Harmonization Code : 3907.30.00.90 |   Polyacetals, other polyethers and epoxide resins, in primary forms; polycarbonates, alkyd resins, polyallyl esters and other polyesters, in primary forms : Epoxide resins : Other
Main features
  • Excellent chemical resistance
  • Low thermal expansion
  • Alternative to FP4654

Product Description

LOCTITE® ECCOBOND FP4651 epoxy encapsulant features very low thermal expansion while retaining syringe dispense capabilities. Its low viscosity and 50 micron maximum particle size gives it improved handling properties over FP4650 for fine wire pitch and cavity-fill applications. It is based on FP4450 resin chemistry, therefore exhibiting excellent chemical resistance and thermal stability properties. With such a high filler rate(82% with 50um max filler size), low CTE and warpage it is essentially a liquid molding compound.

LOCTITE® ECCOBOND FP4651 is a top candidate for a drop in replacement of FP4654 that is slowly being phased out. Even though its viscosity is relatively higher, it is still well within the realms of jetting and dispensing so with the right amount of adjustments to surface and needle heat (and even without them) it should work great as an alternative solution.

Recommended Cure Schedule

  • 1 hour @ 125°C plus
  • 90 minutes @ 165°C
Product Family
10cc Syringe 30cc Syringe 55cc Syringe 6oz Cartridge

Catalog Product

Unlike other products we offer, the products listed on this page cannot currently be ordered directly from the website.

Technical Specifications

General Properties
Pot Life
Pot Life
Pot life is the amount of time it takes for the viscosity of a material to double (or quadruple for lower viscosity materials) in room temperature after a material is mixed.

It is closely related to work life but it is not application dependent, less precise and more of a general indication of how fast a system is going to cure.
48 hours
Specific Gravity
Specific Gravity
Specific gravity (SG) is the ratio of the density of a substance to the density of a reference substance; equivalently, it is the ratio of the mass of a substance to the mass of a reference substance for the same given volume.

For liquids, the reference substance is almost always water (1), while for gases, it is air (1.18) at room temperature. Specific gravity is unitless.
Shelf Life
Shelf Life
Shelf life is the amount of time after manufacturing that a product is guaranteed to retain its properties.

It differs vastly per product and it is based on temperature and storage conditions.

The properties can be guaranteed for the temperature and time range indicated on the TDS since those are the ones tested to be the best for the product.
Shelf Life @ -40°C 274 days
Physical Properties
Viscosity is a measurement of a fluid’s resistance to flow.

Viscosity is commonly measured in centiPoise (cP). One cP is defined as
the viscosity of water and all other viscosities are derived from this base. MPa is another common unit with a 1:1 conversion to cP.

A product like honey would have a much higher viscosity -around 10,000 cPs-
compared to water. As a result, honey would flow much slower out of a tipped glass than
water would.

The viscosity of a material can be decreased with an increase in temperature in
order to better suit an application
130,000 mPa.s
Chemical Properties
Ionic Content
Chloride (Cl-)
Chloride (Cl-)
The amount of Chloride (Cl-) ion extracted from the product in parts per million (ppm)
5 ppm
Potassium (K+)
Potassium (K+)
The amount of Potassium (K+) ion extracted from the product in parts per million (ppm)
1 ppm
Sodium (Na+)
Sodium (Na+)
The amount of Sodium (Na+) ion extracted from the product in parts per million (ppm)
1 ppm
Electrical Properties
Dielectric Strength
Dielectric Strength
Dielectric strength is measured in kV per mm and is calculated by the Breakdown voltage divided by the thickness of the tested material.

Those two properties go hand in hand and while Breakdown voltage is always thickness dependent, dielectric strength is a general material property.

As an example, the dielectric strength of Polyimide is 236 kV/mm. If we place 1mm of Polyimide between two electrodes, it will act as an insulator until the voltage between the electrodes reaches 236 kV. At this point it will start acting as a good conductor, causing sparks, potential punctures and current flow.
49.8 kV/mm
Mechanical Properties
Flexural Modulus
Flexural Modulus @ 25°C 14000 N/mm2
Flexural Strength
Flexural Strength @ 25°C
Flexural Strength @ 25°C
Flexural strength, also known as modulus of rupture, or bend strength, or transverse rupture strength is a material property, defined as the stress in a material just before it yields in a flexure test. This is the flexural strength tested at Room Temperature, 25°C
100 N/mm2
Thermal Properties
Coefficient of Thermal Expansion (CTE)
Coefficient of Thermal Expansion (CTE)
CTE (Coefficient of thermal expansion) is a material property that is indicative of the extent to which a material expands with a change in temperature. This can be a change in length, area or volume, depending on the material.

Knowing the CTE of the layers is helpful in analyzing stresses that might occur when a
system consists of an adhesive plus some other solid component.
Coefficient of Thermal Expansion (CTE), α1
Coefficient of Thermal Expansion (CTE), α1
CTE α1 (alpha 1) is the slope of the Coefficient of thermal expansion in a temperature range below the Glass transition temperature (Tg).

It explains how much a material will expand until it reaches Tg.
11 ppm/°C
Coefficient of Thermal Expansion (CTE), α2
Coefficient of Thermal Expansion (CTE), α2
CTE α2 (alpha 2) is the slope of the Coefficient of thermal expansion in a temperature range above the Glass transition temperature (Tg).

It explains the extent to which a material will expand after it passes Tg.
50 ppm/°C
Gel Time
Gel Time
Gel time is the time it takes for a material to reach such a high viscosity (gel like) that it is no longer workable.

It is usually measured for different temperature conditions and even though it does not refer to full cure it is advisable to never move or manipulate the material after it reached its gel time since it can lose its desired end properties.
Gel Time @ 121°C / 250°F 9 minutes
Glass Transition Temperature (Tg)
Glass Transition Temperature (Tg)
The glass transition temperature for organic adhesives is a temperature region where the polymers change from glassy and brittle to soft and rubbery. Increasing the temperature further continues the softening process as the viscosity drops too. Temperatures between the glass transition temperature and below the decomposition point of the adhesive are the best region for bonding.

The glass-transition temperature Tg of a material characterizes the range of temperatures over which this glass transition occurs.
150 °C

Additional Information

Why are there some gelling differences between FP4651 and FP4654?

Looking at the FP 4651 un-cured properties vs "good old FP 4654"  we see some differences which could be related to the "gelling" of FP 4651"

  • FP 4651 has a shorter work life at 25°C (time to double viscosity) than FP 4654 (2 vs 3 days)
  • FP 4651 has a shorter GEL time at 121°C than FP 4654 (9 vs 11 minutes)
  • FP 4651 has a higher silica filler loading (82 vs 80%) and consequently higher base viscosity than FP 4654

This means FP 4651 can have a certain (and smaller) viscosity range for your application and the equipment than FP 4654. A work life of 2 days of FP 4651 still looks nice on paper, but we assume that doubling of such a high(er) viscosity would not fit some well-defined and tight processes.

Heating up the needle to 40C can help to reduce the viscosity, but will also speed up the gelling.