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Guide to using Graphicode GC-Prevue

• Introduction
• Downloading the GC-Prevue application
• Starting GC-Prevue and importing the assignment files
• Preparing the data – how to rename each layer and arrange them into stack-up order
• File viewing and feature measurement – how to toggle on and off layers and zoom to specific parts of the board to measure distances between features

Introduction

Gerber files are essentially independent views, taken a layer at a time, with information on such aspects as board outline, apertures and test points being kept as separate files, so that it becomes difficult to check layers in relation to each other or to get an overall perspective of the design. The tool we use to give a combined picture is GC-Prevue, the free viewer from a range of Graphicode CAD/CAM programs for fabricators and assemblers.

GC-Prevue is widely used in the electronics industry for viewing and printing electronic manufacturing data, and reads all common formats, including Gerber-X (RS-274X), Gerber-D (RS-274D), and the languages used for NC drilling machines. Whilst cut down, GC-Prevue is not a toy, but a real program that is very useful for verifying CAD data before photoplotting and fabrication, and for adding annotations to layers in order to assist the flow of information. Also, although GC-Prevue has no means of automatic checking for compliance with design rules, it can be used as a tool for manual checking.

Job files prepared using GC-Prevue can be saved in the .gwk format, which integrates all the circuit, solder mask and solder paste layer data, aperture tables (including custom aperture shapes) and drill information that is needed to make a board.

Downloading

1. Go to http://www.graphicode.com/pages/prevue.cfm, which will take you directly to the product page in Graphicode’s web site:

 

2. Access the Download page: Choose Download GC-Prevue by clicking where indicated at the bottom of the page, fill in the registration form, and press Download.

Shortly afterwards you will receive a Welcome e-mail from Graphicode, but the email contains no registration information and is not part of the installation process.

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3. You will be taken to a Downloads page, where you should click on the ‘GC-Prevue v13.4.4’ link to download the software, which comes as a zipped file called gcprevue.zip. Note that this is a large file, and download is best carried out with a fast connection.

 

A ‘File Download’ pop-up will appear, asking you either to ‘Open this file from its current location’ or to ‘Save this file to disk’. Choose the ‘Save this file to disk’ radio button and press OK. A ‘Save As’ pop up will ask you where you would like to save the file. We recommend creating a new directory on your local drive (usually C or D) called ‘GCPrevue’ as the location for both the zipped file and the unzipped application. Click Save.

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4. Extract files and start installation. When the download is complete choose ‘Open Folder’ from the ‘Download complete’ pop up and double-click to open gcprevue.zip. Identify the directory to extract to and use WinZip or an equivalent to extract the zipped files. Afterwards, from this directory, double-click to open setup.exe:

Depending on your security settings, you may have to bypass a security warning before the InstallShield Wizard will open:

Click Next and read through the Graphicode License Agreement:

If you agree to accept the terms then click on the ‘I accept the terms in the license agreement’ radio button and click Next. Then type in your name and organisation and click Next.

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5. Complete installation.

The next part of the Wizard allows you to specify the destination of the GC-Prevue application. Click Next.

Select the ‘Complete’ Setup Type radio button and click Next.

The final screen informs you it is ready to install the program. Click Install to continue.

The installation will take several minutes.

When the installation is finished you will see:

 

Click Finish to close. Unless you have chosen the custom setup option, you will find that an icon has been put on your desk-top:

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Starting GC-Prevue

6. Start up GC-Prevue by double-clicking the icon on your desk-top, or by opening Windows Explorer, finding your GC-Prevue directory and double-clicking on the ‘gcprevue.exe’ icon.

Ignore the splash screen which disappears as the application opens,

close the upgrade offer by clicking the cross in the top right-hand corner,

and you will see the Graphical Viewer. Its default appears as:

 

Make more room for the board image by closing the right-hand side ‘Repair Station’ panel, and maximise the image by clicking the Maximize icon, or dragging the bottom corner handle; the image size can be reduced to the previous small panel using the Restore Down icon near the upper right-hand corner of the screen.

 

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7. Import the relevant file set. The Import feature in the File menu allows separate data files to be selected and imported, but (more usefully) will also import files within a zip file directly into GC-Prevue, recognising readable file types and automatically loading the data files.

We recommend you to:

• download the zipped Gerber files
• create a new directory containing them, which will also be the destination for the GC-Prevue .gwk file created by the program
• print any ‘read_me’ file in the zipped archive, as having a hard copy will be useful both at this stage and later on.

From the File Menu, select Import. The Import dialog appears:

Go to the directory where you have the zipped file (in this case, 4945_ass_02_Gerbers.zip). Highlight the file by clicking on it once, then press Select.

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8. Identify the files.

The selected file will be automatically uncompressed, auto identification of each file attempted, and an Import Verify File Information dialog box similar to that below will appear:

Compare the file list with the manifest (in the read_me.txt file) and uncheck any items (usually text files) that have been incorrectly identified, and then click OK. Once File Verification has taken place, Tool Table Assignment is necessary. A similar dialogue box will appear applying tool tables to each file for the import process. Press OK to accept .

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9. First view of the data layers.

GC-Prevue will then construct each data layer and show a ‘File Import Results’ dialogue box. With luck there will be a green tick next to ‘Status’, but you can expect (and ignore) a small number of warnings. Press OK.

 

The imported assignment files will appear in a manner similar to that shown below. In this case the resulting imported board has 20 layers (designated P1 to P20 in the GC Explorer frame).

 

 

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Preparing the data

You will need the supplied ‘read_me’ file, preferably as a hard copy:

The recommended preparatory work is to identify each layer and reorder the layers to represent the physical stack-up. It is much easier to analyse data if layers have been identified with their type (silkscreen, copper, etc.) and layer number, and have been arranged in stack-up order. At the moment the layers are only identified as P1 to P20, they appear in a random order, and the layer types are marked as ‘unknown’.

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10. Identify each layer

Within GC Explorer, you will find most of the controls for physical layers in the Properties tabs, which can be activated in three ways:

• by double-clicking on a physical layer
• by highlighting a layer and pressing <return>
• with a physical layer highlighted, by right-clicking the mouse and selecting Properties from the drop-down menu.

Using any of the above the following dialogue box appears:

From within the Physical Layer Properties tab you can perform the following actions:

• Assign a unique name to a physical layer
• Assign a layer type
• Make a physical layer visible (viewable or editable) or invisible (not editable)
• Set pad/trace/part colour
• Set a layer to face up or down
• Define as a plane layer
• Assign Top, Inner, Bottom or None to a physical layer
• Add a new physical layer to the board

Let us take as an example the topmost physical layer, in this case 4945_sst.gbx, which the ‘Read_me’ file states is top-side silkscreen layer 1.

Double-click on Physical layer and the Properties tab will appear.

Edit the properties box:

• in the ‘Name:’ text box enter 4945_sst, if this has not already been entered by the Import filter
• choose Silkscreen in the ‘Layer Type’ box
• choose top in the ‘Side’ box.

In this version of the program, the information is automatically applied to the layer.

Click on the next physical layer in the properties tab and repeat the procedure. Note that signal layers have to be defined in terms of their coverage. The final result appears as:

 

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11. Arrange the layers into their physical stack-up order. To move a layer, click on the physical layer in GC Explorer and, with the mouse button still depressed, drag to the required position.

A suggested layer order is:

1. Top side paste mask (4945_spt.gbx)
2. Top side silkscreen (4945_sst.gbx)
3. Top side solder mask (4945_smt.gbx)
4. Tracking layer 1 top side (4945_1.gbx)
5. Power inner layer 2 (4945_2.gbx)
6. Power inner layer 3 (4945_3.gbx)
7. Tracking inner layer 4 (4945_4.gbx)
8. Tracking inner layer 5 (4945_5.gbx)
9. Tracking inner layer 6 (4945_6.gbx)
10. Tracking inner layer 7 (4945_7.gbx)
11. Tracking inner layer 8 (4945_8.gbx)
12. Tracking inner layer 9 (4945_9.gbx)
13. Tracking layer 10 bottom side (4945_10.gbx)
14. Bottom side solder mask (4945_smb.gbx)
15. Bottom side silkscreen (4945_ssb.gbx)
16. Bottom side paste side (4945_spb.gbx)
17. Drill data (4945_1-10.exc.gbx)
18. Board outline (4945_board_outline.gbx)
19. Test points (4945_testpoints.gbx)
20. Fabrication drawing (4945_fab_dwg.gbx)

 

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File viewing and feature measurement

Once the assignment files are imported into GC-Prevue and have been properly identified and annotated, you will need to be able to view individual layers, zoom and pan to specific areas on the board, and measure distances between points on the board.

Viewing layers

There are two ways of viewing, hiding or editing the layers.

1: Right-clicking on the layer offers a drop-down menu:

The options Edit, View and Hide change the status of the layer. Click on the option you want for each layer and when finished move the mouse over the board image area. Note that, when you change the status of a layer in GC Explorer, the view of the board won’t change until you move the mouse over the board image area. [In previous versions of the program, you had to click once in the board image area]

2: Highlighting a layer in GC Explorer (left click once) and on the keyboard pressing <e> for edit, <v> for view, or <h> for hide. When you have changed the status of all required layers, move the mouse to the board image area to see your changes.

If you highlight the Physical Layers directory icon, you can use either method to edit, view or hide all layers simultaneously. The right-click drop-down menu makes this explicit:

Zoom feature

GC-Prevue offers two types of zoom, menu-based and mouse wheel-based.

1: Menu-based zoom. On the board image, place the cross-hair on the top left hand corner of the area you would like to zoom to. Click and hold the left mouse button and drag to the bottom right of the area. A rectangle will form around the area. When you release the mouse button a menu will appear:

• Zoom In moves the focus in to a rectangle that was drawn by holding down the left-click mouse button and dragging.
• Zoom to Window opens another Graphical Viewer window that duplicates the focus of the current window.

Right-clicking anywhere on the board image area generates a different drop-down menu:

• Zoom to Extents moves the focus of the Graphical Viewer to the extents of the board data.
• Zoom Previous returns the focus of the Graphical Viewer to the most recent zoom, if there was one.
• Zoom Out moves the focus of the Graphical Viewer out on the board by a factor of roughly double.

2: Mouse wheel-based zoom. If your mouse is equipped with a small wheel between the two buttons, pushing the wheel towards the front of the mouse (wire side) zooms toward the board, whilst pulling the wheel backward zooms away from the board. In both cases, the zoom changes by a factor of roughly 2:1 for each click, and the cross-hair will appear at the centre of the new viewing area.

Pan feature

There are three ways to pan around a board:

1: On the View menu choose Zoom and then Pan. You can then choose which direction you want to pan.

2: Switch on the <Num Lock> on your keyboard. You can then pan using the keyboard number pad (1–9):

number	direction	number	direction	number	direction
1	down left	4	left	7	up left
2	down	5	none	8	up
3	down right	6	right	9	up right

3: Move the Windows-style sliders at the bottom and right of the main window as in standard Windows applications.

Making measurements

There is no automated feature measurement process in GC-Prevue, but you can measure the distance between two points on a board. For example, the simplest way to measure the gap between two pads is to place the cross-hair on the edge of one pad and press <z> on your keyboard. This zeroes the ‘Relative mm’ or ‘Relative inches’ in the Coordinates Display. Then move the cross-hair to the edge of the other feature and read the separation from ‘Distance’ in the Coordinates Display.

Points to remember:

• Make sure the measurement is the smallest distance between the two features.
• Zoom as close as possible to the feature edges for more accurate measurements.

Symmetric features

If the two features are symmetric pads, you can get a more accurate measurement using the snap facility. Position the cross-hair anywhere over the feature

and press <s>.

The cross-hair then jumps to the centre of the nearest pad.

To measure the distance between two features:

• Snap onto the centre of the first feature, in our case the centre of the left-hand pad.

• Press <z> to user zero.
• Press the space bar to return the cursor to a cross-hair.
• Position the cross-hair over the adjacent pad and press <s>. The cross-hair jumps to the centre of the feature.

• ‘Distance’ in the Coordinates Display is the distance between the two features.

To measure the distance between the edges of the pads, display the feature dimensions by placing the cross-hair over each feature, and looking at the Status Bar at the bottom of the Graphical Viewer. The line of text that appears defines the data type, position and aperture:

In our example, the features are rectangular, and each is 0.889×2.9972mm in size (35×118mil, so probably originally an imperial design). As the pad centres are 1.3792mm apart, the nominal distance between the edges of the pads can be calculated as 1.3792 − 0.889 = 0.4902mm.

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Author: Martin Tarr

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