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Loadpoint is using Heidenhain’s LF481C sealed compact incremental linear encoders in its Microace micro dicing machine.

Loadpoint manufactures cutting, dicing, grinding, polishing, slitting and drilling components used in the semiconductor, printer head, optical, ultra-sound scanning and medical diagnostic sectors.

Its Microace 66 measures 150 x 150 x 10mm.

It had to obtain and maintain an axis-positioning resolution of 0.1 micron when dicing across components to achieve a pitch accuracy of better than three microns.

The Microace 66 has a closed-loop feedback system for ultra-precise control over the programmed cutting process, which can involve dicing wheels as large as 75mm in diameter and wheels as thin as 15 micron.

Heidenhain’s LF481C sealed compact incremental linear encoders give Loadpoint positioning accuracy and repeatability.

With almost 90 per cent of Loadpoint equipment being exported, Clive Bond, chief engineer, explained how one European customer challenged the company’s ability to build a machine that would be able to provide such precise levels of pitch accuracy for slotting silicon wafers.

‘By utilising the Heidenhain VM182 comparator system, we put the customer totally at ease,’ he said.

The VM 182 system incorporates a steel scale with two co-ordinate phase gratings and a scanning head connected to the scale by an auxiliary carriage.

The scale is clamped to the table and the scanning head to the machine spindle.

‘This qualified, without any doubt and according to ISO 230-2, both linear and non-linear error curves as well as any reverse error in each of the machine axes.

‘So successful was the trial that we now take this reference to customer sites when we check and recalibrate machines,’ continued Bond.

Based in Cricklade near Swindon, Loadpoint has progressively built its business over 40 years to provide a micro-machining sub-contract operation as well as a machine, process development and prototyping facility that is reckoned to be one of the most advanced facilities of its type in the UK.

The Loadpoint development laboratory has seen various special machines and processes created for machining silicon, silicon carbide, glass, quartz, gallium arsenide, germanium, lithium niobate, lithium tantalate, sapphire, lead zirconate and titanate (PZT), as well as equipment for ‘processing’ components such as wafers, substrates, plates, laminates, rods, blocks, tubes and assemblies.

Loadpoint has its own Nano control system featuring high-level diagnostics and remote communication.

It also develops its own software and uses in-house programs to monitor process quality by including its own Kerf Check for measuring the width of cut, size and area of chipping while also identifying and correcting alignment offset errors.

The software will also monitor and display spindle current, blade wear, chuck vacuum and the co-ordinates for each of the required machine axes.

The latest Microace 66 machine has X and Y axes travels of 160 x 164mm and a Z-axis able to accept components up to 10mm thick when using the maximum-size slitting wheel of 76.2mm.

Each axis is fitted with the Heidenhain LF481C linear scale for position feedback, which also includes Heidenhain’s mounting spar – this means that in the event of an encoder change, there is no requirement for drawn-out clocking procedures to establish datum positions.

The linear encoder is fully protected from dust and an aluminium housing and elastic sealing lips protect the scale, scanning carriage and guideway.

The sealed nature of the LF481C was a major factor in Heidenhain securing this business against a supplier of exposed scales.

The 1.2kW air bearing spindle has a top speed of 80,000revs/min (optional is 2.4kW 60,000rev/min), which works in conjunction with a Theta axis bearing rotary table with vacuum chuck.

The table has a high-resolution direct-drive torque motor that has an axis resolution of 0.0004 degrees.

A four-direction coolant-delivery system has outlets for main blade jet, side-wash bars, wafer fan jets and flood jets.

Also incorporated in the full-screen display vision-and-alignment system is monocular video alignment that incorporates pattern recognition with a Z-axis autofocus to set up the alignment of the image.

Through-the-lens LED illumination and external high intensity LED fibre-ring illumination are also included.

The LF481C is one of a comprehensive range available from Heidenhain (GB): sealed linear encoders are available with full-size scale housings for high resistance to vibration up to measuring lengths of 30 metres, as well as slimline scale housing for limited installation space for measuring lengths up to 2040mm.

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