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What is silkscreen on a PCB?

Silkscreen PCB markings are the printed identifiers that help people assemble, inspect, connect and service a circuit board. They commonly include component references, polarity, connector functions, revision information and approved traceability marks. The term 鈥渟ilkscreen鈥� is widely used for the legend even when the actual production method is inkjet or another qualified printing route rather than a traditional screen.

This page explains legend manufacturing, ink selection, readability and inspection. The companion PCB silkscreen design guidelines focus on where to place the information in the layout. The solder-mask guide covers the separate protective coating and openings; legend ink should not be confused with that layer.

Print information that somebody will use

A useful legend answers practical questions: which connector is this, which way does the part face, which revision is being built, and where is the relevant test or service location? An attractive board image can still contain labels that are hidden by component bodies or too small to read. Manufacturing quality therefore includes preserving the intended information, not merely depositing ink somewhere on the board.

Prioritize functional identifiers before decoration. Polarity and connector orientation can prevent mistakes during assembly or installation. Component references support inspection and service. A revision mark helps connect the physical board with the right documentation. Logos and nonessential text should use space left after the critical information is resolved.

Do not place a certification or approval mark simply because it makes the board look professional. Such marks must follow the applicable authorization and traceability requirements. The legend artwork should identify what is approved for this product rather than reproduce a generic set of symbols from another board.

Compare the main legend-printing routes

The available route should be selected with the artwork, quantity, surface and required result in mind. One method is not automatically superior for every line width or board construction. Ask what the proposed process can reproduce consistently under the actual mask color and topography. A capability value without those conditions may be difficult to apply to a finished design.

is an example of product-specific ink documentation. Use the actual ink system's processing requirements rather than a generic curing temperature copied from another product. Ink compatibility and cure are part of the qualified manufacturing route.

Release the correct side and actual ink outlines

The legend output must identify the board side and orientation. Bottom-side text can be confusing when viewed through the board in a CAD system. Review the exported layer using an appropriate manufacturing viewer and confirm how it should read from the physical side. A correct on-screen editing view is not enough if the export convention is misunderstood.

Text has a physical outline. The location of its origin or bounding box does not define clearance to a pad opening. Stroke width, character shape, punctuation and rotation all affect the closest edge. This is particularly important near fine-pitch pads, fiducials and other surfaces that must remain free of ink.

The silkscreen layout guide develops those placement decisions. When preparing manufacturing data, keep the final text artwork and board revision synchronized so that a late reference change is not left only in the CAD project while an older layer is sent to production.

Size, stroke, contrast and assembly access work together

Character height alone does not establish readability. A very thin stroke can disappear or break even when the nominal height is generous. Closely spaced characters can merge. A label can be geometrically clear of a pad but hidden after a connector or shield is fitted. Review the actual font and assembled condition rather than a height value in isolation.

Contrast depends on the legend and underlying surface. White ink on a dark mask and dark ink on a light mask can provide different useful combinations. Color names alone do not quantify contrast or process stability. If a particular inspection or service condition matters, specify it and examine an appropriate production sample under that condition.

The text-zone planner checks only a simple geometric envelope using an entered character advance. It is useful for deciding whether a label is likely to need a different location or shorter wording. It cannot prove that the chosen ink, font or printing route will remain legible.

Plan a text zone before shrinking the characters

Enter the available width and height, reserved edge margin, measured character advance, character height and the intended text. The tool assumes fixed character advance; use a value measured from the selected CAD font and spacing. If the label uses a proportional font, review its actual outline instead of treating the result as precise.

In the illustrative example, the eight characters in 鈥淛1 POWER鈥� use a 0.65 mm fixed advance, giving a 5.20 mm width envelope. A 10 mm zone with 0.20 mm margins provides 9.60 mm usable width. The arithmetic fit is easy, but the final decision still depends on stroke, clearance, contrast and access after assembly.

If the text does not fit, consider a shorter useful label, a leader or a different location before reducing everything to the smallest possible font. Preserve the information that helps a person perform the task. A crowded legend that technically prints can be less useful than a concise set of readable identifiers.

Print, cure and inspect as one controlled operation

The board surface must be appropriate for the selected ink. Artwork registration and deposition control establish where the marking appears. Cure then develops the intended properties according to the material and process. Later handling and manufacturing operations must remain compatible with the finished marking.

The exact order relative to surface finishing can depend on the selected factory route and materials. Do not assume every board is marked at an identical point in production. The controlled explanation below shows the functional sequence from released artwork to readable identification and final inspection.

Keep ink away from functional surfaces

Solderable pads, contacts, probe areas and other specified features must retain the required accessible surface. Legend clipping is sometimes used in manufacturing to remove ink from excluded areas, but automatic clipping can also remove the information the designer intended to preserve. A partially missing polarity sign or connector label deserves a layout correction, not merely an assumption that the factory will fix it.

Review clearance against the actual solder-mask openings and final feature geometry. A nominal distance to the copper pad can give a different answer from a distance to a larger mask opening. The companion layout page includes a worksheet that subtracts explicitly entered registration, ink-spread and opening-edge allowances from a measured gap.

What should a legend quality review check?

Verify that required identifiers are present, on the correct side, readable and associated with the intended components or functions. Check clipping, smearing, missing strokes, contrast and local contamination where relevant. Review the result against the released artwork and the agreed acceptance requirements rather than judging only whether the overall board looks attractive.

The marking's durability and adhesion requirements should match the actual ink system and product scope. A visual check immediately after printing does not establish behavior after every later environment or cleaning operation. If those conditions matter to the product, include them in the applicable review and qualification requirements.

is an authoritative starting point for identifying relevant printed-board, assembly and material documents. Use the actual applicable standard and drawing to establish acceptance. A generic online character-height recommendation is not automatically an IPC limit or a 吃瓜tv guarantee.

Make the legend useful to assembly and service

The legend should coordinate with the bill of materials, assembly drawing and placement data. A reference renamed in one document but not another can create confusion even when the ink is perfectly printed. Before release, compare the final reference set and identify any intentionally omitted markings.

Keep test access and service access distinct. A test fixture may locate a pad from data without needing a printed label, while a technician troubleshooting a board may need a visible identifier. Decide which task the marking serves. The design for assembly page helps connect board identification with the wider assembly workflow.

For product-level traceability, define whether the board needs a static revision mark, a variable serial identifier or another controlled method. Those have different data and production requirements. Do not place a placeholder code in artwork and assume it will become a functional traceability system without an agreed process.

Quote special marking requirements explicitly

Ordinary legend requirements and unusual marking work may have different cost implications. Multiple colors, special inks, variable data, tight placement constraints or additional durability evidence can change the process scope. The effect depends on the selected route and quantity; a universal price multiplier would be misleading.

Include the final legend layers and identify critical labels in the fabrication package. If a proposed printing adjustment would affect polarity, connector function or traceability, require review before it is applied. Send the board requirements through PCB Manufacturing so marking, mask, finish and inspection are quoted as one coherent construction.

Silkscreen PCB questions