Basic Adhesive Types
Basic Adhesive Types: A simple guide to the different adhesive types used in engineering and electronics today (IKB-041).
Basic adhesive types: One Part Epoxies
Depending on the exact chemistry, a one-part epoxy will require a typical curing temperature of between 60 and 150°C. It may also require light curing, which is normally best done with high intensity UV lamps. One-part epoxies afford excellent chemical and moisture resistance. Other benefits include high thermal resistance (more than 200°C) and a high tensile strength (of up to 57MPa), and the higher the cure temperature the stronger the bond formed. As for drawbacks, even with the application of heat, cure times can be relatively long. Light curing is much quicker. Also, once cured, the bond is rigid. Regarding storage, the latest one-part epoxies to join the market require a temperature of less than 10°C and some can be as low as -40°C.
Placement of the adhesive is typically by automated dispenser before the board goes into the pick-and-place machine. A consideration here though is the time between the two activities. If it is likely to be a long time, you may need to assess the epoxy’s sensitivity to moisture.
Regarding storage, the latest one-part epoxies to join the market require a temperature of less than 10°C and some can be as low as -40°C. Curing temperatures vary from 60 to 150°C and curing time will typically be less than an hour.
Two Part Epoxies
These offer bond strengths of up to about 28MPa, are relatively easy to process using a mixing system, have a shelf-life of up to about a year and can be stored at room temperature. In addition, once mixed, they cure at room temperature too. The application of heat can shorten the curing time and, as with one-part epoxies, the resultant bond is relatively inflexible.
Acrylates
Predominantly transparent, these are one-part adhesives and are cured using heat and/or light, have a shelf-life of between six months and a year and, once cured, exposed surfaces remain tacky. At about 30MPa, acrylates are more flexible than epoxies. Storage requirements will vary from 0°C to room temperature.
Two-part Polyurethanes
As with two-part epoxies, these are relatively easy to process and curing can be accelerated with the application of heat. Shelf-life is about six months and, once cured, the tensile strength can be up to 23MPa. Perhaps the biggest drawback to polyurethanes is their low UV resistance (susceptibility to sunlight) and relatively low heat resistance, which tends to be limited to 125°C. This limitation also restricts the max heat curing temperature, capping it at about 80°C.
Anaerobics
These are one-part adhesives that afford a relatively high temperature resistance (up to about 200°C) and tensile strength of about 15MPa. They cure in the absence of oxygen and the presence of a metal (though not all metals) and are frequently used for magnet bonding and thread-locking. Curing is at room temperature and, thanks to recent developments within the adhesives industry, any exposed adhesive (i.e. in contact with air) can be cured using UV light. Storage is at room temperature.
Silicones
Silicones are stored at room temperature, and cure at it too – though very slowly (typically at a rate of about 2mm per 24 hours). Once cured, they remain very flexible and can tolerate up to 600% elongation in some cases. They have a very high temperature resistance (up to about 300°C). On the downside, silicones outgas during curing and, post-cure, the resultant bond strength is not that great; at between 2 and 5MPa.
Author
Date
Version
Author
Eamonn Redmond
Date
01 October 2018
Version
IKB041 Rev. 1
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Author Biography
Eamonn Redmond is a Senior Technical Sales Engineer at Inseto (UK) Ltd, leading the Materials and Adhesives divisions. With nearly four decades of experience in microelectronics, he combines strong technical knowledge with practical commercial insight.
After completing a B.Eng. in Electronics at the University of Limerick, Eamonn began his career at Analog Devices, working as an In‑Line Test Engineer and Process Engineer. During this time, he developed hands‑on expertise in die attach, wire bonding and environmental testing, including burn‑in, temperature cycling and thermal shock. He later progressed to IC Production Manager, gaining experience in wafer‑level and package‑level testing and modern semiconductor production operations.
In the early 1990s, Eamonn moved into technical sales, specialising in die attach adhesives, eutectic solders and materials for wire and ribbon bonding. This role established a strong foundation in adhesive technologies for high‑reliability microelectronic applications.
Since joining Inseto in 1996, Eamonn has supported customers with a wide range of microelectronic materials, including die attach adhesives and encapsulation compounds, alongside substrate materials such as thick‑film inks and thin‑film substrates. He is widely regarded as a key technical resource for customers seeking reliable bonding and encapsulation solutions.
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