What to expect when you're expecting ... prototypes (Part 1)

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In earlier article (When to Build, When to Buy; ECN June 2014) presented some key points to help companies identify a suitable design services partner. But how can you maximize the experience once you've selected a partner and move forward with the design? All of the suggestions come directly from experiences our company has had with real customers over the years.

Make a Schedule
One of the best project management tools for both the design services provider and their client is a master schedule of the project development. This is typically generated by the design service provider's program manager. While the need for a schedule might seem rather obvious, most engineers are familiar with projects that were run "open loop" with predictably bad results. A good schedule should cover major development milestones, such as:

  • Completion, review, and acceptance of a design document.
  • Completion, review, and acceptance of the printed circuit board layout.
  • Ordering of prototypes.
  • Firmware completion.
  • Hardware bring-up, hardware/firmware integration, and system validation.
  • Delivery of the client's manufacturing package.
While this is not an exhaustive list, it covers the common phases of most development projects which include both hardware and firmware.

The design document milestone
Of all the milestones in any project, this one is unquestionably the most important. A design document is the specific description of what is going to be built, and what it will do. Even simple projects need to have a design document written because this document serves as the basis for all subsequent reviews and  product validation. In short, the design document defines done or when the product complies with the requirements of the design document. The design service provider should write this document with input from the client. Since the beginning of any outsourced project is the time when the majority of information
flows, developing the design document jump-starts the communication process between the client and the provider. Sometimes, when all of the salient aspects of the design have been written down and reviewed by the client, they may see a need for changes or additions. It's far less expensive and disruptive to make changes at this point in the design, which is another reason the design document is so critical. If the changes are significant enough, this is the time to renegotiate the project costs.

The schematic (circuit design) milestone

The design document has been reviewed and approved, and now it's time to design the schematic. If the design is similar to a client's existing design, and the client wants to reuse parts of the existing design, the client should share this information with the provider in advance of the start of the schematic. Similarly, if the client wants specific components, they should identified. Once again, the goal is to be sure that each milestone starts with all the needed information, so false starts and extra work are avoided. At least one customer review of the schematics should be planned at completion, and if the design is more complex it may be sensible to have one or more interim reviews. In any case, it's very important the client gives timely review feedback to keep the project on schedule.

The printed circuit board layout milestone
Both sides are now satisfied with the schematic, and it's time to start the printed circuit board (PCB) layout. Once again, several items need to be addressed before the layout is started. First, mechanical requirements for the PCB like board size, mounting holes, part size or component height limitations, and connector placement need to be identified. This implies that enough work has been done (by either the client or the provider) on the product enclosure that the mechanical requirements are clear. Lack of clear mechanical requirements up front is the number one cause of PCB layout changes and rework. If your design service provider uses PCB layout tools that allow 3D views of the PCB, and can import or  generate the enclosure drawings superimposed on the PCB, costly addition prototype PCB and enclosure spins can be avoided. Typical review points during the PCB layout should occur after major silicon components and connectors are placed, but before routing begins. This allows the client to make sure that the connector layout is correct, and it also brings to light possible difficult signal routing imposed
by either connector positions or poor component placement. At least one other review should occur after the PCB has been fully routed, and another short review after any changes are rolled into the PCB design. As with the schematic review, timely client feedback is essential.

Posted from: ECN magazine, October 2014 edition

Author: Mike Sims

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