Durable Protection for Demanding Automotive Requirements
HumiSeal chemists have been designing state-of-the-art conformal coatings for nearly 70 years, first producing UV curable coatings more than 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
- little or no VOC content
- smaller manufacturing footprint and nearly zero WIP
HumiSeal has evolved from UV40 (specified by nearly all automotive OEMs) to products such as UV50 and UV500. Each product iteration had 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 and white goods markets resulted in consistent advice from OEMs: There needs to be improvements to thermal and mechanical performance in PCBs 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.
Evolution of UV500: Improved UV500-2
In response to market needs, HumiSeal 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.
UV500-2 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 125um. 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.
Thermal Cycling Results UV500-2
Below we present some of the data specific to thermal cycling and crack resistance using UV500-2. It is important to note that these tests were conducted at a coating thickness of 150 microns, well above recommended maximums of 75 to 100 microns. In addition, it is likely that thicknesses on inside corner areas would be substantially thicker, resulting in a demanding and worst-case scenario to test for thermal cycling cracking.
Thermal Shock Performance
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 as above, 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.
Example: Coating Thickness 150µm, of 40 to +85˚C
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 tested to meet these exact needs.
As a supplier of all major forms and chemistries of conformal coatings, Chase Corporation and HumiSeal® can help you with an unbiased approach to evaluating your application and process. We’ll show you how to maximize efficiency, minimize cost, and improve product reliability. Our outstanding manufacturing and technical support groups can provide your organization with reliable global supply, unmatched quality, and superior technical support.
Please contact us today to discuss your application