Electronic bonding adhesives for design and assembly challenges

We understand that tapes and liquid adhesives not only act as a bonding agent, but also as a sealant or gasket. That’s why we work to find even the smallest leak in bonds so we can help protect vital electronic components.

3M can conduct the following test based on your specific design:

Water seal and ingress protection, IPXX

• Simulated device test that helps determine if your device is suitable for continuous immersion under conditions specified by the ingress protection (IP) rating
• Ability to model narrow bonding areas and identify potential water leaks, helping improve device reliability
• Results depend on design and application parameters such as substrates, adhesive joint geometry and external stress profiles on the adhesive

How can I make my device waterproof?

Waterproof is defined as impermeable indefinitely while, water resistance is impermeable for a specific pressure and time. Our solutions help make your device water resistant. First, it is important to design your device so that there are minimum or no gaps between parts of the housing. Then, it is necessary to select a bonding solution that is soft enough to fill the gaps created by any unmatched surfaces. If the gap is deeper than the thickness of the tape, a thicker tape should be tested. If the gap is too wide or not uniform then consider testing a liquid adhesive. For liquid adhesives, it is important to have no gaps after the liquid adhesive cures. With clamping and ribs to control bond line thickness, there can be air bubbles along the ribs which can result in poor water resistance performance. In particular, special attention needs to be taken for small bond width.

What is the difference between waterproof and water resistance?

Waterproof is defined as impermeable indefinitely while, water resistance is impermeable for a specific pressure and time.

Are all tapes water resistant?

Water resistance depends on your design. It is important to select a tape that is conformable enough to fill the profile variations of the surface you are trying to bond. Acrylic adhesives typically provide a good seal but thickness is important. Soft chemistries typically provide a better wet out over uneven or hard-to-bond surfaces. Some foams like 3M™ VHB™ Tapes have closed cells that help prevent leakage.

To look at water resistance, ingress protection ratings are typically used such as:

• IPX6 – Powerful Water Jets
• Test duration: 5 minutes per face, repeat 2 times
• Water volume: 100 liters per minute
• Pressure: 100 kPa at distance of 3m

At 3M, we know that not every design will use common substrates. We can test to see if the tapes and liquid adhesives being targeted for your application are compatible with your components, so you can keep moving forward.

3M can conduct the following test based on your specific design:

180-degree peel

• Tests our solutions with your unique substrates, such as high surface energy substrates (steel, aluminum, other metals) and low surface energy substrates (plastics, coatings)
• Ability to adjust peeling speed, temperature or both, and thickness of material
• Quick results allow for initial indication and screening for performance

What are the commonly known hard-to-bond substrates?

Substrates that are commonly known to be difficult to bond include: Foam, Graphite, Rubber, Silicone, Metal Mesh, Painted Surfaces, PET Film Polycarbonate with Coating, Polypropylene, Powder-Coated Surfaces.

What kind of substrate treatments can be used in electronics applications?

There are several surface treatments that can be used in electronics applications. In general, these surface treatments do one of two things, they are increasing the surface energy of the substrate or they are eliminating the contamination/providing a homogeneous chemical bonding surface.
Examples include:

Corona

• Dielectric barrier discharge under atmospheric pressure creating oxidation and chain scission
• Improves wettability; Can clean metals and etch surfaces

Flame

• Burning to create oxidation
• Higher treatment level especially on polyolefins; More stable than Corona treatment
• Can clean inorganic substrates such as metals
• Cost effective at high speed/wide widths

Plasma

1. Electrical discharge generated at reduced pressure
2. Wide range of variations; Creates a clean, uniform result
3. Capital intensive

Atmospheric-pressure Plasma:

1. Typically, a helium-based Corona treatment to oxidize the surface
2. With no sparks, reduces risk of damaging electronic parts

How do you “activate” a PSA (Pressure Sensitive Adhesive)?

Achieving proper adhesion of a PSA is done through the following steps:

• Ensure the substrate is clean. Possible cleaning methods include using Isopropyl alcohol (IPA)/water combination or if necessary, a degreaser could be used first, followed by IPA/water solution.
• Tapes should experience a minimum pressure of 15 psi. The intent is to ensure that the tape is in contact with all of the surface that needs to be bonded – even in profile gaps.
• In regard to temperature, typically room temperature is sufficient (typical room temperature 50° - 60°F minimum). Higher temperatures can accelerate wet out but are not required for PSAs. Temperature will not increase final adhesion strength.
• In regard to time, most PSAs typically require 72 hours to reach full bond. The amount of time needed to reach full bond will depend on the firmness of the PSA. Typically, 50% of the bond strength is obtained after 20 minutes, 75% after 1 hour and 90% after 1 day.
• Time, temperature, and pressure are the key parameters to achieve the best performance of a PSA. Increasing pressure can allow you to reduce time or temperature, increasing temperature can allow you to reduce time and pressures, etc.

At 3M, our tapes and liquid adhesives for consumer electronics do more than just bond. We design products that address reworkability in several ways so your manufacturing process can be more efficient.

What are common methods to rework a tape or liquid adhesive?

Common methods used to rework a tape or liquid adhesive include: heat-debonding, chemical release, and stretch release.

When is reworkability needed? Why is reworkability an important property for a tape or liquid adhesive?

Reworkability is typically needed when bonding parts that may need to be disassembled, for example to change a component during assembly. Disassembly may be necessary when there is a scratch on a frame and the display needs to be removed without breaking it. Reworkability also enables easier repair of devices.

What is the difference between rework and reposition?

In general, in the electronics market, reposition is defined as adjusting bonding location during device assembly. This typically takes only seconds or minutes.

Reworking, sometimes described as debonding, is defined as an open bond enabling the change of components without having to discard the entire assembly, therefore helping to reduce waste. An example of when reworking is needed is to replace a defective or damaged display or scratched metal frame. Reworking can take place for up to three days.

In the instance of repairing a device, reworkability is needed to enable repairs such as replacing a damaged screen or changing a battery. Timeframe for reworkability for repair can be months or even years.

Finally, at the device end of life, reworkability helps enable greater recovery and recycling of components and materials used in the device. Timeframe for end of life reworkability is greater than three years.