Semiconductor bonding needs fast and accurate positioning

Citation

(1999), "Semiconductor bonding needs fast and accurate positioning", Assembly Automation, Vol. 19 No. 1. https://doi.org/10.1108/aa.1999.03319aad.003

Semiconductor bonding needs fast and accurate positioning

Semiconductor bonding needs fast and accurate positioning

Keywords Electronics, Part presentation

Die bonding in the electronics industry, in which tiny silicon chips are secured to their substrate, requires accurate positioning to within 50 microns. That is why bonding machine manufacturer Cammax Precima selected an Aerotech linear gantry system for its latest semi-automatic machine design.

The Cammax Precima machines are aimed at developers and low volume production applications. By using manual alignment techniques and then automatic pick and placement, the new DB8000 semi-automatic bonding machine is ideal for companies making hybrid circuits or low to medium volume semiconductor packaging. The machine uses a eutectic bonding process in which a metallic coating (gold) on the substrate on which the chip is placed, is heated to melt temperature to form the bond.

A pre-cut wafer containing the individual dies (chips) is loaded on to a platen in the machine and the operator selects the die to be placed using a vision system and a simple but accurate graticule alignment. The boards on which the die is to be placed index through the machine, first to pre-heat, then to a heated stage. Once the die has been selected by the operator, he/she then switches the pick and place system on and the Aerotech linear gantry takes over to remove and then place the die on to the heated substrate.

An earlier automatic machine from Cammax Precima had used a stepping motor solution for the pick and place assembly. This arrangement was considered too slow for the DB8000 and the machine's designers were attracted to the "packaged" linear gantry solution provided by Aerotech which delivered both the speed and accuracy required.

The Aerotech gantry controls the X-Y positioning and also the height (Z) movements to collect and then insert the dies. The indexing conveyor that carries the heated circuit boards through the machine works independently but is interfaced with the gantry through software to ensure accurate synchronisation. One of the clever programs within the gantry routine creates a slight agitation of the chip as it is placed on to the substrate. This helps to ensure a perfect bond every time.

The gantry is Aerotech's new ALA1000 that harnesses the speed, acceleration and accuracy of linear motors and applies those capabilities to linear actuators ­ products more commonly driven via acme threads or ballscrews. The ALA1000 combines the performance advantage of a linear motor with the integration ease of a packaged positioning stage (see Plate 3).

Speeds up to 3m/sec. are reached at acceleration rates pulling 5G under no load conditions, thanks to the use of brushless linear motors ­ speeds not possible using ballscrew technology.

Plate 3 The gantry is Aerotech's new ALA1000 that harnesses the speed, acceleration and accuracy of linear motors and applies those capabilities to linear actuators ­ products more commonly driven via acme threads or ballscrews

Accuracy that meets Cammax Precima's demands for 50 microns or better is assured by the use of directly coupled linear encoders. The non-contacting device is mounted in close proximity to the work surface and gives low maintenance. The standard linear encoder provides accuracy of up to +5µm over one metre of travel.

Motion control is provided by Aerotech's Unidex U500, a PC-based control solution, with which Cammax Precima's own software specialist has been able to interface the DB8000 machine's own operating system.

For DB8000 derivative machines that will employ a cold bonding process using epoxy adhesives, the Aerotech gantry will be fitted with an adhesive dispenser to apply a thin coating before the die is placed.

For further information contact: Karl St George, Aerotech Limited, Jupiter House, Calleva Park, Aldermaston, Berkshire RG7 8NN. Tel: +44 (0) 118 940 9400; Fax: +44 (0) 118 981 5022; E-mail: karl@aerotech. co.uk; WWW: www.aerotech.co.uk