Protection for harsh environments
13 March 2009
Designer and manufacturer of precision variable speed drives, Control Techniques, is improving product performance with a dedicated conformal coating line and a UV curable coating chemistry from HumiSeal; UV40.
Control Techniques’ drives are used to control motors in a wide range of applications, from precision machines to high performance elevators and from cranes to fans.
From its UK headquarters, Control Techniques design and manufacture a range of drives that are backed up by a global sales and technical network. The company’s product ranges and service aims to bring benefits to its customers such as:
• A long and productive life through advanced design and simulation methods with comprehensive testing, reliability and build quality
• Drive performance – The Unidrive, Mentor and Commander brands are synonymous with motor performance that have established a reputation for open loop, closed loop and servo drive technology
• Easy to use – all Control Techniques’ products are designed to be easy to fit, connect and configure including functional software tools
• Integrated intelligence – having onboard intelligence can significantly increase the overall system performance
However, despite this commitment to quality and reliability, it is apparent that in more demanding operating environments it can be difficult for complex electronic assemblies to continue functioning correctly. Exposure to the elements such as moisture, salts, and corrosive chemicals such as oils or fuels take their toll, and this was a particular issue for one of Control Techniques’ customers who manufactures and installs a range of cranes used by port authorities for the loading and unloading of cargo vessels.
The operating environment for these cranes is such that they are constantly exposed to the worst elements and the operating lifespan of the equipment was severely compromised. The R&D department at Control Techniques recognised that something had to be done and that the properties of a conformal coating solution from HumiSeal called UV40 would make an excellent solution by sealing and protecting, the working electronic control systems from the outside environment.
UV40 was designed to be easy to process and won’t crack under thermal cycling; offering manufacturers a genuine alternative to older solvent based products with none of the problems normally associated with UV curing materials. This is particularly suitable for applications where conditions are notoriously harsh. Other features of UV40 include rapid cure speed, level of processing ease and thermal cycling resistance which have been previously unavailable with UV curable materials.
One of the key benefits of the new UV material is its low viscosity as this dramatically eases processing challenges in terms of being able to uniformly and quickly coat a board and ensure the coating spreads over all required areas. In addition, the UV material is also extremely flexible, particularly in response to thermal cycling duress. This product is also 100% solids (VOC free) and meets all ISO 14001, IPC-CC-830 and major H&S hazardous chemical regulatory requirements. From Control Techniques’ standpoint, the level of approvals was crucial in selecting the right conformal coating, with UL approval a paramount requirement. UV40 was able to meet all of these standards and approval qualifications.
One final benefit that Control Techniques found to be helpful was that UV curing ovens tend to be very compact. This means they occupy far less factory floor space than the kind of equipment and machinery required to cure other types of coating material in a volume production environment.
Control Techniques opted to apply the conformal coating to the board using a system from Asymtek. The SC-300 dispense head is designed to provide non-atomised, selective application of conformal coating materials with three dispense modes in one application head. This technology was selected due to some very particular technical advantages in terms of ease of use and programming. Specifically, it is possible to alter deposition of the coating and precisely programme areas to be coated whilst on the fly. This flexibility ensures accuracy and edge definition, as well as delivering fast coating cycle times.
Dose and irradiance are key concepts when curing UV coatings and are often confused. They are different concepts but closely related together and defined below:
UV irradiance (mW/cm2) is the power or the intensity of the UV energy, which is delivered to a surface per unit area. It is a characteristic of the lamp and geometry of the reflector and does not vary with the speed. The intense focused peak directed under the lamp is referred to as peak irradiance.
UV dose (mJ/cm2) is the total energy delivered to a surface per unit area, passed under a UV light source. It is inversely proportional to the speed under the light source and proportional to the number of exposures or rows of lamps.
Energy is the product of power and time. A low irradiance for a long time does not give the same cure results as a higher irradiance for a proportionally shorter time, due to the differing kinetics of the curing reaction that takes place under the two conditions.
With the material targeting high volume production, HumiSeal UV40 has been optimised for curing in an in-line, high energy, conveyorised curing system.
Through their discussions with HumiSeal, Control Techniques understood that controlling the curing process window is easily quantifiable with a sensing system called a radiometer. This instrument measures the total UV dose and irradiance on four different channels (UV-A, UV-B, UV-C and UV-V) simultaneously, thus ensuring a repeatable and controlled curing process, while monitoring the output of the UV lamps. The procedure is as simple and fast as passing the instrument through the tunnel and removing it at the end, while the radiometer is logging UV dose and energy.
It is extremely important to cure a UV coating within the recommended process window in order to obtain maximum reliability and performance of the coating. It is therefore essential to choose correct UV curing equipment that will enable one to work within this process window.
A product's reliability has the potential to make or break its manufacturer and can be life threatening in many safety critical applications. Conformal coatings have long been used to protect assemblies from their operating environment but can vary hugely in their protective performance. Choosing the right conformal coating and application process isn’t easy and there is no such thing as a ‘perfect’ conformal coating product.
Time and effort invested in getting it right can be amply rewarded by the near elimination of end product failures in the field. And these can be the most expensive, reputation damaging and dangerous problems a company will ever experience. Essentially, if one has to conformal coat boards, it needs to be right. But when one does, customers and profits are protected. By aligning themselves with a material supplier that understands the operating issues and has invested heavily in R&D, Control Techniques can be sure that its range of drives continue to perform in the most demanding environments and deliver real advantages to its customers.
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