Acrylics make better printed circuit boards

Circuit World

ISSN: 0305-6120

Article publication date: 1 December 2002




(2002), "Acrylics make better printed circuit boards", Circuit World, Vol. 28 No. 4.



Emerald Group Publishing Limited

Copyright © 2002, MCB UP Limited

Acrylics make better printed circuit boards

Keywords: Printed circuit boards, Patents

(Advanced Composites Bulletin) Finnish company Ahlstrom Glassfibre Oy has developed a printed circuit board (PCB) based on acrylic fibres and a foam binder.

The company, from Karhula, has been awarded a patent for the new composite, US 6 258 203. The Patent describes a combination of acrylic fibres, preferably high tenacity, and a foam binder process that produces PCBs that are superior to boards based on both aramid fibre and glass fibre.

The foam process developed is said to be efficient at handling acrylic fibres and to create a much more uniform web than can be achieved with the wet lay-up route.

The PCBs are made with 60-80 per cent straight, strong acrylic fibres (3-13 mm in length and about 6-15 [micro]m in diameter). The remainder of the blend is fibrillated acrylic fibre – that is, pulp fibre. Fibre blending is particularly important in the production of layers of acrylic fibres for PCBs.

In the production process, calender rollers densify or compress a web of this type until it is about 0.1-1 and its weight reaches 20-120 gsm.

The web may be binder-free or it can have up to 20 wt% of a substantially electrically non- conductive binder.

To make the finished PCB, circuit board makers carry out several further steps:

  • electrically conductive circuit elements are added between at least one layer of the fibrous sheets;

  • a prepreg is formed by resin impregnation;

  • the prepreg is cured to produce the final PCB.

Key advantages claimed for the process include:

  • conventional non-conductive fillers (plastic or glass particles) can be incorporated in the foam and uniformly distributed in the final structure;

  • the foam process allows for closer control of the density of the fibrous webs or sheets;

  • the process is cheaper and more energy efficient than existing techniques.

The PCBs are superior to those made with aramid papers or woven glass for a number of reasons, the Patent says:

  • the technique offers superior resin wet-out;

  • there is improved fibre consolidation and less fibre fuzz during impregnation;

  • it is easier to cut the material in both impregnated prepreg or laminated form;

  • it is easier to laser cut and drill holes in the composite board;

  • it has less moisture regain than aramid papers;

  • it is more dimensionally stable;

  • the ratio of the strength in the machine direction to the cross-machine direction is improved;

  • the composite is lower in weight than its glass fibre rivals;

  • the acrylic fibres adhere well to the resin.

For further information, see: US Patent 6 258 203, or contact: Ahlstrom Glassfibre Oy, Ahstromintie 19, PL 18, FIN-46801 Karhula, Finland;Tel: +358-5-224-2444; Fax: +358-5-226-1387.

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