Everything You Wanted to Know, But Were Afraid to Ask

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This month, Testing Todd presents readers’ questions about the basics of electrical test, including the different types of testing available today.

 

Reader: I recently found out that all points are not necessarily checked during electrical test. Why is that and which types of boards do not get all of their points tested? Isn’t there a chance that something will be missed? Is there a type of test that hits all of the points?

Todd: When a board is programmed for test, certain points of the board are de-selected. To properly answer this question, we need to revisit IPC-9252A, Amendment 1, which stipulates that Class I and II can remove the mid-points of a net on the board. What this means is that we are only concerned with the end-to-end connectivity of the net. With IPC Class III we need to include the mid-points of the net to quickly isolate any problems in the chain. However, this is cautioned by the additive properties of solder mask encroachment or via-fill. In these cases, although Class III, they cannot be tested and are allowed the waiver under the 9252A with Amendment 1 release.

Within the Class III requirement of 9252A with Amendment 1, we can add probes to validate each landing pad. With Class I and II we are only validating the end points of the net to make sure the signature is intact. By adding mid-points with Class III we validate that the connectivity is valid to all landing pads. This is in case there may be contamination to any of the intermediate landing pads in the chain of the net.

Adding all pads in the net is referred to as Class III per IPC-9252A with Amendment 1, which hits all of the points.

Read the full column here.


Editor's Note: This column originally appeared in the May 2014 issue of The PCB Magazine.

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On the Wednesday of IPC APEX EXPO week, IPC President and CEO Dr. John W. Mitchell stylishly delivered his keynote address, “Fire Your Hiring Habits!” to a packed ballroom full of round tables all immaculately laid for a sit-down lunch. Announced by IPC Hall-of-Famer Joe O’Neil with a Rolling Stones track in the background, Mitchell’s presentation, subtitled “Finding and keeping the best talent is fundamental to building electronics better,” offered relevant and valuable guidance on understanding human nature and how this knowledge can help you find and keep the right individuals for your organisation.

03/22/2023 | John W. Mitchell, IPC

What goes down must also come up. This is not the idiom we’re used to hearing, but I’d like to apply it to IPC APEX EXPO 2023. After a few years of lower attendance numbers due to the COVID pandemic, 2023 ushered in a re-invigorated group of attendees, exhibitors, speakers, event contractors, and staff to the show floor and meeting rooms. IPC APEX EXPO 2023 was fueled by the possibilities of new advances in electronics manufacturing.

03/21/2023 | Christopher Bonsell, Chemcut

This year, I had the great opportunity to come to IPC APEX EXPO in San Diego as a contributing member in Chemcut’s booth. Being an exhibitor is always interesting because you never know what you will learn or who you will meet. Truly, it seems that every IPC APEX EXPO is an eye-opening experience. This was the second show I attended, and last year I was amazed to see how in-depth and interconnected the electronics industry is. Seeing how many different companies contribute to manufacturing today’s core technology never fails to impress me.