WMC-G279 | White Epoxy Molding Compound

Harmonization Code : 3907.30.00.40 | Epoxy Mold Compounds containing by weight more than 70 % silicon dioxide

Main features

White transmitting EMC for optocouplers
Balanced moldability and cycle efficiency
Low stress

Product Description

OPTOLINQ™ WMC-G279 is a white, halogen-free, light-transmitting epoxy molding compound developed for photocoupler and optocoupler packages. It is formulated for good moldability and low-stress encapsulation, with a spiral flow of 85 cm and gel time of 22 s at 175 °C. The cured compound provides a glass transition temperature of 180 °C, flexural strength of 155 MPa, and flexural modulus of 16.6 GPa at 25 °C, supporting package integrity during molding, post-cure, and downstream thermal exposure.

For electrical and environmental reliability, WMC-G279 combines low ionic contamination, 0.5% water absorption after PCT 24 h, extract pH of 6.7, and extract conductivity of 40 µS/cm. It also provides volume resistivity of 5.0 × 10¹⁵ Ω·cm at 25 °C, CTI of 300 V, and UL 94 V-0 flammability. Optical performance is defined by 20% transmittance at 2 mm thickness at 940 nm, making it suitable for optocoupler designs that depend on controlled light transmission rather than reflective cavity behavior. For similar optical isolation molding applications, OPTOLINQ™ WMC-G279 can be positioned as a close functional alternative to Hysol GR180T.

Key Features

White transmitting formulation: Supports optical transmission in photocoupler and optocoupler package designs.
Good moldability: 85 cm spiral flow at 175 °C supports practical transfer molding behavior.
Fast gel time: 22 s at 175 °C supports efficient molding cycles.
High thermal stability: Tg of 180 °C supports reflow and thermal cycling robustness.
Low moisture uptake: 0.5% water absorption after PCT 24 h helps limit moisture-driven reliability risk.
Low ionic contamination: Low chloride and sodium levels support long-term electrical reliability.
Electrical insulation capability: Volume resistivity of 5.0 × 10¹⁵ Ω·cm and CTI of 300 V support isolation-focused packages.
UL 94 V-0 flame rating: Meets a common flammability requirement for electronic package materials.

Applications / Suitable For

Photocouplers
Optocouplers
Optical isolators / opto-isolators
Transfer-molded optoelectronic isolation packages
Packages requiring white transmitting EMC behavior
Applications requiring halogen-free EMC and UL 94 V-0 performance

OPTOLINQ WMC-G279 is available in custom pellet dimensions. Contact us for detailed specifications.

Specifications
Additional Information

Technical Specifications

General Properties

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.

1.88

Thermal Properties

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.

180 °C

UL 94 Rating

UL 94 Rating
Flammability rating classification.
It determines how fast a material burns or extinguishes once it is ignited.

HB: slow burning on a horizontal specimen; burning rate less than 76 mm/min for thickness less than 3 mm or burning stops before 100 mm
V-2: burning stops within 30 seconds on a vertical specimen; drips of flaming particles are allowed.
V-1: burning stops within 30 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.
V-0: burning stops within 10 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.
5VB: burning stops within 60 seconds on a vertical specimen; no drips allowed; plaque specimens may develop a hole.
5VA: burning stops within 60 seconds on a vertical specimen; no drips allowed; plaque specimens may not develop a hole

V-0

Coefficient of Thermal Expansion (CTE)
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.	14 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.	53 ppm/°C

Gel Time
Gel Time @ 175°C / 347°F	22 s

Electrical Properties

Volume Resistivity

Volume Resistivity
Volume resistivity, also called volume resistance, bulk resistance or bulk resistivity is a thickness dependent measurement of the resistivity of a material perpendicular to the plane of the surface.

5e 15 Ohms⋅cm

Water Extract Data
Conductivity	0.04 mmhos/cm

Mechanical Properties

Water Extract Data
pH of extract	6.7

Flexural Modulus
Flexural Modulus @ 25°C	16600 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	155 N/mm2

Chemical Properties

Water Absorption

0.5 %

Ionic Content
Chloride (Cl-) Chloride (Cl-) The amount of Chloride (Cl-) ion extracted from the product in parts per million (ppm)	18 ppm
Sodium (Na+) Sodium (Na+) The amount of Sodium (Na+) ion extracted from the product in parts per million (ppm)	10 ppm