Managing quick-turns: the prototype assembly stage doesn't have to riddle a project with delays.

Choosing an electronics manufacturing service (EMS) provider, with full support of the product life cycle, is a significant first step in the assembly process. Companies should look for a full service EMS provider that can handle as many build phases as possible--prototype, pre-production, production and high volume. This characteristic will save a significant amount of time, redundant tooling and non-recurring expense (NRE) charges throughout the product life cycle. First Things First

Prior to the start of the PCB layout, schematic capture should be virtually complete and a bill of materials (BOM) should be taking form. Additionally, all long lead-time material should be identified and procured. A specific individual should be identified as the EMS liaison. For the project to be quick turn, a resource is needed that can quickly respond to issues that may arise in this segment of the life cycle.

The EMS should participate and review the layout design periodically. EMS engineers should work with the layout team supplying design for manufacturing and test (DFx) by offering opportunities for improvement and identifying assembly cost implications. Turnkey Issues

If the project is turnkey, giving clear definition as to who supplies which component is crucial--especially if long lead-time material has been purchased. Add a column to the bill of materials (BOM) that states whether the customer or EMS provider supplied a particular component. The BOM should be complete at the conclusion of the layout design. Utilize a revision system to ensure that changes, especially additions, are covered. If the EMS provider utilizes computer aided manufacturing (CAM) software to develop the assembly documentation, avoid confusion by including all reference designators used in the layout on the BOM. If parts were added to the layout that will not be installed by the EMS, add a column to the BOM to show these parts will not be used. Costs are always a factor, but for turnkey projects, don't be too stingy. Focus the part cost strategy for the pilot and production runs. However, be prudent in understanding minimum lot sizes and non-cancelable, not returnable (NCNR) material.

Organization is Key

The EMS provider should have a data requirements list--a list of all files and documents needed to fabricate, assemble and test the PCB (if required). Be sure to sign a non-disclosure agreement and don't be afraid to supply all that is requested. By the time layout design is complete, dozens of files will exist--ensure that the EMS liaison is capable of understanding these files and has direct support on which he or she can rely, Many of these files can be quite large (30Mb), so be sure the EMS provider and information technology (IT) infrastructure can handle files of this size. Make use of FTP sites and know how to get these important files to the EMS provider when needed. Once the layout design is complete, freeze the files from changes and transfer a complete file package to the EMS provider.

Typically, the PCB will be fabricated on a three-day turn. During this period, the kit will be finalized, assembly documentation will be developed, stencils will be engineered and ordered, pick-and-place machine programs will be written and reflow profiles will be defined. An EMS provider that focuses on NPI should be able to accomplish each of these tasks while the PCB fabrication is occurring.

Undoubtedly, the design engineers will want to change some aspect of the design after the layout is complete and the files are frozen. Keep engineers happy by using a special build instruction (SBI)--a last minute change to the assembly of the PCB, usually in the form of an e-mail or fax. Issue the SBI to the EMS provider as soon as the change is known and be as clear as possible as to what changes are needed.

Most PCBs should take only three to five days to be assembled--depending on the complexity of the board. During assembly, the EMS provider should keep track of any assembly issues. A good EMS will provide short- and long-term solutions to any problems that may arise.

Conclusion

Rarely does a project move through the prototype stage just once. While the product is being tested, verified and changed, perform a postmortem of the prototype assembly feedback data from your EMS provider and make the appropriate changes to the BOM and/or the PCB layout for the next build. With a little organization and specific responsibilities defined, a project can be completed with relative ease--and especially--without delays from your EMS provider.

Mark Hackathorn is the director of engineering at Manufacturers' Services Limited's NPI Center, Lowell, MA; e-mail: [e-mail].