Layout of Power Planes and Ground Planes- How PCB Software Affects Performance
In PCB design tools, it is important to understand what it takes to create power and ground planes, which provide power and ground to the components on circuit boards. An important aspect of circuit design is to understand how PCB software performance will affect power planes and ground planes layout. Designers know how to create planes, but it is also easy to get lost in design work and forget the meaning of certain terminology or why the planes are created as such.
Looking back at Power and Ground Planes
Power planes and ground planes in PCB design tools are principally created in two ways as a negative image or a positive image.
Positive Planes
The positive plane PCB design is created by having a polygon shape on the board which is then filled by the layout tool resulting in a solid plane image. There is a lot that goes on for this design to be achieved; pads must be connected to the plane, object clearances must be well calculated, and stable and reliable network connectivity is required to protect other net objects from being shorted. This is why creating a positive plane is a complex layout process.
Negative Planes
Negative planes were invented out of necessity as a result of the problems faced in the creation of positive planes. The first generation of CAD layout tools had difficulty creating positive planes because it involved too much data for them to process. So, a negative plane is basically the reverse image of a positive plane; polygons are not filled to create metal like in the positive rather, pads and other shapes create clearances in the metal.
Positive Planes require high-performance
The computers, systems, and CAD tools of old lacked the performance capabilities, the disk space necessary, and the computer the memory to create positive planes. Even where one had the capability for positive planes, there was always the risk of crashing the system if the plane was too large. Consequently, designers opted for negative planes-they did not have contours or shapes and it was left to the designer to assign the characters and markings to the corresponding photo plotter aperture position.
Layout of Power Planes and Ground Planes- How PCB Software Affects Performance
In PCB design tools, it is important to understand what it takes to create power and ground planes, which provide power and ground to the components on circuit boards. An important aspect of circuit design is to understand how PCB software performance will affect power planes and ground planes layout. Designers know how to create planes, but it is also easy to get lost in design work and forget the meaning of certain terminology or why the planes are created as such.
Looking back at Power and Ground Planes
Power planes and ground planes in PCB design tools are principally created in two ways as a negative image or a positive image.
Positive Planes
The positive plane PCB design is created by having a polygon shape on the board which is then filled by the layout tool resulting in a solid plane image. There is a lot that goes on for this design to be achieved; pads must be connected to the plane, object clearances must be well calculated, and stable and reliable network connectivity is required to protect other net objects from being shorted. This is why creating a positive plane is a complex layout process.
Negative Planes
Negative planes were invented out of necessity as a result of the problems faced in the creation of positive planes. The first generation of CAD layout tools had difficulty creating positive planes because it involved too much data for them to process. So, a negative plane is basically the reverse image of a positive plane; polygons are not filled to create metal like in the positive rather, pads and other shapes create clearances in the metal.
Positive Planes require high-performance
The computers, systems, and CAD tools of old lacked the performance capabilities, the disk space necessary, and the computer the memory to create positive planes. Even where one had the capability for positive planes, there was always the risk of crashing the system if the plane was too large. Consequently, designers opted for negative planes-they did not have contours or shapes and it was left to the designer to assign the characters and markings to the corresponding photo plotter aperture position.
Challenges with pioneering photo plotters
The pioneering photo plotters used a bright lamp, directed through a physical aperture so as to create an image on the film, which was then used by the manufacturer to fabricate the board. A lot of time went into to painting the images on the film, especially for a positive plane, because they were vector plotters not, raster plotters.
The other challenge with positive planes earlier on was giving the photo plotter the correct commands. The original Gerber format was used for input and the apertures were assigned to “D-codes”- before the aperture information was embedded in the Gerber file. This meant that a designer was responsible for creating an accurate aperture list. The designer had to have a good grasp of D-code assignments to assign the correct codes to specific functions such as filling in positive planes.
This post was written by Ruchi Gupta.
Challenges with pioneering photo plotters
The pioneering photo plotters used a bright lamp, directed through a physical aperture so as to create an image on the film, which was then used by the manufacturer to fabricate the board. A lot of time went into to painting the images on the film, especially for a positive plane, because they were vector plotters not, raster plotters.
The other challenge with positive planes earlier on was giving the photo plotter the correct commands. The original Gerber format was used for input and the apertures were assigned to “D-codes”- before the aperture information was embedded in the Gerber file. This meant that a designer was responsible for creating an accurate aperture list. The designer had to have a good grasp of D-code assignments to assign the correct codes to specific functions such as filling in positive planes.
This post was written by Ruchi Gupta.
