Marcy’s Musings: Operating Without a Rulebook
It’s Only Common Sense: Hire for Hunger, Train for Skill
Dan’s Biz Bookshelf: ‘The 'NVIDIA Way: Jensen Huang and the Making of a Tech Giant’
An Examination of Glass-fiber and Epoxy Interface Degradation in Printed Circuit Boards
July 12, 2019 | Bhanu Sood, Michael Osterman, and Michael Pecht, Center for Advanced Life Cycle EngineeringEstimated reading time: 9 minutes
Multilayer organic laminates, which make up over 90% of the interconnecting substrates in electronics (standard FR-4 represents 85% of the substrates used for laminates), can develop a loss of electrical insulation resistance between two biased conductors due to conductive filament formation. The probability of conductive filament formation is a function of the temperature, moisture content, voltage bias, manufacturing quality and processes, materials, and other environmental conditions and physical factors.
With increases in design density and tighter spacing between conductors, the probability of failure due to conductive filament formation (CFF) in printed circuit board (PCB) electronic assemblies has increased. CFF is a failure observed within glass-reinforced epoxy PCB laminates caused by an electrochemical process involving the ionic transport of a metal through or across a non-metallic medium under the influence of an applied electric field [1 & 2]. The growth of the metallic filament is a function of temperature, humidity, voltage, laminate materials, manufacturing processes, and the geometry and spacing of the conductors [2]. The growth of these filaments can cause an abrupt loss of insulation resistance between the conductors under a DC voltage bias.
A statistical examination of field returns and root cause analysis performed at the Center for Advanced Life Cycle Engineering (CALCE) at the University of Maryland shows that failures in PCBs account for a significant percentage of field returns in electronic products and systems. Studies on CFF [2 & 3] have found that path formation in a PCB is often along the glass fiber to epoxy matrix interface (Figure 1).
Figure 1: Schematic describing CFF growth [3].
Delamination along the fiber-resin interface can occur as a result of stresses generated under thermal cycling due to coefficient of thermal expansion (CTE) mismatch between the glass fiber (CTE = ~5.5 ppm/°C) and the epoxy resin (CTE = ~65 ppm/°C) (Figure 2). CFF can take place in the plated through-hole to plated through-hole (PTH-PTH), PTH-plane, and trace-trace geometries.
Figure 2: CFF growth path along the glass fiber and resin interface [3].
A two-step model was developed to explain the growth of conductive filaments at the resin-glass interface in PCBs [1 & 3] where degradation of the resin-glass interfacial bond first occurs, followed by an electrochemical reaction. According to Lando [2], the path required for the transportation of metal ions formed by the degradation of the resin-glass interfacial bond results from the mechanical release of stresses, poor glass treatment, hydrolysis of the silane glass finish, or stresses originating from moisture-induced swelling of the epoxy resin.
Path formation was reported to be independent of bias; however, humidity was identified as a contributing factor towards degradation. After path formation, the PCB is viewed as an electrochemical cell. In this cell, the copper conductors are the electrodes, the absorbed water is the electrolyte, and the driving potential for the electrochemistry is the operating or test potential of the circuit. The electrode reactions for the metal migration are:
At the anode:
Equation 1:
Equation 2:
At the cathode:
Equation 3:
Pathway Formation in CFF
In PCBs, one manner in which the pathway between conductors is formed is through chemical hydrolysis of the silane glass finish or coupling agent. Past work has shown that the glass epoxy interface absorbs five to seven times more moisture than the bulk epoxy [5]. A common cross-linking agent used in FR-4 and many other epoxy-based laminated systems is dicyandiamide, or dicy. Dicy and glass surfaces are both hydrophilic. This combination of a hydrophilic surface and cross-linking agent is one of the factors responsible for the degradation of the glass fiber-epoxy resin interface due to hydrolysis. Williams [6] has shown that PCBs manufactured with non-dicy cross-linked epoxy resins are more resistance to CFF failures than PCBs manufactured with dicy cross-linked epoxy resins.
Organosilanes are bifunctional molecules that act as adhesion promoters, crosslink agents, and moisture scavengers in adhesive and sealant products [7]. Silane adhesion promoters act as molecular bridges between two chemically different materials and have been shown to dramatically improve the adhesion of polymeric resins to substrates such as glass, silica, alumina, or active metals.
Page 1 of 3
Share on:
Testimonial
"The I-Connect007 team is outstanding—kind, responsive, and a true marketing partner. Their design team created fresh, eye-catching ads, and their editorial support polished our content to let our brand shine. Thank you all! "
Sweeney Ng - CEE PCBSuggested Items
Nortech Systems Launches Power over Fiber Technology Platform for EMI-Sensitive Applications
04/08/2026 | Globe NewswireNortech Systems Incorporated, a leading provider of design and manufacturing solutions for complex electromedical devices and electromechanical systems, has announced the launch of its Power over Fiber technology platform.
Flexible Thinking: Designing Flex Circuits for Dynamic Reliability
04/09/2026 | Joe Fjelstad -- Column: Flexible ThinkingFlex circuits flex. No surprises there. However, they are also very commonly designed into products because they are thin and offer consistent thickness and dielectric properties, attributes highly prized by present-day product designers of personal electronics. This would include smartphones and, increasingly, wearable electronics for medical monitoring and even fashion.
Understanding Tolerances in Flexible Circuit Design
04/01/2026 | Chris Clark, Flexible Circuit TechnologiesThe challenge with cumulative tolerances is meeting the dimensional requirements for items dimensioned on a drawing or specification for a flexible or rigid-flex circuit. It is critical to understand the fabrication processes and how features are defined when creating your tolerance requirements.
Target Condition: An Exploration of Flooding PCB Layers
04/02/2026 | Kelly Dack -- Column: Target ConditionThe concept of flooding PCB layers with copper has been around for so long, you’d think we’d have it mastered. We haven’t. (Oh, and by “we,” I mean design engineers and the software tools we depend on.) Years ago, PCB artwork was created by hand using light tables, with tape applied to Mylar. Signals were slow, traces were relatively wide, and high-current paths were simply “beefed up” with wider copper. Signal integrity wasn’t yet a driving concern. Today, solid return paths are fundamental to robust design. We understand the importance of continuous reference planes for signal integrity and EMI control.
New, Greener Solutions for Etch: Novel Copper Extraction
03/30/2026 | Richard Nichols, GreenSource Engineering“Novel” is a typical marketing phrase that implies new and unique, but often “novel” actually means an established technology being applied to a new field or application. This, in turn, is often driven by newly relevant external motivation. GreenSource has been working on just such a solution: novel copper extraction, offering a better and greener alternative to traditional LLE control systems for cupric chloride etch.