Electrically conductive adhesives have been around for many decades. In fact it was the advent of the American/Russian space race in the 1960’s 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 PCB’s 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 the early days, products such as Elecolit® 325 a 2 component silver filled epoxy paste offered huge potential. Being a 2-part material it could cure at ambient temperatures by chemical reaction when equal amounts of resin and silver conductive filler were mixed to form a high strength, highly conductive bonded joint and was used in some of the early Apollo missions. It is still widely used in general manufacturing today. Typical applications include:
1. Connecting heat sensitive components to printed circuit boards.
2. Bonding wave guide plumbing, hybrid circuit assembly.
3. Connecting ground wires to components and making conductive lines.
4. Replace metal solder where temperature or convenience in the application is required.
5. Plating base.
6. Chip bonding for discrete devices and hybrid circuits.
From as early as 1972 with the showcasing of the worlds 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.
With increasing legislation comes the need for technologists to design new products to replace outdated methods of joining substrates.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.
Electrically Conductive Adhesives…cont’d.
Today of course, the range of conductive adhesives and their applications is vast and varied. Conductive adhesives are tailored to suit almost any application. When selecting the right adhesive for your specific job then it is important to consider the following points. The type of conductive filler used ie Silver, Copper Nickel or Graphite and whether your application would suit a paste or a liquid adhesive. Typically conductive adhesives fall into two main categories.
- Single component, thermally curing. This type of adhesive material is very sensitive to temperature when stored. Typically these will need to be either deep frozen or stored below +5ºC and brought to room temperature just prior to use. This obviously has an impact on pot life and waste material.
- Two component, chemical/room temperature curing. These are typically much slower curing adhesives and may take up to 24hrs to fully cure. However, cure speeds can dramatically reduce with the application of heat. They are mixed in either a 1:1 or 2:1 ratio by weight or volume and have a much shorter pot life than single component adhesives. However, wastage is kept to a minimum as you only mix what you need.
Some typical applications include applying or repairing conductive paths in heated car windscreens and mirrors, RFID shielding applications, bonding batteries to foil/film, SMD mounting, bonding flexible film LCD’s to hard FR4 boards, circuit track repairs, populating PCB’s the list is almost endless, bonding ground wires etc etc..
Eurobond Adhesives Ltd has been supplying electrically conductive adhesives for over 32 years and has a comprehensive range of products and a wealth of experience to draw on. If you would like to discuss your current application or a future project then please contact our technical team. We would be happy to help.
or visit our website www.eurobond-adhesives.co.uk