Conformal Coating Spraying Complete Coverage Technical Bulletin July 09

     

 

Technical Bulletin July 09 Spraying Conformal Coatings and Spray Conformal coating Processes Complete Coverage Methods Today, several methods for spray application of conformal coatings exist including conformal coating aerosols conformal coating spray booths and automated selective conformal coating spray robots. However, they fall into one of two process categories being complete and selective coverage processing. In part one of a two part bulletin, the Complete Coverage Method will be examined looking at the advantages and disadvantages of the process.

Why choose the conformal coating spraying process? Dipping of conformal coating is the most efficient conformal coating application method available. However, conformal coating spray application is the widest used method in the global electronics industry. The reason that the conformal coating dip process is not used as the main choice is that generally printed circuit boards (PCBs) have devices that must not be conformal coated across the PCB. This can lead to a far more demanding labour process in masking and de-masking, being potentially more time consuming and expensive.

A complete coverage conformal coated spray PCB

Therefore, spraying of conformal coating can often reduce significantly these costs, and the savings and performance depend on the conformal coating spray process selected. Conformal Coating Spray Application Method - Complete versus Selective Coverage Processing Due to the reduction costs associated with conformal coating spraying, the correct selection of the appropriate spray method is critical and is based upon two factors. The first factor is the type of conformal coating spray finish that is required. Different spray processes give alternative finishes and can affect both the long term reliability of the printed circuit board (PCB) and the aesthetic finish of the conformal coating. A completely covered PCB looks and is different for long term reliability compared to a selectively coated PCB (See pictures opposite).

SCH Technologies is a Trading Name of SCH Services Limited  Newburgh Building, McLintock Way, Barnsley, South Yorkshire. S70 6BF    Tel: +44 (0)1226 297711 Fax: +44 (0)1226 297733  www.conformalcoating.co.uk 

A conformal coated automated selective spray PCB The second factor is purely a financial calculation. The difference in costs between a fully automated conformal coating robotic system and a set of aerosol cans is considerable but need to be balanced against the labour costs of masking, demasking and hand processing and the volume of boards to be processed. Therefore, the selection of the correct spray process is an important decision balanced between performance and costs.

SCH Technologies are ISO9001 and ISO14001 certified

          Cove Com mplete erage Metho ods Com mplete cove erage methods include e aerosol an nd   spray booth conformal coa ating techn niques. The confformal coatting is applie ed right acrross the PCB B and any areas that must not be e coated must m be suita ably masked.

Since the conformal coa ating “confforms” to all edges minimising the e slumping effect the performanc p ce of the coating iss superior to o all other methods m whe en tip co overage failures are an n issue. Furth her, the cosmetic fin nish across the PCB will be aesthetically pleasiing to the end user.

Norm mally, the co onformal co oating mate erial is appliied using g an atomissed spray prrocess wherre the confo ormal coatting is spray yed through h a valve or gun by com mpressed airr and is atom mised into tiiny particless whic ch deposit evenly e across the PCB. Due to the atom mising effec ct, the partic cles “stick” to t the area applied, and slu umping, the e effect of the conform mal coatting pulling away from sharp edge es is minimissed.

Co onformal Co oating aero osols are suittable for ve ery low vo olume application whe ere investme ent in confo ormal co oating equip pment is pro ohibitive.

Build d up over sh harp edges using atomised spray and a applying layers forms a com mplete film of conform mal coating from ae erosol or sprray gun

The completed c atomised spray s film (le eft) protectss the tips whereas w a dip d or limited atomised d spray layer can suffe er from slumping and poor p tip cove erage Using g this techn nique the lay yers of confformal coatting are built b up (nominally 2-3 application ns) and the confformal coatting thickne ess is optimissed.

Fu uture Bullettins •

Co onformal Co oating Spra ay booths be ecome eco onomic wh hen the use e of aerosolss reaches > 10 aerosolss per month giving a quick retturn on inve estment.

SC CH Techno ologies offe er •

Confo ormal coatin ng Subconttract Service es

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Globa al supply of Conformal Coating Applic cation Equip pment

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Humisseal Conform mal Coating gs

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Confo ormal Coating Training courses Consu ultation & tro oubleshooting PLEASSE CHECK O OUR WEBSITE FOR DETAILLS

www w.conform malcoating.co.uk

Issue Two T Conforrmal coating g Spraying and a Selectiv ve Spray Co overage Me ethods

  SCH Tech hnologies is a TTrading Name o of SCH Services Limited  Newburggh Building, MccLintock Way, B Barnsley, South Yorkshire. S70 6BF    Tel: +44 (0)1226 29771 1 Fax: +44 (0)12 226 297733  www.con nformalcoatingg.co.uk 

SCH Technolo ogies are ISO9001 1 and ISO14001 certified