What to expect when you're expecting ... prototypes (Part 2)


manufacturing sourcing board assembly prototype development
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.

The prototype ordering milestone

Most design service providers go to outside vendors for PCB fabrication, and many also use external resources for prototype PCB assembly. At this stage, coordinate the availability of the assembled prototype PCBs with the fabrication of the enclosure. Metal enclosures usually have shorter lead times than custom plastic ones, but as 3D printing has become more capable, that disparity is disappearing. The main point is to schedule PCBs and enclosures (and any other component parts of the prototype) to arrive relatively simultaneously so fit checks can be done at the earliest opportunity.

The firmware completion milestone
For designs that have a firmware component, completion of the initial firmware should be scheduled to coincide with the availability of the prototype hardware. In many cases, some level of firmware is needed to support the hardware validation, so scheduling firmware development in parallel with hardware development is the most efficient approach for keeping a project moving ahead. Much of the firmware
needed can be developed on an evaluation platform available from the silicon supplier, allowing firmware and hardware to dovetail.

The hardware/firmware integration and system validation milestone

Once prototypes are received, hardware bring-up and hardware/firmware integration happens. The design document that was developed at the beginning of the project is critical in this stage, as it defines
the expected operation of the hardware and the functional requirement systems. Typically in this stage, minor hardware "green wires" and firmware "bugs" are found, and corrections are implemented on the prototype to make the design conform to the requirements of the design document. These changes should be promptly rolled back into the firmware and hardware by the design service provider. The client should also review and test the prototypes for conformance to the design document. Once the design service provider and the client have verified that the system meets the design requirements, the design is complete.

Delivery of the client's manufacturing package
Although developing the hardware and firmware for a project is where most of the engineering time is spent, the real output of any project is the documentation package that allows the design to be correctly and successfully mass produced. The manufacturing package will include the schematic and PCB layout, PCB assembly files (including Gerber files for PCB fabrication, PCB fabrication drawings, and XY files that indicate placement and orientation of all components on the PCB), a bill of materials (BOM) listing each component on the design, firmware source files, and binary files. A description of the proper programming sequence for the completed product, and equipment needed for programming is often part of the design package. If the design services provider has been contacted to develop manufacturing test procedures, they should also be part of the design package.

While there's no magic formula for making a design services engagement go well, these key ideas will go a long way towards bringing success;

  • Plan - A detailed schedule that outlines what will happen, when it will happen, and what the client's and design service provider's responsibilities are at each step.
  • Communicate - First, last, and always. Good communication, both verbal and written, helps avoid unshared assumptions and expectations.
  • Identify changes early - The further into a project changes occur, the more expensive and time consuming it will be to implement them.
  • Respond quickly - Whether it's review comments or technical information for lhe project, timely client response is important for keeping the project on schedule and running smoothly.

External design resources can give companies the engineering flexibility to stay ahead of their competitors and take advantage of fast developing market opportunities. By observing these suggestions, companies can develop and nurture a long term relationship with one or more design
service providers, and reap the benefits of having access to well-focused engineering support without the costs of permanent in house design staff expansion.



Posted from: ECN magazine, October 2014 edition

Author: Mike Sims

Corporate
11 Flora Spgs,
Irvine, CA 92602
U.S.A. Map

Phone:
714.731.8123

Email:
Email Us

Follow on Social

For Customer Support,
please visit our help center

Help Center


Corporate
11 Flora Spgs,
Irvine, CA 92602
U.S.A. Map

Phone:
714.731.8123

Email:
Email Us

Follow on Social

For Customer Support,
please visit our help center

Help Center