New Method Improves Barrier Film Testing
A new method of testing the effectiveness of transparent film barriers used to protect sensitive electronic components from moisture damage could help manufacturers better ensure the longevity of their products and enable researchers to develop more effective barrier films.
Created by scientists at the U.S. Energy Department’s National Renewable Energy Laboratory (NREL) laboratory, the NREL Electric Calcium Test, or e-Ca, is 100 to 1,000 times more sensitive than current commercial tests designed to detect small amounts of moisture and is capable of detecting one ten-millionth of a gram of water per square meter per day.
According to the researchers, the new method grew out of a problem encountered while researching and making barrier films.
“We realized we didn’t have the means to test in the sensitivity range we needed,” Arrelaine Dameron, who works in NREL’s Chemical and Materials Science Center, said. To solve this problem, Dameron, along with NREL scientist Matthew Reese and NREL Senior Scientist Michael Kempe, combined preexisting barrier testing technology with their own enhancements.
The new e-Ca assembly is composed of a test card with calcium metal traces that serve as moisture detectors and the barrier film, each sealed inside opposite sides of a metal ‘spacer’ element. The assembly is then connected to custom NREL-assembled measurement electronics inside an environmental chamber that delivers specific combinations of heat and humidity according to testing needs. As water vapor passes through the barrier film, it reacts with the conductive calcium to form resistive calcium hydroxide. This change in resistivity is used to determine the water vapor transmission rate (WVTR), or the rate at which the water vapor permeates the film.
Barrier film testing “is an important part of a very large market,” Reese said. “It’s a very enabling technology. Without the ability to measure the barriers, it’s much more difficult to control them and to be able to say that your product is better than someone else’s product.”
According to the researchers, the new test method is ideal for manufacturers of flexible electronic devices that require a WVTR sensitivity of less than one part per million. Most standard commercial systems can only attain a WVTR sensitivity of 50 parts per million, rendering them inadequate for testing these devices. The new NREL test method is applicable to a variety of barrier films for many different devices, including indium gallium diselenide (CIGS) photovolatic cells, outdoor LEDs and almost all new TVs and cell phones.
“We have devised a way to constantly monitor an infinitesimally small change in water presence,” Dameron said. “We can do it reproducibly by integrating a user-friendly assembly process, and we can do it for many samples simultaneously. This is what makes our test unique.”