Depaneling, also referred to as singulation, is the process of separating printed circuit board (PCB) assemblies from large fabricated panels into individual PCB units.
This article provides a comprehensive overview of conventional manual and automated laser-based PCB depaneling approaches. Key aspects covered include:
- Need for panelization in PCB fabrication
- Manual depaneling tools and techniques
- Overview of laser depaneling/singulation
- Working mechanism of laser systems
- Laser parameters and considerations
- Quality comparison between methods
- Advantages of laser depaneling
Why Panelize PCBs During Fabrication?
As PCB technology evolved towards reduced feature sizes and tighter tolerances, handling of individual PCBs through fabrication steps became highly impractical and yield-unfriendly.
Panelization techniques were adopted where instead of processing single boards, multiple circuits are arranged in a large panel format and taken through fabrication flow as a whole:
- Enables batch processing for improved throughput and yield
- Easier handling of small circuits
- Common tooling and nests for uniformity
- Compatible with standard equipment
- Panel stiffeners prevent warpage
- Cost-effective by distributing fixed costs
After completion of all board fabrication and assembly operations as a panel, it then enters the depaneling stage.
Need for Depaneling Before End Use
Although PCBs are fabricated and assembled in panel formats, they need to be separated down into individual boards before final integration and end-use by customers. This is carried out through the depaneling or singulation process.
Why Depanel PCBs?
- Panels sizes incompatible with target enclosures
- Enable handling of PCBs during QA/testing
- Different board formats on same panel
- Route signals between separated boards
- Mounting provisions require board clearance
- Allow unit-level repair/rework
- Accommodate contour dimensions
Thus, depaneling is an indispensable step to retrieve standalone functional boards from panels.
Manual Depaneling Methods
Before the advent of automated PCB singulation equipment, depaneling was performed using manual tools and procedures. These approaches are still relevant for low volume or prototype runs where automation is uneconomical.
Typical Manual Depaneling Techniques:
- Scoring and Snapping
- Shearing/Punching
- Routing
- Cutting with High-Speed Blade
Scoring and Snapping
This involves selectively engraving lines on the panel surface along intended breakout regions using a scoring tool. The residual web is then flexed manually to snap boards apart.
Advantages
- Simple process without investment
- No adhesion issues versus boards
Limitations
- High tear rates with brittle, thin boards
- Incapable of precision cuts
- Large panel flexing difficulties
- High labor involvement
Shearing/Punching
Deploys mechanical dies which impact the board with pressure sufficient to shear through board thickness when panels are loaded between top and bottom tools.
Benefits
- Handles PCBs with components mounted
- No debris generation risks
Shortcomings
- Limited positioning accuracy
- High tooling maintenance
- Slow process speed per station
- Risk of board flexure damage
Routing
Involves programmed drilling machines with routing/milling bits to cut required depaneling profiles through panel thickness.
Advantages
- Handles close conductor spacings
- No extensive tooling upkeep
- Decent dimensional precision
Disadvantages
- Unable to resolve dense board escapes
- Generates cutting debris
- Slow process throughput
Cutting with High-Speed Blade
Uses table-top presses with provision to mount high RPM rotary blades operated manually. Panels are pressed down during blades movement across boards for shearing action.
Pros
- High speeds with no drilling drips
- No plastic deformation versus boards
- Room temperature operation
Cons
- Limited positioning accuracy
- Generates debris and dust
- Risk of conductor nicking
- High blade wear and maintenance
While suitable for small quantities, manual methods compromise production rate, precision, quality consistency and yield. They also rely extensively on operator skills.
Overview of Laser Depaneling
Laser depaneling involves scanning focused laser over lines corresponding to required cut paths for pyrolytical ablation of board materials. The intense laser heat vaporizes polymers, ceramics and composites to singulate boards.
It constitutes a major technological advancement versus manual means by offering:
Benefits of Laser Singulation
- Minimal kerf widths down to ~25μm
- No mechanical contact or tool wear
- High positioning accuracy (~25μm)
- Excellent cut quality with no micro-cracks
- Easy depth control without exit burrs
- Fine pitch compatibility (~100μm)
- No board flexure or dust generation
- Automated, programmable process
- Handling Heat-sensitive boards with components
Thus, lasers present a versatile, non-contact singulation technique. Both UV (355nm) and CO2 (10.6μm) laser configurations are popular for PCB depaneling.
Laser Depaneling Methods
There are two techniques for laser-based PCB singulation:
Scribing:
Laser is used to cut specific dashed lines or patterns along the depanel regions. It creates deep grooves without going fully through the panel thickness. The boards are later snapped apart manually or using a breaking fixture.
Advantages:
- Fast process and low power consumption
- No complicated dust/debris extraction
Limitations:
- Limited thickness scribing capability
- Risk of conductor exposure or tear
- Extra post-processing steps needed
Full/Blind Depth Cutting:
The laser completely cuts through the full board thickness to achieve complete isolation of boards in a single pass. Most common depaneling technique.
Can further be implemented through:
- Sequential Processing: Board is moved relative to stationary laser for tracing separation path.
- Simultaneous Full Cut: Panel traversed under large beam emitting array of laser diodes cutting all dicing streets concurrently.
Among laser techniques, sequential full-depth cutting technique offers optimal quality, precision and capability to handle high board thicknesses.
Working Principle of Laser Depaneling
Key laser ablation mechanisms:
- Laser beam is focused on substrate through optics
- Board material absorb photon energy inducing molecular bond breakup
- Resultant violent vaporization causes clean material removal
- Inert gas (N2) assists blowing away ejected particles
- Multiple passes create cuts through full thickness
Process parameters like average power, frequency, scanning speed govern cut quality characteristics. Computerized G-code programming controls laser firing to trace complex 2D profiles.
Laser Parameters and Considerations
To achieve robust depaneling performance, appropriate laser settings need to be deployed based on board stackup.
Laser Wavelength and Type
Shorter UV wavelengths offer higher resolution but get absorbed easily requiring moisture-free boards. Longer CO2 wavelengths penetrate deeper with lower resolution. Both produce excellent cut quality without heat damage.
Pulse Repetition Frequency
Influences average laser power output. Typical range 100 Hz to 80 KHz. Lower frequencies limit material heating but reduce throughput.
Pulse Width / Duty Cycle
Proportion of laser on-time per cycle governing pulse peak power. Lower duty cycles prevent overburning. Range of 10-100 nS common.
Beam Quality Factor
Defined as laser beam diameter-to-divergence ratio indicating beam sharpness. Higher >0.8 preferred for smaller spot sizes and smooth kerf walls.
Cut Speed
Laser systems support programmable scanning velocities from 10 to 1000mm/s. Faster the cut speed lower the heat exposure for adjacent areas.
Gas Pressure
Process gas pressure between 0.5 to 6 bar helps evacuate melt on time preventing re-deposition.
Quality Comparison of Methods
Depaneling Quality Characteristics
| Parameter | Manual | Laser |
|---|---|---|
| Cut Accuracies | +/- 0.2mm | +/- 0.025mm |
| Width/Channel Compatibility | >2mm | >0.1mm |
| Debris Generation | High | None |
| Conductor Damage Risk | High | None |
| Process Control | Low | Excellent |
| Automation Scope | Minimal | High |
| Throughput Speed | Slow | Very high |
Lasers match closest to the accuracy, precision and quality demands of current-age PCBs designs containing shrinking features and tight clearances while minimizing damage risks.
Advantages of Laser Depaneling
Benefits of Laser Depaneling Systems
- Extremely narrow cut widths with fine control
- Permit very close proximities to conductors
- Clean, dross-free cuts without cracks
- No mechanical stresses or board handling
- High depth resolution without exit burrs
- Excellent precision and repeatability
- Environment-friendly process
- Minimal heat induction in materials
- Works reliably across panel sizes
These characteristics make laser depaneling the technology of choice for next-generation PCB singulation and dicing applications.
FAQs
Can components remain populated during laser depaneling?
Yes, most laser singulation systems permit cutting around components without causing damage. Unique galvo-split optic technology allows navigating around parts and connectors.
What safety measures are essential for laser systems?
Critical precautions involve proper public safety cage around equipment, fail-safe galvo motor controls, dual interlock switches, emission indicators and correctly rated optics among other aspects.
Does laser cutting leave behind harmful fumes?
Laser ablation generates only negligible smoke limited to the kerf width. Extractor systems filter out minute particulate matter to prevent operator exposure. No chemical effluents involved.
Can stress relief be incorporated during depaneling?
Laser systems support adding “mouse bites” or tabs structures at dicing streets which act as stress relieving features preventing pad lift off or solder joint damage.
Is laser cutting technology expensive to adopt?
Although high initial capital investment is required, lasers offer strong ROI through process speed, quality and yield over other alternative approaches to PCB singulation. Operating costs are also minimal without expendables.
