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      <title>Modifying a PCB assembly</title>
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      <div class="title_topic3" id="xps10_pagetitle">Modifying a PCB assembly</div>
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      <p class="para_topic">You can use the PCB.xchange toolbar to modify an existing PCB Assembly, including its mechanical design and the placement of certain critical components. The ECAD file of an existing PCB Assembly can be read by the PCB.xchange application, which in turn can write to an NX assembly.</p>
      <p class="para_topic">If the PCB Assembly requires a detailed component that is not already part of a component collection, you can create it using the modeling application. You will probably want to keep a copy of the new part(s) in an appropriate component collection.</p>
      <div class="title_division"> Procedure for modifying a PCB assembly</div>
      <p class="para_division">The basic procedure for modifying an existing PCB Assembly is much the same regardless of the assembly you are modifying. The following sections of this article provide additional details about each step. See also  <a class="links" href="javascript:void(0)" onclick="top.openFile('pcb/xu_idf_to_nx.html');return(false);"> Importing ECAD Files into NX</a> for more information.
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      <ol type="1" start="1">
         <li>
            <p class="para_item">Import the PCB Assembly's ECAD file into an NX assembly.</p>
         </li>
         <li>
            <p class="para_item">Work in the Assemblies application to make any necessary modifications to the PCB Assembly. Such modification cans include:</p>
            <ul>
               <li>
                  <p class="para_item">Changing the PC board outline, cutouts, or thickness</p>
               </li>
               <li>
                  <p class="para_item">Adding, removing or modifying components </p>
               </li>
               <li>
                  <p class="para_item">Repositioning components </p>
               </li>
               <li>
                  <p class="para_item">Setting the reference designator of components </p>
               </li>
               <li>
                  <p class="para_item">Adding, removing or modifying restriction areas </p>
               </li>
               <li>
                  <p class="para_item">Adding, removing or modifying drilled holes </p>
               </li>
            </ul>
         </li>
         <li>
            <p class="para_item">Work with the PCB.xchange toolbar to make any necessary modifications to the PCB Assembly, including:</p>
            <ul>
               <li>
                  <p class="para_item">Modifying the PC board attributes </p>
               </li>
               <li>
                  <p class="para_item">Creating or modifying component attributes, including part number </p>
               </li>
               <li>
                  <p class="para_item">Creating or modifyin restriction area attributes </p>
               </li>
               <li>
                  <p class="para_item">Creating or modifyin drilled hole attributes </p>
               </li>
            </ul>
         </li>
         <li>
            <p class="para_item">Validate the PCB Assembly and correct any errors detected. </p>
         </li>
         <li>
            <p class="para_item">Save your changes. </p>
         </li>
         <li>
            <p class="para_item">Export the PCB Assembly to ECAD. </p>
            <ul>
               <li>
                  <p class="para_item">You also have the option of working within the PCB.xchange window, which provides access to additional tools. For details, see  <a class="links" href="javascript:void(0)" onclick="top.openFile('pcb/xu_manage_updates.html');return(false);">Managing Assembly Updates</a>,  <a class="links" href="javascript:void(0)" onclick="top.openFile('pcb/xu_using_svg_viewer.html');return(false);">Using the SVG Viewer</a> and  <a class="links" href="javascript:void(0)" onclick="top.openFile('pcb/xu_write_fe_model.html');return(false);">Writing an FE Model for Thermal Analysis</a> 
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            </ul>
         </li>
      </ol>
      <div class="title_division"> Positioning a component</div>
      <p class="para_division">Use the Assemblies application  <b class="uiTerm">Reposition component</b> command to reposition an existing component on the PC board. Position the component so that it at least part of it is within the X-Y boundaries of the board. Ensure that no component overlaps any other component.
      </p>
      <p class="para_division">When the PCB Assembly is exported to ECAD, the software uses the position and rotation of the component part's Absolute CSYS to determine component placement and orientation. If necessary, rotate the part so that the Z-axis points away from the board. Offset mounting is defined by positioning the origin of the component's Absolute CSYS above the board surface.</p>
      <p class="para_division">In the ECAD format, rotations of the component are defined as the rotation from the X of the PC board part's Absolute CSYS to the X of the component part's Absolute CSYS - counter-clockwise is positive rotation. Also note that according to ECAD, the rotations (and board placement) are relative to the board side. That is, X-Y location and rotation is viewed by flipping the board over for the back side and not by looking through the board (as is the ECAD convention).</p>
      <div class="title_division"> Creating new detailed component parts for the PCB assembly</div>
      <p class="para_division">New detailed component parts can be created with standard Modeling application tools.</p>
      <p class="para_division">Define the part correctly positioned with reference to the Absolute CSYS. The Absolute CSYS must exactly match the origin and X-Y orientation of the corresponding component in your ECAD catalog. Refer to your ECAD system documentation or ECAD catalog administrator for this information. For a component, the origin is typically at the center of pin 1, the surface that mates with the PC board is the X-Y plane, and the +Z vector points away from the PC board with the bulk of the component in the positive direction.</p>
      <p class="para_division">The part name should be identical to the package name in ECAD format (with &quot;.prt&quot; added).</p>
      <p class="para_division">Once you have created the new part, add it to the assembly as a component (below).</p>
      <div class="title_division"> Adding existing components to the assembly</div>
      <p class="para_division">Detailed component parts intended for use in building PCB Assemblies should be defined in the proper relation to the part's Absolute CSYS, as described above. To add an existing component to a PCB assembly:</p>
      <ol type="1" start="1">
         <li>
            <p class="para_item">In the Assemblies application, choose <b class="uiTerm">Component</b>&rarr;<b class="uiTerm">Add Existing</b>. 
            </p>
         </li>
         <li>
            <p class="para_item">Select the part representing the component package you want to add. </p>
         </li>
         <li>
            <p class="para_item">Name the component with the reference designator you want to assign to the component.</p>
         </li>
         <li>
            <p class="para_item">Position the component on the boar. </p>
         </li>
         <li>
            <p class="para_item">Click the <b class="uiTerm">Component Attributes</b> button on the PCB.xchange toolbar, and select the component just added. 
            </p>
         </li>
         <li>
            <p class="para_item">Define attributes and part number.</p>
         </li>
      </ol>
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