pcb prototyping process

What to Expect in the PCB Prototyping Process

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If you're ordering PCBs from overseas and have money to spend on multiple batches of inexpensive components, you'll probably go through multiple rounds of simple prototypes that do little more than provide circuit function testing. Professional design teams working on a new product know that prototyping, testing, and re-spinning a design are expensive activities. It's critical to get the design right as soon as possible and ensure your PCB prototyping process gives you test boards that most closely resemble your final product.

To help design teams and innovators master this process, we've compiled this short guide on the PCB prototyping process and what to expect when moving through each stage. The key takeaway is that the PCB prototyping process is both a test of the design and the process used to produce the design, so your prototype PCB should be designed with this mindset.

What to Expect in PCB Prototyping

PCB prototyping sounds like a simple process: you create your intended design and hand it off to a manufacturing house, right?

For simple products that have a low risk of failure and low design complexity, this may be true, and typically less time is spent on things like DFM or qualifying manufacturer capabilities. For many products in today's market, this whole idea is untrue, and there's a much greater element of DFM/DFA that must be incorporated into the design. In addition, many products released to market today do not use only a single board with an off-the-shelf enclosure. Most products have custom-designed housings created in the same phase as the PCB to ensure conformance to mechanical constraints. This is another part of prototyping and testing that often needs to be incorporated into the PCB prototyping process.

When a design team begins work with an external PCB design services firm, their project will move through the process shown in the following flowchart:

 

PCB prototyping process

 

This process takes an initial design, qualifies it against a set of manufacturer capabilities and DFM requirements, applies any required adjustments, and finally puts the board through prototyping and final delivery to the customer.

The Design Review Phase

The most important part of the PCB prototyping process happens before any actual prototyping. This is where a critical design review is performed with an eye toward the manufacturability of the PCB and the assembly. A critical design review is not meant to be an engineering review of the circuits or schematics. Instead, it is meant to be a review of the manufacturing outputs for a product, and the intent is to locate anything that could create a failed prototyping run.

What kinds of things are checked in this phase? We have a short checklist that looks for many important points in your manufacturing outputs:

  • Conformance to IPC Class 2 or Class 3
  • Etch clearances and pad/drill sizes
  • Clear materials and processing specifications
  • Match between product specification and fabrication/assembly data
  • Clear sourcing information in a BOM
  • Match between stated footprint and actual footprint in the PCB
  • Any requirements for specialized boards, such as HDI, via-in-pad, or VIPPO
  • Presence of on-the-line testing requirements
  • Overall check of output data to ensure completeness

Some of these steps can be automated, such as in CAM software often used by PCB manufacturers. When working with a PCB design services company, the client is usually asked to provide the original design files so they can be inspected and compared with Gerber outputs before submitting the outputs to a manufacturing house. In our opinion, this is a much faster way to get through a PCB design review as many simple errors can be quickly located and corrected.

What Happens Next?

Following the design review process, an output files package can be submitted to fabrication for a DFM review. For simpler boards, limited DFM review is sufficient to plan processing and avoid simple defects. If you have never produced your design before and the design is aggressive in terms of feature sizes and tolerances, then a full DFM review by the manufacturer may be in order. There is a small extra fee for this service, but it can make the difference in identifying defects that could cause a failed PCB prototype run.

Once this is complete, the manufacturer typically sends out a brief DFM report that identifies any features requiring changes or sign-off before fabrication.

 

PCB prototyping process

Example DFM report from one of our PCB fabrication partners. Read more about these reports on Zachariah Peterson’s blog on Altium Resources.

 

Most PCB prototypes are not fabricated and assembled by the same company; they will often be handled by different companies, or the PCB will be assembled in-house. When using separate fabrication and assembly facilities, consider having the prototype also reviewed by the assembler using the ODB++ outputs. This output format, or the more advanced IPC-2581 output file, is preferred among assemblers when performing a DFA review. The DFA review is intended to identify anything in the design that could lead to common defects, such as:

  • Closely spaced parts
  • No solder mask dam between SMD pads
  • Asymmetric mask openings
  • Any areas that may need thermal relief pads
  • Common quad package errors, such as center pad mask openings
  • Suggestions for any vias that may require tenting
  • Challenges with double-sided BGA assembly

To learn more about the more advanced IPC-2581 output file format, watch the conversation below between Zachariah Peterson and Dana Korf of Nano Dimension. Dana outlines some of the biggest challenges surrounding output file formats and their drawbacks, and why IPC-2581 is a superior solution.



 

Whether you're designing high-speed PCBs for mil-aero embedded systems or a complex RF product, you should work with a design and development firm that can ensure your product will be reliable and manufacturable at scale. NWES helps aerospace OEMs, defense primes, and private companies in multiple industries design modern PCBs and create cutting-edge embedded technology, including power systems for high reliability applications and precision control systems. We've also partnered directly with EDA companies and advanced ITAR-compliant PCB manufacturers, and we'll make sure your design is fully manufacturable at scale. Contact NWES for a consultation.

 



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