designer has to manage how
that embedded component affects the layer stack, not only in terms
of how it isdisplayed, but also in terms of calculated data such as
solder mask openings and design rule checking. It does this by
creating a stack for each uniquecombination of placed + cut layers
needed by the various embedded components included in the design.
These stacks are referred to as Managed Stacks.
The Managed Stack is created automatically when a component is
embedded within the layers of the board. As managed stacks are
created automatically thereis no user-input needed in their
creation and management. Altium Designer checks for embedded
components, tests if any of the current managed stacks aresuitable
and if not, creates a new one. The same applies when embedded
components are removed, if a managed stack is no longer needed, it
is automaticallyremoved. To force Altium Designer to check if new
managed stacks are needed, switch between 2D and 3D Layout
Modes.
The Managed Stack defines the board structure in the vertical,
of Z plane. In the horizontal, or X Y plane, the region that the
stack extends
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over is defined by the cavity definition built into that
embedded component.
The image below shows the layer stack dialog for a rigid-flex
design that includes embedded components. By analyzing the Managed
Stacks it is possible towork out which layers the components are
embedded on.
Note that:
The stack selector down the bottom of the dialog is set to Show
All Stacks, displaying the two managed stacks, Stack0 and Stack2.
Note that the stackselector setting is not persistent, when the
dialog is reopened it defaults to Show User Stacks.The upper-most
layer in Stack2 is Mid-Layer 1, there are no other layers above
this layer. This indicates that the upper layers are removed by the
cutout(cavity definition) in the component embedded on Mid-Layer
1.The upper-most layer in Stack0 is Mid-Layer 2, there are no other
layers above this layer. This indicates that the upper layers are
removed by the cutout(cavity definition) in the component embedded
on Mid-Layer 2.
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The Layer Stack Manager set to Show All Stacks revealing two
Managed Stacks, Stack0 and Stack1.
DOCUMENTING THE LAYER STACK
Main Article: Documenting the Layer Stack
Documentation is a key part of the design process, and is
particularly important for designs with a complex layer stack
structure, such as a rigid-flex design. Tosupport this, Altium
Designer includes a Layer Stack Table, which is placed (Place Layer
Stack Table) and positioned alongside the board design in
theworkspace. The Layer Stack Table details the:
Layers used in the designMaterial used for each layerThickness
of each layerThe Dielectric ConstantThe name of each stack and the
layers used in that stack
The Layer Stack Table can also include an optional map of the
PCB, this is an outline of the board showing how the various layer
stacks are assigned to regionsof the board. The map can be scaled,
or hidden if required.
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The Layer Stack Table is used to provide detail documentation of
all layers used in the design, note the map included below the
table.
CONFIGURING THE DRILL PAIRS
In a design with multiple layer stacks, the Drill Pairs are
defined for each stack. Drill pairs are configured in the Layer
Stack Manager.
To define the drill pairs:
1. Select the stack in the lower part of the Layer Stack
Manager.2. Click the Drill Pairs button to open the Drill-Pair
Manager.3. Define the drill pairs for that stack, as required.4.
Repeat the process for each Stack in the design.
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Select the stack then click the Drill Pairs button to define the
drill pairs for that stack.
Including a Drill Table
Main Article: Live Drill Drawing Table
Altium Designer includes an intelligent Drill Table, which is
placed like any other design object. The table displays the drills
required for a specified layer pair,you will need to place a drill
table for each layer pair used in the design.
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4 Drill Tables have been placed, one for each of the drill pairs
defined in this rigid-flex design. A title has been added to each
to identify the layer pair.
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