Cherry membrane production
Contents
United Kingdom
Around the mid 1980s, a full travel membrane keyboard type entered production at Cherry’s UK factory. Although little is known about these keyboards beside the patents, and no examples have ever been encountered, this design served as the precursor to Cherry MY. Membrane production for these keyboards was set up in the UK factory, and the membranes for Cherry MY keyboards were also manufactured there. Although the British membrane keyboard product line was discontinued, the factory continued to provide membranes both for Cherry’s own keyboards and directly to other manufacturers.
Around 1987, the membrane production line was rebuilt for higher yields, with the failure rate reduced from 30% to 10%, the most that could be achieved within the available budget. The maximum production rate was 450 sheets per hour from Svecia print machinery. Engineer Keith Jones, responsible for the new membrane production line, developed a new type of press tool to prevent the holes punched in the spacer sheet from having burred edges.
The membrane assemblies were then ultrasonically spot welded together in the four corners.
The ink used for the circuit tracks was an off-the-shelf silver-loaded ink supplied by DuPont. The membrane composition is thought to have been 0.004″ polyester top and bottom layers enclosing a 0.005″ Mylar spacer.
The main reason for rejecting membrane sheets was screen printing errors: the screen printing screen meshes were made from polyester which lacked the strength needed to secure it. A better choice would have been stainless steel, which is able to withstand much higher tensions.
Cherry’s membrane production was eventually transferred to Hungary.
Customer supply
In addition to producing membranes for their own keyboards, Cherry also produced membranes for other manufacturers. The membrane assemblies that they supplied to DEC were of the folded type: single outer sheet folded around the centre spacer sheet, as depicted in various US membrane keyboard patents. Another membrane customer was Nixdorf; these small 2″ × 3″ single-sheet membrane circuits may have gone into cash registers.
United States
Cherry also manufactured membrane keyboards in the United States. The membranes for these keyboards possibly produced in-house for a while, and if not they were sourced from an external manufacturer; they were not imported from Cherry UK.
Sources
- Peter Cherry
- Keith Jones, former Cherry engineer