SIDEBAR.OCT–SC
Box: Common Problems Experienced by PCB Design Tool Users
Today's pc-board CAD programs pack in more features and capability than
ever. Taking advantage of that capability, however, requires a solid
understanding of the program and some adherence to common sense, advises
Jeff Gile, a CAD consultant based in Rossville, CA. Gile, who heads a
service bureau and is experienced in using different CAD packages, debunks
some myths regarding pc-board design tools.
1. Users expect instant success
Users have grand expectations of the short term benefits of a new tool.
No matter how “easy to use” and “user friendly” a tool is, it will take a
period of time to become productive. Even with just a new version of an
old tool, it can take a surprisingly long time to understand the new
features. The more features in a tool, the longer it will take to fully
understand the tool. 2. Users expect it to be easy
Many new users expect to hit a couple of keys and have the tool output a
good board design. A PCB design tool cannot read the mind of the board
designer. Every aspect of a design must be set after a tool knows what you
want, can it do its magic. Unfortunately, even the highest priced tools on
the most powerful platforms need to be guided in the design process. 3.
Users lack design experience
A designer who is new to a tool and also new to PCB design has a double
handicap. Nothing is better than long term experience, but a good observer
can quickly come up to speed. A designer should critically look at every
board he/she comes in contact with. Why was it designed the way it was? It
is truly an art to do a good job of part location, desnity, track spacing,
and layering. Get knowledge from more experienced desingers. 4. Users
assume that the netlist is good
The old proverb, “garbage in, garbage out” is just as descriptive for PCB
tools as it is for accounting programs. A good designer should be able to
look at a netlist and see potential problems. Power and ground nets often
have inaccuracies that will casue a problem downstream. A designer needs
discipline in maintaining a netlist through a board design. It is tempting
to use a text editor to make a quick modification to the netlist, or to
make a change in the board file. The right way to make a change is to
modify the data that was used to create the netlist and then read it back
into the PCB tool. 5. Users assume that the output is OK
Inexperienced users of PCB design tools will create a design, make the
Gerber files and send them to be photoplotted without checking. There are
so many variables to be set in the process of design and postprocessing
that the chances of getting everything right the first time is near zero.
The best way to verify the output is to use a Gerber viewer of some kind.
They cost between $200 and $2000, depending on whether they are just for
viewing, or for viewing, editing and design rule checking. A viewer will
pay for itself in the first few uses by avoiding the need for
replotting. 6. Companies do not set board design standards
Whether you are designing within a large or small company, you can
benefit from internal design standards. Each company may have more than
one standard, for example, one for digital boards and one for power
supplies. The standard will include pad diameters, pad spacing, drill
diameters, track widths for signals and power, isolation, layering,
labeling, board outlines, connector locations, etc. A good standard system
will significantly reduce the design time, give a more consistent result,
and produce better looking boards.
Advertisement
