OPTOLINQ TMC-688L | Transparent Mold Compound

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
  • Low lumen decay
  • Superior moldability and reliability
  • For low stress molding applications

Product Description

OPTOLINQ™ TMC-688L is an optically clear epoxy molding compound specifically designed for the encapsulation of applications that require low lumen decay and low-stress molding. Its low modulus and reduced glass transition temperature (Tg) ensure reliable performance in environments with moderate temperature demands.

OPTOLINQ™ TMC-688L offers excellent moisture resistance, maintaining performance even in high temperature and humidity conditions. TMC-688L stands out with its superior moldability and reliability, ensuring high quality and precision in optoelectronic device molding. A variant of TMC-688L is also available with a higher modulus associated with an elevated glass transition temperature.

OPTOLINQ TMC-688L comes in different sizes to meet various mold design requirements. Contact us for custom sizes or other specific requirements.

Key Features

  • Low Modulus: The low modulus of TMC-688L reduces mechanical stress on delicate components, preventing damage and improving device longevity.
  • Low Moisture Absorption & Excellent Moisture Resistance: Effectively prevents moisture ingress, safeguarding long-term reliability.
  • Reliable Under Harsh Conditions: Maintains consistent performance in environments with elevated temperature and humidity.
  • High Adhesion & Low Stress: Provides strong, durable bonding with minimal internal stress, reducing the risk of delamination or cracking.

Typical Applications

  • LED indicative devices
  • In/outdoor Display
  • Backlight Source
  • White light products

Versions Available

  • Standard low modulus optical molding compound - TMC-688L
  • High glass transition temperature - TMC-688H

Alternative to: XX-830 Series, XX-831 series

Product Family
TMC-688L  

Catalog Product

Unlike other products we offer, the products listed on this page cannot currently be ordered directly from the website.
TDS, SDS & Technical documents

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.
 1.25 - 1.30
Physical Properties
Spiral Flow @ 175°C 170 cm
Mechanical Properties
Flexural Modulus
Flexural Modulus @ 25°C 3050 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
 120 N/mm2
Molded Shrinkage 1.5 %
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.
 75 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.
 190 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 @ 150°C 25-60 Sec
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.
 115 °C
Curing Conditions
Curing Schedule
Curing Schedule
Curing schedule is the time and temperature required for a mixed material to fully cure. While this applies to materials that cure with heat, there are also other materials that can be cured with UV.

Even though some materials can cure on ambient temperatures, others will require elevated temperature conditions to properly cure.

There are various curing schedules depending on the material type and application. For heat curing, the most common ones are Snap cure, Low temperature cure, Step cure and Staged cure.

Recommended cure type, schedule, time and temperature can always be found on the Technical data sheets.
Cure Time 2.5-4 min
Transfer Time 75 s

Additional Information

OPTOLINQ TMC-688L Series Technical Specifications

Property Unit TMC-688H TMC-688L
Transmittance at 400 nm (1 mm) % >85 >85
Pellet Color – White White
Specific gravity – 1.25–1.3 1.25–1.3
Spiral flow at 150 °C cm 170 ± 70 170 ± 70
Glass transition temperature (Tg) °C >145 >115
Coefficient of thermal expansion, α1 ppm/°C 60 ± 20 75 ± 25
Coefficient of thermal expansion, α2 ppm/°C 180 ± 20 190 ± 20
Gel time at 150 °C s 25–60 25–60
Mold Shrinkage % <1.5 <1.5
Flexural strength MPa >120 >120
Flexural modulus GPa 3.55 ± 0.25 3.05 ± 0.15

Processing Instructions

  • Before use, allow TMC-688L to reach room temperature (20±5 °C, 40±15% RH) for a minimum of 24 hours for larger pellets and 12 hours for smaller ones, ensuring the bag remains unopened to prevent moisture contamination.
  • For TMC-688L in larger sizes, preheating can be performed using standard RF equipment. Preheating must be done slowly to achieve uniform temperature.
  • Apply an outer releasing agent, such as silicones or fluorinated compounds, to the mold surface to facilitate easy release from the mold dies.
  • Prior to molding with TMC-688L or any new material, the mold should be cleaned thoroughly. To prepare the mold, the initial three shots should be cured for 5–10 minutes. After this initial preparation period, you can reduce the curing time to a level that provides sufficient hot hardness for effective release.

Storage and Handling

OPTOLINQ TMC-688L is available in pressed pellets in a wide range of sizes to meet specific customer needs. To ensure product integrity, keep it away from oxidizing materials. For long-term storage, maintain a cold environment, ideally at –10°C or lower. The shelf life under this condition  is 6 months.