|Measurements over the edge of a PCB must be made diagonally, which is easy to overlook with a manual calculation of creepage distance.
Preserving the dielectric strength of conductive components is largely a matter of positioning them correctly and maintaining the right distances between them. The miniaturization and combination of PCB net classes and stack-ups makes the determination of air and creepage distances a highly complex task. The EasyLogix team, along with SEW-EURODRIVE, has developed a simple, automatic leakage current analysis software solution. Called PCB-Investigator, it is a visualization and simulation tool, which enables the air and creepage distances of power electronics to be analyzed within minutes, a task that used to take several days to complete.
As an example, when developing circuits of more than 30 VAC or 50 VDC, certain security parameters need to be considered. Since these are already high-voltage values, layout that prevents leakage current must meet minimum distance requirements between the conductive components, such as those outlined in standards like DIN EN 60664 VDE 0110, IPC2 221A or UL60950-1.
For leakage current properties of insulation materials, the degree of pollution needs to be taken into account, and whether expected non-conductive pollution may temporarily develop conductivity through condensation. It gets even more challenging for applications that involve much greater voltages and the risk of damage, including drive technology.
For SEW-EURODRIVE, a specialist in the field of drive technology, power transmission and motion control, it previously took several days to identify, manually measure and test all possible creepage distances and clearances for a new product. The company's electronics team set out to find a more efficient solution. They were unable to find ready-to-use software on the market, but discovered EasyLogix, an organization that was able to work with the engineers to develop an automated leakage current analysis solution.
PCB-Investigator is a flexible CAD/CAM system that uses ODB++ to depict the entire process of PCB design. Over the product's entire lifecycle it bridges the gaps between the tools used by various departments, as well as those between 2D and 3D CAD/CAM systems. The EasyLogix team is continuously developing the base software, adding further analytics and simulation functions. Recently, the company introduced a solution for thermal simulation.
The software was well-suited to the leakage current analysis requirements. PCB-Investigator collates all relevant data about a particular development project. The data are not limited to conductive traces and areas, but also include information about components, networks and the layout of boards and stack-ups.
|PCB-Investigator performs calculations in 2D, with a choice of 2D and 3D views.
All the information is available at the touch of a button, using different search criteria. This can be accessed easily by both individual employees and whole departments during the design process to evaluate and modify layers and parts, including components, pins, networks, and copper.
The tool can process many formats, including GenCAD IPC2851, PC365, Gerber, Excellon, Sieb&Meyer, DPF, DXF, and Grid (BMP, JPG, PNG, TIFF), and converts them into ODB++. In ODB++ all PCB production data are stored in a single record. PCB-Investigator uses this format as a central database and consolidates all the data for the development process with each step in the production sequence through to the box-build enclosure.
To enable an automatic evaluation of clearance and creepage distances, the placement position of different components, as well as each network class, must be known. SEW-EURODRIVE's first implementation of the software solution used information derived from its Cadence CAD landscape. PCB-Investigator's leakage current plugin now allows the selection of distance parameters specified by the standards, as well as the selection of networks to be examined.
The software uses a convenient net group wizard plugin that creates groups of logically related networks, in order to perform analytics on all networks at once. For example, networks within a bus system are categorized and color-coded so they can be considered a single unit. Groups can also be created manually. The automated option can also be used to generate network group proposals. This is useful for leakage current analysis, because groups can be sorted according to their voltage profiles.
The automatic leakage current analysis calculates the shortest distance from the outer edges of the conductive components to one another, and to the outer edge of the board. This also takes into account uncoated drill holes and indentations, which would otherwise be too time-consuming to calculate manually.
Results are displayed as 3D graphics for easy interpretation. This way, many manual measurement errors are avoided. Paths that lead around the edge of a board or around drill edges are measured diagonally, rather than measured with a simple right-angle manual measurement. For thicker stacks, these small deviations can add up and become significant.
The results of the creepage distance and clearance analysis is shown as a percentage of the specified distance parameters. For each calculated path segment between two points of contact, the software determines how much of the specification has been achieved.
If it is less than 100 percent, the vulnerable path is highlighted in the analytics report. PCB-Investigator's leakage current analysis plugin prioritizes data according to the likelihood of hazards. Since the inner layers of stacks have higher dielectric strength, they are evaluated differently than those situated in other areas of a stack-up.
2D or 3D?
SEW-EURODRIVE now uses this software tool to test all of its products at once, significantly improving test speed. It can be done at any time during the development phase, addressing crucial problems early on. Aside from its functionality and accuracy, the speed of the tool alone makes it superior to many other forms of leakage current analysis.
Previous automated measurements of air and creepage distances were done using 3D CAD programs. It may appear to be an obvious approach, especially for the distances between conductors and the housing, or along components. But, similar to the software's approach to thermal simulation, PCB-Investigator saves significant computing power by performing all calculations in 2D, rather than requiring a 3D model. Only the relevant results are then displayed in 3D.
Currently, the leakage current analysis tool is a custom solution, but EasyLogix is developing a standard PCB-Investigator plugin with an expected general market release before the end of 2017. Since the software can visualize every aspect of PCB development and production, developers are able to correct many errors early on in the process. With powerful tools like this, it is easy to imagine a future without faulty manual work and damaged boards.
Contact: Schindler & Schill GmbH, Im Gewerbepark D33, 93059 Regensburg, Germany +49-941-568-136-20 E-mail: firstname.lastname@example.org Web: http://www.easylogix.de