Incorporating Mechanical Size and Cost Into Your PCBA Design

June 9, 2020 Cadence PCB Solutions

What You Can Takeaway

  • What are the differences and similarities between ECAD and MCAD?

  • What are the advantages of merging ECAD and MCAD?

  • How to Incorporate Mechanical Size and Cost Into Your PCBA Design

The different sizes of a computer’s internal systems

Different mechanical sizes for computer electronics

There is an essay by John Donne in which he warns against the false security that can accompany solitude or isolationism. The most famous excerpt from Meditation 17, begins with “No man is an island” and ends with “...and therefore never send to know for whom the bell tolls; it tolls for thee.” These sentiments are especially poignant today as people throughout the world are avoiding physical contact with each other, while also realizing that we are all intricately connected in a fight against an invisible enemy, the COVID-19 virus.  Although humanity will not emerge unscarred, the extent of our injuries can only be lessened by—and are directly linked to—the resolve to stand together that we exhibit. 

As with all difficulties and struggles, there are lessons to be learned and applied to other areas. One such area is electronics and PCBA design, which indirectly touches virtually all aspects of our lives. Like most things, board design should always be guided by good principles; however, the design process for the circuit board, ECAD,  is isolated from the design process for the final product enclosure, MCAD, that will contain it. 

As an example, computers contain PCBAs of various sizes, all of which must be installed in the same enclosure. Yet, the enclosure design is typically not incorporated into the board design process although it affects the board layout. This method of developing electronic products is ineffective and does not allow for the incorporation of mechanical size and cost considerations during board design. Let’s explore a better option, that is the collaboration of ECAD and MCAD and how this integration can result in an optimal product development process.   

ECAD versus MCAD

Before extolling the virtues of merging the design processes for the circuit board and the mechanical structure or enclosure that will house it, let’s clearly define the differences between ECAD and MCAD.

As these definitions illustrate, ECAD and MCAD have different objectives, yet the resulting products must physically mesh together.  This can only be done by merging the PCB size and shape requirements of ECAD with the mechanical system constraints of MCAD  to accurately determine the material costs for your design.   

ECAD and MCAD

The mechanical specifications for the ECAD process are defined by the PCB stackup, as shown in the figure below:

PCB Stackup specifications shown in the Cadence Allegro cross-section editor

ECAD PCB stackup mechanical specifications

Armed with the details above, as well as the other design package data, an accurate cost assessment for your board can be obtained. However, for a comprehensive mechanical size and cost evaluation, the MCAD information for your electronic product must also be included. One of the best ways to represent this data is by using step file enclosure models

PCB Design with Mechanical Size and Cost Considerations

Many electronics developers have realized the advantages of ECAD and MCAD collaboration, which has led to various methods for achieving the best integration of the two. A common method is to generate a step-file representation from the ECAD process that is then used by the MCAD developer to realize a mechanical system design. This is a good solution, provided the board design is finalized. However, PCBA design in contrast to enclosure design is typically a cyclic process consisting of design changes, board respins, and testing. Therefore, a better design option is to incorporate the step file of the mechanical system into the ECAD process allowing for mechanical constraints to be an integral design check during board development, as shown in the figure below:

A 3D STEP visualization of PCBA and enclosure

3D visualization of considerations for mechanical size and cost 

Implementing this superior ECAD-MCAD co-design strategy requires advanced functionality, such as EDMD/IDX or ProSTEP iViP’s EDMD Schema that allows for incremental design between the ECAD and MCAD teams. This paradigm enables continuous and accurate mechanical size and cost considerations throughout product design. 

With Cadence’s PCB Design and Analysis tools, the ECAD-MCAD collaboration can be optimized.  Additionally, Allegro PCB Designer allows for real-time design review and correction using DesignTrue DFM technology.  These tools expedite the board development process by eliminating costly and time-consuming changes once your design is in the hands of the CM. For more detailed information and guidance on using step-files and MCAD integration with Allegro, see Reducing MCAD Iterations with STEP.

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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