Freeware vs Proprietary ECAD Library Parts. Comparison
Importance of ECAD library parts
The importance of library parts might be heavily underestimated; there are so many great engineering companies not paying enough attention to this part of the development cycle. And when it is not significant for management and tech leads, engineers naturally start looking for a shortcut: freely available library parts. But using ECAD library components available on the Internet might be risky and time-consuming in the long run.
To see what is the actual difference between library parts made by engineers for engineers, and automatically generated parts available in the web, we compared 2 parts of one specific dense BGA package of NXP’s i.MX 8M Mini processor MIMX8MM6DVTLZAA with 486 balls.
We utilized the Siemens Xpedition CAD data format, as it has been the primary ECAD tool for global enterprises for decades. Thus, we examined components using this specific tool flow.
The library components we had for comparison had the following names:
- Sintecs ECAD part: MIMX8MM1XVTXXX
- Freeware ECAD part downloaded from the Internet (referred to as “generated ECAD part” or “generated ECAD component” further in the article): MIMX8MM6DVTLZAA
Upon opening both parts with the Library Manager application (see the image below), users can directly observe the difference structure of both components. It is logical for us to separately consider schematic symbols, PCB padstacks, and layout cells (or PCB cells) of the components, as these aspects are of primary importance to electrical engineers.
Sintecs’ schematic symbol
There’s a difference in the number of symbols. The part developed by Sintecs’ ECAD team (MIMX8MM1XVTXXX) comprises 13 associated schematic symbols, compared to only 5 associated schematic symbols in the generated ECAD part (MIMX8MM6DVTLZAA). Sintecs meticulously crafts schematic symbols according to internal guidelines, especially for large ICs, where we adhere to design regulations that entail dividing symbols based on pin functions:
- Separate symbols for vendor-specified I/O banks.
- Separate symbols for vendor-specified special functions.
- Symbols for control pins and programming interface.
- Symbol for the power supply of the device.
- Symbol for all ground and unused pins of the device.
Each symbol’s name includes a function name, indicating which function is covered by that sub-symbol and its specific group of pins. This division by function significantly simplifies the hardware engineer’s task during schematic capture, enabling users to easily locate a suitable pin using the symbol name. Moreover, within these schematic symbols, pins are logically grouped and named according to a common convention, with clear indications of their functions, supplemented with additional graphics revealing extra pin characteristics.
Utilizing such schematic symbols minimizes the likelihood of basic human errors. An accurate and legible schematic design saves time during the design process, cross-verification, debugging, and modifications/updates. Below, you’ll find examples of symbols covering Control signals (such as On/Off, Clock, Boot mode, Reset), USB, and UART interfaces of MIMX8MM6DVTLZAA (MIMX8MM1XVTXXX):
All attributes and elements in symbols are meticulously arranged according to predefined and standardized rules. This ensures that all schematic symbols created by Sintecs maintain the same consistent structure and appearance, which proves to be convenient and clear for engineers.
Generated schematic symbol
However, contrastingly, let’s examine the appearance of the schematic symbol for the generated ECAD part of MIMX8MM6DVTLZAA, downloaded from the internet “for free” (you might already suspect that using such components is actually expensive):
Yes, indeed, all the pins in the symbol are clustered together ordered simply by pin numbers. There are no graphics indicating pin types or functions, and there’s no splitting or grouping based on functions. Consequently, this generated schematic symbol still demands a considerable amount of attention from an engineer intending to use it.
PCB padstacks comparison
In the image below, it’s evident that Sintecs utilized a different padstack compared to the one used by the supplier of the generated ECAD part. Specifically, we applied SMD Round 0.25 M0.35, whereas the generated ECAD component utilized EX12Y120T.
When released by Sintecs, the padstack names are easier to read and contain a wealth of information (refer to the image below). Typically, Padstacks and Cells are constructed using the metric system (mm). In this instance, we have an assembly type labeled “SMD Surface Mount,” featuring pads with a “Round” shape and a size of 0.25 mm. Additionally, the solder mask ID measures 0.35 mm.
Sintecs’ padstacks are calculated in accordance with the IPC-7351 standard for SMD component footprints. This ensures that the footprints conform to the standard manufacturing demands, thereby minimizing the likelihood of production issues.
In contrast, the padstacks and PCB cells of the generated ECAD part are constructed using the imperial system (inches). The calculated pad size is 0.3 mm or 0.012 inches, which aligns with the nominal size of the pin (BGA ball in this case).
In the generated ECAD part, the opening of the solder mask matches the size of the contact pad. However, variations exist among assembly lines, necessitating different tolerances for alignment, positioning, tool care, etc. Consequently, when applying the solder mask, its pattern may slightly shift relative to the board, potentially leading to partial coverage of contact pads. This constitutes a significant technological error that cannot be overlooked.
To avoid such issues, the opening of the solder mask must be at least 0.1 mm larger than the size of the contact pads. Which is taken into account by Sintecs team:
PCB cells comparison
Firstly, there’s a clear disparity in the naming of the cells:
- Sintecs: BGA486C50P27X27_1400X1400X125
- Generated ECAD part: FCPBGA486_14X14_NXP
Sintecs’ cell name encrypts a wealth of information about the cell, including the number of pins, rows, columns, distance between pins, body dimensions, and height. This comprehensive naming convention facilitates quicker analysis of the part through name parsing, particularly when using a larger central database of ECAD library components. Sintecs’ cell naming allows better re-usability and makes finding it easier as an alternative for another similar component. It provides commonality amongst implementations from different vendors of the same package structures.
Let’s look closer on how the PCB cells are made in both cases now. Here is the generated ECAD component:
The PCB footprint made by Sintecs looks as follows:
Placement outline
The Placement Outline shape is critical as it defines the permissible gaps between components. In the footprint of a generated ECAD part, the placement outline mirrors exactly the same shape, size, and location as the component’s Assembly Outline, which delineates the part’s shape in its nominal size.
However, because components have dimensional tolerances, the maximum physical dimensions of a component may extend beyond the Placement Outline. This discrepancy can potentially lead to errors in the generated ECAD part. When a PCB designer arranges components on the board in a dense layout, there may be issues with the physical components fitting together properly.
To mitigate such problems, it’s essential for the Placement Outline to always encompass (be larger than) the Assembly Outline. This way, the Placement Outline defines the maximum physical size of the component, including tolerances.
Traditionally, Sintecs addresses this by creating the Placement Outline with an additional 0.25mm added around the Assembly Outline (for this specifical packade 1 mm added, the added clearance depends on the package).
Silkscreen
The silkscreen layer typically includes the following elements:
- Silkscreen outline around the assembly outline
- Silkscreen RefDes
- Silkscreen dot indicating the location of the first pin
It’s crucial for the silkscreen outline to be positioned outside the maximum size of the assembly outline and to avoid touching any solder mask openings. These requirements are duly met in the library parts created by the Sintecs team.
Additionally, in the Assembly Layer, the first pin is more prominently indicated in Sintecs’ library parts compared to the generated ECAD part, where it is nearly invisible.
Conclusion
| Advantages of Sintecs ECAD library | Advantage of generated ECAD library |
| + Footprints compliant with IPC-7351 standard. + Schematic symbols compliant with international standards ISO and IEC + Uniformity of components released by Sintecs. + Transparent and advanced naming conventions. + Convenient schematic symbols with functional division of pins, saving time for schematic designers. + Enhanced producibility of the board, particularly in dense designs. + Rigorous multi-stage quality control, including automated verification with Valor NPI. | + Generating library parts requires less time and working effort. |
By prioritizing precision and consistency in schematic symbols, padstacks, PCB cells, and silkscreen elements, you are able to empower engineers to navigate the design process with confidence and efficiency. Ultimately, the choice between quality, convenience and development approach in ECAD parts can significantly impact the reliability and manufacturability of electronic products.
Interested in trying Sintecs’ library? Your Next Steps
Learn more about ECAD Library Development service of Sintecs or Contact us.
