Electrically conductive adhesives have been around for many decades. In fact, it was the advent of the American-Russian space race in the 1960s that really propelled conductive adhesive technology to the forefront in electronic design.
At the time, NASA was looking for an alternative system that would replace or reduce wiring, traditional electronic devices and, indeed, die bonding on early PCBs in their rockets and capsules. Driven by a need to reduce the weight of the spacecraft and the inherent dangers of astronauts trying to solder a repair to a wiring loom or electrical system inside a space capsule, conductive adhesives were high on NASA’s R&D programme.
From as early as 1972, with the showcasing of the world’s first electronic hand-held calculator with a conductive epoxy adhesive used to bond in the LCD module, electronics design has rapidly changed – and conductive adhesive technology has had to stay one step ahead.
Nowadays, of course, the trend for ever smaller consumer electronic devices, such as mobile phones, iPads, MP3 players and, more recently, wearable clothing with electronic sensors and data recorders has meant that designers have had to look to alternative methods of conductive joining or conductive pathways. Mechanical electrical connectors are bulky and limit the size of a product. Conductive adhesives can replace these, making space for more electronic features or ultimately reducing the size and weight of the finished product.
With increasing legislation comes the need for technologists to design new products to replace outdated methods of joining substrates. In recent years, the law was changed to ban lead solder being used in electronic applications. Conductive adhesives for surface-mount device applications were now a significant option for electronic design engineers. It was really this sea-change in electronic/electrical manufacturing processes that brought the benefits of using conductive adhesives back into the limelight. These include:
- Faster processing times
- Fewer inventory items needed
- Can be used on heat sensitive substrates
- Large range of chemistries to suit almost any substrate
- Can be used on flexible materials and foils
- No toxic metals used.
Today, the range of conductive adhesives and their applications is vast and varied. Conductive adhesives are tailored to suit almost any application. However, when selecting the right adhesive for your specific application, it is important to consider the following points, advises Simon Dearing (pictured above), managing director, Eurobond Adhesives, which has been supplying high performance electrically conductive adhesives for over three decades:
- The type of conductive filler used – ie, silver, copper, nickel or graphite
- And whether your application would suit a paste or a liquid adhesive, be air cured or thermally cured.
Typically, conductive adhesives fall into two main categories, Eurobond Adhesives states:
- Single-component, thermally curing. This type of adhesive material is very sensitive to temperature when stored
- Two-component, chemical/room temperature curing. These are much slower curing adhesives and may take up to 24hrs to fully cure. However, cure speeds can dramatically reduce with the application of heat.
“Some common applications include applying or repairing conductive paths in heated car windscreens and mirrors, RFID shielding applications, bonding batteries to flexible foil/film, SMD mounting, bonding flexible film LCDs to hard FR4 boards, circuit track repairs, bonding ground wire, populating PCBs – the list is almost endless,” adds Dearing.
In one instance, Eurobond Adhesives was approached by a luxury car manufacturer to solve a fault it had on a PCB installed in the lighting stalk on the steering column of their newly launched model. “The fault was not a critical fault, but it would be time-consuming and very costly to fix by instigating a total global product recall on the vehicle models affected and replacing the whole lighting stalk,” he points out. “The fault lay in a soldered component on the PBC within the stalk. The solder line had cracked and was causing the electrical current to be intermittent.”
The solution was simple. Eurobond Adhesives supplied each luxury car dealership across the globe with a 10g syringe of Elecolit 3024, a silver-filled electrically conductive adhesive. Each faulty PCB could be repaired when the car was next serviced by the dealership.
“Elecolit 3024 is a thermally cured material. However, in this instance, heat would damage the plastic lighting stalk housing. Tests were carried out to see if the adhesive would cure solely by the heat generated by the resistance of the electrical current trying to flow through the bond line. The adhesive cured perfectly and resolved the problem in a simple and effective way for our customer.
“We have been solving problems like this for over three decades,” he comments. “We have vast experience in a huge range of industry sectors. This, together with a wide range of adhesive solutions, make us a very effective partner for our customers.”
