The ACME project - pcb production with reduced cost & environmental impact
By Bob Smith, Project Leader, Coates Circuit Products

SUBTRACTIVE PCB TECHNOLOGY
The traditional PCB manufacturing process "subtracts" copper from a copper clad substrate to create conductive tracks. The chemicals used in this process have harmful environmental effects, which need to be controlled by legislation. This in turn creates costs for the PCB industry. Chemical hazards ­ key chemicals that have an environmental impact

Plating and etching solutions are a source of chemical hazards. In addition, the wastewater invilved is high due to the critical rinsing required between nearly all of the process steps.

Process chemicals ­ estimates of volume consumption and disposal costs per annum for the EU (2).
Etchant and, particularly, wastewater have the biggest environmental and economic impact in the EU. An estimate for the cost of water consumption
for a medium sized PCB producer is around 120,000 per annum (4).

EU legislation
The European authorities publish approximately 100 new directives a week, so keeping abreast of developments is a problem (2). Acceptable limits for copper differ nationally and are fixed locally. Guidelines are:

European Union <5.0 ppm
Scotland (some areas) 0.5 ppm
Europe (some areas) >5.0 ppm

The legislation "Waste from Electrical and Electronic Equipment" (WEE) (4) would impose a requirement on the manufacturers of electronic equipment for the collection, dismantling and recycling of their products. If fully implemented this would impose a major cost that would have to be incorporated into the selling price of the equipment. The emphasis on recycling means that undesirable chemicals used in the manufacture of the equipment would need to be replaced, such as lead from tin/lead plating and soldering, and brominated flame retardants from
dielectric inks and laminate. An environmental impact arises because the
glass-epoxy laminate used as a substrate for Approximately 60% of PCB¹s cannot be recycled or even incinerated, as toxic atmospheric pollution such as bromine and dioxins can be produced (5,6).

The cost of environmental compliance (7)
This is estimated to be 6-8% of sales price. The environmental impact on profitability and business survival is obvious in an industry where margins can be in single figures. Negative impacts will result when costs of compliance within the EU put PCB manufacturers at a disadvantage compared to other International companies where these costs of compliance do not apply as in Asia

ADDITIVE CIRCUITRY ­ ACME PROJECT
An alternative approach to the "subtractive" method is to "add" conductive tracks to the substrate. The ACME project was set up to achieve this. ACME (Additive Conductive Materials to reduce Cost and Environmental Impact) was a European project 50% funded by the Brite-Euram programme, which ended in March 2001. The members of the consortium were:

Coates Electrographics
Materials Suppliers to the PCB Industry
Coates Screen GmbH
Process Development and Screen Printers
Viasystems
PCB Manufacturer

Magneti Marelli
PCB End-User (Automotive)
Alcatel Business Systems PCB End-User (Telecom)
NMRC Microelectronics Research and Testing

Two additive technologies have been developed; UV Screen and Photoimaged. These are described in detail:

ACME UV SCREEN
This is a lower resolution and lower cost alternative than photoimaged. The process is a sequential print and UV cure and relies on good registration between one print and the next. The printing environment, and screen production were tightly specified and a computer driven automatic screen printer was used to achieve print-on-print registration.

The conductive ink is not directly solderable so a thermal curing copper ink was printed onto pads on the last layer. The final bake for the copper ink gives both a solderable surface and also improves the adhesion of the UV cured layers.

ACME PHOTOIMAGED
The same principles applied for screen-printing as for the UV Screen. Further process optimisation was required for dielectric photoimaging and conductive slot filling. After slots were filled the ink was reflowed to give an alloy with a melting point higher than solder. For solder attachment the same method was used as for UV Screen; thermal curing ink on the top layer.

Sequential representation of the photoimage process
1. Use Coated or anodised aluminium, or other suitable substrate

2. Apply around 50 microns of dielectric

3. Photodefine circuit pattern

4. Fill recesses with metal/flux combination Sinter and remove excess
metal from surface by brushing

5. Repeat the process to form multilayer circuit

• ACME OBJECTIVES
  Process cost reduction 25%
• Reduced environmental impact
• Performance targets
• Production of demonstrator circuits
• Compilation of a technical implementation plan

Progress towards objectives is summarised:

• Cost reduction compared to subtractive - Process costs

The manufacturing partner, Viasystems, constructed a cost model for low volume (100 board batches) and high volume (5000 board batches) for 24 x 18inch boards, 2 and 4 layers, assuming 20, 35, and 50% coverage. Other assumptions for UV Screen/Photoimaged were track and gap (200/100µm), minimum hole size (500/250µm) and number of vias (12000/24000).

For a large number of vias there is an advantage in that all vias are produced together quickly in one layer, so process time is not proportional to the number of vias, making the process relatively cheaper for large numbers.

Below: Low Volume

Right: High Volume

At low volumes, both technologies have a favourable cost margin vs. substractive. The high set-up and drilling costs for substractive outweighs the material costs of the additive process. The cost advantage is highest at low track coverage due to the cost of ink. Savings of <20% (50% coverage) to <30% (20% coverage) were achieved. At high volumes the set-up and drilling costs are less significant and material costs have more effect, so that both technologies give a lower saving at 20% coverage but only photoimaged gave a saving at >20% coverage.

- Via production

ACME technologies offer two advantages compared to the standard drilling process:

produced together quickly in one layer, so process time is not proportional to the number of vias, making the process relatively cheaper for large numbers.

For small via diameters, ACME permits lower costs than the high costs of traditional small drill bits, and slow feed rates are overcome.

• Environmental impact
  Advantages were identified:
  - Process elimination
  UV Screen ­ developer and stripper solutions, copper waste from plating and etchants. Photoimaged - copper waste from plating and etchants.
  - Process reduction
  UV Screen ­ water treatment >95%. Photoimaged ­ water treatment 75%.
  - Materials replacement ­ replace FR4 with aluminium.

• Performance
  - Print resolution (µm)
  UV Screen (target 150-250) 200. Photoimaged (target 25-100) 150.
  - Resistance (µ‡/cm)
  UV Screen (target <750) ~450. Photoimaged (target 20-100) ~100

• Demonstrator circuits
  End-user partners Magneti Marelli and Alcatel using PCB¹s manufactured assembled circuits produced by Viasystems using both UV Screen and Photoimaged technologies. Examples are shown.
• This Magneti Marelli demonstrator is used in an engine immobiliser unit for an automobile. It was prepared using the UV Screen process.

Technical Implementation Plan
Commercial exploitation requires an understanding of the advantages and limitations of the technologies.

Left: Soldered top layer

Advantages are cost reduction (depending on coverage and volume), elimination and reduction of environmentally unfriendly processes, and improved recyclability and heat sink properties from being able to use aluminium substrate (UV only) to replace FR4. Also, production can start from a lower capital base, due to less and cheaper equipment and lower space requirement.

Right: Mounted components

Changeover of circuit design is easily achieved by changing screens. Limitations are unsuitability for high current carrying applications and high density interconnect; and for rigid PCB¹s only, not flexible applications.

This Actel demonstrator is used in a headset control unit. It was prepared using the Photoimaged process.

Commercial applications have been identified which are compatible with the above:
Automotive ­ dashboard, in-car circuitry.
Industrial ­ RFID, sensors
Consumer ­ white goods
(i.e. refrigerators, washing machines, etc), toys
Medical - sensors

Our commercial staff are pursuing these applications.

ACME ­ CONCLUSIONS
The ACME technologies offer advantages in cost savings and environmental savings and have met agreed performance targets. Markets have been identified for exploitation and these are being pursued.

REFERENCES
(1) MSDS Sigma-Aldrich ­ copper sulphate 451657; lead
tetrafluoroborate in water 401579; formaldehyde 37% in
water 252549.
(2) Data from M Goosey (Shipley) and R Kellner (PCIF); February
1999
(3) IPC World market for Rigid PCB¹s;1995
(4) MGoosey; Impact of Environmental Issues on the
European PCB Industry; PCIF Conference; Wiesbaden;
September/October 1998
(5) H.Thoma et al, Chemosphere, Vol.15, no.5, pp649-652, 1986
(6) R.Dumler et al, Chemosphere, Vol. 19, no.12, pp2023-2031,
1989
(7) Electronics Manufacture and Test; January 1999; p5

Acknowledgements to Dr WJ Thatcher (Coates Electrographics) and Herr A Eichler (Coates Screen) for their contribution to the above work.

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