Failure Mode: Hole Wall Pullaway


Reading time ( words)

Hole wall pullaway (HWPA) is an insidious defect that is not usually a cause of electrical failure. What happens with HWPA is that the copper plating in a plated through-hole (PTH) is pulled away from the dielectric of the drilled hole wall. The hole must not be filled with any sort of a hole fill in order to see HWPA.

There are two distinct types of HWPA: stress-relieving and stress-inducing. In stress-relieving HWPA, the condition appears to distress the PTH, allowing it to survive hundreds or thousands of thermal cycles without failure. In stress-inducing HWPA, the stress appears to greatly increase, causing the PTH to fail in just a few thermal cycles. What we consider a failure is an increase greater than 10% in the overall resistance in the circuit. A crack that partially bridges the copper at the internal interface is enough to cause a failure.

This column is based on my experience in test reliability of interconnect stress test (IST) coupons. I am addressing HWPA that features moderate to severe outgassing. There may be HWPA due to thermal stressing of the board without any significant outgassing, but this type of HWPA is subtle, and it presents as a dark line between the plating and the dielectric of the hole wall. This type of HWPA is rarely detected.

Stress-Relieving HWPA

Stress-relieving is the most common type of HWPA. It appears that the adhesion of copper plating to the dielectric is reduced most likely due to problems with the application of electroless copper plating adhering to the dielectric of the hole wall. At the same time, the adhesion is strong at the copper’s internal interconnection. In fact, experience suggests that the adhesion of the electroless copper is stronger than the copper plating. This process frequently produces strong interconnections to copper inner layers. This condition may result in a hole wall that looks like a stack of forward or backward “Ds” running the length of the hole where the top and the bottom of the “Ds” is at an internal interconnect.

To read this entire article, which appeared in the August 2015 issue of The PCB Design Magazine, click here

Share

Print


Suggested Items

Real Time with… AltiumLive Europe 2020: Eric Bogatin’s ‘Unlearning’ Keynote

10/27/2020 | Pete Starkey, I-Connect007
Pete Starkey admits to not being a Star Wars freak, but he was impressed by Yoda’s iconic wisdom and philosophy and intrigued by his advice that, “You must unlearn what you have learned.” Here, he describes how attending Dr. Eric Bogatin’s keynote at the AltiumLive Europe 2020 Virtual Summit was an enlightening experience.

Real Time with… AltiumLive: Eric Bogatin on Unlearning What You’ve Learned

10/16/2020 | Andy Shaughnessy, Design007 Magazine
The second day of the virtual AltiumLive 2020 event got off to a great start with a class by Dr. Eric Bogatin. It was officially titled “You Must Unlearn What You’ve Learned,” but it could have just as easily been called “Designing Interconnect That Sucks Less.”

Mentor and Z-zero Collaborate on New Stackup Tool

09/17/2020 | Andy Shaughnessy, Design007 Magazine
I recently spoke with Max Clark, business unit manager with Mentor, a Siemens Business, and Z-zero founder Bill Hargin about the newly formed partnership that resulted in a new stackup tool that Mentor is now selling worldwide. Fun fact: Hargin used to work for Mentor as part of the HyperLynx team, which now has an interface with Z-planner Enterprise. Talk about coming full circle.



Copyright © 2020 I-Connect007. All rights reserved.