LOCTITE 3549

Harmonization Code : 3506.91.90.99 | Prepared glues and other prepared adhesives, not elsewhere specified or included; products suitable for use as glues or adhesives, put up for retail sale as glues or adhesives, not exceeding a net weight of 1 kg ; Adhesives based on polymers of headings 3901 to 3913 or on rubber; Other ; Other

LOCTITE 3549

Main features

  • Reworkable Underfill Material
  • Fast Flow Underfill Material
  • Low Temperature Cure

Product Description

LOCTITE® 3549 is a one-component, heat-curing epoxy underfill specifically developed to protect solder joints in ball grid array (BGA) and chip-scale package (CSP) assemblies. The black, reworkable formulation flows rapidly beneath components to reduce stress concentrations and improve reliability during thermal cycling and mechanical shock events. Designed for low-temperature cure processing, LOCTITE 3549 enhances drop-test performance while providing excellent adhesion to both rigid and flexible substrates. The material is particularly suited for electronic packaging applications where long-term solder joint protection and assembly durability are critical.

Key Features & Benefits

  • One-component, heat-curing epoxy underfill.
  • Reworkable formulation for easier component replacement.
  • Fast-flow characteristics support efficient underfill processing.
  • Low-temperature cure capability for sensitive electronic assemblies.
  • Excellent adhesion to rigid and flexible substrates.
  • Provides outstanding protection of solder joints against induced stresses.
  • Improves drop-test and thermal-cycle reliability of BGA and CSP devices.

Recommended Applications

  • BGA underfill applications.
  • CSP device protection and reinforcement.
  • Electronic packaging and assembly operations.
  • Solder-joint reliability enhancement.
  • Assemblies requiring reworkable underfill materials.
Product Family

LOCTITE 3549

Loading pricing…
TDS, SDS & Technical Documents

Technical Specifications

General Properties
Density (g)
1.3 g/cm3
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.
14 days
Thermal Properties
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.
38 °C
Physical Properties
Viscosity
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
2,350 mPa.s

Additional Information

Technical Properties

As-Supplied / Before-Processing Properties

Property Value Unit Condition
Technology Epoxy — One-component underfill
Appearance Black — Liquid
Density 1.3 g/cm³ 25°C
Viscosity (Haake PK100) 2,350 mPa·s 36 s⁻¹, 25°C
Viscosity (Cone & Plate) 2,100 mPa·s Spindle 52, 50 rpm
Filler Content 18 % Typical
Pot Life 14 days 25°C, time to double viscosity
Shelf Life 365 days -25 to -15°C storage
Technical Properties

After-Processing / Final-State Properties

Property Value Unit Condition / Method
Coefficient of Thermal Expansion (Below Tg) 55 × 10⁻⁶ K⁻¹ ISO 11359-2
Coefficient of Thermal Expansion (Above Tg) 177 × 10⁻⁶ K⁻¹ ISO 11359-2
Glass Transition Temperature (Tg) 38 °C TMA, -50°C to 300°C
Storage Modulus 2,000 N/mm² DMA, 22°C to 300°C
Volume Resistivity 8.1 × 10¹⁵ Ω·cm IEC 60093
Surface Resistivity 0.2 × 10¹⁵ Ω IEC 60093
Recommended Cure 5 min @ 120°C — Standard cure schedule
Exotherm Onset 100 - 115 °C DSC analysis

Leading Brands Trust in Our Products and Services

Products that Perform| Knowledge that Serves| Service that Delivers