Adoption of plug-in electric vehicles (EVs) may be slower than many expected, but there is little question the next few years will see adoption accelerate. Now delivery drivers arrive without notice, driving to your door silently in all-electric commercial vans. Many of the major suppliers and stores have already ordered, or are using, these vehicles. Game-changing battery and charging developments are eliminating range anxiety, and autonomous driving controls and safety innovations are in the final stages of building our trust.
A linchpin in the mainstream acceptance of EVs and autonomous driving will unquestionably be public trust in their safety, reliability, and longevity. EVs are, however, considerably more complex in terms of their electronics and control systems than conventional internal combustion vehicles. HumiSeal has spent the past decade preparing protection and reliability solutions for these complex electronics. This article looks at some of the key areas of product development to meet these challenges.
Printed Circuit Board (PCB) Protection/Conformal Coatings
When it comes to all-electric vehicles, PCAs (Printed Circuit Assemblies) can be found throughout the entire vehicle, powering and controlling all the critical systems and beyond. Two decades ago, there may have been two or three PCAs in a vehicle, controlling fuel systems, engine management and possibly braking. EVs and autonomous vehicles require rugged and reliable electronic control of all systems, and PCAs in these vehicles number in the tens and more. We believe that our conformal coating solutions remain the industry standard in protecting these PCAs from damage and failure due to solids and debris, liquid and chemical attack, and humidity and gaseous damages.
HumiSeal has been designing state-of-the-art conformal coatings for nearly 70 years, first producing UV curable coatings more than nearly two decades ago. At that time, UV curable technology was considered the next generation of coatings, mainly due to its advantages including:
- nearly instantaneous, consistent curing
- superb moisture and environmental protection
- high volume/low-cost capabilities, compared with solvent based material.
- little or no VOC content
- smaller manufacturing footprint and nearly zero WIP
Since then, we have evolved from UV40 (specified by nearly all automotive OEMs) to products such as UV50 and UV500. Each product iteration has improved properties to address the ever-changing requirements of the automotive (as well as other) industries.
Increasing Demands for PCB Coatings
Our experiences with the automotive market highlighted the need for improvements to thermal and mechanical performance in PCAs and coatings. Specifically, thermal cycling tests have advanced from as few as ten cycles to current requirements in the thousands of cycles. In some cases, these cycles also have become faster and more extreme in their rates of change and exposure.
Advances in the demands of thermal cycling and mechanical shock revealed the potential for issues under certain conditions. Many current conformal coatings are at risk for delamination or cracking without the tightest of production controls of thickness and curing. While it remained possible to meet the more demanding testing, there was a universal desire for a wider and more forgiving processing range in the coating process.
In response to market needs, our chemists directed their skills toward the design of the next generation of high-cycle resistant coating. This effort resulted in a new family of products, and the first of these is HumiSeal UV500-2. The product retains all the features of the original UV500 material, including:
- excellent thermal stability
- long-term stable electrical properties
- softer and more flexible material with low modulus and low Tg
- good performance in thermal shock testing
UV500-2 was designed primarily for improved thermal shock performance at higher thicknesses, particularly in high meniscus areas between adjacent SMT components where coating thickness can often exceed 125µm. Our research has shown that it is in these inside corners of taller components where coatings tend to pool and exceed standard thicknesses. These thicker areas of coating are most often zones of failure in cycling testing protocols mainly due to inconsistent through curing and resulting micro-cracking. These cracks, of course, result in opportunities for moisture and contaminants to lead to electrical failures.
HumiSeal Thermal Shock Test Boards (comprising a mix of 0603 and 0804 SMT Resistors and capacitors) were coated at 150µm wet thickness (over top of thickness specification to emphasise any deficiencies in high thickness areas) and cured, then stored for five days at 45˚C, and then allowed to cool to ambient temperature 21˚C.
The boards were subjected to 750 cycles of thermal shock using an Espec TSE-11 Thermal Shock Chamber, -40C to 85˚C, 15-minute dwell. Inspection of the boards was at 30x magnification every 250 cycles.
No observable defects were seen at any stage of the testing.
Thermal and mechanical shock requirements for PCBs are expected to continue to increase in demands in key industries including automotive and white goods among others. The ideal protective coatings will combine superb protection, high throughput capability, and resistance to cracking under cycling conditions. HumiSeal UV500-2 is the latest product in the HumiSeal UV curable line and has been designed and tested to meet these exact needs.
As a supplier of all major forms and chemistries of conformal coatings, HumiSeal can help you with an unbiased approach to evaluating your application and process. We’ll show you how to maximise efficiency, minimise cost, and improve product reliability. Our outstanding manufacturing and technical support groups can provide your organisation with reliable global supply, unmatched quality, and superior technical support.
Electronics Vibration Resistance
All-electric vehicles’ electronics, as mentioned above, must be protected from typical contaminants such as debris, liquids, and gases. However, there is another potential threat to printed circuit assemblies within the automotive industry and that is vibration or mechanical shock. EV circuit boards commonly are populated with large, high-energy components including capacitors. These components are especially susceptible to damage to fragile solder connections due to vibration inherent in driving conditions. HumiSeal has developed several products, including UV20 Gel, designed to prevent damages due to vibration and mechanical shock conditions. These materials are soft but rugged polymers that can be applied on high-volume automated equipment typically found in automotive PCA manufacturing. HumiSeal UV20Gel has been subjected to extensive testing and has proven successful in protecting PCA components from vibration and environmental conditions when traditional conformal coatings alone are not up to the task. This protection depends on the polymer maintaining tensile and elongation strength and flexibility characteristics over time. Our R&D teams recognised the need for data regarding performance over time and under temperature and humidity conditions typical to the automotive industry. The data taken from these tests shows that the product demonstrated consistent tensile and elongation properties when tested at continuous operating temperatures as high as 125°C for 400 hours and combined conditions of 85°C and 85% RH for up to 2000 hours.
Have you had failures of PCA components due to vibration or mechanical shock failure? Are your components going to require long service life in equipment prone to vibration? Using UV staking materials means accelerated testing times, successful product launches, and PCA components that will stand the test of time.
Contact HumiSeal for more information.