All You Need to Know About B-Stage Epoxy Films

B-stage epoxy films for clean reliable bonding/thermal and electrical conductivity

Most of us are familiar with epoxy adhesives and coatings, especially those of us within the electronics and medical device industries. We have all seen and often used two-component liquid epoxies. They are provided in syringes or pails for dispensing as adhesives, sealants, gaskets, and coatings. There is, however, a lesser known relative that can be cleaner, more consistent, environmentally friendly, and capable of unique properties such as thermal and electrical conductivity. It is known as B-stage epoxy film. 

What are B-stage epoxy films?

B-stage epoxy films are partially cured versions of traditional epoxy resins. B-stage films provide the same function as traditional heat-curing epoxies. Films are positioned at the bond interface, and heat is used to complete the polymerization reaction and bond. They are typically provided as a film sheet or more often in precut shapes and forms with release liners. 

What are the advantages of B-stage versus liquid epoxies?

Utilizing partially cured film epoxies can provide a number of unique properties and advantages in your processes, as detailed in the bullet points below. Specifically, the use of films versus liquids provides nearly perfect thickness control and reliability, which is critical for dielectric and thermal properties in electronics. Moreover, film epoxies can be provided heavily filled for improved electrical and thermal conductivity. Liquid epoxies would suffer viscosity and shelf life issues at these fill levels.

B-stage epoxies

• are clean, with superior accuracy in placement -- adhesive only where you want it
• have superior thickness control -- not dependent on viscosity or application equipment
• are capable of high fill levels for thermal and electrical conductivity
• have precise dielectric properties due to thickness reliability
• require minimal equipment for application
• and are environmentally friendly -- no hazardous exposure or cleanup chemicals required

In what forms are B-stage epoxies supplied?

As discussed earlier, B-stage epoxies are supplied most often in roll or die cut sheet forms supplied with release liner separation. They are available in a range of thicknesses from 25-125µm and with varying thermal and electrical properties as required.

• Roll form or die cut (screen print, die cut, laser cutting)
• Activation temperature range 90°C to 150°C
• Electrically insulating versions
• Electrically conductive versions
• Thermally conductive versions
• Fiberglass or carbon filled versions for mechanical strength

How to apply B-stage epoxy films

• Step 1: Remove rolls or cut parts from a frozen storage area and rolls or parts from “clamshell” packaging

• Step 2: Allow parts to acclimatize to ambient temperature for 1-2 hrs.

• Step 3: Remove release paper liner from 1 side

• Step 4: Apply the adhesive film to the desired part and press firmly. Expose to recommended heat, pressure, and dwell time to complete bond

What are some typical uses for B-stage epoxies?

• Gasketing and sealing in medical end electronics devices
• Thermally conductive bonding of heat sinks in electronics
• Display sealing and binding
• Many more….

Some examples of typical applications include:

• semiconductor packaging for flip chip processes
• wafer passivation and wafer back side adhesion
• optical applications include sealing of LCD glass and flat panel displays
• window mounting in optical sensors and fiber optic bonding in ferrules
• heat sinks on PCBs 

B-stage epoxy films are proven to be cleaner and capable of unique properties across a wide range of applications.

We will be happy to discuss your specific application and needs. 

For more information please contact Resin Designs or HumiSeal.