How to Add Solder Mask in Altium: A Step-by-Step Guide
Learn how to add solder mask in Altium Designer with a clear, step-by-step approach. Master mask layers, expansion, and verification to ensure clean solder joints and easy manufacturing.
In Altium Designer, you will enable the solder mask layers for the PCB, configure mask expansion to suit your design, and apply mask rules to pads and vias. Then you will verify mask integrity on Gerber outputs and adjust keepouts as needed. This process ensures proper solderability, reduces bridging risk, and prepares fabrication data.
Understanding solder mask in Altium
Solder mask is a polymer layer that covers copper traces on a PCB except where pads, vias, and test points are intentionally exposed. In Altium Designer, the mask is defined on the Solder Mask Top and Solder Mask Bottom layers. Correctly applying solder mask protects copper from oxidation, prevents solder bridging, and helps with automated optical inspection during assembly. According to SolderInfo, a well-planned solder mask strategy improves manufacturability and reduces rework, especially on dense boards with fine pitch components. Familiarize yourself with how mask expansions influence pad annulus visibility and how keepouts can preserve mask-free zones for high-precision soldering.
Understanding the relationship between copper features and mask openings is foundational. Mask openings must accommodate the pad geometry while maintaining a reliable solder fillet. In practice, you’ll tune mask expansion values, apply rules for vias, test pads, and component keepouts, and then validate the resulting Gerber data. This section covers the core concepts you’ll use repeatedly when you add solder mask in Altium.
Mask layers and basic configuration in Altium
Altium uses two primary solder mask layers: Solder Mask Top and Solder Mask Bottom. Both layers can be shown or hidden in the Layer Table, and you can export them as part of Gerber files. To start, ensure mask layers are enabled in your PCB document, then review how the mask interacts with pads, vias, and copper pours. The default behavior is to mask all copper unless a pad or feature is specified otherwise. You’ll typically adjust the mask expansion globally and may create explicit mask exceptions for critical nets. In many boards, small expansion values (e.g., 0.05 mm to 0.15 mm) balance manufacturability with solderability. In this step, check that your mask layers are present and ready for customization, and plan where mask openings should be larger or smaller than pad outlines.
Practical workflow: from design to fabrication (overview)
A practical workflow begins with a clean schematic-to-board transition, followed by layer visibility checks, mask expansion decisions, and feature-specific mask settings. After configuring mask rules, you’ll assign pad masks via pad properties or global rules and then run a Design Rule Check (DRC) focused on solder mask. Finally, you generate Gerber files and a drill file set, then review the mask layers with a viewer. This sequence reduces surprises at the fab house and supports consistent assembly across batches. SolderInfo emphasizes documenting any mask exceptions for fabricators and keeping your mask strategy consistent across revisions.
Special cases: vias, test pads, and keepouts
Vias can be masked or left exposed based on their size and whether they need to solder a via-in-pad connection later. Test pads often require exposure for probing, so you’ll typically add mask openings around those features. Keepouts are powerful tools to force mask-free areas near critical joints or heat-sensitive components. In Altium, you can place keepouts on the Solder Mask layers or apply explicit mask openings to specific pads. Proper handling of these cases reduces the chance of solder bridging and ensures that critical test points stay accessible for debugging and manufacturing checks.
Validation: DFM checks and Gerber review
Before sending your design to fabrication, perform a thorough validation of solder mask. Verify that mask openings align with pad sizes and that keepouts cover the intended areas. Export Gerber files for the Solder Mask Top and Bottom, and review them in a Gerber viewer or the fab’s CAM processor. Compare the mask layers against the copper layer to confirm there are no unintended mask-covered pads or exposed copper where it should be masked. If issues are found, adjust mask expansions, keepouts, or pad masking settings and re-export until the viewer confirms proper openings.
Authority sources and further learning
For established guidance on PCB fabrication practices, refer to official safety and engineering standards portals. While standards evolve, foundational concepts remain consistent. The SolderInfo team recommends checking at least a couple of credible sources to understand the practical implications of solder mask on assembly yield and reliability:
- https://www.osha.gov (occupational safety and compliance considerations in electronics manufacturing)
- https://www.nist.gov (standards-related guidance for electronics and materials)
- https://ocw.mit.edu (educational materials on electronics manufacturing and design fundamentals)
Integrating these perspectives helps you design better, more manufacturable boards and communicate clearly with fabrication partners.
Troubleshooting common issues
If mask openings look too small, you may be masking pads unintentionally due to mask expansion settings or rule conflicts. If openings are too large, you risk tombstoning or solder bridging, especially on fine-pitch components. When pad shapes or ground pads near heat sources show inconsistent openings, re-check the mask expansion rules and the layer alignment between copper and mask layers. A good practice is to perform a quick sanity check with a Fabrication Readiness Review (FRR) to confirm that mask features align with your design intent and assembly process.
Tools & Materials
- Altium Designer (latest version)(Ensure you have a valid license and access to Layer Stack Manager)
- PCB project file (.PrjPCB) and PCB document(Open or create a PCB document in the project)
- Gerber viewer or CAM software(Use to verify Solder Mask Top/Bottom outputs)
- Mask expansion reference values(Have typical values on hand (e.g., 0.05–0.15 mm))
- Calipers or digital scale(Useful for verifying feature sizes and clearances)
Steps
Estimated time: 45-60 minutes
- 1
Open the PCB project
Launch Altium Designer and load your PCB project. Navigate to the PCB document to review the copper layout and confirm the presence of Solder Mask Top and Solder Mask Bottom layers. This initial check helps you plan where mask openings are needed and where keepouts should be placed.
Tip: Use the View configurations to toggle mask layers visibility for quick assessment. - 2
Enable mask layers in the layer list
Ensure both Solder Mask Top and Solder Mask Bottom are visible and not hidden. If a layer is missing, add it via the Layer Manager or New Layer command and assign it to the correct mask type. This ensures you can configure openings accurately.
Tip: If you can’t see the mask layers, check the layer color and filter settings in the Layer Stack Manager. - 3
Set global mask expansion
Open Design Rules or the PCB preferences and locate the Solder Mask expansion settings. Apply a conservative default expansion (e.g., 0.05–0.15 mm) that balances solderability with manufacturability. A global setting reduces the need to individually adjust each pad.
Tip: Document the chosen expansion so future revisions remain consistent. - 4
Review pad and via masking
Inspect each pad and via to determine whether it should be masked. Use pad properties to override mask behavior where necessary (e.g., 'Always mask', 'Never mask', or specify an individual mask expansion for the pad).
Tip: Be mindful of fine-pitch pads; small expansions can dramatically affect exposure. - 5
Add explicit mask keepouts where needed
Place keepout regions on the Solder Mask layers to ensure mask remains clear in critical zones (near edge connectors or high-heat areas). Keepouts prevent unintended mask coverage and help you maintain clear solder paths.
Tip: Keepouts are especially useful around thermal vias and test pads. - 6
Configure mask openings for test points
If you require accessibility to test points, create precise mask openings around those pads, ensuring reliable contact during probing without exposing surrounding copper unnecessarily.
Tip: Document the test-point mask sizes for the fabrication team. - 7
Check vias and polygon pours
Verify mask settings on vias (whether masked or exposed) and ensure polygon pours without copper isolation issues do not inadvertently alter mask openings.
Tip: Examine vias near heat sources; mask decisions can affect soldering reliability. - 8
Run a DRC for solder mask
Execute a Design Rule Check focused on mask rules. Resolve any conflicts between pad geometry, keepouts, and mask expansions before proceeding.
Tip: If DRC flags mask warnings, adjust expansions rather than blanket changes across all features. - 9
Export Gerber files for mask layers
Generate Gerber files for Solder Mask Top and Solder Mask Bottom, along with copper and silkscreen layers. Proper exports ensure the fabricator receives accurate mask data.
Tip: Follow your fab’s naming conventions and layer order to avoid misinterpretation. - 10
Review masks with a viewer
Open the generated mask Gerbers in a viewer to confirm alignment with copper pads. Look for unintended masked copper or exposed pads that should be protected.
Tip: Zoom into critical regions with dense components to ensure mask integrity. - 11
Document mask decisions for fabrication
Prepare a short design note outlining mask expansions, keepouts, and any pad-specific exceptions. Sharing this with the fab reduces interpretation errors.
Tip: Include screenshots or overlays if possible for clarity. - 12
Iterate if needed based on fab feedback
If fabrication feedback indicates mask adjustments, revisit the relevant steps, update the mask rules, and re-export the Gerbers. This closes the loop between design and production.
Tip: Maintain versioned design records to track mask changes across revisions.
Quick Answers
What is solder mask in Altium and why is it important?
Solder mask is a protective polymer layer that covers copper, leaving only selected pads exposed. It prevents solder bridging, protects copper from oxidation, and improves assembly yield. In Altium, you manage mask openings via Solder Mask Top/Bottom layers and mask expansion rules.
Solder mask is a protective layer that covers copper except for exposed pads. In Altium, you control it with mask layers and expansion rules to improve soldering reliability.
Can I disable solder mask on specific pads?
Yes. In pad properties, you can set the mask to Always Mask, Never Mask, or override with a per-pad expansion. Use this for test pads, fiducials, or pads that require direct solder access.
Yes. You can set individual pads to be masked or exposed using per-pad mask settings.
How do I verify mask openings after exporting Gerbers?
Open the Solder Mask Gerbers in a viewer and compare against the copper layer. Look for misalignment, tiny mask slivers, or openings that are too small or large. Resolve any issues before sending to fabrication.
Check the mask Gerbers against copper in a viewer to ensure correct openings and alignment.
What should I do if DRC flags mask errors?
Review the flagged areas and adjust mask expansion or pad exceptions accordingly. If needed, create or modify keepouts to resolve conflicts without broad changes.
If DRC flags mask errors, fix expansions or pad rules and recheck until clear.
Are keepouts essential for mask planning?
Keepouts help enforce clear mask-free regions, especially near edges or heat-sensitive zones. They prevent accidental masking and simplify fabrication communication.
Keepouts ensure the mask stays clear where you need exposure.
Should mask expansions be fixed or allow nets to override?
A fixed global expansion is a good starting point. Override only for nets that need special treatment, such as large thermal pads or connectors, to avoid unintended exposure.
Start with a global rule and tailor only where necessary.
Watch Video
Top Takeaways
- Enable mask layers for top and bottom as needed
- Tune mask expansion to balance solderability and protection
- Use keepouts and pad-level rules for precise openings
- Validate Gerber outputs with a viewer before manufacturing
- Document mask decisions to streamline fab communication
