As we all know, the continuous progress of electronic equipment and circuit technology, the peak of engineering art in the design, development and manufacture of tavulatu di circuitu stampatu (PCB) hè statu testimone di e persone di u mondu sanu. Our planet is full of highly intelligent machines, automated robots and scientific marvels, and of course, there are plenty of PCBS in every corner of the planet, no matter what country or city it is. Tuttavia, questi PCBS differenu in funziunalità, cumplessità, costu di fabricazione, qualità è affidabilità. This article focuses on the last two points, the quality and reliability of PCBS.

Iè, i clienti putenziali volenu sempre l’elettronica di alta qualità, ma questu hè assai caru è pò comportà processi di fabbricazione cumplessi. In u prucessu cumplessu di fabricazione, assemblea è prova di PCB, ci hè un prucessu assai impurtante chjamatu “revestimentu conformale” di PCB. Stu revestimentu conformale hè assai impurtante in PCBS in termini di qualità è affidabilità.

What is conformal coating and its importance:

Conforming coating, an ultra-thin protective coating of polymer film, can be used in conjunction with assemblies mounted on assembly surfaces to protect assembly leads, solder joints, exposed wiring, and other metal points on the PCB surface from corrosion, dust, or chemicals due to various operating or environmental conditions.

The conformal coating can be as thin as 25 microns and “conforms” to the shape and component layout of the circuit board. Cum’è l’accennatu sopra, a ragione per l’applicazione di un rivestimentu conformu à a superficie (in cima è in fondu) di un PCB hè di prutege u PCB da cundizioni ambientali esterne avverse, aumentendu cusì a vita di serviziu di u PCB è di l’attrezzatura elettronica assuciata.

Like high temperatures found in industrial, factory, and high-power electronics, these PCBS with conformal coatings can withstand extreme temperatures. Similmente, l’attrezzatura elettronica installata in e zone / zone vicine à u mare o l’oceanu pò esse affettata da alta umidità, cume l’attrezzatura navale elettronica di navigazione pò esse soggetta à corrosione / erosione chì pò purtà à l’ossidazione di metalli. Similarly, in microbiology laboratories and the medical industry, sensitive electronic equipment can be exposed to toxic chemicals, acidic and alkaline solvents that can accidentally spill onto a PCB, but the PCB’s “conformation coating” will protect the PCB and components from fatal injury.

Cume applicà un rivestimentu conforme?

In fact, the method of applying “conformal paint” in the right way is so important that careful consideration must be given to how conformal paint is applied. It is as important to choose suitable conformal coating materials.

The main factors determining the proper application of conformal coatings are:

1- Spessore di vernice

2- The level of coverage achieved

3- The degree of adhesion of paint to wood panels and their components.

There are five methods for applying conformal coatings:

1- Paint by hand with a brush

2- Rivestimentu in aerosol

3- Atomizing spray gun coating

4- Automatic dip coating

5- Automatic selection of coating

Metudu di curazione / asciugatura di rivestimentu conforme:

Conformal coatings themselves can be classified according to the drying and curing methods used after conformal coatings are completed. These methods are:

1- Heat/heat curing: Conformal coating is dried at high temperature. Drying rate is much faster than normal room temperature drying/curing.

2- Curingu di cundensazione: U revestimentu conformale di PCB hè seccu à temperatura ambiente, l’umidità in l’atmosfera rallenta u prucessu di curatura o di asciugatura.

3- ULTRAVIOLET (UV) curing: Here PCB with conformal coating is exposed to UV radiation. The uv energy determines the curing speed of PCB conformal coating

4- Curazione di l’ossidazione: In questu metudu, i conformatori PCB sò esposti à un ambiente à l’aria aperta cù grandi quantità di ossigenu atmosfericu, chì aiutanu à l’asciugatura / curatura di conformatori à basa di solventi

5- Catalytic curing: This is the process of curing conformal coating in which two materials are fused together, one of which is conformal coating. Una volta chì u revestimentu hè fusionu cù altri materiali catalizatori, u prucessu di guarigione ùn pò esse fermatu finu à chì hè cumpletu.

Classification of conformal coatings:

There are five main conformal coatings used: acrylic resin, epoxy resin, silicone, polyurethane (PU) and polyparaxylene coating.

L Resina acrilica (AAR):

Acrylics are ideal for (low-cost and high-volume) common electronics because AAR is inexpensive and can be easily applied to PCB surfaces by brush, dip, and manual or automatic spraying, reducing turnaround time and producing cost-effective products.

sviluppi:

1 – low cost

2- Easy for manual or automatic robot applications

3- Easy to rework

4- Excellent moisture protection

5- Good surface elasticity, can withstand static voltage discharge, and does not react with the atmosphere, therefore helps cure through solvent evaporation

Tu me:

1- Due to the use of atmospheric curing/drying methods for this material, proper ventilation systems need to be ensured

2- Mantenimentu à bassa viscosità

3- Resistenza à l’usura bassa è resistenza chimica

L Epoxy conformal coating (ER) :

Conformal coatings based on epoxy resins can be completed by hand brush, spray or dip coating. A spruzzatura hè raccomandata per volumi più grandi è per volumi più chjucu o prototipu PCBS.

sviluppi:

1- High moisture resistance and good dielectric resistance

2- Excellent chemical resistance, abrasion resistance, moisture resistance and high temperatures up to 150 O C

Tu me:

1-epoxy conformal paint is very hard and rigid and can damage PCB and its components if attempted peeling or removal. Remove the coating by using a hazardous solvent

2- Poor low temperature performance

3- Ritrattazione à curazione elevata

4- Sò difficiuli di rifà

Rivestimentu conformale L Resina di Silicone (OSR):

The softest of the above two types of conformal coatings is silicone resin (OSR) conformal coatings. They are widely used in LED lamp PCBS without reducing light intensity or color change. Ideal for PCB installation at high humidity and exposure to air. Suitable for PCB with high operating temperature and high power

sviluppi:

1- Bona resistenza chimica, resistenza à l’umidità, spruzzo di sale è alte temperature finu à 200 OC

2- Good flexibility makes it resistant to vibration stress on PCB from external environment.

3- Adatta per applicazioni esterne PCB cù alta umidità

U male:

1- Not wear resistant due to rubber properties

2- Can be reworked, but not easily, requiring special solvents, long soaking times and stirring like a brush or ultrasonic bath

3- Low mechanical strength, weak adhesion to PCB substrate

L Polyurethane (PU) conformal coating:

Suitable for PCB applications in automotive, industrial, instrumentation and telecommunications. In aeroespaziale, in particulare, i vapori di carburante si scontranu constantemente cù u corpu principale di apparecchiature elettroniche è cusì penetranu in l’internu è influenzanu u bordu PCB

sviluppi:

1- High resistance to moisture, chemicals (acid and alkali) and wear

Tu me:

1- Dopu un longu tempu di prucessu di curatura cumpletu, tende à diventà giallu à alte temperature per via di u so altu cuntenutu VOC

2- Like silicon, it is not easy to remove completely

L polyparaxylene conformal coating:

This type of coating is suitable for avionics, microelectronics, sensors, high-frequency circuits, and densely populated PCB-based components. It is applied by means of vapor deposition.

sviluppi:

1- Excellent dielectric strength

2- High resistance to moisture, solvents, extreme temperatures and acid corrosion

3- Can be applied evenly with very thin paint.

Tu me:

1- Disassembly/rework is very difficult

2- High cost is the biggest drawback.