In simple terms, silkscreen is the non conductive legend printed on the board to identify components, pin 1, polarity, connectors, jumpers, test points, warnings, logos, revision codes. All the human facing info.
It’s usually a non conductive epoxy ink (common colors are white, black, yellow). It sits on top of the solder mask. And it helps assembly techs place parts correctly, helps test engineers find points fast, helps you six months later when you forgot what “J3” was supposed to do.
But here’s the catch.
Silkscreen is easy to design badly. Tiny text, hairline strokes, stuff sitting on pads, legends that disappear under parts. And then manufacturing does what manufacturing does. Slight registration shift, a little ink spread, uneven surface finish, and your perfect labels turn into mush.
So this guide is about practical silkscreen rules that survive real PCB production.
We’ll talk fonts, sizes, line widths, spacing, placement. Also a little about printing methods like LPI vs DLP because it affects how aggressive you can get.
What silkscreen is, and what it is not
Silkscreen is a marking layer. It is not a solder mask substitute.
Solder mask is there to prevent solder bridges and protect copper. Silkscreen is there to communicate. If you try to “fix” a soldering risk with silkscreen, it will not end well. The ink can burn, smear, or simply be removed where it conflicts with pads.
Typical silkscreen content includes:
- Reference designators (R1, C12, U3)
- Component outlines and orientation marks
- Polarity for electrolytics, diodes, LEDs
- Pin 1 indicators for ICs
- Connector labels
- Test points (TP1, TP2)
- Warnings and high voltage symbols
- Logos, QR codes, revision text
Inks are usually epoxy based or UV curable. Epoxy tends to have strong adhesion and survives soldering heat well. UV curable inks dry fast, good for high volume runs.
Substrate and surface finish matter too. FR4 is the usual and prints nicely. Rogers materials sometimes need specific ink formulations. Flex PCBs are trickier because the surface moves and the ink needs to flex too. And finishes like HASL can create uneven topography that makes fine silkscreen harder, while ENIG is flatter and friendlier.
The two big printing methods (and why you should care)
Most silkscreen legends you’ll run into are made using one of these:
Liquid Photo Imaging (LPI)
LPI uses a photosensitive ink and exposure process. It’s common in volume manufacturing and tends to be durable. It can hold decent detail, but like any process, minimum line and text rules still apply.
Přímý tisk legendy (DLP)
DLP is essentially direct printing, often inkjet style, straight onto the PCB. It skips films and developing steps, can be faster, and can do detailed legends. It’s also often described as slightly less durable than LPI, depending on ink system and cure.
The practical takeaway for designers is simple.
Even if a vendor can print very fine features, your yield drops when you push silkscreen to the edge. And your legibility drops even earlier. So we aim for “prints reliably” not “prints in a lab demo”.
Best font style for PCB silkscreen
You want a font that stays readable when:
- the stroke thickens slightly from ink spread
- the print shifts a little from registration tolerance
- the board is viewed at an angle under bench lighting
- flux residue and dust exist (because they always do)
Use simple, standard, sans serif fonts
Practical choices:
- Single stroke / vector like fonts (often what CAD tools use by default)
- Simple sans serif fonts similar to Arial, Helvetica, DIN style
- The built in PCB CAD “Default” or “Proportional” fonts if they are known to plot cleanly
Why not fancy fonts?
Because serifs and thin/thick stroke contrasts get ugly fast on silkscreen. Curls fill in. Tiny gaps close. The “R” and “P” start looking like the same letter. It’s not a design poster, it’s an instruction label on a factory object.
Avoid these font behaviors
- Very thin strokes
- High contrast strokes (thick verticals, thin horizontals)
- Decorative elements
- Italics in small sizes
- All caps in tiny text (caps reduce shape variety, ironically harder to read when small)
One more boring but important point
Keep it consistent. Same font style across the whole board. If you mix styles, it looks messy and makes scanning harder during assembly.
Best text size for PCB silkscreen (what actually works)
A lot of people quote “1.0 mm minimum text”. It’s a decent rule of thumb but we need to unpack it. Text size means almost nothing without stroke width.
In PCB silkscreen, what matters most is:
- character height
- stroke width
- spacing between strokes
- and whether the text is going to get clipped by solder mask openings, pads, or courtyard keepouts
Here are practical, production safe recommendations that tend to survive common fab tolerances.
Recommended silkscreen text sizes (general)
For reference designators and labels you want humans to read without a microscope:
- Character height: 1.0 mm to 1.5 mm preferred
- Character height minimum: 0.8 mm (only if you really must)
- Stroke width: 0.15 mm to 0.20 mm preferred
- Stroke width minimum: 0.12 mm (again, only if you must)
If you’re labeling dense areas and accept that it might be “assembly readable with magnification”:
- Character height: 0.8 mm to 1.0 mm
- Stroke width: 0.12 mm to 0.15 mm
If you need “seen from across the bench” text (connector names, polarity warnings):
- Character height: 1.5 mm to 2.5 mm
- Stroke width: 0.18 mm to 0.25 mm
These ranges aren’t magic laws. They’re “you probably won’t regret this later” values.
Spacing inside letters matters
For example, the hole inside an “O” or “P”. If it’s too small, it fills in and you get blobs. So even if your stroke width is technically printable, the font geometry might not be.
This is why simple fonts win. They keep counters open.
Best line width for silkscreen outlines and symbols
Silkscreen isn’t just text. It’s outlines, pin 1 dots, polarity plus marks, arrows, triangle indicators, test point circles.
Recommended line widths:
- General outlines and symbols: 0.15 mm to 0.20 mm
- Minimum (if your fab allows it): 0.12 mm
- Bolder warnings or polarity marks: 0.20 mm to 0.30 mm
If you go too thin, lines break or fade. Too thick, you lose precision and may collide with other features.
Filled shapes vs outlines
Filled shapes (solid triangles, solid circles) are more forgiving in print. If you need a pin 1 indicator that always shows up, a filled dot is often better than a tiny outline circle.
Clearance rules: where silkscreen should NOT go
Most fabs will automatically clip silkscreen that overlaps solder mask openings, pads, exposed copper. That’s good. But it also means your text might get chopped into nonsense.
So you want to design with clearance in mind, not rely on auto clipping.
Practical clearances:
- Silkscreen to solderable pads: at least 0.15 mm, preferably 0.20 mm
- Silkscreen to via openings: at least 0.15 mm to 0.20 mm
- Silkscreen to board edge: at least 0.25 mm (more if the edge will be routed roughly)
- Silkscreen to component body: leave breathing room so the label is still visible after assembly
Also, avoid placing silkscreen across solder mask dams between pads. Even if it prints, it can look smeared and messy.
Masked vs unmasked vias
If vias are tented (covered by solder mask), silkscreen can run over them more safely. If vias are open, ink can spread into holes or break around the opening. In dense designs, tenting vias under silkscreen often improves print quality.
Color selection: what’s actually readable
Standard silkscreen colors: white, black, yellow. The best choice depends on solder mask color and the viewing environment.
Common pairings:
- Green solder mask: white silkscreen is the default for a reason
- Black solder mask: white silkscreen works, yellow can also pop
- White solder mask: black silkscreen is usually the move
- Red/Blue solder mask: white generally works, but contrast can vary with finish
One thing people forget. Surface finish changes reflectivity. ENIG is shiny, HASL can be uneven and reflective in spots. Under bright light, some legends become harder to read even if the contrast is “theoretically” fine.
If readability matters, don’t pick low contrast for aesthetics.
Placement tips that save you later
A few habits that improve assembly speed and reduce mistakes.
Put reference designators where they can be seen after assembly
Sounds obvious. It’s not always done.
- Place refdes outside the component courtyard when possible.
- For ICs, put refdes near pin 1 side, but not under the chip.
- For passives, put refdes aligned consistently, same reading direction across the board.
Orientation and polarity marks should be redundant
For diodes, LEDs, electrolytics. Use both:
- a polarity symbol on silkscreen
- and a clear footprint graphic (like a notch, bar, plus sign)
- and ideally a consistent library standard
Because if one gets clipped, the other often survives.
Mark test points like you mean it
If the board will be probed:
- Label test points with “TPxx”
- If space allows, include the net name or voltage (TP5 3V3)
- Use a circle or target symbol large enough to find quickly
And keep test point labels out of areas that will be covered by shields, heatsinks, or tall connectors.
How fabrication realities mess with silkscreen (and how you design around it)
Silkscreen printing can fail in a few predictable ways.
Misalignment and registration shift
Causes include registration errors, board warping, and process tolerances. In manual screen printing, alignment is more operator dependent. Automated printers can hit micrometer level alignment, but nothing is perfect.
Design around it by:
- not placing text too close to pads
- avoiding tiny features that rely on perfect alignment
- giving symbols a little extra margin
Smudging and ink spread
Often from excessive ink, wrong viscosity, contamination, or improper curing.
You can’t control the factory’s ink viscosity from CAD, but you can:
- avoid ultra thin strokes
- avoid cramming text between pads
- use simpler letterforms
Missing or faded prints
Worn screens, poor adhesion, environmental exposure, bad cure cycles. Again, manufacturing side issues, but your design helps by staying within comfortable feature sizes.
And storage matters. Humidity and temperature swings can affect quality. If boards are going into harsh environments, talk to the fab about ink type and durability expectations.
IPC and symbol conventions (the sensible approach)
You’ll see references to standards like IPC-7351 for land patterns and placement guidance. There are also standards around marking conventions, inspection, durability, and general fabrication acceptability.
In practice, for silkscreen design, the “IPC mindset” is:
- Use clear, conventional symbols.
- Keep text legible.
- Don’t place markings where they interfere with soldering or inspection.
- Make assembly unambiguous.
If you’re doing medical, automotive, aerospace, then yes, you should align with the exact standard requirements for marking and traceability. For most commercial boards, you still benefit from following the same discipline.
Special cases: flexible PCBs and high density boards
Flexibilní desky plošných spojů
Flex boards bend. Ink needs to flex too, and adhesion can be harder. Printing pressure and screen tension become more sensitive, so very fine legends are riskier.
If your flex design is dense, consider:
- keeping silkscreen minimal
- using larger, bolder markings
- alternative marking methods like inkjet printing or laser marking (more permanent, often higher precision)
High density boards
Sometimes there’s just no room.
What works better than shrinking everything:
- Move some labeling to the assembly drawing instead of the board.
- Use fewer but more meaningful labels (only connectors, polarity, key ICs).
- Use QR codes or 2D codes for revision and traceability if your fab supports it, but test readability on real samples.
Quick checklist: my “safe default” silkscreen rules
If you want a starting point you can apply to most boards:
- Simple sans serif font, consistent across board
- Text height 1.0 mm to 1.5 mm for refdes where possible
- Stroke width 0.15 mm to 0.20 mm
- Silkscreen line width 0.15 mm to 0.20 mm
- Clearance to pads and exposed copper 0.20 mm preferred
- Don’t rely on auto clipping, place legends so they survive
- Make polarity and pin 1 markings obvious and redundant
- Choose silkscreen color for contrast, not vibes
It’s not glamorous. But it prints well and reads well.
A note on silkscreen services and production
Many PCB manufacturers include silkscreen as a standard option, including services like PCBGOGO, and plenty of others. Whether your board is produced with LPI or DLP, the design fundamentals above still apply.
If you are doing manual printing in house, expect more variability and more alignment challenges. Automated silkscreen printers are faster and more consistent for volume work, but your design still needs to be manufacturable.
And yeah, if you’ve ever seen a board where the legends are slightly shifted and half the “R” designators are missing, that’s usually not because the designer “forgot”. It’s because the design was sitting right on the edge of what the process could hold.
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FAQs (Frequently Asked Questions)
What is silkscreen on a PCB and why is it important?
Silkscreen on a PCB is the non-conductive ink layer printed on the board to identify components, pin 1, polarity, connectors, jumpers, test points, warnings, logos, and revision codes. It provides all the human-facing information that helps assembly technicians place parts correctly, assists test engineers in locating points quickly, and aids future reference for maintenance or troubleshooting.
What materials and colors are commonly used for PCB silkscreen?
PCB silkscreen typically uses non-conductive epoxy-based or UV-curable inks. Common colors include white, black, and yellow. Epoxy inks have strong adhesion and withstand soldering heat well, while UV-curable inks dry quickly and are suited for high-volume production runs.
What are the main printing methods for PCB silkscreen and how do they differ?
The two main printing methods are Liquid Photo Imaging (LPI) and Direct Legend Printing (DLP). LPI uses photosensitive ink with an exposure process common in volume manufacturing and tends to be durable. DLP involves direct inkjet-style printing onto the PCB, allowing faster processing and finer detail but can be slightly less durable depending on the ink system used.
What font styles are recommended for PCB silkscreen to ensure legibility?
Simple, standard sans serif fonts such as single stroke/vector fonts or those similar to Arial, Helvetica, or DIN style are recommended. Avoid fonts with serifs, thin strokes, decorative elements, italics at small sizes, or all caps in tiny text. Consistency in font style across the board improves readability during assembly.
What are the best text size guidelines for PCB silkscreen to ensure readability after manufacturing?
For reference designators and labels intended for human reading without magnification: character height should be between 1.0 mm to 1.5 mm (minimum 0.8 mm if necessary), and stroke width should be between 0.15 mm to 0.20 mm (minimum 0.12 mm if needed). Adequate spacing between strokes is also crucial to maintain clarity despite ink spread or registration shifts during manufacturing.
Can silkscreen be used as a substitute for solder mask on PCBs?
No, silkscreen is not a solder mask substitute. Solder mask prevents solder bridges and protects copper traces; silkscreen serves purely as a marking layer for communication purposes such as labeling components and test points. Using silkscreen to fix soldering risks can lead to issues like burning or smearing of the ink.
