3M technical resources for consumer electronics bonding

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 to you to reduce time or temperature, increasing temperature can allow you to reduce time and pressures, etc.

Adhesives and tapes are polymeric materials and unlike metals, are viscoelastic and their properties are frequency and temperature sensitive. This requires advanced testing to create data that describes what the mechanical response will be under differing loads, temperatures, geometries, etc.

3M is uniquely positioned to characterize these frequency and temperature sensitive materials and provide them in a format compatible with a variety of finite element modeling software. These material models can be used to predict mechanical behavior in a finite element analysis. Conventional mechanical properties, such as Young’s modulus and Poisson’s ratio, even when obtained at relevant rates and temperatures, do not accurately capture adhesives and tapes behavior. Consequently, 3M has developed Material Data Cards (MDCs) which are available for common 3M materials in a ready to use format for numerous commercially available FEA software applications. Currently, we can offer an MDC for any 3M PSA which is compatible with Abaqus, ANSYS MAPDL, ANSYS Workbench, and LS Dyna.

Determining whether to use a liquid adhesive or a tape depends on the dimensional gap you have in your design, your equipment and your design challenges. Tapes are typically used for 2D gaps, when easy application is needed, the thickness of the tape defines gap size, as well as a flexible bond and controlled shapes. Liquid adhesives are typically used when you have a 3D gap filling issue, when an automated process is necessary and when low material costs and high strength adhesion for narrow bond lines below 0.5mm are required.

The 3M product TDS contains information and data that should be considered representative or typical only and should not be used for specification purposes. Final product specifications and testing methods will be outlined in the product Certificate of Analysis (COA) that is shipped with the commercialized product.

The 3M Certificate of Analysis (COA) for a 3M product is established when the product is manufactured and is deemed commercially available from 3M. The COA contains the 3M specifications, test methods and test results for the product performance attributes that the product will be supplied against. Contact your local 3M representative for a product COA.

Surface energy is a physical property of a material that determines whether an adhesive will make intimate contact. On a material with high surface energy, a liquid will spread out or wet the surface; on a material with low surface energy, the liquid will resist flowing and bead up. Good wetting or wet-out means the adhesive makes intimate contact, and is necessary to form an adhesive bond.

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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.

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. Learn more about reworkability.

Different designs require different bonding solutions. If you are more concerned with helping to keep a screen from breaking and protecting device components, consider choosing a shock absorbing bonding solution such as 3M™ VHB™ Tapes for electronics which is as thin as 150um. If a strong bond is most important, consider a liquid adhesive such as 3M™ Plastic Bonding Adhesive 2665B or 3M™ Scotch-Weld™ PUR Adhesive 2710p. Finally, if an ultra-thin tape at or below 100um is needed, consider testing 3M™ Impact Resistant Adhesive Transfer Tapes 95005 (50um) or 95010 (100um). It is important to note that adhesive thickness helps in drop resistance and helps to prevent the display from cracking.

One way to determine if a tape will bond to a curved shape is to check its anti-lifting test performance. It is also important to make sure the tape thickness is high enough to bridge the gap all along the bond line. Other factors like conformability or compressibility can influence the adhesion performance.