A case study showed an average cycle time improvement of 70%.

For most printed circuit board fabricators, drilling is a bottleneck. This comes despite improved automation and linear drives. Dual spindle technology is based on the concept that two spindles drill simultaneously on the same panel. Today’s panels contain multiple images of the same circuit – e.g., cellphones, other mobile equipment, USB sticks, or substrates. The number of individual circuits on a panel can be staggering. By drilling with two spindles at the same time, the drill time is divided by approximately two, therefore doubling throughput.

PCB fabricators began experimenting with dual spindle technology about 20 years ago. Some German PCB manufacturers like Würth and Schweizer Electronic found new ways to increase productivity and increase production capacity without changing the floor footprint. Some drills of choice contained up to 80 spindles. But the spindle position could not be changed, and tolerances proved a real challenge. Over time, however, equipment manufacturers improved the technology and their machines (Figure 1).

For years it appeared laser technology would replace traditional mechanical drilling. As it turns out, the two processes complement each other. Mechanical circuit board processes have advantages such as ease-of-adjustment and lower cost. Moreover, dual spindle technology can ramp productivity heavily.

Besides productivity, increasing board requirements are the second challenge for mechanical processing. Today’s boards are increasingly complex and have smaller tolerances. That is why today’s dual spindle technology developments are concentrating on the issue of process accuracy.

An extensive and detailed verification test can help verify a dual spindle machine as a real and beneficial alternative. A Korean PCB fabricator evaluated two drills: a Posalux Ultra Speed G-line dual drilling and routing machine and a Hitachi ND-6NI 210E single drilling and routing machine.

The Posalux machine (“PX”) contains two spindle drills on the same station, and drills on two independent X-axes with an accuracy of +/-15µm. It has full range linear spindles ranging from 200,000 to 300,000 rpm. The X- and Y-axes run with 3150" min and accelerate up to 12.0 m/s2, or 1.22g. The axis positioning accuracy is <+/-0.004", and tolerances are continuously checked during processing. The Z-axis acceleration rate is up to 4.1g, enabling hit rates of up to 850 strokes per minute. The depth control accuracy is +/-0.006". The software optimizes NC-part programs for dual spindle operation, improving the distance, number of hits and targets and drill wear (both spindles).

The Korean PCB manufacturer evaluated process capability (cpk). To ensure consistent results, the following test and production were used:

• Stable room temperature, with a maximum temperature fluctuation of ±1.8°F.
• An absolute temperature between 20°C/68°F and of 25°C/77 °F.
• Compressed air at >7.5 bar at 1410 Nl/min. Cooling water <14°C, 60 l/min at 3.5 bar.
• Vacuum with pressure -2,000 to -2,500 mmAQ, a flow of 25 Nm3/min.
• Floor flatness: < 4mm/m and min thickness of 500 mm (no antistatic covering).

An average delta of 49% cycle time was tested (Table 1). Figure 2 shows the actual running times of the test boards. A significant reduction in process cycle time had been documented. Per Figure 2, the average cycle time for the PX machine was 148 min, 70% less than the Hitachi machine.

Future Projects

Dual spindle technology is ideal for drilling symmetrical patterns like substrates. With an even number of columns on the board, productivity can be increased 100%. Some dual spindle machines are suitable not only for drilling microvias, but also for routing. (Dual routing is possible, provided the design includes an even number of columns; otherwise a manual routing step is needed.)

With a current average board mix, a dual spindle system reduces drill cycle time 60 to 100% (depending on the program layout) as compared with a machine (same type) in single mode. Moreover, a dual spindle system uses half the floor space of two standard machines. If drilling capacity needs to be increased in the same building or department, a dual spindle system can add 100% more capacity without space consumption or new building investments.

In terms of quality, the current machine capabilities are already delivering very good yields. However, if a drill or operating problem occurs, it probably shows up on the doubled amount of spindles and boards. According to Van der Klink, R&D technical manager, Posalux is aiming to reduce dual spindle drill tolerances to +/-3.0µm (compared to single spindle machine technology).

Volker Feyerabend is president of Apros Int. Consulting and Services (apros-consulting.com); This email address is being protected from spambots. You need JavaScript enabled to view it..