 |
|
|
 |
 |
|
 |
|
|
Page 4 of 4
PCB's
An introduction to BoardMaker3 PCB's
General Features
- Fast Custom Graphics Engine
- High Resolution Database
- Large Working Area
- Destination, net and route highlighting
- Most operations available on single
keystrokes
- MDI interface, see both the PCB and
schematic on the screen at the same time
- Dynamic closest node ratsnest
- Full plane DRC
- Autopan
- Net Names/Pin Numbers in pads
BoardMaker3 supports up to 32 copper layers. In addition to this, it supports layers for
Paste Mask, Solder Resist and Glue Layers. The software currently makes use of only a
small fraction of the number of layers available. Future releases of the software will make
use of these layers for additional features.
The preferred net import method in BoardMaker3 is to use the integrated schematic capture
tool with schematics linked to PCBs. In addition to this mode, BoardMaker3 is also able to
read in netlists generated in either BoardCapture or Tango format.
BoardMaker3 contains powerful routing features, a brief description of some of these are described
below.
Planes
 The planes in BoardMaker3 are completely
dynamic. This means that copper placed on the same layer as a copper plane will automatically
plough its way through the plane leaving a user-definable clearance around the tracking.
The plane display is maintained in realtime and the designer is able to see the exact
plane as it will appear when the gerber output is generated.
This includes a clear display of the thermal break connections which join the vias or component
pins to the plane. There is no lengthy copper pouring process and the refresh of the plane
display is instantaneous. A transparent mode is also provided when the plane layer is not
being used for routing.
Planes themselves are defined using polygons. Any number of planes can be placed on any
of the copper layers and one net can be assigned to several planes over one or more layers.
This flexibility allows a ground plane to be placed on multiple layers or alternatively
an internal layer to used for different planes in different regions of the board. Complex
planes can be built from several overlapping polygons.
As well as the basic plane objects, a number of other objects are provided to allow more
control over the planes, these are:
Polycut
 The polycut is useful for cutting away
large irregular shapes in the plane, the polycut
will only "eat" plane copper, so it's perfectly safe to run a polycut over tracks and pads.
This tool together with the Linked Cut allows planes to be tidied up after placement.
Areas of the plane can be trimmed away and additional clearances can be created as necessary.
Linked Cut
 The linked cut also cuts away plane copper
like the polycut above, but linked cuts are rounded. The Polycut can be used to remove
large irregular areas quickly. The linked cut provides an alternative mechanism which
can be used around mounting holes for example or along rows of pads.
Thermal Break
 Because all regular copper objects (tracks, vias etc) plough through the plane, a special
object is required to make a connection with a plane. In most PCB design tools, the thermal
break is built into the pad. In BoardMaker3, the two objects are separate and the user
is given complete control over the thermal breaks. Thermal breaks can be added manually
or automatically. The automatic process will attempt to intelligently place the thermal
breaks to complete the routing. The user can select several parameters to control the process
including prong count, orientation, width etc. Once the automatic process has been run,
the user can manipulate the thermal breaks as necessary. For example additional prongs
can be added or removed or prongs can be reoriented.
Additional thermal breaks can be added on other layers or at other net points to improve
the continuity of the plane.
Design Rule Checking
A comprehensive rule-based design rule system is included with the software. The user can
create any number of rules in the system, and control is provided to select the order
of precedence of these rules. This allows special case rules to be applied ahead of
general tracking rules. A separate plane design rule checker is integrated in the software.
A brief description of rule configuration is as follows:
General OptionsIn the general options, you can name the rule according to its function, for example, one
of the default rules in the system is named "Drills Too Close". You also set up the clearance
and which layer(s) the rule applies to. One of the more powerful features of the rules
is the ability to determine the nets to which the rule is applied. Three options are provided:
- Same - The rule affects items
on the same net. For example, you could
create a rule which imposes a minimum
separation between surface mount pads
and vias on the same net.
- Different - The rule affects
items of differing nets, so for example
VCC and AVCC have to be 6mm apart.
- Either - The net is ignored.
This could be used for example to check
that components are not placed too close
together.
Source and Target options
 These options control what the rule applies to, you have the ability to say which objects
the rule is valid for (tracks, vias, holes
etc) and more specifically you can limit the rule to certain nets and/or components. As
an example this would allow you to make the rule only apply to plated through hole pads
on component U2 on nets VCC and GND. This can be useful for example to override a rule
which needs to be broken in a particular location.
Net and Component GroupsAnother powerful feature is the ability to
set up groups or components or nets. For example, you might have two separate pairs of power
rails on a PCB which required additional segregation
from each other beyond that of the inter-rail separation.
Output Formats
BoardMaker3 provides a number of standard
output formats for production.
Gerber RS274X
The gerber format used by BoardMaker3 is RS274X.
This is the extended gerber format and includes
a number of extra features which the software
makes use of. Aperture tables are embedded
in this format and ground planes images are combined within a single file. The extended
format also supports polygons.
Each gerber layer is written to a separate file, and that file is named logically, such
that the user has control over the "base" filename, but the software appends the layer
name to the file, so a user named file "CPU Module" would output "CPU Module - Top Layer.gbx".
Options are provided to enable the contraction of paste mask apertures and the expansion
of photo resist apertures. Other options control the format of the gerber generation.
NC Drill
NC Drill can be output in metric or imperial, some manufacturers differ in the way that
they prefer to handle NC files, so the software gives the user the option of generating separate
files for plated and non-plated holes or the option of a combined file (which contains
comments that tell the manufacturer which drill codes correspond with plated and non-plated
holes) .
Pick and PlaceThe supplied libraries for surface mount components
include pick and place centroids. The software is able to make use of these in the PCB editor
to generate a file which contains a list of these components together with their Designator,
X,Y position and rotation. This file is used by the manufacturer to enable automatic placement.
Separate files are produced for the top and bottom of a double-side mounted PCB.
DXF
The DXF output is useful for taking the PCB design over to a mechanical drawing system.
If you have an enclosure which has to fit the PCB then it's easy to export the DXF from
BoardMaker3 into your mechanical drawing package. You can also import a board outline defined
in DXF format to be used in BoardMaker3.
BMP and PrintingThe BMP and printing outputs are very closely
related. The bitmap output allows the user to create images which could be embedded into
documents, the user has control over which part of the image is output and the resolution of the output image.
The printing output has a number of controls which allow the user to control the formatting
of the printout.
- Control of the size of print, the user
may fit the printout to the size of the
page, they can scale the printout to a
given percentage and there is also an
option to posterise a printout if the
destination size is smaller than the page
size.
- With layer control, the user has the
ability to select which layers are to
be printed, and whether layers should
be merged or printed as separate pages
- Miscellaneous controls including reversing
the printout, colour control printing
only a required section etc.
- With a suitable printer driver, the
software can produce PDF files.
Grids and Datums
 Datums are objects which can be placed
to denote places of interest, for example you could place a datum at the edge of the
board to denote the board edge and place another datum inside where a keypad is to be placed.
The grids in BoardMaker3 are relative to the current origin, functions are provided which
allow you to quickly move the origin to the position of a datum, this can prove to be
useful when placing objects at specific locations on a special grid, a notable example of this
may be a keypad matrix.
Furthermore, the grid system in BoardMaker3 is designed to allow the user to define any
number of grids, and these can be switched at the press of a button. The configuration
options for a grid allow the user to define
a grid with differing pitches for X and Y,
this is particularly useful when designing
footprints.
Special Features
Star Earth
The star earth track is a powerful feature
for designers with multiple ground nets which
need to be shorted at a single point. Generally
designers solve this problem in CAD software
by routing their design with all the grounds
separately, they confirm that the design is
complete by using the DRC. Once they are satisfied
with the results they then short all the grounds
together using a track. This presents a number
of problems, firstly once this track is added
the design rules are violated, and secondly
to continue working on the design they need
to remove this track to stop the DRC violations,
they then have to remember to place the track
back once their modifications have been done.
 In BoardMaker3 we introduced the Star
Earth track (distinguished by it's stripy
appearance), the track is ignored by the connection
and clearance DRC's, instead a special DRC
is run which checks the nets that are connected
by the star earth track, the user is then
told which nets are physically shorted together.
Using this feature the designer does not have
to keep adding and removing tracks, the DRC
continues to function as normal with information
being displayed for the nets that are connected
with the star earthed track.
Pre-Routes
Although Pre-Routes are defined in the schematic
editor, they become useful in the PCB editor.
Pre-routes are identifiable by a thin stripy
line between 2 or more pins, the purpose of
this line is to show the designer that those
pins are internally connected in the device,
this may be useful on a particularly dense
section of board where it may be convenient
to route through the component, the DRC in
BoardMaker3 is fully aware and capable of
handling these components.
Pin Swapping
Although the schematic capture tool has pin
swapping, it's more likely that the designer
would want to do this from the PCB. If a pin
is swappable you can simply point at it and
select the pin swap option, this will automatically
swap the pins and update the netlist, it also
sends this information back to the schematic
so that the pins also swap on the schematic.
| |
|
 |
|
 |
|
| |
