Laser drilling of printed circuit boards

At Oxford-based Exitech Ltd, a recent major development has been a CNC laser drilling system for printed circuit boards (PCBs).

At Oxford-based Exitech Ltd, a recent major development has been a CNC laser drilling system for printed circuit boards (PCBs), in a strategic joint partnership with American company, Excellon.

To build laser machining systems to perform micro-precision drilling and profiling of miniature electronic and engineering components, Exitech required a reliable and consistent encoder system.

Additional requirements included a compact, precise and preferably, non-contact system, to provide positional feedback data to position the machines' workstages within a few microns.

Renishaw's RG2 encoder system was selected and is now used across the range of Excellon and Exitech machines.

Furthermore, Exitech's need to calibrate machines of such precision, led to the purchase of a Renishaw ML10 laser calibration system for an in-factory and field calibration service.

Laser drilling of PCBs to within a positional tolerance of +/-15µm requires a work stage positioning accuracy of +/-3µm.

Exitech had tried a number of encoder systems on the market, but glass scale types were considered to be too bulky and cumbersome for the miniature machine structures.

Long delivery times were also quoted.

"We found the Renishaw encoder easy to use and quick to get hold of," explained Stephen Angood, Exitech's Senior Mechanical Design Engineer.

"We had tried other suppliers, but they were quoting 12-week deliveries.

Very important to us was to have an encoder that would give us the ability to move and position a workstage within very tight tolerances.

Our machines are built around the customer's product, often within very tight lead times from receipt of order to delivery.

We can now design and build a workstage for a machine within four weeks." The Excellon PCB laser drilling machines typically produce 18,000 holes/min - the holes being in the diameter range of 25-35µm.

The Excellon was one of the first laser drilling machines to appear on the market.

"There was a race on in the market to develop such a machine," said Mr Angood.

"Companies were trying a variety of laser systems, and we were pleased to be one of the first to succeed." The attraction of Renishaw's RG2 encoder system was its low profile scale tape and a compact reading head, which required no special housing.

It enabled Exitech to design a very compact machine structure.

The workstage manipulation is in the X,Y and Z axes, and axes drive is by Aerotech linear motor systems.

Unlike glass scales that have to be ordered and stocked in specific lengths, the scale used in the Renishaw RG2 system can be cut and fitted to suit the application.

"Because the encoder is in tape form, we can produce workstages of different sizes and different travels in a very short time.

We produce all our own stages for our machines.

Some applications, such as the drilling of fine holes in ink jet printer nozzles, require a positioning repeatability of 1æm," explained Mr Angood.

"We perform such drilling in a variety of materials including plastics, tapes and films." The company has also produced larger machines for precision laser drilling and cutting.

"Speed of response is important to us too, as our customers are requiring ever-faster cutting speeds, lately up to 1m/sec.

Our laser machining processes are quite tightly defined in terms of speed," continued Mr Angood.

"Some systems require step and repeat cycles and some are integrated with laser scanning systems.

When a machine is on the move at high cutting speeds, whether on a step and repeat, or on a tightly toleranced profile path, we need good velocity control.

That is why the Renishaw RG2, a compact, fast response and reliable encoder system, is important to us." Calibration of such machines is also essential from a quality assurance point of view, as many of Exitech's customers' quality procedures require regular calibration checks on the machines employed.

"We used to pay £1000/day to service companies to carry out the calibration of our machines' work stages," said Mr Angood.

"We then decided to buy our own laser system and offer the service ourselves.

We settled for the Renishaw ML10 laser calibration system, which we now use all over Europe as well as in our own factory.' He explained that when an Exitech machine is shipped, it is accompanied by a complete report, with accompanying performance data graphs that were generated during acceptance tests.

"We have found the Renishaw products to be very reliable," concluded Mr Angood.

"Renishaw offers speedy delivery and an excellent back-up service.

We are now trying out a new Renishaw encoder system which is even more compact.".

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