PCB Design Perfection Starts in the CAD Library - Parte 14

Part 14 - PCB Design Perfection Starts in the CAD Library

Zero Component Orientation

 

In 2005 IPC and IEC (International Electrotechnical Commission) established a joint standard for land pattern geometries (IPC-7351/IEC 61188-5-1). In order to maintain a consistent method where these two important standards describe the component mechanical outlines, and their respective mounting platforms, a single concept must be developed that takes into account various factors within the global community.

 

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.

 

Figure 1 – IPC-7351 Zero Component Orientation
with Pin 1 in Upper Left Corner

 

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.

 

Figure 2 – IEC 61188-7 Zero Component Orientation
with Pin 1 in Lower Left Corner

 

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.

 

Figure 3 – Example of “Level A” Orientation Concepts

 

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.

 

Figure 4 – EIA-481-D Quadrant Designations

 

Figure 5 – CAD Library Zero Orientation Quadrants

 

IPC and IEC use consistent rotations throughout their standard where EIA uses multiple rotation variations

  • IPC-7x51 “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 location

 

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?

 

Component Family   IPC-7x51   IEC 61188-7   EIA-481-D
Chip (All Families)   Polarization On Left   Polarization On Left   Polarization On Left
Tantalum Capacitor   Polarization On Left   Polarization On Left   Polarization On Right
Molded Body Diode   Polarization On Left   Polarization On Left   Polarization On Left
SODFL   Polarization On Left   Polarization On Left   Polarization On Left
MELF   Polarization On Left   Polarization On Left   Polarization On Left
Aluminum Capacitor   Polarization On Left   Polarization On Left   Polarization On Left
Precision Inductors   Left   Left   Left
PLCC Square   Upper Center   Left Center   Left Center
PLCC Rectangle   Upper Center   Left Center   Left Center
LCC   Upper Center   Left Center   Left Center
QFP Square   Upper Left   Lower Left   Upper Left
QFP Rectangle   Upper Left   Lower Left   Lower Left
Bump QFP Side   Upper Left   Lower Left   Upper Left
Bump QFP Center   Upper Center   Left Center   Left Center
Ceramic QFP   Upper Left   Lower Left   Upper Left
SOIC   Upper Left   Lower Left   Lower Left
SOP    Upper Left   Lower Left   Lower Left
TSO8 (Mini US8)   Upper Left   Lower Left   Lower Right
BGA Square   Upper Left   Lower Left   Lower Left
BGA Rectangle   Upper Left   Lower Left   Lower Left
SOJ   Upper Left   Lower Left   Lower Left
CFP   Upper Left   Lower Left   Lower Left
QFN Square   Upper Left   Lower Left   Upper Left
QFN Rectangle   Upper Left   Lower Left   Lower Lefr
Chip Array   Upper Left   Lower Left   Lower Left
DFN   Upper Left   Lower Left   Lower Right
SON   Upper Left   Lower Left   Lower Right
SOT23-3   Upper Left   Lower Left   Lower Right
SOT23-5   Upper Left   Lower Left   Lower Right
SOT23-6   Upper Left   Lower Left   Lower Right
SOT89   Upper Left   Lower Left   Lower Right
SOT223   Upper Left   Lower Left   Lower Right
SOT143   Upper Left   Lower Left   Lower Right
SOTFL   Upper Left   Lower Left   Lower Right
SOT143 Reverse   Lower Left   Lower Left   Lower Left
TO-252   Upper Left   Lower Left   Upper Left
TO-263   Upper Left   Lower Left   Upper Left
LGA Square   Upper Left   Lower Left   Lower Left
LGA Rectangle   Upper Left   Lower Left   Lower Left
CGA Square   Upper Left   Lower Left   Lower Left
Oscillator (Multi-pin)   Upper Left   Lower Left   Lower Left
Crystal (2-pin)   Left   Left   Left
SMT Connectors   Left   Left   Left
PTH Connectors   Left   Left   Left
DIP   Upper Left   Lower Left   Lower Left
SIP   Left   Left   Left
Axial Lead   Polarization On Left   Polarization On Left   Polarization On Left
Radial Lead   Polarization On Left   Polarization On Left   Polarization On Left
PGA   Upper Left   Lower Left   Lower Left

 

Note: The EIA-481-D rotations marked in Bold 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

 

Coming Up

Additional brief topical articles will appear in future newsletters. You can also read more detail in my blog, which can be found at:http://blogs.mentor.com/tom-hausherr/

 

Written by Tom Hausherr CID+

EDA Library Product Manager

Mentor Graphics Corporation

Reprinted by permission from iConnect007