Electronic mobile and wearable device growth continues to surge. With the adoption of 5G, global smartphone sales are projected to grow by 11% in 2021 while the wearable device category will increase by more than 18% in 2021.

This continued increase in the number of mobile and wearable devices has seen a significant increase in the number of battery cells and magnets that are used both in the devices themselves or in associated accessories such as charge cases and wireless charging pads. Because of this, adhesives are required to provide specific performance levels in respect of bond strength and associated reliability enhancements for the bonding of both magnets and batteries. The critical requirements for an adhesive to bond a battery or a magnet are very similar.

Both magnets and batteries can have performance impacted if they utilize adhesives that require thermal cure cycles that exceed temperatures greater than 60 – 80C. As such adhesives need to provide robust, reliable fixation without exceeding this temperature requirement.

Battery Bonding in Mobile and Wearable Devices

Demand for high-density portable power has never been higher. Lithium-ion batteries are the dominant battery technology used in today’s portable and mobile electronic devices. These batteries are chosen by device manufactures for their high energy capacity and high cycle life, meaning they can be charged and discharged many times without degrading. While significant investment is driving research into new battery technologies Lithium-ion batteries are likely to remain the dominant technology for the foreseeable future, while, in addition, efforts continue to drive existing Li-ion technology to the next level. Therefore, adhesive products that meet the requirements for Lithium-ion battery bonding will be crucial moving forward.

Lithium-ion batteries are negatively impacted if they see temperatures outside a defined process window. For assembly and fixation purposes it is desirable that the batteries do not see temperature excursions greater than 60C. If exceeded the upper-temperature limit when utilizing an adhesive there is a real risk of damage to the Lithium plating and increased degradation of the battery life cycle.

Magnet Bonding in Mobile and Wearable Devices

The most common type of magnet used in electronic device assemblies is Neodymium magnets. Neodymium magnets typically require plating to be used to protect against corrosion. Without the plating, the magnet will quickly oxidize and performance will be impacted negatively. The most common plating used in electronic device magnets is Ni (Ni-Cu-Ni) or Zn because they offer excellent performance at coating thicknesses as low as 10 microns and are also highly cost-effective.

In general, magnets do not like elevated temperatures. If magnets are exposed to elevated temperatures this itself can cause the magnet to demagnetize.  In addition, the plating’s on the magnet surface can be easily damaged if they see temperature excursions greater than 80◦C. At temperatures above 80◦C, there is an increased risk of microcracks forming in the thin plating coat on the surface of the magnet. If this were to happen this would result inreduced performance as a function of magnet corrosion.

Choosing the Right Adhesive: Because of the concerns outlined the type of adhesive used in battery and magnet bonding needs to be chosen with care. Krylex have a range of different product chemistries that meet and often exceed the market requirements for magnet and battery bonding: –

Polyurethane (PUR) Hot Melt:

Krylex Polyurethane Hot Melt adhesives (KH900 Series & KH9000 Series) are heated on the dispense equipment. The heated adhesive is dispensed onto the substrate and rapidly cools to near room temperature (RT) in the time it takes to travel from dispense needle to substrate. Rapid green strength is developed to allow for handling and the product fully cures using atmospheric moisture. The KH900 and KH9000 products offer: –

  • Low process temperature at the substrate
  • Fast green (handling) strength development
  • Excellent, balanced adhesion to metal and plastic surfaces
  • High impact strength
  • Highly moisture resistant
  • Non-corrosive
  • Excellent elevated temperature stability

1K Low-Temperature Thermal Cure Adhesive:

Krylex, one component (pre-mixed) low-temperature cure adhesives (KE1000 Series) are easily applied using an RT dispense process and can be cured at temperatures consistent with the assembly requirements of Lithium-ion batteries and Magnets. The KE1000 Series products offer: –

  • Easy processing
  • Thermal Cure capability between 60 – 80◦C
  • Excellent, balanced adhesion to metal and plastic surfaces
  • Non-corrosive
  • High-Temperature stability

Two-Component, Methyl Methacrylate (2K MMA):

Krylex Two-component MMA’s (KY7000 Series) are applied at RT using dedicated dispense equipment to mix the product to the correct ratio during dispense. The methyl methacrylate chemistry is less sensitive to minor differences in mix ratio than other 2K chemistries to give a fast robust bond. The KY7000 Series products offer: –

  • Easy processing
  • Fast green (handling) strength development
  • Fast, RT Cure
  • Excellent, balanced adhesion to metal and plastic surfaces
  • Good impact strength
  • Excellent temperature and humidity performance

Cyanoacrylate (CA) Adhesive:

Krylex KB5002 Toughened Cyanoacrylate adhesive can be easily applied to a substrate using either manual, Semi-automatic, or fully automatic dispense equipment. Once the substrates surfaces are brought into contact the CA reacts to form a rapid, super-strong adhesive bond at RT. The trade secret toughening agents provide best-in-class impact performance versus other competitive CA Technologies. Krylex KB5002 offers: –

  • Easy processing
  • Very fast bond strength development at RT
  • Excellent adhesion to metal and plastics
  • Best-in-class impact strength
  • Excellent temperature and humidity performance

Contact Us: For recommendation and Technical assistance to ensure the best product for your application contact your local Krylex representative or visit Krylex.com and register your interest.