Encapsulation Adhesives
Knowing which adhesives to use to protect sensitive IC’s and wirebonds can be a little bit of a challenge! This article provides an overview of the options available to customers, and advises on how to cure the adhesives, what the properties of the cured adhesives are, and the advantages and disadvantages associated with the different options (IKB-013).
In the microelectronics industry, encapsulation adhesives are used solely to protect bare silicon and the associated wire bonds. There are usually two adhesive sets to choose from – heat-cured or light-cured! However, recent advances from Delo have combined the two curing mechanisms so that in certain instances, it is more beneficial to use these newer adhesives.
Dam & Fill, or Globtop!
The “globtop” process consists of dispensing an encapsulation adhesive onto the top surface of the silicon and allowing it to form into a dome that covers both the IC and the wirebonds. The globtop is then cured, whether by heat or by light.
However, as ICs get bigger, the area to be protected also increases, and then the dome becomes too high to control. In this case, a “Dam & Fill” process is then used: a high viscosity encapsulant adhesive is dispensed around the area to be protected, forming a wall or “Dam”. A low viscosity, chemically-compatible encapsulant adhesive is then dispensed into the central area within the Dam, until the whole volume within the Dam is covered – this is the “Fill” process.
As a general rule-of-thumb, Globtop is used for areas up to 2mm x 2mm, and then Dam & Fill takes over.
Heat-Cured Encapsulation Adhesives
The properties of heat-cured encapsulant adhesives are summarised here:
1. Properties of the uncured adhesives
These adhesives come in a range of viscosities depending on the use for which they are designed: low- medium viscosity for Globtop, low viscosity for Fill, and highly thixotropic materials for the Dam. They are normally supplied in 30cc syringes, and dispensed using simple time / pressure systems on X-Y tables – minimising capital expenditure. Because they need to be stored at -18°C or -40°C (and therefore shipped in dry ice), the syringes need to be conditioned to room temperature for up to 60 minutes. Never force the thawing process – this induces moisture into the syringe, potentially leading to voids when cured.
Some encapsulation adhesives need the substrate to be heated up to ~80C in order to improve the flowing behaviour of the adhesives. This is usually not necessary with any of the Inseto materials. In addition, some Dam materials have a relatively low minimum dispense height before they start to slump, especially at the start of the curing process when heat is first added. With Delo’s Dam materials, this is not an issue – tests in the lab have shown that these adhesives are stable up to a height of at least 7mm, and heights of 3mm are standard in production environments.
2. Curing method
These adhesives cure over a wide temperature range: 100°C to 180°C. Picking which temperature to use will be decided by the materials being protected, and the throughput / cycle time required. The minimum cure temperature is usually 100°C, but the adhesives then need 4.5 hours to cure (not including the time it takes for the adhesive to reach the required temperature). At the opposite end of the scale, they can be cured at 180°C for approximately 10 minutes (again, not including heating-up time). Most applications will fall somewhere in between the two – a typical cure schedule is 150°C for 20 minutes. Because the speed of cure can have an effect on the properties of the cured adhesive (too fast and stresses can be induced into the adhesive and materials being protected), for some very thin applications using 100°C can actually be very beneficial, despite the long cure time.
3. Properties of the cured adhesives
Heat-cured encapsulation adhesives offer the highest reliability of all materials. The properties of Inseto’s family of heat-cured epoxies for Globtop and Dam & Fill are summarised here:
- Standard operating temperature range: -65°C to +180°C
- Glass transition temperature (Tg): >170°C
- Coefficient of Thermal Expansion (CTE): ≤25ppm
- Decomposition temperature: >300°C
- Ionically pure: <10ppm Na, Cl, K
- Excellent chemical resistance
- JEDEC MSL Level 1
- RoHS / REACH Compliant
The Tg is very important for High Rel applications in the military and automotive markets, as cycling multiple times across the Tg during the operation of the end-product can have serious repercussions on the lifetime of the part. Every time the Tg is crossed the adhesives softens or hardens slightly, which imparts stress into the adhesive.
Equally important is the CTE, as there are usually multiple CTE’s in a typical assembly (FR4 or ceramic substrate, die attach adhesive, IC, wirebonds, and encapsulation adhesive). Therefore, having a CTE that is as close as possible to the CTE’s of the constituent parts also helps minimise stress, due to the fact that the finished device contracts and expands with (sometimes severe) changes in temperature. The graphic below shows the range of CTE’s possible in a typical application, and illustrates the issues of wire breakages:
Because the majority of these adhesives are used to protect bare semiconductors, it is important that any outgassing from the adhesive is kept to a bare minimum. All the encapsulation products in the Inseto range of materials meet this requirement, with measured ionic impurity levels of <10ppm.
As well as protecting the IC and wirebonds from physical damage, encapsulant adhesives also must be able to withstand a wide range of chemicals, including water (one of the most difficult substances to protect against!). Inseto’s encapsulants all meet the highest level of moisture resistance, JEDEC’s MESL 1 standard. A phenomenon known as popcorning can happen and cause catastrophic device failure. If moisture gets into the encapsulant, it can expand during hot temperature cycling and cause the adhesive to bubble. If this gets too extreme, the bubbles “pop”, just like popcorn!
Equally important is the adhesives’ resistance to a range of chemicals, e.g. those encountered in the automotive industry – oil, petrol, AdBlue, diesel, etc. Perhaps the most invasive “chemical” is water – for example, the printing industry uses a considerable amount of water-based inks, which can cause considerable damage to the delicate electronics in the print heads if proper protection is not provided.
Light-Cured Encapsulation Adhesives
The overall purpose of light-cured encapsulants is the exact same as heat-cured encapsulants: to protect the IC and the wirebonds. The major difference is that the light-cured adhesives do not meet the highest reliability properties of the heat-cured adhesives, so they are used in less demanding applications such as Smart Card manufacture.
1. Properties of the uncured adhesives
Light-cured Dams tend to be highly thixotropic and therefore must be dispensed from a large volume (800Gm) cartridge. Therefore, a pressure tank plus a simple pinch valve must be used with this adhesive, using an X-Y table to manoeuvre the substrate. The (much lower viscosity) Fills are available in 1,000ml bottles, so a pressure tank is required for this also. However, unlike the heat-cured encapsulants, the light-cured ones need only to be stored in cool conditions, at <10C. So significant savings can be made on transport (dry ice) and storage containers.
2. Curing method
These adhesives are cured by UVA light between 320nm to 400nm. High intensity LED lamps must be used, as sunlight will only harden the adhesives and will not provide any bond strength. Cure times are <20 seconds at an intensity of 160mW/cm2. While there is extra investment required for the LED lamps (<£10K), the significant advantage of light-curing over heat-curing is process time. For medium to high volume applications, the added cost of dispensing equipment and LED lamps is soon recouped, and process time and cost is significantly cheaper.
3. Properties of the cured adhesives
While light-cured encapsulation adhesives do not offer the same “highest reliability” that is achieved with the heat-cured adhesives, they are suitable for all other applications.
Light-Fixed, Heat-Cured Encapsulation Adhesives
In keeping with other recent developments in the field of dual-curing adhesives, a light-fixing component has been added to the heat-cured matrix of the High Rel encapsulants to enable fixing in place of the encapsulation adhesive, followed by a subsequent (mandatory) heat cure of the adhesive. This prevents ANY movement of the encapsulant, whether it is Globtop or Dam & Fill, between the initial dispensing process and the hardening of the adhesive.
The curing process is a combination of the two already outlined: UV flash on the surface for 5 seconds at 200mW/cm2, and then oven cure at 150C for 30 minutes. Comparisons against the existing heat-only cured Fills show no degradation in chemical resistance.
Conclusions
For optimum protection for bare semiconductors over extended periods of time in the most demanding applications, the best option is to use heat-cured encapsulation adhesives. They offer significant advantages over light-cured products, and are easier to process (if not as quick!). For less demanding applications, and where volumes are so high that very short cycle times are required, then light-curing the adhesives offers a significantly better choice.
New developments, both recent and in the near future, that combine the best of both worlds, should also be considered.
For further information on our full range of encapsulation, glob top adhesives, please click HERE
Author
Date
Version
Author
Eamonn Redmond
Date
11 October 2025
Version
IKB013 Rev. 3
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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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