Electronic Adhesive Bonding Films | Epoxy Preforms, Thermally Conductive Silicone Adhesive

Adhesive Preforms define custom parts that are cut out of an adhesive film material that can come either thermally conductive, or electrically conductive. However, oftentimes they come as both. In addition, some of these films are supported by carriers. These include fiberglass or polyimide films to ease in handling and assembly. Adhesive preforms offer an alternative to conductive thermal pastes that can be difficult for assembly because of operator inconsistency, or product/assembly inconsistency. 

Benefits of Adhesive Bonding Films in Electronics

Cleanliness, and Cleanup

With adhesive preform films, since these films can be preformed to shape it minimizes the amount of post-cleaning that is required to be done before, and after bonding is completed.

Consistency of Application to PCBs/Heatsinks

Conductive Thermal Pastes can be inconsistent for the sole reason of how its applied. Depending on who/how it is applied. Each operator is different when applying conductive pastes. In addition, thermally, and electrically conductive pastes viscoity changes overtime. On the other hand premade adhesive preforms are made the same way every-time. The thickness, cut-outs, and tolerances of the preform can all be held to +/- .002” in some cases.

No Mixing Time

Since adhesive preforms are 1 part pre-cut parts, there is no need to mix anything unlike some of the conductive thermal pastes available. In our experience, mixing 2 part adhesives can actually be a problem. When assembling sensitive electronics, bonding can sometimes give you only one shot. Its important that that shot is taken with great care.

Overall, preform film materials add a lot of consistency and can lower cost per unit of production, especially in very complex circuit boards, or bonding applications.

Supported Adhesive Bonding Films, or Non-Supported?

Benefits/Drawback of Supported Adhesive Bonding Films

Benefits:

1. Handling

I cannot begin to overstate how much easier handling is with a carrier. Unsupported films can fall apart in your hands because of the lack of support. Cutting should be done on the liners, or with the support of something at all times. Being supported can even help when bonding because it helps during pre-tack, and general handling in the application.

Drawbacks:

1. Cutting

Cutting can be a bit more of a challenge with a supported adhesive film. The reason for this is laser cutting is the preferred method of cutting for complex adhesive shapes. Polyimide or fiberglass can make the cut a little rougher, or harder to cut through.

Epoxy Preforms

The material being preformed allows allows for more uniform bond lines and consistent application of the adhesive across the assembly. When there is many cut-outs and close tolerancing using automated machines can offer an incredible amount of consistency. Applications such as bonding to heat-sinks are common for these films. These films can be laser-cut or die-cut.

Isn’t Laser Cutting a Problem with Adhesive Preforms?

The answer to this question, can be yes, or it could be no. Depending on the complexity of an adhesive preform, and the number required, laser cutting can be a great alternative to prevent expensive tooling cost. When there is a complex circuit board, tooling can become prohibitively expensive. However, it can be true, that adhesive preform materials can be charred or burnt by a laser if the proper care is not taken. With most laser converters they are aware of this issue and ensure that the edges are properly cut, and not burnt.

The Choice Between Laser Cutting, and Die-Cutting

The delineation between laser-cutting or die cutting is often stratified by a number of factors including:

-Complexity of the cut-outs

-How many adhesive preforms are being manufactured

-How big/small the adhesive preform is

-Tolerance requirements(recommended +/- .003’’ for cutouts, +/- .005’’ for locations)*

Availability of Bonding Films/Epoxy Films

Many manufacturers use assembly film options that may be a fit for different applications that require preform adhesive materials. Each adhesive preform material is obviously for different applications. Some are for low outgassing applications, or EMI shielding applications. Many of these films fill the need for a few common problems however:

1. Requirement for a High Enough CTE to accomodate stresses that may occur between the PCB, and the heatsink, or whatever difference of metal.

2. There is usually a requirement for thermal conductivity between the PCB, or circuit board, and the surface it is being bonded to.

3. They usually come in a thin profile such as .011” and below to account for little room to store more heat that may already be present in the application.

circuit board

Electrically/Thermally Conductive Films

5025E ™ by Henkel LOCTITE -unsupported silver filled film- meets MIL-STD-883 Method 5011

ECF561E ™ by Henkel LOCTITE -fiberglass epoxy supported silver filled film

CF3350 ™ by Henkel LOCTITE – unsupported silver filled film

ECF550 ™ by Henkel LOCTITE- unsupported silver filled film

ECF563 ™ by Henkel LOCTITE- unsupported silver epoxy film

TECA CoolSpan by Rogers – unsupported epoxy adhesive film

ARLON Thermabond 99950N008 – unsupported silicone silver filled bonding film

TC8750 AI Technology- unsupported silver filled bonding film- MIL-STD-883 Method 5011

Thermally Conductive Films

5020K ™ by Henkel LOCTITE- polyimide supported filled film

561K ™ by Henkel LOCTITE -polyimide -supported filled film

566K ™ by Henkel LOCTITE -polyimide supported  filled film

563K ™ by Henkel LOCTITE- polyimide supported  filled film

506 ™ by Henkel LOCTITE- unsupported filled film

Thermabond Original 99510N008- unupported thermally conductive film

Thermabond Low Outgassing 99000W008- unsupported thermally conductive film

Epoxy Film Preforms

It is wise to consulate about epoxy film sheet sizes before determining sizes of preforms. With these materials tightly controlled performance characteristics and thickness tolerances availability of size can be tricky.

Storage of Adhesive Films

Storage is an important consideration with these films. Oftentimes these films are required to be stored at temperatures at freezing or sub-freezing in order to maximize the shelf life. This includes when shipping these materials that they are shipped at temperatures required by their datasheets. Our team generally refers to two different types of ice. There is Blue Ice and there is Dry Ice. Blue Ice keeps the package at around 30-45°F, and Dry Ice keeps the package sub-zero fahrenheit.

Converting of Electronic Adhesive Preform Films

At NEDC, we laser-cut or die-cut epoxy preforms to many different custom shapes for our customers.  In otherw rods, we are a laser converter, or a die-cutting converter, and a supplier from many adhesive preform films.  Adhesive Preforms are usually very intricate with many twists, and turns in the cuts. With these challenges, choosing between die-cutting or laser cutting is a tough choice sometimes.

If you have an application that you believe could utilize preforms or assembly films, please contact sales@nedc.com.