Damien Kirkpatrick has over 10 years experience working in the electronics manufacturing industry. He gained a BSc from the University of Leeds in Physics in 1992 and an MSc from the University of Salford in Advanced Manufacturing in 1994. Since then he has worked for Nortel Networks at their research base at Harlow Essex before joining the contract electronics manufacturer Celestica Limited as a Technology Specialist. He was heavily engaged in the development of lead-free processes and has a background knowledge of PCB manufacturing including flexible circuit assembly. He joined TWI as a Senior Project Leader in 2003.
Roger Wise joined TWI for the first time in 1986 working in Electron Beam Group and then in Plastics Welding. He gained a PhD from Cambridge in 1999 in ultrasonic welding. In 2001 he left TWI to become Engineering Director of a venture capital funded start-up company engaged in commercialising a novel antenna technology. Roger rejoined TWI in 2003 and now manages the Microtechnology Group.
As disposal of electronic devices invariably leaves an unwanted legacy the issue of designing products to minimise their impact on the environment is becoming increasingly important.
Leading companies have realised the importance of what has become known as Design for Disassembly (DFD). The principle of DFD is to design products for their full design life, but make them easy to disassemble at the end of their life for component reuse and recycling ( Fig.1). As Damien Kirkpatrick and Roger Wise explain this type of design can also serve to make a product more serviceable for users and aid in maintenance and reparability.
Unplanned lengthy disassembly is uneconomical, environmentally damaging and does not enable the full value of the parts to be achieved through recycling. It is for these reasons and the advent of forthcoming legislation that designing products for easy disassembly has increased in popularity enabling more of the product to be recycled economically.
Legislation
Incoming EU legislation will set new formal requirements for end-of-life treatment of waste electronic products. In particular, producers will have the responsibility for obsolete product collection, pre-treatment, and recycling. There are three specific European directives that address these requirements:
The European Restriction of Hazardous Substances in Electrical and Electronic Equipment (RoHS) directive (2002/95/EC):
- RoHS aims to protect human health and the environment by restricting the use of certain hazardous substances in new equipment.
- From 1st July 2006 new electrical and electronic equipment put into the EU market will not contain lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, or polybrominated diphenyl ethers.
The Waste Electrical and Electronic Equipment (WEEE) directive (2002/96/EC) includes the following:
- WEEE aims to reduce the waste arising from electrical and electronic equipment and improve the environmental performance of all those involved in the life cycle of electrical and electronic equipment ( Fig.2).
- WEEE will affect manufacturers, sellers, distributors and recyclers. By 2006 producers of equipment will be required to achieve a series of demanding recycling and recovery targets for different categories of appliance.
The End of Life Vehicle (ELV) directive (2000/53/EC) includes:
- ELV aims to make vehicle dismantling and recycling environmentally friendly. It sets clear, quantified targets for reuse, recycling and recovery of vehicles and their components including electronic parts.
- ELV also pushes producers of vehicles with a view to their recyclability. The aim is to recycle or re-use an average of 85% of a vehicle by weight per year.
Product end-of-life processes
To tackle the issues surrounding the legislation one must understand the nature of end-of-life processes and the treatment electronics products need to undergo at the end of their useful lives ( Fig.3).
The end-of-life system can be divided into three distinct stages, each with different characteristics. The first stage is the organisation of the collection process. The second is the recognition, structural pre-treatment and fragmentation of the product. The third stage is the collection of the material content through recycling processes or by re-using the components.
The financial burden of end-of-life treatment can be reduced by proficient design and through the active use of technologies such as active disassembly and automated sorting. In addition, the material content and product structure must be designed to be compatible for recycling.
Design for disassembly principles and benefits
One of the best ways to pass information on new design principles to designers is in the form of guidelines. These can be used in two ways, firstly full training using the guidelines and case study material enables designers to understand why particular requirements are needed, and secondly giving each designer access to the guidelines whilst they are designing enables them to apply the principles whenever possible.
Design for disassembly enhances maintainability or serviceability of a product, and it enables recycling of materials, component parts, assemblies, and modules. There are a number of principles to facilitate disassembly.
- Provide ready access to parts, fasteners, etc to support disassembly.
- Embrace modular design so that replacement of parts can be maximised.
- Use materials that will biodegrade at the end of life of the product.
- Minimise weight of individual parts and modules to aid disassembly.
- Use joining and snap fit techniques to facilitate disassembly.
- Position joints so that the product does not need to be turned or moved for dismantling.
- Use standardised joints so that the product can be taken apart with a few universal tools, eg, one type and size of screw.
- Use shape memory alloys for fasteners.
- Minimise fragile parts and leads to enable re-use and re-assembly.
- Put parts that are likely to wear out at the same time in close proximity so they can be easily replaced simultaneously.
- Design product with weak spots so it can be dissembled more easily.
- Use connectors instead of hard-wired connections.
- Design to enable use of common hand tools for disassembly.
- Use thermoplastic instead of thermoset adhesives.
There are a number of benefits to the producer of achieving efficient disassembly of products as opposed to recycling a product by shredding. These include:
- Facilitate product take-back and extended producer responsibility, thereby reducing liability and assisting in regulatory compliance.
- Increase part/component re-use, thereby recovering materials and reducing costs.
- Help maintenance and repair, in that way reducing costs.
- Aid material recycling, thus avoiding disposal and handling of waste.
- Assist product testing and failure-mode/end-of-life analysis.
These factors are by no means exclusive. There are many design features that could be incorporated into a design that will aid disassembly.
General considerations and techniques
The production of electrical and electronic equipment is one of the fastest growing sectors of manufacturing throughout the world. Electronics products are used in home applications, entertainment, telecommunication, industrial applications, automotive, military etc. With this growth has come an increase in the amount of waste generated.
One way to minimise this waste in design is to modularise the product such that as one module becomes obsolete, it can be upgraded without having to replace the whole machine. Fuji Xerox has applied this approach for several years to its photocopiers, where redundant parts are refurbished or recycled. In the electronics sector some precious metals are removed, some chips are removed for reuse and the PCBs are shredded and incinerated for energy.
At present most products are disassembled using hand or robotic methods, though neither are high considerations in the majority of products on the market. The disassembly of a material may be improved using active disassembly using Smart Materials, known as ADSM. There are two main areas, Shape Memory Alloys (SMAs) and Shape Memory Polymers (SMPs) that are being developed by several research groups. The principle behind both areas is that the specific material will change shape under a certain change of temperature specific to that material. Various releasable fasteners to aid in disassembly are being investigated.
Thermoplastic hot-melt adhesives soften on the application of heat, allowing the separation of substrates, whereas thermoset systems decompose and a mechanical force is required to separate the substrates. Cooling can also be used to facilitate mechanical breakdown in joints produced with adhesive systems that become brittle below their glass transition temperature. A disadvantage of this method is the likelihood of damage to the assembly by either the extreme temperatures or the mechanical forces. It is also limited to applications where the normal operating environment of the assembly does not reach the de-bonding temperature.
Using a similar approach, but a different energy source, ultraviolet (UV) radiation or lasers may be used to induce failure in an adhesive layer ( Fig.4). This is only suitable for systems that are not exposed to UV during assembly or throughout their working life.
Other concepts that are exploitable in disassembly include de-polymerisable polymeric components as part of a device. These families of polymers are used to perform a specific structural or non-structural function. On demand or at end of their use, they are subjected to high temperatures where the polymer chains unzip to reproduce the precursor monomers ( Fig.5). The monomers are collected, cleaned and polymerised again for use in the same or similar application with negligible loss in their properties. There are only a few polymers that undergo this type of de-polymerisation process. They are unique and invaluable for disassembly purposes. Figure 5 below depicts the concept of polymer polymerisation, use, de-polymerisation, clean and re-polymerisation.
Also, thermally reversible polymers and adhesives could be used to perform a function and on heating they are sufficiently softened (lower their modulus) to allow disassembly of components. These materials can contain either a few blocks of de-polymerisable polymer chains that are de-polymerised on heating as described above or other chemical additives, such as diene or ring-containing polymers, that are initially incorporated into the polymer but they revert back to the original components on heating. The reversible reaction will significantly reduce the modulus of the material to ease disassembly of components used.
Another approach is to embed a small wire within the adhesive layer at a joint. When the wire is connected to a source of electric power, the adhesive in the vicinity of the wire heats up. If the adhesive is a thermoplastic ( ie a hot-melt) it will melt allowing the joint to be dismantled.
What TWI can offer...
In the early 1990s, TWI invented a technology for the rapid joining of structures involving dissimilar materials that it called the polymer coated material (PCM) joining technique. The basic concept was that components to be joined were coated with a thin layer of a thermoplastic polymer before being joined using a polymer welding technique to another coated component. Strong joints can be produced very rapidly using this technique and, more importantly, the joints can be disassembled on the application of sufficient heat energy to re-melt the thermoplastic.
Another approach being developed involves the use of biodegradable materials for use as the circuit board substrate. Such materials could include gelatin, plant extensions or starch, which would potentially meet all of the performance requirements of the product. At the end of the life of the product, digestion of the board would take place in a bioreactor and any remaining materials and electronics components could be removed separately. To prevent premature biodegradation while still in use, hydrophobic coatings could be applied which could be simply removed at the start of the recycling operation (chemically for example). The process is shown in Figure 6.
The biodegradable circuit board offers a method for disassembly and 'closed loop' recycling ie the products of the biodegradation can be fed back into the food chain of the organisms used to create the next circuit boards.
TWI has found itself ideally placed to assist companies in assessing the impact of environmental legislation on current product lines and the design of the next generation products. It is also in the process of developing various joining and disassembly techniques in readiness for the perceived needs.
Proposed disassembly mechanisms for evaluation
TWI has generated ideas for various methods of disassembly published below for use as the basis for potential collaborative projects:
| | Mechanical disassembly methods |
| 1 | Use Surfi-Sculpt TM to generate metal or polymer hook and loop or other novel reversible joints. ( Fig.7) |
| 2 | Use a fastener which can only be made in one direction - like a climbing nut which jams into a crack and will only go in or out one way. |
| 3 | Use hydraulic tension in the structure which when released causes the structure to collapse. |
| 4 | Use microwave to collapse polymer parts for reduced landfill volume or to trigger melting and hence release. |
| 5 | Embed springs in joints whose strain energy can be released. |
| 6 | Use thermal expansion in screw threads so they interfere when cold and come loose when hot - the interfering threads can be near the top of the screw so that the screw driver can input the heat. |
| 7 | Design a product with weak spots to crush more easily. |
| 8 | Low temperature and fatigue. |
| 9 | Use thermal shock for consumer electronics. |
| 10 | Thermally unstable bimetallic or bipolymer foil which moves under heat. |
| 11 | Fatigue failure of a screw socket (perhaps a tab). |
| 12 | Use vacuum or over pressure to rupture a diaphragm. |
Conclusions
Legislation will drive a rapid change within manufacturing industry, which will force companies to reassess the value-chain for products such that minimal, or zero landfill is involved.
Joining, disassembly and recycling concepts will have to be developed before products embracing the 'zero-landfill' approach can be finally designed and manufactured.
TWI is in the process of developing certain key technologies and skills to help its Industrial Member companies meet the challenge of impending changes with the confidence to exploit the many opportunities that will be presented.
