What are CAF issues and how to overcome them ?

Conductive Anodic Filament Issues

CAF Failures

CAF failuresCAF –> First the Formation of Solid Cu Filament between different nets within PCB at different potentials –>follows a glass weave pathway internally in the PCB –>soon acts as dead short –> then possibly it fires up.

Multiple step Process (PCB Internally)

1)Pathway Formation between different PCB Nets internally

a)Separation of glass and resin interface too.

▪Incomplete wetting of initial coating of resin to glass

▪PCB / PCBA Fabrication (Therm / Mech / Chem)

b) Degradation of glass/resin bond – Temp/Humidity

c) As a result, Can be Hollow Fiber

2) Due to Electro-migration-Ionic (EM) down a Pathway –>Subsequently changes from Anode to Cathode

3) Consequently, Growth of Solid Cu Filament –> Cathode to Anode

CAF Failure –> can occur before solid Cu filament formation

Electro-migration (EM) –> Meanwhile, can lead to catastrophic drops in resistance

In the electronics sector, conductive anodic filament (CAF) failure is a prevalent and also developing concern. Although conductive salt containing copper can form within printed circuit boards, which has the potential to be a catastrophic failure scenario (PCBs). Nevertheless, It’s a form of electrochemical migration that occurs from the anode to the cathode sub-surface along the epoxy or glass interface. In addition, The growth of conductive metal filaments across a dielectric medium is further known as electrochemical.

How does CAF look like?


What is Electro-migration (EM) for CAF?

1)The Electro-migration of e and Ions under the influence of applied voltage –> (PCB Internally)

2)Electro-migration of e and Ions Between Via (HWHW)

a)In 2 different electrical nets

b)At different potentials (one hole relative to the other)

3)Must be a electrical pathway between hole pairs

a)not the pure resin

b)but at the glass/resin interface or Hollow-Fiber (microscopic)

c)resin holes between the glass filaments (macroscopic)

Incomplete Resin wetting –> Triple Point

Elements in Addition Needed for CAF / EM Failure

Firstly, Pathway

I.Separation of Glass Fiber / Epoxy Interface

thereafter, Material Fabrication –> furthermore, Incomplete wetting glass/resin PCB + PCBA Fabrication –> Therm / Mech / Chem Stresses Degradation of Glass/Resin Bond (Temp / Humidity)

II. Hollow Glass Fiber? –> Certainly, much better

Later, Moisture

PCB + PCBA Fabrication

Final Part Field Operation, although 

Applied Bias Voltage and then 

Lastly, Operation of Final Part (between Different Nets at Different Potentials)

Because it requires an electrolyte, a higher water content increases the chance of CAF failure. Increased humidity leads to higher moisture content, which decreases CAF performance.

Processes used during fabrication can introduce acid contaminations, which increases the likelihood of CAF formation. The use of some soldering fluxes and the introduction of acid residues during the plating process are examples of this.

Since bias voltage is the force that drives the reaction, a low-voltage bias will significantly decrease the chances of CAF formation. Lower voltages decrease CAF performance as well.

Hollow Fiber Path Formation Example

Hollow Fiber Path formation

Factors influencing electro-migration (EM) and subsequent CAF growth


Proximity of Holes / Features –> Critical


Pre-existing defects such as fracturing, voids, wicking, contamination and misregistration can also create pathways for problematic filaments. You need to be careful when drilling holes so as not to cause damage to the board. Such damage can create these pathways by causing cracks, wicking and other defects. Drill speed, feed rate and other factors influence how likely these issues are to occur. Partial defects such as incomplete bridging between features can contribute as well.

Similarly, Heavier Glass (7628) structures perform worse for EM / CAF Lighter Glass (106) structures can perform worse for EM / CAF . In addition, Glass fiber distribution can cause filament nesting

Type of Glass, Treatment and Resin marriage –> Key

Finally, Environment (End application)

Higher voltage / humidity / temperature –> Extremely Accelerates PCB Processes

Likewise, May Need to optimize for best CAF performance

High temperatures like those from environmental temperature, repetitive thermal cycling and reflow with a high peak temperature create more stress on a board and increase the likelihood of damage as well CAF formation.

(Lamination / Drill / Desmear)

More on Material Influencing Factors for
Electro-migration (EM) and subsequent CAF growth

Do I really need the right Glass/Finish?

Yes !! –> Meanwhile, Passing spacings can go from Especially17 mils to >30 mils

for example = likewise, Supplier A in Country I vs same Supplier A in Country II

Do I really need the enhanced CAF Process at the Material Supplier

Indeed !! –> Whereas, Passing spacings can worsen by 10 mils DHW to DHW

–>On the contrary, Improper wetting of glass filaments –> easy pathways

–>As a result, Triple Point voids –> easy pathways

–>Summing up, All can lead to EM/CAF

Materials –> Pathways

Example of Non-wetted Glass in Hi-Tg Filled Phenolic of a 1501 core in Warp direction

Material Supplier changing Treater Process and Spread Glass to both Warp + Fill

CAF Materials Pathways
CAF Material Pathway

Example of Non-wetted core Glass or classic Triple Point in Mid-Tg Filled Phenolic

Sometimes, Material Supplier Forgot to run Enhanced CAF Process at their Factory

CAF Material Pathways

Same furthermore Example of Non-wetted core Glass but with Large Void in Mid-Tg Filled Phenolic

~Sometimes, Material Supplier Forgot to run obviously Enhanced CAF Process at their Factory

Best Resistant Material Choices CAF Material Cost Adders

a)Preselected Glass Type / Glass surface finish

b)CAF Enhanced Process at Material Supplier

Thus, Some Material Suppliers include Enhanced CAF Process automatically as part of their Standard Process, and then costing structuresome do not

Moreover, Special Glass –> Major Cost Adder of the Two

yet not the Enhanced Process

Other Perspectives

Industry Experts (HLC / Fine Glass / 5-10V Applications)


25 mil –> Most good CAF Resistant Materials should Pass (Glass/Resin?)

20 mil –> Some Risk for good or best CAF Resistant Materials

15 mil –> High Risk for best CAF Resistant Materials

12 mil –> Best CAF Resistant Materials will most likely Fail

Material Suppliers :

Certainly, In any case Better Understanding of variables needed:

–> Glass, Process, Constructions, Better Marriages of Glass/Resin


Find CAF solutions for:

Alternate glass sources with similar performance –> In contrast, Japan Crisis Potential alternate stack-ups for heavy glass

However, Materials that satisfy to demonstrate CAF, LF, ATC + Hi-volt CAF with LF Hvy Cu

Lastly, Extensive CAF Testing Required

Potential Applications Susceptible To
Electro-migration Failure (Hard Leaks)

Summing up,

  1. Automotive Industry

a) Brake Controllers

b) Other Controllers

2.Telecommunications Industry

a) Since, Any circuit with a high impedance therefore it radically affected

b) Phase Locked Loops (control of the system clocks)

c)Analog and RF circuits

and Other Industries

A-D and D-A converters

Cerra Systems is one of the leading PCB manufacturing solutions providers with PCB manufacturing plants located in North America, Asia with certifications for MIL, AS, TS, ISO, & NADCAP. Our products are Rigid, Flex, Rigid-flex, HDI, RF, and hybrid PCBs addressing up to 64 layers and 2 mil technology. In addition, Cerra Systems  Major  PCB Market is Aerospace, defense, Medical, computing, cellular & Industrial.

We manufacture and supply a wide range of Printed Circuit Boards in India from very small, double-sided PCB to high layer count, high-density multi-layer boards to large tabletop size backplanes. We have dedicated and quick-turnaround operations capable of delivering PCB prototypes with a lead time as short as 24 hours. We also offer quick-turn prototyping with a lead time as short as 5 days, depending on the technology and layer counts.

For more details, visit us on – http://cerrasystems.com/

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Argus Sytems (AESPL) –  PCBACable AssemblyBox Build.
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