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Designing and Building PCBs for Harsh Environments
Continued from previous page
PCBs for Other Harsh Environments
Other than temperature ex-
tremes, PCBs may have to face other harsh environments such as extreme buildup of moisture, presence of ag- gressive chemicals, and presence of toxic vapors in the atmosphere. Harsh environments may also include intense mechanical vibrations, and presence of elements such as salt spray and fun- gus.
Presence of any of the above or combinations could damage sensitive
electronic parts mounted on the PCB. Such harsh environments, together with extremes of temperature are often found in the automotive industry, aero- space and defense applications. One of the most common meth-
ods of protecting a PCB and its com- ponents from harsh environments such as toxic gases and corrosive flu- ids is to encapsulate the assembly in a material the toxic or corrosive ele- ment cannot penetrate. This materi- al must also be electrically insulating and thermally conductive. A variety of resins are suitable for encapsulation of a PCB assembly,
and each has its advantages and dis- advantages. These include: urethane resin (UR), acrylic resin (AR), epoxy resin (ER), silicone resin (SR), and Parylene (XY). While Parylene offers the best resistance to solvents and extreme temperatures, it is difficult to remove, and the chemical vapor deposition process requires special- ized equipment. It is also not good for long-term exposure to the outdoors. Acrylic resin is the most affordable option, and is easy to apply and re- move, but offers low resistance to chemicals, low resistance to abrasion and is generally not suitable for
TM
harsh environments. Urethane resin offers good re-
sistance to chemicals, humidity and mechanical wear, but is difficult to remove, has long cure times and adds the risk of peeling. Epoxy resin pro- vides resistance to moisture and abrasion, chemicals, humidity and excellent performance in harsh envi- ronments. However, it is difficult to remove and shrinks during curing. Silicone resin is resistant to
temperature extremes, highly resist- ant to humidity, corrosion and chem- icals, and adheres well to most PCB components and materials. But, it is the most difficult to remove and strong chemicals are needed. Encapsulation also works best
4 Interchangeable Lenses 1 Innovative Magnifying Lamp
Interchangeable Magnification
for PCBs with components of similar heights. PCBs that have components with highly dissimilar heights are difficult to encapsulate. Heat trans- fer out of the PCB is another factor that concerns designers who have to encapsulate PCBs. Heat sinks and the surfaces to which they attach must remain free of encapsulation for better heat transfer. For protecting electronics from
extreme mechanical vibrations, the usual technique designers follow is ruggedization. This involves encas- ing or mounting the PCB assembly or anything that the vibrations may damage in a separate casing with ad- equate cushioning to prevent the parts from moving in the event of an impact or during vibration. It is recommended to gather as
much information about the harsh en- vironment that the PCB will be oper- ating in before deciding on the steps necessary to mitigate damaging ef- fects and keep the PCB working. Contact: Rush PCB, Inc.,
2149-20 O’Toole Avenue, San Jose, CA 95131 % 408-496-6013 E-mail:
roy@rushpcb.com Web:
www.rushpcb.com r
26501-LED-INX
Conecsus Offers SMT Metals Waste Recycling Solutions
(2.25x Magnification)
26501-INX-RL5D 5 Diopter Lens
26501-INX-8L5D 8 Diopter Lens (3x Magnification)
Terrell, TX — Conecsus, LLC, offers SMT metals waste recycling services. The company processes wastes con- taining primarily tin, tin-zinc, lead, silver, gold, and copper, and converts them into usable metal products, paying its customers for their metals waste. Conecsus is an ISO 14001 EMS-
26501-INX-RL12D 12 Diopter Lens (4x Magnification)
Email |
sales@aventools.com (4.75x Magnification)
26501-INX-RL15D 15 Diopter Lens
aventools.com
certified recycling company and a re- finer of SMT solder/solder paste wastes and residues. The company’s mission is to provide innovative and high-quality industrial byproducts management, metal recovery and re- cycling options that provide world- class value and service to its cus- tomers. Contact: Conecsus LLC, 106
Phone | 734.973.0099
Tejas Drive, Terrell, TX 75160 % 859-250-5847 E-mail:
tmitchell@conecsusllc.com Web: http:
www.conecsusllc.com
August, 2019
Easy Lens Exchange No Tools Required!
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