Design Article
Evaluating PCB layout tools: A board developer’s perspective
Syed W. Ali, Nexlogic Technologies
11/28/2011 7:54 PM EST
As edge rates of logic devices become faster and PCB designs become more advanced and geared towards miniaturization, a number of issues and pitfalls can emerge at the layout stage if you do not have appropriate tools at your disposal to handle your requirements.
In-depth experience using the various PCB layout tools available today is the best indicator of the direction to take regardless of densities, application, or speed requirements. Some design tool parameters that require some experience involve design speeds ranging from a few megahertz (MHz) to over 15 gigahertz (GHz) with board layer counts going from single layer to 50 layers, sometimes more.
An experienced designer always works diligently with tighter constraints, and uses the more advanced manufacturing technologies paired the right layout tools.
From the perspective of the experienced PCB designer, compared to the ideal PCB layout tool (See Table 1 below), most current commercial tools lack key features and attributes described in the chart.
Table 1: My ideal PCB layout tool
Today’s PCB layout tools have a combination of some of them, but no vendor has all of those capabilities embodied in one tool. Thus, no tool can be perfect. One can only choose the best tool that is most suitable for his/her needs. Since we’re not at the ideal design scenario yet, we have to make do with today’s available tool technologies.
Among the most popular PCB layout tools today are Cadence Allegro, Mentor Graphics Pads, and Altium designer. Each has its own unique capabilities, advantages, caveats and limitations. Although you can use any of these three tools to design virtually every kind of board, it doesn’t mean you should. Choosing the right tool for the layout should be at the forefront of PCB layout planning and must never be ignored.
As an example, using Cadence Allegro to layout a single sided board with a few components will be counter productive when you have tools like PADs and Altium Designer also at your disposal. Similarly it is not advisable to design a high speed board with edge rates in excess of 10 GHz on any tool other than Cadence Allegro.
The three tools offer some sort of portability. Altium allows import of Orcad schematic, Allegro board files, as well as Pads PCB database. Pads allows import of Altium board file. Allegro allows import of Pads Ascii file.
Having said that, when one applies any sort of import, it is never a 100% clean transition from one CAD tool to another without tweaking the data to a certain extent and running design rule checkers (DRCs) and netlist checks on the schematic afterwards. Therefore the only time the designer would port the data is when the company is switching platforms.
Next: Page 2
|
|
|
|
|
James123
12/1/2011 1:43 PM EST
What about Zuken CADStar? Any comments on it and its signal integrity analysis capabilities vs. say Altium?
Sign in to Reply
grok450
2/1/2012 7:45 AM EST
I have found Cadstar to be user-friendly, easy to build libraries and as a pcb designer who has worked with several pcb design packages (including Allegro) I prefer to use Cadstar for all my designs until such time something better (and cheaper)comes along.
Sign in to Reply
JackGrat2
12/1/2011 1:59 PM EST
Many large companies use Allegro and have a great deal invested in the libraries associated. The complexity of Allegro frequently impedes engineers from being able to apply it to quick turn designs, forcing them to try tools like Altium, PADS and even on-line solutions.
That said, it is possible to begin a layout in Allegro, then finish it in Altium or PADS. Altium needs both the schematic and the layout converted, but it does work. To migrate to the PADS layout, you first export the Allegro design to ODB++. This utility is available at Cadence. Then you need to convert the ODB++ to PADS, which can be accomplished with CAM350 and the PADS export option. This is best performed on an unrouted layout for a clean library in PADS.
Regards,
Jack Gratteau
Sign in to Reply
Magnus Sundberg
1/30/2012 5:10 PM EST
Who says that Hyperlynx works above 2GHz? It presents some results, but how good are they? Altium might just be honest about their SI simulation limitations.
Why was Mentor Graphics expedition not mentioned?
Sign in to Reply
Derek-Ohio
2/2/2012 4:44 AM EST
We just moved from Altium to OrCAD PCB Designer, which is practically the Allegro Tool with a restricted Constraint Manager but all the powerfull features like dynamic shapes (in milliseconds vs. Altium in hours). The price tag of OrCAD was surprisingly cheaper than Altium.
I agree, some GUI features take a while to remember, but the allegro philosophy inside the new OrCad is very efficient. We had to design two similar boards and one did it on Altium and I on OrCAD. Guess what it took me only half the time to get the job done. Including Gerber output.
I don't know CadStar but we evaluated Pads as well and I am happy with the decision to go to OrCad. I am a real fan of the Constraint Manager and all the DRCs which are online in real time!
Sign in to Reply