Copper Pouring

The POLYGON command enables you to define areas which belong to a signal, connecting all of the related pads to this signal with thermal symbols. Such a signal retains a user-defined distance to any other signal path.

You can PCB design layers that contain multiple polygons such as different ground areas, and you can design polygons on multiple layers.

To demonstrate this feature of EAGLE, let’s fill the Top layer of a board with the GND signal. Reload the board demo2.brd once again, enlarge the window, and ripup the GND signal:

RIPUP GND ←

Use the DISPLAY command to switch on the layer 1Top, 17 Pads, 18 Vias, and 20 Dimension. (PCB Design Services) Use the button None, in the menu, to switch off the display of all other layers first.

Click the POLYGON icon in the command toolbar and type:

GND ←

to provide the name GND for the polygon to be defined. Only then will it belong to the GND signal.

Select the LayerTop from the combo box in the parameter toolbar. Then:

• left hand upper corner of the board outlines,

• right hand upper corner,

• right hand lower corner,

• • left hand lower corner.

The double click closes the polygon.

To start the calculation of the filled area, click the RATSNEST icon.

Since this is a very complex operation it can take some time.

As before, the pads belonging to the GND signal are connected with thermal symbols. Check this with:

SHOW GND ←

In this case everything shown in the layer color is copper, since this layer is not plotted inversely (only supply layers defined with $name).

After a board has been loaded, polygons are displayed with their outlines. PCB CAD Services filled areas are displayed only after the RATSNEST command has been executed. Inversely, the RIPUP command and a single click on the edge of a polygon results in the outline display of this particular polygon.

 

PCB Documentation

The PCB’s documents should include the hardware dimensional drawings, schematic, BOM, layout file, component placement file, assembly drawings and instructions, and Gerber file set. User guides also are useful but aren’t required. PCB Design Gerber file set is PCB jargon for the output files of the layout that are used by PCB manufacturers to create the PCB. A complete set of Gerber files includes output files generated from the board layout file:

• Silkscreen top and bottom
• Solder mask top and bottom
• All metal layers
• Paste mask top and bottom
• Component map (X-Y coordinates)
• Assembly drawing top and bottom
• Drill file
• Drill legend
• FAB outline (dimensions, special features)
• Netlist file

The special features included in the FAB outline include but are not limited to notches, cutouts, bevels, back-filled vias-in-pad (used for BGA-type IC packages that have an array of pins under the device), blind/buried vias, surface finish and leveling, hole tolerances, layer count, and more.

Schematic Details

Schematics control the project, so accuracy and completeness are critical for success. PCB Design Services include information that is necessary for the proper operation of the circuit. A schematic should include adequate design details, such as pin numbers, names, component values, and ratings.

Embedded within each schematic symbol is the manufacturer part number used to determine price and specifications. The package specification determines the size of the footprint for each component. The first step should be to make sure the exposed copper for each pin is in the proper location and is slightly larger than the component pins (3 to 20 mils) depending on available area and soldering method.

 

Consider assembly when designing footprints, and follow the manufacturer’s recommended PCB CAD services footprint. Some components come in microscopic packages and do not allow room for extra copper. Even in these cases, a stripe of 2.5 to 3 mils of solder mask should be applied between every pin on the board.

Follow the rule of 10. Small vias have a finished hole size of 10 mils with 10 additional mils of pad ring. Traces should be 10 mils or further from the edge of the board. Trace-to-trace pitch is 10 mils (5-mil air-gap, 5-mil trace width, 1-oz copper). Vias with 40-mil diameter holes or larger should have a pad ring added for reliability. An additional 15 to 25 mils of clearance beyond the design rule should be instated for copper planes on outer layers from plane to pins. This reduces the risk of solder bridging at all solder points.

Component Placement

Component placement is next in the process and determined based on thermal management, function, and electrical noise considerations. PCB Service Bureau first-pass component placement step commences after the outline of component and interconnect position has been assigned. Immediately after the individual components are placed, a placement review should be held and adjustments made to facilitate routing and optimize performance.

Placement and package sizes are often reconsidered and changes are made at this point based on size and cost. Components absorbing greater than 10 mW or conducting more than 10 mA should be considered powerful enough for additional thermal and electrical considerations. Sensitive signals should be shielded from noise sources with planes and be kept impedance-controlled.  

Power management components should utilize ground planes or power planes for heat flow. Make high-current connections according to the acceptable voltage drop for the connection. Layer transitions for high current paths should be made with two to four vias at each layer transition.Place multiple vias at layer transitions to increase reliability, reduce resistive and inductive losses, and improve thermal conductivity.

 

Looking for the High Frequency Design Techniques?

High frequency design is where you really need to consider the effects of parasitic inductance, capacitance and impedance of your PCB layout. If your signal is too fast, and your track is too long, then the track can take on the properties of a transmission line. pcb design If you don’t use proper transmission line techniques in these situations then you can start to get reflections and other signal integrity problems.

A “critical length” track is one in which the propagation time of the signal starts to get close to the length of the track. On standard FR4 copper boards, a signal will travel roughly 6 inches every nano second. A rule of thumb states that you need to get really concerned when your track length approaches half of this figure. But in reality it can actually be much less than this. Remember that digital square wave signals have a harmonic content, so a 100MHz square wave can actually have signal components extending into the GHz region.

In high speed design, the ground plane is fundamental to preserving the integrity of your signals, and also reducing EMI emissions. It allows you to create “controlled impedance” traces, which match your electrical source and load. pcb design services It also allows you to keep signals coupled “tight” to their return path (ground).

There are many ways to create controlled impedance “transmission” lines on a PCB. But the two most basic and popular ways are called Microstrip and Stripline.

A Microstrip is simply a trace on the top layer, with a ground plane below. The calculation involved to find the characteristic impedance of a Microstrip is relatively complex. trace, the height above the ground plane, and the relative permittivity of the PCB material. multi layer pcb design This is why it is important to keep the ground plane as close as possible to (usually) the top layer.

A Stripline is similar to the Microstrip, but it has an additional ground plane on top of the trace. So in this case, the trace would have to be on one of the inner layers. The advantage of stripline over microstrip is that most of the EMI radiation will be contained within the ground planes.

There are many free programs and spreadsheets available that will calculate all the variations of Microstrip and Stripline for you.

Some useful information and rules of thumb for high frequency design are:

• Keep your high frequency signal tracks as short as possible.
• Avoid running critical high frequency signal tracks over any cutout in your ground plane. This causes discontinuity in the signal return path, and can lead to EMI problems. Avoid cutouts in your ground plane wherever possible. A cutout is different to a split plane, which is fine, provided you keep your high frequency signal tracks over the relevant continuous plane.
• Have one decoupling capacitor per power pin.
• If possible, track the IC power pin to the bypass capacitor first, and then to the power plane. This will reduce switching noise on your power plane. For very high frequency designs, taking your power pindirectly to the power plane provides lower inductance, which may be more beneficial than lower noise on your plane.
• Be aware that vias will cause discontinuities in the characteristic impedance of a transmission line.
• To minimise crosstalk between two traces above a ground plane, minimise the distance between the plane and trace, and maximise the distance between traces. The coefficient of coupling between two traces is given by 1/(1+(Distance between traces / height from plane)^2))
• Smaller diameter vias have lower parasitic inductance, and are thus preferred the higher in frequency you go.
• Do not connect your main power input connector directly to your power planes, take it via your main filter capacitor(s).

Double Sided Loading

Loading components on both sides of a PCB can have many benefits. Indeed, it is becoming an increasingly popular and necessary option when laying out a board. There are two main driving factors behind a decision to go with double sided loading. The first is that of board size. If you require a particular board size, and all your components won’t fit on one side, then double sided load is an obvious way to go. The second reason is that it is required to meet certain electrical requirements. Often these days, with dense high speed surface mount devices packed onto a board,high speed pcb design  there is either no room for the many bypass capacitors required, or they cannot be placed close enough to the device to be effective. Ball Grid Array (BGA) devices are one such component that benefit from having the bypass capacitors on the bottom of the board.

 

 

searching for multi layer pcb design?

Multi layer  PCB Design

What is a Multilayer PCB?

A printed circuit board (PCB) is a thin board “printed” with electrical wires and made from fiber glass or similar material. PCBs are commonly used in computer devices such as motherboards, network interface cards, and RAM chips.multi layer pcb design They are relatively cheap and quite fast. When the PCB is fabricated with several layers placed over one another, it is known as a multilayer PCB. The multiple layers establish a reliable set of predetermined interconnections for the electronic circuits.

There are several techniques that can be used to accomplish this task. Some of these techniques are handicapped by their reliance on a large number of chemical processes to condition the substrate. A large number of chemical processes are needed to activate the through-holes and electrolytic copper plate between the adjacent layers. The general procedure is as follows:

1. Obtaining the material and equipment that you will need, such as drills and electrolytic copper-plating cell.
2. Formatting the copper substrates so that the orientation of each can be uniquely determined. This is sometimes known as patterning and can be done using a variety of methods.
3. Drilling the layers with specific drilling equipment to create holes or vias. These vias are plated with copper to form plated-through holes.
4. Properly cleaning the copper substrates on your board.
5. Electroplating the PCB substrate using acid copper electroplating.
6. Laminating the multilayer board.
Under high pressure and heat, the layers fuse together. The conductors will be separated, and signals and power between layers will be connected. pcb design  This technique ensures that all the layers are drilled and plated first, and then laminated. This can help reduce the number of chemical processes needed to accomplish this difficult task. Multilayer PCBs can have as many as 14 layers. However, this may be quite expensive, and it is more common for PCBs to have either 6 or 8 layers.

A multilayer PCB contains two reference planes and a signal via. The signal via allows a signal to flow through all the planes. A stitching via is connected to one of the planes next to the signal via and serves to reduce the area through which the signal passes through. This is very important as it may assist in reducing noise and cross talk.

Product functionality of the multilayer PCB depends on the interconnection between the layers. Thus it is very critical to be concerned about micro vias and overall HDI.

Multilayer boards can either be rigid or flexible. Rigid multilayer PCB technology can prove to be very expensive because of the expertise required and the expensive drilling equipment. Flexible multilayer PCBs make use of flexible circuits and reduce the size of the end product. pcb design services However, flexible multilayer PCBs must have fewer layers because an increase in the number of layers means a loss in flexibility of those layers.

Advantages of multilayer PCBs include high reliability and uniform wiring. However, the initial costs are higher than that of one-layered PCBs. Also, repairing a multilayer PCB is quite difficult.

Vias

With multi layer design comes the options of using different types of vias to improve your routing density. There are three types of vias – standard, blind, and buried.

Standard vias go through the whole board, and can connect any of the top, bottom or inner layers. These can be wasteful of space on layers which aren’t connected.

“Blind” vias go from the outside surface to one of the inner layers only. The hole does not protrude through the other side of the board. The via is in effect “blind” from the other side of the board.

“Buried” vias only connect two or more inner layers, with no hole being visible on the outside of the board. So the hole is completely buried inside your board.

Blind and buried vias cost more to manufacture than standard vias. But they are very useful, and almost mandatory for very high density designs like those involving Ball Grid Array (BGA) components.

Power Planes

It is good practice to use “power planes” to distribute power across your board. Using power planes can drastically reduce the power wiring inductance and impedance to your components. This can be vital for high speed digital design for instance. It is good design practice to use power planes whenever possible. They can even be used on double sided boards, if most of your signal tracks are on the top layer.

A power plane is basically one solid copper layer of board dedicated to either your Ground or Power rails, or both. Power planes go in the middle layers of your board, usually on the layers closest to the outer surfaces. pcb layout On a 4 layer board with complex power requirements it is common to dedicate one layer to your ground plane, and another layer to your various positive and negative power tracks. Your ground rail is usually your signal reference line, so a ground plane is first preference before a power plane is considered.

Many PCB packages have special Power Plane layers that are designed and laid out in reverse to your other normal tracking layers. high speed pcb design On a normal tracking layer, your board is assumed to be blank, and you then lay down tracks which will become your actual copper tracks. On a power plane however, your board is assumed to be covered with copper. Laying down tracks on a power plane actually removes the copper. This concept can take some getting used to.

 

Searching for the Multi layer pcb design?

Multi layer  PCB Design

What is a Multilayer PCB?

A printed circuit board (PCB) is a thin board “printed” with electrical wires and made from fiber glass or similar material. PCBs are commonly used in computer devices such as motherboards, network interface cards, and RAM chips. They are relatively cheap and quite fast. When the PCB is fabricated with several layers placed over one another, it is known as a multilayer PCB. The multiple layers establish a reliable set of predetermined interconnections for the electronic circuits.
There are several techniques that can be used to accomplish this task. Some of these techniques are handicapped by their reliance on a large number of chemical processes to condition the substrate. A large number of chemical processes are needed to activate the through-holes and electrolytic copper plate between the adjacent layers. The general procedure is as follows:

1. Obtaining the material and equipment that you will need, such as drills and electrolytic copper-plating cell.
2. Formatting the copper substrates so that the orientation of each can be uniquely determined. This is sometimes known as patterning and can be done using a variety of methods.
3. Drilling the layers with specific drilling equipment to create holes or vias. These vias are plated with copper to form plated-through holes.
4. Properly cleaning the copper substrates on your board.
5. Electroplating the PCB substrate using acid copper electroplating.
6. Laminating the multilayer board.
Under high pressure and heat, the layers fuse together. The conductors will be separated, and signals and power between layers will be connected. This technique ensures that all the layers are drilled and plated first, and then laminated. high speed pcb design This can help reduce the number of chemical processes needed to accomplish this difficult task. Multilayer PCBs can have as many as 14 layers. However, this may be quite expensive, and it is more common for PCBs to have either 6 or 8 layers.
A multilayer PCB contains two reference planes and a signal via. The signal via allows a signal to flow through all the planes. A stitching via is connected to one of the planes next to the signal via and serves to reduce the area through which the signal passes through. This is very important as it may assist in reducing noise and cross talk.

Product functionality of the multilayer PCB depends on the interconnection between the layers. Thus it is very critical to be concerned about micro vias and overall HDI.

Multilayer boards can either be rigid or flexible. Rigid multilayer PCB technology can prove to be very expensive because of the expertise required and the expensive drilling equipment. Flexible multilayer PCBs make use of flexible circuits and reduce the size of the end product. However, flexible multilayer PCBs must have fewer layers because an increase in the number of layers means a loss in flexibility of those layers.

Advantages of multilayer PCBs include high reliability and uniform wiring. However, the initial costs are higher than that of one-layered PCBs. Also, repairing a multilayer PCB is quite difficult.

Vias

With multi layer design comes the options of using different types of vias to improve your routing density. There are three types of vias – standard, blind, and buried.

Standard vias go through the whole board, and can connect any of the top, bottom or inner layers. These can be wasteful of space on layers which aren’t connected.

“Blind” vias go from the outside surface to one of the inner layers only. The hole does not protrude through the other side of the board.multi layer pcb design The via is in effect “blind” from the other side of the board.

“Buried” vias only connect two or more inner layers, with no hole being visible on the outside of the board. So the hole is completely buried inside your board.

Blind and buried vias cost more to manufacture than standard vias. But they are very useful, and almost mandatory for very high density designs like those involving Ball Grid Array (BGA) components.

Power Planes

It is good practice to use “power planes” to distribute power across your board. Using power planes can drastically reduce the power wiring inductance and impedance to your components. This can be vital for high speed digital design for instance. It is good design practice to use pcb design power planes whenever possible. They can even be used on double sided boards, if most of your signal tracks are on the top layer.

A power plane is basically one solid copper layer of board dedicated to either your Ground or Power rails, or both. Power planes go in the middle layers of your board, usually on the layers closest to the outer surfaces. pcb design services  On a 4 layer board with complex power requirements it is common to dedicate one layer to your ground plane, and another layer to your various positive and negative power tracks. Your ground rail is usually your signal reference line, so a ground plane is first preference before a power plane is considered.

Many PCB packages have special Power Plane layers that are designed and laid out in reverse to your other normal tracking layers. pcb layout On a normal tracking layer, your board is assumed to be blank, and you then lay down tracks which will become your actual copper tracks. On a power plane however, your board is assumed to be covered with copper. Laying down tracks on a power plane actually removes the copper. This concept can take some getting used to.