PCB Design Perfection Starts in the CAD Library – Part 10
The land pattern standards clearly define all the properties necessary for standardization and acceptability of a “One World CAD Library”. The main objective in defining a one world CAD library is to achieve the highest level of “Electronic Product Development Automation”. This encompasses all the processes involved from engineering to PCB layout to fabrication, assembly and test. The data format standards need this type of consistency in order to meet the efficiency that electronic data transfer can bring to the industry.
Many large firms have spent millions of dollars creating and implementing their own unique standards for their own “Electronic Product Development Automation”. These standards are proprietary to each firm and are not openly shared with the rest of the industry. This has resulted in massive duplication of effort costing the industry millions of man hours in waste and creating industry chaos and global non-standardization.
The Land pattern standards (both IPC-7351 and IEC 61188-5-1) put an end to the “Proprietary Intellectual Property” and introduce a world standard so every electronics firm can benefit from Electronic Product Development Automation. The data format standards (IPC-2581 and IEC 61182-2) are an open database XML software code that is neutral to all the various CAD ASCII formats. For true machine automation to exist, the world desperately needs a neutral CAD database format that all PCB manufacturing machines can read.
One of the factors in global standardization is that of establishing a CAD component description and land pattern standard that adopts a fixed Zero Component Orientation so that all CAD images are built with the same rotation for the purpose of assembly machine automation. The IPC-7351 indicates that in the CAD library, all pin 1 locations are in the upper left corner for multiple pin components and pin 1 on left for 2-pin components. Figure 1 represents IPC-7351 default and IEC 61188-7 “Level A” zero component orientation.
In May 2009, IEC land pattern committee voted and approved a new Level B Zero Component Orientation and redefined the IPC-7351 Zero Orientation as Level A. The new IEC 61188-7 defines Zero Component Orientation pin 1 locations in the bottom left corner except 2-pin components Pin 1 is on the left side and labeled it “Level B”. Figure 2 represents IEC 61188-7 “Level B” zero component orientation.
Since the basic rules allow two variations of levels in the description of the CAD system library, it is a mandatory requirement to define which level was used (level A or Level B) for the component descriptions in the data file. This information is a mandatory requirement in the Header of any file that incorporates land patterns using these principles of zero-based orientation. See Figure 3 for the “Level A” zero orientation and machine rotation.
The industry association EIA (Electronics Industry Association) is responsible for component descriptions and tape and reel orientation in the EIA-481-D standard. EIA has tried valiantly to influence the industry by making good standards that describe the component outlines and how they should be positioned in the delivery system to the equipment on the manufacturing floor. Suppliers of parts have either not adhered to the recommendations or have misunderstood the intent and provided their products in different orientations.
Here are the EIA-481-D standard tape and reel pictures (Figures 4 & 5) that illustrate quadrant designations.
IPC and IEC use consistent rotations throughout their standard where EIA uses multiple rotation variations
IPC-7×51 “Level A” uses Quadrant 2 for Pin 1 Upper Left and Quadrants 2-4 for Upper Center
IEC 61188-7 “Level B” uses Quadrant 1 for Pin 1 Lower Left and Quadrants 1-2 for Left Center
EIA-481-D uses Quadrant 1 for Pin 1 Lower Left BGA, SOIC, SOP, QFN (rectangle), DIP
EIA-481-D uses Quadrant 2 for Pin 1 Upper Left TO-252, TO-263, QFN (square), TSOP
EIA-481-D uses Quadrant 3 for Pin 1 Lower Right for all SOT and miniature parts
EIA-481-D uses Quadrants 1-2 (Pin 1 Left Center) for PLCC, LCC
None of the 3 standards use Quadrant 4 for Pin 1 locations
The main purpose of creating the land pattern standards is to achieve reliable solder joint formation platforms; the reason for developing the data transfer structure is to improve the efficiency with which engineering intelligence is converted to manufacturing reality. Even if the neutral CAD format can drive all the manufacturing machines, it would be meaningless unless the component description standard for CAD land patterns was implemented with some consistency. Zero Component Orientation has a key role in machine automation.
The easiest way to illustrate the 3 world standards is to list every component family and their respective Zero Component Orientation for each standard. The big question is – Which standard will prevail?
Note: The EIA-481-D rotations marked in Red conflict with both IPC and IEC
Download the complete IPC-7351B Electronic Component Zero Orientation document here – http://www.mentor.com/resources/appnotes/upload/zero-orientation-cad-libaray.pdf
Posted January 14th, 2011, by Tom Hausherr
- PCB Design Perfection Starts in the CAD Library – Part 19
- PCB Design Perfection Starts in the CAD Library – Part 18
- PCB Design Perfection Starts in the CAD Library – Part 17
- PCB Design Perfection Starts in the CAD Library – Part 16
- PCB Design Perfection Starts in the CAD Library – Part 15 QFN
- Inch to Metric Conversion Tables for PCB design
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- PCB Design Perfection Starts in the CAD Library – Part 13
- PCB Design Perfection Starts in the CAD Library – Part 12
- PCB Design Perfection Starts in the CAD Library – Part 11
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