DFT in PCBs: Design for Testing

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 layout, the cost of components, the assembly costs, and the cost of testing. That last one, the cost of the PCB test, can comprise as much as 25% to 30% of the total cost of producing the entire product. Best practices for Printed Circuit Board 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, design for testing becomes paramount in for profitability. What are some design best practices to follow to ensure your board has the highest PCB 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 administer the PCB testing of your assembly?

2. What are their circuit board 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 PCB testing capabilities and make you aware of the different test methodologies they’re able to provide. Most test engineers much rather communicate and prevent problems than to fail PCBs.

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.

Determining PCB 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 PCB Testing 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 out your DFT process prior to your PCB design. This first begins with knowing the capabilities of your manufacturer and what PCB test coverage is 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 for the best DFT Printed Circuit Board process.