What is Conformal coating? it is a common question in the mind of PCBA professionals. Conformal coating is a thin polymeric film coating on a Printed Circuit Board to protect the electronic components mounted on boards from environmental extremes.
Normally the thickness of polymer film is 25-75µm thick (50µm typical). The purpose of conformal coating is to protect the electronic circuitry against dust, moisture, salt, chemical, and varying temperatures.
What is conformal coating? Why do I need Conformal Coating?
In production when we manufacture the electronic product its performance and reliability are up to mark. But this product is used in extreme environmental conditions like dust, salt, moisture, chemicals, etc. Can start corrosion and cause electrical failure and reliability issues.
The electronic device may suffer degraded accuracy that impacts the life and performance of the product and also cause customer dissatisfaction.
– Insulating properties can allow a reduction in PCB conductor spacing.
– Can help eliminate the need for a complex, sophisticated enclosure.
– Completely protect the assembly against chemical and corrosive attacks.
– Minimize environmental stress on a PCB assembly.
– Eliminate performance degradation due to environmental hazards
– Improve performance and reliability of products subject to environmental conditions
Which Type of conformal coating is Right for My PCB?
The selection of PCB conformal coatings material depends upon the application and required functionality of the electronic product. It is the most critical decision of a process engineer.
The selection criteria include what we want to protect (e.g. Moisture, Chemicals), at what temperature the device will operate, what are the physical, chemical, or electrical requirements of the coating material, etc.
Based on the above factors the selection of material can be done and it can be one of acrylic, polyurethane, silicone, epoxy, etc.
Which industry requires Conformal Coatings?
The concept of conformal coating on PCB was developed through research to meet the military demands. Due to the latest developments in the electronics sector, the conformal coating is mainly used in industries like Aerospace, Automotive, military, and marine where accuracy and reliability are most important.
Below is the list of companies where the application of conformal coating for electronics is recommended due to accuracy and product reliability.
– Aerospace industries
– Industrial Controls
– Automotive industries
– Medical equipment
– Telecoms industries
– Deference equipment supply industry
What are Methods of conformal Coatings?
Based on your volume and product requirements an appropriate method of printed circuit board conformally coated can be used. For inspection aids in all modern electronics conformal coating contains a fluorescent dye. Below are common methods of coatings
The following are common application methods mainly used for the conformal coatings process
Brush coating – The simple conformal coatings for circuit boards application technique is coating through a brush. This application method is mainly used after the rework and repairing of the circuit boards and suited for small production runs.
Spray application coating – The Spray application conformally coated can be divided further based on its usage. Manual Sparing is done through a spray gun manually for low volume and automated spraying done by machines where the PCB is placed on a moving conveyor for large volumes.
Conformal coating dipping – Dipping conformally coated is mainly used when doing coating on both sides and circuited board dipped and withdrawn into the coating solutions.
Selective coating by machine – This application is performed by programmed automated robots spraying on a very specific area for the circuit board.
How do I measure conformally coated thickness?
The thickness of conformal coatings for circuit boards recommended by the IPC standards is 50–210 μm (0.0020–0.0083 in).
There are several ways to measure the thickness of the conformal coating on printed circuit boards but they fall into two categories: wet film and dry film.
Wet film conformal coating thickness measurement: – This measurement is applicable when the coating is still wet. For thickness measurement, wet film gauges are used.
Dry film conformal coating thickness measurement: – The fastest method of measuring the dry film thickness is using eddy currents. This system works by placing a head-on PCB conformal coatings surface.
The test coupon method is also used for thickness measurement and can be kept as a permanent record of performance.
How do I do conformally coated PCBA testing?
For reliability testing one can perform the adhesion test described in the IPC-TM-650 2.4.1. On a frequent basis for each new batch of the coating.
Basically, this test consists of scarifying the varnish, applying the adhesive tape, and removing it. To pass the test, no coating should stick to the tape.
What Are The Most Common conformally coated Defects?
What is Conformal Coating defects, below are the list of most common Conformal Coating defects list
Capillary Flow – This PCB conformal coatings defect is also known as scavenging in which due to low viscous high surface tension, or excess coating amount migrate one area of printed circuit boards to another causes the uneven coating layer.
Cracking – Cracking is observed in layers of the coating due to thicker coating, thermal resistance, or quick curing.
De-Wetting – When the conformally coated is not evenly layered on printed circuit boards due to uneven application, not properly mixing the parts material, residue on surfaces, etc.
Delamination – in this defect the coating layer lifted away, unable to protect the circuit board. The main reasons for these defects are quick curing, the coating on contaminated surfaces or not adhering to the previous coating.
Orange Peel– when the conformally coated on PCB layer is very dull and looks like orange peeling of the skin. The main contributing factors are coating on too hot a surface, the local environment is too dry when activity executed, or improper solvent ratio.
Bubbles, Pinholes, and Foam – when Bubbles trapped inside the conformally coated layer forms bubbles, and if bubbles burst makes Pinholes in the layer. The main reasons for such defects are the viscosity of solvent too high, the coating is too thick, and not applied properly.
Methods Of Drying Or Curing conformally coated?
There are a lot of drying and Curing methods of Conformal Coatings of printed circuit boards. Few of them are listed as per below
Heat Cure / Evaporation Cure Coating – Solvent-based coatings cured when exposed to a certain temperature by evaporation of the solvent.Suitable for most applications.
UV (Ultraviolet) Cure – Ultraviolet light-curing becoming more popular due to faster curing speed for large volumes in industrial requirements such as automotive and consumer electronics.
Moisture (Humidity) Curing:- Silicone and Urethane resins get cured by the Moisture (Humidity) Curing method.As the resin and forms a polymer when exposed to Moisture.
What are Conformally coated PCB removal methods?
Sometimes need component replacement due to damage for repairing the printed circuit board. To do this activity require the removal of a conformal coated layer.
According to IPC below methods are recommended to remove the conformal coating in PCB without any quality compromise.
Thermal or Burn‐through method –
Grinding or Scraping method
Where to buy conformal coating?
Where to buy conformal coating is a very important question for small project owners because it was normally used in bulk for industrial usage.
You can buy the conformal coating online from Amazon portal