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T|Tech Tips - AKA Ron's Rules
Rubouts
How do you eliminate those pesky islands of copper that remain once you have run the various isolation layers for you newly designed circuit board project ? This subject is often a source of confusion to many users. In many cases these islands of copper must be removed. Otherwise they could interfere with the proper performance of the circuit. This is particularly true in RF or microwave designs and some high speed digital designs. There is an easy to use feature in all versions of IsoPro that allows the prototype engineer to easily remove those areas of copper. It is the Rubout feature of IsoPro.
The Rubout feature can be found under the TOOLS button on the Main Tool bar along the top of the IsoPro screen. There is also an icon in the Edit Tool bar, which is typically located down the right side of the IsoPro screen. But wait, before you go roaming and clicking with the mouse, there are a couple of rules you must follow in order to obtain a clean rubout. Those of you who have participated in one of my training sessions, have heard me refer to these as "Ron’s Rules".
First rule: You must always rubout using the tool of the largest diameter for a given layer. For example, let’s say you utilized three different tool sizes in creating your top layer isolations we’ll use 10 mils, 20 mils and 31 mils for our example. To create a rubout layer for our top layer, the 31 mil tool becomes the tool for our rubout.Which brings us to the next rule.
Second Rule: At a minimum, the 31 mil layer in the example above must be in EDIT mode. Our 31 mil layer becomes the source data for creating the rubout layer. IsoPro software is written in such a way that when the RUBOUT feature is selected, the software searches for the largest diameter tool size that is in EDIT mode. You can place all of the isolation layers for the top layer of your board in edit mode and allow the software to choose the tool. A word of caution, Ensure that only the top layer isolations are in edit mode. All other layers should be either hidden or in view mode to prevent them from interfering with the rubout creation for the top board layer. There is one final rule that is sometimes violated I’ve taken many a phone call from Quick Circuit users who describe how the rubout operation is eating their pads or traces.
Final Rule: You must not make any alterations to the 31 mil isolation layer prior to creating the rubout layer.
Now you are ready to create rubout layers. You can use a single rubout that removes copper islands for the entire board or you may create several small rubout areas within a single layer to make soldering a particular area easier around an edge connector or a IC pack.
Next time, I’ll comment on another aspect of circuit board prototyping with the Quick Circuit. If you have a suggestion for a topic, send an email to: techtips@t-tech.com
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