Engineering Sales Representative
Adhesives are often expected to hold up under significant environmental stress. Heat poses unique challenges that can alter the chemistry and durability of a material. One attribute used to better understand what an adhesive can endure is glass transition temperature (Tg). Scientific journal
Nature Communications defines Tg as “the transition into a brittle glassy state, making [Tg an] accurate prediction for conjugated polymers crucial for the design of soft, stretchable, or flexible electronics.” It’s at this temperature, or more often temperature range, that the free volume (gap between the molecular chains) increases by 2.5 times. In short, knowing the glass transition temperature of a material indicates when the material changes from a rigid state to a more flexible state, and vice versa.
Achieving a high Tg often requires a heat cure and can be impacted by moisture, making temperature and humidity control an important part of the production process. Other attributes impacted by Tg include coefficient of thermal expansion (CTE), die shear, lap shear, and modulus.
By observing how a material’s physical properties change across a particular temperature range, lab technicians can calculate Tg. There are a variety of available test methods, each with slight variations that can impact results. Using more than one method is common for quality control or research situations.
Working with an experienced lab is recommended, as they can identify the right test or combination of tests that best suit your application needs. ResinLab, a sister company of Ellsworth Adhesives, offers thermal analysis testing including glass transition temperature with both DSC and TMA methods.
Glass transition temperature plays an important role in the encapsulation process for a variety of industries. For example, an application that experiences extreme weather conditions will be subject to very hot or very cold temperatures, which can impact the strength of an adhesive bond. If a high degree of adhesion is desired at high temperatures, a polymeric system that provides a high Tg is the best option. The Tg is also important when considering the coefficient of thermal expansion (CTE). At the Tg, the coefficient of thermal expansion shifts from a lower value to a higher value. This expansion can lead to components on a circuit board being “popped” off of the board. Selecting a product with a Tg greater than the upper limit of an electronic part's thermal exposure can limit the likelihood of this occurring.
Similarly, electronic encapsulation sometimes requires Tg values below the lower limit of an electronic part's thermal exposure. These products tend to be softer and more pliable. Although they have higher CTE values, they generally lack the force required to break components off of a circuit board.
Electronic Encapsulation Application Examples:
Examples of Epoxies for Electronic Encapsulation:
|Manufacturer||Product Name||Glass Transition Temperature (Tg)|
|Henkel Loctite||STYCAST 2850GT||≤111 °C (depending on hardner)|
|Parker LORD||Thermoset EP-830||175 °C|
|ResinLab||ResinLab EP1350||203 °C|
|ELANTAS PDG||Epoxylite® E 5302||230 °C|
Typically, the glass transition temperature will be located on a material’s technical datasheet (TDS) provided by the manufacturer. Ellsworth Adhesives offers a library of technical documentation including safety data sheets, technical data sheets, REACH, and RoHS documents for all products offered both on and offline. If the glass transition temperature is not provided in the technical documentation our team can reach out to the supplier for more detail, or coordinate with our sister company ResinLab® to perform lab tests for a more complete picture of the material.
With a host of other chemical attributes to consider, sometimes an expert’s assistance is needed. The Ellsworth Adhesives team of Glue Doctors® draws from over 800 years of combined experience in chemical, electrical, mechanical, and aerospace engineering. They are equipped to help identify your application needs and select the right material.