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New Scientist 12 June 1986   New Scientist 12 June 1986   page35

Ivor Catt: The image of the inventor.
High-tech products for the high street - but how useful are they? Ivor Catt (above) sold Sir Clive his patents to wafer-scale technology. According to who you speak to in the semiconductor industry, Catt is either a crank or a visionary

Sir Clive's initiation into the world of the wafer took place in the summer of 1983, with the arrival of Ivor Catt who had answered Sinclair's advertisement for people to work at Metalab. Depending on who you talk to in the generally conservative semiconductor industry, Catt is either a crank or a visionary. For 20 years, he had been refining the theoretical foundations for a revolution in the semiconductor industry, and thus was tailor-made for the Sinclair project. Sir Clive took on Catt as a consultant and bought up Catt's patents to the wafer-scale process.

Catt himself has succinctly summarised the appeal of the wafer against existing chips and methods of manufacture: "I noticed that the silicon wafer was a hundredth of the cost of the total system, so why not use that cheap commodity to build the system on the wafer instead of sawing it up to form separate circuits?"

Currently, the computer industry produces multiple chips on each wafer of silicon. The production process involves chopping up the wafer, testing each chip and then separating the working chips from a significant number of faulty chips. The working chips, after mounting, wiring and packaging in plastic, become part of a larger system mounted on a printed circuit board. Catt's alternative method involves preserving the entire wafer (including the faulty chips), which has internal connections between chips so as to eliminate the printed circuit board. It also avoids the need to test and encapsulate each chip. An electronic logic test built into the wafer circuitry allows each chip to be tested. If functional, the chip becomes incorporated in the circuit and then tests an adjacent chip. Faulty chips are bypassed as a spiral sequence of working chips is established on the wafer. The simplest form would be a memory wafer, but there is a potential to develop new, alternative computer architectures on the wafer.

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