Printed Circuit Design & Fab - July 2008 - (Page 36)

EnvironMEnt greener PCB CoATiNgs Balance cost, performance and environmental impact when selecting a conformal coating. by Kent larson Many of today’s circuit boards benefit from the use of protective, yet environmentally “green” conformal coatings that allow them to operate reliably, even in harsh environments. The usage of conformal coatings has been rapidly expanding in recent years, not only in highly demanding applications such as avionics, military and automotive, but also in portable electronics that sometimes face more severe use – and abuse – than you might at first recognize. Conformal coatings have a proven track record of protecting boards from dust and debris, liquids, and contact with a wide range of harsh conditions that they encounter. Such coatings must protect in very cold to very hot environments, and withstand vibrations and mechanical shocks that range from those encountered in automotive engine compartments to personal electronics that are frequently dropped, kicked, run over, and even immersed in the ocean. In all of these conditions, coatings must protect electronics from shorts and other damage. Protective coatings work by closely conforming to surfaces, components, wire bonds and solder joints and forming a barrier to conductive contaminants. Additionally, they electrically insulate and isolate conductors that may be in close proximity to each other. An application of a coating to a PCB is shown in FiGurE 1. Conformal coatings are applied at the end of the assembly process, but like the components on the PCB, these coatings are most often selected early in the design process, based on specific performance requirements. Even with greatly enhanced durability that can come from protecting electronics with a conformal coating, all too often such protection is added as an afterthought or as a last-minute correction to prevent failures brought to light by design-validation testing just before production launch. At this late stage in the game, only limited material characteristics can be considered, and trade-offs between performance, material price and production costs must be made very quickly. Ideally, such durability performance should be designed in from the start. When improved reliability and durability requirements 36 lead to coating choices made earlier in the commercialization cycle, designers can not only factor in board layouts that simplify coating application processes, but also consider the potential environmental and material regulatory aspects of their materials choice. There can be considerable differences in the possible environmental impacts of various coatings, and these differences may factor into the decisions of circuit board companies that want to improve the “green” credentials of their electronics. There are many factors that go into the selection of the best conformal coating for a given application. Cost draws the laser focus of purchasing agents and buyers, and is the bane of suppliers’ sales agents. It is easy to concentrate on the price per kilogram of a material when considering various types of coatings, but that is only part of the total cost of ownership. Even materials that meet performance specifications may differ wildly on the cost associated with delivery, inventory, han- FiGurE 1. Conformal coating operation, photo Courtesy: Precision value and Automation. JULY 2008 ! printEd circuit dESign & fAB

Table of Contents Feed for the Digital Edition of Printed Circuit Design & Fab - July 2008

Printed Circuit Design & Fab - July 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.