Copper pour areas on given layer are defined as polygons assigned to selected nets. Polygonal definition allows creation of complicated shapes. Nevertheless, it may be simpler in certain instances to adjust shape of copper pour areas by removing copper within roughly drawn polygon. This task may be performed while editing layer artworks in preparation for generating Gerber ASCII output.
Copper may be removed by placing so called copper relieve items within boundaries of copper pour area polygons. These copper relieve items are basic EDWinXP graphic elements, like lines, circles, rectangles and arcs. Circles and rectangles may be either open or filled. By placing such elements at desired position and adjusting their size (and rotation), the user removes equivalent shape of copper. This effect is achieved through drawing / printing copper relieve items in white over black background and in cases of photo plotter output, by plotting these elements in reversed polarity after first plotting copper pour areas in positive polarity. In other words, it is done in similar way as when air gaps for pads and traces are drawn or plotted.
Functions for manual creation and edition of copper relieve items are available in Fabrication Manager. The toolbox appears when editing artwork containing copper pour areas and when user clicks View->Artwork->Copper Relieve Edit View. The repertoire of available copper relieve items have been recently enhanced by polygons (EDWinXP version 1.40).
As mentioned before, copper relieve may be used to adjust shape of copper pour areas. For example, it may be necessary to cut out copper free window within copper pour polygon or isolate two parts of the same polygon from each other (analog and digital ground). Additional problems usually arise in situations when copper pour area polygons are placed on layers where there are also trace connections. Traces running within air gaps and air gaps around pads may create isolated pockets of copper. These may lead to loss of connectivity if pads that should be connected by copper are inside those isolated areas. In order to detect this kind of errors, the user should run copper pour connectivity test (from version 1.40 available even in Layout Editor).
Even if copper pour connectivity test does not find any errors, the isolated pockets usually still exist on the layer. Isolated copper is usually not needed and in many cases undesirable. Tiny pieces of copper or “slivers” between parallel traces may curl and created shortcuts. Isolated copper may be removed by placing copper relieve items over it, but because of their number and irregular shapes it is a tedious task even with recently introduced copper relieving polygons. Equally laborious is removing slivers between traces by adjusting air gaps for each trace segment.
Visionics was aware of this problem and worked hard to find a solution. We have developed an algorithm that allowed us to introduce two new functions in Fabrication Manager - automatic copper cleanup and semi-automatic copper trimming. These functions will be released through Live Update to all users of EDWinXP, version 1.40 in August, 2005.“black” copper areas from the artwork. The program analyzes display of the artwork after test and generates copper relieve items (filled rectangles) in number and sizes necessary to cover all detected black spots. This solution has this advantage that results of automatic copper cleanup are fully editable. The user may fine tune copper relieve by removing or adjusting items that cleaned “too much” of the copper. The existing copper pour polygons are not affected by automatic copper cleanup.
The results of copper pour connectivity test are presented graphically. Copper areas that are connected are drawn in red color. Those isolated are drawn in black. Providing that the test did not detect unconnected pads, the user may subsequently invoke automatic copper cleanup function to remove all
This function reminds of erasing with help of movable “rubber”. The user can define shape (rectangle or square) and size of trimming tool. Removing copper works in similar way as in automatic copper cleanup, with this distinction that copper relieve items are generated only within boundaries of trimming tool. User may also select (while in trimming mode), whether to trim isolated (“black”) copper or connected (“red “) copper. Trimming is necessary complement to automatic cleanup, especially when there are areas of connected (“red”) copper that are superfluous and should be removed. It is advisable to re-test copper pour connectivity in cases where connected copper has been trimmed.
Perform copper pour connectivity test (check “All layers with reference net connections”; uncheck “Check for bottlenecks”). Three new option tools will then appear in option toolbox upon completion of the test. Automatic copper cleanup may be invoked by clicking on fourth tool from the top (F4). It is possible to execute cleanup even if errors were discovered by the test, but this practice is not advisable. In such case, the program will issue warning that cleanup may give incorrect results. Execution time depends on number of copper pour polygons defined for tested net on current layer and their size.
Automatic cleanup applies only to the net selected for test and only to currently edited layer. Procedure has to be repeated for each net that has copper pour polygon on currently edited layer and for each layer that contains copper pour polygons. This approach is necessary because copper pour (flood) point has to be defined by the user to obtain correct test results.
Perform copper pour connectivity test (check “All layers with reference net connections”; uncheck “Check for bottlenecks”). Three new option tools will then appear in option toolbox upon completion of the test. Copper trimming may be invoked by clicking on fifth tool from the top (F5). Running test is not necessary if trimming is executed after automatic cleanup. Before entering copper trimming mode, the program displays dialog where copper area to trim (“black” or “red”) as well as trimming tool shape (rectangle or square) and its size may be selected. The trimming tool is presented as floating rectangle (square) following the mouse. Trimming is executed by placing the tool at desired position and clicking left mouse button. Program refuses to trim copper outside boundaries of copper pour polygons assigned to currently tested net or when trimming tool floats over areas displayed in other color than has been selected to trim. Clicking on sixth button from the top in the option toolbox (F6) allows resetting trimming parameters while still in trimming mode. Press ESC button to exit trimming mode.