Viasystems’ Approach to CAD-to-CAM Data Transfer Print E-mail
Written by Kent Balius, Stephan Hackl and Julian Coates   
Thursday, 01 March 2012 23:34

How a major PCB/EMS company saves time and improves quality with ODB++.

Viasystems’ PCB fabrication division in Forest Grove, OR, has been scratching their collective heads for quite awhile trying to understand why companies designing PCBs have been slow to accept the ODB++ data format for delivering designs for fabrication. Our number one issue is the amount of time required to successfully import, analyze and prepare design packages for production tooling. With full utilization of ODB++ files, we can greatly reduce the amount of manual time-consuming human interaction, and reduce opportunity for quality errors.

What ODB++ brings to the design and manufacturing table is that it produces a manufacturable design, requiring very little work to prepare at the fabricator. This combination of a manufacturable design and intelligent data means products are fabricated in the minimum cycle time, significantly improving quality at new product introduction.

The majority of Viasystems’ customers submit product data as a combination of Gerber, Excellon and netlist files, together with separate drawings and written specifications. The Gerber format has been used since 1980 and, while containing much of the information required to begin PCB fabrication, it has some significant limitations. For example, drilling information is not contained in the file and is communicated with a separate file in another format, usually Excellon. Significantly, there is no information about how PCB layers stack up, and there is no information about nets; all that comes in separate files or documents that have to be reintegrated by the fabricator. To make matters worse, in recent years the use of buried and blind vias, and complex sequential lamination techniques, combined with much greater diversity of surface finish requirements, has escalated the problem of CAD/CAM data exchange – taking it even further from the scope of traditional formats such as Gerber, Excellon and netlists.

Gerber files require a great deal of manual intervention before a fabrication-ready dataset can be produced. The fabricator must manually examine each file and determine how the layers in the stackup fit. In addition, Gerber files often contain syntax errors or precision errors from rounding. The effort to extract a complete PCB specification from the Gerber, drill, netlist and document-information is significant.

Success is achieved through a combination of a completely defined format, tools that work with it, and an organization behind it that supports customer deployment and ensures the format’s vitality. The ODB++ format supplies the fabricator with a complete set of data. The files contain not only stackup information, but drilling, masking, net data and a wide range of intelligent attributes that make separate drawings unnecessary. The complete manufacturing-level definition of the product is contained in one self-contained file structure. Figure 1 demonstrates the advantage of supplying ODB++ data to the fabricator instead of the Gerber-type data. The low failure mode and effects analysis (FMEA) means the quality of the fabricated board is also improved when using the full capability of ODB++.



It’s important to note that a complete ODB++ file set is necessary to take full advantage of the automation capabilities of the format. This is best realized by defining a complete data transfer process. This process should include design for manufacturability (DfM) analysis, adherence to those DfM rules, and ensuring that full communication of all appropriate attributes is included in the file set. Submitting just a partial file set to the fabricator will not permit it to take advantage of the significant intelligence that ODB++ is capable of providing. Once the full set of files has been specified, those files should then be compressed as a single .tgz file for the fabricator. Fabrication software automatically recognizes the .tgz file and understands the file structure and how to use those files.

With Gerber data, Viasystems executes a multi-step workflow just to get a set of data from which fabrication can proceed. First, we manually inspect all Gerber files to determine that they contain a complete set of data. Next, we verify the data are correct and of sufficient resolution to produce the boards. Then, we must manually “reverse engineer” the data to reassemble the layer stackups as they will be fabricated. We merge the drill specifications and again check for accuracy. We also merge soldermasks and silkscreen information.

At any place in the workflow, there may be errors or omitted data, which can mean multiple communications with the customer to correct errors or get additional data. On average, about 25% of the data packages received have issues related to:

  • Missing layers, fabrication drawings, drill files, etc.
  • Netlist format violations.
  • Netlist exception violations.

Viasystems has collected extensive data to support our preference for ODB++ over any other format. Standard Gerber input takes us one to two hours just to import, analyze and prepare data for production CAM tooling. While ODB++ has been around for several years, designers and fabricators have not taken advantage of integrating the potential intelligence, such as incorporating the many attributes available that can drive automation and reduce manual interaction. ODB++ with these intelligent attributes included can significantly reduce our pre-CAM time, depending on the design complexity. It is a single file with intelligent attributes and an all-inclusive data package. Table 1 shows the time reduction and quality improvement (FMEA) Viasystems has experienced with ODB++ compared to Gerber. (Data are shown as a factor of ODB++.)



As Viasystems sees it, ODB++ provides the following benefits over Gerber across the entire fabrication process:

  • Import and Export diagnostics are significantly reduced compared to Gerber.
  • Errors can be identified and communicated to the customer much earlier in the process.
  • Eliminates format errors and net exceptions common with Gerber.
  • Fabricator can be permitted to see actual net name used by customer, easing the process.
  • Less data required for handling positive planes.

Advantages for the PCB Customer

The advantages of ODB++ data are not limited to the fabricator. The PCB designer can realize significant benefits as well. These benefits can save significant cost and design time, and even result in getting product to market more quickly. More important, the risk to the PCB customer is substantially reduced. The higher-quality data supplied to the fabricator account for that risk reduction, propagating into board assembly as well.

Based on the data we’ve assembled, Viasystems has concluded that a validated and complete intelligent ODB++ file carries a five-times lower risk of errors in NPI tooling. The following list highlights the more significant advantages to using ODB++ from the viewpoint of the PCB designer:

  1. Reduced overall risk of errors in fabrication and assembly.
  2. Intelligent data means more on-time deliveries of fabricated and assembled PCBs.
  3. Less time spent correcting errors and resending data sets because of missing files.
  4. Reduction in the chance of wrong data passing into manufacturing and creating rejects, lost time and money.
  5. Less chance of incorrect file definitions (stackups and polarity errors).
  6. Elimination of the fairly common Gerber problem of drill pattern misalignment.
  7. Quicker feedback from fabrication and assembly engineers – quicker resolution of errors.

In our experience, those designing printed circuit boards find it extremely easy to switch to supplying ODB++ files. Most major PCB design software tools support ODB++ output. We’ve found that the vast majority of our customers have tools to view and check the ODB++ they generate before sending it to fabricators. And those tools are generally more comprehensive and easier to use than any available Gerber viewers.

ODB++ is supported by the majority of CAD/CAM tools within the design-to-manufacturing ecosystem, including:

CAD: Zuken, Cadence, Mentor Graphics, Altium, Intercept.
Fabrication CAM: Frontline, UCAMCO, WISE, Downstream, Graphicode.
Assembly CAM: Mentor Graphics, Siemens PLM, Aegis, Fuji, Assembléon, Universal Instruments, Nagoya Electric.

Mentor Graphics’ OpenDoor program permits any CAD tool supplier to incorporate the format free of charge. Mentor Graphics continues to support and develop ODB++ as a completely open format (Figure 3). Mentor is continuing to develop ODB++ and will be adding more intelligent features and capabilities in the near future. Mentor is working with fabricators, such as Viasystems, to identify new and enhanced capabilities for the future of ODB++.



IP Concerns

Some customers are concerned about sending IP to their fabricators. In truth, after reverse engineering, Viasystems ends up with virtually the exact information as ODB++ and is not getting the true IP from the customer. Today, Viasystems receives approximately 10% of the data packages in ODB++ format, however; many are not incorporating intelligent attributes that provide the benefits of automation and reductions in cycle times. Further, many customers that have switched are very happy with the results and savings.

Kent Balius is vice president, global front end engineering, and Stephan Hackl is CAM lead at Viasystems (viasystems.com). Julian Coates is director of business development, Valor Division, Mentor Graphics (mentor.com).

Last Updated on Friday, 02 March 2012 21:40
 

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