Prototypes provide an interesting way for electronics engineering and manufacturing teams to communicate. We consider prototypes to be any of the 4 types of preliminary electronic assemblies that may be built and used internally, before a production job is started with products going to the customer.
A prototype allows both engineering and production departments to validate design production documentation before committing to large scale production. This may all seem obvious to those experienced in electronics, but because it is a task that is shared by engineering and production, it is important to clearly define the roles involved with and purposes of prototypes.
Martin Company always recommends building prototypes as a routine part of every electronics design project. There are several types of prototypes that may be built to provide critical information in the product development cycle. Following is a flow diagram of how the data would best flow from engineering through our “Prototype folder” to final production documentation. Regardless of the type of prototype being built, a standard process such as this should be followed to remove ambiguity and improve communication, resulting in large scale production of successful products. Prototypes have still proven to be very helpful even after the simulation and digital modeling is complete.
Prototypes serve the following important roles:
1) Risky design concepts can be tested early in the design flow.
2) Purchasing can verify for engineering that all components are available.
3) The hardware engineer can confirm that the footprint models, pin assignments, and other mechanical parameters that are used for pcb layout are completely correct.
4) Hardware engineers can test functionality of the design based on an assembly built according to the final production documentation.
5) Firmware/software engineers have an early platform on which to test their code.
6) Mechanical engineers can verify the enclosure design with real hardware.
7) Test engineering can test the test plan and test equipment for this product. A current trend is to have the test equipment for production testing finished by the time the product is released to production.
8) The production process and team can be tested with this product before large scale production.
Following are 4 different types of prototypes we typically recommend:
Proof of concept prototypes: Often these prototypes may use off the shelf evaluation boards or various types of tiny or difficult chip interface boards hand wired together to build a prototype circuit to test some initial concepts that may need to be confirmed at the very beginning of the project. The objective is to validate these basic concepts as early as possible, at as low a cost as possible. Often these test results will change the whole direction of a project. A good example might be to accurately evaluate power dissipation on a board. A rough prototype could be built and some test code written. Then battery life could be accurately estimated. Following in Figure 2 is a good examples of such a prototype. There is no pcb layout – just off the shelf modules and boards wired together. Code development may start or continue with this prototype.
6”X6” Preliminary Design Prototypes: This name came from the number of prototypes built that were this size. The final board designs were going to be very tightly populated board designs with many small SMT parts, tiny geometries, and not enough room for test points. This board was laid out with more room, larger components, and plenty of test points. Typically, this layout can be done faster and less expensively due to the relaxed spacing of components and lands than the actual final design. The black connectors shown below would not be on the final board design, but they made hookup much easier. The hardware engineers were able to test the design more easily, with the better scope and DVM probe access. The software engineers also benefited from the additional test points and larger components. Following in Figure 3 is an example of a 6X6’ prototype board that will be much denser and more difficult to troubleshoot and program in its final form factor.
Below in Figure 4 is a board that was so dense that we brought out the test points to external test points so that we could more easily connect to them. Circuit debug and final code development can continue with these “6×6 inch prototypes.
First Revision Hardware Design Prototypes: Upon completing the schematics with BOM and PCB Gerbers for a new electronics design project, a first revision final prototype is built and carefully tested. Our objective was for the first revision prototype to be the final one, but often there is more than one as shown below in figure 5 where this revision has changes. This revision is used to verify the following:
1) The basic schematic design is correct and works as required.
2) The production documentation has been reviewed and is completely correct.
3) All parts on the BOM are correct and available from good sources.
4) The footprints for the pcb layout are correct. Datasheets can be incorrect or misleading.
5) Final code development can continue with this phase.
Final Prototype/Pre-Production Stage, the step of building 5, 10 or 20 “preproduction prototypes,” can add much value and save money and time for the overall project. Following is an example of these prototypes after the design is completely tested and we want to be sure that there are no problems in volume production.
Typical Design and Prototype Documentation: The prototype documentation should be done well enough that it can become the Revision 1.0 product manufacturing documentation after testing. A comprehensive design review should be done and documented at the stage where the final production documentation is being prepared for release. Following are the standard files that we recommend for a prototype production document package:
Product name BOM Revision XA Excel document
Product name BOM Revision XA Excel document
Product name Gerbers Revision XA Zip folder
Product name Pick and Place XA Zip Folder
Product name PCB Fabrication Drawing Revision XA PDF document
Product name PCB Assembly Drawing Revision XA PDF document
Product name Programming files (.hex, etc) and Instructions Revision (PDF) XA Zip Folder
Product name Test Plan Revision XA PDF document
Product name Additional Instructions Revision XA PDF document
To restate the goal, the prototype documentation ideally should be complete enough that it could be sent to any contract manufacturer who is competent in electronics, or be kept in-house and built by the internal production department. In either case, a correct working prototype should result.
Well done prototypes have saved electronics design projects a significant amount of time and money by making the verification, debugging, programming, and testing of very dense pcbs with tiny geometry surface mount components much easier. Even with the advent of reuse of components and circuits, design Ai, automated pcb layout and checking, design rule checking, simulation, and modeling there are many electronics design projects that will benefit from appropriate prototypes.
We have a goal at Martin Company to continue to streamline the prototype quoting and assembly process to offer the fastest delivery possible. Faster delivery time on prototypes can often offer a very good return on investment especially with embedded systems where code development will be the pacing task. The sooner that code can start to be tested on real prototype hardware the shorter the code development timeline.
