MultiSIM BLUE – PCB Layout Basics on designing a Printed Circuit Board (PCB) Introduction This document serves as an overview of the major steps involved when designing a circuit for a printed circuit board (PCB) for the designer using MultiSIM BLUE. This document discusses the major steps in the ‘PCB design flow’ – from basic terminology that will be encountered to the primary steps required to move an example design through the schematic, layout and manufacturing stages. Understanding the Terminology MultiSIM BLUE – A circuit design platform from Mouser Electronics in partnership with National Instruments. The schematic program allows the user to draw a document representing the electrical component symbols and the interconnections between them. Before generating a PCB, the symbols are mapped to component footprints and the symbol interconnections are converted to a netlist that specifies the connections between the component footprints in the layout process. MultiSIM BLUE also allows the user to do interactive circuit simulation with the same schematic circuit representation used for layout which can be useful for both initial design analysis and testing the design (i.e. verification testing and troubleshooting) once complete. The PCB layout program also known as Ultiboard, is used to generate the mechanical and wiring connection structure of the PCB from the netlist. The layout program allows the wiring connection structure to be placed on multiple layers and once complete allows the user to generate the CAD (computer aided design) files needed to manufacture a PCB. Gerber Files – The CAD files needed to send to a PCB manufacturer so they can build the PCB layer structure. The RS-274X is the most commonly supported Gerber file format. NC Drill Files – The numerically controlled (NC) drill files indicate the size and position of holes used for unplated holes, plated through-holes or holes for vias. Some quick-turn PCB manufacturers have only select hole sizes available. Printed Circuit Board (PCB) – A wafer board defining the mechanical and copper wire structure of the circuit (sometimes called a PWB for Printed Wiring Board). Printed Circuit Board Structure and Details a. A PCB can be considered a layered structure, usually with multiple copper and insulating layers.

The main portion is a non-conductive (insulative) material (substrate) usually made from fiber glass & epoxy.

b. The substrate material used to separate layers comes in different thicknesses, from 0.005” to 0.038”.

c. Conducting layers consist of copper (Cu) foils that are etched away in specific areas where the user does NOT want connections to occur.

d. A single layer PCB has the substrate with one layer of copper foil on the top.

A double layer PCB has two layers of copper foil (one on the top and one on the bottom).

e. If more than two layers are required due to increased complexity of the PCB, other layers of

copper can be built-up or added to the ones shown above (usually in pairs). For example, a 4 layer PCB can be made up of two double-layered PCB’s laminated (sandwiched) together with a core material in between. This core layer is called a prepreg (pre-impregnated) and it insulates and supports the other layer structures and is made out of epoxy/fiber. It is common for modestly complex boards to have 6, 8 or 10 layers (with increased manufacturing cost). Some highly complex PCBs have up to 32 layers or more of traces and copper planes.

Note: The height of the substrate is usually the thickness of one or multiple sheets of laminate material and is usually much smaller than the height of the core prepreg material layer. Multilayer PCB – A PCB with more than one copper foil layer. The layers can be renamed in to unique names (such as Power or Ground) as desired by the user.

Layer Stack Up – The copper organization of multiple layer PCBs with the intent of having specific signal and ground planes on certain layers for routing convenience and electromagnetic shielding purpose. A four layer board will typically have the following layer structure, where the top and bottom layers are reserved for signal routing and the inner layers are reserved for ground and power planes:

Copper Top

Inner 1

Inner 2

Copper Bottom Finished PCB Height - Standard finished PCB thicknesses are commonly found as shown – this thickness includes all copper, substrate and prepeg layers:

.031” (also .039" is common)

.062" (mostly commonly used size)

.093"

.125" Shown here is a more realistic layer stackup of a four layer PCB showing the various thicknesses of the layer structures from a typical PCB manufacturer yielding the common 0.062” finished PCB height.

Bare PCB – A finished PCB without electrical parts and other components (unpopulated or unassembled). Assembly Drawing – A mechanical and schematic drawing with engineering notations specifying how and in what order the PCB needs to be assembled and packaged. For automated assembly the assembly drawing also contains information about solder paste and other information for component population and other board manufacturing purposes. Some basic mechanical assembly information can be completed within the PCB layout environment; however any complex mechanical assembly information typically needs to be completed in an external CAD package.

Trace – A portion of the copper foil that is remaining on the PCB after the etching process for a signal connection (net) from point A to point B. Traces for nets can have various widths which need to be sized by maximum current expected to run through the trace. Plane – A large portion of the copper foil that is remaining on the PCB for a signal connection that attaches to many components. This is a layer where little copper is etched away. Power and ground signals are typically connected to a plane, since the power and grounds need to route to many components on the PCB. Since a plane has a lot of copper and the plane covers a large area, traces can be routed to the plane with an effective lower resistance and inductance from a connection point to the plane. This will create smaller voltage drops (versus placing discrete traces) when the components conduct power and ground current and thus will create a design with lower power dissipation. Also circuits with power and ground planes will be less likely to radiate electromagnetic (EM) energy, as well as being less susceptible to EM energy (such as 50/60 Hz AC line noise). Below is an example of a 4-layer PCB with power & ground planes:

Substrate – The non-conductive material (substrate) is usually a fiberglass epoxy. A flame retardant material called FR-4 is the most common PCB material used in North America. For specialized applications, other materials can be used (such as G10) but these other materials will typically exhibit lower flammability resistance. Other substrate materials (with favorable dielectric properties) are available and sometimes available materials vary by geographic region.

Copper thickness (weight in ounces) – The copper foil thickness is measured not in linear dimensions, but with the weight of the copper if poured onto a 1 square foot sheet. For instance, a common copper thickness (weight) is 1 oz. This means 1 oz. of copper per square foot. A 2 oz. weight would indicate 2 oz. per square foot. Some common copper weights are as follows:

¼ oz (not common since it is so thin it can vaporize with a soldering iron)

½ oz (common), Copper will be 0.7 mils thick.

1 oz (most common), Copper will be 1.35 to 1.37 mils thick.

2 oz (very common for higher current boards)

3 oz (not common except for high current applications as it acts as a heat sink, also difficult to solder to since it drains the heat from the soldering iron)

The copper weight and width needs to be considered when designing a PCB. Consider the current in the traces versus the added cost for higher copper weight when deciding on the copper oz. weight to use. For application specific information, the user can look up quantitative design criteria by referring to the tables in IPC-2221, Generic Standard on Printed Board Design. PCB Styles – Most modern PCBs typically have a combination of surface mount and through-hole parts, however PCBs can generally be organized into two categories:

Plated Through Hole (PTH or also indicated as TH) – In this type of PCB, the majority of components will have wire leads that extend from the part that are inserted into the holes of the PCB which are copper plated for soldering. Shown below is a cross section of a two layer board with four PTHs. Also shown are two copper traces on the board; the one shown on the bottom is connecting two PTHs together.

Surface Mount Technology (SMT) – In this type of PCB, the majority of parts have no

leads that go through the PCB. These parts will typically have pads or leads that get soldered to the surface of the board. These components are referred to as Surface Mount Devices (SMDs). Below is a Surface Mount Technology PCB with four SMT pads. A resistor is shown soldered to the board. With SMT, the designer has the option to place parts on the

bottom of the board since there are no PTHs located near the SMDs to obstruct the placement of the SMD. SMDs can typically be manufactured smaller than their through-hole equivalents, thus the use of SMT can usually lead to significant increases in the parts density within a PCB.

Note: When considering PTH or SMT technology for the PCB, be careful on selecting the correct technology and components for the application. Prototyping will generally work better with PTH or larger SMD style components, however the larger technology may not meet final size or density constraints on a final production design. Conversely SMT style PCBs can be packed very tightly together and can typically yield lower manufacturing costs (per board in larger volumes) through automated assembly. However hand soldering small SMD components or components with ball grid array (BGA) technology can be very tricky for all but those with very experienced soldering skills. Consider these important tradeoffs when selecting components and designing the PCB. Some components will be available in both through-hole and SMD styles, whereas others will be available in only one style. Solder Mask – This is a shielding or insulating layer (this is also what makes common PCBs green) installed over the top and bottom layer to cover copper traces. The layer usually is not installed over the top of pads since this exposes the copper area to be soldered. This layer protects these covered conductors so that solder will not inadvertently adhere to them (creating shorts) when connecting nearby parts to pads or through-hole connections. Silkscreen (also called Screen Print) - This is the final layer applied over the top solder mask and also over the bottom solder mask (if required) to display part outline and reference designator information on the board. Besides displaying part outline and reference designator information, the silkscreen can display orientation information (such as anode/cathode direction) and any other symbol or textual information the user wants to be displayed on the board (such as internal board model numbering, logos, PCB revision numbering and other manufacturing or standards marking). Footprint – The mechanical and electrical pattern of the part. The information included in the part typically includes the copper land pattern, mechanical outline and any important dimensional information of the component such as the body information, height and size. The footprint for a component will typically include a silkscreen layer displaying part outline and orientation information and the copper pads or holes (land pattern) that are associated with the parts. As in the case of connectors, the footprint of the part may extend beyond the board outline, so the detail in the

footprint should give the designer adequate information for part placement, orientation and copper connections. Land pattern – This is the pattern of pads or holes on the circuit board, sometimes including the part body information. A standards body known as IPC is often used to accurately specify the required copper size and shape required to ensure the proper bonding and adhering of the component’s pads or wires to the PCB. The land pattern can include non-electrical pad information such as thermal relief pads or heat sink patterns that may be required. Overview of Steps Involved – Example Design Flow Schematic drawing and footprint selection The first step in successfully creating a PCB is the proper creation of an appropriate schematic drawing of the circuit with MultiSIM BLUE. It will be necessary that all of the components selected in the schematic have correctly assigned packages associated with them so that the generated part list and netlist representing required connections will be correct. The following MultiSIM BLUE schematic will be used to highlight the basic steps to go from schematic to final PCB generation:

In the example, notice that the resistor, R4, has a black symbol whereas other components have blue symbols. In MultiSIM BLUE this indicates that R4 does not have an associated footprint. In MultiSIM BLUE, all parts that intend to be part of the PCB design need to have footprints associated with them for the design to be properly sent to the layout stage. Notice here that power ( VDD) and ground

symbols ( and ) are considered virtual parts that connect into a single net and these symbols

are treated specially in MultiSIM BLUE. Since these are net connections only and do not connect to a footprint for layout purposes, it is appropriate to have them show up as a black color. An effective way to check the whole schematic for valid footprints is to view the Bill of Materials report by selecting from the menu (Reports » Bill of Materials) and then clicking on the Vir button to show virtual components. The displayed report will indicate any parts that do not have footprints associated with them. It will also list power and ground symbols but as discussed previously it is fine to have these displayed as virtual components. When a schematic still has virtual components when transferred for PCB layout, a message similar to the following will be displayed:

A footprint can be added several ways.

1. By double clicking on the component and selecting Value » Edit Footprint. 2. By appending a new footprint from the Database Manager (requires same footprint mapping

if one already exists). 3. By saving the component as a new component (right-click and select the Save component to

database... option) and then attaching a new footprint with a new symbol-footprint mapping from within the Database Manager (preferred method over #2 since new manufacturer part number or vendor information will apply). You will need to replace component with new component.

After adding a footprint to the resistor, the schematic will now look like this:

Once satisfied with the schematic (and functionality or performance through the use of simulation), it is time to prepare the schematic for transfer into Ultiboard. Preparation Steps before Transferring

In the example schematic, both an analog ground ( ) and a digital ground ( ) are used. For layout purposes, MultiSIM BLUE will need to specify whether the analog and digital grounds should be considered one ground signal (i.e. connected together) or be kept separated for the purpose of routing two separate ground connections. To configure the ground connections in MultiSIM BLUE, select the PCB properties from the menu. (Options » Sheet Properties » PCB) PCB Properties Settings Check the box to select that the analog and digital grounds be connected together (if desired). In this example it is necessary to have this option checked or C2 would not have the same common return path as the rest of the circuit. As shown in the schematic that the digital ground shows a net name of GND and the analog ground has a net name of 0. When the grounds are connected, the netlist transferred to Ultiboard will use the net name ‘GND’ for both analog and digital ground net names. Set the export settings (mils, mm, etc…) that will be used for clearance and trace width. Mils (0.001 inch) are the most common units in North America, whereas Millimeter (mm) is preferred common in other regions.

Set the number of layers. If the circuit is relatively simple and electromagnetic compatibility is not an issue, a cost-effective single layer PCB design may be able to be used. If power or ground planes are required or the circuit is slightly more complex, two, four or more layers can be selected. When planning for the board design, the cost impacts will need to be considered as layers are added to the board. Note: Layers can always be added or subtracted during the layout process (usually in pairs). However, it is more difficult to remove layers once copper has been placed on specific layers.

For this circuit example, four layers will be selected so that the design can utilize a power and ground plane. Transferring design to Ultiboard Once the final preparation steps are complete in MultiSIM BLUE it is now possible to start transferring the schematic design into Ultiboard for layout. To transfer your design to Ultiboard select the appropriate item from the menu. (Transfer » Transfer to Ultiboard » Transfer to Ultiboard Component Evaluator 13)

MultiSIM BLUE will save a copy of the component footprint list and netlist to a single file (it will default to the same folder in which the schematic resides). The default file name will have the same name as the schematic but with a .ewnet file extension. Keep the default location or navigate to a new folder location and rename as desired. Clicking on the Save button will also cause Ultiboard to launch if it is not already opened. Note: The .ewnet file is a footprint and netlist file only and is different than the .ewprj file. The .ewprj file is the project file generated by Ultiboard that will contain the actual mechanical and electrical CAD data for the PCB board layout.

A popup window will be displayed showing all of the components and nets that are being transferred from the MultiSIM BLUE netlist file into Ultiboard. Leave all items selected and click OK.

This will then cause the default layout screen to display showing a default board outline and the footprints associated with each component in the schematic. From the example design, the footprint shapes shown are now the layout representations of the footprint-symbol associations that were selected in MultiSIM BLUE. Board Outline Selection

As shown, a generic board outline will be initially created. At this point, a custom board outline shape will need to be created to match package dimensions or other specifications. To start, select the layer called Board Outline. You can do this by double clicking on the layer desired on the Design Toolbox to the left of the workspace.

The selection filter Enable selecting other objects ( ) needs to be selected (depressed as shown in the green circle). This will allow the board outline to be selected in order to change it.

The default rectangular board outline can be repositioned or resized or one of the following methods can be used to customize the shape of the board outline. With any of these techniques, the existing board outline will first need to be selected and deleted and a new shaped created.

1. Place a polygon on the Board Outline layer to define a custom or complex shape.

2. Import a board outline shape via DXF file (File » Import » DXF).

Component Verification

When the parts are now placed within the project, it is always a good idea to double check the datasheet for your parts and adhere to any recommended pad sizing or thermal pad adjustments prior to routing. Also if you plan on manually soldering components for your project, you can visualize pad size and spacing to confirm part selections are adequate for manual soldering. You can also confirm part, pad and object sizes easily using the Dimensioning tools. To use or place a dimension on the board, simply click on one of the mechanical layers, go to Place » Dimension from the menu and measure the desired object. CAUTION: Although attempts are made to ensure part accuracy (mapping, sizing, and footprint information), the user has ultimate responsibility in verifying the design and component information versus the datasheet and other technical information. Datasheet and other design information from the manufacturer is readily available from the attached component links in the Mouser Database. Among the component data a PCB designer should be checking is: Footprint, land pattern (pad) shape Hole sizing (finished hole diameter size) Thermal requirements (adjusting pad size) Height and other clearance requirements Component Placement Tips and Strategies

To begin part placement, make sure the Copper Top layer is active and also make sure that only the

Enable selecting parts filter ( ) is active as shown below.

There are several lines that will be displayed on the screen connecting the parts together and the parts to the boards. The most important lines are the brighter yellow lines called the Ratsnest lines indicating the specific net connections between component pins within the design (these are the connections you made in the schematic within MultiSIM BLUE). In general it is a good practice to group parts together in a way that is consistent with the arrangement of the schematic design (such as the parts for a front end filter, digital section, power supply, etc…) to keep the ratsnest and thus the copper connections between parts short. By minimizing the length of the ratsnest, the physical trace length will be minimized allowing for an easier routing process. Attempt to minimize the crossing of the ratsnest lines by rotating parts <Ctrl+R> and moving associated components closer together as shown below.

Also keep in mind that with multiple layer boards, components can also be placed on the backside of the board (check component height clearances) which may help minimize trace length and trace crossings. In the example design below, the DB-9 connector and the 8 pin DIP are manually placed into the design. Typically connectors and other parts that have specific physical placement locations or restrictions are done first.

After arrangement

Before arrangement

An automated approach for part placement is available by using the Autoplacement feature Before performing an autoplacement step on remaining parts, any manually placed parts will first need to be locked down prior to autoplacement. To lock a component, highlight the component, click the right mouse button and select the Lock menu item. As shown locked parts will have an orange outline around them indicating they are fixed and will not move during the autoplacement process. After checking to make sure any critically located parts are locked start autoplacement from the menu (Autoroute » Autoplace parts).

In this example design, all of the parts are now placed. The autoplacement algorithm made sure to adhere to any design rules when placing the components. At this time, you can simply make any manual adjustments (move, rotate) to the component placement as desired. Layer Management Before placing any planes or signal routes, it is recommended to first verify and check initial net-layer assignments. Additional layers can be added at this time – or anytime throughout the design process. Remember it is easier to add or remove layers before a design is started rather than trying to delete copper and remove unwanted layers after routing begins. Note: Incorrect net-layer assignments are the most typical DRC errors created. If any DRCs are created due to incorrect net-layer assignments they should be corrected prior to performing additional routing as shown below. Once the net-layer assignments are corrected, any DRC errors should automatically be cleared or a manual DRC check may have to be performed from the menu (Design » DRC and netlist check). To start specifying the net-layer assignments select the Spreadsheet View from the menu and navigate to the Nets tab as shown (View » Spreadsheet View » Nets).

For simplicity in this example design, all nets will be allowed routing on all layers. The net-layer assignments will vary from design to design and it is usually a good practice to consider separating the signal routing layers with those intended for ground and power planes if possible. To enable all net-layer assignments, start by highlight all the rows in the Nets tab by selecting the top row, then hold the <Shift> key down and selecting the bottom row. Click on one of the highlighted rows in the Routing layers column and then select Check all as shown below to complete the net-layer assignments.

Once the layers are properly configured, routing traces can be started. If a ground or power plane is desired, it is typically best to create this first before routing any signal traces. If a ground or power connection is made first, a through-hole part will automatically connect to the plane if one of the pins is assigned to ground or power. When using a SMD part, vias can easily be dropped near ground or power pins to the required planes. Ground and Power Plane Creation

In this example design, the power plane will be placed on Inner Layer 1. From the menu select the power plane option (Place » Power plane) and set the layer and net as shown:

In the next example, the ground plane will be placed on Inner Layer 2. From the menu select the power plane option (Place » Power plane) and set the layer and net as shown:

Note: Users may optionally want to consider placing the ground plane on the Inner Layer 1 and power on the Inner Layer 2. The stackup is important to consider for EM shielding purposes and when placing matched pair traces (microstrip or differential pairs) on the PCB.

Tip: If you prefer the copper plain to appear in the background, you can simply assign the layer a darker color within the Layer/visibility settings. Darker colors will usually appear in the background. Routing Signal Traces Once the ground and power plane is complete, the remaining traces can be routed. There are several methods for signal routing, of which four will be discussed here. In general it is recommended that you plan a strategy for routing in the following way:

Manually route any critical signals first. Critical signals that need to be routed in specific routing paths need to be prioritized first (examples include traces for low voltage or sensitive signals, high speed signals, differential pairs etc…).

(Optional) Autorouting can be used for any remaining signals.

Manually place or adjust any remaining traces as needed.

Here are the steps required to create traces using the three standard manual routing methods and the autorouting method. The bus routing method (used for routing digital bus lines and differential pairs) is not discussed here.

Follow-Me ( ) – <Ctrl+T> This method is semi-automatic and is the standard way of manually routing most traces. This mode interactively suggests trace routes or trace segments while including DRC error checking in-process with the routing. To complete a trace using the Follow-Me method, follow these steps:

From the Design Toolbox, select the layer in which to begin the trace.

Select the Follow Me icon ( ) or use the shortcut <Ctrl+T)>.

Place the mouse over the component pad (through-hole or surface mount) where the trace is to be started. Anchor the trace by left-clicking; the display will show an “X” over the pad to indicating it is selected for creating a trace.

Move the mouse away from the starting pad location and an outline of the trace will follow the mouse cursor from the starting point and a ghosted trace will precede the cursor to show a possible completion path.

Move the mouse around holes, pads, traces or parts and both the trace outline and the ghosted trace will change its path automatically following any design constraints that are set.

Complete a trace segment by left-clicking to anchor a corner in an open space.

Continue routing in this way or double-click at any time to finish placement of the ghosted portion of the trace. Any additional nets can be routed while the Follow-Me routing mode is still active.

Press <ESC> to exit the Follow-Me mode return to the selection mode ( ).

Line Style ( ) – <Ctrl+Shift+L> Line style routing is a fully manual method of placing traces and will allow design rule checking errors to be overridden while routing (so be cautious when using this mode). Once a routing segment is complete, the DRC errors will be indicated if real-time checking is enabled. This mode is acceptable for routing any trace lengths requiring routing in very specific paths. To complete a Line style trace follow this procedure:

From the Design Toolbox, select the layer in which to begin the trace.

Select Line icon ( ) or use the shortcut < Ctrl+Shift+L >.

Place the mouse over the component pad (through-hole or surface mount) where the trace is to be started. Anchor the trace by left-clicking; the display will show an “X” over the pad to indicating it is selected for creating a trace.

Move the mouse away from the starting pad location and an outline of the trace will follow the mouse cursor.

Trace segments can be created by left-clicking to anchor a corner in an open space.

Continue routing in this way and double-click on the terminating pad to complete the trace.

Additional routing can be ‘daisy-chained’ from the terminating pad by simply continuing the routing from this location.

Press <ESC> once to terminate routing the assigned trace. Any additional nets can be routed while the Line routing mode is still active.

Press <ESC> again to exit the Line mode and return to the selection mode ( ).

Connection Machine ( ) This method is also semi-automatic but it allows a trace to be automatically constructed from a ratsnest line. This method suggests a full trace route but allows some selectivity on how the route is place. This method allows trace construction in fewer steps and also combines automatic DRC error avoidance while creating traces. In this mode, since the ratsnest line is required, the ratsnest layer needs to be set to visible ( ) for this routing technique to work. Follow these steps to complete a trace route using the Connection Machine method:

From the Design Toolbox, select the layer in which to begin the trace.

Select the Connection Machine icon ( ) to begin.

Place the mouse cursor over a selected ratsnest connection.

Left-click the mouse and the display will show a recommended completed trace.

Move the mouse cursor around and Ultiboard will automatically avoid other objects but leave the terminating points of the trace connected.

Once the trace is satisfactorily positioned, right-click to fix the trace placement. Additional nets can be routed from the ratsnest lines while the Connection Machine routing mode is still active.

Press <ESC> to exit the Connection Machine mode return to the selection mode ( ).

Autorouting ( ) The Autorouter is a fully automatic method for routing traces and can be an effective way of entirely routing a PCB or completing the routing on a PCB that was partially routed using manual methods. The successful completion of the autorouter depends on the PCB settings and the overall design constraints in addition to the autorouter settings. In the MultiSIM BLUE, you can autoroute up to 4 layers at a time. Follow these steps to complete autorouting:

Fix any manually routed traces that should not be removed or shoved. Traces can be locked () using the same technique as used for locking components.

From the menu configure the autorouter settings (Autoroute » Autoroute/place options). Consult the help for suggestions on what selections to make.

Start the autorouter from the menu (Autoroute » Start/resume autorouter) or with the

shortcut icon ( ).

Upon completion check the results within the Spreadsheet View.

If some routes are not completed, manually route remaining traces or reconfigure autorouter settings and retry.

Clean up traces by shoving them as needed in the selection mode ( ) to completely route the board.

In the circuit example, the autoroute method was used to complete the PCB routing. As shown, the Spreadsheet View can be checked to verify what percentage of the board the autorouter completed. In this example, the autorouter completed 100% of the trace routing automatically.

Via Creation (Navigating between layers while drawing a trace)

It is common (especially with PCBs utilizing Surface Mount Technology components) to route signals from one layer to another using vias (sometimes called feedthroughs). For example, a signal may need to be routed from the top layer to the bottom layer; a via allows the signal trace to be redirected from the top trace to the bottom trace (or an inner layer) with a via component. Vias are holes that are drilled into the board and then plated to create an electrical contact between traces or planes on various layers. Here are some details on via specifications:

Board manufactures will have limits to the dimensions of vias due to reliability issues and resource constraints (such as hole tolerances drill sizes).

A finished via considers the hole and plating size. Any minimum (or maximum) via size is based on the finished hole size.

Drill Diameter is the diameter of the hole prior to plating. Some quick-turn PCB manufacturers have hole size requirements of 15 mils or more. Full service manufacturers typically will have a minimum hole size between 3-5 mils (sometimes smaller at increased cost), depending on the weight of copper that is requested.

The Annular Ring is the portion of conductive material surrounding the via-hole. It is the “doughnut” shaped material around the hole to which traces and solder can adhere. It is related to the pad diameter. For instance, if the setting for the drill diameter is 15 mils, and the via pad diameter is 25 mils, then the width of annular ring is 10 mils. Any specifications for the annular ring size may apply for via holes as well as plated through holes, however check the board manufacturer’s specified minimum dimensions for each as they can sometimes be different.

The default via size can be set from the Pads/Vias tab from within the PCB Properties (Options » PCB Properties).

A commonly used size for vias is a hole size (Drill Diameter) of 10 mils and an annular ring (Pad Diameter) of 20 mils, however hole size for quick-turn PCB manufacturers may be 15 mils or more. Try to use the smallest sized hole possible to accommodate flexibility in placement and trace constraints.

Vias can be created manually from the menu or from the Via icon ( ) and then assigned a net from its properties. However the easiest way to create vias is by placing a connecting via in-line with trace routing. To route a trace, create a via and then continue routing on another layer follow these steps:

Select manual Line style routing mode ( )

Start a route from a pin connection and while routing hit <Q> to switch between a paired layer (the previous layer you selected) or <F2> to swap opposite layers.

Optionally while routing you can simply select a new copper layer from the layer control and

the trace routing will jump to the new layer and a via will be formed ( ).

This action will create an automatic via to the new layer at a previously set corner.

Continue routing on the selected layer. It is also common to route a via to a ground plane. Follow these steps to create a via to a ground or power plane:

Select manual Line style routing mode ( ).

Start routing a trace that has an associated plane connection (such as ground (net 0) or VCC) and hit <Q> or <F2> to swap layers to the plane layer or select a new layer from the layer

control ( ).

This will create via. Continue to wire away from the via using a small trace segment and hit <ESC> to stop.

The via will automatically connect to the plane with the selected connection styles (as show in inset).

Adjusting Placed Traces ( ) Once traces have been routed, it is common for the user to want to move or nudge traces around on the board for various reasons (such as moving a sensitive analog signal away from a potentially noisy clock or power signal).

To perform an adjustment on a trace, choose the Select tool ( ) from the top menu or press <Ctrl+Shift+S> to enable the selection mode. Also

confirm that the selection tool ‘Enable selecting traces’ ( ) is activated. For desired trace (or trace segment), choose the layer in which the trace is positioned. Click on the midpoint of the trace segment you plan to move to highlight the trace segment. The segment will highlight with three blue boxes (2 solid boxes indicating the endpoint of the trace segment and an open box to indicate the midpoint).

Use the mouse to grab the selected trace segment and move the trace into a new position. The other attached trace segments should move accordingly into new positions. Note that currently the tool does not support jumping an existing trace over another object (such as a placed component or hole) but you can move the segments into a variety of new positions. Also other traces that are parallel to the segment can also be nudged slightly to accommodate repositioning of the selected trace. In cases where you need to ‘jump’ over a placed component or hole, simply select and delete the appropriate trace segment and manually reroute around the object using one of the previously described routing techniques. Other Routing Finishing Steps to Consider

There are other things to consider before considering the routing process complete. Corner Mitering can add finishing steps to the routing to ensure the integrity of the pin to trace connections and the overall structural soundness of the trace itself. Corner Mitering is a process to reduce or remove sharp angles for placed traces by creating 135° angles in their place. Sharp angles within traces can be susceptible to voiding in the PCB manufacturing process. Also reflections can be caused in transmission lines if traces contain any sharp corners. To process corner mitering on the traces select the Corner Mitering from the menu (Design » Corner Mitering…). Final Checks and Visual Board Inspection After completing the routing process, final checks can be done on the board to do final verification on both the correct placement and routing of the PCB. First, a DRC and Connectivity check should be done to ensure that all design constraints were met and that the board is fully routed. From the menu select and perform a DRC check noting and correcting any warnings or errors given (Design » DRC and netlist check). A Connectivity check on all nets will verify all required routing is complete (Design » Connectivity check…). Next a visual inspection on each layer should be done to verify correct power, ground and other signals are going to the required locations. To view the layers independently of each other, select the Layers tab on the bottom of the Design Toolbox. For thoroughness, it is suggested that each net be analyzed to make sure there are no visible gaps in the trace connections and that critical signals are not placed in close proximity to areas of the board prone to noise (such as clock signals or switch mode power supplies). A useful tool for visualizing a single net is the Net Preview allowing the user to visualize the entire path of an individual net. It can be found on the right hand side of the Spreadsheet View when a net is selected under the Net tab.

By clicking the Highlight selected nets box ( ) in the Nets tab from the Spreadsheet View, the specific net(s) that you selected will be highlighted in white. Select individual nets by clicking on each row and then use the preview window to follow the path of the trace on all layers.

Another visual inspection technique is to use the 3-D rendering capability. The component footprints include 3-D modeling data allowing the dimensional height and relative component positions to be viewed. Select the 3-D preview from the menu to visualize a rendering of the final populated PCB (View » 3D Preview). Any custom created parts will need to include 3-D modeling data (contained on the 3D Info Layer) before these parts can be viewed with this tool.

Note: The mechanical dimensioning (such as height and width) may vary by manufacturer even though the same footprint shape may be used. It is always advised to check final component dimensions before generating the final PCB files.

Tip: Use the print screen key (<Prnt Scrn> or sometimes <Fn+Prnt Scrn>) on the computer to capture a screen image to the virtual clipboard. The image can be pasted <Ctrl+V> into a report or email as a way of documenting the project. Consultants can use this 3D rendering as part of the communication process to ensure the design matches initial conceptual ideas. Tip: Test fitting the parts onto a paper copy of the board is not always needed, but for smaller boards, it sometimes is worth the effort as a means to thoroughly performing final size verification of the PCB land patterns. To perform a test fit, print the top and bottom layers as 100% size to show the land patterns for the board. You can even place the components onto the printout to be sure they will fit. Common errors can be found during this process (such as selecting a wide SOIC versus a narrow body SOIC). Some planning ahead to purchase the parts from Mouser.com is required when using this technique, but the extra effort (plus the cost of an extra sheet of paper) will be much less than the time and money lost to produce a corrected copy of the PCB. PCB File Generation After verifying all components and completing the final PCB checks, the Gerber files will need to be generated (these should be inspected as well) and emailed or uploaded to the board manufacturer’s web page. To begin generating the PCB files, the configuration for each of the various file types will need to be set. The first files needed are the Gerber files which allow the manufacturer to create the basic artwork for each of the layers. From the menu launch the Export setup window from the menu (File » Export…). Use the Gerber RS-274X format as this standard is widely used and automatically assigns the D-code aperture drawing tool sizes automatically. In the middle of the Export window, select the required Exported layers items and use the check boxes to select which are exported. Among the layers that may be required include the board outline, copper layers, solder mask layers (will cover top and bottom traces), silkscreen layers (if screen print is used) and the drill and drill symbols layer (sometimes optional).

Finally the all of the Gerber files and NC Drill files will need to be generated. The NC Drill files are reports indicating the hole sizes and locations for all drilled holes to be included in the PCB design. Select the Gerber RS-274X and NC Drill items by selecting the checkbox on the left to activate both export items. Press the Export button and a simple DRC check will be done and then a progress bar will allow you to see the progress of the export process. When complete, each layer will generate a file with a ‘.gbr’ extension and the NC drill export will generate two files with a ‘.drl’ and ‘.rep’ extensions.

Once the save operation is completed, reorganize the files as required by the board manufacturer. Some manufacturers require the files to be zipped into a folder with a simple format with just the layer names for each file type. In some cases the exported file PeakDetect - Copper Top.gbr will need to be changed to Copper Top.gbr before sending. Send the files to the PCB manufacturer for quotation. After getting a quote on the requested PCBs and placing the order, make preparation steps to order BOM components, keeping in mind any longer lead components that may be required. From within the MultiSIM BLUE application, you can quickly verify cost and lead time information from mouser.com using the BOM Management tool. Before receiving the PCBs prepare a plan to populate and assemble the board when the ordered items arrive.

Optionally, PCB manufactures can sometimes provide assembly services or make recommendations on third-party companies that provide assembly services.