Traditional PCB fabrication relies on a subtractive process - fully metallizing a copper surface then selectively etching away unwanted material to construct circuit traces and features. The resulting loss of material leads to inherent process and product limitations.
In contrast, newer additive techniques build up patterns on laminate layers by directly depositing metals only in target shapes through a “mask and plate” approach. Not consuming base material, additive processes minimize waste while overcoming key restrictions for better performing boards.
This article explores multiple improvements additive process offers circuit designers by reducing costs, enabling more densely-integrated boards, supporting ultra-fine features, cutting chemical usage, shortening cycle times and allowing flexible hybrid electronics integration. Understanding these advantages allows properly leveraging benefits within emerging PCB additive technologies from an array of manufacturers.
Advantages Explained
Additive techniques address primary issues with subtractive methods for cost and product enhancements:
Non-Consuming Process
Plating only required circuit traces and pads directly onto base laminates eliminates etching away unwanted copper layers to isolation. This avoids permanent material loss increasing metal usage efficiency.
Complex Pattern Constructions
Shaping intricate pad geometries through photolithographic masks and precisely targeted electroplating satisfies rising demands for high-density interconnect (HDI) board integration without dependence on large contiguous foil sheets. Vias connect layers additively.
Enhanced Material Purity
Targeted direct copper or silver crystal lattice deposition in ideal alignments avoids dislocations and deviations inflicting rolled annealed sheet metal from subtractive steps of full foiling, etching then drilling. This produces improved material properties.
Fine Feature Resolutions
Plating conductive pastes and liquids into tiny openings with high dimensional accuracies enables trace widths and spacings down to ~10μm supporting increasing interconnect densities and component pin pitches.
Lower Environmental Impacts
Reducing chemical etchants, metal waste generation and water usage over full panel subtractive processes cuts pollution through efficient material use only where needed on additive fabrication.
Cost Savings Opportunities
When executing appropriate designs fully embracing additive manufacturing strengths for density, layer counts and tolerances, overall board expenses reduce from process optimizations.
Additive PCB advancements deliver compelling product enhancements beyond conventional approaches.
Additive Process Background
Appreciating benefits starts with examining modern PCB additive manufacturing techniques compared to traditional methods.
Typical Subtractive Workflows
Conventional processing sequences involve:
1. Laminate layer preparation
2. Copper foil application across full panel surface on each side
3. Photoresist patterning via lithography
4. Masked panel etching to remove unwanted copper
5. Photoresist stripping
6. Drilling holes for vias/interconnections
This approach consumes base copper layers driving material inefficiencies.
Additive Processing Basics
In contrast, additive relies on:
1. Laminate preparation
2. Photoresist dispensing onto bare laminates
3. Lithographic imaging to form plating windows
4. Electroplating conductive materials only into openings
5. Resist removal leaving traces behind
6. Layer bonding
No initial metal layers etched away afterward. Additional plating forms vias between layers.
Table 1 highlights differences:
| Subtractive | Additive | |
|---|---|---|
| Base Metal | Full foil panel | None initially |
| Primary Shaping | Etch removal | Plating growth |
| Conductor Formation | Subtract material | Deposit locally |
| Via Connection | Drill then plate | Plate then bond |
Table 1: Comparing fundamental PCB subtractive and additive production
Understanding divergent workflows sets context for specific benefits.
Detailed Manufacturing Benefits
Beyond fundamentals, inspecting details on process improvements unlocks advantages for application.
Density Improvement Cases
Additive photolithography patterns tiny plating windows on laminates creating pads and traces pushed to extreme density levels. This enables cutting-edge component interconnects and wire spacing:
- 01005 passive components
- <0.3mm pitch BGAs
- Escape routing within 20 μm gaps
Subtractive processes struggle matching such resolutions.
Layer Count Increases
Plating conductive vias during layer bonding avoids needing to mechanically drill interconnections. Skipping drill steps enables stacking additional layers novel ways:
- High layer counts >30+
- Thin layers down to 25 μm
- Mixed layer heights
This facilitates complex HDI integrations impossible subtractively.
Novel Routing Options
With no initial metal foil layers, routing design can expand into fully arbitrary 3D shapes enabled by additive plating. This opens novel pathways applications like:
- Non-planar flex circuits
- Curved circuits
- Embedded components
- Hybrid electronics
Additive liberation from 2D plane restrictions unlocks new possibilities.
Financial Savings
Reducing metal waste by avoiding full panel etching coupled with smaller features translates into reduced costs through:
- 20-30% less materials usage
- 5-15% savings in laminate substrates
- 10-20% drop in processing fees
Exact savings depend on design optimization.
Additive manufacturing stretches possibilities for electrical engineers.
Additive Technology Selection
Many equipment and material options exist for additively building printed circuits. Select optimal choices balancing capabilities against design needs.
Available Plating Materials
Wide material selections meet conductivity needs:
Copper - Most common lower cost traces
Silver - enhanced conductivity for high frequency
Gold - Oxidation resistant plating
Palldium - Alternate oxidation barrier
Determine suitable metals against product requirements like operating frequency, corrosion, conductivity and termination finishes. Localized plating allows mixing compositions.
Laminate Options
Range of mounting substrates suit applications:
- FR4 Glass Weave
- Rigid-Flex Composites
- Polyimides
- Ceramics
Match mechanical and electrical needs like flexibility, dielectric constants and loss tangents.
Dimensional Precision
Equipment determines minimum achievable features and alignments:
- 10 μm structures using laser photoplotters
- 25 μm lines/spaces available on advanced tools
- 50 μm features accessible on entry systems
Evaluate tradeoffs between capabilities, volumes and expenses.
Throughput Considerations
System production capacity ratings guide additive adoption:
- Prototyping - Small batch
- Low/Mid Volume - Up to ~5000 m2/month per system
- High Volume - Over 5000 m2/month capacity
Determine breakpoints between parallelized systems or hybrid subtractive supplementation based on total volume needs.
Additive solutions scale across diverse applications.
Candidate Designs Benefiting
While additive techniques continue evolving broader applicability, certain designs already achieve immediate improvements.
High Density Interconnects
HDI signal routing dense designs reduce layers through blind and buried vias between fine L/S traces avoiding subtractive process limits by lowering costs over equivalent etched build-ups.
Miniaturized Products
Ultra-compact form factors shrink PCB outlines capitalizing on space savings from additive’s high-density assembly.
Flexible Circuits
Curving flex boards around structures simplifies with plated traces surviving repeated bending exceeding etched copper foil cracking endurance.
5G Components
Fast growing 5G infrastructure relies on increasingly finer pitch radio components amenable to additive capabilities supporting dense interconnects.
Hybrid Integrations
Mixing discreet and integrated electronic components embedded within structural surfaces simplifies using direct additive formation.
High Layer Count Controllers
Data processing products like servers and switches pack routing exceeding 20+ layers enabled purely additively.
Hybrid Manufacturing Approaches
Blending additive plating with traditional subtractive SBU laminate processing combines strengths:
Semi-Additive Plating
Plate resist openings on full copper foils leaving unpatterned regions unaffected instead of fully etching panels. This simplifies some steps.
Interposer Fabrication
Construct intermediate interposers for package connections using high density additive patterning then integrate into conventional PCBs.
Selective Mixed Lines
High speed signals route on additive traces between driver ICs while lower frequency nets remain subtractive allowing cost balancing.
Heterogeneous Integration
Embed additively formed components like capacitors or resistors into standard laminate layers taking advantage of 3D freedom.
Choose approaches maximizing performance for cost by applying additive advancement judiciously where most beneficial per designs.
Conclusion
Continual refinement of additive printed circuit board manufacturing technology outpaces constraints faced by conventional etched subtractive techniques for building boards thanks to fundamental process innovations.
Tremendous performance enhancements from designers’ perspectives enable pushing fabrication boundaries through increased routing densities with finer lines, additional layer stacks, improved material quality,
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