PCB News - Textual markings on PCB circuit boards in the PCB design

Textual markings on PCB circuit boards usually include component numbers, polarity markings,test point markings, version numbers, manufacturer's information, and so on. These markings are printed directly on the surface of the PCB by means of silk-screen printing or laser printing, etc. to facilitate various aspects of production, testing, maintenance and traceability.

It is as important as our circuit boards and printed metal circuit lines, and no "magic ghosts" can be caused here.

Common PCB markings have etching marking oil and ink markings. Let's follow the footsteps of the Canadians to see what quality control standards they have.

1.Etching marks

The production of etching marks is the same as the production of conductors on the printed board.Therefore,the etching mark should meet the following requirements.

•Each character is legible.

• Maintain minimum conductor spacing requirements between etched characters and active conductors.

• In the case of legible characters, marking defects (such as solder bridging, over-etching, etc.) are acceptable.

• The mark does not violate the minimum electrical clearance requirements.

• When the general meaning of a character or mark can be distinguished, the edges of the character appear slightly irregular.

• The defect does not meet or exceed the above requirements.

2.Ink marking

Ink mark refers to any type of mark printed on the surface of the printed circuit board.The production of this type of mark must not involve cutting or etching.

•The ink is evenly distributed without blurring or ghosting.

•The ink mark is at most tangent to the connecting plate.

•The characters are legible.

•As long as the characters are recognizable, the ink can be accumulated outside the character lines.

•As long as the required orientation is still clear and clear,the outline of the electronic component orientation symbol shown in the figure below can be partially peeled off.

•The marking ink of the component hole connecting plate shall not penetrate into the component mounting hole, or cause the ring width to be lower than the minimum ring width.

•Unless the procurement documents require that the holes be completely filled with solder, marking inks are allowed in the plated holes and via holes that do not solder component leads.

•The marking ink does not encroach on the printed contact sheet or the surface of the test point on the edge of the board.

•For surface mount connection disks with a pitch greater than or equal to 1.25 mm [0.04921 in], ink can only encroach on the tip of the iceberg,and the pool must not be half-year-old (0.05 mm [0.0020 in]).

•For surface mount lands with a pitch of less than 1.25 mm [0.04921 in],the ink can only invade one side of the lands,and no more than 0.025 mm [0.000984 in].

The specific role of text marking in PCB design

Identification of components: Through text marking, you can clearly identify the location, number and type of each component on the PCB. This is crucial for subsequent assembly, debugging and maintenance work, can greatly improve efficiency and accuracy.

Indication of polarity: for diodes, transistors and other components with polarity, text marking can clearly indicate its positive and negative poles or pin order, to prevent circuit failures due to misplugging or wrong insertion.

Auxiliary test: In PCB design, test point marking is essential. Through the text marking, you can easily find the test point for circuit testing and verification to ensure product quality and performance.

Version management: PCB version number marking helps to distinguish between different batches or versions of boards, facilitating traceability and management during production and maintenance.

Manufacturer information: Through the text marking, you can easily understand the PCB manufacturer, production date and other information, which helps product traceability and quality control.

Precautions for text marking design

Clear and easy to read: text markers should be clear and easy to read, avoid the use of overly complex or difficult to recognize fonts and patterns. At the same time, the size and location of the markers should also be based on the size of the PCB and the layout of the components for a reasonable design.

Durability: Since PCBs may be affected by various environments and mechanical stresses during production and use, the text marking should have good durability and be able to maintain clarity and integrity for a long time.

Accuracy: The content of text marking should be accurate to avoid errors or omissions. At the same time, when updating or modifying the PCB design, the corresponding text marking should also be updated in time.

Text markings on printed circuit boards have an irreplaceable role in PCB design. They not only improve productivity and quality, but also facilitate subsequent testing, maintenance and traceability.