What is Conformal coating ? it is a common question in the mind of PCBA professional. Conformal coating is a thin polymeric film coating on Printed Circuit Board to protect the electronic components mounted on boards form environmental extremes.
Normally the thickness of polymer film is 25-75µm thick (50µm typical).The purpose of conformal coating is to protect electronic circuitry against dust, moisture, salt, chemical and varying temperatures.
Why do I need a Conformal Coating?
In production when we manufacture the electronic product its performance and reliability is up to mark. But this product used in extreme environment conditions like dust, salt, moisture, chemicals etc. Can start corrosion and cause the electrical failure and reliability issues.
The electronic device may suffer degraded accuracy that impact the life and performance of product and also cause of customer dissatisfaction.
Which industry requires Conformal Coatings?
The concept of conformal coating was developed through research to meet the military demands. Due to latest developments in electronics sectors the conformal coating is mainly used in industries like Aerospace, Automotive, military and marine where accuracy and reliability is most important.
Which Type of Conformal Coating is Right for My PCB?
The selection of conformal coating 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 includes from what we want to protect (e.g. Moisture, Chemicals), at what temperature device will operate, what are the physical, chemical or electrical requirements of the coating material etc.
Based on above factors the selection of material can be done and it can be one of acrylic, polyurethane, silicone, epoxy, etc.
What are Methods of conformal Coatings?
Based on your volume and product requirements appropriate method of printed circuit board coating can be used. For inspection aids in all modern coatings contains fluorescent dye. Below are common methods of conformal coatings
- Brush coating
- Spray application coating
- Conformal coating dipping
- Selective coating by machine
How I measure conformal coating thickness?
The thickness of conformal coating recommended by the IPC standards is 50–210 μm (0.0020–0.0083 in). There are several ways to measure thickness of conformal coating on a printed circuit boards but they fall in to two categories wet film and dry film
Wet film conformal coating thickness measurement: – This measurement is applicable when coating is still wet. For thickness measurement the wet film gauges are used.
Dry film conformal coating thickness measurement: – The fastest method of measuring the dry film thickness is system using eddy currents. This system works by placing a head on conformal coating surfaces.
The test coupon method is also used for thickness measurement and can be kept a permanent record of performance.
How I do Coating reliability testing ?
For reliability testing one can perform the adhesion test described in the IPC-TM-650 2.4.1. On frequent base for each new batch of coating. Basically, this test consists in scarifying the varnish, in applying an adhesive tape and in removing it. To pass the test, no coating should stick to the tape.
Further reading
