Flex PCB Corrosion: All You Need To Know

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Oakley Mae

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Flex PCB corrosion and manufacturing errors are the main source of damage to circuit boards.

Corrosion is known to increase the copper track surface resistance, thus reducing current flow.

And in worst cases, corrosion can even stop the circuit board from performing its functions. 

Therefore, you must understand the causes of flex PCB corrosion to resolve the problems.

Fortunately, we have several ways, like using baking soda and a household cleaner to remove corrosion from a flex PCB surface. 

Today’s piece provides important information on flex PCB corrosion, including causes, types, and how to correct the situations.

Let’s get rolling. 

Table of Contents

What Is Flex PCB Corrosion?

Remember, a flex circuit board has a copper layer capable of reacting with oxygen.

This oxidation process that involves a metal bonding with oxygen to form a copper oxide layer is what we call corrosion

The metal oxide is a non-conductor of power, and as it flakes off, the PCB copper track will automatically lose its volume.

As a result, it increases in resistance, thus affecting the board’s performance.

For your information, thin layers of lead, tin, nickel, and copper can corrupt.

However, we have some graphite, silver, gold, and copper alloys that resist corrosion.

Therefore, you’ll find manufacturers take advantage of this and cover the flex PCB copper layer with such metal to eliminate cases of corrosion. 

Potential Corrosion Types of Flex PCB

A corroded circuit board

(A corroded circuit board)

General Corrosion

This is the most common corrosion we know, and we sometimes refer to it as atmospheric or uniform attack corrosion.

It results from a reaction between copper and moisture/oxygen in the atmosphere.

As a result, a copper oxide layer is formed, which limits current transmission through the circuit. 

And while the board maintains its mechanical properties, you’ll notice a color change.

Therefore, this type of corrosion is easy to identify and correct. 

Localized Corrosion

From the name, this corrosion type limits itself to a small section of the flex PCB.

However, it’s available in three types: 

Pitting corrosion: This option manifests as cavities or holes in the copper layer, causing conductive surface deterioration.

Your circuit board might fail as the cavities grow in depth and diameter.

However, the components responsible for this corrosion type might hide the extent of damage, making it hard to identify. 

Crevice corrosion: Crevices under components collect different contaminants like flux.

Therefore, copper will react with such materials causing serious corrosion. 

Filiform corrosion: This corrosion results from the detachment of copper coating.

And when moisture gets through the surface, it reacts with copper causing corrosion that will then spread to other sections. 

Galvanic Corrosion

This is otherwise known as bimetallic corrosion and results from the availability of two dissimilar metals.

In most cases, it occurs between a copper layer and component metal, especially tin or gold plating.

This happens in the presence of corrosive electrolytes and when both metals are in contact with it. 

Dendrite Formation

Copper traces develop dendrites in the presence of moisture and ionic contamination on a circuit board surface.

As a result, your circuit board might develop some circuit board challenges, causing total failure. 

Inter-Granular Corrosion

This corrosion type results from the copper trace grain boundaries having chemicals.

In most cases, grain boundaries contain high impurities levels and are thus prone to this type of corrosion. 

Cleaning Corrosion on Flex PCB

A man cleaning a disassembled PCB with a small brush

(A man cleaning a disassembled PCB with a small brush)

No matter how much your flex PCB corrodes, the good news is that you can always correct the issue.

Fortunately, you’ll need to use cleaning equipment and solutions that are both readily available and affordable. 

However, since the process might involve disassembling the board, only qualified people should be allowed to clean it to avoid causing more damage.

This section focuses on ways you can clean a corroded flex PCB.

But first, let’s look at the material you need. 

Baking soda: This product has abrasive and alkaline qualities that make it possible to clean off corrosion from a surface.  

Household cleaner: We are talking about a phosphate-free cleaner.

This product is an effective corrosion cleaner but can pollute water if you don’t handle it with care. 

Deionized water: The water we use for this purpose must be free from contaminants.

Otherwise, the ions in normal water experience conductive properties that could cause serious damage. 

Oven: One main cause of PCB corrosion is exposure to moisture. Therefore, exposing your PCB to indirect oven heat will dry it effectively. 

Lint-free towel: You can use towels designed from microfiber and lint-free materials to clean moisture from a circuit board. 

Thin, soft-bristle brush: The brush should be soft enough not to scratch delicate components. 

Steps

First, disassemble all circuit board components, chips, and cables.

Secondly, mix one part of baking soda and two parts of water until they form a paste-like substance.

Apply this solution with a soft brush and leave the board to settle for about 20 minutes. 

Next, rinse your circuit board with distilled water to remove any chemicals and impurities from the surface.

Wipe the PCB with a towel and set your oven to preheat to about 170 degrees. 

Place the circuit board in the oven to dry any remaining moisture.

Finally, reassemble all components back to your board and test whether it works effectively.

And if there is still some stubborn corrosion on the board, try using an eraser to remove them. 

Environmental Factors That Cause Flex PCB Damage

A PCB with components damaged

(A PCB with components damaged)

There are factors due to the environment surrounding the circuit board responsible for its corrosion and damage.

These factors include: 

Moisture: A moist surface brings a circuit board into contact with water, and when this water crosses two channels, failure occurs.

Also, high moisture encourages mold growth, resulting in board damage. 

Static charges: When the circuit board gets into contact with carpets or fabric, a static charge is generated.

In most cases, static charges blow off the whole PCB etch. 

Dust: When the dust settles on the circuit board surface, it acts as an insulator.

As a result, it limits heat dissipation from the board, thus causing high temperature and thermal stress. 

Extreme temperature: Extreme temperature, in this case, means both hot and cold temperatures.

For example, if the temperature is high, it’ll warp the PCB substrate, thus affecting linkages. 

Chemical Exposure: Chemicals and fumes are major contributors to circuit board corrosion.

This is common in situations where you store chemicals near circuit boards. 

Pest exposure: A common problem with most warehouses is the presence of pests and animals like rats that can chew circuit board connections.

This might create short circuits or even total damage to your board. 

Handling and Manufacturing Errors That Cause Flex PCB Damage

A clear photo of a damaged circuit board

(A clear photo of a damaged circuit board)

Apart from corrosion, we have different handling and manufacturing errors responsible for PCB damage:

Physical force: Although flex PCBs have more resistance to stress than rigid boards, you still have to protect them from physical force.

For example, dropping them carelessly might damage some components. 

Trace damage: Damage on traces will affect the PCB’s overall performance.

Traces are usually damaged due to dust contamination, lightning strikes, or power surges. 

Faulty components: Any faulty component in a PCB forces it to work ineffectively, thus damaging the board.

Manufacturing and design errors: Flex circuit boards are delicate and must go through strict and careful manufacturing to keep them in shape when bending. 

FAQs

Can corrosion damage your flexible PCB?

Yes, corrosion causes short circuits in the board, which might force voltage surges and damage.

A metal oxide layer sometimes forms, affecting the heat dissipation process.

And when such happens, components are greatly affected. 

Does corrosion affect current?

Yes, corrosion creates unnecessary metal oxides on the PCB surface, which increases its resistance.

Generally, an increase in resistance leads to a reduction in conductivity and current flow.

As a result, your circuit board won’t function at optimum levels. 

Can a corroded PCB be repaired?

When your circuit board corrupts, you’ll have the option of repairing it or buying a replacement.

However, buying a replacement is an extra expense to drain your pockets.

Therefore, PCB repair should be your first alternative.

All you need is baking soda, deionized water, an oven, and clean, and you’re set. 

Final Remarks

Sometimes, the flex PCB in your device might rust and affect the overall performance.

In most cases, the copper layer reacts with oxygen in the presence of a mixture to form an oxide layer.

This layer increases the circuit resistance, thus reducing conductivity. 

Fortunately, you can correct the issues by applying a baking soda solution, as highlighted in this article.

However, as preventive measures, ensure your circuit board is moisture-free and dust-free.