It’s easy to take much of the technology in modern electronic devices for granted. But at some stage in every part and component, engineers must make decisions and develop solutions that allow a device to operate and to improve its performance. One example is the materials and requirements that must be considered when making printed circuits.
Printed circuit boards (PCBs) are typically made up of laminates of a non-conducting substrate (frequently, fiberglass reinforced resins) and a thin layer of conducting copper foil. Although PCBs have been around for a long time, the constantly evolving performance of electronics continues to push their development.
Faster Rates, Higher Demands
According to Mark Shields, director of OEM sales and marketing, North America for Nan Ya Plastics Corporation, USA, “The issue that we are addressing is with the demand for higher frequency and faster data transmission rate. There is going to be resulting higher operating temperatures. Our paper tests and addresses the relationship between temperature and electrical performance. In this case, electrical performance is defined as insertion loss.”
All PCBs exhibit insertion losses, which result in the following: an attenuation of electrical signal strength through conduction losses resulting from resistance in the copper conductor, and dielectric losses resulting from the electric field polarization that occurs within the insulating laminate material. With 5G technology, enhanced Internet performance requirements, and next generation CPUs, there is going to be a lot more heat generated. This will require an examination of the impact of heat on insertion loss.
Testing inside a chamber allowed the insertion loss measurements of laminates to be made at elevated temperatures. (Image source: Nan Ya Plastics)
Examining Different Materials
Shields will present a paper titled, “Thermoelectric Performance of Copper Clad Laminate,” on January 31st at DesignCon 2019. In it, he will detail research undertaken at the Nan Ya technology center in Taiwan. “What we did is to choose ten laminate materials—different grades (of resin), if you will, that range from standard loss to ultra-low loss,” explained Shields. “They go from standard loss phenolic epoxy blends to some modified phenolic epoxy blends in our mid-loss, to some PPE and PTFE materials in our ultra-low loss. We have a combination of halogen-free and halogen or lead-free brominated systems,” he added.
The Intel Standard Delta L test was used to characterize the insertion losses. Shields pointed out that the results from the Delta L testing provides engineers a common language and the insertion loss numbers are well understood. “We did a twelve layer stack-up. The layer being measured was layer ten. We had two environments that we subjected the boards to—a high moisture environment (85% relative humidity) and a high-temperature environment (85°C) with conditioning for two weeks,” said Shields.
The results for the moisture tests were not unexpected. “There was not much of a moisture effect—in this case, up to 20 GHz. The lower loss, higher performance materials have lower moisture absorption characteristics. So that was even smaller than the low effects on the standard loss material,” said Shields.
Temperature Effects Were Significant
The effects of elevated temperature were more significant. “There is a correlation with elevated insertion loss at higher temperatures. Measurements were taken at 20°C and then the boards were put into a chamber and heated at a stable temperature of 60°C and at 80°C. Insertion loss measurements were taken at these elevated temperatures. Measurements were taken at 4, 8, and 12.89 GHz, and the conclusion was that there is a temperature effect that correlates to the loss class of the material. The standard loss materials had the greatest increase in terms of percentage. And then progressively, the increase percent decreased as you went from standard loss to low loss and to ultra-low loss. The increase in loss was greater at 80°C than it was at 60°C, and that was found at the three frequencies,” explained Shields.
The purpose of the research and the reason Mark Shields wants to speak at DesignCon are similar. “My goal is to engage with the end users, and the topic of what impact temperature has on loss is an important topic right now,” said Shields. “For signal integrity engineers, when they are designing the next generation stack-ups and circuit designs, looking at the heat that the boards are going to be in means that they need to factor in what the insertion loss is going to be at elevated temperature,” he noted.
Senior Editor Kevin Clemens has been writing about energy, automotive, and transportation topics for more than 30 years. He has masters degrees in Materials Engineering and Environmental Education and a doctorate degree in Mechanical Engineering, specializing in aerodynamics. He has set several world land speed records on electric motorcycles that he built in his workshop.