Monday, June 18, 2018
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Successful Prototyping at Screaming Circuits
Technician prepares the selective solder machine.

Prototyping customers have one thing in common. They are working with far fewer internal resources than they had a few years ago. Everyone runs "lean" today, and this will probably not change. This situation in turn creates challenges in the prototyping process. Engineers who once had a team that addressed issues such as parts procurement, documentation development and prototype builds, now find that they themselves have to perform all of these functions.

As a result, we at Screaming Circuits see two main challenges. First, we need to be able to be fast and flexible across a wide range of unique customer needs. Second, we need to have enough of a systems approach that we can offer services at competitive cost and provide our customers with high quality prototypes that ultimately lead to high quality products in mass production.

We address this in several ways. We do both formal and informal customer surveys to better understand the challenges our customers face. We provide free educational resources such as Screaming Circuits blog: to help engineers who understand how to design leading edge products, and who also understand the manufacturability and testability issues that are associated with newer technologies. Finally, we try to make our systems thorough, yet streamlined enough to catch common errors without adding non-value-added time to the process.

Better Guidance
In response to our most recent surveys, we have further improved our processes and thought we'd share some of what we've learned. Downsized engineering departments translate to more questions and common errors in the prototyping ordering process. We've set up an automated e-mail notification system in our order audit/acceptance process that immediately e-mails the customer when information is needed. There is also better guidance provided to determine just when customers should be called to expedite a corrective action in our ordering processes.

Our surveys also have flagged a number of common areas where customers have questions or make mistakes such as:

  • Parts kit packaging assumptions.
  • Required documentation.
  • Third-party component drop ships.

Parts kit packaging. Many companies are unsure of whether or not partial reels or trays are acceptable, and/or the best way to label and package. Cut strips, partial reels or full reels are all equally acceptable, provided they are bagged and properly labeled. Simply writing the part reference designator on the outside of the bag is the most efficient solution. In the case of trays, the answer is not as simple. Non-leaded parts, such as LGAs, QFNs and BGAs, can be carefully individually bagged and shipped.

Be extra careful to not damage any of the solder balls on BGAs. Trays are needed to protect leaded parts from handling damage. One solution is to put the required number of components in a spare tray. Just be sure to not bend any leads while transferring the parts. The other option is to ship the full tray and have the prototype house ship the remaining parts back.

Moisture-sensitive parts. When we receive moisture-sensitive parts in a sealed package, we pull the parts we need and reseal the package immediately. However, when moisture-sensitive parts are received in unsealed packages we are forced to bake the parts prior to use. This adds both time and cost to the prototype process.

Documentation. At Screaming Circuits, we only require the documentation needed to build prototypes. That said, since SMT components are machine-placed and we often procure components for our customers, we do need documentation packages that will meet those requirements.

For example, most engineers are familiar with Gerber files, but may not be familiar with which layers are required to program placement machines. Similarly, while most engineers understand BOMs, they may provide BOMs which lack manufacturer's part numbers or complete component descriptions, such as the wattage or voltage parameters. In many cases, they've previously pulled from internal boxes of parts and simply haven't needed to provide that level of detail. Drop-shipped parts. Turn times don't start until the parts have arrived; the assembly ship date is determined by parts arriving on a specific date. Production dates slip if the parts don't arrive on time and when the parts are being drop-shipped from the supplier, we and the customer both lose some visibility as to when they will arrive. The reality is that most customers don't know if the parts are arriving on time or not. Another process improvement we've implemented is earlier notification if drop shipped parts don't arrive on schedule. We recognize that while this part of the process isn't within our control, driving a fast corrective action gives our customers more options in addressing the problem.

Definitive Source
Not every improvement we've made has generated positive feedback. As an example, we've found that giving advice on land patterns can be a minefield at times. One example is our answer to the question: "Is IPC or the manufacturer the definitive source for land patterns?" Our answer, "it depends," drew some criticism from both sides. The reality is that while IPC land pattern documents are the right choice for most components, leading edge components may not be incorporated in those documents. Manufacturers such as TI with OMAP processors and Freescale with their QFN Zigbee chips, have done an excellent job of testing and making solid recommendations for land patterns. However, some other manufacturers have not done a good job. For those reasons, we stand by our recommendation that the definitive source for land patterns varies case-by-case. You may have to take the time to check both the manufacturer's documentation and IPC standards.

Another question that comes up: "If time and money are tight, but money is tighter, can you save money by ordering a faster turn on PCB fab or a faster turn on prototypes?" Since bare boards are generally less expensive to process on a 24-hour turn and ship overnight than finished assemblies, the answer is usually to expedite the PCB fab and opt for slower service on the prototypes.

Service packages. Quickturn prototypes carry premium pricing that is driven by turnaround time. Consider your required turn time when buying services. Our survey showed that over 30 percent of our customers were purchasing quickturn prototyping services to support low volume end-production needs. They were doing it because they found it preferable to trying to outsource a short-run of production boards in a traditional EMS environment. They were also trying to avoid excessive tooling or non-recurring engineering (NRE) charges. Our solution was to offer a lower cost hybrid service with a simplified project launch and a longer turn time than found in the quickturn prototyping realm. We've also created a simple prototype ordering option that helps customers save time when ordering small quantity, simple PCBAs.

Efficiently supporting prototype production is a team effort. At Screaming Circuits, we continue to work to more flexibly support our customers' needs with a mix of customer-accessible tools and improved processes.

Contact: Screaming Circuits, 1140 NW 3rd Ave., Canby, OR 97013 866-784-5887 E-mail: Web: or

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