Using the Mosaic™ Laser for PCB Processing

The demand for laser micromachining applications is ever increasing due to the growing trend of miniaturization and economical production of electronic devices and products. The availability of compact, powerful, reliable and cost-effective laser technology advancements such as nanosecond pulsed Q-switched laser sources has realized the commercial viability of more micromachining applications.

The ability of non-invasive, cost-effective, and rapid processing of tiny, high precision features is the decisive factor behind the selection of laser technology as a solution. One common example is PCB manufacturing processes, where lasers are used in laser direct imaging (LDI), via drilling, profiling (cutting), depaneling, marking, trimming, repair and skiving processes.

This article demonstrates the advantage of using Spectra-Physics’ new generation of Q-switched DPSS nanosecond pulsed Mosaic 532-11 laser in certain rigid and flexible PCB processes (Figures 1 and 2).

Figure 1. Example of Rigid PCB. a) Rigid PCB and b) schematic cross-section of rigid PCB showing 1) blind via and 2) through via

Figure 2. Example of Flexible PCB. a) Flexible circuit board and b) schematic cross-section of flexible PCB showing 1) blind via and 2) through via

The Mosaic 532-11 Laser

Spectra-Physics’ innovative new product, the Mosaic 532-11 laser integrates a range of proprietary technologies and solutions to tackle market pressure for lower cost and better efficiency. It is a very compact laser, thanks to its Box™ design integrating both the power supply and laser head in one package.

This feature facilitates integration of the laser into any machine tool. The Mosaic laser is specially engineered for micromachining applications in an around-the-clock production environment where system uptime is a crucial factor. The specifications of the Mosaic laser are as follows:

Wavelength : 532nm
Average Power : > 11W at 50kHz
Peak Power : ~11kW at 50kHz
~22 kW at 30 kHz
Repetition Rate : 0–500kHz
Pulse Width : < 15ns
M2 : < 1.2

Laser Depaneling of Thin Rigid PCB

The thin rigid PCB sample comprises a 300µm thick PCB resin material devoid of stiffening material or copper. Low carbonization and good quality cuts can be achieved when the Mosaic 532-11 laser is operated at 64μJ energy with high pulse repetition frequency (PRF) of 150kHz. Higher throughput can also be attained using multiple scans, yielding an average cutting speed of 50mm/s (Figure 3).

Figure 3. Microscope picture showing a) rigid PCB panel with individual boards linked together, b) entrance side cut quality of depaneled thin rigid PCB, and c) cross-section of a cut

Laser Drilling of Flexible PCB (FPCB)

A 180-μm-thick FPCB was used as the sample to be drilled. It comprised an acrylic adhesive sandwiched between polyimide-copper-polyimide. The wavelength of 532nm is strongly absorbed by the copper layer in this material combination. Moreover, the energy is more efficiently coupled into the neighboring polyimide material by the copper layer, yielding a superior quality through vias.

The data demonstrates the influence of the pulse energy and corresponding PRF on the drill rate and hole size (Figure 4), achieving a good compromise between throughput and hole quality at ~200μJ pulse energy with 50kHz PRF. This setup allowed drilling 65µm entrance and 35µm exit holes at a rate of < 1ms/hole.

Figure 4. Microscope picture shows 50μm target diameter through vias drilled in 180μm thick polyimide-copper-polyimide FPCB sample at various PRFs.

Laser Profiling of Thick FPCB

Here, the FPCB materials used were a 160-μm-thick all-insulator FPCB structure of polyimide-polyimide sandwiching the acrylic adhesive and a 180-μm-thick FPCB layered structure of polyimide-copper-polyimide sandwiching the acrylic adhesive. The Mosaic laser was used to trepan cut 5mm circles in both FPCB materials at an average speed of 11.5mm/s using multiple passes. The optimized setting was 20kHz PRF with ~390μJ pulse energy, yielding good quality cuts (Figure 5).

Figure 5. Microscope picture [a) entrance side and b) exit side] showing 5mm circular trepan cuts in FPCB processed at 20 kHz PRF.

Conclusion

The results show the advantage of using the Mosaic 532-11 to cut and profile FPCB material composed of copper and polyimide materials.

About Spectra-Physics

Spectra-Physics, a Newport Company, is the world's premier supplier of innovative solutions for precision laser applications. Our broad portfolio of lasers are proven in 24/7 applications and are backed by our global support team. Our innovation driven culture strives to create breakthrough products that achieve new levels of cost-performance that power our customers' success.

This information has been sourced, reviewed and adapted from materials provided by Spectra-Physics.

For more information on this source, please visit Spectra-Physics.

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