Writing Gerber Files from Cadence APD/Allegro for NETEX-G

Transcription

1 Writing Gerber Files from Cadence APD/Allegro for NETEX-G Steve DiBartolomeo Applications Manager Artwork Conversion Software, Inc.

2 Artwork's NETEX-G program uses Gerber files and drill files to extract the net geometry from IC packages and PCBs. If you are using Cadence APD or Allegro as your design tool there is a right way (and many wrong ways) to create your Gerber data. Here are guidelines on how to do it the right way. Crossection Examine the design's crossection. If this is a wirebond part you will have at least one wirebond layer. A typical crossection (the one used to illustrate this paper) is shown below: For this design we need to output the following conductor subclasses to Gerber films TOP - this will contain only the wires and is used by NETEX-G to pass the wire data (it would have been better to call this subclass wirebond to avoid confusion) TOP_COND - this is the top layer of metal VCC - this is the VCC power plane GND - this is the GND plane BOTTOM - this is the bottom of the BGA Dec. 03 Exporting Gerber from Cadence APD for NETEX-G Page 2

3 Artwork To get Gerber files out, you must use the Manufacturing Artwork dialogs. There are two dialogs. One is used to set up general parameters and the other defines the photoplot layers and how to build them. you must select Gerber RS274X don't really care - since we are going 1:1 our film is typicall onl 2 to 3 inches across. Select leading zero suppression only and suppress equal coordinates. Use 5.3 places for mm and 3.5 places for inches. If your design is in mm or um use Millimeters. must be Dec. 03 Exporting Gerber from Cadence APD for NETEX-G Page 3

4 Artwork Configuration cont... no rotation! no offset don't care For power planes you can use positive or negative but I find it less confusing if all Gerber files have the same polarity. No mirroring. Special Hints on Setting up the Films wirebond - a new film named wirebond is created and the CONDUCTOR/TOP layer is assigned to this film. You do not want the VIACLASS/TOP or PIN- CLASS/TOP on this film. Just the wires which are classified as conductors.if there were more than one wirebond type subclass you would create a new film for each wirebond subclass. On the top.art (top metal) I remove the PIN/TOP_COND subclass because this contains the die pads and I don't want them as part of my top metal. I created a new film called via and assign it the VIA- CLASS/BOTTOM subclass. This saves me the need to create a drill file for my vias and convert it back to Gerber. Dec. 03 Exporting Gerber from Cadence APD for NETEX-G Page 4

5 View of top.art and wirebond.art View of top.art and bottom.art NETEX Stackup the top item in the stackup is the wirebond. Then comes the top metal. No dielectric is needed between a wirebond layer and the metal layer below it. Dec. 03 Exporting Gerber from Cadence APD for NETEX-G Page 5

6 NETEX-G Preference Settings for ANF output you must select Leonov polygons. these parameters control how many vertices are used. NETEX-G Drill Dialog In order to interconnect the planar layers we must use a "drill" or via info. The Gerber layer created called via contains info about where each via is located. The via runs from stackup layer 2 (top metal) to stackup layer 8 (bottom). Dec. 03 Exporting Gerber from Cadence APD for NETEX-G Page 6

7 Labeling NETS and Creating Padstacks for Solder Balls To make a more useful ANF file it is helpful to label the nets since the Gerber data has no net labels. It is also necessary to create a pad stack where each solder ball is to be attached. The easiest way to do this when working with Cadence is to export an AIF file that contains information about the die pads, wires, fingers and ball pads. Then import the AIF file into NETEX-G. To create the AIF file use the File Export AIF menu selection and then select the output file from the dialog. Importing AIF into NETEX-G Creating Net Labels: to get to this dialog go the Labels button and then select Import AIF Select the AIF file and get the net coordinates from the Ball Pads. Make sure to assign the correct stackup layer to examine - in this example it is the bottom.gbr or stackup 8. Solderballs - to create a padstack for the solder balls check the Node section and use the ball pads on stackup layer 8. Padstacks - make sure to check Import Padstacks from AIF if you are creating pads for solderballs. Dec. 03 Exporting Gerber from Cadence APD for NETEX-G Page 7

8 ANF Output Having properly built the stackup and defined the via in NETEX-G and having imported the AIF file to label the nets and create padstacks for the solder pads we start NETEX-G and output an ANF file. This file is then imported into Ansoft Links in order to assign wire parameters, add the solder balls and export a 2D or 3D simulation databse. the Ansoft Neutral File (ANF) produced by NETEX- G from the Gerbers output from Cadence APD. Here you can see two selected nets. The wire is part of the net even though it does not highlight. Dec. 03 Exporting Gerber from Cadence APD for NETEX-G Page 8