A Study on Effects of Copper Wrap Specifications on Printed Circuit Board Reliability

Area of Science:

• Materials Science
• Electrical Engineering
• Reliability Engineering

Background:

• European printed circuit board (PCB) manufacturers were found to be non-compliant with IPC-6012 Rev B, Class 3 standards regarding copper wrap on vias.
• This deviation from standards raised concerns about the reliability and usability of the manufactured PCBs for a Flight Project.

Purpose of the Study:

• To determine the reliability and usability of PCBs with reduced copper wrap.
• To investigate the impact of copper wrap on the thermal fatigue life and failure modes of PCBs.

Main Methods:

• Three sets of experimental tests were conducted, including thermal cycling and accelerated fatigue testing on various PCB materials (FR4 and polyimide).
• Finite-element analysis (FEA) was used to simulate plated-through holes under thermal stress.
• Destructive physical analysis (DPA) was performed to examine failure mechanisms.

Main Results:

• Thermal cycling up to 17,000 cycles showed no failures in PCBs with reduced copper wrap.
• Accelerated fatigue tests and interconnect stress tests revealed that failures primarily occurred as barrel cracks, not at the copper wrap location.
• FEA simulations corroborated that stress maxima are internal to the barrels, indicating copper wrap has no significant effect on reliability.

Conclusions:

• Standard requirements for copper wrap on PCBs do not contribute to overall board reliability and can potentially decrease it due to manufacturability challenges.
• Reducing procurement requirements for wrap plating thickness from Class 3 to Class 2 poses minimal risk to reliability.
• The study suggests that copper wrap is not a critical factor for PCB reliability, with barrel integrity being the primary concern.