A series of articles on best practice - part 4

VSure DFM : A series of articles on best practice - part 4

This article is part 4 of a series that is intended as an introduction to the process flow of performing DFM Analysis using the Mentor vSure product.

 

 

 

This article will focus on the Cleanup step in our default flow. Before we can start any DFM analysis we have to make sure that the native EDA/CAM data which we imported into the vSure and saved as ODB++ format has elements, has features that the software can recognize.
 

For example, how do we know that a round pad on an outer layer is used as fiducial or perhaps used as a testpoint. The method of identification of features in vSure is done through attributes.

 

Attributes are system or user definable identification strings that can be attached to layer features or components with the purpose to create DFM analysis results that will help a user to quickly understand what the issues are about. Once attributes are attached an issue will not be reported e.g. as “spacing violation for round pad” but perhaps as “Spacing violation for testpoint”.
 

A typical list of questions that allows us to identify some of the features :

  • What are the smd pads
  • What are the blind, buried and thru drill vias
  • What are the board and component fiducials
  • What are the testpads, the testpoints
  • Do we have any mechanical or tooling holes

 

To be able to identify some of the component attributes that we need to set we use this typical list :

  • Are there components that require a local fiducial
  • Are there components that should be ignored during DFM analysis
  • Are there components with specific spacing requirements
  • Do we need to take into account the soldering process and transport direction.

 

 

Within the vSure application the function “Design Preparation – Rule Set Editor” can be used to find features and/or components and automatically set the attributes by using a list of rules.

 

The screenshot shows the assignment of the .smd attribute to pads is done in 3 steps :

  1. Set a filter for pads from SMT packages
  2. Select these pads
  3. Set the attribute .smt to identify them as SMD Pads
     
  Once the attribute assignments are done we can run a DFM analysis and see that the results are categorized allowing any user to quickly identify the issues that are presented like “VIA pad annular Ring” or “Missing Testpoint clearance” keeping misunderstandings to a bare minimum.