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Does your PCB Layout Designer have a good handle on testing?

A critical practice at any EMS Provider and contract manufacturer is close interaction between the PCB layout designer and test engineer. Unfortunately, that practice is often lost in a myriad of tasks solely focusing on shipping the PCB project on time to the OEM customer. OEMs not adamantly demanding evidence of this highly important practice usually incur the highest probability for extra costs, wasted time, and latent field failures.

That often happens when the OEM hands his PCB design to a vendor located in one sector of the U. S. Then, that OEM gets the Gerber files to the fab house of his choice at another geographic location. Afterward, the OEM goes to the trouble of purchasing components and locating a third party to perform assembly. Each stage – design, fab, and assembly – is distinctly separate from one another and in effect, operates within its own confines with the OEM trying to successfully orchestrate the entire production cycle.

Fig 1 - Functional TestSo, it’s to your advantage to go with a PCB layout designer who has a close working relationship with his or her test engineer and also has familiarity with such testing as functional test, Fig. 1.

There are innumerable benefits to this special close working relationship besides the fact you can be assured of having high test coverage for your PCB project. You should read our article appearing in PCDandF Magazine to get more details about this important design/testing practice.

Meanwhile, here are some tips and hints to get you more familiar with the importance of that close coordination between PCB layout design and test engineering.

  • You want assurances you’ll get the highest testing coverage possible, 85 to 95 percent.
  • Find out if your PCB layout design engineer is familiar with flying probe and ICT test guidelines and limitations.
  • Ask how often the PCB layout design engineer engages with test engineering.
  • Does the PCB layout engineer step out of his traditional role and learns about test-related practices, procedures, and disciplines?
  • Is the PCB layout design engineer savvy enough to understand special design cases that may have special testing significance? For example, emphasis is important for a high-speed bus design’s geometry and traces to develop proper test coupons.
  • The PCB layout design engineer must fully understand the importance of a smoke test, gain and frequency response test, analog signature analysis, propagation velocity test, and a host of other test procedures and characteristics.

PCB layout and test are inextricably intertwined. Some CMs maintain an in-house staff of layout designers as well as assembly/test engineers. In cases like this, the layout engineer delays creating all the necessary test points to avoid hindering routing. But once he or she has finished the critical routing and bus routing an initial routing analysis and preliminary test points to achieve, say 50 or 60 percent coverage, he or she has the benefit of consulting with in-house test engineering to determine the right strategy to increase test coverage for the product.