How to Successfully Design for Testing or DFT

November 2, 2016 Chris Carlson

ict-test-pcb-dft

 

The overall cost to produce a completed printed circuit board can be broken down into several basic categories: the cost of manufacturing the blank PCB, the cost of components, the assembly costs, and the cost of testing. That last one, the cost of testing the completed board, can comprise as much as 25% to 30% of the total cost of producing the entire product. Best practices for DFT is key.

By designing a product to have the highest test coverage and the ability to isolate faults quickly regarding both PCB manufacturing errors and component failures, DFT becomes paramount in designing for profitability. What are some design best practices to follow to ensure your board has the highest test coverage? Let’s take a look.

Design for Testing (DFT) Tip: Always Plan Ahead

The first two questions to ask when planning a design are:

  1. Who is going to test your assembly?

  2. What are their capabilities?

The DFT guideline will be helpful in the initial planning of the layout. However, it is a good idea to contact the contract manufacturer (CM) directly and discuss your specific needs with a knowledgeable test engineer. The test engineer will be able to discuss their capabilities and make you aware of the different test methodologies they’re able to provide.

A combination of a boundary scan (JTAG), automated ICT test, X-ray laminography (AXI) and visual inspection (manual and machine vision) will provide the most comprehensive test coverage. It will also give you access to immediate feedback on the PCB manufacturing process so that workflow can be quickly adjusted as needed, and defective components can be spotted and rejected.

 

dft-bed-of-nails-tester
Bed of Nails Tester (ICT Test)

Determining Test Coverage

Next, you should consider what test coverage is necessary to guarantee a quality finished product. Utilizing the full arsenal of test capabilities available may or may not be required for your application, and in fact, may be cost prohibitive. For example, if you are fielding a one-of-a kind-satellite orbiting earth, you will want to perform every type of test available, to ensure that the finished product will function reliably for years in an environment where repair is not an option. However, if you are producing musical greeting cards, a simple, functional test may be all that is required.

      

What Test Coverage Is Best for You?

With the testing phase of a completed printed circuit board comprising up to 30% of overall costs, it’s more important than ever to fully plan and strategize your DFT process within your PCB design software. This first begins with knowing the capabilities of your manufacturer and what test coverage is considered necessary to guarantee a quality finished product. Download a free Design for Testability white paper to learn more about the available testing coverage and which one is best for your PCB design. Plan the best DFT process.

 

 

About the Author

Chris Carlson

Sr. Field Application Engineer Chris Carlson came to Altium in August of 2007 and brings with him his background in power electronics, data acquisition, and controls. Chris earned his Bachelor of Science degree from Oregon State University in 1993 and has worked as a design engineer in the Bio-Medical, Industrial Controls, Motor Drive, and Defense industries.

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